Secondary Agriculture Residues Pretreatment Using Deep Eutectic Solvents

Abstract

The purpose of this work is to investigate a new class of solvents for separating secondary agricultural residues, which have already been transported to processing centers, into individual biomass components. Using biocompatible deep eutectic solvents (DES) on secondary agricultural residues could valorize these wastes into bioproducts by separating lignin from cellulose. DES pretreatment to achieve this separation involves chemicals that are less hazardous for the environment than other pretreatments. Methods Five deep eutectic solvents that are biocompatible have been investigated for their ability to deconstruct rice hulls and sugarcane bagasse. Mass yield, enzymatic hydrolysis of the pretreated biomass, fiber analysis, pKa analysis and Fourier transform infrared spectroscopy (FTIR) were performed to explore the effect of the DES on these secondary agricultural residues. Results Experimental results confirmed that the DES formic acid:choline chloride (FA:CC), lactic acid:choline chloride, and acetic acid:choline chloride were effective in removing lignin, thus concentrating cellulose in both pretreated biomass. Addition of water precipitated lignin from the spent DES, as confirmed by FTIR. However, the higher pKa DES lactic acid:betaine and lactic acid:proline had little effect on rice hulls or sugarcane bagasse. FA:CC was the most effective of the DES tested in preparing the biomass for enzymatic saccharification. All the effectively pretreated samples had higher inorganic content compared to the relevant raw biomass. Conclusions DES with stronger acidity (lower pKa) were found to be more efficient for delignification, leading to higher glucose yield. Further work is required to determine how inorganics affect waste biomass pretreatment.

Structure of choline chloride-carboxylic acid deep eutectic solvents by wide-angle X-ray scattering and DFT calculations

“…10 Choline chloride-carboxylic acid DESs have the characteristics of low cost, high boiling point, easy preparation, environmental friendliness, and designable structure, and have attracted much attention as a good medium for lignocellulose pretreatment, 11 dearomatization of gasoline, 12 battery recycling 13 etc. For example, Kumer et al 14,15 found that both ChCl/formic acid (FA) and ChCl/ acetic acid (AA) were effective in lignin separation from biomass rice hull and sugarcane bagasse. The choline chloride-carboxylic acid DESs can preferentially dissolve lignin at 60 1C and are stable at 100-160 1C.…”

Bioethanol production from coconut husk using DES-NADES pretreatment and enzymatic hydrolysis method

“…Glucose content at the delignification ratio of 1:4 and 1:6 for 2 h increased compared to the initial coconut husk samples. According to [49], delignifi-cation can increase glucose content due to an increase in cellulose accessibility due to the removal of hemicellulose and lignin content. DES and NADES solvents broke down the lignin bond from lignocellulose and diluted it to wash water after the delignification process.…”

Pretreatment of Loblolly Pine Tree Needles Using Deep Eutectic Solvents

“…Dried and sieved biomass of a mass of 3 g was mixed with 30 g of each of the three types of DES: FA:CC (2:1 ratio), LA:CC (10:1 ratio), AA:CC (2:1 ratio) in separate flasks with a magnetic stirrer for continuous stirring and kept in the preheated oil bath for 1 h at 125 • C. Time and temperature were chosen as the minima found to be effective in prior work [12]. The flask with this solution mixture was connected to a condenser to collect liquid from the vapor of the slightly volatile DES in order to maintain the solvent volume constant.…”

“…A visual inspection of the pine needles treated with FA:CC and LA:CC appeared to show a greater extent of biomass breakdown compared to AA:CC. FA:CC pretreatment may be more effective because it has a lower pKa value than the other DES [12].…”