| abstract |
In the prodn. of terephthalic acid by liquid phase oxidn. of a mixt. of p-xylene and/or p-tolualdehyde and methyl p-toluate with a gas contg. O2 in the presence of a heavy metal catalyst, heat treatment of the oxidised reaction mixt. and sepn. of the terephthalic acid from this, the reaction mixt. is contacted with H2 in the presence of a hydrogenation catalyst before or during heat treatment. Prod. is used for the mfr. of polyester fibres, films, resins etc. It is obtd. in a large particle size in high yield and high puity, since hydrogeneation causes decomposition of coloured oxidn. prods. and conversion of intermediates and by-prods., e.g. aldehydes, alcohols, ethers and esters, to ore useful cpds., e.g. p-xylene, p-methylbenzoic acid, methyl p-toluate, terephthalic acid or monomethyl terephthalate, some of which are converted to terephthalic acid in the heat treatment stage. |