The method of obtaining terephthalic acid (options)

 

(57) Abstract:

Use: in the production of polymer fibers. The inventive slurry of terephthalic acid in acetic acid is obtained by oxidation of p-xylene in acetic acid, removal of water by evaporation of water and acetic acid, with return of acetic acid to the degree of oxidation. Terephthalic acid is recovered from the reaction medium in the first zone, and a residue remains on the tape, the residue is washed first aqueous medium in the second zone, is removed from the tape in the third zone and mixed with the second aqueous medium, the reaction medium is withdrawn from the first reaction zone to the degree of oxidation and remove terephthalic acid, the process is carried out at a higher pressure from the moving tape, which serves a suspension, compared to its opposite side, and the differential pressure is 0.1 - 15 bar, in the preferred embodiment, after additional purification using water, obtained in the previous stage. 3 C. and 28 C.p. f-crystals, 1 table. 2 Il.

The invention relates to methods of producing terephthalic acid.

Terephthalic acid in the industry is produced by oxidation of paraxylene with oxygen in a liquid medium, katica as a by-product, regulated by removing from the reactor steam flow containing water and acetic acid. Water may be extracted from at least part of the stream, separated from the stream enriched in acetic acid which may be recycled to the reactor.

Terephthalic acid is obtained in the form of a suspension of crystals of terephthalic acid in the liquid phase comprising acetic acid, a quantity of catalyst and impurities. Terephthalic acid member can be separated from the liquid, for example, by centrifugation or by filtration, washed with acetic acid and dried in order to remove acetic acid dissolved in water at elevated temperature, gidrirovannah for recovery of organic impurities and recrystallized to obtain the pure product.

This technology includes drying, manual control, storage and re-suspension of the powder terephthalic acid; to perform all these operations require special equipment, which accordingly affects capital and operating costs. In addition, this method enables the residual quantity of the catalyst and impurities to enter the next stage of the process.

In the patent GB N 970492 rusk is holding acetic acid, obtaining a suspension of crystals of terephthalic acid in the reaction medium, followed by separation of the crystals of terephthalic acid from the reaction medium and recycling at least part of it, and mixed crystals of terephthalic acid with an aqueous medium, from which the acid is then isolated.

The present invention provides significantly improved flushing of terephthalic acid in the reaction zone. Improved washing can further improve the stage of oxidation so that it becomes valid high content of impurities on phase oxidation while maintaining acceptable quality of terephthalic acid.

The present invention relates to a method for producing terephthalic acid comprising the oxidation of p-xylene in a reaction medium containing acetic acid, to obtain a slurry of crystals of terephthalic acid in the reaction medium; separating the crystals of terephthalic acid from the reaction medium, followed by recycling at least part of it; a mixture of crystals of terephthalic acid with an aqueous medium, from which subsequently the secrete acid, characterized in that the separation of crystals therephtale is at a temperature of at least 60oC with a movable strip of filter material, and then remove the reaction medium from the suspension through the tape in the first zone with a first wet sediment, and part of the separated reaction medium is sent directly or indirectly to the stage of oxidation, while moving the first residue on the tape in a second zone in which it is washed with a first aqueous medium, which is removed along with the reaction medium present in the first wet sediment, through the ribbon to obtain a second wet sludge which is sent to the third area where the sediment is removed from the tape and mixed with the second aqueous medium, from which extract terephthalic acid, the process is carried out at a higher pressure from the moving tape, which serves a suspension, compared to the opposite side? and the differential pressure is 0.1-15 bar.

Preferably, the second aqueous medium consisted of essentially pure water to prevent impurities in the product terephthalic acid. In addition, in the preferred embodiment, terephthalic acid allocate after further purification, preferably in a plant for the purification of terephthalic acid.

To regulate the temperature of the Noah environment at the stage of oxidation by evaporation, water is extracted from at least part of the mentioned mixture under distillation to obtain acetic acid with low water content. Further depleted water acetic acid can be recycled to the reactor at a stage of oxidation.

