A method of obtaining a purified terephthalic acid

 

(57) Abstract:

Use: in the production of polymer fibers. The inventive method of obtaining purified terephthalic acid containing p-Truelove acid, present at a concentration equal to or lower than 200 parts per million by weight, in the pre-treatment of an aqueous solution with hydrogen, followed by the introduction of the filter cell, or series of filter cells in the zone of filtration at a temperature in the range of from about 38 to about 205oC and a pressure from atmospheric pressure up to 1620 kPa, water sludge, including purified terephthalic acid, present in the form of crystals, and p-Truelove acid present in the aqueous solution and in cocrystallization form together with the crystals mentioned purified terephthalic acid, and referred to the filtration cell or a series of filter cells supported in a suitable position, which ensures the possibility of formation of each filter cell filter cakes or filter cakes mentioned in the introduction of the slurry into each said cell; and subsequent movement of each No leaching; the introduction of water flow in each of the mentioned filter cell for the formation of a reservoir of water in each filter cell above mentioned filter cake or filter cakes, where the said stream of water is when the pressure gradient is at least (3,45 kN/m2) relative to that of the system pressure and temperature are in the range of from about 38 to about 205oWith that mentioned washing of filter cakes with water for a period of time sufficient to reduce the concentration of p-Truelove acid to a value equal to or less by mass to 200 parts per million, by moving each of the mentioned filter cells containing the washed filter cake, in the area of pressure relief where the above-mentioned pressure in the system to relieve pressure in the range from atmospheric pressure to about 620,55 kN/m2to reduce the temperature mentioned filter pellet to a temperature equal to or less 166oWith, and unloading mentioned the washed filter cakes, including purified terephthalic acid, of each of the mentioned filter cells, and the concentration of p-Truelove acid in the above-mentioned purified t

The invention relates to an improved method of extraction of purified terephthalic acid (hereinafter referred to as the MOUTH) of an aqueous slurry containing a solution of p-Truelove acid. Get purified terephthalic acid in which the concentration of p-Truelove acid is by weight less than 200 parts per million. In the oxidation of p-xylene to terephthalic acid as an intermediate product is formed 4-carboxybenzene. When carrying out the purification of terephthalic acid in the presence of water 4-carboxybenzene subjected to hydrogenation with the formation of a more soluble derivative - p-Truelove acid. Purified terephthalic acid containing residual p-Truelove acid, washed with water to remove residual soluble p-Truelove acid. Wash water containing p-Truelove acid, is subjected to recirculation or discharge in the device processing wastewater. Method of leaching purified terephthalic acid with water under pressure with flooding allows you to lower the quantity of wash water to reduce the content of residual impurities in the purified terephthalic acid and/or to reduce the load on downstream device processing wastewater. Izobreteny and atmospheric pressure and separation at atmospheric pressure, which stages of the presently known methods of extraction of purified terephthalic acid from the aqueous slurry, at a single operation, i.e., on the operation of the filtration under pressure, with the proper reduction of equipment costs.

Typically terephthalic acid is obtained by liquid-phase oxidation of p-xylene and/or p-Truelove acid. Terephthalic acid is of great industrial interest, and it is widely used in the production of various polymers, such as fiber-forming polyesters (polyesters). The method of obtaining polyesters of terephthalic acid, in particular of polyethylene terephthalate, includes direct condensation of terephthalic acid with the corresponding polyhydric alcohol. For example, terephthalic acid reacts with the glycol with the formation of bis( -hydroxyethyl)terephthalate, which is then polymerized in the second stage. This method of direct condensation is simpler than other known methods, such as transesterification of dimethyl terephthalate with the corresponding glycol. However, during the direct esterification you must use the medium or high-purity terephthalic acid. To ensure suitability for the floor is x pollution, which can lower the melting temperature of the complex of the polyester and/or cause staining complex polyester. In fact, some impurities contained in the crude terephthalic acid are color-forming precursors.

All these impurities are not yet identified. However, 4-carboxybenzene, which is an intermediate product of the oxidation process and which hereinafter will be abbreviated to enroll as a 4-CBA, commonly found in crude terephthalic acid. It is known that the degree of the coloring complex of the polyester is below if terephthalic acid is a low content of 4-carboxybenzene. Although pure 4-carboxybenzene will not necessarily contribute to staining during polymerization, this mixture is a convenient label when assessing the extent to which was purified terephthalic acid. The way in which it can lower the levels of 4-carboxybenzene, terephthalic acid, can also lower the levels of color-forming precursors.

Industrial crude terephthalic acid by mass contains 800-7000 parts per million 4-carboxybenzene and 200-1500 ppm p-Truelove the 0-200 ppm also contains aromatic compounds a yellow colour, having a structure of benzil, fluorenone or anthraquinone, which are characteristic yellow compounds, representing impurities generated in the course of adverse reactions combination during the oxidation of p-xylene.

