Liquid Fuel Production from Woody Biomass via Oxygen-enriched Air/CO₂ Gasification on a Bench Scale

抄録

On a bench scale, we successfully produced 16 L/d, equal to 0.1 BPD (barrel per day), of hydrocarbon liquid fuel from woody biomass throughout a proposed biomass-to-liquid (BTL) process, which consisted of gasification, wet and dry gas cleaning, water-gas shift reaction, gas compression, and Fischer-Tropsch (FT) synthesis reaction. In the oxygen-enriched air/CO₂ gasification using a downdraft fixed-bed gasifier, the addition of CO₂ to oxygen-enriched air as a gasifying agent led to an increase in both the conversion to gas on a carbon basis and the syngas content because of the enhancement of CO₂ gasification (C + CO₂ → 2CO). The CO and H₂ contents increased to 40.8 vol%, 28.7 vol% and the N₂ content decreased to 6.9 vol% monotonously with an increase in the pure oxygen flow rate. When a mixture of 19.1/63.4/17.5 vol% of N₂/O₂/CO₂ was used as the gasifying agent, the conversion to gas on a carbon basis was 90.1 C-mol% and the product gas composition was 27.9 vol% H₂, 40.4 vol% CO 21.2 vol% CO₂, 4.0 vol% CH₄, 1.0 vol% hydrocarbons with a carbon number greater than 2 (C₂+H.C.) and 5.5 vol% N₂. Feed gas with a H₂/CO ratio appropriate for the FT synthesis reaction (57.4 vol% H₂, 28.5 vol% CO, 0.9 vol% CO₂, 5.0 vol% CH₄, 1.3 vol% C₂+H.C., and 6.9 vol% N₂) was prepared through the water-gas shift reaction, desulfurization, CO₂ removal. In the FT synthesis reaction at 4 MPa and 290-320 °C using a Ru/Mn/Al₂O₃ catalyst, the CO and H₂ conversions were 73.5% and 83.9%, respectively, and the chain growth probability was 0.82; further, the selectivity and space time yield of hydrocarbons with a carbon number greater than 5 as a liquid fuel were 81.4% and 1.793 kg/(kg-cat. h), respectively.