Pretreatment of sugarcane by-products using triethylammonium hydrogen sulfate: Assessment of the recovery of cellulosic pulp and lignin

Abstract

The conversion of lignocellulosic biomass into renewable bioproducts requires a pretreatment step to disrupt the cell wall matrix, thereby facilitating the access of hydrolytic enzymes to cellulose. Several studies have examined pretreatment using the ionic liquid; triethylammonium hydrogen sulfate [TEA][HSO₄] in sugarcane bagasse (SB) and sugarcane straw (SS). This study aimed to evaluate the fractionation of SB and SS using [TEA][HSO₄], focusing on the recovery of lignin and cellulose pulp. The methodology involved the synthesis of [TEA][HSO₄] and its application in the pretreatment of SB and SS, both in their raw forms and after hydrothermal pretreatment (HP). The recovered lignins and cellulose pulps were chemically and structurally characterized. The cellulose pulp was subjected to enzymatic hydrolysis using the commercial enzymatic preparation Cellic™ CTec II. Pretreatment with [TEA][HSO₄] demonstrated selectivity in the removal of lignin and hemicellulose, resulting in cellulose-enriched pulps. The recovered lignins showed an average yield of 75% and a purity of 85% purity and exhibited well-defined aromatic bands characteristic of grass lignins, indicating structural preservation. Thermogravimetric analysis revealed similar decomposition profiles among the lignin samples, with thermal stability influenced by reaction time. The lignins presented average molar masses (Mn = 3.5-4.6 kDa) and low polydispersity. Pretreatment with [TEA][HSO₄] significantly increased cellulose-to-glucose conversion during enzymatic hydrolysis, reaching values of 60-80%. Overall, the results highlight the potential of [TEA][HSO₄] for the efficient fractionation of SB and SS, confirming that the recovered lignins are structurally close to native biomass lignin. This distinguishes them from Kraft lignin and reinforces their potential for higher-value applications.