In U.S. patent N 3584039 issued to Meyer (Delbert H. Meyer), speaks about the possible industrial useful purification method such manufactured products from crude terephthalic acid by liquid-phase processing solutions thereof in water at temperatures 200-374oC with hydrogen in the presence of a solid hydrogenation catalyst (e.g. palladium metal deposited on a carbon substrate and crystallizing terephthalic acid from free from catalyst of liquid-phase solutions at temperatures in the range from 50 to 150oC. When the catalytic hydrogen treatment 4-carboxybenzene turns into p-Truelove acid and discoloration of the terephthalic acid.

In the United Kingdom patent N 1152575 talks about the improvement of the method, patented by Meyer (Meyer), in relation to its industrial use, in which case offers superior modes of carrying out the entire process, starting from the stage of dissolution signage solution. On the crystallization in the above-mentioned UK patent mentions the use of the evaporation process of the solvent to achieve the cooling necessary for carrying out the deposition of crystalline terephthalic acid, but the warnings, the essence of which is that when carrying out such evaporative cooling should avoid very rapid cooling of the solution, which can occur when the instantaneous single evaporation of the solvent, such as shock cooling is accompanied by coprecipitation of dissolved impurities that contaminate the resulting terephthalic acid. To eliminate the possibility of contamination with this shock cooling in the United Kingdom patent recommended evaporative cooling effect on the evaporation equilibrium back pressure, for example, throttling the discharged stream of vapor at equilibrium pressure. This actually is achieved the possibility of evaporative cooling with controlled velocity.

The crystallization process when evaporative cooling at a controlled rate applied according to the mentioned patent in the UK for a continuous and which for 3.4 h temperature difference 150oC change from the initial temperature of the solution at 277oC to the temperature of the third step 109oC. This mode of carrying out the aforementioned crystallization is realized at an average cooling rate in 1,48oF per minute, which is not only unusually low, but when applied to aqueous solutions of terephthalic acid with a content of p-Truelove acid 2400 parts per million, also obtained terephthalic acid containing 1200 ppm p-Truelove acid. This product should not be acceptable for direct interaction with ethylene glycol in the production of fibers from a complex polyester.

In U.S. patent N 3452088 repeated warning about shock cooling and refers to further improve the technique of continuous cooling with controlled velocity with respect to crystallization of terephthalic acid from aqueous solutions containing dissolved p-Truelove acid. The improvement is reduced to the finite temperature of crystallization and/or the temperature of the separation of the crystalline product temperature lying in the range 121 - 149oC than preventing contamination of the crystallizing terephthalic acid p-tashih in the field 121-149oC, can be and has been industrially obtained terephthalic acid with a content of p-Truelove acid in 150 parts per million and less coming from solutions containing 500-6000 ppm p-Truelove acid at a slightly higher cooling rate in 3-4oF (1.7 TO 2.2oC) per minute. However, if you focus on such a faster way of carrying out the evaporation at a controlled speed no prospects of developing even more fast way to make continuous instantaneous evaporative crystallization, in which case there was no problem of contamination of the p-Truelove acid, which is referred to as the United Kingdom patent and in U.S. patent.

U.S. patent N 3497552 describes a method of purification of crude terephthalic acid by crystallization from aqueous solution at 150-300oC. the Solution is continuously cooled in a series-connected cooling zones having a receiving tank and the outer contour of recycling. Three flowing stream consisting of injected water supply flow and flow from the bottom of the receiver, unite, and the injected water is enough to provide the necessary cooling. Crystallization was carried out after treatment is the appropriate fields in General have long been known and its use, deriving mainly from a significant instantaneous drops as temperature and pressure with concomitant substantially instantaneous vaporization of the solvent as the introduction of a hot solution of the solute in the crystallization vessel, operating at low temperature and pressure. The advantage is that it provides fast removal of solvent vapours, as quickly vaporized portion of the liquid solvent instantly goes from a liquid to a vapour phase. And crystallization, and crystal growth occur rapidly with cooling and concentration, caused by the rapid cooling of the solution to a lower temperature. The crystal growth was almost entirely the result of low temperature and does not depend on time. The size of the crystals in the crystallization vessel, where the solvent evaporates instantly, can be, as is well known, increased circulation of the slurry of crystals within the lower part of the crystallization vessel. For example, one of the ways of formation of such a circulation in the mix crystallization zone is reduced to the removal of sludge from the surface region and submission, for example, by pumping, extracted was going nd evaporation of the solvent of crystallization of terephthalic acid from the aqueous solution, also containing dissolved p-Truelove acid in quantities 500-6000 parts per million based on the content of the terephthalic acid can without the proper conduct thereof to be involved in the mechanism of contamination p-Truelove acid, which is mentioned in the patent in the UK and in more General form is described in a later patent of the United States. This phenomenon pollution is somewhat anomalous, because despite the fact that the water, which solvent is present in amounts more than sufficient to prevent saturation or supersaturation with respect to p-Truelove acid, p-tolarova acid, however, leaves the solution. In these later U.S. patent suggests that the phenomenon of pollution in some way dependent on the rate of crystallization and the final temperature of crystallization and separation of the product and not solely on the concentration of the p-Truelove acid in solution.