In accordance with another variant of the invention, the separation is carried out by feeding the slurry onto a movable belt of filter material at a temperature of at least 60oC to move through the first zone in which the reaction medium is removed from the slurry of terephthalic acid to obtain the first wet sediment with subsequent displacement of the first wet sediment at the specified mobile belt filter material through the second zone, in which the first wet sediment was washed with water and get a second wet sludge by removing wash water together with the reaction medium in the first wet sediment using the supplied tape, followed by a move of the specified second wet sludge on a movable strip of filter material in the third zone in which the second wet sludge is removed from the filter belt, and the process is carried out at a higher pressure from the moving tape, which serves the suspension compared to Eiendom of the invention the separation is that the suspension is placed on a movable strip of filter material is moved at a temperature of at least 60oC through the first and second zones, in this case, initially expose the suspension is filtered at the intersection of the first zone to remove through the belt filter material of the reaction medium and receiving the first wet sediment crystals of terephthalic acid, which is subjected to washing by passing through successive water wash steps at the intersection of the second zone and will filter through the belt of filter material separating crystals of terephthalic acid wash water from the reaction medium remaining in the first wet sediment, these wash steps, except the last exercise using water obtained at the subsequent stage, and the process is carried out at a higher pressure from the moving tape, which serves a suspension, compared to its opposite side, and the differential pressure is 0.1-15 bar.

Constant concentration of impurities in the method can be adjusted by blowing, for example, removing at least part of the non-volatiles extracted after byarianespace possibly together with water and acetic acid from a stream, obtained by evaporation on the stage of oxidation, to obtain the acetic acid-depleted water. Acetic acid with a low content of water can be fed to the stage of oxidation, and water obtained by distillation, can be used as the first and/or second aqueous medium. You can use at least part extracted by distillation of water at other stages of the method and at the treatment plant, if available.

Due to the improved leaching in accordance with the present invention becomes valid high content of impurities in the reaction medium at the stage of oxidation, and therefore, there is recirculation of the reaction medium from the first zone and/or the first aqueous medium and the reaction medium from the second zone and, consequently, reducing as far as possible blowing. Reduction blowing is an advantage if such substances as, for example, terephthalic acid, preceding the products of terephthalic acid and the residual quantity of the catalyst remain in the process.

Improve rinsing allows to obtain a slurry of terephthalic acid in the second aqueous medium with a lower content of impurities, such as residual catalyst. In predpochte due to the above reasons.

Low content of impurities in suspension allows recycling the mother liquor from the treatment unit, for example, obtained by precipitation of the purified terephthalic acid, which reduces the exhaust amount of exhaust flow while maintaining an acceptable level of product quality. In addition, recirculating the mother liquor can be used as possible after further processing, for example, after cooling, filtration, distillation and/or evaporation to flush the first wet sediment in the second zone. This allows to reduce the fresh water consumption at the present rate of leaching or essentially eliminate the amount of fresh water.

No need for separate stages of drying and expensive equipment and, accordingly, in the regulation of solid impurities and storage leads to lower capital costs, which is a significant economic advantage.

The belt filter is a corresponding metal mesh fabric or cloth, including plastic materials, for example, polyester or polypropylene fibers. The belt is a continuous belt, which is moving continuously or Phu zone. The second zone, respectively, includes a sequence of process steps, where at each step (except the last) supplied water passes through the solid and the tape, and in aqueous medium passes through the solid and the tape on the subsequent stage. On the last step in the preferred embodiment, use fresh water. This served fresh water respectively includes at least a portion of the water separated from the acetic acid in the above process of distillation and/or evaporation, or other water streams that are covered by this way, the advantage of which is to reduce the consumption of fresh water and disposal of water within the process.

In the third zone of the sediment can be removed by scraping with a ribbon, and in the preferred embodiment, washed her an aqueous medium, preferably essentially pure water, which may be submitted in the form of jets into the end of the tape. In the case of a continuous belt, it is desirable to allow passage of fluid, such as water or alkaline solution, through the return portion of the belt for flushing stuck sediment in the collection.

