Reactions of di-n-butylphthalate in water at near-critical temperature and pressure

Abstract

Water has a significant influence on the thermal decomposition pattern of di- n-butylphthalate (DBP) in the temperature range from 305 ° up to 390 °C and bomb water densities of up to 0.31 g cm −3. It favours hydrolytic decomposition, which results in o-phthalic acid, butanol and butene as main primary products. Subsequent reactions convert o-phthalic acid into benzoic acid and some benzene. In the absence of water the thermolysis of DBP results only in butene and a mixture of benzoic acid and benzene as the main products. Decarboxylation of benzoic acid into benzene and the formation of char appears to be strongly retarded in supercritical water. Polycondensation of phenyl species, which contributes significantly to the amount of polycondensates formed by thermolysis of DBP, is completely suppressed in supercritical water; on the contrary, polycondensation of C 4 species remains active also in supercritical water, albeit with a slower rate than in thermolysis. Butene and butanol not only consist of the 1-isomer, of which DBP is made up, but also of the 2-isomer. The latter configuration increases with the bomb water density.