Production of Hydrocarbon Fuels from Biomass by Catalytic Fast Pyrolysis

Catalytic fast pyrolysis is a promising technology for producing transportation liquids that are compatible with the current petroleum products and infrastructure. Catalytic fast pyrolysis involves the rapid heating of biomass at intermediate temperatures (400-600°C) and short residence times (1-2 s) in the presence of catalysts. Fast pyrolysis in the absence of catalysts can produce a liquid oil in high yield but the product is highly oxygenated (contains typically 40% O), acidic, and chemically unstable and cannot be used for transportation fuels without further upgrading. Catalysts can promote the deoxygenation of the nascent pyrolysis vapors and convert them to highly deoxygenated oil consisting mainly of hydrocarbons. Zeolite catalysts and in particular HZSM-5 have been found to give the highest yields of hydrocarbons and lowest yields of unwanted by-products such as coke. A major advantage of catalytic pyrolysis is that it can convert all of the main components of biomass - cellulose, hemicelluloses, and lignin - into hydrocarbons. We studied the liquid hydrocarbon formation from woody biomass and biomass fractions over zeolite catalysts. Similar hydrocarbon mass yields were obtained both from cellulose and lignin in micro-scale experiments. Woody biomass gave up to 36% carbon conversion to pure hydrocarbons at optimum conditions. Alkylated one-and two-ring aromatic compounds were the main products though some phenolic compounds were present at lower catalyst-to-biomass loadings as well. Oil with oxygen content of less than 3% was successfully produced in a bench-scale fluidized bed reactor.