Investigating use of metal-modified HZSM-5 catalyst to upgrade liquid yield in co-pyrolysis of Wheat Straw and Polystyrene

Abstract

Co-pyrolysis of wheat straw (WS) and polystyrene (PS) at a weight ratio of 1:1 was conducted in a fixed bed reactor. The effect of ex-situ application of HZSM-5 and its metal modified versions (MZSM-5s) on organic liquid product (OP) upgradation was explored. MZSM-5s were synthesized by adding metal (Co, Ni, Zn and Fe) oxides to parent HZSM-5 catalyst through wet impregnation method. The catalysts were characterized by XRD, SEM-EDS, and N2 physisorption. In first phase, the effect of co-pyrolysis temperature (500-650 oC) on product distribution was evaluated. The liquid yield varied in the range of 49–55 wt.%, with a maximum at 550 oC. In second phase, results obtained from vapor catalyzed co-pyrolysis conducted at 550 oC showed that impregnation of HZSM-5 with metals resulted in relatively higher OP oil yield as compared to parent HZSM-5. Co-ZSM-5 produced maximum OP yield (39.0%) followed by Zn-ZSM-5 (38.2%), Fe-ZSM-5 (37.7%) and Ni-ZSM-5 (36.1%). Whilst, the coke yield was reduced for all MZSM-5s by approximately 50%. Moreover, the addition of metals significantly favored the catalytic selectivity towards monoaromatic hydrocarbons (MAHs). Fe-ZSM-5 proved to be most effective catalyst exhibiting the highest de-oxygenation potential (97.4%) and displaying maximum MAHs content (83.3%). Simultaneously, MZSM-5s reduced undesirable polyaromatic hydrocarbons (PAHs) yield noticeably.