Pyrolysis of polyolefins in high-boiling solvents

Abstract

The pyrolysis of polyethylene and polypropylene in vacuum residue and coal-tar pitch solvents was studied in a batch reactor at atmospheric pressure in a temperature range of 380–420°C. Aliphatic hydrocarbons and C5–C32 normal olefins and isoolefins were the main pyrolysis products of the polyolefins and vacuum residue, which also underwent thermal degradation at these temperatures. The total conversion of a polypropylene-vacuum residue mixture into gaseous and distillate products was nearly additive; upon the pyrolysis of polypropylene in pitch and of polyethylene in vacuum residue and pitch, the yield of distillate products decreased and the paraffin/olefin ratio in these products increased. The observed regularities were explained by hydrogen transfer from the solvents to the intermediate radical products of the thermal decomposition of polymer chains. The reactions of the resulting of olefins with the solvents can also occur to a lesser degree. The greatest deviations from additivity were observed in the pyrolysis of polyethylene in the solvents used.