It is preferable to maintain the pressure difference along the moving tape; so I pressure, respectively, is at least 0.05 bar absolute. and does not exceed the pressure maintained on the degree of oxidation, for example, 30 bar abs. In a preferred embodiment, the pressure difference is from 0.1 to 15 bar abs., more preferably from 0.2 to 7 bar abs., and in particular from 0.3 to 3 bar abs., for example, to 0.6 bar abs. In the area of low pressure tape is under such pressure that the reaction medium and the aqueous medium removed through the tape in the second zone, remain in the liquid phase.

Increased pressure in the corresponding portion of the tape coincides with or exceeds the pressure of the previous step of the way, for example, the stage of crystallization or oxidation.

The slurry of terephthalic acid in acetic acid is then precipitated onto a moving belt at a temperature of at least 60oC, in the preferred embodiment, from 70 to 200oC, in particular from 80 to 150oC. the Corresponding suspension is deposited at a temperature high enough pressure to low pressure tape was not lower than 1 bar abs.

The advantage of the precipitation suspension at elevated temperature is that it allows to improve the filtering due to the lower viscosity of the reaction medium at elevated temperatures. In addition, when povyshen is with terephthalic acid. Thus, receive as an intermediate in the production of high-quality terephthalic acid with a correspondingly high content of impurities, for example, 4-carboxybenzene, in the reaction medium. This can further improve the technological conditions at the stage of oxidation, resulting in lower operating costs.

Increased temperature also contributes to the utilization of heat, so that even more reduced operating costs. In addition, if the stage of purification of the slurry of terephthalic acid in the second aqueous medium is typically heated to dissolve the terephthalic acid is filtered at an elevated temperature to obtain terephthalic acid at elevated temperature, which also reduces the cost of heat on the dissolution of the terephthalic acid in suspension.

Other individual stage of the present method may be carried out under standard conditions. The liquid reaction medium typically includes a catalyst, e.g. cobalt/manganese/prominy the catalyst dissolved in the reaction medium. The oxidation is carried out in the presence of a source of oxygen, for example air, at a pressure of from 5 to 30 bar abs. and when the preferred content of wny process which in a preferred embodiment, is carried out in the reactor under stirring. This is an exothermic reaction, the heat which usually dissipate by evaporation of water and acetic acid from the reaction medium.

The corresponding slurry of terephthalic acid in the second aqueous medium is cleaned by a process comprising dissolving the terephthalic acid in the second aqueous medium to obtain a solution containing terephthalic acid interaction in the conditions of the reduction reaction of the above-mentioned solution with hydrogen and a heterogeneous catalyst to restore at least part of the impurities, cooling the solution with precipitation of the solid purified terephthalic acid and removing said product from the solution.

Suitable heterogeneous catalyst used for purifying terephthalic acid, may be a noble metal on a carrier, for example, platinum and/or in the preferred embodiment, palladium on an inert, for example, carbon, media. Restoration of conduct, passing an aqueous solution containing terephthalic acid and impurities, for example, 4-carboxybenzene, flooded through the catalyst bed at a temperature of from 250 to 350oC in the presence of vtoroj cooled to a temperature of from 100 to 250oC to separate pure terephthalic acid from solution. In the preferred embodiment, this solution is successively cooled to a temperature of from 15 to 100oC or evaporated with getting less pure precipitate and mother liquor. Less pure precipitate was separated from the mother liquor. Mother liquor after separation may directly or indirectly be recycled to the step of distillation and/or be used as the second wave environment for re-suspension of terephthalic acid. If necessary, less pure precipitate may be recycled to the stage of oxidation.

Otherwise, in the absence of further treatment, terephthalic acid can be removed from the second aqueous medium, dried, for example, in a stream of inert gas. Dry terephthalic acid can be used in subsequent stages of the process. You can use the stage crystallization to increase the yield of terephthalic acid from a mixture of the second aqueous medium with terephthalic acid.

