Method of production of the purified terephthalic acid

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

 

This invention relates to a new method of obtaining purified terephthalic acid by a new combination of stages, beginning with the oxidation dialkylanilines compounds, such as p-xylene. More specifically this invention relates to the production of purified terephthalic acid based on the oxidation method, in which first dialkylanilines connection oxidized to terephthalic acid using a two-stage method that uses certain conditions to obtain terephthalic acid, having a greater purity, and then purified terephthalic acid by hydrogenation and allocate using new method of crystallization.

Aromatic dicarboxylic acids such as terephthalic acid and isophthalic acid, are of great interest from a commercial point of view and are widely used for obtaining a variety of polyester polymers, such as fiber-forming and moulding types of polyesters. Terephthalic acid (TPA) is one of the basic building blocks upon receipt of a linear polyester resins used in the manufacture of polyester films, packaging materials and bottles. TPA used in the production of such polyester resins must meet certain requirements minimum purity. The condition of purity terephthalic acid is pervo the turn the lack of significant content 4-carboxyanhydride (4-KBA) and p-toluene acid, which are present in significant quantities in crude grades of commercially available terephthalic acid. As KBA, and toluene acid are products of partial oxidation, formed during the production of TPA by the catalytic oxidation of p-xylene. Purified form also means the absence of colored particles, which give the characteristic yellow hue of the crude material. Colored particles are aromatic compounds having a structure benilov, fluorenone and/or anthraquinones. 4-KBA and p-toluene acid partially inhibit polymerization, since they lead to chain breakage during the condensation reaction between terephthalic acid and ethylene glycol in obtaining poly(ethyleneterephthalate) (PET).

The crude terephthalic acid may be purified by hydrogenation. In the usual method of hydrogenation of crude terephthalic acid is dissolved in water at elevated temperature and pressure and hydronaut for the conversion of 4-KBA in p-toluene acid. Hydrogenation also makes colored particles in unpainted connection. One of the limitations in the development of the method of separation of purified terephthalic acid from hydrogenated liquid solution is acceptable content is 4-KBA and p-toluene acid in the final product. For example, purified terephthalic acid (TPA) typically contains less than 150 wt. mlnc p-toluene acid. The methods of selection to obtain a purified terephthalic acid is used many ways the separation of solid - liquid, including crystallization, centrifugation, filtering, and their combination.

The crude terephthalic acid obtained by the initial oxidation dialkylanilines connection, usually p-xylene, typically has a total content of 4-KBA and p-toluene acid from 150 to 1100 wt. mlnc in the calculation of the solids present. The crude terephthalic acid also contains smaller amounts, for example in the range from 20 to 200 wt. mlnc, characteristic yellow compounds. These compounds are colored aromatic compounds having the structure of benzil, fluorenone and/or anthraquinone, which result from side reactions, combinations occurring during the oxidation of p-xylene. It is necessary to clean the crude terephthalic acid when it is used as a starting material for the production of polyester fibers, which are necessary purified terephthalic acid (TPA) as the starting material.

This cleaning usually includes a combination of the crude terephthalic acid is separated from the oxidation of water on the I education of its suspension, which is heated to dissolve the crude terephthalic acid and impurities in the water and receiving water solution. This solution is then transferred to the stage of recovery, in which the solution is injected into contact with hydrogen in the presence of a heterogeneous catalyst, typically palladium on carbon substrate, at elevated temperatures, such as from 200 to 375°With, for purification of TPA. Stage hydrogenation converts various colored particles present in the crude terephthalic acid in colorless products. A mixture of 4-KBA turns into p-toluene acid.

Subsequent separation and isolation of the product of terephthalic acid can be carried out using various methods of separating solid - liquid. Method stage equilibrium crystallization is one of the ways of separation. In this way, the evaporation is controlled by regulating the back pressure in multiple stages of crystallization to control the speed with which crystallizes the stream, past the hydrogenation. For terephthalic acid is considered that the shock cooling of the stream, past the hydrogenation, to a temperature below 165°promotes joint deposition (cocrystallization) impurities, especially p-toluene acid, which pollute TPA product.

U.S. patent 3931305 reveals that the main factor is the PR, determining the concentration of impurities in the product terephthalic acid, is the lowest temperature to which instantly cool the stream, past the hydrogenation. The concentration of impurities to a lesser extent depends on the speed with which the cooled stream that has undergone hydrogenation. This purpose is recommended that the bulk of terephthalic acid is crystallized at a temperature higher than 160 to 182°that is limiting the temperature at which cocrystallization p-toluene acid becomes critical. If the stream is terephthalic acid, the last hydrogenation, the concentration of p-toluene acid is from 500 to 6000 Mas. mlnc, it is recommended that the filter after crystallization at a temperature of from 121 to 149°to obtain the TPA product concentration p-toluene acid 150 wt. mlnc or below. Other methods of allocation using effective filtering, washing and drying methods in the temperature range from 100 to 205°to reduce the deposition of p-toluene acid.

The present invention relates to a method of obtaining purified TPA, starting with the oxidation of p-xylene. The present invention provides a method of preparation and the selection of crystalline terephthalic acid containing less than 150 wt. mlnc p-toluene acid by weight therephtale the Oh of the acid, with the stages, including:

(1) load (i) dialkylanilines connection, (ii) the reaction of aqueous acetic acid medium containing dissolved components of the oxidation catalyst, and (iii) gas containing oxygen, in the first pressure zone of oxidation, in which there is a liquid-phase, exothermic oxidation dialkylanilines connection, in which the temperature and pressure inside the first pressure oxidation reactor support at from 150 to 180°and from about 3.5 to 13 absolute bar - bara (from about 50 to 189 pounds per square inch (psia);

(2) removing from the top of the first reactor steam containing the vaporized reaction of aqueous acetic acid medium and the gas depleted in oxygen, including carbon dioxide, methane, inert components, and less than 9 volume percent in the calculation of the non-condensable components of the vapor, oxygen;

(3) removing from the lower portion of the first reactor of the oxidized product, including (i) solid and dissolved terephthalic acid and the products of incomplete oxidation, and (ii) the aqueous, acetic acid reaction medium containing dissolved catalyst oxidation;

(4) load (i) oxidized product from step (3) and (ii) a gas containing oxygen, the second pressure zone of oxidation, in which liquid-phase, exothermic oxidation products nepolnoj the oxidation, the temperature and pressure in the second pressure reactor oxidation of the support at a temperature of from 185 to 230°and from about 4.5 to 18.3 bara (about from 65 to 265 psia);

