Method of removing iron containing pollutant substances from liquid streams during production and/or cleaning of aromatic acids

FIELD: chemistry.

SUBSTANCE: invention pertains to the perfection of the method of regulating quantities of dissolved iron in liquid streams during the process of obtaining aromatic carboxylic acids or in the process of cleaning technical aromatic carboxylic acids, characterised by that, to at least, part of the liquid stream for regulating the quantity of dissolved iron in it, at least one peroxide with formula R1-O-O-R2 is added. Here R1 and R2 can be the same or different. They represent hydrogen or a hydrocarbon group, in quantities sufficient for precipitation of the dissolved iron from the liquid. The invention also relates to the perfection of the method of obtaining an aromatic carboxylic acid, through the following stages: A) contacting the crude aromatic material which can be oxidised, with molecular oxygen in the presence of an oxidising catalyst, containing at least, one metal with atomic number from 21 to 82, and a solvent in the form of C2-C5 aliphatic carboxylic acid in a liquid phase reaction mixture in a reactor under conditions of oxidation with formation of a solid product. The product contains technical aromatic carboxylic acid, liquid, containing a solvent and water, and an off-gas, containing water vapour and vapour of the solvent; B) separation of the solid product, containing technical aromatic carboxylic acid from the liquid; C) distillation of at least part of the off gas in a distillation column, equipped with reflux, for separating vapour of the solvent from water vapour. A liquid then forms, containing the solvent, and in the upper distillation cut, containing water vapour; D) returning of at least, part of the liquid from stage B into the reactor; E) dissolution of at least, part of the separated solid product, containing technical aromatic carboxylic acid, in a solvent from the cleaning stage with obtaining of a liquid solution of the cleaning stage; F) contacting the solution from the cleaning stage with hydrogen in the presence of a hydrogenation catalyst and under hydrogenation conditions, sufficient for formation of a solution, containing cleaned aromatic carboxylic acid, and liquid, containing a cleaning solvent; G) separation of the cleaned aromatic carboxylic acid from the solution, containing the cleaning solvent, which is obtained from stage E, with obtaining of solid cleaned aromatic carboxylic acid and a stock solution from the cleaning stage; H) retuning of at least, part of the stock solution from the cleaning stage, to at least, one of the stages B and E; I) addition of at least, one peroxide with formula R1-O-O-R2, where R1 and R2 can be the same or different, and represent hydrogen or a hydrocarbon group, in a liquid from at least one of the other stages, or obtained as a result from at least one of these stages, to which the peroxide is added, in a quantity sufficient for precipitation of iron from the liquid.

EFFECT: controlled reduction of the formation of suspension of iron oxide during production of technical aromatic acid.

19 cl, 1 dwg, 6 ex, 4 tbl

 

The scope to which the invention relates.

This invention relates to the regulation of the content or the removal of dissolved iron, which contains or may contain liquid process streams in the production of aromatic carboxylic acids. In addition, this invention relates to regulating the content or the removal of dissolved ferrous contaminants contained in the liquid flows in the production process technical aromatic acid. The present invention also relates to content regulation and the removal of dissolved ferrous contaminants contained in the liquid flows in the cleaning process technical aromatic acid. The present invention relates also to reduce the formation of oxides on the surface of the equipment used in the production of technical aromatic acid and/or purification of technical aromatic acid.

Background of invention.

Aromatic acids contain at least one aromatic ring, usually benzene or naphthalene ring, substituted by at least one carboxyl group. Examples of aromatic acids include phthalic acid, isophthalic acid, terephthalic acid, 2,6-naphthaleneboronic acid and benzoic Ki the lot. By interacting with other monomers, such as diols (e.g. ethylene glycol), aromatic acids may be used to obtain valuable polymers such as polyesters (e.g. polyethylene terephthalate). These resulting polymers are used for various purposes, including the manufacture of containers, films, packaging materials, fibers, etc.

Aromatic acids are usually obtained by the oxidation of aromatic compounds, when raw, representing an aromatic compound substituted by at least one oxidizable group, for example, alkyl or acyl group, or combination thereof, is oxidized to obtain technical aromatic acid. Typically, raw materials, suitable for oxidation with the formation of aromatic acids include ortho-xylene, meta-xylene, para-xylene, 1,5-dimethylnaphthalene, 2,6-dimethylnaphthalene etc. these raw materials are usually oxidized in a reactor in the presence of a solvent, carboxylic acid, oxidation catalyst and a source of oxygen. The catalyst used in the oxidation process usually contains one or more oxidizing metals, including those metals which have an atomic number from about 21 to about 82.

The oxidation process of aromatic compounds is usually exothermic reaction, which leads to the formation of technical aromatica is some acid in the oxidation reactor. Usually technical aromatic acid is precipitated with formation of a suspension with a solid phase containing the precipitated technical aromatic acid and liquid oxidation product. The liquid stream contains a solvent for the carboxylic acid, water and various substances in solution, including unreacted raw materials, not osadovskaya technical aromatic acid, not saducees by-products of the oxidation reaction and oxidation catalysts, such as cobalt, manganese and bromine. Technical aromatic acid may be separated from the liquid stream oxidation products by separation of suspensions of oxidation on solid and liquid. After separation of the liquid stream oxidation products from technical aromatic acid this liquid product is often referred to as "mother liquor oxidation products". The whole amount or a portion of this mother liquor is often recycled, that is returned to the oxidation reactor.

Technical aromatic acid is usually cleaned by the method of purification of aromatic acids, when technical aromatic acid is dissolved in water and treated with hydrogen and a hydrogenation catalyst at elevated temperature and pressure. After lowering the temperature and pressure of this method of purification of aromatic acids leads to the production of suspensions with solids the second phase, containing precipitated purified aromatic acid and a liquid cleaning product. The purified aromatic acid may be selected from liquid cleaning product through the implementation of phase separation of the suspension into solid and liquid. After separation from the treated aromatic acid liquid cleaning product is often called the "mother liquor cleaning products". This mother solution cleaning products typically contain mainly water and usually contains a small number of additional components, such as soluble by-products of the hydrogenation and, in the case where the cleaning is done as part of the whole process of the production of aromatic acids, which includes stages of oxidation and purification may also contain residual carboxylic acid and a small amount of metal oxidation catalyst. The mother liquor of the cleaning process or part thereof, remaining after removal of the soluble by-products are often returned in whole or in part in the process.

In the process of the above-mentioned oxidation of aromatic compounds and purification of aromatic acids occur some problems that appear due to contamination of the liquid streams of dissolved iron. This dissolved iron containing pollution occurs when the fluid flows are directed to the iron-containing p is the surfaces of equipment, used in the implementation process. For example, the mother liquor of the oxidation process and/or cleaning is usually sent to the iron surfaces of the equipment. Problems associated with contamination of dissolved iron, can be solved by reducing the action of iron-containing surfaces of equipment on the liquid flows when the alternative use of equipment made of titanium or equipment, clad titanium.

However, because of the relatively high cost of titanium remains typical action of the surface of iron-containing equipment (e.g., stainless steel) liquid flows. Examples of equipment from ferrous surfaces include pumps, transfer lines, vessels, etc. Contamination dissolved iron is undesirable because of its ability to precipitate in the form of iron oxide. The accumulation of iron oxide with time usually begins to affect the usefulness of the item of equipment. For example, the accumulation of iron oxide on the surface of the cladding titanium can accelerate corrosion. Accordingly, it is desirable to create a method of removing dissolved iron from the liquid flow of the processes of oxidation and/or cleanup.

The problems associated with the deposition of iron from aqueous streams contaminated with dissolved iron, can be better understood with reference to a specific element of the s equipment. Oxidation of aromatic compounds involves an exothermic reaction, usually resulting in the formation of off-gas containing the evaporated solvent and evaporated water. This off-gas or its part can be directed to a distillation column for separating the solvent from the off-gas in order to return it to the cycle. Passing through the distillation column off-gas is cooled in contact with the inner nozzle or plates. This cooling allows components with low boiling point such as water, to be removed from the upper part of the column, while the components with high boiling point are returned to the bottom of the column and can be used again, for example, as a solvent for the oxidation reaction. Cooling is usually facilitated by the introduction of phlegmy in the upper part of the column. This phlegm usually includes a liquid stream (preferably, water)containing substances, which is the same as the components of the oxidation process, or merging with them. Examples of such liquid flow include water, condensed from the distillate of the upper shoulder strap or mostly aqueous stream obtained by first condensing the off-gas oxidation reactor for separating the solvent carboxylic acid and subsequent condensation of part of the resulting gaseous stream, or, in the beam method, where integrated phase oxidation and purification mother liquor from the cleanup phase obtained in the separation of liquid stream treatment process from the purified aromatic acid and soluble by-products cleansing stage. The use of this stock solution stage cleaning or other liquid flows, which may contain dissolved iron as a result of contact with the surface of the equipment made of iron or steel, in the phlegm can contribute to the formation of solid iron oxides on the surface available inside the distillation column heads.

The accumulation of iron oxides on the surface of the nozzle containing the titanium is particularly undesirable. In one of the articles concluded: "the Accumulation of iron oxides... on the nozzle containing titanium, may contribute to or accelerate the combustion of titanium. It may be desirable to periodically remove the accumulation of these materials by chemical or other methods." (Centerline, Vol.5, No. 2, Summer 2001, p.p.6-8, 15-18, published by Mary Kay O'conner Process Safety Center). This publication further reported case of a fire at a chemical manufacturing and concludes that the presence of iron oxides "accelerated oxidation of titanium [attachment] the mechanism of the reaction of thermite type, when the oxygen for combustion is taken from a less reactive metal oxide".

In the application U.S. No. 60/32464, filed October 5, 2001 proposed treatment process for removal of accumulated metal oxides from the surface equipment for the preparation of aromatic acids, which is in contact with the liquid flow, which may contain dissolved iron. However, it would be desirable to eliminate or reduce the need for cleaning by creating a method of removing dissolved iron impurities from liquid streams during the above-mentioned oxidation process and/or cleaning process.

The invention

According to this invention in the liquid stream in the oxidation process and/or purification of aromatic compounds add peroxide to cause precipitation of dissolved iron impurities that might appear. By deposition is regulated by the amount of dissolved ferrous contaminants contained in the liquid streams, which take place in the reactor and come into contact with the equipment, but it is regulated by the formation of iron oxides on the surfaces of such equipment. In addition, the precipitated iron is usually present in quantities that are small enough and do not require special measures for its removal, although it may be selected from liquid streams by conventional means, for example, by filtration. According to the present from which briteney instead of the formation of iron oxide on the surface of the equipment precipitates insoluble iron. Accordingly, the invention can be used to extend equipment life and reducing the need for removal of oxide of iron by cleaning.

