Hydrolysis of cellulose to glucose by solid acid catalysts

As the main component of lignocelluloses, cellulose is a biopolymer consisting of many glucose units connected through β-1,4-glycosidic bonds. Breakage of the β-1,4-glycosidic bonds by acids leads to the hydrolysis of cellulose polymers, resulting in the sugar molecule glucose or oligosaccharides. Mineral acids, such as HCl and H2SO4, have been used in the hydrolysis of cellulose. However, they suffer from problems of product separation, reactor corrosion, poor catalyst recyclability and the need for treatment of waste effluent. The use of heterogeneous solid acids can solve some of these problems through the ease of product separation and good catalyst recyclability. This review summarizes recent advances in the hydrolysis of cellulose by different types of solid acids, such as sulfonated carbonaceous based acids, polymer based acids and magnetic solid acids. The acid strength, acid site density, adsorption of the substance and micropores of the solid material are all key factors for effective hydrolysis processes. Methods used to promote reaction efficiency such as the pretreatment of cellulose to reduce its crystallinity and the use of ionic liquids or microwave irradiation to improve the reaction rate are also discussed.