DD155142A5 - OBTAINING AND REUSE OF HEAVY METAL OXIDATION CATALYST FROM THE WITTEN-DMT PROCESS - Google Patents

Abstract

In a process for the recovery of heavy metal compounds in the form of particularly cobalt and manganese acetate-containing solutions from acetic acid, aqueous extracts of high-boiling distillation residues or mineral acid extracts of the combustion products of these residues from the Witten-DMT process, these extracts are extracted with strongly acidic ion exchangers in Na +. Form treated and the heavy metal-containing solutions obtained by elution with sodium acetate solutions. The Regeneratloesungen obtained are free of trimellitic acid and Trimellithsaeuremomomethylester or of mineral acids. They are directly attributed to the oxidation of mixtures of p-xylene and p-Toluylsururethylester with atmospheric oxygen in the liquid phase as catalyst solutions.

Description

-1- 225898

09/04/1981

AP BOU / 225 898

58 304 11

Recovery and Reuse of Heavy Metal Oxidation Catalyst from the Witten-DMT Process' .

• Field of application of the invention

The invention relates to a process for the recovery and reuse of heavy metal oxidation catalyst from the Witten-DMT process starting from high-boiling distillation residues having a cobalt content of 1 to 10 g / kg and optionally a manganese content of 0.1 to 5 g / kg of residue and / or or a nickel content of 0.1 to 5 g / kg of residue, the in the oxidation of mixtures containing p-xylene (PX) and / or p-toluate (PTE) in liquid phase with oxygen-containing gases at a pressure of 4 to 8 bar and a temperature of 140 to 170 ⁰ C in the presence of dissolved Schwermetalloxidationskatalysator, subsequent esterification of the oxidation product with methanol at a pressure of 20 to 30 bar and a temperature of 230 to 280 ⁰ C and distillative separation of the esterification product in a p-Toluylsäuremethylester- ( PTE) -rich fraction, a di-

-2-, 225898

methylterephthalate (DMT) -rich fraction urd a high-boiling distillation residue incurred by extraction of the heavy metal oxidation with V / asser, dilute mineral acids, aqueous low molecular weight aliphatic monocarboxylic acids or alcohols in the heat, optionally after combustion of the high-boiling distillation residues.

DMT is required as a raw material for the production of polyester by reaction with ethylene glycol or tetramethylene glycol for fibers, filaments, films or moldings. It is produced in numerous large-scale plants according to the process known as the Witten or Witten-Hercules process.

Technically, the mixture is worked in such a way that the PX- and PTE-containing mixture in the absence of solvents and halogen compounds in the presence of cobalt and manganese compounds dissolved in the reaction mixture results in a predominantly of p-toluic acid (PTS), monomethyl terephthalate (MMT) and terephthalic acid (TPS ) existing oxidate and, the oxidate at 230 bis'280 ⁰ C and 20 to 30 bar esterified with methanol. The heavy metal oxidation catalyst system is preferably used in amounts based on the amount of oxidate and on metal content of about 70-200 ppm cobalt and 7-100 ppm manganese. The esterification product is separated by distillation in a so-called crude ester distillation into a PTE-rich fraction, a DMT-rich fraction and into a high-boiling distillation residue. The RFE-rich fraction is fed to the oxidation, the DMT-rich fraction to a subsequent purification and work-up. The high-boiling residue contains, in addition to the organic components, the compounds of Schwermetalloxidationskatalysatorsystems, Z..B. Cobalt and manganese.

- 3 - '2 2 5 8 9 8

09/04/1981

AP BOU / 225898

58 304 11

Characteristic of the known technical solutions

It is technically possible, high-boiling distillation residues of the oxidation of alkylaromatics from which no more useful products, whether it can be obtained by isolation or by conversion, the combustion, if necessary, using the heat of combustion supply, and located in the flue gases of combustion heavy metal-containing To separate ashes via cyclones or electrostatic precipitators (see US-PS 3 341 470).

The heavy metal content of ashes of the type mentioned is composed of the catalyst constituents still present in the high-boiling distillation residues, insofar as they have not previously been present, eg. B. have been removed by extraction, also from the materials of the manufacturing plant by corrosion and the components of the added fuels of residue combustion, ζ. Β. Masut or heavy fuel oil. ·. ...