The following is one of the variants of the present invention with reference to Fig. 1 and 2.

In Fig. 1 shows a schematic diagram of the process of Fig. 2 - filter and capacity for repullo acid, containing the dissolved catalyst containing cobalt, manganese and bromine ions, and served in the air line 2. The product from reactor A is supplied in the sector crystallization B on line 3. The temperature in the reactor And is regulated by evaporating a mixture of acetic acid with water from the reactor in the condensation system C on line 4. A large part of the condensate is returned to the reactor A through line 5, the non-condensable residue is discharged through line 6. To regulate the water content in the reactor A portion of the condensate is removed from the system condensation on line 7 and fed to the distillation column D.

In section crystallization B the temperature is reduced to approximately 75-120oC and the thus obtained suspension containing crystalline terephthalic acid in the mother solution, arrives on stage filtration E. Acetic acid can be made from a section of crystallization of B-threads 8 and 9 in the distillation column D and/or threads 8 and 10 and/or 11 in the reactor A.

Stage filtering E and capacity repulpable F shown in Fig. 2.

In Fig. 2 schematically shows a filter with a continuous strip E, used in the method according to this invention, which includes a filter tape 100, the driven rollers (not pokazali. The dotted lines show the location of the first zone to the left, where the suspension of terephthalic acid and acetic acid together with the dissolved catalyst is supplied via line 103 to the tape, and acetic acid flows through the ribbon precast Chan 104, where it is removed via line 105, the second (middle) zone in which water is introduced through line 106 and passes through the tape three times, and comes in assorted pallets 107, 108 and 109, thereby flushing precipitation on the ribbon, all with plenty of clean water as soon as it passes through each of the three wash steps and the third zone in which water is sprayed on and/or through the tape for flushing sediments from the tape on the inclined plate 102, descending into the tank F, which may be submitted if necessary, an additional amount of water in the lines 14, 15, 16 and/or 17. Water from line 106 may come from lines 14, 15, or from any other appropriate source.

Uterine fluid extracted at this stage, partly returned through line 10 into A reactor, optionally in a mixture with fresh catalyst, paraxylene and acetic acid supplied through the line 1. A number of remaining mother liquor and the wash fluid from the second zone with aneroussa and fed into the reactor A or, not necessarily directed to distillation column D, and by-products and catalyst is removed from the system with the flow 13.

In reulatory F crystals diluted with water, extracted from distillation column D, in the form of a stream 14 and/or other water which may be recycled mother liquor in the form of a thread 15, recirculating mother liquor in the form of a stream of 16 and demineralized water as stream 17.

Obtained in this step, the suspension is heated in section H to a temperature of from about 250 to 350oC to obtain a solution, which is in the form of a thread 19 is directed into the reactor J, where it reacts with hydrogen over a fixed bed of palladium catalyst, resulting in the recovery of impurities in the solution, and then again carry out the crystallization solution in section K, from which derive the net product, and dried it on level L, which may include a centrifuge and/or filters and dryer.

The temperature to which a cooled solution in section crystallization K, and the cooling rate is chosen in such a way as to obtain the desired purity of the commodity terephthalic acid. Pure terephthalic acid output with level L, and the mother liquid with stupen to ensure removing additional amounts of solid substances, which can be returned to the reactor in the form of A thread 20. In stage M liquid temperature can be lowered to 100oC by steam discharge from this level under atmospheric pressure. This steam can be further purified, e.g. by distillation and, if necessary, be used as washing liquid in stage L, used in any other way in the process or be removed from the process. The remaining liquid can be cooled, or in addition to evaporate for discharge from her solids. Uterine fluid output from the degree M part can return to the distillation column D and processed, as will be described below, partially may return to the level of repulpable F as stream 16, which partially may be discharged as stream 21. In the preferred embodiment, when using evaporation evaporated liquid return to the level of repulpable F.

