Effect of pretreatment temperature on the yield and properties of bio-oils obtained from the auger pyrolysis of Douglas fir wood

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• Treating biomass below 300 °C does not have a major effect on product yields. • Guiacyl (G) units decrease when the biomass is heated over 300 °C. • The yield of levoglucosan reduces when the biomass was heated over 260 °C. • The yield of water increases in the whole range of temperature studied. This paper investigates the effect of thermal pretreatment temperatures between 200 and 370 °C on the yield and composition of products (bio-charm gasm water and organics) obtained when Douglas-fir wood was subsequently pyrolyzed in an auger reactor at 500 °C. The yield of products was reported for the pretreatment and pyrolysis steps separately, and for the two steps added. The maximum yield of bio-oils achieved without pretreatment was close to 59 mass%. A decrease in total liquid yield was observed when the biomass was pretreated at 300 °C. At higher temperatures, the yields of Douglas-fir primary degradation products (lignin oligomers, anhydrosugars and alkylated and methoxylated phenols) decreased. The overall water yield increased gradually to 14 mass% at a pretreatment temperature of 290 °C. The yield of lignin oligomers also decreased as the pretreatment temperature increased. A drastic reduction in the yield of methoxylated phenols derived from guaiacyl (G) was observed when the biomass was pretreated at temperatures over 300 °C. This drastic reduction in the yield of methoxylated lignin derivatives can be explained by the formation of liquid intermediates that facilitate the formation of ionic species, enhancing dehydration reactions leading to the production of o-quinone methide intermediates critical for bio-char formation.