According to one variant of the invention provides a method for preparation of aromatic carboxylic acids, which includes stages:

A) contacting capable of oxidizing an aromatic feedstock with molecular oxygen in the presence of an oxidation catalyst containing at least one metal with an atomic number from 21 to 82, and solvent, representing2-C5aliphatic carboxylic acid in the liquid phase of the reaction mixture in the reactor under the conditions of oxidation with formation of a solid product containing technical aromatic carboxylic acid, liquid, solvent and water, and off-gas containing water vapor and solvent vapours;

B) separating the solid product containing technical aromatic carboxylic acid from the liquid;

B) distilling at least a portion of the off-gas in a distillation column equipped with phlegm, to separate the solvent vapor from the water vapor, the formation of a liquid stream containing solvent, and the upper distillation wrap containing water vapor;

G) returning at least part of the liquid stream from the stage In the reactor;

D) restorani is, at least part of the separated solid product containing technical aromatic carboxylic acid in a solvent purification stages, to form a liquid solution phase purification;

E) contacting the solution stage cleaning with hydrogen in the presence of a hydrogenation catalyst containing at least one metal of group VIII of the Periodic table of the elements and conditions of hydrogenation at temperatures from 233 to 316°and pressure from 6205 up 10340 kPa, effective for the formation of a solution containing purified aromatic carboxylic acid, and a liquid solvent for cleaning;

G) separating the purified aromatic carboxylic acid from a solution containing a solvent for cleaning, which is obtained in stage E, obtaining solid purified aromatic carboxylic acid and the mother liquor purification stages;

C) returning at least part of the mother liquor cleanup phase on at least one of the stages b and D; and

I) adding at least one peroxide of the formula R1-O-O-R2where R1and R2identical or different, denote hydrogen or a hydrocarbon group, in the liquid residing on at least one of the other stages, or resulting from, at least one of these stages, where the peroxide is added to the number, effective to precipitate the dissolved iron from the liquid stream. According to a preferred variant of the invention the method comprises the additional step of recycling in the liquid reaction mixture in the reactor, at least part of the liquid remaining after separation of the technical aromatic carboxylic acid. Adding peroxide to the liquid contained or formed in one or more stages of the process, allows you to control the amount of dissolved iron, which can be contained in such fluids and lower liquids contained or formed during the process, so that the deposition of solid iron oxides on the surface of the equipment is prevented or reduced.

Not limited to any one theory, believe that the dissolved iron in the liquid flow process for the oxidation of aromatic compounds and/or cleaning is an iron(II). When the fluid stream is treated with peroxide, I think that the peroxide oxidizes dissolved iron(II) and a precipitate of iron hydroxide(III).

Adding peroxide causes the precipitation of iron even in the presence of other dissolved metals, usually contained in a liquid stream of the oxidation process of aromatic compounds and/or cleaning. Amazing is the fact that dissolved iron is precipitated p is racist at that time, like other metals, such as metal oxidation catalyst, which can be kept even in large quantities, almost not deposited.

In accordance with this invention the liquid flow of the oxidation process of aromatic raw materials and/or liquid stream treatment process may in addition contain iron and other dissolved metals. In particular, these dissolved metals other than iron are usually contained in the liquid stream of the oxidation process of aromatic compounds and/or in the liquid stream treatment process as a result of application of oxidation catalysts containing metals that are used for technical education aromatic acid. These dissolved metals (other than iron) usually include dissolved cobalt and/or manganese, as usually they are used in the implementation in industry of the oxidation method of obtaining aromatic acids, although there may be other dissolved catalytic metal in addition to, or instead of them. For example, a typical amount of dissolved metal (not iron) in the liquid stream of the oxidation process and/or in the liquid stream treatment process may be 10-100 ppm, or more. The amount of dissolved cobalt and/or manganese contained in the liquid stream of the oxidation process and/or in the liquid stream treatment process may be 10-100 is/million or more. The amount of dissolved iron contained in the liquid stream of the oxidation process of aromatic compounds and/or in the liquid stream treatment process can typically range from 0.1 to 10 ppm, or more. Because the peroxide does not cause appreciable precipitation of dissolved metals oxidation catalyst (for example, cobalt and/or manganese), the ability to return these metals, for example, by recycling the mother liquor of the oxidation process, is stored.

Also unexpectedly found that the addition of peroxide causes the precipitation of dissolved iron, even when the liquid flow in the oxidation of aromatic compounds and/or in the liquid stream in the purification process contains large amounts of terephthalic acid and/or capable of oxidation of organic impurities, such as bartolommea acid. The amount of terephthalic acid and/or oxidizing impurities in the liquid flow varies and depends on various factors, including temperature, specific components of this liquid stream and the applicable specific conditions of oxidation. For example, terephthalic acid is usually found in such liquid flows in large quantities and intermediate oxidation products, such as para-tolarova acid and benzoic acid, may also contain appreciable quantities. Although those to whom icesta usually much more than the amount of dissolved iron, resulting from contact of liquid process streams with surface equipment, made of steel, or other iron sources, and can lead to competing reactions with peroxide, is added to remove dissolved iron, significant deposition of iron is achieved even in the presence of large quantities of organic compounds and intermediate compounds.

Peroxide suitable for use according to the invention have the General formula R1-O-O-R2where R1and R2can have identical or different meanings and represent hydrogen or hydrocarbon group. Thanks, at least in part, the relatively low cost of most preferred is hydrogen peroxide. To accelerate the precipitation of the dissolved iron is preferable to add an excess of peroxide to the liquid product, intermediate product, process stream or part of it. For example, it is preferable to add the peroxide in a molar excess relative to the amount of dissolved iron contained in the mother solution phase oxidation or cleaning or other liquid process stream. The amount of dissolved iron in the liquid flow can be determined by ICP (plasma spectroscopy).

It was also unexpectedly setup the network, that peroxide is able to precipitate dissolved iron, when added to the liquid stream in the oxidation process of aromatic compounds and/or in the cleaning process at elevated temperatures, for example, at 200°F (93°C) or higher. For example, the peroxide may be added to the mother solution at the stage of purification with a temperature of 200°F (93° (C) to cause precipitation of dissolved iron. Peroxides tend to easily decompose. For example, hydrogen peroxide (H2O2) decomposes into gaseous hydrogen and water. If it is left for a year at room temperature, about half of the peroxide to decay. The rate of peroxide decomposition increases with temperature. So amazing is the fact that the peroxide added to the liquid stream at the stage of oxidation of aromatic compounds and/or cleaning at elevated temperatures, does not decompose before it can cause the precipitation of dissolved iron.

According to one variant of the invention, the peroxide is added in the liquid flow in the process of obtaining technical aromatic acid. Technical aromatic acid is usually produced by oxidation are capable of oxidation of the raw material (for example, orthoxylene, metaxylene, paraxylene, 1,5-dimethylnaphthalene, 2,6-dimethylnaphthalene) in the oxidation reactor in the presence of a solvent to benovoy acid, oxidation catalyst and a source of oxygen. The catalyst used in the oxidation process, is usually such a catalyst which contains one or more metals that are included with oxidation catalysts, which typically include metals having an atomic number from 21 to 82. Typically, the pressure during the oxidation reaction is maintained so that it is effective to maintain the oxidized raw material and at least 70% of the solvent in the liquid phase. The pressure in the oxidation reactor is generally from 0 kPa to 3430 kPa, preferably, it ranges from 981 kPa to 2940 kPa. The temperature in the oxidation reactor is generally 120-240°preferably 150-230°C.

The oxidation reaction usually results in a suspension containing precipitated technical aromatic acid and liquid flow. They are usually separated using a device for separating solids from fluids (e.g., centrifuge or filter device, such as a vacuum filter or a filter, pressure). At least part of the separated liquid stream (also referred to as mother liquor phase oxidation), which typically contains one or more solvents stage of oxidation, unreacted raw materials, partially oxidized by-products and catalyst, predpochtitelno, is returned to the oxidation reactor.

According to a particular variant of this invention, the peroxide is added in the liquid flow at the stage of oxidation to return the mother liquor stage of oxidation, which causes the precipitation of the dissolved iron. In this way, in the mother solution returned in the cycle, decreases the amount of iron contamination.

It is preferable to add hydrogen peroxide in the liquid flow at the stage of oxidation before it is sent to the device for separating solids from liquids. Thus, the dissolved iron is precipitated from this liquid stream at the stage of oxidation. Precipitated iron may be removed from the liquid stream by means of a device for separating solids and liquids, which is intended for disposal of solid iron or maybe just to circulate in the implementation process so that it is removed completely or partially in other separators for separating solids from liquids included in the schema.

The oxidation reaction with obtaining technical aromatic acid is usually also leads to the formation of off-gas containing the evaporated solvent and evaporated water. To reduce the loss of solvent entire off-gas or its part can be directed to a distillation column containing a liquid phlegm, so that the gaseous phase, containing low-boiling components such as water, removed from the upper part of the column, and the liquid phase more high-boiling components such as solvent, was returning from the bottom of the column in the reactor. According to one variant of the invention, the peroxide is added to the liquid used as phlegmy before it is fed to a distillation column that is used to process off-gas from the oxidation reactor for technical aromatic acid. Thus, the dissolved iron is removed from phlegmy by deposition, thus reducing the possibility of formation of iron oxide on the surface of the nozzles, and other internal surfaces of the distillation apparatus.

According to another variant of the invention, the peroxide is added in the liquid flow in the cleaning process of the aromatic acid. It is preferable to add the peroxide in the liquid flow at the stage of the cleaning during the cleaning aromatic acid. This process involves the hydrogenation of dissolved technical aromatic acid in the liquid stream at the stage of purification of obtaining dissolved purified acid. The temperature and pressure of the hydrogenation reaction is chosen so that technical aromatic acid remained dissolved in the liquid medium at the stage of purification. Usually the temperature in the reactor is in the range 450-00° F (233-316°). The reactor pressure during the hydrogenation is in the range from 900 to 1500 F./inch2(6205-10340 kPa) and usually ranges from 900 to 1300 F./inch2(6205-8963 kPa).

After hydrogenation the temperature and pressure of the liquid stream cleanup phase containing dissolved purified aromatic acid, decreases, which causes crystallization of the purified aromatic acid, which can be separated from the liquid stream, usually by filtration. Accordingly, the peroxide may be added prior to filtration or other methods for separating solids from liquids used for the selection of crystalline purified acid from the liquid, so that the precipitated iron could be isolated from the liquid environment. In addition, the peroxide may be added to the stock solution at the stage of purification after the implementation of phase separation of solids and liquids, this further reduces the presence of precipitated solid iron-containing particles in the purified aromatic acid that is released. Obtained in any such case, the liquid flow is also called, as indicated earlier, the mother liquor cleanup phase, contains a reduced amount of dissolved iron. All such mother liquor or part thereof with a reduced content of dissolved iron contamination of the advantages of the NGO is used as phlegm for distillation columns, used to separate solvent from the off-gas produced during the oxidation reaction, used for technical aromatic acid. The reduction of dissolved iron impurities in this way is particularly preferable, since the nozzle inside such distillation columns are particularly susceptible to the formation on the surface of iron oxides due to the presence of molecular oxygen in the off-gas from the oxidation reactor. Due to the precipitation of iron oxides from the mother liquor at the stage of purification before this mother liquor is used as phlegm for such distillation columns may be reduced by the formation of iron oxides on the surface of the nozzle in the distillation column.

The drawing shows the variants of the invention in the case of integrated circuits, including phase oxidation of aromatic acid purification step.

Detailed description of the invention

In accordance with this invention, the peroxide is added in the liquid flow at the stage of oxidation upon receipt of an aromatic acid and/or liquid flow at the stage of purification or part of this stream to precipitate dissolved iron-containing contaminants that might appear, thus reducing the formation of oxides on the surface of the equipment, coprocesses is with such liquid flows. Effect of liquid flow on ferrous surfaces of the equipment used during the oxidation of aromatic raw materials and/or cleaning, can cause contamination of the liquid flux of dissolved iron. It is preferable to add the peroxide in the liquid stream after it was in contact with iron-containing surfaces. Received the treated liquid stream contains a reduced amount of dissolved iron in comparison with dissolved iron, which is contained in the streams before treatment with peroxide.

Accordingly, preferably, the peroxide was added to the liquid stream thus to reduce further action received processed liquid flow on ferrous surfaces. More preferably, the peroxide was added to the liquid stream after it was in contact with the majority or a significant part of the iron-bearing surfaces of equipment used in the oxidation process of aromatic compounds and/or during the cleaning process.

