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.