SA00210612B1 - Method for the extraction of purified terephthalic acid (PTA) - Google Patents

Abstract

Abstract: This invention relates to a method for preparing purified terephthalic acid, the method comprising first introducing a liquid paste containing crystalline terephthalic acid with impurities into a high-pressure rotary filter, then filtering the slurry with the high-pressure rotary filter and collecting at least some of the solid fraction. Preferably the filter consists of a case, compressed at method pressure, and a cylinder covered with a filtering device, such as, for example, a filter cloth or equivalent, compressed at a pressure suitably lower than the housing. Typically the cylinder is divided into three zones: a first zone, where the mother liquor is removed; a second zone, where the solid is washed off; A third area, where the excess is removed from the washing satellite and the solid matter is discharged. The solid part, on the filter drum, is washed with additional amounts of water. The washed solid part is then conveyed to a lower region, which is at a lower pressure than the region in which the solid part is collected. After the steel part is moved to the lower area, the connection between the lower area and the assembly area is loosened, so that a change in pressure in the lower area will not affect the pressure in the assembly area. Then the lower region pressure gradually decreases and the solid matter increases. The bottom area is then again compressed so that it is equipped to accept additional solids from the rotary filter.

Description

A method for the extraction of terephthalic acid (PTA) ile Full Description Background of the invention:- This invention relates to a new method for the production and extraction of purified and more specific terephthalic acid (PTA); This application relates to the use of a rotary pressure filter used for the extraction of crystalline terephthalic acid as well as a method for the extraction of the resulting 0 crystals at atmospheric pressure. The process involves moving the crystalline material through at least two valves marked for separate regions; In which each successive region is at a slightly lower pressure than the region that precedes it. Terephthalic acid is used in the production of many different polymers. Containing polyethylene terephthalate (PET) The typical method used to produce PET consists in direct condensation of terephthalic acid with a polyalcohol. This direct esterification reaction requires purified terephthalic acid; for the product of the reaction to be acceptable. LBL LE acid is produced by direct oxidation of beta = xylene and then successive crystallization from the mother liquor to extract crude terephthalic acid (CTA) and this acid CTA still contains approximately 1.7 to 700.4 By weight of 4;-Yo-carboxybenzaldehyde (4-CBA) as an impurity in significant amount. To reduce the 4-CBA content CTA is preferably dissolved in water and then the resulting solution is treated in a hydrogenation reactor; This is to convert 4-CBA into beta-toluic acid. The solution from the hydrogenation reactor is then cooled preferably by flashing in a crystallizer battery to precipitate purified terephthalic acid (PTA) in crystal form. We find that the paste released from the crystallizer still contains, Yo, a large amount of beta-toluic acid, which must be separated from the PTA in order to comply with the commercial description, which is no more than 1051 parts per million. It should be noted that to purify PTA two successive steps of solid separation are followed. We find that the traditional method for separating PTA from its mother fluid is through AVY centrifugation

It should be noted that to purify PTA, two successive steps of solid separation are followed. We find that the traditional method for separating PTA from its mother liquid is through centrifugation of the paste at a temperature of 100 C to 700 C and at a pressure of 1 to 1 bar. Under these conditions, most of the beta-toluic acid will remain in solution; Forgiving that © by dismissing him. We find that the PTA crystals from the centrifuges contain only a small amount of beta-toluic acid; But it also contains a residual mother liquor (about 0m (%)) and to get rid of these impurities, the crystals are usually mixed with additional water; it is in a ratio of approximately 1.1 to Ta V,0 water/PTA clay and that to wash off the mother liquor in which the Vo is still present. This results in a paste with 0 965 lbs solids. This pulp is then flash-treated and shipped to either a second stage centrifugation or to rotary vacuum filters (RVE) The PTA containing a residual water of up to = 9619 is then dried, preferably in a cyclic desiccator, and stored.The PTA crystals still contain trace amounts of beta-toluic acid (typically less than 1510 p.m.). per million) 0 while the content of 4-CBA is less than YO ppm SAL It is noteworthy that these traditional methods require large capital costs due to the need for a centrifuge with pressure Measuring Je as well either High-gauge RVE or a second high-gauge centrifugation. This in turn leads to large maintenance costs with unreliability. Moreover, we find that centrifugation causes significant crystal breakage so Ye the molecular size distribution increases in a manner Alls especially sl aa particles are less than 6 µm. This method also requires more water to be heated to operating temperature. Finally, the process results in a product with a relatively large amount of moisture which needs to be removed through the Law dryer in a high energy combustion. US Patent No. 00757308 investigates a method for purifying terephthalic acid Yo comprising pressure filtration. This likely considers the introduction of a water-based paste (including AVY

