Method of preparation of terephthalic acid and installation for implementing it.

摘要

A process for the production of terephthalic acid by thermal rearrangement of a salt selected from the group consisting of potassium phthalate, potassium isophthalate, mixtures of potassium isophthalate and terephthalate and mixtures of potassium phthalate, isophthalate and terephthalate, the acidification of the resulting reaction mixture by phthalic anhydride to separate free terephthalic acid from the potassium salt and the re-use of the potassium values in the procedure comprises the steps of separating solid potassium biphthalate from the aqueous solution formed in the acidification process, adding an acid selected from the group consisting of phthalic anhydride, phthalic acid, isophthalic acid, mixtures of isophthalic and terephthalic acids and mixtures of phthalic, isophthalic and terephthalic acids, heating the mixture thus formed to a temperature at which fusion occurs and phthalic anhydride distils off leaving a salt directly reusable in the rearrangement process thereby forming a closed potassium cycle and reusing the liberated phthalic anhydride in the acidification of the rearrangement reaction product thereby forming a closed phthalic anhydride cycle. The terephthalic acid produced may be esterified with methanol e.g. using potassium salts of isomeric phthalic acids as catalyst. Zinc dust is specified for use as catalyst in the rearrangement reaction. An apparatus for carrying out the process is described with reference to a diagram (not shown). Examples are furnished.