Lignocellulosic biomass

Lignocellulosic biomass^[1] refers to plant biomass that is composed of cellulose and hemicellulose, and lignin. The carbohydrate polymers (cellulose and hemicelluloses) are tightly bound to the lignin, by hydrogen and covalent bonds. Biomass comes in many different types, which may be grouped into four main categories: wood residues, including sawmill and paper mill discards, municipal paper waste, agricultural residues, including corn stover (stalks and straw) and sugarcane bagasse, and dedicated energy crops, which are mostly composed of tall, woody grasses.

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Application

Fermentation of lignocellulosic biomass to ethanol is an attractive candidate as a source of renewable, alternative energy to our rapidly depleting stores of fossil fuels. Biomass is a carbon neutral source of energy, since it comes from dead plants, which means that the combustion of ethanol produced from lignocelluloses will produce no net carbon dioxide in the earth’s atmosphere. Also, biomass is readily available, and the fermentation of lignocelluloses provides an attractive way to dispose of many industrial and agricultural waste products. Finally, lignocellulosic biomass is a very renewable resource. Many of the dedicated energy crops can provide high energy biomass, which may be harvested multiple times each year.

One drawback to ethanol production from biomass is that the sugars necessary for fermentation are trapped inside the lignocellulose. To get the sugars, one must first remove the celluloses from the lignin, and then acid hydrolyze the newly freed celluloses to break them down into simple monosaccharides. Another stumbling block in biomass fermentation lies in the fact that a high percentage of the monosaccharides produced are pentoses, like xylose, or wood sugar, instead of hexoses, like glucose, which are easiest for yeast to ferment. More research must be done in order to make the purification of sugar more economically feasible, as well as to improve ethanol yields from pentose sugars like xylose.

References

1. ^ Lin, Yan, and Tanaka, Shuya. "Ethanol fermentation from biomass resources: current state and prospects." Applied Microbiology and Biotechnology 69.6 (2006): 627-642.