It contains purified terephthalic acid in crystal form and beta-toluic acid in aqueous solution and in concomitant crystal form) to one or more filter cells. The paste is filtered under a system pressure of 1 atm to 11 atm. Then a filter cell with the resulting filter cake is transferred to a washing area where a stream of water heated to 5010 m is introduced into the filter cell to form a water reservoir above the filter cake. Displacement washing is then achieved by forcing water through the cake at pressure; Which is at least 1.5 atm more pressure than the system pressure while the water reservoir is maintained. The displacement washing is allowed to continue for a sufficient period for the purpose of removing a desired amount of impurities. The filter cell is then conveyed to a pressure-applied zone in which 0 and rapidly system pressure is applied for flash evaporation of the water still in the cake and the product is extracted. The pressure-applied zone is then recompressed back to the system pressure, ready to accept additional output. This process frequently produces terephthalic acid containing less than 00,000 parts per million by weight of beta-toluic acid. Whereas, this method is based on the production of a pure product; It is considered the Vo method time consuming because the pressure applied zone needs to be repeatedly recompressed to the system pressure before it can accept more displacement washed material. General description of the invention: - The applicants for this invention discovered that the method can be improved by transferring the washed filter cake to a low area (or a pressure area) which is at a pressure Ys less than the pressure of the washing area. In this way the time required to compress the low zone is preferably reduced. The students discovered for this invention that the pressure of the lower region preferentially approaches the desired pressure. That is, most of the pressure variation between the exertion zone and the system pressure occurs in the early stages of recompression; While the last stage takes a relatively longer period of time. so; It is by allowing the low region Yo to return to a pressure lower than that of the system; More time can be entered. And we find that AYY

Coe shorter cycle time allows front end production to run more quickly or alternatively allows smaller rotary pressure filters to be used without bottlenecking or moreover; It has been discovered that the existence of a pressure contrast between the low region where it is carried for a distance by the flow (mal) and the washing region effectively facilitates the movement of the gaseous ©; Which occurs when the barrier between the two regions is removed. It has been observed that this helps to keep the filter itself free of build-up. For peal In addition, the applicants of the present invention have discovered that the best mechanical performance of the system is to avoid primarily blockage of the vent line; To exert pressure more slowly than the flash evaporation studied by US Patent No. containing crystalline terephthalic acid, which is drawn into a high-pressure rotary filter by impurities; Then the paste is filtered by a high-pressure rotary filter 1 and at least some of the solid part is collected. Then the solid part is washed with additional amounts of water. Then the washed solid part is moved to a lower area; Which is at less pressure than the region in which the solid part was assembled. After moving the solid part to the low area; The connection between the depression area and the collection area is broken; thus, a change in pressure in the depression area will not affect the pressure in the YL area, and then it is reduced to the depression area and the solid is removed. Then the pressure 0 is re-assembled in the low area, and thus it is ready to accept an additional amount of solid material resulting from the rotating filter. We find that the liquid paste containing terephthalic acid containing impurities may come from any method of production of terephthalic acid . These are known in the industry and are few Yo

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+ Importance to be covered by the invention. The special pressure-pressure rotary filter used for filtration of the paste is also not necessary of the present invention. Any filtration system capable of operating at pressures greater than atmospheric pressure may be used. Preferably for instances of dull operation the filter becomes capable of treating the total terephthalic acid © flow of the plant; It has the ability to operate under a pressure of 1 to 10 bar. A suitable filter was the Bird Young rotary filter sold by Baker Process Inc. The filter used in the apparatus of the present invention was a Bird Young rotary filter, which had a filter area of 1 square foot and was capable of operating from 1 to © MT watch in solid PTA. Ve Preferably the filter consists of a jacket; compressed at process pressure; A cylinder covered with a filter, eg a cloth or REIS filter pressed at an appropriately lower pressure than the casing. Ad shu is typically divided into three regions: a first region; where the mother fluid remains. Vo (Als) region where the solid is washed off. (AG) region where the excess of the washing liquid is removed and the solid is discharged. The casing pressure is preferably in the range from * to 6.5 bar with about 4.5 bar being preferred The filtration is carried out at a temperature of 70 C to VY with EY, then it is the most preferred, and the pressure difference between the casing and the cylinder is in the range from 1.1 to ?bar and it is preferable to be in the range from 1.79 to 1.7 bar, the best is 5 bar.The mother liquor removed from the rotary pressure filter can be separately extracted and reused during the production process or sent to waste treatment devices, as is known in the industry. Etc.

Do not wash the remaining solid part with additional amounts of water. It has been discovered that it requires very little rinsing water in the current process to achieve a purity comparable to conventional methods. Thus, when using any amount of water in the washing stage subject of the present invention; it is preferably less than 1 mm' per ton of PTA used; This is to conserve water© and reduce the energy associated with heating this water to the temperature of the method. It is preferable that the amount of water be in the range from 17 to MT [Ta 0.7 of PTA, and the most preferred is about 0.* m” / MT of PTA, and it is preferable to perform washing at the same temperature as it is during filtration; Although this is for convenience, not necessarily. The temperature of the water used to wash the solid is in the range from 00"C to 110"C; the best is in the range from 10C to von Ys and most preferably 057C. The washing liquid can then be collected preferably from the mother liquor and reused through the production method or recycled back into the production method, as is known in the industry.After (Jail) the solid is preferably collected in a collection area and then passed to a lower area; which is at a pressure of less than the collection region.In order to maintain the pressure V difference, it is preferable to separate the collection region from the lower region by means of a tool of any kind, which can promptly open and close to isolate the low region from the collection region.Therefore, during operation when collecting a quantity of solid In the collection region the device will be opened and we find that the combination of gravity with the pressure difference will cause some (preferably all) of the solid to be moved to the depression. Domes) such as those manufactured by Macawber Engineering Inc. have demonstrated their effectiveness. When the device is opened the lower area is at a pressure which is somehow lower than the pressure of the assembly area. Preferably, this pressure difference is in the range of 1.00 to 1.7 bar, and the best is in the range from 1.0 to 11 bar, and the most preferred is AVY.

