Extraction of valuable chemicals from sustainable rice husk waste using ultrasonic assisted ionic liquids technology

Abstract

Rice husk is one of the most abundant waste lignocellulosic materials. Prob sonication assisted ionic liquid treatment being time effective and environmental benign was utilized for conversion of such waste residue into valuable products. Ionic liquids have been emerged as effective and benign solvents in this regard. Here, two ionic liquids mono- and di-cationic were synthesized and compared for the processing of rice husk biomass. The synthesized ionic liquids’ structures were confirmed by Nuclear Magnetic Resonance (NMR) as well as their thermal stability was investigated using thermogravimetric analysis (TGA). The acidity values were measured using Uv–Vis spectroscopy which showed that di-cationic ionic liquid has higher acidity. For the processing of rice husk, the conventional heating and probe sonication methods were used and compared. The probe sonication assisted ionic liquid method exhibited better performance. The process was optimized with respect to type of ILs, biomass loading, particle size, time and recycling effect etc. The regenerated fibrous material was characterized through, Fourier-Transform Infrared (FTIR), X-Ray Diffraction (XRD) and Scanning Electron Microscope (SEM) techniques. Moreover, about 39% of the lignin was successfully extract. High-Performance Liquid Chromatography (HPLC) result shows that 41.78% levulinic acid (LA) was obtained for ILs treated samples. In addition, the silica was successfully extracted from treated biomass and characterized with FTIR and Brunauer-Emmett-Teller (BET) analysis for surface area, pore size, and average diameter. It is steadily believed that the present approach would open new pathways for the efficient conversion of rice husk into sustainable products for numerous applications.