Preferred examples of cases where the liquid flow experienced the action of the greater part of the iron-containing surfaces in the oxidation process of aromatic compounds and/or in the cleaning process, is the liquid flow immediately after the implementation of phase separation of solids and liquids or directly edstone before carrying out this stage. As will become clear, the peroxide may be introduced into one or more liquid streams at one or more points during the process and in a continuous way the peroxide may be added continuously or intermittently, as desired. Most often for the introduction of peroxide in the liquid at a given speed directly in the process piping or vessels or piping connected to these pipelines or vessels used metered-dose pump or similar device.

The amount of peroxide added to the liquid flow can be any, causes the precipitation of dissolved iron. Effective to reduce the amount of dissolved iron quantities of peroxide are significant excess in relation to the quantities that affect the efficiency and effectiveness of the process in other aspects. In the specific case of the deposition promotes the addition of peroxide in the liquid flow at the stage of oxidation of aromatic compounds and/or cleanup phase in a molar excess relative to dissolved in the liquid stream gland. The amount of dissolved iron can be determined by ICP (plasma spectroscopy). Preferably, the peroxide was not added in such quantity that causes substantial precipitation of the dissolved catalytic metal(e.g., cobalt and manganese) in the liquid stream. Preferably, the amount of peroxide does not exceed a reasonable amount. For example, the average person can easily determine when the amount of the peroxide has a small impact or no impact on the precipitation of iron. Preferably, the molar ratio of peroxide to the dissolved iron was at least 10:1, more preferably at least 25:1, even more preferably at least 50:1 and even more preferably at least 100:1. In the case of large-scale production of aromatic acids, which includes stages of oxidation and purification, suitable molar relationship in the range of from about 5:1 to 100:1, required for the deposition of iron compounds without significant loss of catalytic metals, and relationships from about 10:1 to 50:1 are particularly suitable when the peroxide is added to the dissolved aromatic acid, which is purified, or stock solution cleanup phase after separation of the purified acid due to the reduced amounts of dissolved catalytic metal at the stage of purification compared to their quantities in liquid flows on the stages of the process or resulting in the result of the implementation of these stages, such as oxidation, separation of aromatic Carbo the OIC acid from the liquid reaction mixture after oxidation and recycling the mother liquor oxidation steps.

The preferred amount of peroxide that you want to add to the liquid flow, can also be expressed in relation to the flow rate or quantity of liquid flow at the point of addition of the peroxide. In this case, the peroxide is preferably added in amounts of 1-100 g of peroxide per 1000 kg liquid stream to provide an adequate amount of peroxide to iron deposition without significant formation of solid particles of catalytic metal, although in General suitable large quantities, for example, to 250 g of peroxide per 1000 kg liquid flow, especially in the case of peroxides such as hydrogen peroxide, lower alkylperoxide and benzoyl peroxide, which is compatible with other used or generated during oxidation or cleaning components or decompose on such compatible products.

The amount of dissolved iron in this liquid stream may vary and depends on several factors, such as corrosion and location of liquid flow over the course of the oxidation process of aromatic compounds and/or cleaning. For example, the amount of dissolved iron is usually up to about 10 h/million But harmful can be such amount as 0.5 h/million the Invention can be effective at any dissolved iron, which has or may be contained in the liquid flow path R. the regulation of the amount of peroxide, add in the liquid flow depending on the content of dissolved iron, which is determined by any method of analysis.

After processing liquid stream by adding peroxide to precipitate dissolved iron the liquid stream contains a reduced amount of dissolved iron. Preferably, the treated liquid stream contains not more than 6 ppm, preferably not more than 3 ppm, and most preferably not more than 0.5 ppm of dissolved iron. After addition of the peroxide, the amount of dissolved iron is preferably reduced at least 40 wt.%, more preferably at least 70 wt.%, even more preferably, at least 85 wt.% and most preferably at least 95 wt.% in the calculation of the amount of dissolved iron contained before adding peroxide.

For technical aromatic carboxylic acids using various metals, except iron, they lead to the oxidation of aromatic compounds and/or purification of liquid streams containing these catalytic metals dissolved in these threads. Despite the presence of catalytic metals peroxide may apply for removal of dissolved iron by precipitation. In some liquid flows, especially in the liquid flux is Ah at the stage of oxidation in the mother solution dissolved catalytic metals are usually found in large quantities, than dissolved iron. Surprisingly, these dissolved metals, but not iron, do not prevent the precipitation of dissolved iron peroxide. For example, some liquid flows phase oxidation of aromatic compounds and/or the stage of purification of the weight ratio of dissolved metals other than iron, dissolved iron may vary from 25:1 to 100:1 or more. The weight ratio of dissolved cobalt to the dissolved iron in some liquid flows at the stage of oxidation of aromatic compounds and/or cleanup phase can range from 5:1 to 50:1 or more, and the weight ratio of dissolved manganese dissolved iron may be from 5:1 to 50:1 or more. The amount of dissolved cobalt, manganese and other catalytic metals contained in the liquid stream at the stage of oxidation of aromatic compounds and/or at the stage of purification is usually 1-50 ppm or more for each metal. The predominant aspect of the present invention is that the peroxide does not cause significant deposition and subsequent removal of dissolved metals in the composition of the oxidation catalyst in the stream at the stage of oxidation of aromatic compounds and/or at the stage of purification. These dissolved metals oxidation catalyst, preferably contained in the liquid flow after the liquid is Otok peroxidized, to be able to reuse these metals. Dissolved catalytic metal contained in the liquid stream at the stage of oxidation of aromatic compounds and/or at the stage of purification, preferably, are removed in an amount of not more than 30 wt.%, preferably, not more than 20 wt.% and, even more preferably not more than 10 wt.% the number of such metals in the solution before it is processed peroxide for the removal of dissolved iron, which can be found there. Dissolved cobalt is removed, preferably, in an amount not more than 15 wt.%, preferably, not more than 10 wt.% and, most preferably, not more than 5 wt.%. Dissolved manganese in the liquid stream at the stage of oxidation of aromatic compounds and/or cleanup phase is removed, preferably, in an amount not more than 15 wt.%, preferably, not more than 10 wt.% and, most preferably, not more than 5 wt.%. As is evident, a significant saving of dissolved metals oxidation catalyst in the liquid stream is especially desirable in the case of the mother liquor phase oxidation and other liquids that you want to return to the stage of oxidation.

The invention is particularly suitable for the oxidation process with the purpose of obtaining technical terephthalic acid and/or process for purification of aromatic acid to clean technical terephthalic acid is. Usually, obtaining technical terephthalic acid involves the catalytic oxidation of para-xylene with the formation of crude terephthalic acid, which may also include partially oxidized by-products, such as p-Truelove acid and 4-carboxybenzene. According to this invention the peroxide used for deposition or regulate the amount of dissolved iron in the mother solution, which usually contains significant amounts of terephthalic acid, and is also able to oxidize organic impurities normally found in much larger quantities than dissolved iron, but does not affect the process of deposition of dissolved iron, which is amazing. For example, in a typical liquid flow, the weight ratio of oxidizing organic impurities in dissolved iron can be up to 50000:1, and the liquid flows stages of oxidation are observed much higher ratio, for example, 1000:1 or higher than in the liquid flow at the stage of purification, where they are, for example, from 100:1 to 10000:1.

Peroxide suitable for use according to the invention have the General formula Ri-O-o-R2where R1and R2identical or different, denote hydrogen or a hydrocarbon group. Preferred are peroxides, in which R1and R2the same formula is or different and selected from hydrogen, C1-8-alkyl, C1-8-alkenyl, C1-8-quinil,6-12-acyl, benzoyl or benzoyl substituted C1-With4is lower alkyl. Can be used in combination of two or more peroxides, which are entered in one or more of these cars in the process or each peroxide is injected at various points. Examples of peroxides suitable for use in the invention include hydrogen peroxide, Dietrich, peroxide Dibenzoyl, Gidropress trebuie. Thanks, at least in part, the relatively low cost and ease of handling most preferred is hydrogen peroxide.

Peroxide used according to the invention, are relatively clean, which is commercially available as peroxide chemical and food. Preferably, the degree of purity was such that impurities sulfates contained in the amount of 500 ppm or less and, more preferably, less than 100 h/million If you prefer, you can apply a more pure form, such as those used in semiconductor manufacturing, although a large degree of purity may not provide more efficiency to the process according to the invention. Less pure forms may contain impurities such as sulfates in an undesirable large quantities. When used according to the invention, preferably, note the change peroxide in the form of a solution in water or another solvent, compatible with the process for preparation of aromatic acid and/or cleaning to facilitate technological problems and eliminate corrosion, for example, tanks, pumps, pipelines, used for storing and adding peroxide in the liquid streams in the process. Preferably, to enter peroxide with a concentration of 0.1-70 wt.% in solution, the concentration change depending on the location of the point or points of addition of the peroxide, integration of equipment that need be used along with other equipment, the type of peroxide and other factors, as it is obvious for specialists in this field.

Due to the increase in the peroxide decomposition with increasing temperature has been amazing is the fact that the peroxide is capable of deposition of dissolved iron, and not to degradation, when it is added to the reaction stream at the stage of oxidation of aromatic compounds and/or cleanup phase, with a high temperature, for example above 200°F (93°C). According to this invention the peroxide can effectively precipitate dissolved iron in the stream at the stage of oxidation of aromatic compounds and/or cleanup phase at a temperature exceeding 200°F (93° (C) or 300°F (149°C). However, the peroxide is added to the stream at the stage of oxidation of aromatic compounds and/or cleaning when sufficient what about the low temperature, so the peroxide causes the precipitation of dissolved iron before it decomposes. Accordingly, it is preferable to add the peroxide in the mother liquor or other liquid stream at a temperature not exceeding 500°F (260°C), more preferably not higher than 400°F (204°C).

According to one variant of the present invention, the peroxide is added to the liquid stream at the stage of the cleaning during the cleaning aromatic acid, which comprises the hydrogenation of technical aromatic acid. This invention can be applied to any method of purification of aromatic acids known from the prior art, these methods, such as described in U.S. patent 5354898 and 5362908, the contents of which are included in this description as a reference. Typically, the method of purification of aromatic acids include hydrogenation dissolved technical aromatic acid in the liquid stream cleanup phase comprising the solvent, obtaining dissolved purified aromatic acid. Dissolved purified aromatic acid then crystallizes and the resulting solid purified acid is released from the liquid stream, usually by filtration. The peroxide can be added to the liquid stream cleanup phase at any point during the process, but in order to avoid the application of high temperature hydrogenation, the peroxide type, predpochtitelno, after hydrogenation. The peroxide may be added after crystallization, but before the separation of the acid (filtering), so that the precipitated iron can be separated from the liquid stream at the stage of purification, together with the purified aromatic acid. Or peroxide type after separating the crystallized purified aromatic acid to the stock solution at the stage of oxidation, which is wholly or partly returned to the cycle. It is most preferable to add the peroxide in this mother liquor cleanup phase after separation of the purified aromatic acid, the resulting stream is returned to the cycle as phlegmy for distillation off-gas from the oxidation reactor, where it turns aromatic acid.

