Biofuel production and kinetics analysis for microwave pyrolysis of Douglas fir sawdust pellet

Microwave pyrolysis of Douglas fir sawdust pellet was investigated to determine the effects of reaction temperature and time on the yields of bio-oil, syngas, and charcoal using a central composite design (CCD) and response surface analysis. The research results indicated that thermo-chemical conversion reactions can take place rapidly in large-sized biomass pellet by using microwave pyrolysis. The yields of bio-oil and syngas were increased with the reaction temperature and time. The highest yield of bio-oils was 57.8% (dry biomass basis) obtained at 471 °C and 15 min. GC/MS analysis indicated that the bio-oils were mainly composed of phenols, guaiacols, furans, ketones/aldehydes, and organic acids. The yield of specific chemicals such as furans and phenolic compounds were highly related to the reaction temperature. The syngas contained high value chemicals, such as carbon monoxide, methane, and short chain hydrocarbons. A third-order reaction mechanism fits well the microwave pyrolysis of Douglas fir pellet with activation energy of 33.5 kJ/mol and a frequency factor of 3.03 s−1.

► High bio-oil yield from microwave pyrolysis was obtained close to conventional fast pyrolysis in optimum conditions. ► Bio-oils and syngases from microwave pyrolysis of Douglas fir sawdust pellets contained important chemicals which have high values for potential utilization. ► High selectivity and maximum yield of specific phenolic chemicals was achieved through controlling the reaction temperature and reaction time. ► A reaction pathway/mechanism of Douglas fir pellet pyrolysis was proposed. ► A reaction kinetics model fits well the microwave pyrolysis of Douglas fir pellet.