Refinery of Biomass by Utilization of Specific Effects of Microwave Irradiation

The results of application of microwave (MW) irradiation to achieve refinery of various kinds of recalcitrant biomass were summarized with special emphasis on recent innovative utilization of sensitizers for MW irradiation. The saccharification rates of lignocellulosic plant biomass consisting of softwoods, hardwoods and monocotyledons attained by the simple MW irradiation treatment were in the orders of 35-65% (softwoods), 70-80% (hardwoods) and around 80% (monocotyledons), respectively. The corresponding values of cellulose were around 69-81% (230-240 °C), while xylan was susceptible to the MW energy and easily decomposed into oligomers including xylose by heating at >150 °C, optimally at 204 °C, to give 99% solubility rate. However, the effects of the MW treatment on the agro-food byproducts varied highly depending upon their origins. These results indicate necessity of troublesome specification of the optimum condition for each case. For development of more versatile and comprehensive refinery method we tried to use sensitizers for MW irradiation.We found that hydrogen peroxide was remarkably effective for biomass refinery. Utilization of activated carbon as a sensitizer for MW irradiation was also effective for saccharification of starchy materials. Enhancement of the surface charge of the activated carbons by oxidation and preparation of microwave absorption solid acid catalysts were recommended to further enhance their effectiveness. The overall results showed the importance of four factors, less affinity toward oligosaccharides in relation with pore size, quantity of surface negative charges in addition to electro-conductivity, faster filtration ability and unknown hot spot productivity. Due to removal of the coloured materials by the activated carbons, clear saccharified solution produced by one pot conversion could be directly used for further fermentation to produce biofuels such as ethanol.