Abstract
Existing bioethanol operations rely on starch-based substrates, which have been criticized for their need to displace food crops in order to be produced. As an alternative to these first generation biofuels, the use of agricultural residues is being considered to create more environmentally-benign second generation, or cellulosic biofuels. Recalcitrance of these substrates to fermentation requires extensive pre-treatment processes, which often consume more energy than can be extracted from the ethanol that they produce, so one of the priorities in developing cellulosic ethanol is an effective and efficient pre-treatment method. This study examines the use of superheated steam (SS) as a process medium by which wheat straw lignocellulosic material is pre-treated. Following enzymatic hydrolysis, it was found that 47% of the total glucose could be liberated from the substrate, and the optimal conditions for pre-treatment were 15 min in hot water (193 kPa, 119˚C) followed by 2 min in SS. Furthermore, a preliminary relative economic analysis showed that the minimum ethanol selling price (MESP) was comparable to that obtained from steam explosion, a similar process, while energy consumption was 22% less. The conclusion of the study is that SS treatment stands to be a competitive pre-treatment technology to steam explosion.
Highlights
Growing concern surrounding the scarcity of fossil fuels has spurred research into alternative renewable sources for high energy density liquid fuels, such as biologically-derived ethanol
This study examines the use of superheated steam (SS) as a means of pretreating wheat straw prior to enzymatic hydrolysis without the use of chemical catalysts and at a potentially reduced energy expenditure
high performance liquid chromatography (HPLC) analysis of the hydrolyzed samples showed that the glucose yields increased significantly as a result of SS pre-treatment
Summary
Growing concern surrounding the scarcity of fossil fuels has spurred research into alternative renewable sources for high energy density liquid fuels, such as biologically-derived ethanol. Existing operations rely heavily on sugar- and starch-based ethanol production from dedicated crops such as corn in the United States and sugarcane in Brazil, though the former has been criticized in terms of the net energy balance achieved by the conversion. Association of Official Agricultural Chemists Association of American Feed Control Officials High performance liquid chromatography Minimum ethanol selling price National Renewable Energy Laboratory Superheated steam process (Shapouri et al, 2002). Among the manifestations of these concerns is the shift from sugar and starch substrates (referred to as 1st generation biofuels) to cellulosic substrates (2nd generation biofuels), obtained from agricultural residues and byproducts, forgoing the need to displace existing food crops for the purpose of fuel production
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