Distillation column D provides the fractional distillation of a mixture of water and acetic acid, evaporated from the reaction medium and, if necessary, this column can be used for treatment of uterine fluid that is separated in stage m

Column D has three zones: the upper zone 1 contains NAP has about 5 theoretical stages.

Part of a mixture of acetic acid and water evaporated in the reaction stage of oxidation of p-xylene to terephthalic acid in A reactor, is directed as stream 7, optionally together with a thread 11, lines 9 to a point between the middle and lower zones of the column D. Uterine fluid from the degree of precipitation of the terephthalic acid can be sent in the column between the upper and middle zones as stream 22. Acetic acid and heavy material is removed from the base of the column D in the form of a stream 23 into the reactor A. the Water condense in the condenser, and it can be reused in the process as stream 14.

Below are the following examples without limiting the scope of invention.

Example 1. Samples of crude terephthalic acid in the reaction medium (crude suspension) received at the installation of oxidation. The samples were filtered according to the method, the providing step countercurrent washing and filtering.

A sample of the crude suspension was filtered at 80oC through the flask, Buechner funnel, from which it was pumped out of the gas phase through the filter cloth, which was reinforced retaining mesh and is placed over the flask funnel. Over a filter cloth was reinforced cylindrical vessel, brezec washed with demineralised water and the filtrate was designated as F1 (I). The precipitate was thrown down. A second sample was filtered and washed with filtrate F1 (I), and the resulting filtrate was designated F2 (I). The sample was then washed with demineralised water and the filtrate was designated as F1 (II). The precipitate was thrown down. This procedure was repeated with a new sample, washing the filtrate F2 (I), obtained filtrate F3 (I), washing the filtrate F1 (II), obtained filtrate F2 (II), and washed with demineralised water, was obtained filtrate F1 (III). The precipitate was thrown down.

New sample was washed sequentially F3 (I) [received the filtrate F4 (I), which dropped], F2 (II) [F3 having (II), F1 (III)], [receiving the filtrate F2 (III)], and demineralized water [after receiving the filtrate F4 (IV)]. This final washed residue was analyzed for the determination of residues of a catalyst of cobalt and manganese in the sediment. By comparison with known amounts of these residues in the sample suspension is possible to determine the leaching efficiency.

The filtrate F4 represents the final filtrate, the resulting four-stage countercurrent rinsing. At the same time, the filtrates obtained after the first (F1), second (F2), third (F3) and fourth (F4) - speed four-stage process counterflow rinsing, were used for washing new obessession sample until while the number of contaminants in sediments obtained from the subsequent wash cycles remained almost constant.

The results are shown in the table.

Example 2. The procedure of example 1 was repeated to study a three-stage countercurrent leaching, i.e. the filtrate is denoted by F3, dumped, and the residue obtained was analyzed to determine the residual amounts of cobalt and manganese.

The results are shown in the table.

Example 3 (comparative). Researched conventional methods of washing and drying, do not meet this invention. Samples of crude terephthalic acid in the reaction medium (crude suspension), identical in composition to the samples used in examples 1 and 2 (obtained from the same source and at the same time), filtered, using industrial vacuum filter and washed with acetic acid. The samples were dried using industrial vacuum tube steam dryer. Dried sediments were analyzed to determine the content of cobalt and manganese in accordance with the method used in examples 1 and 2. Filtration and drying was carried out at a temperature of 80oC and at the same differential pressure, and flushing in Examples 1 and 2.

the invention provides a more effective leaching compared with the known method of leaching.

