Co-gasification of high-density polyethylene and pretreated pine wood

Abstract

Co-gasification of biomass and plastic blends has been extensively studied, however the effect of AAEMs (alkali and alkaline earth metals) in biomass on the co-gasification behavior still remains unknown. Acid and alkali pretreatment were used here to remove or introduce the AAEMs in biomass by ion-exchange method. SEM was used to obtain morphological characteristics of three pretreated pine wood (PW) samples; TG analysis of pure and blend feedstocks was used to examine the decomposition behavior. CO2 assisted co-gasification of high-density polyethylene (HDPE) and pretreated PW samples at different blend ratios were conducted in a fixed bed reactor, and the resulting flow rate and yields of H2, CO, light hydrocarbons (HC), total syngas, and output energy determined. Synergetic effects from these blends during co-gasification were evaluated by comparing the experimental results with the weighted results from individual components. Results showed that the presence of AAEMs in biomass resulted in increased char yield and char reactivity, that enhanced the syngas yield and energy output. However, acid pretreatment with low AAEM content showed the opposite trend. Irrespective of the biomass pretreatment, synergistic effect was found in the yield of each syngas component, total syngas, and energy yield during its co-gasification with HDPE plastic. The synergy during co-gasification of HDPE and alkali treated PW was more pronounced at high PW content, while those from acid pretreatment preferred low PW fraction. The highest energy yields of 28.1, 34.3 and 30.1 kJ/g were obtained from co-gasification of HDPE and water, acid and alkali pretreated PW samples at PW fraction of 44%, 22% and 55%, respectively. Maximum synergistic effect with energy yield of 69% was obtained from the gasification of HDPE and acid pretreated PW at 27% PW fraction. These results help to our understanding of the influence of biomass pretreatment on co-gasification of biomass-plastic mixtures. The results also help to achieve relatively stable energy output for varying mixtures of plastic and biomass.