Published February 1966
This report is concerned with terephthalic acid (TPA) (the para isomer of phthalic acid) and dimethyl terephthalate (IMT). The principal use of these chemicals is as raw material for the manufacture of polyesters by reaction with ethylene glycol. The process studies were confined to those believed to be in commercial operation. The oldest process, however, nitric acid oxidation of p-xylene, was modified to reduce nitric acid consumption. Also, process alternatives which would produce extensive amounts of by-products were avoided, since it is difficult to arrive at a meaningful production cost when the choice of by-product credit values becomes a highly significant factor. Thus the bromine-promoted catalytic air oxidation route was evaluated on the basis of p-xylene feed rather than a mixed xylene feed. Had the latter choice been made, an additional unit for separating the mixed acids and purifying the by-products would have been necessary, A similar decision was made in choosing to use the process employing phthalic anhydride rather than benzoic acid as raw material for the high temperature rearrangement of the potassium salt. With phthalic anhydride the by-products are slight and can be treated as contaminants, whereas benzoic acid, under the more usual process conditions, leads to large amounts of benzene by-product.
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