Microwave-assisted In-situ catalytic co-pyrolysis of polypropylene and polystyrene mixtures: Response surface methodology analysis using machine learning

Polypropylene (PP) and Polystyrene (PS) are the major plastic fractions found in mixed plastic waste. Hence, the current study was focused to convert PP and PS into useful products via microwave-assisted pyrolysis (MAP). In addition, the understanding of feedstock conversion, product yields, and energy requirements in pyrolysis, copyrolysis, and catalytic co-pyrolysis was investigated. Experiments were conducted at a constant microwave power of 450 W till the reaction temperature reached up to 600 degrees C. When PS pyrolyzed, a heating rate of 56 degrees C/ min resulted in 80 wt% of oil yield. Whereas PP pyrolysis produced 42 wt% of oil at a heating rate of 76 degrees C/min. In the PP: PS co-pyrolysis, the heating rate was decreased to 52 degrees C/min by yielding 51 wt% of oil. In catalytic copyrolysis of PP: PS with KOH resulted in variation in product yields and heating rate. An increase in PS quantity at a constant mass of PP resulted in the enhancement of oil yields from 58 to 84 wt% and a decrease in gas yields. The specific microwave power in the catalytic co-pyrolysis (7-18 W/g) is lower compared to the non-catalytic case (22-30 W/g). Whereas, the pyrolysis time in non-catalytic pyrolysis (7-11 min) is lower compared to catalytic co-pyrolysis (14-37 min). The addition of a catalyst resulted in a decrease (23-50%) in microwave conversion efficiency than that of the non-catalytic case (60-85%). The difference in predicted and actual result analysis proved co-pyrolysis synergy in product formation and energy consumption.