Effect of reaction conditions on the hydrogenolysis of polypropylene and polyethylene into gas and liquid alkanes

Hydrogenolysis of polypropylene (PP) and polyethylene (PE) provides a pathway to convert these plastics into smaller hydrocarbons at relatively low temperature. Among carbon (C)-supported transition metals, ruthenium (Ru) exhibited the highest efficacy, producing mixtures of C-1-C-38 alkanes. The branching degree of the products depends on the position of the C-C cleavage, which can be tuned by the pressure of H-2. Liquid alkanes are produced below 225 degrees C and 200 degrees C from PP and PE, respectively, at 30 bar. The C distribution and branching level of the products remain invariant below full conversion of the initial polymer. Increasing H-2 pressure favors the hydrogenolysis of internal C-C bonds, reducing methane (CH4) production, and favors linear over branched products. A liquid yield of >57% was achieved with PE under optimum conditions. We reveal the impact of the starting polyolefin structure, reaction conditions, and presence of chlorine on the product distribution and branching degree.

Automated summary

Hydrogenolysis of polypropylene (PP) and polyethylene (PE) can convert these plastics into smaller hydrocarbons. Among transition metals, ruthenium (Ru) is the most effective in producing C1-C38 alkane mixtures. The branching degree of the products depends on the position of the C-C cleavage and can be tuned by the pressure of H2.