Effect of Torrefaction on Bio-oil Upgrading over HZSM-5. Part 1: Product Yield, Product Quality, and Catalyst Effectiveness for Benzene, Toluene, Ethylbenzene, and Xylene Production

A three-step bio-oil production process involving torrefaction pretreatment (at 225, 250, or 275 °C with a 20 min hold time), pyrolysis (at 500 °C with two heating rates), and secondary catalytic processing over HZSM-5 (at 400, 450, or 500 °C) was studied to determine process effects, particularly of torrefaction, on the yield of liquid and aromatic hydrocarbons and the quality of upgraded bio-oil. When bio-oils derived from torrefied biomass were catalytically cracked, average yields (%, w/w of feed) of reactor char (100% reduction), catalyst coke (21.4%), and catalyst tar (8.1%) were significantly reduced relative to the best-case conditions using non-torrefied feedstock. The reduction in coke (%, w/w of feed) as a result of torrefaction was 28.5% relative to the respective control for slow-pyrolysis bio-oil upgrading and 34.9% for fast-pyrolysis bio-oil upgrading. The concentration of aromatic product (benzene, toluene, ethylbenzene, and xylene, i.e., BTEX) was highest at 95 g L –1 for upgraded (at 500 °C) fast-pyrolysis bio-oil derived from biomass torrefied at 275 °C. Catalyst effectiveness for BTEX production significantly increased with increased torrefaction and catalytic cracking temperatures.