ABSTRACT
Many structural and compositional hinder the hydrolysis of polysaccharides present in biomass to sugars that can later be converted to energy and non-energy products. Overcoming the recalcitrance of biomass is a key step in the production of biofuels and biochemicals. The main goal of pretreatment is to overcome this recalcitrance, to separate cellulose, hemicelluloses and lignin, and to make polysaccharides more accessible. This goal is achieved by degrading and removing hemicelluloses and lignin, by reducing the crystallinity of cellulose and by increasing the porosity of the biomass material.
Pretreatment technologies aiming at producing for example, bioethanol must meet the following requirements: (1) improve the formation of sugars, (2) avoid the degradation or loss of carbohydrates, (3) avoid the formation of byproducts that are inhibitory to microbial fermentation, (4) allow lignin recovery to generate valuable co-products, and (5) be cost-effective.
During the last years, a variety of pretreatment methods that change the physical and chemical structure of the components of lignocellulosic biomass and improve hydrolysis rates have been developed. The main pretreatment methods include liquid hot water, acid hydrolysis, alkaline hydrolysis, organosolv/solvent fractionation, oxidative delignification, room temperature ionic liquids, steam explosion, ammonia pretreatments, carbon dioxide explosion, mechanical/alkaline pretreatments, and biological pretreatments.
