No abstract

Rice husk is an agricultural lignocellulosic-rich waste which can be used in the production of second-generation ethanol. A biomass pretreatment is necessary to release structural sugars because of the recalcitrance-related properties of lignin and silicon. The use of a long chain imidazolium ionic liquid (IL), 1-hexadecyl-3-methylimidazolium bromide ([C16MIM][Br−]), for rice husk pretreatment is reported for the first time. The influence of the [C16MIM][Br−]:water ratio and temperature on reducing sugars yield was investigated using an experimental design. Structural, chemical, and morphological modifications were observed by Scanning Electron Microscopy (SEM), X-Ray Diffraction (XRD), Fourier Transform Infrared Spectroscopy (FTIR) and Thermogravimetric Analysis (TGA). Higher temperature (160°C) and lower water content (1:5, IL:water) improved sugar yield. The validation assay (180°C, 1:20 IL:water ratio, 10% (w/v) of biomass, 12 h) resulted in 38% yield of reducing sugars and 60% dissolution of biomass, whereas untreated biomass showed only 0.18% yield of reducing sugars. The characterization analysis confirmed the changes in rice husk structure and morphology after pretreatment with IL. Rice husk pretreatment with [C16MIM][Br−] resulted in a higher concentration of reducing sugars compared to untreated biomass. Therefore, solid ionic liquids combined with water could be used as an alternative solvent for lignocellulosic biomass pretreatment.