In situandEx situCatalytic Pyrolysis of Microalgae and Integration With Pyrolytic Fractionation

Microalgae are attractive feedstocks for biofuel production and are especially suitable for thermochemical conversion due to the presence of thermally labile constituents-lipids, starch and protein. However, the thermal degradation of starch and proteins produces water as well as other O- and N-compounds that are mixed-in with energy-dense lipid pyrolysis products. To produce hydrocarbon-rich products from microalgae biomass, we assessedin situandex situcatalytic pyrolysis of a lipid-richChlorellasp. in the presence of the HZSM-5 zeolite catalyst over a temperature range of 450-550 degrees C. Results show that product yields and compositions were similar under bothin situandex situconditions with benzene, toluene and xylene produced as the primary aromatic products. Yields of aromatics increased with increasing temperature and the highest aromatic yield (36.4% g aromatics/g ash-free microalgae) and selectivity (87% g aromatics/g bio-oil) was obtained at 550 degrees C. Also, at this temperature, oxygenates and nitrogenous compounds were not detected among the liquid products duringex situcatalytic pyrolysis. We also assessed the feasibility of a two-step fractional pyrolysis approach integrated with vapor phase catalytic upgrading. In these experiments, the biomass was first pyrolyzed at 320 degrees C to degrade and volatilize starch, protein and free fatty acids. Then, the residual biomass was pyrolyzed again at 450 degrees C to recover products from triglyceride decomposition. The volatiles from each fraction were passed through anex situcatalyst bed. Results showed that net product yields from the 2-step process were similar to the single stepex situcatalytic pyrolysis at 450 degrees C indicating that tailored vapor phase upgrading can be applied to allow separate recovery of products from the chemically distinct biomass components-(1) lower calorific value starch and proteins and (2) energy-dense lipids.