A DES or LTTM: Eco-friendly solvent mediums for conversion of biomass to levulinic acid as a key chemical

Abstract

In this study, the effect of using environmentally friendly, less toxic, low cost, and easily recyclable deep eutectic solvent (DES) and low-transition temperature mixture (LTTM), which are alternatives to ionic liquids, on the conversion of biomass to levulinic acid (LA) was investigated. The reaction conditions such as temperature, the amount of feedstock, and the water ratio were optimized to ensure maximum product formation in DES (ChCl-EG)-water medium. The highest amount of LA (143.2 ± 2.5 mg) under optimum reaction conditions was achieved by using glucose in a newlydesignedLTTM (SA:EG)-water solvent medium. Newly designed low-transition temperature mixture (SA:EG) characterized by Fourier Transform Infrared Spectroscopy (FT-IR) and differential scanning calorimetry (DSC) analyses. A comprehensive theoreticalstudy was also performed to provide a deep understanding of the formation mechanisms of new LTTM by density functional theory (DFT), reduced density gradient (RDG), frontier molecular orbitals (FMOs), and molecular electrostatic potential (MEP) methods. The glucose conversion ratio increased from 70.2 % to 96.1 % in SA:EG-water medium. When microcrystalline cellulose, corn straw, and sorghum were used under the same conditions, 118.9 ± 5.4, 36.8 ± 9.4, and 32.6 ± 3.4 mg of LA were obtained per g of feedstock. A typical Brønsted acid; phosphotungstic acid (H3O40PW12) showed high catalytic activity, resulting in 229.0 ± 0.32 mg of LA per g of glucose in SA:EG-water medium. This shows that the use of SA:EG LTTM for cellulosic/lignocellulosic biomass sources can be used favorably in conversion reactions.