(5) removing from the top of the second reactor steam containing vaporized aqueous acetic acid reaction medium and the gas depleted in oxygen, including carbon dioxide, methane, inert components, and less than 5 volume percent in the calculation of the non-condensable components of the vapor, oxygen;

(6) removing from the lower portion of the second reactor of the second oxidized product comprising (i) solid and dissolved terephthalic acid and (ii) the aqueous, acetic acid reaction medium containing dissolved catalyst oxidation;

(7) separating terephthalic acid from (ii) aqueous acetic acid reaction medium from step (6) to obtain terephthalic acid containing impurities 4-carboxybenzene and p-toluene acid content in total from 400 to 900 wt. mlnc;

(8) the dissolution of the terephthalic acid obtained in stage (7), in water to form a solution containing from 10 to 35 wt.% dissolved terephthalic acid, at a temperature of from 260 to 320°and a pressure sufficient to maintain the solution in liquid phase, and the introduction in the interaction of the solution with hydrogen in the presence of a hydrogenation catalyst to obtain restaurierung product;

(9) loading the solution stage (8) in the crystallization zone, including many series-connected crystallizers in which the solution is subjected to evaporative cooling with variable speed by a significant downward pressure and temperature, to initiate crystallization of terephthalic acid, the pressure of the solution at the end of the crystallization zone is atmospheric or below;

(10) the condensation of the solvent evaporated from the mold, and returning the condensed solvent in the crystallization zone at a point following the mould from which it was obtained;

(11) isolation of crystalline terephthalic acid containing less than 150 wt. mlnc p-toluene acid based on the weight of terephthalic acid, separation of solid-liquid at atmospheric pressure.

The method according to the present invention provides at least two significant advantages. First, the primary and secondary oxidation described in stages (1)to(7), yield of terephthalic acid, in which the total content of 4-carboxybenzene and p-toluene acid is less than 900 wt. mlnc This low content of impurities makes possible more efficient hydrogenation, which may allow to reduce the size of the apparatus for gidrirovanny the I and/or the contact time of the loaded solution in the hydrogenation zone. Secondly, since the total content of 4-carboxyaldehyde and p-toluene acid loaded into the hydrogenation reactor, less than 900 wt. mlnc in a solution of the product of hydrogenation is less than p-tolulene acid (in comparison with the known purification methods). As a result, the number and size of molds for isolation and purification of terephthalic acid can be reduced and crystallization can be simplified. The quantity of the material, i.e. an aqueous solution containing dissolved impurities that must be removed from the production system, decreases as the content of p-toluene acid becomes lower. Another advantage of the new method is the presence of a stage (10), in which the solvent is evaporated from at least one of the mold forming the crystallization zone, and condense and recycle in one of the later stages of crystallization. The benefits of this stage include the selection of terephthalic acid in the superior crystalline form with less "stuff", i.e. small crystals or particles of TPA, which can cause problems during operation and transportation of TPA. Another advantage is that the selection of the product is carried out at atmospheric or nearly atmospheric pressure.

1 and 2 are flow charts illustrating a system implementing the principles of the method according to the present invention. Although the present invention will allow implementation in a variety of forms, figures 1 and 2 and described in detail a preferred execution of the invention. The present disclosure should be considered as an illustration of the invention, however, is not limited to the specific described execution.

With reference to figure 1, stage (1) of the new method can be carried out in the first oxidation zone, including the digester tank 12. Downloadable mixture comprising dialkylanilines connection, such as p-xylene, aqueous acetic acid and a suitable oxidation catalyst, served in the first oxidation reactor 12 through line 10. The reaction acetic acid medium or loaded solvent typically contains up to 15 wt.% water. If desirable, dialkylanilines connection and/or acetic acid solvent containing components of the catalyst can be loaded into the reactor 12 through a set of points along the wall of the reactor 12. The gas containing molecular oxygen, under pressure continuously upload via line 14, into the reactor 12 through or near the base of the columnar reaction vessel. The gas containing oxygen, such as oxygen, air enriched with oxygen, or preferably the air is usually loaded through or near the base of the columnar reaction vessel. The flow rate of the gas containing C is slort, in reactor 12 regulate to maintain the volumetric percentage of oxygen from 2 to 9, preferably from 2 to 5 (calculated on a dry composition containing no solvent) in the output gas, which exits the reactor through line 16. The reagents in the reactor 12 is supported at an elevated pressure sufficient to maintain the contained volatile reaction medium substantially in the liquid state at the reaction temperature. The temperature and pressure inside the reactor 12 ranges from 150 to 180°and from about 3.5 to 13 bara (about 50 to 189 psia), preferably from 155 to 165°and about from 5.2 to 6.9 bara (about 75 to 100 psia).

The reactor 12 is typically a columnar, under pressure, the reaction vessel for oxidation, in which liquid-phase, exothermic oxidation dialkylamino compound gas containing oxygen, in the presence of the oxidation catalyst. The first oxidation zone may include a single reactor or multiple reactors in parallel. The reaction medium contained in the reactor 12 thus includes a gas containing oxygen, dialkylanilines connection, which must be oxidized to a product of terephthalic acid, catalyst and aqueous acetic acid solvent. The amount of water present is usually not more than 15 wt.%, predpochtitelno 4 to 6 wt.%, on the basis of water and acetic acid. Generally cylindrical first vessel to oxidation has a ratio of height to diameter in the range from 3 to 20.

Catalytic systems that can be used in the method include a catalytic oxidation system, typically used for liquid-phase oxidation of alkylaromatic hydrocarbons. Suitable catalytic system, includes a mixture of compounds or complexes of cobalt, manganese and bromine, dissolved in aqueous acetic acid. The atomic ratio of the combination of Co:Mn:Br in the catalytic elements is preferably in the range 5 - 40:1,0:4 - 40, more preferably the atomic ratio of Co:Mn:Br 16 - 40:1,0:16 - 40.

During the oxidation reaction exothermic reaction heat generated by the oxidation dialkylanilines connection away from the reactor 12 by evaporation of the particles of the liquid reaction medium. In accordance with stage (2) of this method one stripped off the liquid reaction medium (exhaust gas) together with the process gas depleted in oxygen, containing a small amount of decomposition products and compounds containing bromine, means upward through the reactor 12 and is fed through the pipe 16 into the condensing system such as water column 18. Condensed vapor components going in the column 18, consist primarily of uksusnokislykh the solvent, then return to the reactor 12 through the pipes 30 and 32 and the spray head 34.

As shown in figure 1, the upper water vapor out of the top Vodolaga column 18 through line 20 and is served in the refrigerator 22. The composition of the condensed components of water vapor, gathering in the refrigerator 22, known as distillate, more than 98% is water. Part of the distillate is returned in the form of phlegmy in the zone of the fractionation column 18 through the pipes 23 and 24. The remaining distillate is removed through the pipes 23 and 26. Non-condensable components are produced through the output 28 of the production system or they can be transferred, if it is desirable in devices for controlling the cleaning for additional processing.

