Two-step optimization (catalyst and process) to maximize the liquid yield from the waste plastics mixture by hydrocracking process using hierarchical zeolite catalysts

The objective of the study was to maximize the liquid yield by hydrocracking a waste plastic mixture (by weight 24.76% low-density polyethylene, 29.85% high-density polyethylene, 10.57% polypropylene and 34.82% polystyrene) over different hierarchical (containing both micro- and mesosized pores) zeolite catalysts. Two optimizations were performed, i.e., catalyst synthesis optimization followed by the process parameter optimization to maximize the liquid yield and oil yield, respectively. Response surface methodology with central composite design approach was used for both the optimizations. Preliminary experiments were carried out using mesoporous ZSM-5 and Beta Zeolite by desilication/dealumination approaches, where desilicated alumina impregnated Beta Zeolite showed the best results in terms of liquid yield. Alumina loading and synthesis temperature were considered as the significant factors for the catalyst optimization. The experiments were carried out at catalyst-to-plastic ratio of 1:20 and a temperature of 400 degrees C in an atmospheric pressure setup. For the process parameter optimization, a high-pressure (parr autoclave) setup was used. The parameters selected were temperature (360-440 degrees C), pressure (1-40 bar) and catalyst-to-plastic ratio (1:5-1:40 wt/wt). The results indicated that pressure and catalyst-to-plastic ratio were not as statistically significant in comparison with temperature. At optimized conditions of 420 degrees C, 20 bar and catalyst-to-plastic ratio of 1:30 wt/wt, 11.27 g (37.57 wt%) of oil yield was achieved. Two quadratic regression models were developed for each optimization, i.e., process optimization (R-2 similar to 91%) and catalyst optimization (R-2 similar to 95%) that show good fit with the experimental data. [GRAPHICS] .