From the graphs saturation of terephthalic acid and supersaturation (the dependence of the concentration of terephthalic acid from temperature and considerations described in the aforementioned patents great Britain and the United States could be invented a continuous process cristalla stage operates at a temperature lower than the previous stage, and where the approximation of periodic crystallization smooth process temperature profile make essentially repeating schedule saturation of terephthalic acid. In the case of this invented process continuous crystallization should be at least about 40 dependent on the speed of crystallization stages. However, due to the number of stages and the duration of their actions such continuous crystallization does not seem economically attractive or acceptable for industrial applications.

Therefore, the purpose of the invention is to develop a method of displacement p-Truelove acid from the sludge formed purified terephthalic acid and an aqueous medium, where the aqueous medium containing p-Truelove acid is displaced from the sludge formed purified terephthalic acid by the method of positive displacement using a filtration pressure of purified terephthalic acid in the washing conditions with submergence, also referred to as flushing piston flow, the filter cakes produced at high temperature and pressure, followed by pressure release and the achievement of appropriate low t is held purified terephthalic acid, weight is 200 or less parts per million.

The purpose of the invention is to develop a method of displacement p-Truelove acid from the sludge formed purified terephthalic acid and an aqueous medium, in which p-tolarova acid is displaced from the sludge formed purified terephthalic acid, by way of positive displacement using filtration of purified terephthalic acid in the form of sludge at high temperature and pressure, in which case the concentration of the p-Truelove acid retained by the filter cake is by mass to 200 parts per million or less and the pressure is released to atmospheric pressure.

A further object of the invention is to develop an improved method of producing purified terephthalic acid, containing by weight to 200 parts per million or less p-Truelove acid and purified terephthalic acid is at atmospheric pressure, and thus it is in the condition in which it can be processed in a drying apparatus at atmospheric pressure.

Was developed a method of obtaining a purified terephthalic acid (TA), containing by weight to 200 parts per million or manebit applied to aqueous slurry of terephthalic acid, containing by weight 500-6000 ppm p-Truelove acid in solution. An aqueous slurry containing crystallized terephthalic acid and an aqueous solution of dissolved p-Truelove acid, is filtered. The filter cake is exposed to the process of positive displacement aqueous solution of p-Truelove acid at a temperature in the region from about 38 to about 205oC, and the differential pressure relative to the pressure in the system is enclosed in a region of about 0.5 (3,4 kN/m2and up to about 65 pounds per square inch (448,18 kN/m2). An aqueous solution containing a soluble p-Truelove acid, displace water under pressure from the filter cakes formed crystalline terephthalic acid, carrying out the filtration under pressure at high temperature. A solution of p-Truelove acid remaining in the filter cake, displace water under pressure. Rapid evaporation of water under pressure, which remained in the filter cake, occurs when the pressure relief in the system and the proper temperature to atmospheric pressure. The crystalline product in the form of terephthalic acid containing 200 parts per million or less p-Truelove the Tata which one obtains the desired product.

The invention alkyl aromatic compound such as p-xylene and/or p-tolarova acid, oxidized in acetic acid medium with molecular oxygen in the presence of a catalytic system containing bromine and one or more heavy metals such as cobalt, manganese and the like. Although this method is well known in the art and it is used at the industrial level, the course of the oxidation reaction accompanied by the formation of impurities that can be removed or made no changes color, which is necessary to obtain terephthalic acid suitable for production of fibers. The main use of related and unrelated terephthalic acid is reduced and limited to use in the production of high molecular weight polyesters, necessary for the production of fibers and films.

From U.S. patent N 3584039 it is well known that terephthalic acid with purity, suitable for receiving the fibers, can be prepared by purification of crude terephthalic acid by carrying out the recovery process. This process involves spraying an aqueous solution of crude terephthalic acid with hydrogen in the presence of marked or nenanesenie in solution under operating conditions. When carrying out this process is the restoration of an intermediate stage of oxidation products, such as 4-carboxybenzene and other coloring impurities present in the terephthalic acid, and the formation of removed products. Purified terephthalic acid is then extracted by crystallization and drying.