Distilled liquid at the bottom, comprising a partially dehydrated acetic acid solvent such as acetic acid, containing from 4 to 12 wt.% the water goes through the lower part Vodolaga of the column through line 30. Part of the partially dehydrated solvent recycle directly into the reactor 12 through line 32. This number varies from 10 to 100%. Partially dehydrated solvent is loaded into the reactor 12 through one or more spray nozzles 34, which may be located below the output pipe 16 or higher phase separation of the gas/liquid content of the reactor tha part of the partially dehydrated solvent may be removed through line 40. Part or all of the condensed acetic acid may be returned to the reactor 12 through the loading thread 10.

In operation, the first pressure oxidation reactor 12 produces the product of terephthalic acid, which trudnorastvorim in water technology the solvent and removed through the bottom outlet which is located at or near the base of the reactor, in the form of a suspension in a solvent, which also contains dissolved components of the catalyst. The process of oxidation in the reactor 12 also leads to the production of by-products in the form of monocarboxylic acids, such as 4-carboxybenzene and p-toluene acid. At least part of these monocarboxylic acids are solids that may be contained in the crystals of terephthalic acid. Usually these monocarboxylic acids are present in the form of 4-carboxybenzene and p-toluene acid in the amount of 900 wt. mlnc These monofunctional compounds are undesirable by-products, because they act as terminators of the polymer chain and, thus, can lead to the formation of low molecular weight polyesters, such as poly(ethyleneterephthalate)derived from terephthalic acid and ethylene glycol.

In accordance with the stages (3) and (4) the method according to the invention a suspension of the product of terephthalic acid and p is non monocarboxylic products are continuously removed in the form of a suspension in water technology acetic acid solvent, which also contains dissolved catalyst from the lower portion of the reactor 12 and is transferred through line 36 to the second pressure zone of oxidation, as shown in figure 1, the reactor 42. The second oxidation zone may be one, a mixing reactor, as shown in figure 1, or two or more stirred reactors, which can be arranged in parallel or sequentially. Aqueous acetic acid solvent typically contains from 5 to 12 wt.% water relative to the weight of water and aliphatic carboxylic acids. The gas containing molecular oxygen, is also loaded through line 48 to the second oxidation reactor 42, in which by-products 4-carboxybenzene and p-toluene acid optionally oxidized to the desired terephthalic acid. As in the case of loading in the first oxidation reactor, the gas containing oxygen may be oxygen, air enriched with oxygen, or, preferably, air. The gas containing oxygen, usually download through or near the bottom of the second oxidation reactor 42 above the surface of the liquid contained in the reactor.

The flow rate of gas containing oxygen into the reactor 42 may be regulated by staying at a value of from 0 to 5, preferably from 0 to 1 volume% of oxygen (calculated on a dry composition containing no solvent) in the exhaust gas is, which leaves the reactor through line 50. The flow rate of gas containing oxygen, in the rector 42 is usually from 0.001 to 3 volume percent, preferably from 0.001 to 2 volume percent of the velocity of the gas stream containing oxygen in the reactor 12. A small amount of air that is loaded into the second oxidation reactor 42, limits the oxidative decomposition of the acetic acid solvent, further facilitating the transformation products of monocarboxylic acid to terephthalic acid.

The first oxidation reactor, described above, provides substantially all of the oxidation, although operating at moderate pressure and temperature. The main obstacle in achieving sufficient conversion dialkylanilines connection terephthalic acid in the primary oxidizing system is the limitation of mass transfer associated with the diffusion of oxygen to partially oxidized products, or are contained in terephthalic acid, i.e. partially oxidized by-products of monocarboxylic acids can be enclosed in crystals of terephthalic acid. Therefore, it is easy enough to oxidize a large part dialkylanilines connection to terephthalic acid even under moderate conditions. However, to achieve sufficiently complete conversion of the need to overcome these constraints is to be placed on mass transfer. The first oxidation zone at moderate conditions of pressure and temperature can help in the formation of small or fine crystals, which can be dissolved and recrystallized in the second zone of oxidation. When a small or fine crystals dissolve in the second oxidation zone, cocrystallization by-products are available for further oxidation.

The materials in the second oxidation reactor 42 is supported at an elevated pressure sufficient to maintain the contained volatile reaction medium substantially in the liquid state at the reaction temperature. The temperature and pressure inside the reactor 12 is equal to from 185 to 230°and from about 4.5 to 18.3 bara (about from 65 to 265 psia), preferably from 205 to 215°and from about 13.4 to 17.2 bara (about 195 to 250 psia). The heat required for the operation of the second oxidation zone may be provided with a supply of solvent vapor to the second oxidation reactor, allowing the solvent vapor to condense. Headspace solvent will generally be at a pressure sufficient to allow steam to pass to the second oxidation reactor and to provide a sufficient supply of heat to the contents of the second oxidation reactor. For example, partially dehydrated acetic acid can boot from in dudleya column 18 in the evaporator acids 44 through pipes 30 and 40. The evaporator acid 44 translates partially dehydrated acetic acid to a temperature and pressure sufficient to maintain a predetermined temperature within the second oxidation reactor 42. Evaporator design acetic acid usually requires the presence of the fluid heat transfer medium, such as Dowtherm, or stream of high pressure, which can be used for evaporation of acetic acid. Pairs of acetic acid is transferred from the acid evaporator 44 to the second oxidation reactor 42 through line 46.

The exhaust gas includes one stripped off the liquid reaction medium together with the process gas depleted in oxygen, containing a small amount of decomposition products and compounds containing bromine is removed from the upper part or top of the second oxidation reactor 42 and upload via pipelines 50 and 16 in condensing system such as water column 18. Condensed components of the flow of exhaust gas is composed primarily of acetic acid solvent, which can be selected as described above.

