DE3041293A1 - Terephthalic acid prepn. from di:methyl terephthalate - comprises crude di:methyl terephthalate or para-methyl toluate addn. as auxiliary to hydrolysate mother liquor - Google Patents

Abstract

Parent patent disclosed prepn. of terephthalic acid, (I), from dimethyl terephthalate, (II), as intermediate, by first oxidn. of p-xylene and p-Me toluate, (III), (1:1-1:3 ratio) with O2-contg. gases in presence of heavy metal-contg. catalysts at 140-170 deg.C and 4-8 bar. The oxidn. mixt. is then esterified with MeOH at 230-280 deg.C and 20-30 bar. The crude ester is sepd. by distn. into a (III)-rich fraction, which is recycled to oxidn., and a residue and into crude-(II). Crude-(II) is hydrolysed with water at (II) to water ratio 3:1 and 0.1:1, at 350 to 140 deg.C, under pressure to maintain liq. phase. (I) is crystallised at 300-150 deg.C, the mother liquor is replaced by desalinated water and (I) is recovered from the reaction. Crude-(II) has a limited oxidn. intermediate- and other by-prod. content. Hydrolysis takes place in 2 steps. After the 1st hydrolysis step reaction mixt. is expanded and sepd. into conc. suspension of solid (I) and mother liquor and into residual mother liquor- contg. liq. phase. The mother liquor is then continuously diluted and replaced, under hydrolysis conditions, with desalinated water passed countercurrently to the crystallising (I). (e) The combined mother liquors are cooled so that only dissolved (I) and by-prods. are pptd. and sepd. The liq. phase is sepd. by distn. into an MeOH-water mixt., sepg. overhead, and aq. phase as sump prod. Part of the aq. phase is discharged. The residue is combined with the sepd. solids, reheated and returned to 1st hydrolysis step. Improvement comprises adding crude-(II), or (III), as auxiliary for sepg. useful prods., mono-Me terephthalate, (IV) in addn. to (I) and (II) as solids, by cooling, from the combined mother liquors. The useful prods. are then sepd. with the auxiliary as organic phase. Auxiliary addn. improves useful prod. (IV), (I) and (II) sepn. and the filterability of (IV).

Description

! 3ΪΗ1293

Troisdorf, the pi. October 19SO OZ: 80080 (5091)

STOCK J

Troisdorf, 3rd dec. Cologne

DYEAMIT N02EL AKTIENGESELLSCHAFT J

Improved Process for the Production of Terephthalic Acid from Dimethyl Terephthalate as an Intermediate j (addition to patent ... patent application P 29 16 197 * 5) I 10

I The invention relates to a method of the type indicated in the preamble of claim 1.

1 Subject of the previously known main passport registration? 29 16 J I 197 · 5 is the continuous hydrolysis of Hoh-Dinethyl-! I 15 terephthalate under elevated pressure and elevated temperature, i where in an Eeaktionsstufe at temperatures of about j j 250 to 260 ⁰ C a conversion to terephthalic acid (TPS) of about jj 2/3 takes place, the TPS formed crystallized and from j I dem Process is discharged. The remaining mother liquor j 20 is cooled to such an extent that still dissolved TPS and by-products precipitate separately or together, are separated off as pesticides and are further worked up. j

The hydrolysis of dimethyl terephthalate (DMT) leads to an equilibrium re-

COPV BAD ORIGINAL

. : ■ ·: · ^: 3 ο a 12 9 3

action does not result in a quantitative turnover. Therefore, the most complete possible recycling does not have to be implemented Methyl esters of TPS, namely DMT and monomethyl terephthalate (MMT), are guaranteed by special measures

After the TPS has been separated off and discharged when the mother liquor is cooled further, the solid remains about 65% by weight of MMT, about 25% by weight of DMT, and about 10 wt .-% from TPS and is returned to the hydrolysis, while the remaining residual solution is further worked up J will. j

When separating the useful products from the mother liquor J

the TPS crystallization by lowering the temperature to 50 -

j 15 170 C, at which the isomers of TPS, namely ortho- and Iso-phthalic acid and other by-products are still in solution remain, the crystals of MMT, DMT and TPA fall as j voluminous precipitation that only

! difficult to separate, so that considerable-20 Lent amounts of mother liquor with a corresponding content of ί impurities are retained by this precipitate and severely impair its reusability.

The filtration properties of a precipitate obtained in this way are such that after a short duration of filtration [j (approx. 5 min) and with a filter cake thickness of approx. 8 mm, the filtration comes to a complete standstill. \ The filtration properties of a precipitate, which consists only of MMT in the j essentially, are due to the small plate-j-shaped Eristallform of MMT so that already at a j filter cake thickness of 1 - 2 mm hardly filter throughput is observed.

