The Pyrolysis of Plastics in Molten Salts

Abstract

A laboratory scale reactor has been built and operated for the pyrolysis of polyethylene in a bath of molten salt between 490 and 700°C. Products of pyrolysis have been identified and measured. The effect of temperature and stirring on pyrolysis products have been investigated. Observations have been made to allow a reasonable description of the mechanism of the pyrolysis process. A theoretical model has been produced by which the process can be compared with conventional naphtha pyrolysis with good agreement. Technical and economic considerations for commercial operation of the process are discussed with examples. In the experiments, ethylene was a major product of pyrolysis, with a yield from 7 to 14%, which is unlike conventional analytical pyrolyses, but in agreement with some other work on bulk pyrolysis of the plastic. It is estimated that a commercial unit would be self-sufficient in energy if it used one third of the pyrolysate as fuel. A unit dealing with 5 tonnes per day of plastic would probably be economic, but larger sizes are limited by the cost of waste collection to about 30 tonnes per day.