The product of terephthalic acid is removed from the second oxidation reactor 42 in the form of a suspension in water technology acetic acid solvent, which also contains dissolved components of the catalyst through line 52. The suspension is removed from the reactor 42, typically includes the 20 to 40 wt.% solids and contains less than 900 wt. mlnc based on the weight of solids present, products of incomplete oxidation and, first of all, 4-carboxybenzene and p-toluene acid. The total content of 4-carboxybenzene and p-toluene acid is usually in the range from 400 to 900 wt. mlnc

Suspension of the product from the second oxidation reactor 42 (second oxidized product may be cooled before introduction into the system of separation of solid/liquid and, if desired, in a system for drying solids. Preferably the suspension of the product from the second oxidation reactor 42 is loaded into the zone of immediate evaporation, in which the temperature and pressure of the second oxidized product of a lower instant evaporation. Zone instant evaporation may contain one or, preferably, a multitude of vessels for instant evaporation, in which the suspension product is cooled stepwise or sequential evaporation by reducing the pressure. As shown in figure 1, for cooling of the suspension pipe 52 enters the first vessel 54 for flash evaporation. From his pipe 58 is in the second vessel for flash evaporation 56. The first and second vessels for flash evaporation 54 and 56 provide a stepped decrease in the pressure of the reactor 42. It is a step, or a sequential decrease in pressure serves two purposes. what about the first it eliminates the need for discharge between nodes. Second, the adiabatic evaporation at low pressure between the reactor 42 and the first evaporation vessel 54 allows to play the first evaporation vessel 54 as evaporative crystallizer. The average size of the crystals of terephthalic acid may increase in the first evaporation vessel 54. Pairs of both evaporative vessels 54 and 56 may be placed in a refrigerator (not shown). The first evaporation vessel 54 can operate at temperatures from 170 to 190°and a pressure of from about 2.4 to 5.2 bara (about 35 to 75 psia). The flow of the suspension from the first evaporation vessel 54 load in the second evaporation vessel 56, which represents another adiabatic evaporative tank at a temperature of from 60 to 100°and a pressure of from 0.3 to 0.8 bara (about 5 to 12 psia). Although figure 1 shows two of the evaporation vessel for cooling and crystallization can be used as more or less than two, or may use a different cooling method.

Chilledsuspensiontransferred through the pipe 62 into the zone of separation solid/liquid 60, in which the solid terephthalic acid is separated from the aqueous acetic acid solvent/reaction medium using standard methods of separation of liquid/solid is the second substance. After separation of the precipitate of terephthalic acid on the filter is washed, for example, chilled acetic acid from Vodolaga columns 18. Wet the filter cake may be dried to evaporate the residual acetic acid in the precipitate on the filter. The dried product obtained from the device for the separation of solid/liquid 60. The composition of this product is substantially the same as the composition of the solids present in suspension of the product from the second reaction zone 42.

Purification of the second oxidized product in accordance with stage (6) under this method involves the hydrogenation of the second oxidized product for the conversion of 4-carboxybenzene in p-toluene acid and coated particles or precursors of the colored particles in unpainted connection. Referring to figure 2, the water and the second oxidized product (one HUNDRED) is loaded into the vessel for dissolution HUNDRED 160. The solution typically comprises from 10 to 35 wt.% solid terephthalic acid in an aqueous solvent, preferably from 25 to 35 wt.% terephthalic acid in an aqueous solvent. A solution of terephthalic acid obtained by heating the solvent or suspension of terephthalic acid to a temperature sufficient to dissolve the terephthalic acid to the desired concentration, for example at a temperature in the range from 260 to 320°C. When the temperature range from 260 to 320° When using a solvent, such as water, it is necessary to maintain the solution at an elevated pressure, for example pressures in the range of about 46.9 to 113 absolute bar - bara (680-1640 pounds per square inch (psia)).

A solution of terephthalic acid load in the hydrogenation reactor 110, in which the solution is subjected to liquid-phase hydrogenation introduction to the liquid contact of the solution with hydrogen in the presence of a hydrogenation catalyst, for example a noble metal of group VIII on the material of the catalyst carrier to cause hydrogenation of significant amounts of impurities in the other compounds. For example, fluorenone and 4-KBA transferred to fluorine and p-toluene acid, respectively. Assuming that this takes place in substantially complete conversion of 4-KBA in p-toluene acid and assuming that loaded into the reactor for the hydrogenation of a solution of terephthalic acid has a total content of 4-KBA and p-toluene acid less than 900 wt. mlnc, for example from 400 to 900 wt. mlnc, the content of the actual p-toluene acid in the product stream from the hydrogenation reactor 110 is less than 900 wt. mlnc in the calculation of the present terephthalic acid.

The temperature of the product stream of the hydrogenation is typically in the range from 260 to 320°C. the Flow hydrogenated product download through valve 130 and speaker the wires 131 in the crystallization zone, includes a set or sequence of parallel connected crystallization stages, which operate together to reduce the temperature after crystallization stream to a lower temperature, typically from 75 to 150°more often from 90 to 110°C. Reduction in temperature is accompanied by a parallel loss of terephthalic acid from solution in the form of a white crystalline solid. Crystalline terephthalic acid in the final stage of crystallization is separated from the solvent using conventional device for separating solid-liquid, such as a centrifuge or a rotary vacuum filter. The crystallization zone may contain from two to eight, preferably three to six, more preferably from four to five, mold or crystallization stages. The number of crystallization stages used in the way that can affect the quality of the final product. The correct temperature setting sequence connected in series crystallization stages can increase the purity of the final product from the point of view of p-toluene acid.

Many of crystallization stages includes the first and last stage. The temperature within the first crystallization stage is typically in the range from 200 to 260°and the temperature is within the last crystallization stage is typically in the range from 80 to 100° C. operating Temperature crystallization stages can be consistently below from the first to the last stage. On the last crystallization stage get purified suspension of terephthalic acid, which contains the calculation of the solid is less than 150 wt. mlnc p-toluene acid. In accordance with the present invention, terephthalic acid is crystallized in the first crystallization stage by cooling the hydrogenated downloadable flow evaporative cooling with variable speed (or instantaneous evaporation) by reducing the pressure compared to the pressure of the loaded stream) inside the first mold or the first crystallization stage. The solvent is removed in the form of steam from the crystallizer, is condensed, and a portion of the condensed solvent is returned to the crystallization zone at a point after the mould from which the vapor of the solvent was removed. Additional aromatic dicarboxylic acid is crystallized in the second crystallization stage at a second temperature lower than the first temperature, thus allowing the solvent to evaporate. The solvent is condensed from the vapors of solvent received during the previous mold, and/or can be added to a pure solvent in the verge of crystallization stage.

Each of the multiple crystallization stages has a specific mass flow rate of material entering and exiting the crystallization stage. The specific mass flow rate of the material included in the crystallization stage may range from 0.7 to 1.3 specific mass flow rate of material leaving the last crystallization stage. Preferably, the specific mass flow rate of the material included in the first crystallization stage, substantially equal to the specific mass flow of material emerging from the last crystallization stage.