Ashes of the type mentioned can be treated with mineral acids and the heavy metals are precipitated as carbonates or hydroxides from the solutions (cf. DS-OS 22 60 498). The separation of such precipitates by filtration or centrifugation and the removal of the adhering corresponding mineral acid by washing the Pilterkuchens prepares or technical difficulties. The complete removal of inorganic mineral acid residues is one of the prerequisites for the reuse of the heavy metals originating from the soy-boiling residues as Oxidationskatalysatpren in the oxidation of alkylaromatics in the liquid phase with atmospheric oxygen. In such ashes of the combustion of high-boiling distillation residues of the manufacturing process for alkyl aromatic by. Oxidation in the liquid phase in the presence of heavy metal oxidation catalysts enriches heavy metal

- 4 - 225898

09/04/1981

AP B01J / 225 898

58 304 11

components such as iron, chromium, vanadium, molybdenum, copper and titanium, which originate from the materials of the production plant and the fuels of the residue combustion and. which significantly reduce or inhibit the activity of the cobalt, manganese or nickel catalyst or their mixtures in the return to the oxidation reaction.

It is extremely advantageous for the DMT process to recover the oxidation catalyst, which is a mixture of cobalt and manganese compounds and / or nickel compounds from this high-boiling residue, if appropriate after combustion of the residue, and to reuse it for the oxidation of PX and PTE.

Patent Application P 29 23 681 proposes a process for the recovery of oxidation catalyst from the catalyst-containing distillation residue obtained in the DMT production and reuse of the recovered catalyst in the oxidation with the aim of the oxidation selectivity at the same high level as in Use of Prischkatalysator to keep. There it was shown that in the extraction of the catalyst-containing distillation residue of Rohesterdestillation trimellitic acid (TMS) and Trimellithsäuremomomethylester (TMME) are dissolved out with the catalyst and that TMS and TMME can significantly affect the course of the oxidation reaction when recycled with the catalyst in the oxidation · Therefore in the aforementioned method in the extract, the quantitative ratio of TMS · * · TMME to Schwetalalloxidationskatalysator measured to a value of at most 1.8 5 1. -

• "5 _ 225898

9-4.1981

AP BO1J / 225 898

58 304 11

Object of the invention _:.

The object of the invention is to provide an improved process for the recovery and reuse of heavy metal oxidation catalyst from the acidic extracts from the Witten-DMT process to obtain a catalyst regenerate containing interfering organic constituents, in particular TMS and TMME, further from tallverbindungen from the materials of the production plant is largely free by corrosion.

- 225898

9.o4.1981

AP B01J / 225 898

58 304 11

Explanation of the essence of the invention

The invention has for its object to recover from the distillation residues of Rohesterdestillation the catalyst components and from the extract for the simplest possible workup without evaporation or by the presence of TMS and TMME required additional measures directly for use in the oxidation or otherwise use of the to provide valuable catalyst components with suitable aqueous solutions «

This object is achieved with the invention. The solution is that in a method of the type specified

- * - 22 5 898

a) the aqueous, acidic, Schwermetalloxidationskatalysatorhaltige extract having a cobalt content of 0.2 to 20 g / l, optionally a manganese content of 0.05 "to 10 g / 1 and optionally a nickel content of 0.05" to 10 g / l is treated with a strongly acidic cation exchange resin in the alkali metal form, eg Na ⁺ or K ⁺ form "at elevated temperature until the exchange capacity is reached, and

b) the cation exchange resin is then washed at elevated temperature and regenerated at room temperature with Na ⁺ or K ⁺ acetate-containing solutions to displace the catalyst components and obtain an aqueous solution containing the catalyst components, acetic acid,

The heavy metal residues of combustion of high-boiling distillation residues are in mineral acids ,. e.g. Hydrochloric acid with the addition of oxidizing agents e.g. Hydrogen peroxide solution for the oxidation of u.a.

