The Influence of Alkali and Alkaline Earth Metals and the Role of Acid Pretreatments in Production of Sugars from Switchgrass Based on Solvent Liquefaction

This study investigated the influence of alkali and alkaline earth metals (AAEM) and the role of acid pretreatments in the production of sugars during solvent liquefaction of lignocellulosic biomass using 1,4-dioxane and water as solvents. The present study found that removal of AAEM by acid washing/water rinsing did not enhance sugar production during solvent liquefaction of pretreated switchgrass nearly to the extent observed for fast pyrolysis nor did it inhibit lignin decomposition, suggesting that AAEM play less of a role in determining product yields in solvent liquefaction. On the other hand, acid infusion greatly enhanced the yields of sugars during solvent liquefaction, presumably because the strong acid catalytically promoted both the depolymerization and the dehydration of polysaccharides. The main monomeric sugars formed were levoglucosan, glucose, and xylose. Levoglucosan was the predominant sugar when 1,4-dioxane was the solvent, whereas glucose was the major sugar when water was the solvent. When 1,4-dioxane and water were cosolvents, partial hydrolysis of levoglucosan to glucose was observed. The maximum yield of the total sugars (19.8 wt %) from AI switchgrass occurred when 9:1 mixtures of 1,4-dioxane and water were used as cosolvents. In addition, the sugars were more stable in the 1,4-dioxane and water mixture compared to water alone.