US 4,081,464 AGranted

Iso- or terephthalic acid production in and recovery from benzoic acid-water solvent system

AssigneeThe Standard Oil Company

InventorsDavid R. Marsh, Leonard E. Stark

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Abstract

This invention relates to the continuous production of iso- or terephthalic acid in a stirred reaction zone by catalytic air oxidation of m- or p-xylene in the presence of a benzoic acid-water liquid solvent system at constant gauge pressure within the range of 7 to 21 kg/cm.sup.2 wherein oxidation temperature within the range of 175.degree. to 235.degree. C. is maintained substantially constant by the novel control thereof by only varying the flow rate of water condensate reflux to the oxidation zone. The invention further pertains to novel means for achieving such temperature control. Also, the present invention relates to a novel continuous recovery of the phthalic acid product from the fluid effluent of said continuous process by a process wherein crystalline phthalic acid product is separated from essentially water-free benzoic acid mother liquor; the crystalline product is successively washed with liquid benzoic acid and the corresponding xylene; the washed product is dried; and the water removed from said fluid effluent, the benzoic acid and xylene wash liquors, xylene recovered from product drying, and a major proportion of the benzoic acid mother liquor are charged to the oxidation process. The invention further relates to a novel combination of apparatus for the continuous conduct of said oxidation and recovery processes.

In a continuous process for iso- or terephthalic acid product production in and recovery from a benzoic acid-water solvent system wherein m- or p-xylene is oxidized with air in the presence of catalysis provided by manganese, cobalt or cobalt and manganese and a source of bromine and a liquid phase of said solvent system at a temperature within the range of from 175.degree. to 235.degree. C. and a constant gauge pressure within the range of 7 to 21 kg/cm.sup.2 in a stirred reaction zone to produce a suspension of crystalline phthalic acid product in said solvent system as fluid oxidation zone effluent and a gas-vapor mixture containing nitrogen, oxygen, oxides of carbon and vapors of benzoic acid and water as exhaust effluent;

wherein heat of reaction is removed at least in part by cooling said exhaust to provide a benzoic acid-water liquid reflux to the oxidation zone;
and wherein said phthalic acid product is separated as a crystalline mass from the fluid oxidation effluent, washed to remove mother liquor and dried;
the improvements comprising, conducting the m- or p-xylene oxidation in the presence of from 2 to 6 weight parts of solvent system consisting essentially of 90-97 weight percent benzoic acid and 10-3 weight percent water for each weight part of xylene and at a substantially constant oxidation zone temperature within said temperature range controlled by varying the rate of water condensate returned to the oxidation zone inversely with respect to change required in oxidation zone temperature;
evaporating water from fluid effluent from the oxidation zone under conditions maintaining benzoic acid in the liquid phase;
separating the suspended crystalline product mass from the water-free oxidation zone fluid effluent;
and washing the separated crystalline product mass at a temperature of from 122.degree. up to 135.degree. C first with liquid benzoic acid and then with xylene corresponding to the product.

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Abstract

Claims7