Dissolved Fe ions and enriched in the solution impurities derived from the materials of the plant and the fuels, such as iron, chromium, vanadium, molybdenum, copper and titanium by adjusting the solution to a pH of about 6 or above precipitated with, for example, aqueous sodium hydroxide solution as hydroxides and filtered off together with the insoluble Antei len of the ash. The solution thus purified is adjusted to a pH of 5 or less by addition of linear low molecular weight aliphatic monocarboxylic acids having 1-4 C atoms, for example acetic acid. The Na ⁺ ions contained in the solution are treated by treatment with a Co ²⁺ , Mn ²⁺ and / or Ni ⁺ ions loaded strong acid cation exchange resin removed. The acetic acid heavy metal solution is then mixed with a strongly acidic cation exchange resin in the Na -

- * - 22 5 898 i

or K ⁺ form is treated until the exchange capacity is reached and the cation exchange resin is then washed at elevated temperature and at room temperature with Na ⁺ or K acetate-containing solutions displacing the metal ions of the catalyst components and obtaining an aqueous acetic acid solution containing the metal ions of the catalyst components regenerated.

With the work-up according to the invention of the combustion products of the high-boiling distillation residues, it is possible in a simple manner to obtain a water-soluble organic catalyst solution which is free from mineral acid residues and the activity of the catalyst components. ;

The aqueous catalyst solutions obtained contain cobalt and manganese acetate with a content of et v / a 5 to 70 g / l cobalt, 1 to 35 g / l manganese and optionally nickel acetate with a content of about 1 to 35 g / l nickel. These aqueous solutions containing the catalyst components as acetates are advantageously returned directly to the oxidation of the methyl-p-xylene and / or p-toluic acid-containing mixtures.

In addition to the cations of the alkali metal group, preferably sodium or potassium, the ion exchanger for absorption of the catalyst metal constituents can also be used in the H ⁺ ion form

It is preferred to regenerate the exchanger loaded with catalyst metal ions with dilute aqueous sodium acetate solutions, in the strongly acidic ion exchangers used according to the invention the regeneration equilibrium R- (Co ⁺ ) + 2Na ⁺ ^ zzzR- (Na) p + Co '" compared to the regeneration equation

weight R- (Co ²⁺⁾ + 2 H ^{+ <>} R- (H ⁺⁾ ₂ + Co ^2+, wherein R

9 - 8 - 2 2 5898

9 * 4.1981

AP B01J / 225

58 304 11

the stationary ion exchange matrix means more in the direction of the right side of the reaction equation.

With the inventive treatment of the extracts obtained with strongly acidic cation exchangers, a concentration of the catalyst metal content in the extract to values up to about 20 times the Eingangskonaentration in a surprisingly simple manner possible without comparatively high levels of TMS and TBSME by complex formation, the replacement of the catalyst metal ions by the counterion, z. B · Disrupt sodium ion on the exchanger.

Concentration of the extract, by evaporation, which would lead to losses of catalyst metal by precipitation and precipitation at elevated TMS and TMME concentrations, can be omitted according to the invention.

Rather, a quantitative separation of TMS and TME and other accompanying organic substances is achieved in a simple manner. This result is of particular value given the perturbations that cause significant levels of TMS and TMME in the oxidation of PX and / or PTE-containing blends.

AO

- β »- 225898

·, 9.4 * 1981

AP BOU / 225 898 58 304 11

According to the invention, the content of TMS and TMME in the extract of the distillation residue by a multiple, z. B. be five times higher than the content of cobalt-manganese and thus almost three times the permitted in patent application P 29 23 681 ratio of TMS + TMME- to Schwetalalloxidationskatalysator »

The content of TMS and TMME in the extract depends on the type of crude ester workup and thus the chemical composition of the high-boiling distillation residue

 As the content of TMS and TMME in the extract increases, an increased consumption of heavy metal oxidation catalyst is required in order to ensure a perfect course of the oxidation reaction when the extracted catalyst is recycled.

Furthermore, the invention permits the recovery and reuse of cobalt or cobalt and manganese compounds together with nickel compounds.

The process of the invention is technically carried out in a preferred embodiment so that the acidic aqueous extracts are cooled from a temperature of about 95 ⁰ C to about room temperature and thereby precipitating organic components are separated. It reheats to about 70 ⁰ C to avoid Nachfällungen. During the subsequent loading of the strongly acidic cation exchanger in the Eia ⁺ form at about 70 ^° C., the amount of organic constituents present in the extract, in particular TMS _? TMME, TPS, MMT and the like, are not adsorbed on the exchanger, but remain in the aqueous phase and pass through the exchanger. ...

