Depolymerisation of polycaprolactam - by melt depolymerisation in presence of alkaline catalyst, with addn. of di- or poly-carboxylic acid anhydride to form imide co-catalyst

摘要

A process for the rapid alkaline depolymerisation of polycaprolactam (I) comprises depolymerisation in the melt in the presence of conventional catalysts (e.g. alkali metals, hydroxides and/or carbonates) (II), with addn. of di- and/or poly-carboxylic acid anhydrides (III), opt. contg. additional functional gps., so as to form imide co-catalysts and reduce the melt viscosity. Pref. (III) are, e.g. cyclic anhydrides of succinic, maleic, phthalic, trimellitic, pyromellitic or benzophenone- tetracarboxylic acid. USE/ADVANTAGE - The process enables the rapid depolymerisation of (I) (esp. scrap polyamide) at relatively low temp. to give relatively pure caprolactam without producing any toxic residues with disposal problems. The added anhydride (e.g. trimellitic anhydride) reacts with (I) to form, e.g. 5-carboxyphthalimido-n- hexanoic acid and its homologues, which act as imide co-catalysts to displace the equilibrium towards depolymerisation. The process also reduces the viscosity of the melt, thus facilitating dispersion of catalyst (II) and removal of caprolactam from the melt.