1. The method of obtaining terephthalic acid, comprising the oxidation of p-xylene in a reaction medium containing acetic acid, to obtain a slurry of crystals of terephthalic acid in the reaction medium, separating crystals of terephthalic acid from the reaction medium, followed by recycling at least part of it, and mixed crystals of terephthalic acid with an aqueous medium, from which subsequently the secrete acid, characterized in that the separation of the crystals of terephthalic acid from the reaction medium containing acetic acid, is carried out by contacting the suspension at a temperature of at least 60oWith the moving strip of filter material, and then remove the reaction medium from the suspension through the tape in the first zone with a first wet sediment, and part of the separated reaction medium is sent directly or indirectly to the stage of oxylene, while moving the first residue on the tape in a second zone in which it is washed with a first aqueous medium, which is removed along with the reaction medium present in the first wet sediment, through the ribbon to obtain a second wet sludge which is sent to the third area where the sediment is removed from the tape higher pressure side movable tape, which serves a suspension, compared to its opposite side, and the differential pressure is 0.1 - 15 bar.

2. The method according to p. 1, characterized in that at least a portion of the first aqueous medium and the reaction medium removed through the tape in the second zone, optionally together with at least part of the reaction medium, remote from the first zone, return to the stage of oxidation and/or is subjected to distillation.

3. The method according to PP.1 and 2, characterized in that the second zone includes successive stages, which, except the last stage, the incoming water passing through solid matter and the tape is a water environment, passing through solid matter and the tape at a later stage.

4. The method according to any of paragraphs.1 to 3, characterized in that the movable belt is a continuous belt moving continuously or periodically with a view to the transfer material containing terephthalic acid, from the first zone to the third zone through the second zone.

5. The method according to any of paragraphs.1 to 4, characterized in that the said second aqueous medium is essentially pure water.

6. The method according to any of paragraphs.1 to 5, characterized in that terephthalaldehyde dissolution of the terephthalic acid in the second aqueous medium to form a solution, containing terephthalic acid, contacting the reductive conditions of the solution with hydrogen and a heterogeneous catalyst for recovery, at least a certain amount of impurities, cooling the solution to precipitate solid purified terephthalic acid and removing the mentioned product from the solution.

7. The method according to p. 6, wherein the solution is then cooled and/or evaporated to obtain a less pure precipitate and mother liquor, the precipitate was separated from the mother liquor and the mother liquor recycle, directly or indirectly, by distillation and/or repulpable crude terephthalic acid in the second aqueous medium and, optionally, referred to or less pure precipitate is recycled to the stage of oxylene.

8. The method of obtaining terephthalic acid, comprising the oxidation of p-xylene in a reaction medium containing acetic acid, to obtain a slurry of crystals of terephthalic acid in the reaction medium, separating crystals of terephthalic acid from the reaction medium, followed by recycling at least part of it, and mixed crystals of terephthalic acid with an aqueous medium, from which subsequently the secrete acid, characterized in that rainy least 60oWith to move through the first zone in which the reaction medium is removed from the slurry of terephthalic acid to obtain the first wet sediment with subsequent displacement of the first wet sediment at the specified mobile belt filter material through the second zone, in which the first wet sediment was washed with water and get a second wet sludge by removing wash water together with the reaction medium in the first wet sediment using the supplied tape, followed by a move of the specified second wet sludge on a movable strip of filter material in the third zone in which the second wet sludge is removed from the filter belt, and the process is carried out at a higher pressure from the moving tape, which serves a suspension, compared to its opposite side, and the differential pressure is 0.1 - 15 bar.

9. The method according to p. 8, characterized in that the second zone contains a series of washing stages, where each stage except the last, the incoming water passing through solid matter and the tape represents the water that passes through the solids and the tape at a later stage.

10. The method according to p. 8 or 9, from the R.

11. The method according to any of paragraphs.8 to 10, characterized in that the strip of filter material moves continuously through the said first zone and the wash sequence of stages forming the second zone.

12. The method according to any of paragraphs.8 to 11, characterized in that the slurry of terephthalic acid is fed to the tape at a temperature in the range from 80 to 150oC.

13. The method according to PP.8 to 12, characterized in that after removal of the second wet sludge from the filter material in the third zone, the filter material is washed before it is returned to the first zone for separation of the adhered sediment.

14. The method according to any of paragraphs.8 to 13, characterized in that the second wet sediment without the intermediate stage of drying additionally suspension in water after removing it from the filter tape, after which the resulting suspension is heated, and the resulting aqueous solution of terephthalic acid podvergaut hydrogenation to reduce the content of impurities.