Each crystallization stage of the method according to the invention has many similar operating elements, including the following main components:

1. Crystallization unit or vessel (mold), equipped with devices for mixing, such as one or more impellers;

2. Line feed raw material into the mould;

3. Line removal of the product from the mold;

4. Line removal of distillate solvent or steam from the mould, leading to the refrigerator, in which a portion of the solvent vapor is condensed;

5. The line loading of the solvent below the point or part of the crystallization zone for feeding the condensed liquid in the refrigerator.

The crystallization unit is a good displaced ivemy vessel, containing a suspension of crystals of terephthalic acid. The solvent is typically water saturated terephthalic acid at the operating temperature of the mold. The working temperature of each crystallization unit in combination with the temperature and concentration of the feed stream, determines how much of terephthalic acid will crystallize at each stage. In order to crystallize a substantial portion of the terephthalic acid, it is necessary to lower the temperature at the point at which the solubility of terephthalic acid in an aqueous solvent decreases, which leads to crystallization of a larger amount of terephthalic acid. Independent control of the pressure determines the operating temperature of crystallization units. Pressure control may be effected by regulating the pressure in the crystallization blocks using, for example, but not limited to, a valve in the steam line.

In the low pressure (relative to the pressure of the loaded thread in the crystallization unit) the solvent evaporates and is removed from the crystallization unit in the form of steam, thus leading to the concentration of the solution. Part of the terephthalic acid is precipitated, crystallizing the crystals already present in the vessel, and a part of the terephthalic acid to the way the t the nuclei of crystallization as a separate new crystals. The amount of terephthalic acid, which is transferred from the liquid phase to the solid phase depends on the operating temperature (adjustable reduced pressure) of the mold and saturated equilibrium concentration of TPA at this temperature.

Usually the download in the first crystallizer is served below the surface of the suspension therein, in the direction of the bottom of the vessel, where the hydrostatic pressure maximum. Increased temperature in the crystallization point of the block and the surrounding liquid exclude excessive instantaneous evaporation. In crystallization units are devices for mixing, such as the impeller. When entering the flow of products from the hydrogenation reactor in the first crystallization unit area sufficient mixing can be reduced local oversaturation, which promotes the formation of smaller (or fine) crystals. The product stream is continuously removed from each crystallization unit. The product stream is preferably removed from the well mixed zone of crystallization unit so that the contents of the product flow is the average total content within each crystallization unit. The product stream is loaded into the serial or subsequent crystallization stage operated at a lower temperature is, preferably in a well-mixed zone following crystallization unit. As each subsequent crystallization unit operates at a lower temperature, a part of the terephthalic acid remaining in the solution, crystallizes, this part is determined by the equilibrium concentration of terephthalic acid at the operating temperature of the second crystallization unit 124.

As mentioned above, the distillate solvent or vapor is continuously removed from the first and subsequent crystallization stages and transferred to a refrigerator for cooling and condensing steam. Part or all of the steam can be condensed at this point. Additional subcooling vapor to a temperature substantially below the boiling point can also be accessed from inside the refrigerator. All or part of the condensed solvent is recycled to the crystallization zone at a point after the mould, from which the solvent has been removed in the form of steam. Preferably the condensed solvent is recycled to the crystallization zone, the flow of condensed solvent in-line product removal crystallizer from which the solvent was removed in the form of steam. Any condensed solvent, unreturned or precirculation in the crystallization zone, can be used in another IU is the cleaning system of terephthalic acid, for example, upon receipt of an aqueous solution fed to the hydrogenation reactor. The final crystallization unit serves to hold the suspension, accumulating suspension before phase separation solid-liquid. The second and subsequent crystallizers operate similarly to the first crystallization stage.

The condensed solvent from the preceding crystallization stage can be recycled directly in the subsequent crystallization stage or recycled in the crystallization stage, which is not directly subsequent crystallization stage. As the condensed solvent, and fresh solvent may be submitted in one of the subsequent crystallization steps.

The product stream from any or all of crystallization stages may be diluted when using a dilution liquid, such as water, at a temperature that is the same or substantially the same as the operating temperature crystallization stage, which removes the product stream. Adding dilution liquid to the product stream has the effect of lowering the total concentration of terephthalic acid and any impurities present in the product stream. Unless you are adding dilution liquid to the product stream from each crystallise the ora, the total concentration of terephthalic acid in each product stream continues to rise. In the methods of crystallization, in which the dilution liquid recycle, the product stream from the hydrogenation reactor is so diluted that way will lead to a pre-defined concentration of the solid terephthalic acid after the final stage of crystallization. Thus, knowing the amount of liquid added and the remote, and knowing the volume of the crystallizing terephthalic acid, it is possible to determine the concentration of solid TPA. Adding dilution water to the product stream from each crystallization stage, the dilution required for initial load flow is much lower.

Dilution liquid is added to the product stream may originate from numerous sources. First, the condensate from the crystallization stage, which removes the product may be condensed and partially or completely recycled back into the product stream from this stage. Secondly, it can be used served with fresh solvent, for example water, in quantity, more than, less than or equal to the amount of liquid removed as distillate. Thirdly, if you use more than one crystallization stage, the condensate from the stage, not the two is considered immediately preceding stage, can be recycled in this crystallization stage. This condensate is usually heated to the same temperature as the operating temperature of the preceding crystallization stage.

In each case, or a portion of the condensed solvent recycle the product supplied in the crystallization stage, or additional solvent is served in the crystallization stage, or use a combination of these two methods. If there are more than two crystallization stages, the percentage of solvent supplied to each crystallization stage may vary. For example, in some crystallization stage can be fed the amount of solvent equal to the number of evaporated at the previous stage, and in some crystallization stage, the solvent may not be submitted.

An additional point to return dilution water in the system can be in the same line point of transfer between the molds. This line usually contains a valve to regulate the speed of product flow from one crystallization stage to the next. Resident time for crystallization stage is determined by the amount of crystallization stage, divided by the volume flow rate of suspension of the product from the crystallization stage. Alternatively added the in-line transfer line download dilution liquid can be added directly to the crystallization unit. In this case, the dilution water is preferably added below the surface of the liquid, more preferably in the basis of the crystallization unit in a well-mixed zone.

If the entire distillate from each crystallization unit recycle product stream from this crystallization unit, the concentration of terephthalic acid, a member of the crystallization stage, will be equal regardless of whether TPA in the liquid phase or the solid phase. Thus, the initial liquid concentration of TPA in the download thread will be approximately equal to the concentration of withholding the final solid products. This leads to the fact that only a small part of the terephthalic acid will remain in solution and do not crystallize.

