Utilization of Lignocellulosic Biomass

The current ethanol supply is, in the large part, derived from starch. Nevertheless, vast amounts of agricultural residues and other lignocellulosic biomass can serve as the feedstock for ethanol production. Theoretically, enough ethanol can be produced from cellulosic biomass to meet most of the liquid fuel requirements in the US. The expanded utilization of lignocellulosic biomass for ethanol production can also free starchy crops for food and other uses. In addition, less carbon dioxide emission can be realized if more ethanol can be produced from lignocellulosic biomass and if the market for ethanol as a transportation fuel can be expanded beyond the current level. 

Utilization of wood-biomass residues as well as waste polymers is the important direction of recent research activities. It is known that direct catalytic liquefaction of plant biomass can be used to produce liquid fuels and chemicals [1,2]. Co-pyrolysis and co-hydropyrolysis processes have the potential for the environmentally friendly transformation of lignocellulosic and plastic waste to valuable chemicals. 

Based on the abilities discussed above, including the simultaneous utilization of a sugar mixture comprised of glucose, xylose, arabinose, and cellobiose and tolerance toward inhibitory by-products generated during pretreatment of lignocellulosic biomass, Corynebacterium has the potential to be developed into a useful ethanologenic bacterium. 

Alonso et have eliminated pre-treatment steps to fractionate biomass. They made use of certain composition in biomass to obtain fuels and chemicals, and the rest of fraction was separated. The work used gamma-valerolactone (GVL) as solvent, and the cellulosic fraction of lignocellulosic biomass can be converted into levulinic acid (LA), while at the same conditions the hemicellulose fraction can be converted into furfural. The furfural can be separated by distillation during the reaction or can be kept in the reactor and subsequently processed to produce furfutyl alcohol and LA. The lignin was solubilized in the GVL and separated. This process not only obtains the production of fuels and chemicals by utilization of hemicellulose and cellulose, but also it benefits from the elimination of pre-treatment and extraction/separation steps. 

Pyrolysis of lignocellulosic biomass leads to an array of useful products including liquid and solid derivatives and fuel gases. At the beginning of the twentieth century, pyrolysis processes were utilized for the commercial production of a wide range of fuels, solvents, chemicals, and other products from biomass feedstocks. At the time, the dry distillation of wood for the production of charcoal was the mainstay of the chemical industry. 

R. oryzae strains have several advantageous characteristics, including the ability to directly utilize non-pretreated cellulose and hemicellulose, tolerance to the inhibitors present in acid hydrolysates of lignocellulosic biomass, and the ability to produce fumaric acid, a four-carbon unsaturated dicarboxylic acid [57]. Recently, the white rot fungus Trametes hirsute was shown to be capable of directly fermenting starch, wheat bran, and rice straw to ethanol without prior acid or enzymatic hydrolysis [58]. 

Galbe, M., Zacchi, G. Pretreatment The key to efficient utilization of lignocellulosic materials. Biomass and Bioenergy 2012, 46, 70-78. 

Cellulose is found in nature in combination with various other substances, the nature and composition of which depend on the source and previous history of the sample. In most plants, there are three major components cellulose, hemicelluloses, and lignin. Efficient utilization of all three components would greatly help the economics of any scheme to obtain fuel from biomass. Hemicelluloses, lignocellulose and lignin remaining after enzymatic degradation of the cellulose in wood would require chemical or thermal treatment - as distinct from biochemical - to produce a liquid fuel. 

The development of pretreatment technologies that are tuned to the characteristics of the biomass is still needed. Ideally, lignocellulose should be fractionated into multiple streams that contain valuable compounds in concentrations that make purification, utilization, and/or recovery economically feasible. Predictive pretreatment models should enable the design of this step to match both the biomass feedstock and the fermentation technology. 

Lignocellulose, which comprises the main construction material of plant biomass, accounts for up to 90% of all biomass and is formed in amounts of approximately 1.5 trillion tons per year [12]. Consequently, lignocellulose is much more abundant than available amounts of vegetable oils, starch, and sugar crops. In addition to the high abundance of lignocellulose, it is inedible, and its utilization as feedstock for production of biofuels and chemicals could drastically reduce challenges of food versus fuel production. 

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