Although the described procedure and has various advantages, there are still problems, which consist in the fact that the contamination of purified terephthalic acid p-Truelove acid represent a phenomenon that is dependent on the cooling rate, and not on temperature. The sharp drop in temperature caused by the release of pressure, accompanied by the deposition of p-Truelove acid from a solution of purified terephthalic acid in crystalline purified terephthalic acid. However, the solubility of p-Truelove acid remains high in the aquatic environment at a temperature which is found in the region from about 38 to about 205oC.

It was found that when the positive displacement aqueous solution of p-Truelove acid from the filter cakes formed crystalline purified terephthalic acid, is effective displacement of the p-Truelove acid is slots water at high temperature and pressure. The pressure is then dropped to the ambient atmospheric pressure. Found that the concentration of p-Truelove acid held in the crystal of purified terephthalic acid after carrying out the specified operation is by mass to 200 parts per million (0.02 percent) or less.

Under the proposed method, the crystals of purified terephthalic acid coming from the mould and placed in water, is filtered at the temperature of at least about 38oC, and preferably enclosed in a region from approximately 100 to approximately 205oC and a pressure of at least about 0.5 pound per square inch (3,45 kN/m2), and preferably lying in the region from about 40 (275,8 kN/m2and approximately 110 pounds per square inch (758,5 kN/m2), in which the formation of filter cakes.

An aqueous slurry containing crystals of purified terephthalic acid, is introduced into the filtration cell or in the sequence of filter cells are physically arranged in such a manner that the possibility of formation of filter cakes with a sufficient receipt and proper distribution of sludge coated the entire area of the filter cakes when strbody. On the surface of the filter cells is convenient to form a filter cake thickness of at least about 0.5 (12.7 mm) and approximately 8 inches (203.2 mm), preferably a thickness of at least about 1 inch (25.4 mm) and greater in thickness from approximately 2 (50.8 mm) and about 4 inch (101,6 mm). The aqueous mother liquor may be subjected to regeneration and processing to extract p-Truelove acid and/or feed in device processing wastewater.

Upon reaching the proper or preferred height of the filter cake, comprising approximately 0.5 to 8 inches (from 12.7 to 203.2 mm) pellet leaves the filtration zone and fed to the washing area where the pellet is washed with water flow when the pressure gradient allows the rise of water above the filter cake at the proper height, it is desirable for the minimum height of the order of 0.25 inches (6.35 mm). Then the flow of water put pressure gradient value of at least 0.5 psi (3,45 kN/m2) relative to the pressure in the system, and better value from 5 (of 34.5 kN/m2and up to about 85 pounds per square inch (448,18 kN/m2) relative to the pressure in the system than is provided by the displacement of an aqueous solution of p-Truelove acid from Phil is terephthalic acid then undergoes a decrease in pressure in the system up to pressure, in the range from atmospheric pressure to the gauge pressure value of about 90 pounds per square inch (620,55 kN/m2), concomitant lowering the system temperature to a temperature equal to or lower than approximately 166oC. Rinsed with water purified terephthalic acid is then subjected to drying at atmospheric pressure.

The minimum height of the pellet of purified terephthalic acid value of at least 0.5 inch (12.7 mm) is acceptable to obtain the filter cakes sufficient compactness in terms of water retention, i.e. as a result of the filter cake, from which the solution containing the dissolved substance may be effectively removed by carrying out pressure washing. If the height of the pellet is less than approximately 0.5 inches (12.7 mm), then the degree of retention of the solution containing the dissolved substance, the filter cakes is greatly increased, despite the flow of wash water at high pressure. Because of the loss of efficiency at the process pressure washing of filter cakes with water to remove the solution containing the dissolved substance, it is desirable that the minimum height of the pellet of purified teratologist was located at a minimum height, in which there is pressure washing. This height must be sufficient to ensure complete coverage of the surface of the pellet. If the surface of the pellet is uncovered by water, then it may happen hack the flow of drilling fluid without full replacement of the mother liquor from the inner region of the pellet. Due to the presence of irregularities in the surface of the pellet preferably above the surface of the pellet, the minimum height of the liquid was approximately 0.25 inches (6.35 mm).

It is established that the process of positive displacement aqueous solution of p-Truelove acid using water as the displacing medium in the filtration cycle at high temperature and pressure allows for efficient exchange of solution p-Truelove acid on the environment, including water, and removing the purified terephthalic acid from the aqueous component of the slurry, which contains soluble p-Truelove acid. If a positive displacement solution of p-Truelove acid from the filter cakes formed purified terephthalic acid, at elevated temperature and pressure decreases cocrystallization p-Truelove acid by crystallization of purified SUP>2), and a temperature equal to or lower than about 205oC, when dropping the pressure in the system and lowering the temperature of the system.

