Valuable oil recovery from plastic wastes via pressurized thermal and catalytic pyrolysis

Abstract

The accumulating amounts of long-life plastic wastes simultaneously with the global emerging need to discover alternative energy sources, have both increased the importance of plastic pyrolysis-based refineries. This study was devoted to examine the effectiveness of municipal plastic wastes recycling into a potential source of hydrocarbon fuel. Thermoplastic wastes of polypropylene (PP), polystyrene (PS), high-density and low-density polyethylene (HDPE) (LDPE), were converted into a combustible oil via semi-batch pressurized thermal (Th-PP) and catalytic pyrolysis (Cat-PP) in a fixed-bed reactor. During Th-PP, the recovered amounts of oil were (67.6 % −89.25 %) in the order PP > LDPE > HDPE > PS. Moreover, it was shown that 77.5% of the PP pyro-oil was in the range of gasoline fraction (C6 – C12) with maximum iso-paraffins of 12.52% compared to other plastic pyro-oils. The Cat-PP process, involved the catalytic cracking via a Ni-Mo-w/zeolite-based catalyst (Z-503). It was noticed that the catalyst resulted in further cracking reactions leading to the increase of the light gases vs oil product. Oil yields via Cat-PP were (55.1%–68.2%) in the order LDPE > PP > PS > HDPE. The catalytic pyrolysis showed a major tendency to the formation of diesel (C12 – C24). However, the selectivity analysis regarding both physical and chemical characteristics of the obtained oils vs conventional fuels, indicated that PP pyro-oil produced via the thermal pyrolysis, exhibited the highest selectivity of all oils towards conventional gasoline. This study has introduced a promising alternative energy source together with an effective recycling technology, solving the environmental plastic dilemma.