The separation of such a product from the Mut-cerlauge on an industrial scale is difficult under

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would take particular hatred to accomplish.

The invention is based on the problem of the separability of the useful products MMT, DMT and TPS from the mother liquor the TPS crystallization by the addition of auxiliaries to facilitate significantly and thus their ßtrackbarkeit to improve in the process.

It has now been found that after larger amounts of DMT have been added to the mother liquor of the TPS crystallization and the solubility limit is exceeded, the DMT is present in the form of an emulsion ^{at temperatures of 125 180 ° C.} After addition of PTE to the mother liquor of the TPS crystallization at temperatures of 30-170 ⁰ C IN_ analogous phenomenon is observed. During cooling, the precipitating MMT and TPS crystals are preferentially dissolved or enveloped by the emulsion droplets consisting of DMT and PTE. In the case of a conversion of DMT go when the temperature falls below "• 120-130 ⁰ C - 70 ⁰ C then fall only small amounts of solids, and the - these agglomerates in the solid state having excellent filtration property than Upon further cooling to 50th The resulting precipitation shows only a small amount of small goods.

The invention consists in making 2weeks better ? -5 Separability and return of unmeasured useful products MMT in addition to TPS and DMT as a solid from the combined Mother liquors according to features c) and d) of claim 1 by cooling as an auxiliary raw DMT adds and separates the useful products together with the auxiliary as an organic phase. So that is the task at hand solved in an advantageous manner.

In this way, multiple 10-weight is by the addition of crude DMT as excipient at 125 to 180 ^0C in the 0.3 to amount, relative to the amount of useful products, to the mother liquor of the TPS-crystallization, depending on the bulk "

: 30A1

of the emulsion droplets to achieve almost any desired grain size distribution of the MMT crystals. The filtration properties of the crystals produced according to the invention are excellent and are shown for a temperature of 20 ^° C. in curve 2 of the drawing. Here, the amount of piltrate that has passed through is plotted in relation to the filter area as a function of the filtration time. The mixture used in the measurement of curve 2 had a ratio of MMT crystals to DMT addition of one to one. The crystals by means of solid-I ^l-lüssig Trennope: ation recovered and recycled in the process.?.

Instead of DMT, PTE in 0.3 to 10 times the amount by weight, based on the amount of useful products at about 30 to 170 ° C., can also be added to the mother liquor of the TPS crystallization as an auxiliary. However, when the mother liquor is cooled to temperatures of up to about 20 ^° C., the emulsion state is retained. The precipitated MMT crystals are released from the PTE phase and can now be separated from the remaining mother liquor by means of a liquid-plus-liquid separation operation. After the PTE has been separated from the MMT crystallizate, it can be returned to the hydrolysis.

25 -... ■ -

A preferred embodiment of the method according to the invention is described below:

After running through the hydrolysis is at about 250 ⁰ C to. 260 ⁰ G, the cooled Eeaktionsmischung to 170 ⁰ C to 200 ⁰ C, the major part of the TPS formed precipitates. After the discharge of the precipitated TPS the remaining mother liquor Eoh-DMT is added at ⁰ C I50. Based on the amount of organic substances still dissolved in the aqueous mother liquor, an organic substances: DMT ratio of about 1: 0.5 to 1 ^: 1 is set.

. f.

The mother liquor is cooled to temperatures of about 60 "to 120 ⁰ C, the precipitated MMT crystals

• can now easily be carried out by a plague-liquid separation operation V / water methanol and still dissolved isomers of the TPS are freed and the phase containing solids is subjected to hydrolysis to be led back.

The advantage of the procedure described lies in the improved filtration properties of the MMT crystals produced. This makes it possible to use very simple solid-liquid separation operations.

In the following 2 examples, the inventive Procedure explained. The stated flow rates mean parts by weight per hour, the compositions are expressed in percent by weight.

= 304129

example 1

15 parts by weight of crude DMT with a DMT content of 96.4 % DMT are mixed with 117.9 parts of a recycle stream consisting of 84.6% water, 7.3 % DMT, 5.8 % MMT and the remainder to 100 % of Weiloren by-products are combined and subjected to a continuous, two-stage hydrolysis at 250.degree.

The reaction mixture is brought to a temperature of 200 ^° C. and has a total amount of 132.9 parts with the following composition:

Water 71.9%, methanol 5.5%, TPS 16.1%, the an. Part of the dissolved TPS is 1.9% and the proportion of solid TPS is 14.2%, IMT 5.2%, and a remainder to 100 % of by-products. The solid TPS is separated off in the second hydrolysis stage and the remaining mother liquor is fed to a mixer. Here, the resulting filtrate with 132.9 parts ⁰ C is cooled whereupon the entire reaction mixture in a crystallizer to a temperature of 70 'to be 7.5 parts by weight of the crude DMT of the above composition at 150 C blended. The solid containing 44.6% DMT, 35.7 % MMT, 13.6 % TPS, 5.7 % water, the remainder by-products, is separated from the suspension formed on cooling and returned to the hydrolysis in a total amount of 19.2 parts .