Because of the insolubility of the p-Truelove acid in water at temperatures less than 38oC and a pressure less than 10 psi (68,95 kN/m2) excess of the value of the typical methods of filtering are not suitable for the removal of p-Truelove acid from the filter cake. Although the problem of solubility and can be partially circumvented by carrying out filtration at elevated temperature and pressure, filtration and washing with water are typically less successful in the sense of removal of p-Truelove acid crystalline purified terephthalic acid, when used vacuum or spend filtration under pressure without the use of the method of washing with a piston flow, or a method of washing with flooding water. In such methods, filtration under vacuum or under pressure may occur in the formation of channels in the wafer, and in this case the water does not penetrate into the cake.

In the case of the method corresponding to the invention, it is established that can be received unexpected high efficiency removal of p-Truelove acid at carrying out the acid. The content of p-Truelove acid in purified terephthalic acid can be mass reduced to 200 parts per million (0.02 percent) or less.

From an engineering point of view, the presence of incremental steps filter, working under pressure, allows you to reset the pressure to the atmospheric value, resulting in be eliminated problems associated with the discharge of solids in the drying apparatus operating at atmospheric pressure. When implementing the method, responsive to the invention, it is necessary to use a ball valve for lowering the pressure in the system to atmospheric values.

When using incremental stages pressure washing under pressure, you can reduce the amount of water held in the pellet of purified terephthalic acid, as it was demonstrated on the example of the quantities of water used incremental stages positive pressure washing, in which case the target was to reduce the amount of water required to lower levels of acetic acid, captured from an aqueous solution of acetic acid.

For this reason it is convenient to use the proper number of stages positive wieskirche which reduces the need to use set below the device processing wastewater. In accordance with the foregoing, in the event of a way that meets the invention, applied to a positive displacement p-Truelove acid from the mother liquor held by the filter cake of purified terephthalic acid, with the aim of reaching a level of about 200 parts per million (0.02 percent) or less in the cake by filtration can be used a multi-stage pressure leaching of purified terephthalic acid.

It is clear that the method with multi-stage pressure washing may be replaced by a single-stage technique with pressure washing, in which the amount of water is sufficient to obtain the levels of p-Truelove acid held in purified terephthalic acid value of about 200 parts per million (0.02 percent) or less. In addition, the method of countercurrent washing can be useful and when it is concluded that the benefit can be gained from reducing the number of wash water.

In case that meets the invention, p-colorability a slurry containing crystals of the purified terephthalic acid is injected into one or more consecutive filter thickness by passing the flow of sludge from the purified terephthalic acid. In the formation of filter cakes minimum height in the range of about from 0.5 (12.7 mm) and approximately 8 inches (203.2 mm) pellet leaves the area of the filter and enters the zone of leaching, where the cake is washed with water flow. The water flow then applied the pressure required to move the p-Truelove acid in the mother liquor held by the filter cake, which occurs under the influence of positive pressure. After the process of displacement from flooding the filter cakes of the filter cake is discharged from the filter appropriate means, and the cycle repeats. The ratio of the area flush to the area of education pellet is located in the region from about 1:20 and about 20:1 than decreased levels of p-Truelove acid in the filter cake. Then the pressure in the system is reset, and the washed filter cake is discharged from the filter.

The equipment necessary for carrying out the desired cycle may include a sequence of filter cells installed so that water could flood filter cells. The proper equipment can include a rotary drum filter with many f which have to be provided for controls, to introduce a stream comprising purified terephthalic acid in solution p-Truelove acid for the formation of filter cakes, to transfer the filter cakes from the filter in the washing area, where the filter cake is washed with water flow, in which case water is supplied under pressure, so that the positive displacement p-Truelove acid found in mother liquor held purified terephthalic acid. The filter cake can be washed as many times as necessary to achieve the minimum concentration of the p-Truelove acid in the filter cake to discharge the washed filter cakes with a rotary drum filter.

Acceptable rotary drum filter, which can be adapted to the requirements of the method corresponding to the invention is a pressure filter type BHS-FEST(TM)(trademark) manufactured by BHS-WERK, Sonthofen, D-8972, Sonthofen, West Germany, although other filters, which can meet the required cycle, can be used; for example, there may be used a belt filter company "Pannevis", Utrecht, the Netherlands or etelnost filter cells located on the periphery of the rotating drum. As rotation of the drum on the filter cell enters an aqueous slurry consisting of purified terephthalic acid and soluble p-Truelove acid, and the capacity of the filter cakes to the desired height. During the rotation of the drum filter cake leaves the area of the filter and enters the zone of leaching, where the flooding of the filter cakes with water to the desired depth. The pressure applied to the surface of the water, forcing the water to move through the filter cake, displacing p-Truelove acid, withholding water, located on the crystals of purified terephthalic acid. Upon further rotation of the drum of the washing cycle may be repeated at least once, if necessary, after which the system pressure drop with the proper temperature drops to their values at ambient conditions. The filter cake is then discharged from the drum, the feeding pressure of the inert gas.

