Mesoporous Structures for Catalytic Pyrolysis of Plastic Waste

Waste plastics commodities have heterogeneous composition, variable and inherent structural complexity, and cannot be exclusively recovered by mechanical reprocess. An alternative to recycling these materials is conversion of plastic waste to products of high added value through pyrolysis. The thermocatalytic method provides greater selectivity, resulting in narrow fraction of molecules with appropriate molar mass that can be used directly as fuel oils1,2. Larger pores allow greater access of the polymer chains to more internal acid sites, which increases the catalytic activity and decrease the catalyst deactivation. The mesoporous mordenite was synthesized by soft template hydrothermal routes using cationic surfactant by means of moist (MOR 200) and dry syntheses (MOR DRY). Mesoporous ZSM-5 was synthesized by the hydrothermal method using structure-directing agent. The synthesized samples showed characteristic peaks of mordenite and ZSM-5, confirming the formation of the desired crystal structure (Figure 1). Total density of acid sites (Table 1) and distribution of these sites were determined by temperature-programmed desorption of ammonia (NH3-TPD) (Figure 2). Mordenite has higher ratio of stronger/weak sites than ZSM-5, however, it has a more homogeneous distribution of acid forces. Two plastic waste mixtures were prepared according to Abisplast (2016). The components of these blends are polyethylene (58.5%), polypropylene (31.6%) and polystyrene (9.9%). The MP mixture corresponds to the mixture of post-consumer plastics that are useful for mechanical recycling, while the MF mixture corresponds to that of non-usable plastic wastes directed to the landfills. These materials were extruded with each catalyst (10% m/m) and evaluated in thermogravimetric analysis (Table 2). The results show that all the evaluated catalysts were able to decrease the degradation temperatures of both plastics mixtures, especially ZSM-5 zeolite.