Lignin and cellulose are the two most abundant natural polymers with wood being the main global source. Cellulose is a sugar polymer which can be converted into biofuel. Lignin is a complex organic structure that encapsulates the cellulose. Due to the vast abundance of these materials and their propensity for being discarded as waste by industry, there exists a strong argument for using it as a cheap and sustainable source of biofuel. The process in which cellulose is converted to biofuel consists of two main stages, hydrolysis, and fermentation. The combined structure of lignin and cellulose undergo hydrolysis to break the sugar polymers of cellulose into glucose monomers. The glucose is then fermented into an ethanol and water mixture which can be separated to obtain the value product of ethanol. During these two processes the lignin disrupts the reaction times and, in some cases, poisons the process. This causes a lower process efficiency and drives up costs making the marketability of the product less feasible.
In this study, deep eutectic solvents (DES) are evaluated to extract lignin. The benefit of DES is that they are made from the physical mixing of a hydrogen bond donor (HBD) and a hydrogen bond acceptor (HBA), generally made from a quaternary salt and acid/alcohols. In this study, a conductor like screening model (COSMO) is adopted to screen suitable HBAâs and HBDâs for Lignin extraction based on hydrogen bond properties using a triple-zeta valence polarization (TZVP) basis set. This model is evaluated compared to literature experimental studies to verify integrity of the results. Over 1000 combinations of HBA and HBD spanning type three and 5 DES were evaluated for this task. Novel DES combinations involving tetrabutyl ammonium chloride were predicted to offer significant improvements in lignin solubilization over the commonly studied choline chloride-based DES. Experimental procedures were undertaken to determine the validity of the predictions by COSMO. The experiments supported the findings.
