Abstract
Miscanthus is a major bioenergy crop in Europe and a potential feedstock for second generation biofuels. The most efficient and realistic method to produce fermentable sugars from lignocellulosic biomass is by enzymatic hydrolysis, assisted by thermo-chemical pretreatment. Recently, microwave technology has drawn growing attention, because of its unique effects and performance on biomass. In this work, microwave energy was applied to facilitate NaOH and H2SO4 pretreatment for Miscanthus under different temperatures (130–200 °C) for 20 min. The yields of reducing sugars from Miscanthus during the pretreatment 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 H2SO4. 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 H2SO4 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 H2SO4/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. 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.
Highlights
Miscanthus is a major bioenergy crop in Europe and a potential feedstock for second generation biofu‐ els
High temperature leads to the formation of compounds that are harmful to subsequent hydrolysis and fermentation [38]
According to Fan et al, when the temperature is below 180 °C the CH2OH groups on cellulose are hindered from interacting with microwaves when they are strongly involved in hydrogen bonding within both the amorphous and crystalline regions
Summary
Miscanthus is a major bioenergy crop in Europe and a potential feedstock for second generation biofu‐ els. A number of pretreatments have been studied to improve the yields of fermentable sugars from cellulose and hemicellulose, such as mechanical [4, 5], steam explosion [6, 7], ammonia fibre explosion [5, 8], hot water [9], sub/supercritical fluid [10,11,12], ozone [5], biological [5], ultrasound [13], acid or alkaline pretreatments [14,15,16], ionic liquid [17, 18] and so forth. It is worth mentioning that novel pretreatment media, such as sub/supercritical fluids and ionic liquid are drawing attention due to their unique solvent properties. Compared with ionic liquid and sub/supercritical fluids pretreatments, microwave assisted pretreatment offers great advantages because of its unique heating mechanism. It has been claimed that the electromagnetic field used in the microwave might create non-thermal effects that accelerate the destruction of the crystal structures [31]
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
