Sequential acid and alkaline pretreatment of rice straw for bioethanol fermentation
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Author list: Weerasai K., Suriyachai N., Poonsrisawat A., Arnthong J., Unrean P., Laosiripojana N., Champreda V.
Publisher: North Carolina State University
Publication year: 2014
Journal: BioResources (1930-2126)
Volume number: 9
Issue number: 4
Start page: 5988
End page: 6001
Number of pages: 14
ISSN: 1930-2126
Languages: English-Great Britain (EN-GB)
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Abstract
Pretreatment is a prerequisite step for increasing the enzymatic digestibility of agricultural residues for conversion to fuels and chemicals in biorefineries. In this study, a sequential acid and alkaline process was developed for pretreatment of rice straw for ethanol fermentation. Effects of key parameters in acid pretreatment were studied using a full factorial design model, which showed the higher influence of time compared to acid concentration and temperature on reducing sugar yields. The combined sequential process involved an initial hemicellulose solubilization by dilute acid using 1% (w/v) H2SO4 at 125 ฐC for 10 min, followed by alkaline delignification using 1.25% NaOH at 90 ฐC for 10 min. Under these conditions, a glucose recovery yield of 70.9% from saccharification of the cellulose enriched fraction was obtained with 2- to 4-fold savings in chemical usage as compared with single-step processes. Scanning electron microscopy revealed modification of biomass micro-structure and increases in reactive surface area. Simultaneous saccharification and fermentation of the solid residues by Saccharomyces cerevisiae, using 25 FPU/g Accelleraseฎ 1500, led to a final ethanol concentration of 21.0 g/L with the productivity of 0.27 g/L/h, equivalent to 84.6% theoretical yield. The results indicate the potential of the sequential process for increasing pretreatment efficiency and allowing stepwise separation of lignocellulose components for multi-product biorefineries.
Keywords
Alkaline pretreatment, Dilute acid pretreatment, Ethanol, Lignocellulose, Rice straw
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