Pretreatment Methods for Overcoming Biomass Recalcitrance

A large amount of lignocellulosic waste biomass is generated which can be effectively valorized to fuels and other chemicals. The major structural components of lignocellulosic biomass are cellulose, hemicellulose, and lignin. In the conversion of lignocellulosic biomass to value-added products, the pretreatment process is a crucial step for annihilation. The pretreatment efficiency depends on the recalcitrance of the biomass. A pretreatment method modifies the structural impediments to the enzymatic saccharification, thereby enhancing the rate of hydrolysis. Various conventional pretreatment methods such as physical and chemical processes have been adopted for lignocellulosic biomass over the years. Physical pretreatment methods such as milling, grinding, pyrolysis, steam explosion, and radiations (microwave, ultrasonic) break the hydrogen bond and soften the fibers in the biomass. Chemical pretreatments of biomass by acid, alkali, organosolv, ionic liquid or deep eutectic solvent delignify and reduce the crystalline structure of cellulose making it accessible for enzyme hydrolysis. However, other pretreatment methods such as physicochemical, biological, and a combination of pretreatments have also been implemented in the lignocellulosic biorefineries. The need of the hour is to develop a green, biodegradable, nontoxic, efficient, and cost-effective pretreatment process for a sustainable lignocellulosic biorefinery.