This review catalogs the process research in direct thermochemical conversion of biomass to liquid hydrocarbon fuels. Subject areas include pyrolysis, high-pressure liquefaction, upgrading of both pyrolysates and high-pressure oils, supporting analytical and basic research, and technoeconomic assessments. Much progress is presented for the time period from 1983 to 1990. The pyrolytic processes with lower investment costs and higher yields of more oxygenated oils are moving more quickly forward in development. Further development is still required for the upgrading processes for the production of hydrocarbons from the primary oils. Based on these developments, potential exists for economical production of substitute liquid hydrocarbon fuels and chemicals from biomass.

Glossary of TermsFast pyrolysis -thermal conversion in the absence of oxygen at short residence time, for woody biomass typical conditions are <2 seconds at ~500 °C Hydrothermal -processing in hot pressurized water Bio-oil -liquid product of fast pyrolysis Biocrude -liquid oil product from hydrothermal liquefaction Upgrading -multi-step hydroprocessing to convert bio-oil in liquid hydrocarbon products Hydrotreating -single-step hydroprocessing to convert biocrude into liquid hydrocarbon products Hydroprocessing -chemical reaction with hydrogen gas, typically a catalytic process operated at elevated pressure, usually to remove heteroatoms, remove unsaturation, and reduce molecular weight.Heavy hydrocarbon --hydrocarbon product distilling at temperatures higher than diesel Nth plant -commercial plant operating an established process, not a pioneer plant 14 http://www.fortum.com/en/mediaroom/Pages/fortum-invests-eur-20-million-to-build-the-worlds-first-industrialscale-integrated-bio-oil-plant.aspx 15

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Poplar wood, when heated rapidly (70‐90 s) in water to 350°C and quenched, yields oil in 55 per cent mass yield. Approximately 75 per cent of the wood carbon and hydrogen is retained in the oil. The oil contains 25 per cent oxygen (wood contains 45 per cent). Extended reaction significantly lowers yields which are the same in the presence of both nitrogen and hydrogen atomsopheres. Nickel carbonate addition lowers yields significantly. Experiments have been limited to wood particles less than 35 mesh (0.73 mm grid) but heat transfer studies are being extended to larger particles.