Catalytic co-conversion of glycerol and proton-donor species to gasoline-range aromatics over alumina
University of New Brunswick
Glycerol is the main by-product of the biodiesel production process. Saturation of this by-product in the market would negatively affect the growth of biodiesel production industry. Due to complexities in the purification processes of crude-glycerol, less costly chemical conversion of glycerol to value-added products and feedstocks such as propenal and aromatics has gained more attention recently. In this work, the influence of co-feeding proton-donor and olefin-donor species on the catalytic conversion of glycerol over alumina catalyst to gasoline-range aromatics is studied. During the individual catalytic conversion of glycerol over alumina, because of the shortage of proton-donor intermediates in the process and high activity of glycerol on alumina at 470℃, glycerol mostly leads to form high carbon deposit content and aqueous phase stream, but less liquid organic production. Introducing methanol and ethanol as compound models of alcohols, and dodecane and hexadecane as compound models of long-chain alkanes next to glycerol remarkably decreases the formation of undesired stream, while selectivity to aromatics substantially increases. In terms of liquid aromatics generation and restricting the excessive carbonization on the catalyst surface, co-feeding 25 wt.% hexadecane with 75 wt.% glycerol has the highest efficiency among the selected compound models; with increasing the liquid aromatics selectivity from 17.7% to 42.5%. Additionally, Co-processing the latter compound model, noticeably shifts the distribution of produced aromatics from heavy undesired aromatics range to the gasoline-range aromatics such as xylenes and toluene. The potential influence of hexadecane on the glycerol to aromatics reaction pathway over alumina catalyst is also proposed, and the effective reactions between glycerol and hexadecane intermediates are discussed. It is also found that selecting a very high or low operational temperature would inversely affect the optimization of aromatics formation through the co-processing runs of glycerol and hexadecane.