Enhancement of bio-oil quality: Metal-induced microwave-assisted pyrolysis coupled with ex-situ catalytic upgrading over HZSM-5

Metal-induced microwave-assisted pyrolysis followed by ex-situ catalytic upgrading of vapors using a packed HZSM-5 bed was designed and investigated for the production of upgraded bio-oil from peanut shells. Effects of the pyrolysis method, catalyst bed temperature, and microwave power on both the product yield and the chemical composition of bio-oil were investigated. Results showed that compared with conventional pyrolysis, microwave-metal-assisted pyrolysis promoted the yield of aromatic hydrocarbons, which could be further enhanced by applying ex situ HZSM-5 bed. The catalyst bed temperature has a significant effect on the product yield, bio-oil chemical profile and coke deposits on catalyst. The bio-oil yield reached its maximum value (5.6 wt.%) at 600 degrees C, with the proportion of oxygen-free hydrocarbons of 67% and coke deposits of 0.6%. With the further increase of temperature to 700 degrees C, the proportion of oxygen-free hydrocarbons increased to 77%, that of coke deposits decreased to 0.5%, and that of the bio-oil yield decreased to 4.7 wt.%. Besides the catalyst bed temperature, higher microwave power led to higher bio-oil yield; however, the proportion of oxygen-free components decreased slightly owing to the reduction in contact time. Considering the outstanding performance in bio-oil deoxygenation, this work provides an important reference for bio-oil upgrading technology development.