A similar sequence of operations occurs when using a band filter.

Example 1. The following example illustrates the way that meets the invention, when ecoleetage acid and mother liquor, served on working under pressure rotary filter type BHS-FEST(TM)what you are doing at a pressure of 60 psi (413,7 kN/m2) and a temperature of 149oC. Filter type BHS-FEST(TM)used to separate the solids from the mother liquor, washing the solids, removal of excess moisture from the pellet and unloading solids at atmospheric pressure. The filter housing is divided into five chambers designed to hold five different operations at filtering: education cakes, pressure washing, drying the pellet, the pellet unloading and washing of the filter cloth. The drum filter, operating at speeds in the region of 0.5 to 2.0 rpm, divided into twenty-filter cells. The total surface area of the fabric filter, which has the drum is approximately 1.3 square feet (0,1208 m2). The performance of the sludge is, if it is expressed through consumption, about 360, 720 and 1440 lb/h (163,29, 326,59 and 653,17 kg/h), when the speed of rotation of the filter, respectively, 0.5, 1.0, and 2.0 to rpm

Because the filter operates continuously, all filter operations - education cakes, pressure washing, drying the pellet, the pellet unloading and washing Piestany one filter cell.

The filter cell is rotated into a camera filter with the formation of the pellet. The feed slurry containing about 45% of solid substance purified terephthalic acid and about 1000 ppm (0.1%) by weight of p-Truelove acid, is continuously pumped into the chamber, acting under pressure of about 60 psi (413,7 kN/m2). As the rotation of the filter cells with passage through the chamber, the solid is collected on filter fabric, forming a pellet with a thickness of one inch (25.4 mm). Uterine fluid passes through the filter cloth and is supplied into the inner tube of the filter. The pressure of the mother liquor in this inner tube is in the range of from about 30 (206,85 kN/m2and up to about 50 pounds per square inch (344,75 kN/m2). Uterine fluid is directed to a device for the extraction of p-Truelove acid and/or recycling of wastewater.

The filter cell containing now the filter cake, leaves the chamber filter with the formation of the pellet and enters the pressure chamber. The camera continuously pumped clean water supplied under pressure 60 psi (413,7 kN/m2) on the excess amount and at a temperature of about 149oC. Receiving the oC. This water, given the effectiveness of pressure washing effectively removes p-Truelove acid from the filter cake. Wash water passing through the cake, is now at a pressure lying in the region from about 30 (206,85 kN/m2and up to about 50 pounds per square inch (344,75 kN/m2). This water is collected separately from the mother liquor and is used at other stages of the process of purified terephthalic acid.

The washed cake in the filtration cell, leaves the chamber pressure washing and enters the drying chamber cakes In the drying chamber continuously served the compressed inert gas being at a pressure of 60 psi (413,7 kN/m2), which ensures the removal of excess moisture from the filter cake.

The filter cell, then the rotation is transferred from the drying chamber into the chamber unloaded pellet. In contrast to other described cameras, this camera operates at ambient pressure. Due to the pressure drop at the transition from the drying chamber of the pellet into the chamber unloading cakes of it is some extra moisture. The cake is then discharged from the filter that comes at a cost of 190, 380 and EU pellet contents p-Truelove acid is by mass to 200 parts per million (0.02 percent) or less of dry matter.

After unloading pellet filter cell is rinsed with water, what happens in the flushing chamber of the filter fabric, which ensures the removal of any traces of the unloaded pellet. Filter the cell then enters the chamber of the filter with the formation of the pellet, and the process repeats.

The data for the appropriate experiments are given in the table. Wash ratio characterizes the amount of clean water used for pressure washing the pellet from the p-Truelove acid, which is measured relative to consumption on lepeshechnika material. The purge ratio characterizes the amount of compressed inert gas used for drying the pellet before unloading, which is measured relative to consumption on lepeshechnika material.

Example 8. The following example illustrates the application of the method conforming to the invention, using a belt filter.

A slurry containing 48% of the crystallized solid purified terephthalic acid and mother liquor, served in a pressure belt filter with a flow rate of 780 lb/h (353,8 kg/h) at a pressure of 90 pounds per square inch (620,55 kN/m2) and a temperature of 166oC. Belt filter eudermic and in the zone of drying.

The slurry is fed to the first section of the ribbon, where the separation of solids and mother liquor. Solids form on the continuous ribbon cake thickness of 3 inches (76.2 mm). The filtrate mother liquor through the filter cloth and is pumped or extraction device p-Truelove acid, and/or in device processing wastewater.

Continuous pellet is then transferred into the area pressure washing. This zone operates at a pressure of 90 pounds per square inch (620,55 kN/m2) and a temperature of 166oC. In this zone, pure water is supplied on the cake with a flow rate at which the mirror is located above the pellet.

