Influence of temperature on the products from the flash pyrolysis of biomass

Biomass in the form of mixed wood waste was pyrolysed in a fluidized bed reactor at 400, 450, 500 and 550 degrees C. The char, liquid and gas products were analysed to determine their elemental composition and calorific value. In particular, the liquid products were analysed in detail to determine the concentration of environmentally hazardous polycyclic aromatic hydrocarbons (PAH) and potentially high-value oxygenated aromatic compounds in relation to the process conditions. The gases evolved were CO2, CO and C-1-C-4 hydrocarbons. The liquids were homogeneous, of low viscosity and highly oxygenated. The molecular weight range of the liquids was 50-1300 u. Chemical fractionation of the liquids showed that only low quantities of hydrocarbons were present and the oxygenated and polar fractions were dominant. PAH up to MW 252 were present in the liquids; some of the PAH identified have been shown to be carcinogenic and/or mutagenic. The concentration of PAH in the liquids increased with pyrolysis temperature, but even at the maximum pyrolysis temperature of 550 degrees C the total concentration was < 120 ppmw. The liquids contained significant quantities of phenolic compounds and the yield of phenol and its alkylated derivatives was highest at 500 and 550 degrees C. Some of the oxygenated compounds identified are of high value. Copyright (C) 1996 Elsevier Science Ltd.