Modified organosolv pretreatment for improved cellulosic ethanol production from sorghum biomass

Abstract

Development of an efficient pretreatment strategy to breakdown recalcitrant lignocellulosic biomass is a crucial prerequisite for commercial success of second generation ethanol production. Pretreatment using organic solvents has huge potential to release maximum sugars from the biomass. This study showed that the modified organosolv pretreatment using high boiling point glycerol solvent and ammonia as catalyst significantly improved the saccharification yield from sorghum (Sorghum bicolor (L.) Moench) biomass. The addition of ammonia as a catalyst helped in improving the xylan recovery with partial lignin removal and reduced the severity of the pretreatment process. The optimum concentrations of glycerol and ammonia for pretreatment were found to be 51.11% (w/w) and 5.14% (w/w), respectively, using response surface optimization methodology. The saccharification of biomass pretreated with the optimized concentration of solvent at 120 °C for 1 h resulted in a maximum total sugars of 421.35 mg/g. Crude glycerol, being the byproduct of biodiesel industry, could be used as a cheaper solvent for the process. The ammoniacal glycerol pretreatment of a variety of feedstocks showed high efficiency of hydrolysis of cellulose and xylan. Simultaneous hydrolysis and co-fermentation (SSCF) of the ammoniacal glycerol pretreated biomass using fed-batch strategy for 20% (w/w) solids loading gave maximum ethanol concentration of 36 g/L. Low cellulase CTec2 dose of 4 U/g solid was used to hydrolyze 20% (w/w) solids loading along with the addition of xylanase and polyethylene glycol (PEG), which gave maximum reported cellulose digestibility of 72% for sorghum biomass. Thus, ammoniacal glycerol pretreatment using crude glycerol improved the sugar and ethanol yield from sorghum biomass, benefiting both biodiesel and bioethanol industry.