Conversion of Marine Plastic Litter into Chemicals and Fuels through Catalytic Pyrolysis Using Commercial and Coal Fly Ash-Synthesized Zeolites

Abstract

A marine plastic litter (MPL) sample, collected during a beach cleanup campaign, underwent thermal and catalytic pyrolyses to demonstrate that valuable hydrocarbon oil and gas can be produced from heterogeneous plastic waste, partly aged and not mechanically recyclable. A low-cost H-X zeolite lab synthesized from coal fly ash (CFA) was tested and compared with two commercial zeolites (H-USY and H-ZSM-5) commonly used in the industrial cracking field. MPL characterization revealed it is mainly composed of polyethylene and polypropylene (52 and 45 wt %, respectively), and it has ideal physicochemical properties as feed for pyrolysis processes. Thermogravimetric analyses demonstrated that catalysts can reduce the degradation temperature of MPL from 472 to 425 °C and from 450 to 421, 342, and 380 °C for H-ZSM-5, H-X/CFA, and H-USY, respectively. These results were confirmed by thermal and catalytic pyrolyses tests performed in a bench-scale reactor. All the catalytic tests were carried out at 450 °C with a liquid phase contact mode. In particular, H-X/CFA, avoiding tar and wax formation, produced up to 87 wt % of light oil with a high content of short chain aliphatic hydrocarbons, obtaining results very similar to those gained with the expensive commercial H-USY. For all the catalytic pyrolysis tests, the produced gases proved to be more than sufficient to sustain the process heat requirement.