This invention can be used in the cleaning process of aromatic acids, when technical aromatic acid (e.g., crude terephthalic acid) dissolved in the liquid stream cleanup phase, which contains the solvent, and treated with hydrogen in an autoclave in the first reaction zone containing a hydrogenation catalyst. The catalytic hydrogenation in an autoclave typically contains one or more active components of the hydrogenation catalyst supported on a carrier. The carrier is usually in the form of granules, although there may be pills or other forms in the form of particles. If enaut granules, their average size is from -2 to -12 mesh mesh (U.S.Sieve Series), more preferably from -4 to -8 mesh mesh. The carrier preferably is an active carbon, more preferably, charcoal coconut palm. Such active carbon typically has a surface area equal to at least 600 m2/g (N2, BET method), preferably, from 800 m2/g to 1500 m2/, Although the active carbon obtained from charcoal of coconut palms, in the form of granules is the preferred material for the carrier of the catalyst for hydrogenation, can be applied to other porous carbon materials, metal oxides or other media or substrate.

The hydrogenation catalyst contains at least one active component of a catalyst for hydrogenation. Particularly suitable catalytic hydrogenation components are metals of Group VIII of the Periodic table of elements (IUPAC version), including palladium, platinum, rhodium, osmium, ruthenium, iridium and mixtures thereof. Catalytic component of the hydrogenation catalyst may be precipitated by coal or other media in any suitable way, for example, by treating the carrier with a solution of one or more soluble compounds of metals VDI Group, such as palladium chloride, followed by drying to remove excess solvent or added to this is the media.

Preferably, the content of metal of Group VIII on a carrier was in the range of from 0.01 to 2 wt.% calculated on the total weight of the catalyst, where the total weight is the sum of the weights of dry carbon carrier and a hydrogenation active component. More preferably, the content of metal of Group VIII of the carbon media amounted to 0.2-0.8 wt.%.

Suitable catalysts and carriers for them are suitable for carrying out this invention relating to the purification of aromatic acids described, for example, in U.S. patent No. 4394299, 4629715, 4728630 and 4892972. A suitable catalyst is palladium on coal can be obtained, for example, Engelhard Corporation, Edison, N.Y. Suitable catalysts rhodium coal can also be obtained in Engelhard Corporation.

A suitable reactor to effect the hydrogenation is any reaction vessel which can withstand the temperature and pressure used for the hydrogenation of technical aromatic acid, dissolved in a solvent for cleaning. The preferred configuration of the reactor is a cylindrical reactor, the axis of which is vertical, containing a hydrogenation catalyst in a fixed layer. According to the preferred technical option aromatic acid dissolved in the cleaning solvent, is added to the reaction vessel at the point of th is th in the upper part of the reaction vessel and its vicinity, and technical aromatic acid, dissolved in a liquid medium, flows down through a layer of a hydrogenation catalyst, in the reaction vessel in the presence of hydrogen gas, while the impurities react with gaseous hydrogen.

According to this preferred variant technical aromatic acid is purified and the purified product is removed from the reaction vessel at a point located in the lower part of the reactor or near the bottom.

The hydrogenation catalyst, preferably containing carbon carrier and an active component of the hydrogenation catalyst supported on a carrier, is held in the reaction vessel, screen or other means which holds the catalyst particles in the reactor and still provides a fairly free passage technical aromatic acid, dissolved in the liquid stream at the stage of purification. The means used to hold the catalyst particles may be flat mesh sieve or screen made of close-together rows of wire. Other suitable means for retaining the catalyst include, for example, tubular Johnson screen or perforated plate. Means for retaining catalyst particles made of a material which is corrosion resistant which has an appropriate strength, in order to effectively retain the catalyst bed.

Most preferably, the tool to hold the catalyst particles had a hole size of 1 mm and was made of such metal as stainless steel, titanium or Hastelloy C.

The reactor can operate in several ways. For example, the predetermined liquid level is maintained in the reactor and there is hydrogen for maintaining in the reactor a predetermined pressure at a rate sufficient to maintain a given liquid level. The difference between the actual reactor pressure and the vapor pressure of the liquid stream cleanup phase represents the partial pressure of hydrogen in the vapor space of the reactor. If the hydrogen serves else in a mixture with an inert gas, such as nitrogen, the difference between the actual reactor pressure and the vapor pressure of the solution technical acid is a combined partial pressure of hydrogen and an inert gas mixed with it. In this case, the partial pressure of hydrogen can be calculated from the known relative quantities of hydrogen and inert gas contained in the mixture.

According to another method, the reactor can be filled with liquid flow purification stages so that in the reactor remained space is filled with pairs. That is, the reactor can in order to work as a hydraulically filled the system with dissolved hydrogen, fed to the reactor by regulating the flow. In this case, the concentration of hydrogen in solution can be controlled by regulating the feed rate of hydrogen in the reactor. If this is desirable, it is possible to calculate the value of the partial pressure of pseudanodonta based on the hydrogen concentration in solution, which, in turn, can be correlated with the flow rate of hydrogen in the reactor.

When the adjustment process is carried out by changing the partial pressure of hydrogen, the partial pressure of hydrogen in the reactor preferably is in the range from 10 f/inch2to 200 F./inch2(69-1379 kPa) or higher depending on the nominal value of the operating pressure, the degree of contamination of the above-mentioned technical aromatic acid, activity and lifetime of the catalyst particles and other process parameters, known in the art. When the control process carried out by changing the concentration of hydrogen in the feed solution, the latter is unsaturated with respect to hydrogen, and the reactor itself is hydraulically filled. Thus, regulation of the flow rate of hydrogen supplied to the reactor, will lead to desirable to control the concentration of hydrogen in solution. In General, the amount of hydrogen which must be filed in the reactor, where production is titsa cleaning, under the reaction conditions, of course, is sufficient to implement the desired hydrogenation.

The volumetric rate indicates the number of technical aromatic acid per weight of catalyst per hour, during the hydrogenation is usually from 1 hour-1up to 25 h-1preferably from 2 h-1up to 15 h-1. The residence time of the liquid stream cleanup phase in the catalyst bed varies with flow rate.

After hydrogenation of the stream containing the now purified aromatic acid and the solvent is removed from the reactor and cooled to the crystallization temperature. The crystallization temperature is low enough (for example, 160°or lower) for the crystallization of purified aromatic acid, in liquid phase crystals are formed. The crystallization temperature is high enough impurities and products of their recovery (products obtained by hydrogenation) remained dissolved in the liquid phase. Then, the liquid containing dissolved impurities and products of their recovery, separated (usually by filtration) from the crystallized purified aromatic acid.

It is preferable to add the peroxide to the liquid product after crystallization, in order to avoid high temperatures during gidrirovaniem adding peroxide, a precipitate of iron, which can then be separated (e.g., filtered) from the liquid together with purified crystalline aromatic acid.

As already mentioned, the iron oxide can be harmful when it is formed on such surfaces of equipment due to the impact on this equipment is a liquid flow phase oxidation of aromatic compounds and/or stage of cleaning contaminated with dissolved iron. Accordingly, it is preferable to add the peroxide to the liquid stream to precipitate dissolved iron before it will be in contact with such surfaces of equipment.

For example, the peroxide is preferably added to the phlegm, before it is served to a distillation column used in the oxidation process of aromatic compounds. In the case of some of the ways in which the United oxidation of aromatic compounds and cleaning, phlegm may contain liquid stream cleanup phase (for example, the mother liquor) as its component. This invention can be used for deposition or regulation of dissolved iron impurities in the liquid stream cleanup phase or part thereof before it is administered as a component of phlegmy distillation columns. During the oxidation of aromatic compounds on stellazine columns are usually used to separate the low-boiling components (e.g., water from the high-boiling (for example, the reaction solvent). Specifically, the distillation column can be used in the oxidation process of aromatic compounds, including the introduction of raw materials (for example, paraxylene) in a reactor in the presence of a solvent carbolic acid, oxidation catalyst and a source of molecular oxygen (usually air). The reactor is exothermic oxidation obtaining technical aromatic acid and off-gas coming from the reactor. This off-gas contains a pair of aliphatic carbolic acid, water vapor (a byproduct of the reaction) and molecular oxygen. The entire quantity or part of the off-gas is directed to the lower part of the distillation column, and phlegm is added in the upper part of the column to cool the off-gas as it rises in the casing and in contact with the nozzle or plate distillation column. As there is a cooling off-gas high-boiling components such as solvent used in the preparation of carboxylic acids by oxidation, migrate into the lower part of the column and may be returned, at least partially, into the reactor. Low-boiling components such as water, migrate to the upper part of the column where they can be removed. Thus, the distillation column facilitates recycling dissolve the I and simultaneously facilitates the removal of water, a by-product of the oxidation reaction. Examples of distillation columns used according to the invention described in U.S. patent No. 5612007 and 5723656, the contents of which are included in this description as a reference. High-pressure steam or other top gas from stage distillation can be a source of energy that can be selected, for example, by means of the expander. Another example of a method that uses a distillation column to process off-gas from the reactor oxidation of aromatic compounds by condensation of a part of the top gas from the distillation column and returning the condensate as phlegmy in the distillation column described in U.S. patent No. 6504051, which is also included in this description by reference.

Because of the off-gas, which comes into contact with phlegm, contains molecular oxygen, it is especially important to reduce the amount of dissolved iron in the phlegm, to prevent its oxidation and the resulting formation of iron oxide on the surface inside the distillation column. This can be done by adding the peroxide to the components of the liquid phlegmy and/or the phlegm to significant precipitation of dissolved iron to feed phlegmy in the distillation column. Time to make significant deposition (i.e. time) depends on the t of various factors, including the amount of dissolved iron, which should precipitate. The typical time between 5-30 seconds.

Control options for implementation easier to understand with reference to the drawing, which reflects the integrated process, which includes stages of oxidation of aromatic compounds and purification of aromatic acids.

The oxidation process of aromatic compounds begins to stir the reactor (10), while the cleaning process begins in the vessel for suspension (110).

When carrying out the oxidation process of aromatic compounds raw materials (not shown) is introduced into the reactor (10). These raw materials include raw materials, the solvent, the catalyst and oxygen. The raw material is an aromatic compound substituted by at least one oxidizable group, such as alkyl, or acyl, or a combination thereof. Typical raw materials suitable for the oxidation of obtaining aromatic acids, comprises orthoxylene, betaxolol, paraxylene, 1,5-dimethylnaphthalene, 2,6-dimethylnaphthalene and other Solvent may be any aliphatic or aromatic carboxylic acid and, preferably, is a2-C5-aliphatic carbolic acid, more preferably acetic acid. The catalyst typically comprises cobalt, manganese and bromine. A suitable source of oxygen is the air, although it can be used pure oxygen, air enriched with oxygen, and other suitable oxygen-containing gases. In the presence of solvent, catalyst and oxygen feedstock is oxidized in the liquid reaction mixture with formation of the corresponding technical aromatic acid. For example, paraxylene is oxidized to form crude terephthalic acid. Part of this technical aromatic acid, formed by oxidation, deposited from a liquid reaction mixture, forming a slurry with the solid phase containing technical aromatic acid, and a liquid stream containing solvent, water and unreacted feedstock. The oxidation reaction is carried out under conditions that lead to the formation of off-gas, which contains water and solvent vapours, usually with unspent oxygen, inert gases from a source of oxygen, also contains gaseous by-products. Off-gas is removed from the space for vapors in the reactor to a distillation column (20) line (12).

The slurry from the oxidation reactor (10) is introduced into the mold (120), in which the temperature and pressure drop and liquid phase deposited an additional amount of aromatic acid. This suspension is preferable to send in additional molds (not shown), the connection is built sequentially, in which the temperature and the pressure gradually reduced in each of the following apparatus. This gradual decrease of pressure and temperature allows more effective deposition of technical aromatic acid. After lowering the temperature of the suspension and the pressure to an appropriate value, the suspension is sent to the phase separation of solids and liquids (135) line (128), where technical aromatic acid is released from the liquid flow stage of oxidation. This dedicated liquid stream is also known as the "mother solution phase oxidation". Although for separating solids and liquids, you can use the separator (135), the use of centrifuges and filtering devices is preferred.

