Direct Ethyl Levulinate Production from Raw Lignocellulosic Biomass Mediated by a Novel Taurine-Based Imidazolium Ionic Liquid

In this work, a novel renewable taurine-based ionic liquid (IL), [TauIm][HSO4], was synthesized via the Debus–Radziszewski reaction. The synthesized IL was then used to produce ethyl levulinate (EL) from several lignocellulosic substrates under microwave irradiation. Experimental conditions (temperature, time, and IL quantity) for EL production from a model substrate (microcrystalline cellulose, MCC) were first investigated by design of experiment (DoE) using a central composite design (CCD). The highest EL yields (over 80%) in MCC were achieved at the upper limits of all factors (190 °C; 60 min; 10 equiv of IL). Computational studies revealed that the IL–cellobiose interaction is stronger than the IL itself at the reaction temperature (190 °C), indicating the efficiency of the IL in interacting with cellulose in the optimal reaction conditions. Moreover, the formation of the IL–cellobiose complex was mediated by the hydrogen sulfate anion, while the cation worked as a spacer. Optimized conditions from DoE were also applied to sugarcane bagasse and straw, elephant grass leaves and stems, rice husks and straw, and corn biomass. EL production yields from 12 to 59% were obtained from these biomasses using this novel imidazolium IL, with the highest EL yields obtained with raw sugarcane bagasse (SCB) without any pretreatments. The superior performance of SCB was associated with the higher content of hemicelluloses in its composition compared to that of the other biomasses. Together, these results presented herein open new possibilities for increasing biomass valorization using renewable and straightforward routes.