ABSTRACT
Increasing concerns related to energy, economic, and environmental security have led to increasing attention on renewable energy in recent years. Fossil-based energy such as liquid fuel, coal, and natural gas accounts for 82% of the world’s total commercial energy. These energy reserves are declining at an increasing rate; there might be shortages in the near future. This increasing dependence on fossil fuels has led to increasing carbon emissions and increasing global warming. The limited supply of fossil-based resources, yearly increases in the price of fossil-based fuels, and an increasing demand for energy due to rising population and climate change have spurred researchers to develop new and alternative energy technologies.
Among other energy resources, for example, solar and wind energy, biomass energy resources are extremely promising. They are widespread and cheaply available, and they constitute approximately 10% of the global primary energy demand.
Biomass is any organic matter of biological origin. Major biomass resources include agricultural residues, agroprocessing by-products, food waste, and energy crops. These biomass materials have recently received much attention as renewable alternatives to fossil-derived fuels, as they are ecofriendly and release low concentrations of toxic chemicals such as carbon dioxide and sulfur compared to conventional fossil fuels. The major difficulty in producing biofuels from this biomass includes the high cost involved in pretreating the biomass. Pretreatment has been seen as the most important step in the conversion of biomass to biofuels. Pretreatment selection process configuration requirements and impacts the enzyme hydrolysis rate, enzyme loading, and fermentation process variables. In past decades, a great deal of interest focused on physical, chemical, and thermal pretreatment strategies for the production of biofuels. Various methods such as acid, alkali, steam explosion, and ammonia fiber expansion (AFEX) have been used to improve enzyme hydrolysis. However, most of these methods require intensive water resources and produce undesirable by-products.
Microwave treatment is an environmentally benign technology and an energy-efficient way to pretreat biomass. Selectively heating the most polar part results in enhanced disruption of recalcitrant lignocellulose. This improved destruction of the crystalline structure of lignocellulosic biomass affects the supermolecular structure of biomass and helps improve reactivity. This ultimately results in rapid and selective heating and raises the possibility of developing a compact process. This technique is a well-established thermo-chemical method for accelerating and improving chemical reactions, as energy is directly imparted to the reactant. Microwave-based pretreatment helps deliver a morphologically improved material for hydrolysis. Compared to conventional heating, the electromagnetic radiation is transformed into heat and provides a uniform distribution of heat throughout the volume of material, which is due to the combination of thermal effects, specific microwave effects, and nonthermal effects. The ability to complete chemical reactions in a short time is the main advantage of this technique. This chapter critically assesses microwave-assisted pretreatment, the influencing process parameters, and biomass reactions that are involved in the production of biofuel. This assists in analyzing the role and mechanism behind microwave intensification and how it can be exploited in future biorefineries.