Compared to sequential methods crystallization of terephthalic acid, in which there is no recirculation of condensed solvent in the subsequent stage, the stream from the hydrogenation reactor to the first block of crystallization can be more concentrated and have a lower flow rate. Similarly, the reduction of flow velocities from one crystallization stage to the next leads to a decrease of the velocity of product flow. To maintain the seat reservation for a certain time processing at lower speeds the boot stream, need to reduce the amount of crystallization units. At substantially constant flow rate, for example higher temperature in the preceding and lower the temperature in the subsequent crystallization stage may have a substantially equal volume, while maintaining equal processing time.

In General, the method of selection of the temperature profile for a large number of crystallization stages is to select a temperature at which at each stage crystallizes smaller part of terephthalic acid compared with the previous stage. It was determined that this method not only allows you to crystallize a smaller amount of terephthalic acid in each subsequent stage, but it also reduces the contamination of the product with p-toluene acid. The ideal case in which this mechanism can lead to the greatest advantage - in the series of an infinite number of crystallization stages, approximating periodic conditions. Limit the practical functioning is not possible to achieve this. In the present invention has a higher concentration of terephthalic acid in the original feed stream improves this mechanism, because the higher the concentration of terephthalic acid cause crystallization of large quantities of terephthalic acid at higher temperatures (the previous stages).

Line removal of the product from end of the mold load a standard device for separating solid-liquid for separation of the crystalline product of terephthalic acid containing less than 150 wt. mlnc p-toluene acid. As the temperature of the last crystallization stage may be less than the normal boiling point of the solvent, can be used for vacuum filtration (instead of filtering under pressure). Wet crystalline terephthalic acid may be washed before loading it into the dryer. The filtered mother liquor and the liquid used for washing is collected for reuse in the stage hydrogenation. Part of the filtered liquid can be purified to reduce the amount of impurities in the system.

Again, referring to figure 2, the hydrogenation product is removed from the hydrogenation reactor 110 and served through the valve 130 in the first crystallization unit 122 at a point below the surface of the slurry contained in the vessel 122, near the bottom of the vessel 122, where the hydrostatic pressure is higher. Device for mixing, such as the impeller 170, have in the first crystallization unit 122 as well as in other crystallization units. The product stream is continuously removed from the first crystallization unit 122 through line 140. About Aktovy stream is removed from the well mixed zone of crystallization unit 122, thus, the contents of the product flow is the average from all content of this crystallization unit 122. The product stream is fed through the valve 134 in the second, subsequent crystallization vessel 124, which operates at a pressure and temperature lower than the pressure and temperature inside of the mold 122. The product stream is served in the well-mixed zone of crystallization unit 124. Because subsequent crystallization unit 124 operates at a lower temperature, part of the TFK remaining in the solution, crystallizes, this part is determined by the equilibrium concentration of TPA at the operating temperature of the second crystallization unit 124.

Vapor of the solvent is continuously removed from the first crystallization unit 122 through line 142 and is loaded into the heat exchanger 150, in which all or part of the solvent is condensed. Subcooling vapor to a temperature substantially below the boiling point also can be carried out inside a heat exchanger. Part or all of the condensed solvent serves in the product stream 140 through the valve 136. All of the condensed solvent is not recycled in the product stream may be removed through line 144. The vessel is the second crystallization stage 124 operates in a similar manner with the first cristalli which include stage 110 and includes a crystallization unit 124, inside the impeller 172. The product is removed from the crystallization unit 124 through line 146. The evaporated solvent is removed from the second crystallization unit 124 and is directed to the refrigerator 152, in which the evaporated solvent is condensed and the condensed solvent is recycled through valve 138 and/or removed through conduit 148. Fresh, additional solvent, for example water, can be added in a sequential crystallization system, depicted in figure 1, through line 143 and/or line 147.

The product of crystallization is removed from the mold 124 through line 146 and is transferred through valve 137 in the zone of separation solid/liquid 180. The temperature in the last crystallization stage may be below the normal boiling point of the solvent, which makes possible the separation of solid-liquid by means of filtration under vacuum. In the zone of separation solid-liquid 180 remove the mother liquor from the crystalline precipitate on the filter in the first zone. The crystalline precipitate on the filter is then washed in the second zone.

The benefits and advantages derived from the method of the present invention include:

1. The same selection of terephthalic acid on the stage, as in the prior art technology, can be obtained by setting the temperature crystallizatio is the R stages, closer to each other at higher temperatures. This method of operation can minimize abrupt cooling flow Postretirement in the temperature range in which a large part of the terephthalic acid is crystallized from the solution. Using conventional crystallization temperatures with cleaner crude aromatic dicarboxylic acid leads to the fact that during the crystallization of a greater number of aromatic dicarboxylic acid crystallizes out of the solution at ordinary temperatures.

2. For a given resident time and speed of obtaining the volume of the previous (above, earlier in the thread) moulds with more high temperature and high pressure, can be significantly less than the amount required according to the known methods, since the initial concentration of terephthalic acid in the solution may be significantly higher, while also leading to the same content of suspended solids in the final product stream. Smaller volumes of molds lead to a significant cost reduction.

3. Thanks to the possibility to separate the crystals of the aromatic dicarboxylic acid from the mother liquor at a temperature below the boiling point of the solvent, there is no need to use equipment for a closed filter, the Finance and filtering under pressure to effect the separation. This allows the use of more cost-effective device for separating solid-liquid, while maintaining the efficient separation.

Examples

The method according to this invention is further illustrated by the following examples. In the examples, parts are given by weight and percentages by weight, unless otherwise stated.

Example 1

This example shows the ability to purify the crude terephthalic acid having a concentration of p-toluene acid 429 mass. mlnc to concentrations below the limit of acceptable purity for purified terephthalic acid (150 wt. mlnc). It also shows that this specification can be achieved by selection of terephthalic acid at a temperature below the boiling point of the solvent.

In a high pressure autoclave was loaded water (solvent) and the crude terephthalic acid in the amount shown in table I for experiments 1, 2 and 3. This number corresponds to approximately 30% solution of terephthalic acid in water. The content of p-toluene acid in the crude terephthalic acid was 429,37 wt. mlnc in relation to the solid matter. The contents of the autoclave were heated to 280°C and kept at this temperature for one hour to ensure that all solids dissolved. In order to stabimaterial many serially connected crystallizers, the contents of the autoclave were cooled to room temperature at a speed of 30°With in the hour. Then the contents of the autoclave was again heated to 60°Since, at this temperature, the contents were maintained for one hour. Then, the autoclave was opened and conducted the separation of solid-liquid received suspensions at 60°C. After cooling to 60°With the concentration of p-toluene acid in a purified solid terephthalic acid is presented in table I.