After the solids have been removed to the low zone, the device is closed and the low zone is isolated from the collection zone and/or the rotary pressure filter. At that time apply pressure. While flash evaporation can be used with the invention; It prefers to apply pressure more slowly.

° at a low pressure is applied over a period of time from 0.9 to 10 seconds; and better than; to 7 seconds; Although time will factor in to the individual mechanism and to how fast the reaction proceeds. We find that the slow application of pressure can be achieved in many ways. There is only way ud exists in the presence of a narrow choke in the ventilation line; which can be set. This may be used alone or in combination with a coun valve which maintains actual pressure

0 in the line (as well as the low area). Other methods such as bleeder valves are well known in the industry and can be used within the present invention. A second vent line without any chokes can also be used as a double stopcock to ensure that the low area remains pressurized.

Once the pressure in the low zone has been depressurised, a second isolating device is opened

Vo and the solid contents are removed as in the transition from the collection region to the depression region; It is preferable to communicate this transition with a small pressure difference so that when the Jad device is opened, the contents are carried by gravity and the flow of gases inside the region of lower pressure. to 10 bar and most preferably 1.05 bar. Again, any device that has the capacity can be used

Yo isolates the low area; However, locking valves are preferred. Then the solid can be passed to a desiccator by a suitable means; for example, an IUD; This is to pass through the processing as it is known in the industry. and when the contents were removed from the lowered area; The low zone is again isolated by stop valves (or other means) and the low zone Yo is pressurized back to a suitable pressure to accept more wash. preferably; AVY

_q- the time it takes to apply pressure in the depression; trigger output; recompressing the low area to match the time it takes to fill the collection area; Thus, once the low area is evacuated; sequestered and re-compressed water filled collection area; Thus, there is no decrease in time during the cycle. As mentioned before; it without the need for the area to be the rotary pressure filter housing); The lower ff) at the same pressure of the collecting region © can compress the reduced region to acceptable limits more quickly; Thus the method can be started again possibly temporarily. For relay operation (PLC) preferably; A programmed logic controller is used to enable the opening and closing of various isolation devices. ventilators; (lis described) and pressure lines to an optimum. 95 dad Casing and cylinder to 1 The description of the operating values is subtracted in the Yo table The description of the quality results is accomplished in the table 1 Table of operating conditions Pressure filter Two stages of centrifugal bar 8 bar gy cold pressure 0 bar 5 A shan) The pressure difference between the cover/ . TPTA kg/0-0 wash water

TPTA (kg/0 ~ paste sale) water - 1-10 seconds (1) decompression time neem (0). Pressure difference between zones

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Y table Output quality Pressure filter Two stage centrifuge ppm 1-15 Other by-products 0-12 ppm ppm 0110-0 ppm 0-0 Beta-toluic acid 9616-0 9611-4 Humidity Decompression time of the lower chamber. (1) The pressure difference between the collection chamber and the lower chamber and between the lower chamber and the line (7) The final discharge at atmospheric pressure.

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Claims (1)

_1 \ —_ protection_elements 1-1 A method for preparing purified terephthalic acid, where the method includes: Y A- Entering a liquid paste containing terephthalic acid with impurities into a rotating filter Je -' pressure; ; mali im the said dough and the assembly of at least some of the solid part; © c- Washing the solid part with additional amounts of water and collecting the washed solid part in 34 Cia assembly area pressure from 1 to yo bar 1" d- Passing the washed solid part from the assembly area to a lower area where the area is lower A at a pressure of at least 1.09 bar below the assembly area; 4 e- Isolate an existing connection between the lower area and the assembly area; Thus, any change in pressure 0 in the bottom region will not affect the pressure in the collection region; 11 f- Reducing the pressure of the lower region. NY g- Remove the washed solid part from the lower region; and 0" h - increase the pressure of the lower zone to 101 to 7 bar below the pressure of the 04 collecting zone so that the zone may accept additional solids washed from the high pressure rotary filter 0 |. 01 method according to item 1; In which the pressure is applied in step and for a period of time exceeding 7-1 7 seconds. AVY is set to 0 method according to item 1; In it, the washing temperature is from -1 ¥ +- method according to item 1 in which the solid part is washed at a rate less than Val) of 7 water per ton of solid matter. ‎AVY 117 - - co 1 method Wy for element 1 in which the pressure in the lower region is not lowered to atmospheric pressure "thus there is a difference in pressure to help remove the product. AVY