Dynamit Nobel Aktiengesellschaft

Huls Aktiengesellschaft

Huls Aktiengesellschaft, Werk Troisdorf

Rudolf Modic

Anton Schoengen

Jorg Porschen

Hermann-Josef Korte

Ralf Wirges

Johann-Heinrich Schroeder

J Org Porschen

Friedrich Struss

Karl-Heinz Diessel

Process for the purification of an oxidation off gas

In the purification of an off-gas stream originating from a process of oxidizing a liquid mixture of para-xylene with methyl para-toluate with an oxygen-containing gas under pressure, the off-gas being contaminated with at least one of an aliphatic and an aromatic impurity, which comprises expanding the off-gas stream in an expansion turbine for generating mechanical or electrical energy so as to obtain an at least partial recovery of the energy contained in the off-gas, the improvement comprising subjecting the off-gas to at least one absorption step under pressure to remove at least one component from the off-gas and subjecting the resultant off-gas stream to combustion under a pressure of more than 3 bar prior to expanding the off-gas stream in the expansion turbine.

Process for the purification of an oxidation off gas with energy recovery

A process for the production of terephthalic acid from p-xylene and methanol by way of the dimethyl terephthalate obtained by oxidation, in the liquid phase with atmospheric oxygen in the presence of dissolved heavy metal compounds as the catalyst, of a mixture of p-xylene and a fraction containing predominantly methyl p-toluate, which fraction is recycled into the oxidation, to obtain an oxidation product containing primarily p-toluic acid and monomethyl terephthalate at a temperature of 140.degree.-170.degree. C. and under a pressure of 4-8 bar; by esterification of the oxidation product in a reactor with liquid and subsequently vaporized methanol brought to an elevated pressure, at a temperature of 220.degree.-280.degree. C. and under a pressure of 20-25 bar to obtain a raw ester containing primarily methyl p-toluate and dimethyl terephthalate; by withdrawing the raw ester fraction and a methanol-containing vapor fraction from the esterification reactor; by distillatory separation of the raw ester into a methyl p-toluate fraction and a fraction rich in terephthalic aldehyde methyl ester, which fractions are recycled into the oxidation, a raw dimethyl terephthalate fraction, and a residual fraction; and by hydrolysis of the raw dimethyl terephthalate fraction with water, obtaining the thus-formed terephthalic acid and separation of a methanol-water mixture. In this process, the methanol-containing vapor fraction and the methanol-water mixture are separated by rectification under elevated pressure and elevated temperature into a methanol-rich head fraction and an aqueous sump phase, the methanol formed at the head of the rectification stage is withdrawn in vapor phase under elevated pressure, and esterification of the oxidation product is conducted with the methanol-containing vapor brought by compression to esterification pressure and esterification temperature.

Process for producing terephthalic acid from p-xylene and methanol by

A process for the production of dimethyl terephthalate from p-xylene and methanol by oxidation in a reactor, in the liquid phase with atmospheric oxygen in the presence of dissolved heavy metal compounds as a catalyst, of a mixture of p-xylene and a fraction containing predominantly methyl p-toluate, which fraction is recycled into the oxidation, to obtain an oxidation product containing primarily p-toluic acid and monomethyl terephthalate, at a temperature of 140.degree.-170.degree. C. and under a pressure of 4-8 bar; by esterification of the oxidation product with liquid and subsequently vaporized methanol brought to an elevated pressure, at a temperature of 220.degree.-280.degree. C. and under a pressure of 20-25 bar in a reactor to obtain a raw ester containing primarily p-toluate and dimethyl terephthalate; by withdrawing the raw ester fraction and a methanol-containing vapor fraction from the esterification stage, by distillatory separation of the raw ester into a p-toluate fraction which is recycled into the oxidation, a raw dimethyl terephthalate fraction which is subjected to further processing by recrystallization in methanol, and a residual fraction which is optionally subjected to a thermal aftertreatment or a reactive treatment with methanol and is partially recycled into the process after a subsequent working-up step by distillation. In this process, the esterification of the oxidation product is conducted with a methanol-containing vapor, brought by compression to the elevated pressure and elevated temperature required for esterification, which methanol-containing vapor has been obtained from the filtrate of the recrystallization of the raw dimethyl terephthalate fraction by vaporization or also by rectification of the methanol-containing vapor fraction and optionally additional methanol-containing process streams, under a pressure lying below the pressure utilized in the esterification reactor.

Process for the production of dimethyl terephthalate from p-xylene and

A process for the recovery and reuse of a heavy-metal oxidation catalyst solution from a high-boiling distillation residue having a cobalt content of 1-10 g/kg of residue is disclosed. The distillation residue is obtained in the production of dimethyl terephthalate by the oxidation of mixtures containing p-xylene and/or methyl p-toluate in the liquid phase with oxygen or an oxygen-containing gas under an elevated pressure and at an elevated temperature in the presence of dissolved heavy-metal oxidation catalyst, by subsequent esterification of the oxidation product with methanol and by a distillatory separation of the esterification product into a fraction rich in methyl p-toluate, a fraction rich in dimethyl terephthalate, and the high-boiling distillation residue. The process involves the steps of effecting extraction of the heavy-metal oxidation catalyst from the high-boiling distillation residue with aqueous low-molecular aliphatic monocarboxylic acids under heating; treating the aqueous, acidic extract, which contains the heavy-metal oxidation catalyst and has a cobalt content with a strongly acidic cation exchange resin in the alkali metal form at an elevated temperature until the exchange capacity has been reached, and washing the cation exchange resin at an elevated temperature with water and regenerating the cation exchange resin at room temperature with a solution containing Na.sup.+ or K.sup.+ acetate to displace the catalyst components and to obtain an aqueous acetic acid catalyst solution containing the catalyst components.

Recovery and reuse of heavy-metal oxidation catalyst from the Witten DMT

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Steyerberg, Germany

Rudolf Modic