(264a) Catalytic Pyrolysis of Microalgae for High-Quality Bio-Oil Production

Pyrolysis is a thermal decomposition process of biomass at high temperatures (ca. 500 °C) in the absence of oxygen with the organic vapors condensed as pyrolysis oil. Our previous studies indicate that microalgae can be converted to an energy-dense bio-oil by pyrolysis. This technique can readily transform the whole algal biomass into biofuels without the need of oil extraction and transesterification typically being used for biodiesel production. However, algal bio-oil (31 to 36 MJ/kg), although with much higher heating values than lignocellulosic bio-oil, still requires significant modification to remove the heteroatoms (N and O) to become an acceptable transportation fuel. Catalytic upgrading using zeolites is a promising process for the direct conversion of microalgae into hydrocarbons. Several commercial and laboratory-prepared catalysts, including Y zeolite, HZSM-5 zeolite, nickel, cobalt, copper and ruthenium-substituted ZSM-5, were investigated on their effects of deoxygenation and denitrogenation. Egg albumin, starch and canola oil were used as the model compounds of protein, polysaccharide and lipid fractions in microalgae. And these model compounds and microalgae Chlorella vulgaris respectively were pyrolyzed in quartz tubes with two catalyst beds at both ends. Pyrolytic vapors passed through the catalysts and were then identified with Gas chromatography-Mass spectrometry. Results indicate that all these catalysts showed the effects of O, N removal to some extent with aromatic hydrocarbons (benzene, toluene and styrene) dominating at the highest yield of approximately 25% based on the starting algal biomass. Based on the results of model compounds, it is proposed that these catalysts eliminated the O, N-containing functional groups and advanced aromatization due to their shape-selectivity and acidic catalytic sites. Details on the reaction pathways and product distribution will be presented. The results implicate that this one-step pyrolysis/upgrading method could be a promising way to make high-quality bio-oil from microalgae.