15. The method according to p. 14, characterized in that, after hydrogenation of the resulting solution vykristallizovyvalas terephthalic acid with obtaining purified terephthalic acid and a mother liquor, separating donno, in which carry out the fractional distillation vaporized mixture of water and acetic acid from the stage of oxylene for separation of acetic acid and water.

16. The method according to p. 15, characterized in that the separated from purified terephthalic acid mother liquor prior to being fed into distillation column is evaporated or optionally cooled to produce a less pure precipitate, which is recycled to the stage of oxidation.

17. The method according to any of paragraphs.8 to 16, characterized in that the tape is continuous.

18. The method according to PP.8 to 17, characterized in that the strip of filter material is a having a horizontal stroke of a continuous strip that moves through these areas.

19. The method according to any of paragraphs.8 to 18, characterized in that the filter material includes a plastic material.

20. The method according to PP.8 to 13, characterized in that the second wet residue optionally dissolved in water to obtain an aqueous solution of crude terephthalic acid, which was subjected to purification to reduce the amount of impurities associated with crude terephthalic acid, the cleaning is performed by treating the aqueous solution with hydrogen in the presence of getai.

21. The method according to p. 20, characterized in that the specified water mother liquor obtained in the second stage, used as a source of water for washing the crude terephthalic acid.

22. The method according to p. 20, characterized in that the specified water mother liquor obtained in the second stage, used as a source of water for dissolving the crude terephthalic acid.

23. The method according to p. 21 or 22, characterized in that the aqueous mother liquor is used as such, in the washing of the crude terephthalic acid.

24. The method according to p. 21 or 22, characterized in that the aqueous mother liquor is filtered before use in the washing of the crude terephthalic acid.

25. The method according to p. 20, characterized in that the temperature and/or water content of the oxidation reaction is controlled by removing a mixture of acetic acid and water from the reaction medium at the stage of oxidation, evaporation, and water is separated from at least part of the above-mentioned mixture in the distillation column, leaving acetic acid with a lower water content, which recycle to the reaction medium at the stage of oxidation.

26. The method according to p. 25, wherein the specified aqueous mother liquor obtained the settlement of Agency acetic acid and water, when this extract water from it, which is used for washing and/or dissolving crude terephthalic acid.

27. The method according to any of paragraphs.20 to 26, characterized in that the washing of the crude terephthalic acid is carried out by moving the filter cakes through the zone of leaching, while passing the washing liquid through the filter cake many times in a counter so that the filter cake is in contact with the water increasing purity, when it moves through a specified area of flushing.

28. The method of obtaining terephthalic acid, comprising the oxidation of p-xylene in a reaction medium containing acetic acid, to obtain a slurry of crystals of terephthalic acid in the reaction medium, separating crystals of terephthalic acid from the reaction medium, followed by recycling at least part of it, and mixed crystals of terephthalic acid with an aqueous medium, from which subsequently the secrete acid, characterized in that Department is that the suspension is placed on a movable strip of filter material is moved at a temperature of at least 60oThrough the first and second zones, with original piala reaction medium and receiving the first wet sediment crystals of terephthalic acid, which is subjected to washing by passing through successive water wash steps at the intersection of the second zone and will filter through the belt of filter material separating crystals of terephthalic acid wash water from the reaction medium remaining in the first wet sediment, these wash steps, except the last exercise using water obtained at the subsequent stage, and the process is carried out at a higher pressure from the moving tape, which serves a suspension, compared to its opposite side, and the differential pressure is 0.1 - 15.0 bar.

29. The method according to p. 28, characterized in that the tape is continuous.

30. The method according to PP.28 and 29, characterized in that the strip of filter material is a having a horizontal stroke of a continuous strip, which moves through these areas.

31. The method according to any of paragraphs.28 to 30, characterized in that the filter material includes a plastic material.

 

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