Terephthalic acid prodn. - with selective extn. of unreacted cpds. and useful by=products from isomeric acids using e.g. para-xylol for recycling

摘要

In the prodn. of terephthalic acid (I) by continuous hydrolysis of crude dimethyl terephthalate (II)- obtd. as an intermediate by oxidising p-xylol (III) and/or methyl-p-toluate (IV) with O2-contg. gases over heavy metal-contg. catalysts and esterifying the mixt. with methanol at high temp. and pressure- useful unreacted prods. e.g. monomethyl terephthalate (V), dimethyl terephthalate, p-toluic acid (VI) etc. contd. in the aq. soln. channelled out of the hydrolysis reaction after removal of (I) are sepd. from isophthalic acid (VII) and orthophthalic acid (VIII) by selective extn. with (III) and/or (IV) for recycling. The procedure necessitates only a single hydrolysis step to achieve high conversion of (II) to (I), compared to the prior art use of two. Complete recovery of (II), (V) and (VI) is achieved.