-. -Λ * - · 2 2 5 8 9 8

unhindered. In the event that this mainly loaded with alkali metal ions and organic compounds wastewater can not be fed to a biological workup, but must be thermally treated v / earth, the alkali metal ions can be exchanged by treatment with a strongly acidic cation exchanger, in the H-ion form and by elution with a strong acid, preferably hydrochloric acid, as a neutral salt, eg NaCl, in aqueous solution. Upon reaching the Austausehkapazität nit Co ²⁺ and Mn, the loaded exchanger ⁺ is treated with heated to about 7O ⁰ C also demineralized water as the washing liquid. This treatment serves to remove the organic components absorbed on the exchange resin, which

If the films were not removed at each cycle, they would precipitate on the exchange resin matrix and significantly reduce the exchange capacity. The resulting wash water is expediently returned to the extraction.

In the subsequent regeneration, which is carried out at room temperature, about two bed volumes of an aqueous sodium acetate solution, which was collected in the preceding regeneration cycle as a wake and combined with the run of the previous regeneration cycle, to the Co ⁺ and Mn " ⁺ be. Approximately 50 % of the bed volumeris is stripped off as a Co / Mn-free solution (50x) and then about 15 % of the bed volume is considered to be weak Co ²⁺ / Mn ²⁺ As the next fraction, about 135 % of the bed volume is taken as the Co ²⁺ / Mn ²⁺ acetate solution (hereafter referred to as the concentrate) for rust-free displacement of the catalyst metal components from the exchanger

ΛΙ

- 1 = © - 225898

April 9, 1981 AP BOU / 225 - 58 304 11

For example, about 80 % of the bed volume of an about 15% aqueous sodium acetate solution containing about 10 to 15 g / L of free acetic acid and subsequently about 80 % of the bed volume of fully desalted water to remove the sodium acetate solution containing Co and Mn ions The resulting solutions in a total amount of about 160 % of the bed volume are stripped to the significant drop in Co / Ton concentration in an amount of about 5 to 10% of the bed volume and combined with the concentrate and the following fractions in an amount of about 150 to 155% of the bed volume withdrawn as a wake, combined with the previously incurred forerun and returned for use in the following regeneration cycle.

Au sführungsbeispiel

The following examples serve to further illustrate the invention. \

The combustion residue used in Examples 3 and 4 was obtained by burning a high-boiling distillation residue from the Witten-DMT process at 800 - 1200 ⁰ C and deposition in an electric filter from the flue gases «'-

In this case, 95 wt .-% of such a residue was burned with the addition of 5 wt .-% heavy fuel oil. The high-boiling distillation residue fed to the combustion contained about 0.1 to 1.0% by weight of ash-forming heavy metal components.

225898

example 1

100 kg distillation residue from the crude ester distillation, in an industrial plant for DMT production by common continuous oxidation of PX and PTE-containing mixtures in liquid phase with atmospheric oxygen at 8 bar pressure and temperatures of I50 to 17O ⁰ C using a solution of Cobalt acetate and manganese acetate in aqueous acetic acid, v / obei in the oxidation product a stationary concentration of et v / a 90 ppm cobalt and 10 ppm manganese set.Wird, followed by continuous esterification of the oxidation product at temperatures of about 25O ° C and 25 bar pressure with methanol and continuous separation of the esterification product by vacuum distillation, v / obei in a first Destilla

In the second column a PTE-rich fraction is taken off, which is recycled to the oxidation, and the bottom product of this column in a second downstream column in a DMT-rich fraction removed from the top, and a high-boiling distillation residue with a Kobaltgehait of 2.3 g / kg and a manganese content of 0.2 g / kg residue was obtained, were calculated with 60 1 of water of reaction DMT production with an acid content of about 3%, calculated as acetic acid, at about 95 ° C extracted to a residual Co ^{+ +} content of 20 ppm.

After decantation, 56 l of a Co ⁺ / Un "'' -containing extract having a Co ⁺ content of 3 ₅ 8 g / l and an Mn ⁺ content of 0.3 g / l were obtained cooled to 2O ⁰ C and precipitated organic substances separated by filtration.

