Catalytic co-pyrolysis of waste corn stover and high-density polyethylene for hydrocarbon production: The coupling effect of potassium and HZSM-5 zeolite

In this work, acid-washing corn stover (ACS) impregnated with various concentrations of potassium was co-pyrolyzed with high-density polyethylene (HDPE) in a fixed bed reactor. The coupling effect of potassium and HZSM-5 zeolite on product yields and mono-aromatic selectivity was studied. As the concentration of potassium increased, a reduction in liquid and an increase in gas and char yields were observed in both catalytic and non-catalytic co-pyrolysis. Potassium enhanced alkenes production with a maximum value of 54.2 % obtained from 0.8 wt%K-ACS/HDPE, indicating that potassium dispersed in char exerted catalytic effect on promoting the degradation of HDPE. Compared to ACS/HDPE, the catalytic co-pyrolysis of K-ACS/HDPE over HZSM-5 pro-duced higher yield of mono-aromatics in the range of 77.3-82.5 % due to the fact that potassium optimized the co-pyrolysis intermediates diffused into HZSM-5 zeolite. The coupling effect of potassium and HZSM-5 also favored the selectivity of toluene and xylene while suppressed the selectivity of alkylnaphthalene. The ICP-MS result showed that only a trace amount of potassium was deposited on the HZSM-5 zeolite during the ex-situ catalytic co-pyrolysis process. The BET surface area and acidity of spent HZSM-5 zeolites increased and the coke amount decreased with the potassium concentration, indicating that potassium alleviated the deactivation of HZSM-5 zeolite by changing the yield and distribution of co-pyrolysis intermediates.