Mitsubishi Gas Chemical Company, Inc.

Toyo Boseki Kabushiki Kaisha

Mizushima Aroma Company, Ltd.

Masato Inary

Fumiya Zaima

Fumio Ohkoshi

There is disclosed a process for producing highly pure terephthalic acid by the use of a dispersion medium replacement apparatus equipped with a stirring unit at the bottom portion for uniform dispersion, wherein an original slurry comprising a first dispersion medium and terephthalic acid crystals is introduced into a dispersion medium replacement apparatus at the top portion, a second dispersion medium is introduced into the apparatus at the bottom portion, a replaced slurry comprising principally the second dispersion medium and the terephthalic acid crystals is taken out from the apparatus at the bottom portion, and the first dispersion medium as a major component is taken out from the apparatus at the top portion, which process comprises maintaining a uniformly dispersed slurry at the bottom portion of the apparatus at a concentration higher than that of a slurry at the intermediate portion; maintaining the upper portion at a higher temperature in a vertical temperature distribution therein to form a temperature change zone; and controlling the feed rate of the second dispersion medium and/or the takeout rate of the replaced slurry according to the location of the temperature change zone. By virtue of the specific control system, that is, taking advantage of the temperature change zone, the apparatus can be steadily operated with ease and high reliability at a high replacement efficiency, and thus highly pure terephthalic acid is stably obtained.

Process for producing highly pure terephthalic acid by use of dispersion

There are disclosed a method for replacing a dispersion medium wherein an original slurry comprising solid particles and an original dispersion medium is introduced in a dispersion medium replacement column at the top thereof, a replacing dispersion medium is introduced in the column at the bottom thereof to replace the original dispersion medium with the replacing dispersion medium, the resultant replaced slurry comprising the solid particles and the replacing dispersion medium is taken out from the column at the bottom thereof, and the original dispersion medium is taken out from the column at the top thereof, which method comprises dividing the fluid in the intermediate portion into a plurality of parallel streams, stirring the slurry in the bottom of the column to uniformize the slurry, and controlling the feed rates of the replacing dispersion medium and the replaced slurry to maintain the slurry in the bottom portion of the column at a concentration higher than that of the slurry in the intermediate portion of the column; an apparatus for carrying out the method; and a process for producing highly pure terephthalic acid from the slurry comprising an original dispersion medium and crystalline particles of terephthalic acid. The method and apparatus are capable of producing highly pure terephthalic acid at a high replacement efficiency of the dispersion medium with simplified equipment in an extremely advantageous manner.

Process for producing highly pure terephthalic acid

A process for producing highly pure terephthalic acid comprising: (a) oxidizing a p-phenylene compound in the liquid phase in the presence of acetic acid, to produce a liquid-phase oxidation product, (b) separating the liquid-phase oxidation product into the following: (i) a first mother liquid containing acetic acid and (ii) a crude terephthalic acid, (c) evaporating, in whole or in part, the first mother liquid, to produce a vapor, (d) feeding the vapor, or a condensate thereof, to an intermediate stage of a distillation tower, carrying out an azeotropic distillation and withdrawing through a bottom of the distillation tower a concentrated acetic acid, (e) subjecting the crude terephthalic acid to a refining treatment, which is a catalytic hydrotreatment, a catalytic treatment or a recrystallization, which is carried out in the presence of is water, (f) cooling and crystallizing the resultant liquid from step (e), to produce a pure terephthalic acid and a second mother liquor, (g) subjecting the second mother liquor to an extraction in the presence of an azeotrope-forming agent to extract aromatic carboxylic acids contained in second mother liquor, to produce a liquid extract, and (h) recycling the liquid extract to the distillation tower in step (d). The process can greatly reduce the effluent water treatment load and enhance the yield of the objective terephthalic acid, in addition to providing recycling of useful reactants.

There is disclosed a process for producing highly pure terephthalic acid by converting a slurry of terephthalic acid crystals in acetic acid solvent which crystals are obtained by liquid-phase oxidation of p-alkylbenzene, into a slurry thereof in water solvent by mother liquor replacement and then subjecting the latter slurry to a catalytic hydrogenation treatment which process comprises the steps of introducing the slurry of terephthalic acid crystals in acetic acid into a mother liquor replacement column at the top portion; forming an accumulation layer of the terephthalic acid crystals at the bottom portion by the sedimentation of the crystals; feeding replacing water sufficient for the formation of upward rising stream of water to the inside of the column at the bottom portion; and withdrawing the accumulation layer of the crystals from the bottom portion of the column. The accumulation layer is kept at a slightly fluidized stable state and is smoothly withdrawn from the bottom of the column by slowly rotating an arm-type agitation blade placed in the layer or by feeding the replacing water dividedly into two trains.

There is disclosed a process for producing terephthalic acid which comprises oxidizing in a liquid-phase a starting raw material comprising p-xylene incorporated with 3 to 35% by weight of p-tolualdehyde based on the same at a temperature in the range of 120.degree. to 240.degree. C. by means of a molecular oxygen-containing gas by using a lower aliphatic monocarboxylic acid as a solvent in the presence of a catalyst comprising a manganese compound having 50 to 1000 ppm by weight of manganese atoms, a cobalt compound having 50 to 2000 ppm by weight of cobalt atoms and a bromine compound having 100 to 4000 ppm by weight of bromine atoms, each based on the solvent. By virtue of the above specific constitution, it is made possible to produce high-quality terephthalic acid with a high residual rate of the lower aliphatic monocarboxylic acid as a solvent minimized in its loss, thereby enabling the production of high-quality polyester with high whiteness from the above terephthalic acid and a glycol.

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Kurashiki, Japan

Masato Inary