Dynamit Nobel Aktiengesellschaft

Heinz Schroeder

Georg Schreiber

Anton Schoengen

Bernhard Piotrowski

Helmut Von Branchel

Hans-Walter Overhausen

Wolfgang Hoppe

Eugen Hadamovsky

Wehrhart Schmid

A process for the production of a crude dimethyl terephthalate suitable for hydrolyzing into a fiber grade terephthalic acid involves separating a crude ester obtained from the production of dimethyl terephthalate by the Witten process by vacuum distillation at elevated pressure in a three-column series arranged distillation system. In the first distillation column of the system the crude is separated into a methyl p-toluate-rich fraction as head product; in a second column of the series, into a fraction rich in methyl ester of terephthalaldehydic acid as head product; and in a third distillation column, a crude dimethyl terephthalate fraction. The crude dimethyl terephthalate fraction has a methyl ester of terephthalaldehydic acid content of 0.01-0.1% by weight as a head product.

Preparation of terephthalic acid from a crude dimethyl terephthalate

A process for the production and maintenance of a fluidized layer in a heterogeneous system includes the steps of:

Process and apparatus for the production and maintenance of a fluidized

In a process for the preparation of fiber-grade terephthalic acid from intermediate stage crude dimethyl terephthalate, the crude dimethyl terephthalate, which has a limited content of intermediate oxidation products including a content of terephthalaldehydic acid methyl ester of up to 0.1% by weight based on the weight of the crude dimethyl terephthalate, is hydrolyzed with water at a weight ratio of the crude dimethyl terephthalate to water of between 3:1 and 0.1:1 and at a temperature between 140.degree. C. and 350.degree. C. and under a pressure required to maintain a liquid phase (e.g., from 6 to 200 bars) to produce a reaction mixture containing crystalline fiber-grade terephtalic acid and thereafter the terephthalic acid is recovered from the reaction mixture. The initial crude dimethyl terephthalate used as a starting material is obtained from a crude ester mixture produced by the oxidation of p-xylene and/or methyl p-toluate with oxygen-containing gases in the presence of heavy metal-containing oxidation catalyst at an elevated temperature and under an elevated pressure and by esterification of the oxidation mixture with methanol at an elevated temperature and elevated pressure followed by separating the resulting crude ester mixture by distillation into a methyl p-toluate enriched fraction, a residual high-boiling fraction and the crude dimethyl terephthalate having the limited content of intermediate oxidation products.

Process for the preparation of terephthalic acid by the hydrolysis of

A process for mass transfer between heterogeneous systems or phases in a vertical exchange column having at least one plate, a heavier stream of matter being introduced above the plate and, a lighter stream of matter being introduced countercurrently thereto from the bottom of the plate, wherein (a) a heavier stream of matter fed from the top is deflected, above the plate, into a mixing zone in which the heavier stream undergoes vertical rotary movement and is mixed with a lighter stream of matter passing from below through a first passgeway of the plate and introduced into the mixing zone to also undergo vertical rotary movement, (b) a heavier phase, suspension, or the like fluid-like mass forming in the mixing zone during the mass transfer therein is accumulated in a zone superjacent to a second passageway of the plate; and (c) after a sufficient pressure gradient has been built up, the accumulated mass flows as another heavier stream through the second passageway into a space underneath the plate and is at this location deflected into another mixing zone in which another heavier steam undergoes vertical rotary movement, having a sense or direction of rotation opposite to that in the mixing zone above the plate, and is mixed with a lighter stream of matter fed from below.

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Witten, Germany

Heinz Schroeder