Effect of Spent Fluid Catalytic Cracking Catalysts on Syngas Yield during CO2-Assisted Gasification of Solid Waste

Abstract

This research examines the synergistic effects of using CO2, spent fluid cracking catalyst (sFCC), and municipal solid wastes (MSW) for energy and chemical production. The effect of utilizing sFCC catalysts on syngas yield and its quality and energy yield is examined during CO2-assisted gasification of MSW components, pinewood, polyethylene terephthalate (PET), polystyrene, and waste tyres. The influence of catalyst position (in-situ and quasi-in-situ) and temperature were also investigated. In all cases, the sFCC catalyst resulted in doubling the yield of hydrogen and tripling methane which reveals that the spent FCC catalyst promoted the hydrocracking and CO2 reforming of hydrocarbons in the gas phase. As such the presence of sFCC in-situ catalytic CO2-assisted gasification increased the overall syngas yield by 62.5%, for PET, by 55% for waste tyres, 3.5 % for polystyrene and no change for wood when compared to their respective non-catalytic gasification cases. A comparison of quasi-in-situ gasification to in-situ catalytic gasification showed that quasi-in-situ gasification increased syngas yield and energy yields of pinewood by 21% and 22%, respectively. For PET, the quasi-in-situ catalytic gasification increased the syngas yield and energy by 27.5% and 23.8%, respectively. In the case of waste tyres, the syngas yield and energy yields increased by 24% and 23%, respectively. For polystyrene, the quasi-in-situ catalytic gasification increased the syngas yield and energy by 103.4% and 62.5% as compared to the in-situ catalytic gasification case. This implies that quasi-in-situ catalytic gasification is more efficient and effective at increasing the syngas yield. When comparing the carbonaceous sources, materials with higher volatile matter such as polystyrene had the highest overall syngas yield compared to other materials. Materials that have a higher tendency to form char had the least increase in syngas yield and energy due to soot and coke formation over the catalyst.