دانلود رایگان مقاله تولید اتانول سلولزی از کاه برنج پیش درمانی حلال سبز

Abstract

Cellulosic ethanol production from green solvent (GS) -pretreated rice straw and the effects of green solvents on cellulase enzyme cellic ctec2 and cellobiose-fermenting yeast strain Clavispora NRRL Y-50464 was comprehensively investigated. Using choline chloride/glycerol (CC-GLY) treated rice straw, maximum reducing sugars of 226.7 g/L was obtained with a saccharification efficiency of 87.1% at 20% solids loading and 12 FPU cellic ctec2. An ethanol production of 36.7 g/L was observed from 8% of glucose within 36 h with a conversion efficiency of 90.1%. Incubation of cellulase in green solvents (CC-GLY, choline chloride/1,2-propane diol (CC-PD), choline chloride/ethylene glycol (CC-EG)) at high concentrations (up to 30%, v/v) had no inhibitory effect on cellic ctec2. Moreover, CC-GLY and CC-PD at 10% (v/v) did not affect the growth rate, sugar consumption and ethanol production from Clavispora NRRL Y-50464, while 10% (v/v) CC-EG repressed and delayed the cell growth of the microbe. While, strain Y-50464 was highly sensitive in other green reagents that were evaluated in this study. The green solvent-pretreatment efficiently removed lignin from the ricestraw and improved fermentation efficiency significantly. Green solvents with pH<3.0 inhibited of cellic ctec2 enzyme activity and growth of Clavispora strain NRRL Y-50464. When pH of the green reagents was neutralized or adjusted to pH 5.0, normal enzyme activity and cell growth was observed. Moreover, with selective green reagents i.e. CC-GLY, CC-PD, and CC-EG, cellulosic ethanol production can be accomplished using cellic ctec2 and strain NRRL Y-50464.

3. Results and discussion

3.1. Physicochemical properties of green solvents Recently we have reported few physicochemical properties for selected NADES reagents (Kumar et al., 2015). In this report, we have presented the research work on preparation and characterization of few more green solvents (Fig. S1). The conductivity profile of the green solvents varied considerably among each other. Addition of water to the green solvents showed significant variability in solvent conductivity. The conductivity of the green solvents may be correlated with their individual chemical components. The plausible reason attributed to the ionic form of the choline chloride and partial ionization of the hydrogen bond donars (acids/sugars/diols). Francisco et al. (2013a, 2013b) reported extensively on the physico-chemical properties and the effect of water and ethanol on few selected choline chloride based NADES reagents. CC-EG solvent had the highest conductivity (7.659 mS/ cm), while CC-CA showed lowest conductivity (0.081 mS/cm) (Table 2). The detailed conductivity profile of the acidic and neutral green solvents with increasing water content is shown in Fig. 1. Recently, Dai et al. (2015) evaluated the viscosity and conductivity of 16 different NADES reagents. The conductivity profile of the green solvents tested in this study was closely correlated with their study, where initially the conductivity was increased with water addition and thereafter decreased reaching a peak value. CC-OA had the highest conductivity (96.75 mS/cm) with 70% water dilution. Dai et al. (2015) also reported that increase in conductivity of NADES reagent was mainly due to the decrease in the viscosity of the solvent. The viscosity of the green solvents was suddenly dropped after addition of 20% (v/v) water and thereafter no significant change was detected. Maximum viscosity was observed with CC-MA, followed by CC-MAL (Fig. S2). The detailed viscosity measurement of CC-LA with water addition was reported recently (Kumar et al., 2015).