Table I
MaterialExperiment 1Experiment 2Experiment 3
The crude terephthalic acid (parts)37.505137.50537.4948
Water (parts)87.733787.513187.4698
p-toluene acid (wt. mlnc)429.37429.37429.37
p-toluene acid (wt. mlnc), which is present in purified terephthalic acid (60°)155.7191.6679.12
p-toluene acid (wt. mlnc), which is present in purified terephthalic acid (95°)113.0364.9636.81

In the Vuh of the three experiments, the purity of the obtained solid matter was within 150 wt. mlnc maximum content of p-toluene acid to terephthalic acid. Terephthalic acid, selected in experiment 1, has a concentration of p-toluene acid 155,71 wt. mlnc

Example 2

This example shows the effect of temperature selection on the purity of the final product, the loading of the autoclave at room temperature, obtained in experiments 1, 2 and 3 of example 1 was separately placed in a well-mixed vessel. Instead of re-heating to 60°that was carried out in example 1, in example 2, the part was re-heated to 95°C and maintained at this temperature for 1 hour. Separation of solid-liquid was carried out at 95°to obtain samples of solids which are analyzed for the concentration of p-toluene acid. Results are also presented in table 1. As you can see the selection at a higher temperature 95°leads to a product with low content of p-toluene acid compared with the material, highlighted at lower temperature 60°C. Increase the purity of the products can be achieved by raising the temperature selection from the 60°With, while maintaining the temperature of the separation of solid-liquid below the boiling point of the solvent.

Example 3

In a high pressure autoclave was loaded water (solvent) and untreated Tere is traveling acid number, are given in table II for experiments 4 and 5. These samples correspond to about 20% solution of the crude terephthalic acid in aqueous solution. The content of p-toluene acid in the solid crude terephthalic acid was 429,37 wt. mlnc Samples were heated to 280°C and kept at this temperature for one hour to ensure that all solids dissolved. The samples were cooled to room temperature at a speed of 30°With in the hour. Then, as was done in the case of examples 1 and 2, a portion of each sample was heated up to 60°and shared at this temperature, and a portion of each sample was heated to 95°and shared at this temperature. The concentration of p-toluene acid in the obtained solids are presented in table II.

Table II
MaterialExperiment 4Experiment 5
The crude terephthalic acid (parts)25.010425.0017
Water (parts)99.9537100.2292
p-toluene acid (wt. mlnc)429.37429.37
p-toluene acid (wt. mlnc), which is present in purified terephthalic acid (60°)65.7 51.23
p-toluene acid (wt. mlnc), which is present in purified terephthalic acid (95°)40.4944.56

Example 3 used a greater amount of dilution of the solution in comparison with example 1 (20% versus 30%). The crude terephthalic acid used for example 1 and example 2 had the same content of p-toluene acid (429,37 wt. mlnc). Thus, in the case of example 3 in initially diluted solution contained less p-toluene acid. Comparing table II with table I shows the advantages of a lower content of p-toluene acid in the original solution from the point of view of the purity of the final product.

Separation of solid-liquid removes solids from the mother liquor. In table III compares the concentration of p-toluene acid in the mother solution for the experiments presented in example 2 and example 3, in which purified terephthalic acid was isolated in 95°C. At lower concentrations used crude p-toluene acid solution were fewer p-toluene acid. This leads to a lower content of p-toluene acid in the mother solution obtained after separation of solid-liquid. Balancing mass displays is, when a lower content of p-toluene acid in the mother solution, the solid product also has a lower content of p-toluene acid.

The crude terephthalic acid used for experiments 1-5 are presented in table III contained 429,37 wt. mlnc p-toluene acid. The amount of diluent was changed. However, by analogy it can be assumed from table III that if the purity of the crude starting material is increased while maintaining a constant level of dilution, can be obtained more pure product.

Table III
MaterialExperiment 1Experiment 2Experiment 3Experiment 4Experiment 5
The crude terephthalic acid30%30%30%20%20%
The concentration of p-toluene acid in the mother solution (with 95°)144.48164.07157.85107.9298.63

1. The method of preparation and the selection of crystalline terephthalic acid containing less than 150 wt. mlnc p-toluene acid, by weight of terephthalic acid, stipulating

(1) download the cu (i) para-xylene, (ii) water reaction of acetic acid medium containing dissolved components of the oxidation catalyst, and (iii) a gas containing oxygen, in the first pressure zone of oxidation, in which there is a liquid-phase, exothermic oxidation of para-xylene, in which the temperature and pressure inside the first pressure oxidation reactor support at 150 ÷ 180°and 3.5 ÷ 13 absolute bar;

(2) removing from the top of the first reactor steam containing one stripped off aqueous acetic acid reaction medium and the gas depleted in oxygen, including carbon dioxide, inert components, and less than 9%vol., in the calculation of the non-condensable components of the vapor, oxygen;

(3) removing from the lower portion of the first reactor of the oxidized product, including (i) solid and dissolved terephthalic acid and the products of incomplete oxidation, and (ii) the aqueous, acetic acid reaction medium containing dissolved catalyst oxidation;

(4) load (i) oxidized product from step (3) and (ii) a gas containing oxygen, the second pressure zone of oxidation, in which liquid-phase, exothermic oxidation of products of incomplete oxidation, the temperature and pressure in the second pressure oxidation reactor support at 185 ÷ 230°and 4.5 ÷ 18,3 absolute bar;

(5) UD is executed from the top of the second reactor steam containing the vaporized aqueous, acetic acid reaction medium and the gas depleted in oxygen, including carbon dioxide, inert components, and less than 5 vol.%, in the calculation of the non-condensable components of the vapor, oxygen;

(6) removing from the lower portion of the second reactor of the second oxidized product comprising (i) solid and dissolved terephthalic acid and (ii) water, the reaction medium of acetic acid containing dissolved catalyst oxidation;

(7) separating terephthalic acid from (ii) water reaction of acetic acid medium stage (6) to obtain terephthalic acid containing less than 900 wt. mlnc 4-carboxybenzene and p-toluene acid;

(8) the dissolution of the terephthalic acid obtained in stage (7), in water to form a solution containing from 10 to 35 wt.% dissolved terephthalic acid containing less than 900 wt. mlnc 4-carboxybenzene and p-toluene acid relative to the weight of the present terephthalic acid, at a temperature of 260 ÷ 320°and a pressure sufficient to maintain the solution in liquid phase, and the introduction of contact of the solution with hydrogen in the presence of a hydrogenation catalyst to obtain a solution of a hydrogenated product;

(9) loading the solution stage (8) in the crystallization zone, including many United the series of crystallizers, in which the solution is subjected to evaporative cooling with variable speed by a significant downward pressure and temperature, to initiate crystallization of terephthalic acid, the pressure of the solution at the end of the crystallization zone is atmospheric or below;

(10) the condensation of the solvent, one stripped off from the mold, and returning the condensed solvent in the crystallization zone by feeding part of the condensed solvent in-line product removal crystallizer from which to remove the solvent in the form of steam; and

(11) isolation of crystalline terephthalic acid containing less than 150 wt. mlnc p-toluene acid based on the weight of terephthalic acid, separation of solid-liquid at atmospheric pressure.