After passing zone pressure washing continuous pellet enters the drying zone. Excess water allowed to drain out of the pellet and to remove additional amounts of moisture serves inert gas. This zone also operates at a pressure of 90 pounds per square inch (620,55 kN/m2) and a temperature of 166oC.

The dried pellet, containing now on weight only 200 parts per million (0.02 percent) or less p-Truelove acid calculated on dry substance, unloaded from the tape in the device (devices) low pressure, such elefteriou acid, now at atmospheric pressure, then transferred to the drying apparatus operating at atmospheric pressure.

1. A method of obtaining a purified terephthalic acid containing p-Truelove acid, present at a concentration equal to or less than 200 hours on 1 million by weight, including the processing of terephthalic acid pre-treated by contacting an aqueous solution of terephthalic acid with hydrogen, characterized in that the specified treatment is carried out by typing in the filter cell, or series of filter cells in the zone of filtration at a temperature of at least 38 of 205oAnd the system pressure is from atmospheric up to 1620 kPa, an aqueous slurry containing purified terephthalic acid, present in the form of crystals, and p-Truelove acid present in the aqueous solution and in cocrystallization form together with crystals of purified terephthalic acid, and filter the cell or the sequence of filter cell support in such position that allows education to each filter cell filter cakes or filter cakes with the introduction of its water slurry, after che is in which in each filter cell is injected a stream of water to form a water reservoir in each filter cell above the filter cake or filter cakes, when it entered the water flow is at a pressure gradient of at least 3,45 kPa relative to the pressure in the system and the temperature being in the range from 38 to 205oC, then washed filter cake with water for a time sufficient to reduce the concentration of p-Truelove acid to a value equal to or less 200 hours on 1 million by weight, and then move each filter cell containing the washed filter cake, in the area of pressure relief, in which the pressure in the system to relieve pressure in the range from atmospheric pressure up to at least 620 kPa, the temperature of the filter cakes is reduced to a temperature equal to or less 166oS, after which the washed filter cake containing purified terephthalic acid, unloaded from each filter cell.

2. The method according to p. 1, characterized in that the height of the filter cakes is 1,27 see

3. The method according to p. 1, characterized in that the water tank above the filter cake is 0.6 cm in height.

4. The method according to p. 1, characterized in that the water from the stage washing of filter cakes is extracted in the form of wash water and recycle>/P>5. The method according to p. 1, characterized in that the flow of water is under pressure in the range of at least from 3.45 to 448,18 kPa relative to that of the pressure in the system.

6. The method according to p. 1, characterized in that said flow of water is under pressure at least 34,5 - 448,18 kPa relative to the pressure in the system.

7. The method according to p. 1, characterized in that the height of the filter cakes is equal to at least 1,27 - 20,0 see

8. The method according to p. 1, characterized in that the height of the filter cakes is equal to at least 2,5 - 10,0 see

9. The method according to p. 1, characterized in that the height of the filter cakes is equal to at least 5 - 10 cm

10. The method according to p. 1, characterized in that the pressure in the system is equal to at least 3,45 - 758,0 kPa.

11. The method according to p. 1, characterized in that the pressure in the system is equal to at least 275,0 - 448,18 kPa.

12. The method according to p. 1, characterized in that the temperature of the flow of water equal to at least 100 - 205oC.

 

Same patents:

The invention relates to methods of producing terephthalic acid

The invention relates to chemical technology, namely the production of monostearate polyhydric alcohols used in the cosmetic and food industry

The invention relates to methods of producing terephthalic acid
The invention relates to the selection of 2.5-biphenyldicarboxylic acids from oxidation products of 2,5-dimethylbiphenyl

The invention relates to chemical technology, and in particular to methods of allocation of dichloracetic acid, which finds application in the production of chemical fibers, pharmaceuticals

The invention relates to wastewater treatment, in particular to a method of cleaning wastes sorbic acid

The invention relates to methods for purifying sebacic acid derived from domestic castor oil

FIELD: organic chemistry.

SUBSTANCE: invention relates to method for purification of monochloroacetic acid from dichloroacetic acid impurities. Claimed method includes hydrogenolysis in presence of hydrogen in film regime at 135-145°C in cascade of sequentially bonded reactors with fixed bed of heterogeneous catalyst namely palladium on activated carbon. Preferably reactor cascade with intermediate cooling with cold flow of monochloroacetic acid as cooling agent is used.

EFFECT: simplified process; product of improved quality.

3 cl, 7 ex, 3 dwg

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

FIELD: chemistry.

