Effects of Ultrasonic Treatments on Cellulose in Cellulosic Biofuel Manufacturing: A Literature Review

Cellulosic biofuels are one type of renewable energy, and have been proposed to replace traditional liquid transportation fuels. Cellulosic biomass is the feedstocks in cellulosic biofuel manufacturing. Cellulose accounts for approximately 30% of the total weight in cellulosic biomass. Glucose, one type of monosaccharide convertible to ethanol, can be obtained by hydrolyzing the polymeric structure of cellulose. Currently enzymatic methods are the most common for the hydrolysis of cellulose. However, the low efficiency of enzymatic hydrolysis increases production cost and hinders the large-scale manufacturing of cellulosic biofuels. Ultrasonic treatments applied on cellulosic biomass were found to improve the efficiency of hydrolysis and subsequently increase the sugar yield of hydrolysis. To understand the effects of ultrasonics on cellulose, investigations have been conducted on the effects on cellulose characteristics caused by ultrasonic treatments during hydrolysis. This paper reviews the effects of ultrasonic treatments on cellulose during hydrolysis in terms of sugar yield and some characteristics of cellulose, such as accessibility, crystallinity, degree of polymerization, and morphological structure.