Elucidation of the effect of ionic liquid pretreatment on rice husk via structural analyses

Abstract

BackgroundIn the present study, three ionic liquids, namely 1-butyl-3-methylimidazolium chloride ([BMIM]Cl), 1-ethyl-3-methylimidazolium acetate ([EMIM]OAc), and 1-ethyl-3-methylimidazolium diethyl phosphate ([EMIM]DEP), were used to partially dissolve rice husk, after which the cellulose were regenerated by the addition of water. The aim of the investigation is to examine the implications of the ionic liquid pretreatments on rice husk composition and structure.ResultsFrom the attenuated total reflectance Fourier transform-infrared (ATR FT-IR) spectroscopy, X-ray diffraction (XRD) and scanning electron microscopy (SEM) results, the regenerated cellulose were more amorphous, less crystalline, and possessed higher structural disruption compared with untreated rice husk. The major component of regenerated cellulose from [BMIM]Cl and [EMIM]DEP pretreatments was cellulose-rich material, while cellulose regenerated from [EMIM]OAc was a matrix of cellulose and lignin. Cellulose regenerated from ionic pretreatments could be saccharified via enzymatic hydrolysis, and resulted in relatively high reducing sugars yields, whereas enzymatic hydrolysis of untreated rice husk did not yield reducing sugars. Rice husk residues generated from the ionic liquid pretreatments had similar chemical composition and amorphousity to that of untreated rice husk, but with varying extent of surface disruption and swelling.ConclusionsThe structural architecture of the regenerated cellulose and rice husk residues showed that they could be used for subsequent fermentation or derivation of cellulosic compounds. Therefore, ionic liquid pretreatment is an alternative in the pretreatment of lignocellulosic biomass in addition to the conventional chemical pretreatments.

Influence of High-Pressure Steam Pretreatment on the Structure of Rice Husk and Enzymatic Saccharification in a Two-Step System

“…Additionally, the presence of a silica body protrusion was noticed. A similar morphology was reported for the micrographs of RH in previous studies (Ang et al 2012;Johar et al 2012). After pretreatment, the surface of the RH became rougher, irregularly coarser, and disordered due to the removal of superficial non-cellulosic layers, such as pectin, hemicellulose, wax, and other impurities, covering the surface of the RH.…”

“…This result indicated that there was an increase in the cellulose proportional content of the RH after the HPSP. It was suggested by Ang et al (2012) that the increase in intensity of this band may also imply the dissolution of noncellulose components, thereby increasing the cellulose content of the RH proportionately. This result was in agreement with the increase in the cellulose and lignin content observed in the compositional analysis of the pretreated RH earlier in this study.…”

“…Ang et al (2012) and Wei et al (2009) suggest that pretreatment is a crucial step to improve the efficiency of rice husk bioconversion and to obtain a high yield of fermentable sugars through enzymatic hydrolysis. Although various pretreatment techniques have been developed, such as acid, alkali, organosolvent, and ionic liquids, the high cost of chemicals and their environmental toxicity are major impediments to chemical utilization in biofuel production.…”

Influence of the crystalline structure of cellulose on the production of ethanol from lignocellulose biomass

“…With the use of scanning electron microscopy (SEM) and X-ray (XRD), Ang et al (2012) analyzed structures of rice husks prior to and after pretreatment with the use of 1-ethyl-3-methylimidazolium acetate, 1-ethyl-3-methylimidazolium phosphate, and 1-butyl-3 -methylimidazolium chloride. They showed that, as a result of 1-ethyl-3-methylimidazolium acetate pretreatment, there was an increase in the number of termination sites in the polymer chains of the husk structure, compared to purified samples obtained for the two remaining ionic liquids.…”

Effects of Soaking in Glycerol and Conventional Solvents on the Grinding of Kempas Wood (Koompassia malaccensis)

“…However, for kempas wood treated with silicon oil, the appearance of additional strong peaks at 2958, 1257 and 789 cm -1 represented the methyl stretching, CH 3 deformation in Si-CH 3 and Si-C stretching in Si-CH 3 of silicon oil. According to Ang et al (2012), the band at around 800 cm -1 is sensitive to the amount of amorphous cellulose present in the regenerated material and the broadening of this band indicates the higher amorphousity of regenerated cellulose. In the DMSO-soaked kempas wood and organosolv spectra (Figure 2(a)), the peak observed at 895 cm -1 was broad as the untreated kempas wood implied the similar amount of the disordered cellulosic structure.…”