Optimization of Alkali, Switchgrass, and Extruder Parameters for Maximum Sugar Recovery

The US Department of Energy wants to replace 30 % of transportation fossil fuel with biofuel by 2025. A viable biomass pretreatment method might be found through extrusion. Extrusion pretreatments show a significant improvement on sugar recovery from different biomass feedstocks. However, glucose and combined sugar recovery from extrusion pretreated switchgrass was less than 50 %. Extrusion combined with other pretreatment methods could improve sugar recovery from switchgrass. Low‐concentration alkali acts as delignification agent without degrading the carbohydrates. In order to evaluate the combined effect of alkali soaking and extrusion, switchgrass samples of different particle sizes were soaked at different alkali concentrations for 30 min at room temperature and then extruded, using a lab‐scale single screw extruder at various barrel temperatures and screw speeds. Statistical analyses confirmed that all the independent variables considered had significant effect on sugar recoveries. The optimum pretreatment conditions resulted in a maximum combined sugar recovery of 88 %. Switchgrass has potential as an energy crop because of its high biomass production capability. This article presents the results of sequential evaluation of alkali soaking and extrusion of switchgrass. Optimal pretreatment conditions resulted in a maximum sugar recovery of 90 % without potential fermentation inhibitors. The results show that extrusion can be a viable continuous biomass pretreatment.