Effective Biomass Delignification with Deep Eutectic Solvents

Efficient valorization of biomass is one of the most important aspects of circular economy. Obtaining valuable products from renewable materials, using ecological methods, is a key factor in natural environment protection. In many cases the first step of biomass valorization is removal of lignin from plant material. This process can significantly improve further transformations to final products, such as organic acids or monosaccharides. Deep eutectic solvents (DESs) are green chemicals, which have the ability to extract lignin from lignocellulosic material with high efficiency. In this paper we present an efficient method for lignin removal from plant material, using ecological deep eutectic solvents, based on choline chloride. We used waste biomass such as grass, rye straw and walnut shells. The best results were achieved in processes with DESs containing organic acids, such as lactic acid and malonic acid. Also, the impact of temperature of a process was examined—the largest amounts of extracted lignin were gained by delignification at 100 °C. The main goal of lignin removal from plant material is enhancing further transformation of biomass, e.g. enzymatic hydrolysis, in order to increase the yield of valuable products. We carried out the enzymatic hydrolysis of pretreated plant material with cellulase from Aspergillus niger. The effectiveness of biological transformations was improved, if delignification of biomass was previously performed. This effect was especially visible in case of soft material processing.