Fluidised bed pyrolysis of low density polyethylene to produce petrochemical feedstock

Abstract

Pyrolysis of plastic waste has been proposed as a tertiary or feedstock recycling route where the plastic waste materials are processed back to produce basic petrochemicals that can be used as feedstock to make virgin plastic or refined fuels. The detailed analysis of the derived products from the pyrolysis of plastics provides data on the suitability of the process and the influence of process conditions on the compatibility of the feedstock produced with the conventional petroleum feedstock. Low density polyethylene (LDPE) is a major component of municipal solid waste and this paper describes the influence of pyrolysis temperature from 500 to 700°C on the yield and composition of the derived products. The main gases produced from the pyrolysis of LDPE were hydrogen, methane, ethane, ethene, propane, propene, butane and butene. There was a dramatic increase in gas yield with increasing temperature of pyrolysis. Analysis of the derived oils and waxes showed that the pyrolysis of LDPE gave a mainly aliphatic composition consisting of a series of alkanes, alkenes and alkadienes which showed a decrease in concentration as the pyrolysis temperature was increased. The oil showed an increase in aromatic composition with increasing temperature of pyrolysis and at 700°C significant concentrations of single ring aromatic compounds and polycyclic aromatic hydrocarbons were detected. The derived oil and wax have great potential to be recycled back into the petrochemicals industry as a feedstock for the production of new plastics or the production of refined fuels.