Synergistic effect of Hami coal and polystyrene on products properties during co-pyrolysis: Evaluation on the contribution of different interaction sources

Abstract

Co-pyrolysis with low rank coal is an important way to treat waste plastics and recycle them into valuable materials. Complex interactions between volatiles-feedstock, volatiles-volatiles, and volatiles-char co-exist during co-pyrolysis, which will influence the synergistic effects and have not been extensively understood. In this work, some new feedstock configurations were conducted in a fixed-bed reactor to explore the contribution of these complicated interactions between different sources to the synergy effect observed during co-pyrolysis of Hami coal (HM) and polystyrene (PS). Results show that the interaction between PS-volatiles and HM-volatiles is found to be a dominant contributor to tar lightening in co-pyrolysis, which accounts for 5.67 wt% increase in the content of gasoline fractions (<180 °C) compared to the theoretical calculated value. Meanwhile, the content of gasoline fractions in tar increases with the enhancement of the interaction between volatiles and unreacted-HM. The volatiles and unreacted-HM interaction is the main contributions to synergy in aromatization of char, while the PS-volatiles and HM-char interaction plays an opposite role. The co-pyrolysis of HM-char locating on the top of PS also reveals the catalytic activity of HM-char on PS decomposition. Furthermore, the interaction between unreacted-HM and PS-melt is not conducive to the production of gas, but favorable to the production of char with high aromaticity. These results provide a valuable supplement for the understanding of the interaction mechanisms during co-pyrolysis, and also help to enhance synergistic pathways of the target products while simultaneously reducing inhibitory interactions.