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

Abstract

In this work, a novel renewable taurine-based ionic liquid (IL), [TauIm][HSO 4 ], 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.

Solvent effects on carbohydrate transformation: insights into chemical pathway modulation

“…These advantages make ILs promising materials in carbohydrate science and technology. [70][71][72][73][74][75][76][77] ILs engage in complex interactions involving Coulomb forces, hydrogen bonds, and van der Waals forces. 78 These facilitate interactions with polysaccharides, resulting in successful solubilization.…”

“…175 A recent investigation by Zhou and colleagues 176 demonstrated that incorporated carboxylic acid anions displayed a tunneling effect with acylation reagents in imidazole-derived ILs, which promoted rapid and efficient homogeneous acylation of cellulose via dynamic hydrogen bonding. In another study, Gomes et al 73 employed a taurine-based IL, [TauIm][HSO 4 ], as both solvent and catalyst under microwave-assisted conditions (190 °C, 60 min, 10 eq. of IL) and achieved 81% yield of ethyl levulinate via the conversion of MCC as the feedstock.…”

Highly Efficient Conversion of Lignin into Diethyl Maleate Catalyzed by Molybdenum-Based Hybrid Catalysts

“…The conversion of biomass into chemicals has become a priority for reducing dependence on fossil fuels and mitigating greenhouse gas emissions. − Biomass is a renewable source of carbohydrates that immobilizes CO 2 , producing approximately 170 billion tons per year. ,− Lignin, a natural aromatic heteropolymer, accounts for ∼40% of the energy content and 10–35% of the weight of lignocellulosic materials . Lignin is composed of sinapyl alcohol, coniferyl alcohol, and p -coumaric alcohol, which are connected by β-O-4, β-5, 5-5, and other linkages. , Despite the abundance of lignin, only ∼3% is currently utilized for commercial applications, and the rest is typically burned, resulting in air pollution .…”