Microwave assisted chemical pretreatment of Miscanthus under different temperature regimes

Abstract

Background: Miscanthus is a major bioenergy crop in Europe and a potential feedstock for second generation biofu-els. The most efficient and realistic method to produce fermentable sugars from lignocellulosic biomass is by enzy-matic hydrolysis, assisted by thermo-chemical pretreatment. Recently, microwave technology has drawn growing attention, because of its unique effects and performance on biomass. Result: In this work, microwave energy was applied to facilitate NaOH and H 2 SO 4 pretreatment for Miscanthus under different temperatures (130-200 °C) for 20 min. The yields of reducing sugars from Miscanthus during the pretreat-ment process increased up to 180 °C and then declined with increasing temperature. Out results here showed a remarkable sugar yield from available carbohydrate (73 %) at the temperature of 180 °C by using 0.2 M H 2 SO 4. In comparison with conventional heating pretreatment studied at same temperature with same biomass material, the reducing sugar release in this study was 17 times higher within half the time. It was highlighted that the major sugar component could be tuned by changing pretreatment temperature or pretreatment media. Optimally, the glucose and xylose yield from available carbohydrate are 47 and 22 % by using 0.2 M H 2 SO 4 and NaOH respectively when temperature was 180 °C. The digestibility of pretreated Miscanthus was 10 times higher than that of untreated biomass. 68-86 % of the lignin content was removed from biomass by 0.2 M NaOH. Simultaneous saccharification fermentation (SSF) results showed an ethanol production of 143-152 mg/g biomass by using H 2 SO 4 /NaOH microwave assisted pretreatment, which is 7 times higher than that of untreated Miscanthus. Biomass morphology was studied by SEM, showing temperature has a strong influence on lignin removal process, as different lignin deposits were observed. At the temperature of 180 °C, NaOH pretreated biomass presented highly exposed fibres, which is a very important biomass characteristic for improved enzymatic hydrolysis. Conclusion: Compared to conventional pretreatment, microwave assisted pretreatment is more energy efficient and faster, due to its unique heating mechanism leading to direct interaction between the polar part of biomass and electromagnetic field. The results of this work present promising potential for using microwave to assist biomass thermo-chemical pretreatment.