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

Abstract

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 %.

Application of Response Surface Methodology to Optimize Alkali Concentration, Corn Stover Particle Size, and Extruder Parameters for Maximum Sugar Recovery

“…No glycerol was found in any of the pretreatment combinations in contrary to the results reported by Karunanithy and Muthukumarappan (Karunanithy & Muthukumarappan, 2010c, 2011a, 2011b, 2011c, 2010a, 2010b.In addition, no furfural and HMF were found in any of the pretreated corn stover samples. The possible reason could be short residence time and no acidic conditions during pretreatment as compared most of the pretreatment methods listed in the table.…”

“…These pretreatment conditions differed from the maximum sugar recovery conditions (180°C, 155 rpm, 20% moisture content, and 8 mm) reported by Karunanithy and Muthukumarappan (2011b). These authors reported a glucose, xylose, and combined sugar recovery of 88, 90, and 90%, respectively, for optimum pretreated corn stover with only extrusion.…”

“…Solutions for optimal and validation conditions (assumption a thumb rule is 50% of the glucose will be converted into ethanol during fermentation with an efficiency of 90%).This optimization study revealed that a larger p a r t i c l e s i z e ( 8 m m ) c o u l d b e u s e d f o r b i ofuels production; thereby the biomass size reduction energy cost can be saved to a greater extent. Although the optimum pretreatment condition differed from corn stover, similar sugar recovery was reported for switchgrass and prairie cord grass (Karunanithy & Muthukumarappan, 2011b, 2011c. The biomass digestibility depends on the specific types of phenolic acids that constitute the non-core lignin of lignocellulosic biomass (Jung & Deetz, 1993).…”

“…An extruder has the ability to provide high shear, rapid heat transfer, effective and rapid mixing in a short residence time, as well as adaptability to many different processes -all in a continuous process. A few extrusion pretreatments (Dale et al, 1999;de Virje et al, 2002;Karunanithy et al, 2008;Karunanithy & Muthukumarappan, 2010a, 2010b, 2010c, 2011a, 2011b, 2011c Lee et al, 2009;Muthukumarappan & Julson, 2007 ) showed a significant improvement on sugar recovery from corn stover, switchgrass, miscanthus, prairie cord grass, big bluestem, and Douglas fir through enzymatic hydrolysis. Potential fermentation inhibitors such as furfural and HMF were not reported in any of the above studies.…”

Continuous alkaline pretreatment of Miscanthus sacchariflorus using a bench-scale single screw reactor

“…Continuous pretreatment approaches such as screw extrusion have been shown to satisfy the criteria mentioned above (Lin et al, 2012;Karunanithy and Muthukumarappan, 2011a). Extrusion is a well-known process used in food industry and plastic production, which provides high level of shearing and homogenization, and rapid heat transfer, resulting in physiochemical transformations of the treated materials (Miller and Hester, 2007).…”