A Feasibility Study on a Continuous-flow-type Microwave Pretreatment System for Bioethanol Production from Woody Biomass

Efficient pretreatment prior to enzymatic saccharification process is essential for profitable bioethanol production from woody biomass. Microwave pretreatment is expected as an efficient and energy-cost-saving method to enhance enzymatic susceptibility. The objective of the present study is to develop an efficient, high-volume, and continuous microwave pretreatment system toward commercially-based bioethanol production. As a feasibility study, we developed prototypes of a continuous-flow-type microwave pretreatment system for bioethanol production from woody biomass. A unit of the microwave irradiation sections of a continuous-flow-type microwave pretreatment system was designed with a 3D electromagnetic simulator. Prototype experiments and quantitative estimation of energy balance were also conducted. Microwave pretreatment provided 45.9% of the total saccharide yield woody biomass weight by electric consumption of 552 kJ; whereas conventional heating pretreatment provides 43.6 % of the total saccharide yield by 498 kJ, when the mixture was composed of 70 g of woody biomass (Japanese cedar sapwood chips) and 770 g of solvents (ethylene glycol : phosphoric acid = 95 : 5). We estimated 14.8g of bioethanol and 439 kJ of bioethanol energy could be produced by the prototype microwave pretreatment. Although heat dissipation from the metal pipe to the air and the ratio of solvents to woody biomass are immediate problems, microwave is a future potential energy-saving pretreatment method without loss of the saccharide yield.