Catalytic Pyrolysis of Waste Plastics using Staged Catalysis for Production of Gasoline Range Hydrocarbon Oils

The two-stage pyrolysis-catalysis of high density polyethylene has been investigated with pyrolysis of the plastic in the first stage followed by catalysis of the evolved hydrocarbon pyrolysis gases in the second stage using solid acid catalysts to produce gasoline range hydrocarbon oil (C8-C12). The catalytic process involved staged catalysis, where a mesoporous catalyst was layered on top of a microporous catalyst with the aim of maximising the conversion of the waste plastic to gasoline range hydrocarbons. The catalysts used were mesoporous MCM-41 followed by microporous ZSM-5, and different MCM-41:zeolite ZSM-5 catalyst ratios were investigated. The MCM-41 and zeolite ZSM-5 were also used alone for comparison. The results showed that using the staged catalysis a high yield of oil product (83.15 wt.%) was obtained from high density polyethylene at a MCM-41:ZSM-5 ratio of 1:1 in the staged pyrolysis-catalysis process. The main gases produced were C2 (mainly ethene), C3 (mainly propene), and C4 (mainly butene and butadiene) gases. In addition, the oil product was highly aromatic (95.85 wt.% of oil) consisting of 97.72 wt.% of gasoline range hydrocarbons. In addition, pyrolysis-staged catalysis using a 1:1 ratio of MCM-41: zeolite ZSM-5 was investigated for the pyrolysis–catalysis of several real-world waste plastic samples from various industrial sectors. The real world samples were, agricultural waste plastics, building reconstruction plastics, mineral water container plastics and household food packaging waste plastics. The results showed that effective conversion of the real-world waste plastics could be achieved with significant concentrations of gasoline range hydrocarbons obtained.