Abstract
Cotton stalks (CS) are considered a good candidate for fuel-ethanol production due to its abundance and high carbohydrate content, but the direct conversion without pretreatment always results in extremely low yields due to the recalcitrant nature of lignocelluloses. The present study was undertaken to investigate the effect of various chemical and physicochemical pretreatment methods, i.e., alkali, microwave-assisted acid, organosolv, hydrothermal treatment, and sequentially organosolv and hydrothermal pretreatment, on chemical composition of CS and subsequent ethanol production applying pre-hydrolysis and simultaneous saccharification and fermentation (PSSF) at high solid loading. The best results in terms of ethanol production were achieved by the sequential combination of organosolv and hydrothermal pretreatment (32.3 g/L, using 15% w/v substrate concentration and 6 h pre-hydrolysis) with an improvement of 32% to 50% in ethanol production compared to the other pretreatments. Extending pre-hydrolysis time to 14 h and increasing substrate concentration to 20% w/v, ethanol production reached 47.0 g/L (corresponding to an ethanol yield of 52%) after 30 h of fermentation.
Highlights
IntroductionAccumulation of atmospheric CO2 , increasing energy demand, national energy security and rural economic development are the main reasons bringing about a transitional change from a fossil fuel based economy to a more sustainable carbon-neutral bio-economy, where agriculture will continue to provide food security and biomass as a renewable raw material for industry [1,2]
Cellulose content of native Cotton stalks (CS) ranged from 30% to 39.8% (w/w) while hemicellulose from 10.7% to 16.7% (w/w)
Cotton stalk can be a promising feedstock for bio-ethanol production and preferably suited to the biorefinery approach due to its worldwide abundance, its high carbohydrate content and the fact that it does not compete with the land available for food and feed production
Summary
Accumulation of atmospheric CO2 , increasing energy demand, national energy security and rural economic development are the main reasons bringing about a transitional change from a fossil fuel based economy to a more sustainable carbon-neutral bio-economy, where agriculture will continue to provide food security and biomass as a renewable raw material for industry [1,2]. Like agricultural crop residues such as wheat straw, corn stover, rice straw, and cotton stalks, forestry residues, grasses, sawdust, wood chips offers a promising source for biofuels because it is abundant, inexpensive and does not compete with food and feed applications. Cotton stalk (CS), a by-product of cotton production, generated in huge volumes annually, approximately 2 metric tons of dry matter/ha, is a major low-cost source of sugars that can be converted into bio-based products such as fuel ethanol [6]
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