Microwave pretreatment of rape straw for bioethanol production: Focus on energy efficiency

The energy efficiency of microwave-assisted dilute sulfuric acid pretreatment of rape straw for the production of ethanol was investigated. Different microwave energy inputs and solid loadings were tested to find economic pretreatment conditions. The lowest energy consumption was observed when solid loading and energy input were fixed at 50% (w/w) and 54 kJ (900 W for 1 min), respectively, and amounted to 5.5 and 10.9 kJ to produce 1 g of glucose after enzymatic hydrolysis and 1 g ethanol after fermentation, respectively. In general, 1 g ethanol can produce about 30 kJ of energy, and therefore, the energy input for the pretreatment was only 35% of the energy output. The approach developed in this study resulted in 92.9% higher energy savings for producing 1 g ethanol when compared with the results of microwave pretreatments previously reported.