After separation of the solid phase and liquid (135), at least a portion of the mother liquor phase oxidation may be on the line (145) returned to the reactor (10), while technical aromatic acid on line (136) is sent to the vessel for suspension (110), where begins the cleaning process. The solid phase, including technical aromatic acid may be dried and/or sent to storage until the beginning of the cleaning process. In the vessel (110) technical aromatic acid is mixed with water supplied through line (105), and then sent to a hydrogenation reactor (160), where technical aroma is practical acid is dissolved in water and treated with hydrogen at elevated temperature and pressure. Effluent from the hydrogenation reactor (160) is sent to the crystallizer (170), in which the temperature and pressure decrease, which leads to the precipitation of the purified aromatic acid. In the mould (170) is formed slurry containing a solid phase, comprising the purified aromatic acid and a liquid stream cleanup phase containing water and the precipitated acid. This suspension, preferably, to send in additional series-connected molds (not shown)in which the temperature and pressure decrease gradually in each successive vessel. This gradual decrease of pressure and temperature allows for a more efficient deposition of purified aromatic acid. After lowering the temperature of the suspension and the pressure to an appropriate value, it is sent to the separator (180) for separating solids and liquids, where the purified aromatic acid is separated from the liquid medium.

The selected liquid flow from the stage of oxidation is also called "mother liquor cleanup phase". Although for separating solids from liquids (180) can be used in any suitable device, preferably, to use a centrifuge or filter device.

Using the process of oxidation and purification shown in the drawing, the various liquid streams is oiti in contact with iron-containing equipment (e.g., stainless steel), while in these liquid streams appears dissolved iron. For example, pipelines for liquid transfer, denoted 115, 128, 145, 158, 165, 175 and 200 may have a surface made of ferrous materials (e.g. stainless steel), which contact the liquid flows along these lines.

In addition, vessels, designated 110, 160, 170 and 180 may have a surface made of ferrous materials (e.g. stainless steel)which are in contact with the liquid flow or passing in this equipment. Dissolved iron contamination can lead to the formation of iron oxide on the various elements of the equipment and pipelines shown in the drawing.

In accordance with the present invention the formation of iron oxides on the surface of the equipment is reduced or regulated by adding peroxide to the liquid stream at the stage of oxidation of aromatic compounds and/or at the stage of purification, while the dissolved iron precipitates. More preferably, to enhance the removal of dissolved iron by precipitation, the peroxide is added to the liquid stream in the time interval (the time) before the liquid flow is directed to the phase separation of solids and liquid is ti, in order to cause sufficient precipitation of dissolved iron. Most preferably, the precipitated iron is at least substantially removed from the liquid stream in such a stage of separation of solids and liquids. It is preferable to add the peroxide upstream at the stage of separation of solids and liquids.

According to another variant, the peroxide is added in at least one point downstream of the separator for separating solids and liquids. If desired, removing precipitated solids iron can be achieved by using one or more filters or other devices for separating solids and liquids, which are available in the flowsheet or added to remove solid particles of iron. Stay peroxide in the liquid flow depends on various factors, including the amount of dissolved iron, which must be besieged. Typically, the residence time is at least 5 seconds.

As shown in the drawing, a peroxide (e.g., H2About2) add, for example, (215) and/or on line (228) before the liquid stream containing a suspension of technical aromatic acid, is introduced into the separator (135) for separating solids and liquids.

In addition, or alternatively peroxide type (the example line (265) and/or (275)) before the liquid stream with the addition of a suspension of purified aromatic acid is introduced into the separator (180) for separating solids and liquids.

According to another variant of the invention, the peroxide is added in the liquid flow, which is used as phlegm in the distillation column before the stream is sent to the column. Adding peroxide causes the precipitation of dissolved iron contained in the liquid phlegm, thus reducing the amount of dissolved iron, capable of formation of iron oxide on the inner surfaces of distillation columns, such nozzles, when phlegm is fed to a distillation column.

Preferably, to increase the degree of removal by precipitation of dissolved iron, add the peroxide to the phlegm for at least 5 seconds before phlegm is sent to a distillation column. As shown in the drawing, the peroxide direct on line (300) in the phlegm that is transmitted via line (200) to a distillation column (20). According to the variant shown in the drawing, phlegm in the distillation column (20) contains at least a portion of the mother liquor obtained after separation of the purified aromatic acid in the separator (180). Because adding the peroxide does not cause substantial precipitation of the dissolved catalytic metal with the stage of oxidation (for example, cobalt and/or manganese), recycling of these catalytic metals together with the solvent used in the oxidation, or with solvent and water from the distillation column in the oxidation reactor through line (25) is less concerned with the problems associated with the formation of iron oxide on the nozzle distillation column (20).

The addition of peroxide in the liquid flow can be accomplished by any known method. For example, you can apply the peroxide pump from the tank to the pipe leading to the line containing the liquid flow. The tank is preferably kept at a temperature of preventing unacceptable decomposition, for example, at a temperature between about 0°and about 50°preferably, between approximately 0°and about 30°C. As shown in the drawing, the peroxide may be pumped from a reservoir (not shown) in one or more lines 215, 228, 265, 275 and 300, which are respectively connected and send peroxide in line 115, 128, 165, 175 and 200. Although the peroxide type in almost any convenient point in the process shown in the drawing, preferably, added to the fluid contained or formed in one or more stages of the process: the Department of technical aromatic acid from the liquid stream stage oxidation; education solution at the stage of purification technical aroma is achieved acids in solvent for cleaning; the selection of the purified aromatic acid from the reaction mixture obtained by hydrogenation, or recycling the mother liquor cleanup phase.

Examples

In Examples 1-4 hydrogen peroxide (H2About2) was added to the stock solution at the stage of purification in order to cause precipitation of dissolved iron. For all these examples, the mother liquor stage of purification was obtained from the mother liquor stage of purification of terephthalic acid. Purification of terephthalic acid were carried out by hydrogenation of crude terephthalic acid is dissolved in the cleaning solvent containing water, obtaining dissolved purified terephthalic acid, the crystallization of purified terephthalic acid and isolation of the purified terephthalic acid from the solvent. The mother liquor stage of purification used in Examples 1-4, was a mother liquor after separation of the terephthalic acid. In Example 1 ICP (plasma spectroscopy) was performed using Spectro Flame Compact S, obtained from Spectro Analytical UK Limited. In examples 2-4 ICP was carried out on the spectrometer S.A.J.Y. Ultima, manufactured by Jobin Yvon Inc. of Edison, New Jersey.

Example 1

About 400 ml of the mother liquor cleanup phase was heated up to 80°and filtered. Analysis of the filtrate by ICP showed that the iron content is 0.47 h/million Then to the stock solution add the wheelie about 1 ml of 30%aqueous hydrogen peroxide. After about 10-15 seconds was filtered sample of the mother liquor stage of purification, analysis of the filtrate showed that the amount of dissolved iron decreased to 0.3 h/million As this example shows, the amount of dissolved iron in the mother solution, the cleanup phase decreased with the addition of peroxide.

Example 2

Examples 2A and 2b were conducted to show that the dissolved iron may be precipitated from the mother liquor cleanup phase even in the presence of significant quantities of dissolved manganese (Mn) at a temperature of 300°F (149°C).

For Examples 2A-2b mother liquor cleanup phase was filtered at room temperature to remove suspendirovanie solid terephthalic acid was analyzed by ICP to determine the quantity of dissolved metals to use. In these examples used a flow-through reactor for the continuous processing of the mother liquor stage of purification of hydrogen peroxide. The reactor consisted of a vertical tubular device made of titanium (inner diameter of 1 inch (2.54 cm)length 12 " (30, 48cm))filled with glass spheres with size 3 mm Tubular reactor was heated by an external heating to 300°F (149°C), the temperature was measured with internal thermocouple. The mother liquor cleanup phase was pumped from cutting the upstream reservoir in the main line, connected to the reactor, the solution flowed through the reactor in an upward direction with a speed of 1 l/h. In Example 2A, the hydrogen peroxide is not used. In Example 2b 25 ml/hour, 0.03 wt.%-Noah hydrogen peroxide (aqueous solution) was pumped from a reservoir through a transmission line, connected with the main line to the reactor. The resulting single stream of mother liquor stage cleaning and hydrogen peroxide solution containing 7,5 ppm, hydrogen peroxide was supplied by a short pre-heated line and then up through the tubular reactor at a pressure of 185 F./inch2(1274 kPa) and a temperature of 300°F (149°). The calculated residence time of liquid in the reactor was about 5 minutes. The product resulting from the reactor, passed through a heat exchanger, a back pressure regulator and then to the vessel for sampling, where he was selected periodic samples of the liquid. Liquid samples after filtration were analyzed for dissolved metals by ICP.

The results of Examples 2A and 2b, are shown in Table I, show the effectiveness of the treatment with hydrogen peroxide to remove iron (Fe) from the mother liquor stage of treatment, even in the presence of appreciable quantities of manganese (Mn). In Example 2A, where the peroxide was not used, reached 10 wt.% removal of iron. I believe that small amounts of oxygen caused e is the nominal removal of iron due to oxidation and the formation of oxide of iron. In Example 2b, where peroxide was used, was removed 90 wt.% iron.

Table I
The mother liquor purification stages (initial material)Example 2AExample 2b
The use of N2About2-noYes
Dissolved Fe0,40 h/million*0,36 h/million**0,04 ppm***
Remove Fe-10 wt.%90 wt.%
Dissolved Mn51 h/million*52 h/million**49 ppm***
Remove Mn-0%4%
* the average of 8 samples;

** the average of 2 samples taken after 4-5 5 h in the course of the stream

*** the average of 3 samples taken through 5-23 h along the stream

Example 3

Examples 3A and 3b were carried out in order to show that dissolved iron may be precipitated from the mother liquor cleanup phase even in the presence of large quantities of dissolved cobalt (Co) and manganese (Mn) and at a temperature of 300°F (149°C).

For Examples 3A-3b mother liquor cleanup phase was filtered pikantnoi temperature to remove splendiani solid terephthalic acid and analyzed by ICP to determine the quantity of dissolved metals to use.

In these examples used a flow-through reactor, as in Example 2, for the continuous processing of the mother liquor purification stages. The mother liquor cleanup phase flowed through the reactor in an upward direction with a speed of 1 l/h In Example 3A, the hydrogen peroxide is not used. In Example 3b 25 ml/hour, 0.03 wt.%-aqueous hydrogen peroxide solution (water) by means of a pump filed out of the tank on the line associated with the main supply line to the reactor. The resulting single stream of mother liquor stage cleaning and hydrogen peroxide solution containing 7,5 ppm, hydrogen peroxide was passed through a short line with preheating and then up through the tubular reactor at a pressure of 185 F./inch2(1274 kPa) and a temperature of 300°F (149°C). The residence time of the liquid in the reactor was approximately 5 minutes. Stream from the reactor was passed through a heat exchanger, the regulator back pressure and then fed into the vessel, periodically taking samples. Liquid samples after filtration analyzed by ICP for dissolved metals.

The results obtained in these Examples 3A and 3b, are shown in Table II, show the effectiveness of the treatment with hydrogen peroxide for removal of iron (Re) from the mother liquor cleanup phase even in the presence of appreciable amounts of cobalt (Co) and manganese (Mn). In Example 3A when the peroxide was not used, achieved the degree of removal of dissolved iron, equal to 28 wt.%. I believe that this is the nominal removal of iron by oxidation and formation of oxide of iron is caused by small amounts of oxygen. In Example 3b, where peroxide was used, the degree of removal of dissolved iron was equal to 75 wt.%.

