A Novel Recyclable Alkaline Biphasic 2-Phenoxyethanol/Water System for Rice Straw Biorefinery under Mild Conditions

Abstract

A novel recyclable alkali-assisted biphasic pretreatment process under mild conditions with low water consumption is first developed. After conditions were optimized with the uniform design method, the biphasic 2-phenoxyethanol system presented superior delignification performance with only 6 mL of water consumption per gram of rice straw. Namely, the lignin removal reached 82.16% at 80 °C or 78.15% even at 55 °C. Then, according to the characteristics of the biphasic system, the entire solvent circulation process was constructed. The recycled 2phenoxyethanol and washing wastewater were directly reused three times at 80 °C, giving more than 80% of lignin removal. Meanwhile, enzymatic digestibility of corresponding residues still exceeded 80% in acetate buffer, or 71% even in black liquor at 72 h. These show the possibility of constructing a biorefinery system based on an alkaline biphasic pretreatment process, with less water and energy consumption, fractionable composition, solvent recyclability, and black liquor utilization.

Recent advances in biomass pretreatment using biphasic solvent systems

“…The phenoxyethanol/ water biphasic system could also be performed under alkaline conditions, which demonstrated superior delignification performance (82.16% lignin removal) at 80 °C to achieve a good enzymatic digestibility (>80%) for rice straw. 90 Except for acid/ alkaline solutions, acetone has also been proposed in a phenoxyethanol/water system to pretreat different biomasses, which could result in excellent delignification (>92%) satisfying enzymatic digestibility (>80%) for bagasse and corncob. 91 All of the above references demonstrate that a phenoxyethanol/ water biphasic system has the advantages of being green, environment-friendly, and recyclable, which can achieve high lignin and hemicellulose removal and enzyme digestibility.…”

Catalytic transformations for agro-waste conversion to 5-hydroxymethylfurfural and furfural: Chemistry and scale-up development

“…[140][141][142][143][144][145][146][147][148] Hence, for a long time, most of the bio-refinery development related to this biomass has been concerned with the pre-treatment approaches for monosaccharide production and then the further conversion (of the pre-treated sacchar-ides) to bio-ethanol. [149][150][151][152][153][154][155][156] Over the past 5 years, researchers have followed the similar concept of pre-treatment for 5-HMF and FAL synthesis as well. [157][158][159][160] However, during the past decade, the research community has shown a very keen interest in the direct utilization of such biomass for 5-HMF and FAL production.…”

Comparative Study of Effective Pretreatments on the Structural Disruption and Hydrodepolymerization of Rice Straw

“…The current pretreatment and degradation methods include physical methods (ball milling [20], microwaving [21], and ultrasonication [22]), physical and chemical methods (steam explosion [23], supercritical fluid extraction [24], and hydrothermal methods [25]), chemical methods (acids [26], alkaline chemicals [27], ionic liquids [28], organic solvents [29], deep eutectic [30] and metal salts [31]), and biological methods (microorganisms [32] and enzymes [33]). However, some limitations for certain pretreatment methods have been reported: the high cost of reagents in pretreatment with chemical ionic liquids, high investments for the equipment required in ultrasonication, steam explosion, and supercritical pretreatments, consumption of high levels of mechanical energy in the ball milling pretreatment, secondary pollution caused by pretreatments with chemical acids, alkali reagents, organic solvents, and metal salts, or demanding process controls during pretreatments with microorganisms and enzymes [34]. Among these methods, hydrothermal pretreatment (HP) has been reported to be economical and ecofriendly; the water undergoes self-ionization to generate protons that cleave the acid-labile glycosidic bonds, resulting in a more acidic medium, contributing to the further depolymerization of hemicellulose and removal of lignin, increasing cellulose accessibility in the biomass [35].…”