SUBSTANCE: invention relates to an improved method, by which the carboxylic acid/diol mixture, that is suitable as the initial substance for the manufacture of polyester, obtained from the decolourised solution of carboxylic acid without actually isolating the solid dry carboxylic acid. More specifically, the invention relates to the method of manufacturing a mixture of carboxylic acid/diol, where the said method includes the addition of diol to the decolourised solution of carboxylic acid, which includes carboxylic acid and water, in the zone of the reactor etherification, where diol is located at a temperature sufficient for evaporating part of the water in order to become the basic suspending liquid with the formation of the specified carboxylic acid/diol mixture; where the said carboxylic acid and diol enter into a reaction in the zone of etherification with the formation of a flow of a complex hydroxyalkyl ether. The invention also relates to the following variants of the method: the method of manufacture of the carboxylic acid/diol mixture, where the said method includes the following stages: (a) mixing of the powder of damp carboxylic acid with water in the zone for mixing with the formation of the solution of damp carboxylic acid; where the said carboxylic acid is selected from the group, which includes terephthalic acid, isophthatic acid, naphthalenedicarboxylic acid and their mixtures; (b) discolourisation of aforesaid solution of damp carboxylic acid in the zone for reaction obtaining the decolourised solution of carboxylic acid; (c) not necessarily, instantaneous evaporation of the said decolourised solution of carboxylic acid in the zone of instantaneous evaporation for the removal of part of the water from the decolourised solution of carboxylic acid; and (d) addition of diol to the decolourised solution of carboxylic acid in the zone of the reactor of the etherification, where the said diol is located at a temperature, sufficient for the evaporation of part of the water in order to become the basic suspending liquid with the formation of the carboxylic acid/diol mixture; where the aforesaid carboxylic acid and diol then enter the zone of etherification with the formation of the flow of complex hydroxyalkyl ether; and relates to the method of manufacture of carboxylic acid/diol, where the said method includes the following stages: (a) the mixing of the powder of damp carboxylic acid with water in the zone for mixing with the formation of the solution of carboxylic acid; (b) discolourisation of the said solution of damp carboxylic acid in the reactor core with the formation of the decolourised solution of carboxylic acid; (c) crystallisation of the said decolourised solution of carboxylic acid in the zone of crystallisation with the formation of an aqueous suspension; and (d) removal of part of the contaminated water in the aforesaid aqueous solution and addition of diol into the zone of the removal of liquid with the obtaining of the said carboxylic acid/diol mixture, where diol is located at a temperature sufficient for evaporating part of the contaminated water from the said aqueous suspension in order to become the basic suspending liquid.

EFFECT: obtaining mixture of carboxylic acid/diol.

29 cl, 4 dwg

FIELD: chemistry.

SUBSTANCE: method lies in the following: concentrated solution of lithium salt is introduced into mixture of sodium salts of naphthenic acids, mixed and left for separation into layers and formation of viscous mass of lithium salt of naphthenic acid high-molecular fraction with molecular weight more than 200 in sediment, and in upper water layer - of low-molecular fraction of naphthenic acids lithium salt with molecular weight less than 200, with subsecutive separation.

EFFECT: separation of concentrated water solutions of naphthetic acids lithium salts according to their molecular weight.

2 cl, 2 ex

FIELD: chemistry.

SUBSTANCE: method of obtaining product - purified carboxylic acid, includes: (a) oxidation of aromatic initial materials in primary oxidation zone with formation of raw carboxylic acid suspension; where raw carboxylic acid suspension contains terephthalic acid; where said oxidation is carried out at temperature within the range from 120°C to 200°C; (b) withdrawal of admixtures from raw suspension of carboxylic acid, removed at temperature from 140°C to 170°C from stage of oxidation of paraxylol in primary oxidation zone and containing terephthalic acid, catalyst, acetic acid and admixtures, realised in zone of solid products and liquid separation with formation of mother liquid flow and product in form of suspension; where part of said catalyst in said suspension of raw carboxylic acid is removed in said mother liquid flow; and where into said zone of solid products and liquid separation optionally additional solvent is added; (c) oxidation of said product in form of suspension in zone of further oxidation with formation of product of further oxidation; where said oxidation is carried out at temperature within the range from 190°C to 280°C; and where said oxidation takes place in said zone of further oxidation at temperature higher than in said primary oxidation zone; (d) crystallisation of said product of further oxidation in crystallisation zone with formation of crystallised product in form of suspension; (e) cooling of said crystallised product in form of suspension in cooling zone with formation of cooled suspension of purified carboxylic acid; and (i) filtration and optionally drying of said cooled suspension of purified carboxylic acid in filtration and drying zone in order to remove part of solvent from said cooled suspension of carboxylic acid with obtaining of said product - purified carboxylic acid.

EFFECT: purified carboxylic acid with nice colour and low level of admixtures, without using stages of purification like hydration.

8 cl, 1 tbl, 1 dwg, 1 ex

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