The filtered solution was heated to 7O ⁰ C to prevent Nachfällungen and from below by a Na ⁺ ion-loaded strong acid cation exchanger with the trade name.! "Lewatit S 100" filled pipe

22 58 93

passes. The resin volume was 1.1 liters. The loading was continued at the onset of exhaustion of the ion exchange capacity. , Of the prepared 56 1 Co-Mn extract 19 1, - accordingly ent a total content of 78.4 E Oo + Mn ⁺ or 2.66 VaI Co ⁺ , passed at 70 ⁰ C over the cation exchanger. Subsequently, the cation exchanger with demineralized water 1 was washed from above at 7O ⁰ C. Thereupon the elution of the cation exchanger was followed from above with 2.2 l of a 10% strength aqueous acetic acid sodium acetate solution, corresponding to 1.3 VaI Na / l, and subsequent washing with 1 l of fully desalted water at room temperature. There were 0.4 1 feed, 2.0 1 concentrate and 0.8 1 caster obtained. · ^:

, , , '""' "". The aqueous concentrate contained the following components:

30.1 g / l Mn ²⁺ 2.6 g / l Na ⁺ 1.0 g / l CH ^ COOH 12.0 g / l organic . Impurities. Not fe

(Polarographic) The resulting Co ⁺⁺ , Mn ^++, and Na ⁺ -containing lead were pooled and used again as the elution solution to add Co ⁺ " ¹ " and Mn ⁺⁺ loss avoid.

Example 2

In a continuous extraction plant, 300 kg / h of the high boiling distillation residue of the crude ester distillation obtained as in Example 1 was recovered at about 95 ° C with 150 kg / h of acidic DMT production water whose origin and acid content according to Example 1, extracted with stirring.

22 5 8 98

The aqueous solution obtained after separation from the organic phase contained 4-6 g / l Co " ⁺ and 0.4 g / l Nn * V. This was cooled to about 20 ^° C. and filtered by filtration from the precipitated organic products which were dissolved in the process were fed back, separated and collected in a container. After heating to about 7O ⁰ C, to prevent subsequent precipitation of organic substances were 650 1 / hr. of this solution at a temperature of 7O ⁰ C over a column packed with 180 l of a Na ⁺ ion-loaded resin was traded under the trade name "Lewatit S 100." The loading of the exchanger was complete in about 3 hours.

Thereafter, with the removal of organic compounds, 400 l of hot, fully deionized water were rinsed. Subsequently, the catalyst ions were eluted with a sodium acetate-containing solution containing 10-15 g / l of free acetic acid, consisting in part of the pre- and post-runs of the previous elution and a 15% sodium acetate solution, at about room temperature. A total of 5 ^ 5 1 solution were used for the elution.

After elution, the exchanger was washed with 17 O 1 of demineralized water.

Four fractions were collected: 90 1 Co ⁺⁺ and Mn ⁺⁺ free solution, 35 1 feed, 240 1 concentrate and 320 1 caster.

The concentrate contained.

37.0 g / l Co ⁺⁺ and

3.1 g / l Mn ⁺⁺

 Organic constituents except acetic acid were polar

not identifiable graphically. Pre and post run were combined and used again for the next cycle. The concentrate was used again directly in the oxidation described in Example 1. The activity of this concentrate was identical to that of fresh catalyst solution of equal cobalt and manganese acetate concentration.

2 25 8 98

Example 3

50 »5 g of a combustion ink octane from the DMT process was added with stirring with 30.0 ml of dilute HCl solution. (= 12% HCl) and 2 ml of 30% I ^ Og solution _ZV; ei hours at 95 ° C open. , , The sample used contained: 50.7% cobalt .5.4 % manganese 0.37% iron 0.13% nickel 100 ppm chromium 1000 ppm molybdenum

100 ppm vanadium. '. .... . · ... , ··. , 100 ppm copper.

100 ppm of titanium.

Subsequently, the digest was diluted with 11 demineralised (DI) water and washed with approx. 40% sodium hydroxide solution to pH 7. 9 ml of sodium hydroxide solution were consumed.

The digest was then heated to 95 ^° C. for one hour and filtered through a pleated filter.

The filtrate, after dilution with deionised water, was adjusted to 8 liters and 5 ml of concentrated acetic acid to pH 4.

The solution contained: 2.9 g cobalt / l 0.2 g manganese / l 6 ppm nickel 'Ό ppm iron

<5 ppm chromium, molybdenum, vanadium, copper, titanium. The resulting solution was used to substantially remove the Na ⁺ ions through a column of ?. ¹ ) 0 ml of a strongly acidic catalyst exchanger loaded with Cp '''' ¹ '' and Mn ''' ^T- clays

225898

passed on.

