Optimization of alkali soaking and extrusion pretreatment of prairie cord grass for maximum sugar recovery by enzymatic hydrolysis

Apart from corn stover and switchgrass, there are several other types of biomass that have comparable yield and can be grown across the country, and prairie cord grass (PCG) is one among them. Biomass pretreatment is an essential step in the conversion of biomass to bioethanol. Till date, no perfect conversion technology has been established for biofuel production from biomass on commercial scale. Extrusion pretreatment of PCG showed significant improvement on sugar recovery (63.5%). However, there is still room to improve sugar recovery from PCG by combining with alkali soaking. The current study was undertaken to investigate the influence of alkali (NaOH) concentration on sugar recovery and optimize extruder barrel temperature, screw speed, and particle size for maximum sugar recovery. In order to evaluate the sequential effect of alkali soaking and extrusion, PCG (2–10 mm) was soaked at different alkali concentrations (0.5–2.5%, w/v NaOH) for 30 min at room temperature and then extruded using a lab scale single screw extruder at various barrel temperatures (45–225 °C) and screw speeds (20–200 rpm). All the independent variable had a strong influence on sugar recovery and it was confirmed through statistical analyses. The proposed quadratic model to predict sugar recoveries had high F and R2 values with low p value adequately representing the relationship. The optimal pretreatment condition 114 °C barrel temperature, 122 rpm screw speed, 1.70% alkali concentration, and 8 mm particle size resulted a maximum glucose, xylose and combined sugar recoveries of 86.8, 84.5, and 82%, respectively, by enzymatic hydrolysis.

Research highlights
► Optimization of alkali soaking and extrusion pretreatment of prairie cord grass for maximum sugar recovery by enzymatic hydrolysis.
► Biomass pretreatment is an essential step in the conversion of biomass to Bioethanol and extrusion is one of the promising continuous methods.
► In order to improve sugar recovery from prairie cord grass, influence of alkali soaking, extruder barrel temperature, screw speed, and particle size were studied.
► Statistical analyses revealed that all the independent variable had a strong influence on sugar recovery.
► The proposed quadratic model to predict sugar recoveries had high F and R2 values with low p value adequately representing the relationship.
► The optimal pretreatment condition 114 °C barrel temperature, 122 rpm screw speed, 1.70% alkali concentration, and 8 mm particle size resulted a maximum glucose, xylose and combined sugar recoveries of 86.8, 84.5, and 82%, respectively, by enzymatic hydrolysis.