Effect of Extruder Parameters and Moisture Content of Switchgrass, Prairie Cord Grass on Sugar Recovery from Enzymatic Hydrolysis

Abstract

Research on biomass pretreatment to enhance enzymatic digestibility has been done for more than decades, but a viable continuous pretreatment method needs to be developed. Extrusion has the potential to be a viable continuous pretreatment method. This study investigated the effect of compression ratio (2:1 and 3:1), screw speed (50, 100, and 150 rpm), and barrel temperature (50, 100, and 150 degrees C) on the sugar recovery from switchgrass (SG) and prairie cord grass (PCG) over a range of moisture contents (15, 25, 35, and 45% wb).The pretreated samples were subjected to enzymatic hydrolysis for sugar recovery measurement. Statistical analyses revealed that a 3:1 screw compression ratio (compared to 2:1) increased glucose recovery by 12% and 8% and combined sugar recovery by 37% and 40% for SG and PCG, respectively. For SG, the highest sugar recovery (45.2%) was obtained at the lowest screw speed (50 rpm) and the highest temperature (150 degrees C) with moisture content of 15%. The highest glucose, xylose, and combined sugar recovery of 61.4%, 84.3%, and 65.8% were recorded for PCG extruded at a screw speed of 50 rpm and a temperature of 50 degrees C with a moisture content of 25%. Glycerol and acetic acid were byproducts found in low concentration (0.02-0.18 g/L) for both biomass.

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.…”

“…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.…”

Sugarcane and Woody Biomass Pretreatments for Ethanol Production

“…These functions can be performed in the same process, depending on the size of the extruder and the screw design. Since the 1990s, there has been an increase in the number of studies that use extrusion for biomass processing, such as for the extraction of compounds [74][75][76], densification [73,77] and biomass pretreatment for enzymatic saccharification [78][79][80][81][82][83][84][85][86][87]. For lignocellulosic biomass pretreatment, extrusion processing can provide a unique continuous reactor working at higher throughput and solid levels.…”

“…Significant improvements in sugar yield after enzymatic hydrolysis have been reported for biomass pretreatment based on extrusion; examples include corn stover [92], Miscanthus [99], big bluestem, prairie cord grass, switchgrass, Indian grass [78,[83][84][85][86][87]. Nevertheless, there are no reports for the use of extrusion for pretreatment of sugarcane bagasse and straw aimed at cellulosic ethanol production.…”

“…If extrusion is combined with chemical pretreatment, due to its effective ability of kneading and mixing, the process requires less chemical loadings and thus less residual effluents are formed; the combination of extrusion with chemical pretreatment can further reduce energy consumption as it is economically suitable for large-scale operation. Furthermore, extrusion does not produce fermentation inhibitors, such as furfural and hydroxyl methylfurfural; nevertheless, low concentrations of acetic acid have been reported [84][85][86][87]. However, the extrusion pretreatment of lignocellulosic biomass requires the use of additives to increase the flow ability inside the barrel and avoid the accumulation, burning and blocking of the die during the process.…”