Table II
The mother liquor purification stages (initial material)Example 3AExample 3b
The use of N2About2-noYes
Dissolved Feof 0.57 ppm0,41 ppm*0,14 ppm**
Remove Fe-28%75%
Dissolved Mn32 ppm33 ppm*32 ppm**
Remove Mn-0%0%
Dissolved Co12 ppm12 ppm*12 h/m**
Delete From-0%0%
* the average of 3 samples taken 2-4 h;

** average for 4 samples taken after 2-8 h in the process.

Example 4

Example 4 was performed to show that the dissolved iron may be precipitated from the mother liquor cleanup phase even in the presence of terephthalic acid and appreciable amounts of cobalt (Co) and manganese (Mn).

The mother liquor cleanup phase was filtered at room temperature to remove suspended solid terephthalic acid and analyzed by ICP to determine the quantity of dissolved metals to use. Terephthalic acid was added to the filtered stock solution cleansing stage, receiving the concentration of suspended terephthalic acid in the mother solution, the stage of purification of 0.1 wt.% (1000 ppm). In this example, used as in Example 2, the flow reactor, where it was processed continuously the mother solution at the stage of purification of hydrogen peroxide. The mother liquor stage of purification was applied to the reactor upwards with a speed of 1 l/h In this example, 25 ml/hour, 0.03 wt.%-aqueous hydrogen peroxide solution (aqueous) was filed by the pump from the reservoir through the line associated with the main supply line to the reactor. The resulting single stream of mother liquor and hydrogen peroxide containing 7,5 ppm, hydrogen peroxide was passed through a short line pre-heated line and served up in a tubular reactor at a pressure of 185 F./inch2(1274 kPa) temperature 300° F (149°C). The residence time of the liquid in the reactor was approximately 5 minutes. Stream from the reactor was passed through a heat exchanger, the regulator back pressure and then fed into the vessel, periodically taking samples. Liquid samples after filtration analyzed by ICP for dissolved metals.

The results of Example 4 are shown in Table III, show the effectiveness of the treatment with hydrogen peroxide to remove iron (Fe) from the mother liquor cleanup phase even in the presence of terephthalic acid and appreciable amounts of cobalt (Co) and manganese (Mn).

Table III
The mother liquor purification stages (initial material)Example 4
The use of N2About2-Yes
Dissolved Feof 0.56 ppm0,12 ppm*
Remove Fe-79%
Dissolved Mn34 ppm32,5 h/m*
Remove MP-4%
Dissolved Coto 11.9 ppmto 11.3 ppm*
Delete From-5%
* average mn is necessary for 4 samples, selected through 2-8 h in the process.

Example 5.

In this example, the peroxide was added during normal operation of an industrial reactor, where she spent the oxidation of aromatic raw materials, including paraxylene, obtaining the crude terephthalic acid and purification of the resulting crude acid. The oxidation was carried out in liquid phase in a solvent containing acetic acid and water, in the presence of a catalyst containing cobalt and manganese with a source of bromine as a promoter and air as the oxygen source, the off-gas from the oxidation reactor containing water vapor and acetic acid, was applied to a distillation column equipped with a titanium nozzle and liquid phlegm. Chemical hydrogen peroxide were purchased in the form of a 50 wt.%-aqueous solution in water, was pumped through the supply line, in which it is mixed with the flow of demineralized water to dilute hydrogen peroxide to a concentration of about 0.3 wt.%, in suspension, solid purified terephthalic acid, which was applied to a filter to separate the solid acid from the liquid. Dissolved iron in the liquid was equal to approximately 0.7 to 0.8 ppm, by weight. The hydrogen peroxide solution was injectively with speed, providing approximately 10-20 g of hydrogen peroxide per 1000 kg slurry purification stages applied to the filter. The experiment was carried out with two inter is Alami, each of which lasted approximately fromtohours. Purified terephthalic acid obtained by this process contain a sufficient amount of coloring impurities, but did not contain virtually iron and other indicators was comparable to the product obtained without the addition of peroxide.

Table IV shows the content of iron remaining in the liquid after treatment with peroxide.

Table IV
SampleAdding peroxide (l/h)Peroxide in liquid (ppm, wt)F.e in liquid (wt.% from the original. Fe)Fe, remove from the liquid (wt.%)
And0,8193763
In0,515982
0,8287030
D1,28134357
E1,78184951

As can be seen from this example and Table, iron was oxidized by adding hydrogen peroxide as dissolved VC is for the sample stock solution, selected after addition of the peroxide, was lower than in samples taken before the addition of the peroxide. Concentrations of metals oxidation catalyst contained in the mother solution, not dependent on the addition of peroxide.

Example 6

Another experience to add peroxide were performed for obtaining purified terephthalic acid on an industrial scale, when conducting a liquid-phase oxidation of paraxylene with obtaining the crude terephthalic acid and purification of the resulting crude acid. The oxidation was performed using acetic acid and water as a solvent, air as a source of oxygen and a catalyst comprising cobalt and manganese and bromine, as a promoter. Off-gas from the reactor was submitted to a distillation column. Phlegm in the distillation column consisted of the mother liquor cleanup phase obtained after separation of the solids of purified terephthalic acid from the solution phase cleanup.

The peroxide used in this example was a peroxide, which is used in the manufacture of semiconductors, in the form of a 31 wt.%-aqueous solution in water. The peroxide contained in the feeder and fed by the pump into the hole storage tanks for the mother liquor cleansing stage, located below in the course of the filtration process solid purified acid, sod is ramasa in liquid medium for cleaning, in line with an inner diameter of 25.4 cm by means of a dosing pump Pulsafeeder diaphragm with a maximum speed of approximately 6 l/h. The pump was a twin with two diaphragms, made of Teflon for compatibility with hydrogen peroxide. A flexible hose connecting the collector to supply peroxide pump was made of Teflon Goodyear (HI-PER", inner diameter equal to 2.54 cm) and was intended for the continuous feed of hydrogen peroxide. Point for selection of the sample was located below the point of injection pump and corresponded to a residence time of about 10 seconds at normal speeds passing the mother liquor. Although this point for sampling ensured a relatively short time under normal flow velocities, for the purposes of this example, it was considered appropriate.

The peroxide solution was injectively with speed, providing 15-17 g of hydrogen peroxide solution per 1000 kg of the mother liquor for a period of time equal to about 26 hours, in one series of experiments, and the speed corresponding to 9-10 g of hydrogen peroxide per 1000 kg of the mother liquor for a period of time equal to about 6 hours, in the second series of experiments. In all experiments, the temperature of the liquid, which was injectively the peroxide solution, was approximately 150°C. the Sample liquid, which was added to the solution, otbi the Ali at the point of sampling and analyzed for metal content by ICP. Control samples were taken within one hour when feeding peroxide has been disabled.

In the samples taken in the first series of experiments, the dissolved iron was about 80% less, than in samples taken at shutdown, injection, which is the result of the introduction of the peroxide solution.

In the samples taken during the experiments with a lower rate of addition of hydrogen peroxide was observed in about 40%oxidation of iron. Purified terephthalic acid obtained during these experiments, comparable with the industrial product obtained without the addition of peroxide.

It should be borne in mind that this invention is not limited to specific examples, many other variants of this invention may be made within the scope of this invention defined by the following claims and equivalents.

1. Method for preparation of aromatic carboxylic acid, including stage

A) contacting capable of oxidizing an aromatic feedstock with molecular oxygen in the presence of an oxidation catalyst containing at least one metal with an atomic number from 21 to 82, and solvent, representing2-C5aliphatic carboxylic acid in the liquid phase of the reaction mixture in the reactor under oxidation conditions with about what adowanie solid product, contains technical aromatic carboxylic acid, liquid, solvent and water, and off-gas containing water vapor and solvent vapours;

B) separating the solid product containing technical aromatic carboxylic acid from the liquid;

B) distilling at least a portion of the off-gas in a distillation column equipped with phlegm, to separate the solvent vapor from the water vapor, the formation of a liquid stream containing solvent, and the upper distillation wrap containing water vapor;

G) returning at least part of the liquid stream from the stage In the reactor;

D) dissolving at least part of the separated solid product containing technical aromatic carboxylic acid in a solvent cleanup phase to form a liquid solution phase purification;

E) contacting the solution stage cleaning with hydrogen in the presence of a hydrogenation catalyst containing at least one metal of group VIII of the Periodic table of the elements and conditions of hydrogenation at temperatures from 233 to 316°and pressure from 6205 up 10340 kPa, effective for the formation of a solution containing purified aromatic carboxylic acid, and a liquid solvent for cleaning;

G) separating the purified aromatic Carbo the OIC acid from the solution, solvent for cleaning, which is obtained in stage E, obtaining solid purified aromatic carboxylic acid and the mother liquor purification stages;

C) returning at least part of the mother liquor cleanup phase on at least one of the stages b and D; and

I) adding at least one peroxide of the formula R1-O-O-R2where R1and R2identical or different, denote hydrogen or a hydrocarbon group, in the liquid residing on at least one of the other stages, or resulting from, at least one of these stages, where the peroxide is added in amounts effective to precipitate the dissolved iron from the liquid stream.

2. The method according to claim 1, characterized in that the peroxide is added to the liquid stream obtained in stage A.

3. The method according to claim 1, characterized in that the peroxide is added in a liquid stream, located or obtained in stage B.

4. The method according to claim 1, characterized in that the peroxide is added into the liquid flow, or are obtained at the stage J.

5. The method according to claim 1, characterized in that the peroxide is added into the liquid flow under Z.

6. The method according to claim 1, characterized in that it further includes a step of recycling the mother liquor oxidation steps consisting in the recycle liquid is ABC in the reactor, at least part of the liquid after the separation stage B solid product, including technical aromatic carboxylic acid.

7. The method according to claim 6, characterized in that the peroxide is added in the liquid flow at the stage of recycling the mother liquor oxidation steps.

8. The method according to claim 1, characterized in that the peroxide is added in at least a portion of the mother liquor cleanup phase remaining after separation of the purified aromatic acids on stage W, and the mother liquor after the addition of peroxide return to the stage, so the phlegm on stage contains a solvent purification stages.

9. The method according to any of the preceding paragraphs, characterized in that it additionally includes the stage at which carry out the separation of the liquid stream, to which was added peroxide, solid and liquid, suitable for removal of solid iron from the liquid stream.

10. The method of regulating the quantities of dissolved iron in liquid flows in the process of producing aromatic carboxylic acids, including the state of the probe is capable of oxidizing an aromatic feedstock with molecular oxygen in the presence of an oxidation catalyst containing at least one metal with an atomic number from 21 to 82, and solvent, which represents a C2-C5aliphatic carboxylic to the slot, in the liquid-phase reaction mixture in the reactor under the conditions of oxidation with formation of a solid product containing technical aromatic carboxylic acid, a liquid stream containing solvent and water, and off-gas containing water vapor and vapors of the solvent, characterized in that at least part of the liquid flow to regulate therein the amount of dissolved iron add at least one peroxide of the formula R1-O-O-R2where R1and R2identical or different, denote hydrogen or a hydrocarbon group, in an amount effective to precipitate the dissolved iron from the liquid stream.

11. The method according to claim 10, characterized in that the liquid stream contains at least one dissolved metal that is part of the oxidation catalyst having an atomic number from about 21 to about 82, and the amount of dissolved iron in the liquid flow is adjusted without significant deposition of metal catalyst.