2. The method according to claim 1, wherein stage (2) and (5)include the

(2) removing from the top of the first reactor steam containing one stripped off aqueous acetic acid reaction medium and the gas depleted in oxygen, including carbon dioxide, methane, inert components, and less than 9% vol. oxygen in the calculation of the non-condensable components of the vapor;

(5) removing from the top of the second reactor steam containing vaporized aqueous acetic acid reaction medium and the gas depleted in oxygen, comprising dioxide of plastics technology : turning & the Yes, inert components and from 0 to 1 vol.% oxygen in the calculation of the non-condensable components of the vapor;

3. The method according to claim 2, in which stage 1 is carried out at 155 ÷ 165°and 5.2 ÷ 6,9 absolute bar in the presence of aqueous acetic acid reaction medium containing from 4 to 6 wt.% water containing dissolved components of the oxidation catalyst comprising cobalt, manganese and bromine; and the second pressure zone oxidation stage (4) support at a temperature and a pressure of from 205 to 215°and about from 13.4 to 17.2 absolute bar; terephthalic acid in stage (7) contains from 400 to 900 wt. mlnc p-carboxyaldehyde and p-toluene acid.

4. The method according to claim 3, in which the atomic ratio of Co:Mn:Br is from 5 to 40:1,0:4 to 40.

5. The method according to claim 1, wherein the second oxidized product of stage (6) is loaded into the flash evaporation zone in which the temperature and pressure of the second oxidized product is reduced by flash evaporation.

6. The method according to claim 2, in which the second oxidized product of stage (6) is loaded into the flash evaporation zone, including (i) a first vessel for flash evaporation, operating at a temperature of from 170 to 190°and a pressure of from 2.4 to 5.2 absolute bar and (ii) a second vessel for flash evaporation, operating at a temperature of from 60 to 100°and a pressure of from 0.3 to 0.8 absolute bar, where the temperature is round and the pressure of the second oxidized product reduce instantaneous evaporation.

7. The method according to claim 1, in which the solution stage (8) contains from 25 to 35 wt.% dissolved terephthalic acid; a solution of the product of the hydrogenation stage (8) contains from 400 to 900 wt. mlnc dissolved p-toluene acid relative to the weight of the present terephthalic acid, and many serially connected crystallizers consists of from two to eight molds.

8. The method according to claim 7, in which the temperature of the first mould is in the range of 200 ÷ 260°and the temperature of the mold is in the range of 80 ÷ 100°and many serially connected crystallizers consists of from three to six molds.



 

Same patents:

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

The invention relates to an improved process for the preparation of terephthalic acid

The invention relates to a method for the production of terephthalic acid and installation for its implementation

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: crystal growing.

SUBSTANCE: invention relates to adipic acid crystals and treatment thereof to achieve minimum crystal caking. Crystals are prepared by crystallization of adipic acid from aqueous medium or between treating it with aqueous solution. Crystals are then subjected to ripening stage, that is crystals are held at temperature between 10 and 80°C until content of exchangeable water in crystals falls below 100 ppm, while using an appropriate means to maintain ambient absolute humidity at a level of 20 g/m3. Renewal of ambient medium is accomplished by flushing crystal mass with dry air flow having required absolute humidity. Means to maintain or to lower absolute humidity contains moisture-absorption device placed in a chamber. Content of exchangeable water in crystals is measured for 300 g of adipic acid crystals, which are enclosed in tightly sealed container preliminarily flushed with dry air and containing 2 g of moisture absorbing substance. In chamber, temperature between 5 and 25°C is maintained for 24 h. Content of water will be the same as amount of water absorbed by absorbing substance per 1 g crystals. Total content of water exceeds content of exchangeable water by at least 20 ppm.

EFFECT: minimized caking of crystals and improved flowability.

13 cl, 5 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 method of processing the reaction mixture obtained by direct oxidation of cyclohexane to adipic acid, in liquid phase, in a solvent and in the presence of dissolved in the reaction medium, catalyst, including decantation two liquid phases: upper non-polar phase containing mainly unreacted cyclohexane, and the lower polar phase containing mainly solvent, adipic acid and the resulting acid, the catalyst and other reaction products and unreacted hydrocarbons, distillation of the lower polar phase or, if necessary, the entire reaction mixture with obtaining, on the one hand, distillate, containing, at least a part of the most volatile compounds such as unreacted cyclohexane, the solvent, the intermediate reaction products and water, and, on the other hand, residue from distillation, containing adipic acid and the resulting carboxylic acid, the catalyst, and the method includes a step of adding to the residue after distillation of the organic solvent in which adipic acid has a solubility less than or equal to 15 wt

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 an improved process for the preparation of terephthalic and isophthalic acids

The invention relates to an improved method for producing isophthalic acid used in copolymerization ways of producing fibers, films, plastic bottles and structures made of polyester resin, which consists in the oxidation of metaxalone in the reaction solvent to obtain a liquid dispersion

The invention relates to chemical technology of obtaining low molecular weight aliphatic acids, which are valuable raw materials for the chemical, petrochemical and forestry industry

The invention relates to a method of purification by crystallization or recrystallization in water adipic acid, which is one of the main substances used to obtain polyamide 6-6, which contains traces of catalyst, with a minimum purity specified adipic acid is at least 95%, and the specified crystallization or recrystallization is carried out in the presence of a strong proton acid and/or in the presence of carbon monoxide

The invention relates to a method of purification of adipic acid, which is used to obtain polyamide

FIELD: organic chemistry, chemical technology.

SUBSTANCE: invention relates to the improved method for preparing dimethyl-1,5-naphthalene dicarboxylate that is used in preparing polymers based on thereof and articles made of these polymers. The economic and effective method involves the following stages: (1) dehydrogenation of 1,5-dimethyltetraline to yield 1,5-dimethylnaphthalene; (2) oxidation of 1,5-dimethylnaphthalene prepared at dehydrogenation stage to yield 1,5-naphthalene dicarboxylic acid being without accompanying isomerization stage, and (3) esterification of 1,5-naphthalene dicarboxylic acid prepared at oxidation stage in the presence of methanol to yield the final dimethyl-1,5-naphthalene dicarboxylate.

EFFECT: improved preparing method.

9 cl, 3 dwg, 5 ex

Up!