Microwave assisted pretreatment for C4 plants in biorefinery

There is a rising global demand for energy and growing concerns about greenhouse gas emissions. Lignocellulosic biomass offers great potential for second generation bioethanol production, based on the biorefinery philosophy. It is composed of a network of interconnected polymers cellulose, hemicellulose and lignin which has evolved to develop recalcitrance against enzyme hydrolysis produced by microorganisms in nature. Therefore, pretreatment is necessary to make the biomass structure more accessible for enzyme to hydrolysis. The aim of this thesis is to demonstrate the potential of using microwave to assist thermo-chemical pretreatment for lignocellulosic biomass, namely Miscanthus, sugarcane bagasse and maize. The pretreatment process was influenced by pretreatment temperature, pretreatment media and holding time. 0.2 M -1 M H2SO4 and NaOH were used as preteatment media. Firstly, temperature optimisation was carried on Miscanthus and the results showed that 180 oC was the optimal temperature to efficiently release monosaccharides from biomass. In comparison with classic conventional heating pretreatment, microwave assisted pretreatments maximally released 12.5 times more reducing sugars during the pretreatment process. Secondly, the reducing sugar constitutions were tuned by change holding time or pretreatment media, because hemicellulose was easier to be broken down than cellulose. Xylose and glucose were selectively produced by using NaOH and H2SO4 (or FeCl3) respectively as pretreatment media. Chemical compositions and biomass morphological changes were investigated and compared. The significant removal of hemicellulose and lignin, as well as more dismantled fibre structure led to enhanced bioethanol conversion via SSF process (simultaneous saccharification fermentation). Similar study was conducted on sugarcane bagasse and maize. The performance of pretreatment media was similar. However, their optimal conditions for reducing sugar release were different, probably due to different chemical compositions percentages and biomass structure. Overall, in comparison with conventional heating pretreatment, microwave assisted pretreatment is much energy efficient and effective, showing promising potential in the biorefinery process.