12. The method according to claim 10 or 11, characterized in that it further includes a step of separation of the liquid stream from the technical aromatic acid, and a peroxide is added to at least part of the liquid flow and after phase separation.

13. The method according to item 12, characterized in that it further includes a step of recycling into the reaction vessel at measures which, part of the liquid stream that was added peroxide.

14. The method according to claim 10, characterized in that it further includes a step of distillation, at least, part of the off-gas to separate the solvent vapor from the water vapor in the distillation column equipped with phlegm containing at least a portion of the liquid stream obtained after separation of the liquid stream from the solid technical aromatic acid, and a peroxide is added to the liquid stream prior to the introduction of phlegmy in the distillation column.

15. The method according to claim 10, characterized in that the technical aromatic carboxylic acid is a terephthalic acid, the solvent is an acetic acid, the catalyst contains at least one metal selected from cobalt and manganese, and the peroxide is a peroxide.

16. The method of regulating the quantities of dissolved iron in liquid flows in the cleaning process technical aromatic carboxylic acid, including the hydrogenation of technical aromatic carboxylic acid in the presence of a hydrogenation catalyst containing at least one metal of group VIII of the Periodic table of elements, and solvent purification stages, in the conditions of hydrogenation at temperatures from 233 to 316°and pressure from 6205 up 10340 kPa, to produce clean, aromati eskay carboxylic acid, dissolved in the liquid stream, and adding at least one peroxide of the formula R1-O-O-R2where R1and R2identical or different, denote hydrogen or a hydrocarbon group, to the liquid stream in a quantity effective to regulate it dissolved iron.

17. The method according to item 16, characterized in that it includes a step in which at least part of the purified aromatic carboxylic acid precipitates before adding peroxide.

18. The method according to 17, characterized in that it includes a step in which at least part of the precipitated purified aromatic carboxylic acid is separated from the liquid stream.

19. The method according to 17 or p, characterized in that the purified aromatic carboxylic acid is a terephthalic acid and peroxide is a peroxide.

Priority items:

23.04.2002 - according to claims 1-19.



 

Same patents:

FIELD: carbon materials and hydrogenation-dehydrogenation catalysts.

SUBSTANCE: invention relates to improved crude terephthalic acid purification process via catalyzed hydrogenating additional treatment effected on catalyst material, which contains at least one hydrogenation metal deposited on carbonaceous support, namely plane-shaped carbonaceous fibers in the form of woven, knitted, tricot, and/or felt mixture or in the form of parallel fibers or ribbons, plane-shaped material having at least two opposite edges, by means of which catalyst material is secured in reactor so ensuring stability of its shape. Catalyst can also be monolithic and contain at least one catalyst material, from which at least one is hydrogenation metal deposited on carbonaceous fibers and at least one non-catalyst material and, bound to it, supporting or backbone member. Invention also relates to monolithic catalyst serving to purify crude terephthalic acid, comprising at least one catalyst material, which contains at least one hydrogenation metal deposited on carbonaceous fibers and at least one, bound to it, supporting or backbone member, which mechanically supports catalyst material and holds it in monolithic state.

EFFECT: increased mechanical strength and abrasion resistance.

8 cl, 4 ex

FIELD: chemical industry; methods of production of the purified crystalline terephthalic acid.

SUBSTANCE: the invention is pertaining to the improved method of production and separation of the crystalline terephthalic acid containing less than 150 mass ppm of the p-toluene acid in terms of the mass of the terephthalic acid. The method provides for the following stages: (1) loading of (i) para- xylene, (ii) the water reactionary acetic-acidic medium containing the resolved in it components of the oxidation catalyst, and (iii) the gas containing oxygen fed under pressure in the first zone of oxidation, in which the liquid-phase exothermal oxidization of the para-xylene takes place, in which the temperature and the pressure inside the first being under pressure reactor of the oxidization are maintained at from 150°С up to 180°С and from 3.5 up to 13 absolute bars; (2) removal from the reactor upper part of the steam containing the evaporated reactionary acetic-acidic medium and the gas depleted by the oxygen including carbon dioxide, the inertial components and less than 9 volumetric percents of oxygen in terms of the non-condensable components of the steam; (3) removal from the lower part of the first reactor of the oxidized product including (i) the solid and dissolved terephthalic acid and (ii) the products of the non-complete oxidation and (ii) the water reactionary acetic-acidic medium containing the dissolved oxidation catalyst; (4) loading of (i) the oxidized product from the stage (3) and (ii) the gas containing oxygen, into the second being under pressure zone of the oxidation in which the liquid-phase exothermal oxidization of the products of the non-complete oxidization takes place; at that the temperature and the pressure in the second being under pressure reactor of the oxidization are maintained from 185°С up to 230°С and from 4.5 up to 18.3 absolute bar; (5) removal from the upper part of the second steam reactor containing the evaporated water reactionary acetic-acidic medium and gas depleted by the oxygen, including carbon dioxide, the inertial components and less, than 5 volumetric percents of oxygen in terms of the non-condensable components of the steam; (6) removal from the lower part of the second reactor of the second oxidized product including (i) the solid and dissolved terephthalic acid and the products of the non-complete oxidation and (ii) the water reactionary acetic-acidic medium containing the dissolved oxidation catalyst; (7) separation of the terephthalic acid from (ii) the water reactionary acetic-acidic medium of the stage (6) for production the terephthalic acid containing less than 900 mass ppm of 4- carboxybenzaldehyde and the p-toluene acid; (8) dissolution of the terephthalic acid gained at the stage (7) in the water for formation of the solution containing from 10 up to 35 mass % of the dissolved terephthalic acid containing less than 900 mass ppm of the 4- carboxybenzaldehyde and the p-toluene acid in respect to the mass of the present terephthalic acid at the temperature from 260°С up to 320°С and the pressure sufficient for maintaining the solution in the liquid phase and introduction of the solution in contact with hydrogen at presence of the catalytic agent of hydrogenation with production of the solution of the hydrogenated product; (9) loading of the solution of the stage (8) into the crystallization zone including the set of the connected in series crystallizers, in which the solution is subjected to the evaporating cooling with the controlled velocity using the significant drop of the temperature and the pressure for initiation of the crystallization process of the terephthalic acid, at the pressure of the solution in the end of the zone of the crystallization is atmospheric or below; (10) conduct condensation of the dissolvent evaporated from the crystallizers and guide the condensed dissolvent back into the zone of the crystallization by feeding the part of the condensed dissolvent in the line of removal of the product of the crystallizer, from which the dissolvent is removed in the form of the vapor; and (11) conduct separation of the solid crystalline terephthalic acid containing less than 150 mass ppm of the p-toluene acid in terms of the mass of the terephthalic acid by separation of the solid material from the liquid under the atmospheric pressure. The method allows to obtain the target product in the improved crystalline form.

EFFECT: the invention ensures production of the target product in the improved crystalline form.

8 cl, 3 tbl, 2 dwg, 3 ex

FIELD: organic chemistry, chemical technology.

SUBSTANCE: invention relates to the improved method for isolating crystalline terephthalic acid comprising less 150 mas. p. p. per million (ppm) of p-toluic acid with respect to weight of terephthalic acid. Method involves the following steps: (1) preparing a solution containing from 10 to 35 wt.-% of dissolved terephthalic acid wherein from 150 to 1100 ppm of p-toluic acid is dissolved with respect to mass of terephthalic acid at temperature from 260°C to 320°C and under pressure providing maintaining the solution in liquid phase; (2) charge of solution from step (1) to crystallization zone comprising multitude amount of associated crystallizers wherein the solution is subjected for cooling at evaporation at the controlled rate by the moderate pressure and temperature reducing resulting to crystallization of terephthalic acid and wherein the solution pressure at the end of crystallization zone is equal to atmosphere pressure or lower; (3) condensation of solvent evaporated from crystallizers and recovering the condensed solution to the crystallization zone to place of descending flow from crystallizer wherein solvent is removed by evaporation, and (4) isolation of solid crystalline terephthalic acid comprising less 150 ppm of p-toluic acid with respect to the terephthalic acid mass by separation of the phase liquid-solid substance under atmosphere pressure. The advantage of method is preparing the end product in improved crystalline form and carrying out the process under atmosphere pressure or pressure near to atmosphere pressure.

EFFECT: improved method of crystallization.

3 cl, 1 dwg, 1 tbl, 2 ex

FIELD: organic chemistry, chemical technology.

SUBSTANCE: invention relates to the improved method for chemical reutilization of depleted polyethylene terephthalate, especially to non-classified crumbs of utilized polyethylene terephthalate articles resulting to preparing terephthalic acid and ethylene glycol. Method involves hydrolysis of utility waste polyethylene terephthalate with aim for its depolymerization and involves the following steps: (a) separation of polyethylene terephthalate component in the parent raw by its transfer to fragile form by using crystallization, grinding and the following screening processes; (b) continuous two-step hydrolysis of polyethylene terephthalate carried out at the first step by injection of steam into polymer melt followed by carrying out the hydrolysis reaction of products from the first step with ammonium hydroxide and by the following (c) precipitation of terephthalic acid from aqueous solution of hydrolysis products from the second step with inorganic acid and separation of terephthalic acid by filtration method and by the following (d) extraction of ethylene glycol by rectifying from solution of the second step hydrolysis products after separation of terephthalic acid. This technologically simple and effective method provides possibility for treatment of very contaminated the parent raw and providing high purity of end products.

EFFECT: improved treatment method.

5 cl, 1 ex

FIELD: organic chemistry, chemical technology.

SUBSTANCE: invention relates to a continuous method for preparing highly pure terephthalic acid. Method involves oxidation of p-xylene with oxygen-containing gas in acetic acid medium in the presence of catalyst comprising heavy metal salts, such as cobalt and manganese and halide compounds under increased pressure and temperature up to the definite degree of conversion of para-xylene to terephthalic acid at the first step and the following two-step additional oxidation of prepared reaction mixture and isolation of the end product. Mixing time of reagents is <25 s, oxidation at the first step is carried out at temperature 180-200°C up to conversion degree of p-xylene 95%, not above, oxidation at the second step is carried out at temperature 175-185°C and before feeding to the third step of oxidation the reaction mass is heated to 200-260°C, kept for 8-12 min and oxidized at temperature 180-200°C in the presence of catalyst comprising Ni and/or Zr salts additionally. As halide compounds method involves using XBr or XBr + XCl wherein X is H, Na, Li followed by isolation of solid products of oxidation after the third step and successive treatment with pure acetic acid and water in the mass ratio terephthalic acid : solvent = 1:3. Invention provides intensification of process and to enhance quality of terephthalic acid.

EFFECT: improved method for preparing.