A column of 250 ml of strongly acidic cation exchange resin Lewatit S 100 in the Na ⁺ form was loaded with the solution.

The wastewater obtained contained: JO ppm cobalt 2 ppm manganese.

Load the exchanger up to the beginning of exhaustion with 3 »5 l of the above solution (limit value = 300 ppm of cobalt in the effluent.)

Subsequently, the. Exchanger nit 250 ml VE-Y / asser washed.

The elution of the cobalt and manganese ions was carried out using the following solutions: 400% pre- and post-run fractions from the previous experiment - 200 ml of a 18% sodium acetate solution containing 15 g of free acetic acid / liter 200 ml of deionised water.

Obtained during elution:

60 ml of a flow-through fraction 400 ml of a Na ⁺ -arene main fraction 340 ml of a Na ⁺ -rich trailing fraction.

The pre- and post-run were combined and used for elution in the next experiment

 The main fraction contained: 30.9 g · cobalt / l 2, 1 g manganese / l 75 ppm nickel

<5 ppm chromium, molybdenum, vanadium, copper, titanium 175 ppm sodium.

- * ί- 2 2 5 8 9 8

The resulting main fraction can be used as a catalyst; in the DHT process verv, ^r ends.

Example 4

50.1 g of a combustion residue was mixed with 350 ml

12% hydrochloric acid and 2 ml of 30% H ₃ O ₂ solution 2 hours at 95 ° ^C digested *

The ash residue used contained:

40 , 6 % Co 4 3 % Mn 19 ,8th % Ni. 2970 ppm Fe <100 ppm Cr 800 ppm Mo <100 ppm .. V. 80 ppm Cu <100 ppm Ti 1280 ppm N / A.

The digest was adjusted to pH 6.2 with 7 μl of an approximately 40% sodium hydroxide solution. After one hour, the heated to 95 ⁰ C solution was filtered through a pleated filter. The filtrate was diluted to 10.sup.1 with deionised water and adjusted to pH 3.9 with 10 ml of concentrated acetic acid. The solution contained:

1.84 G Co / 1 0.16 6 Mn / 1 0.87 ppm Ni / 1 <5, ppm Fe <5 ppm Cr <5 ppm Mo <5 ppm V <5 ppm Cu <5 ' Ti.

, , - τ? - 225898

The resulting solution was treated to remove most of the Na ⁺ ions with 250 ml of a strongly acidic cation exchange resin loaded with Co ²⁺ , Mn ²⁺ and Ni ²⁺ ions.

* A column with 250 "ml of a strongly acidic cation exchange resin LEV / ATIT S 100 in the Na form was loaded with the solution.

The effluent obtained at the effluent contained: 25 ppm Co 2 ppm. Mn 10 ppm Ni.

To load the exchanger until the beginning of the Creation, 4.7% of the solution was consumed.

The exchanger was then washed with 250 ml of deionized water.

The following solutions were twisted to elute the Co ²⁺ , Mn ²⁺ and Ni ²⁺ ions:

390 ml of combined lead and lag fraction from previous experiment 200 ml of 18% sodium acetate solution. 15 s free

Acetic acid per liter contained 210 ml of deionized water.

Upon elution, the following solutions were obtained: JO -

80 ml of a forerunner fraction 400 ml of a Na-arms main fraction 32Ο ml of a Na ⁺ -rich caster fraction.

10 Dr.Li/Ra Co / 1 2 2 5898 • "λ, -"; · · -; ; .;. · ·· · · · · · · ·. '. ..- ·:. - '· ^; ; , 1 The main fraction contained: Mn / 1 21.5 ε Ni / 1 - 1.9 β Fe 5 10.2 g Cr <5 ppm Mo c 5 ppm V <5 ppm Cu <5 ppm Ti 10 ^ 5 ppm N / A. <5 ppm 240 ppm 15 20 • 25 30 Y?

