Investigation into the Catalytic Activity of Microporous and Mesoporous Catalysts in the Pyrolysis of Waste Polyethylene and Polypropylene Mixture

Abstract

Catalytic pyrolysis behavior of synthesized microporous catalysts (conventional Zeolite Socony Mobil-5 (C-ZSM-5), highly uniform nanocrystalline ZSM-5 (HUN-ZSM-5) and β-zeolite), Mesoporous catalysts (highly hydrothermally stable Al-MCM-41 with accessible void defects (Al-MCM-41(hhs)), Kanemite-derived folded silica (KFS-16B) and well-ordered Al-SBA-15 (Al-SBA-15(wo)) were studied with waste polyethylene (PE) and polypropylene (PP) mixture which are the main constituents in municipal solid waste. All the catalysts were characterized by Brunauer-Emmett-Teller (BET), X-ray powder diffraction (XRD), and NH3-temperature programmed desorption (TPD). The results demonstrated that microporous catalysts exhibited high yields of gas products and high selectivity for aromatics and alkene, whereas the mesoporous catalysts showed high yields of liquid products with considerable amounts of aliphatic compounds. The differences between the microporous and mesoporous catalysts could be attributed to their characteristic acidic and textural properties. A significant amount of C2-C4 gases were produced from both types of catalysts. The composition of the liquid and gas products from catalytic pyrolysis is similar to petroleum-derived fuels. In other words, products of catalytic pyrolysis of plastic waste can be potential alternatives to the petroleum-derived fuels.

Experimental Study of Thermal and Catalytic Pyrolysis of Plastic Waste Components

“…However, the derivative thermogravimetric analysis (DTG) curves have two partially overlapped peaks (Figure 3b), which indicate an interaction between LDPE and PP. This complies with results reported by Kaixin et al [22].…”

“…The second step is catalytic pyrolysis, where the catalyst cracks the liquid products further to lower hydrocarbon products, leading to a lower liquid yield. The role of the catalyst in this work is consistent with other reports [14,22].…”

“…This might be explained by the uneven distribution of heat in the furnace. The presence of PP in the mixture initiates the cracking of LDPE in the mixture at a lower temperature, leading to low liquid production, which corresponds to other reports [22,25,26]. However, an unusual behaviour was observed in the mixture with a higher PP portion, where a higher liquid yield was observed.…”

“…The mechanism of degradation of LDPE and PP is a radical chain mechanism; the tertiary radical which is present in the polymeric chain of PP, initiated by random chain scission captures the hydrogen from LDPE, thereby enhancing the degradation of LDPE at a lower temperature and amplifying the degradation of the LDPE/PP mixture [22]. It is important to note that no residue was left at the end of the experiments.…”

Polyolefins and the environment

“…Similarly, survey of interaction among the other factors indicated that there is not a significant interaction [151]. The effects of catalysts on the catalytic degradation of polymer have also been investigated by contacting melted polymers with catalyst in fixed bed reactors [152,153], heating mixtures of polymer, and catalyst powders in reaction vessels [154,155], and passing the products of polymer pyrolysis through fixed bed reactors containing cracking catalysts [156].…”