1 tbl, 1 dwg, 14 ex

The invention relates to an improved method of reducing the content of 4-carboxybenzene in the production of terephthalic or 3-carboxymethylthio in the production of isophthalic acid, comprising: (a) dissolving crude terephthalic acid or crude isophthalic acid in a solvent at a temperature of from 50 to 250With obtaining a solution; (b) crystallization of the purified acid from this solution by reducing the temperature and/or pressure; (C) the Department specified crystallized terephthalic acid or isophthalic acid from the solution; (d) adding an oxidant to the reactor oxidation carboxyanhydride for oxidation specified filtered solution of stage (C), leading to the transformation of 4-carboxybenzene or 3-carboxymethylthio in terephthalic acid or isophthalic acid; (e) evaporating the solvent from this solution from step (d); (f) cooling the concentrated solution from step (e) for crystallization additional quantities of purified terephthalic acid or isophthalic acid and filtering the specified slurry and recycling the most part, the mother liquor from step (f) in the devices is

The invention relates to an improved process for the preparation of terephthalic and isophthalic acids

The invention relates to the purification of terephthalic acid which is a raw material for producing polyester resin

The invention relates to a method for producing aromatic carboxylic acids by exothermic liquid-phase oxidation reaction of the corresponding alkylaromatic parent compound in the liquid-phase reaction mixture consisting of water, low molecular weight monocarboxylic acid as a solvent, the oxidation catalyst on the basis of heavy metal and a source of molecular oxygen in the reaction conditions leading to the gaseous exhaust stream of high pressure water-containing gaseous by-products and gaseous low molecular weight monocarboxylic acid, followed by distillation of the aromatic carboxylic acid and separation of the exhaust flow high pressure, while the exhaust flow high-pressure direct high-performance distillation column to remove at least 95 wt.% low molecular weight monocarboxylic acid from the waste stream, with the formation of the second exhaust flow high-pressure containing water and gaseous by-products formed in the oxidation process, and then the second exhaust stream of high pressure is directed to the means for the release of energy from the second exhaust flow

The invention relates to a method for and apparatus for producing purified terephthalic acid from its liquid dispersion containing impurities in the form of unreacted starting materials, solvents, products of side reactions and/or other undesirable materials

FIELD: carbon materials and hydrogenation-dehydrogenation catalysts.

SUBSTANCE: invention relates to improved crude terephthalic acid purification process via catalyzed hydrogenating additional treatment effected on catalyst material, which contains at least one hydrogenation metal deposited on carbonaceous support, namely plane-shaped carbonaceous fibers in the form of woven, knitted, tricot, and/or felt mixture or in the form of parallel fibers or ribbons, plane-shaped material having at least two opposite edges, by means of which catalyst material is secured in reactor so ensuring stability of its shape. Catalyst can also be monolithic and contain at least one catalyst material, from which at least one is hydrogenation metal deposited on carbonaceous fibers and at least one non-catalyst material and, bound to it, supporting or backbone member. Invention also relates to monolithic catalyst serving to purify crude terephthalic acid, comprising at least one catalyst material, which contains at least one hydrogenation metal deposited on carbonaceous fibers and at least one, bound to it, supporting or backbone member, which mechanically supports catalyst material and holds it in monolithic state.

EFFECT: increased mechanical strength and abrasion resistance.

8 cl, 4 ex

FIELD: industrial production of methacrylic acids at reduced amount of industrial wastes.

SUBSTANCE: proposed method is performed by catalytic oxidation of propane, propylene or isobutylene in vapor phase at separation of final product and forming of high-boiling mixture as by-product which contains (according to Michaels addition) water, alcohol or methacrylic acid added to methacrylic group. By-product is decomposed in thermal decomposition reactor at simultaneous distillation of decomposition products in distilling column from which methacrylic acid is taken in form of distillate. Flow of liquid decomposition residue is forced for peripheral direction by means of mixing blades before withdrawal from reactor. Peripheral direction is obtained with the aid of liquid fed from the outside of decomposition reactor; to this end use is made of initial high-boiling material or flow of liquid discharged from decomposition reactor. If necessary, etherification stage is performed through interaction with alcohol for obtaining methecrylic ester. Decomposition of by-product formed at obtaining methacrylic acid by oxidation of propylene or isobutylene or at obtaining methacrylic acid by interaction of acid with alcohol by alcohol through introduction of by-product into thermal decomposition reactor provided with distilling column which has plates made in form of disks and toroids for simultaneous decomposition and distillation. Plant proposed for realization of this method includes thermal decomposition reactor and distilling column, level meters and lines for discharge of liquid containing easily polymerized compounds. Level indicator mounted at area of accumulation of liquid shows pressure differential. Line for detecting the side of high pressure of this level meter is connected with accumulated liquid discharge line.

EFFECT: updated technology; increased yield of target products.

38 cl, 14 dwg, 2 tbl, ex

FIELD: chemical technology.

SUBSTANCE: invention relates to technology for synthesis of acetic acid by the cabonylation reaction of methanol with carbon monoxide. Method involves preparing the productive flow in the reaction section containing acetic acid, acetaldehyde, water and other impurities. In the cleansing treatment the reaction products are subjected for treatment wherein acetaldehyde impurities are oxidized to either acetic acid after its isolation and recovered to the reaction zone or to carbon dioxide and water that removed from the system. As result, method provides excluding the negative effect of acetaldehyde at step for separation of the reaction products. Oxygen, air or their mixtures, ozone, carbon peroxide or peracetic acid are used as oxidant. As possible variants of the method, the productive flow is fed to distillation column wherein flow of light products or heavy products are isolated under condition that each of these flow involves acetic acid, acetaldehyde and water. Then "light" or "heavy" flow is subjected for oxidation as said above to reduce the concentration of acetaldehyde. As a variant of the method the flow of heavy products can be treated by extraction with water followed by oxidation of acetaldehyde-containing aqueous phase. Invention provides improvement of method due to exclusion of the necessity of purification of the end product from acetaldehyde impurity.

EFFECT: improved treatment method.

20 cl, 3 tbl, 35 ex

FIELD: industrial organic synthesis.

SUBSTANCE: method comprises contacting vapor-phase mixture at 150-205°C with alkali and/or alkali-earth metal carboxylate dispersed on activated carbon resulting in conversion of alkyl iodides into corresponding carboxylic acid esters, while iodine becomes bound in the form of inorganic iodide.

EFFECT: facilitated freeing of carboxylic acid product from organic iodine compounds.

4 cl, 2 tbl, 32 ex

FIELD: chemical technology.

SUBSTANCE: invention relates to the improved method for extraction of carbonyl and (or) acid compounds from the complex multicomponent organic liquid mixtures. Method involves treatment of organic liquid mixtures with sodium sulfite an aqueous solution at intensity of mechanical stirring providing formation of uniform emulsion. The content of carbonyl compounds and acids in the parent mixture to be treated is determined and treatment is carried out with 4.16-26% aqueous solution of sodium sulfite as measured 1.05-1.1 mole of sodium sulfite per 1 g-equiv. of carbonyl compound, and in exceeding of the content of acids (g-equiv.) in the parent mixture over the content of carbonyl compounds - with 1 mole sodium sulfite per 1 g-equiv. of acids and in the mass ratio of sodium sulfite aqueous solution to organic mixture = (1-2.5):(2-1) at temperature 15-30°C; if the content of acids in the parent mixture (g-equiv.) is less the content of carbonyl compounds (g-equiv.) then under control of pH value change in an aqueous phase method involves additional addition of mineral or organic acid in the amount as a difference in the content of carbonyl compounds (g-equiv.) and the content of acids (g-equiv.) in the parent charge of organic mixture per treatment at such rate that pH value of aqueous would decrease constantly but not less 6.5. This simple method provides removing both carbonyl compounds and acids being without significant limitations for the content of carbonyl compounds and acids in the parent mixture. Invention can be used in different branches of industry for treatment of compositions or for utilization of carbonyl compounds and (or) acids.

EFFECT: improved method for extraction.

5 cl, 3 tbl, 26 ex

FIELD: organic chemistry, chemical technology.

SUBSTANCE: invention relates to a method for purifying naphthalene carboxylic acid. Method involves contacting crude naphthalene acid with solvent used for purifying in the presence of hydrogen and catalyst that comprises a precious metal of VIII group taken among palladium, platinum and ruthenium and metal of group IVB taken among silicon, germanium, tin and lead at temperature about from 520 to 575°F. Proposed method provides preparing reduced amount of organic pollution in purified acid as compared with other methods of purification.

EFFECT: improved purifying method.

19 cl, 1 dwg, 5 tbl, 5 ex

FIELD: chemical technology.

SUBSTANCE: invention relates to the improved method for treatment of organic mixtures from carbonyl compounds and acids by their treatment with sodium sulfite. Method involves using organic mixtures comprising carbonyl compounds and carboxylic acids in the ratio = 1 g-equiv. : 1 g-equiv. or with excess of acids, or with excess of carbonyl compounds. In this case before treatment with sodium sulfite carboxylic acid is added to the parent mixture in the amount to obtain the ratio of carbonyl compounds to acids as 1 g-equiv. per 1 g-equiv. and treatment is carried out with solid sodium sulfite in beaded mill with the mass ratio of the composition charge to glass beads as a grinding agent = 1:(1-2) at the rate of mechanical mixer rotation 1440 rev/min, not less, and in dosing sodium sulfite 1.2-1.5 mole per 1 g-equiv. of carbonyl compounds or excess of acid in the presence of stimulating additive up to practically complete consumption of carbonyl compounds, or carbonyl compounds and acids. Process is carried out in the presence of sodium and potassium hydroxide and acetate and sodium nitrate also as a stimulating additive taken in the amount 1-4% of mass sodium sulfite to be added up to practically complete consumption of carbonyl compounds and acids in composition to be treated. This simple method provides high degree of purification being even in small parent content of carbonyl compounds and acids.

EFFECT: improved method for treatment.

4 cl, 3 tbl, 19 ex

The invention relates to an improved method of isolation and purification of adipic acid, used for the production of polyamide-6,6 or polyurethanes, which consists in treating the reaction mixture obtained by direct oxidation of cyclohexane to adipic acid by molecular oxygen in an organic solvent and in the presence of a catalyst, removing by-products from the reaction mixture and the adipic acid by crystallization, and before adipic acid from the reaction environment carry out consistently the following operations: the decantation of the two phases of the reaction medium with the formation of the upper organic the cyclohexane phase, containing mainly cyclohexane, and the lower phase, containing mainly the solvent, the resulting dicarboxylic acid, the catalyst and other reaction products and unreacted cyclohexane; distillation bottom phase to separate, on the one hand, distillate containing at least a part of the most volatile compounds, such as organic solvent, water and unreacted cyclohexane, cyclohexanone, cyclohexanol, complex cyclohexylamine esters and possibly lactones, and, with the pin acid from residue from distillation by means of crystallization and thus obtained crude adipic acid is subjected in aqueous solution purification by hydrogenation and/or oxidation with subsequent crystallization and recrystallization of the purified adipic acid in water
The invention relates to a method of regeneration vysokotirazhnyh carboxylic acids of the flow of exhaust gases

The invention relates to new (+) or (-)-8-halogen-6-hydroxyoctanoic acids of the formula I, where X denotes Cl, Br, I, alkyl esters of formula II and their salts with-methylbenzylamino formula III

FIELD: coordination compound chemistry.

SUBSTANCE: invention relates to technology of complexes of iron with salicylic acid suitable for use in a variety of technical areas and in medicine. Title complex is obtained via interaction of metal with acid using air oxygen as oxidant. Salicylic acid is used in butyl acetate or n-butyl alcohol solution with dissolved molecular iodine or potassium iodide. Iron is provided in the form of steel or cast iron shell, shaft, and blade of mechanical mixer as well as, agitated by the mixer, reduced iron powder fractions, broken cast iron or broken steel cuttings, cast iron or steel filings. Process is carried out at stirring with high-speed mechanical stirrer and air bubbling allowing self-heating of reaction mixture to 70-80°C until 1.72-1.85 mole/kg iron compounds is accumulated in reaction mixture in the form of suspension, whereupon mixing is stopped. Suspension is freed of unreacted fine iron and/or alloy(s) thereof and subjected to hot filtration, Filtrate is warmed to eliminate precipitated solid phase and then slowly cooled to ambient temperature. Precipitated solid phase is filtered off, dried, and recrystallized, while filtrate is recycled.

EFFECT: improved technology required only accessible starting materials and increased yield of desired product.

2 cl, 4 ex

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