Example 2

The according to example 1 withdrawn from the two hydrolysis steps FiItrat with an amount of 132.9 parts is cooled to a temperature of 70 ⁰ C and the suspension formed during cooling are "7.5 parts by weight of PTE added.

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1 The two resulting liquid phases are allowed to settle and split into an organic and an aqueous phase separated.

5 The separated organic phase with a composition of 41.5% PTE, 14.5 % TPS, 5.9 % DMT, 38.0 % MMT, the remainder by-products, is fed to a distillation in a total amount of 18.0 parts. Here PTE is separated off overhead, the remainder is returned to hydrolysis 10. '

35 Dr Li/Ra

Number:
Int. Cl. ³ :
Registration date:
Disclosure date:

T = 20 ° C

3041293 C 07 C 63/26

November 3, 1980 June 16, 1982

(l / m ² ) 3000H

2000 -

1000 -

500 -

1 MMT crystals: H ₂ O = 1: 8

2 MMT ~ crystals with DMT addition: HpO = 1: 8

10 12 (min)

Filtration time

Piltration properties of MMT crystals

Dynamit Möbel Aktiengesellschaft / Roisdorf

Claims (1)

T claims 1., Improved process for the production of terephthalic acid (TPS) from dimethyl terephthalate (DMT) as an intermediate product by oxidation of p-xylene and p-toluic acid methyl ester (PTE) in a ratio of 1: 1 to 1: 3 with oxygen-containing gases in the presence of heavy metal-containing oxidation catalysts at a temperature of 140 to 170 ⁰ C and a pressure of 4 to 8 bar, esterification of the oxidation mixture with methanol at a temperature of 230 to 280 ⁰ C and a pressure of 20 to 30 bar and distillative separation of the crude ester in a PTE-rich "ROUP, which is recycled into the Oxidatior and a residual fraction and in - a crude DMT by continuous hydrolysis of crude DMT with water at a mass ratio of the crude DMT to water is between 3 '1 and 0.1 : 1 and at temperatures between 35O ⁰ C and 140 ⁰ C and the pressure required to maintain the liquid phase, crystallization of the TPS at temperatures between 300 ⁰ C and 150 ⁰ C, Replacement of the mother liquor by. Demineralized water and recovery of the TPS from the reaction mixture and a) Use of a crude DMT with a limited content of oxidation intermediates and other by-products, b) two-stage hydrolysis, c) Relaxation of the reaction mixture after the first hydrolysis stage and separation in a manner known per se Way into a thickened suspension of solid TPS and mother liquor, as well as the remaining mother liquor containing liquid phase, d) ongoing dilution and quantitative replacement in the second hydrolysis stage of the mother liquor in the Suspension under hydrolysis conditions through desalted material passed in countercurrent to the crystallized TPS Water, e) Cooling the combined mother liquors according to features c) and d) to the extent that TPS and by-products are still dissolved precipitate separately or together, separating them off as solids and separating them by distillation the liquid phase in a methanol-water mixture, which is at the top, as well as a bottom product resulting aqueous phase, part of which is discharged and the remaining part with the separated th solids combined and after reheating is returned to the first hydrolysis stage according to the main patent ... Patent application P 29 16 197 * 5 » characterized in that for the purpose of improved separability of the remaining useful products Monomethy! terephthalate (MMT) in addition to TPS and DMT as solids by cooling from the combined mother liquors. measured the features c) and d) as an auxiliary raw DMT adds and separates the Futzprodukte gene alone with the auxiliary as an organic phase. 2. The method according to claim 1, characterized in that PTE is added as an auxiliary. 3. The method according to claim 1, characterized in that the auxiliary raw DMT is added at about 125 to 180 ⁰ C in 0.3 "to 10 times the weight of the amount of useful products. 4. The method according to claim 3, characterized in that the phase nutzprodukthaltige organic phase is separated off as a liquid at about I35 · to 170 ⁰ C. 5. The method according to claim 1, characterized in that separating the nutzprodukthaltige organic phase as a precipitate at about 60 to 135 ⁰ C by means of a solid-liquid separation operation, ·. _ 3 - 16. The method according to claim 2, characterized in that PTE at about 30 to 17O ⁰ C, preferably 50 to 100 ⁰ C in the 0, $ - to 10 times the amount by weight, based on the amount of useful products, and the nutzprodukthaltige organic phase is separated at about 30 preferably 30 to 170 ⁰ C, to 100 ⁰ C, as ITüssigphase by means of a liquid-liquid separation operation. Dr Li/Ea