POTENTIAL OF PROSOPIS JULIFLORA FOR BIO-ETHANOL PRODUCTION
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Date
2015-06-30
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Lignocellulose-to-ethanol conversion is a promising technology to supplement corn-based ethanol production. Prosopis juliflora, a perennial deciduous thorny shrub and considered to be a problematic weed has been recently suggested as one of the alternative lignocellulosic biomass materials for long and sustainable production of cellulosic ethanol. Hence, an investigation was conducted to study the potential of Prosopis juliflora for bioethanol production. Sodium hydroxide (NaOH) pretreatment of Prosopis juliflora woody substrate was performed at 100, 120 and 140 °C in an autoclave at 15 psi, with combination of residence times (15, 30, and 60 min) and NaOH concentrations (1, 2 and 3%). The desirability index of solids recovery, acid insoluble lignin and reducing sugar content were found to be 0.9935, 0.7348 and 0.9719 respectively for pretreatment combination of 2.0% NaOH, 60 min at 120 °C with highest combined desirability of 0.7303. Hydrolysis was carried out with CTec2 Cellulase enzyme at different loading levels (0, 15 and 30%) on the untreated and selected pretreated samples for fermentable sugar production. As the enzyme loading level increased, the sugar yield also increased for all the untreated and pretreated samples hydrolyzed. The maximum rate of saccharification (26.07 mg/g/h) was attained at 12 h for sample pretreated at 120 °C, 60 min, 2% NaOH loaded with 30% enzyme. A total maximum yield of saccharification (583.9 mg/g) was achieved after 72 h of incubation, with a saccharification rate of 8.11 mg/g/h. The maximum carbohydrate conversion of 90.86% was recorded for the sample pretreated at optimal conditions (120 °C, 60 min, 2% NaOH) loaded with 30% enzyme. Batch fermentations of enzymatic hydrolyzates were carried out with 5 g/l Saccharomyces cerevisiae at 30 °C. Fermentation of hydrolyzate containing 46.71 g sugar/l sample gave maximum ethanol of 21.84 g/l with a yield of 0.47 g/g sugar (0.27 g/g dry biomass) and productivity (0.91 g/l/h) after 24 h of fermentation.
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