Comparison of sugar yields from switchgrass following pretreatment with co-solvent enhanced lignocellulosic fractionation (CELF) and dilute acid

Over the decades, numerous environmental and political concerns have motivated research into sustainable, domestic sources of fuels to replace those derived from petroleum. Lignocellulosic biomass represents the most abundant renewable resource and provides the only known route to sustainably produce liquid fuels on a large scale and low cost. Due to its complex and recalcitrant structure, raw biomass hinders biological conversion of polysaccharides, thus necessitating pretreatment to deconstruct the plant by allowing cellulose and hemicellulose to be more accessible to enzymes for release of fermentable sugars. Several pretreatment methods, including hydrothermal and dilute acid approaches, have been developed to improve enzyme accessibility, but each is limited in their ability to remove lignin, a key contributor to biomass recalcitrance.  Recently, we developed a novel pretreatment called Co-solvent Enhanced Lignocellulosic Fractionation (CELF) that applies aqueous tetrahydrofuran (THF) with dilute sulfuric acid to effectively remove lignin, while simultaneously achieving high yields of five carbon sugars from hemicellulose during pretreatment and subsequently of six carbon sugars from glucan using very low enzyme dosages (Nguyen et al., ChemSusChem, 2015). In this study, we first applied CELF to switchgrass to determine optimum conditions for maximum sugar release at low solids loadings. For comparison, DA pretreatment was also performed at conditions that were previously determined to be optimum (Lloyd, Bioresource Technology, 2005). We then evaluated total sugar yields in the pretreatment liquor from both pretreatments in addition to measuring the digestibility of the resulting pretreated solids produced over a range of enzyme loadings for each pretreatment.