Claims (2)

ι * - · 22 5 8 98 AP BOU / 225 58 304 11 invention claim 1 · Process for the recovery and reuse of Schwieletalloxidationskatalysator from the Witten-DMT process, starting from high-boiling distillation residues having a cobalt content of 1 to 10 g / kg and optionally a manganese content of 0.1 to 5 g / kg residue and / or a Kickelgehalt of 0.1 to 5 g / kg residue, in the oxidation of mixtures containing p-xylene and / or p-toluate in the liquid phase with oxygen or an oxygen-containing gas at a pressure of 4 to 8 bar and a temperature of 140 to 170 ⁰ C in the presence of dissolved Schwermetalloxidationskatalysator, subsequent esterification of the oxidation product with methanol at a pressure of 20 to 30 bar and a temperature of 230 to 280 ⁰ C and distillative separation of the esterification product in a p-Toluylsäuremethyl- , ester-rich fraction, a dimethyl terephthalate-rich fraction and a high-boiling distillation residue obtained by extraction of the Schwermetalloxidationska with water, dilute mineral acids, aqueous low molecular weight aliphatic monocarboxylic acids with 1-4 carbon atoms or alcohols in the / poor, possibly after combustion of the high-boiling distillation residues , characterized in that a) the aqueous, acidic, Schwermetalloxidationskatalysatorhaltige extract having a cobalt content of 0.2 to 20 g / l optionally a manganese content of 0.05 to 10 g / l and optionally a Uiekelgehalt of 0.05 to 10 g / l with a strong acid cation exchange resin in the alkali metal form, e.g. B · Ha - or K - - se. - 2 25898 09/04/1981 AP B01J / 225 58 304 11 Form is treated at elevated temperature until the exchange capacity is reached and b) the cation exchange resin is then washed at elevated temperature and regenerated at room temperature with Na ⁺ or K ⁺ acetate containing solutions displacing the catalyst components and obtaining an aqueous acetic acid catalyst solution containing the catalyst components. Process according to item 1, characterized by the extraction of the ashes obtained after combustion of the high-boiling distillation residues with aqueous mineral acids with the addition of oxidants in the heat, subsequent dilution with water and increasing the pH by addition of alkali, heating to precipitate iron and chromium as hydroxides, co-filtering off the hydroxides and insoluble Aechebereinteile, diluting with water and acidification of the filtrate with linear, low molecular weight, aliphatic monocarboxylic acids having 1-4 carbon atoms. Process according to item 2, characterized in that the recovery of the catalyst constituents from the ashes of the combustion of the high-boiling distillation residues by treatment with aqueous hydrochloric acid with the addition of aqueous HpOg at about 95 ° C for the period of 0.1 to 4 hours, then increasing the pH to a value of 6 or above by addition of aqueous alkalis, heating to about 95 ⁰ C for , 4t - 225 893 09/04/1981 AP BOU / 225 898 58 304 11 0.1 to 2 hours, collectively filtered off the formed hydroxides of iron, chromium and the insoluble ash constituents and acidification of the Piltrats with acetic acid to pH 5 or below and removal of the Na ⁺ ions contained in the filtrate with a Co, Mn and / or Ni ion-loaded strong acid cation exchange resin was carried out Process according to item 2, characterized in that the recovery of cobalt or cobalt and manganese compounds together with nickel compounds from extracts of ashes of the combustion of high-boiling cobalt, cobalt and manganese, cobalt and nickel or cobalt, manganese and nickel-containing distillation residues having a content of 0.2 to 20 g / l cobalt, 0.05 to 10 g / l manganese or 0.05 to 10 g / l nickel · Method according to one of the items 1 to 4, characterized in that the catalyst solution obtained according to step b) of item 1 comprises cobalt and manganese acetate having a content of 10 to 70 g / l of cobalt and optionally a content of 1 to 35 g / contains manganese, and less than 5 mg iron / 1, 5 mg chromium / 1, 5 mg molybdenum / l, 5 mg vanadium / l, 5 mg copper / l and 5 mg.titanium / 1 respectively. Process according to one of the items 1 to 4, characterized in that the catalyst solution obtained according to step b) of item 1 contains cobalt, manganese and nickel acetate with a content of 10 to 70 g / l of cobalt, 1 to 35 g / l · manganese and 1 to 35 g / l nickel 'and less than 5 mg iron each / 1, 5 mg chromium / 1, 5 mg molybdenum / l,' r,. "- f" - »/ T .._ -mz λ J'i ~