Employing deep eutectic solvent synthesized by cetyltrimethylammonium bromide and ethylene glycol to advance enzymatic hydrolysis efficiency of rape straw

Exploration of biomass fractionation and lignin removal for enhancing enzymatic digestion of wheat-stalk through deep eutectic solvent Cetyl trimethyl ammonium chloride:Lactic acid treatment

The cationic surfactant-based deep eutectic solvents (DESs) have attracted extensive attention due to their effectual destruction of the natural anti-degradation barrier structure in lignocellulose. In this research, functional DES Cetyl trimethyl ammonium chloride:Lactic acid (CTAC:LA molar ratio 1:0.5 to 1:6) was fabricated for pretreating wheat-stalk. The relationships of accessibility, lignin removal, xylan separation, and enzymolysis efficiency were explored. The highest delignification (88.3 %) and xylan removal (89.0 %) were obtained through the treatment with CTAC:LA (1:4, mol/mol, 160 °C, 60 min), acquiring 86.8 % of enzymolysis efficiency. The structure of CTAC:LA-treated wheat-stalk was changed to porous state, while the accessibility and crystallinity were substantially improved to 668.2 mg/g and 57.6 %, respectively. The lignin surface area declined from 672.7 to 335.4 m2/g. Furthermore, the structure of lignin disrupted by CTAC:LA was analyzed by 2D-HSQC NMR, implying that CTAC:LA could cleave the CO covalent bond and CC bond and degrade the S- and H-units in wheat-stalk lignin through interaction. The potential pretreatment mechanism was proposed through comprehensive exploration at the molecular level and macro level, and this built pretreatment process held great promise for valorizing biomass into highly valuable chemicals.

Tailored bamboo fractionation with ternary deep eutectic solvent system to maximize biorefinery toward enzymatic saccharification and lignin recovery

Six different ternary deep eutectic solvent (DES) of tetraethylammonium chloride (TEAC)/oxalic acid (OA)-polyols were synthesized to improve the production of fermentable sugars and lignin by-products. The bamboo fractionation and bioconversion of cellulose residues can be enhanced by the ternary DES pretreatment, and its increasing efficiency was positively related to the alkyl carbon chain length and hydroxyl number of polyols in the hydrogen bond donor. The 1,4-butanediol (BDO)-assisted DES pretreatment showed excellent performance in achieving high xylan removal (86.7 %) and delignification (91.98 %). The pretreated bamboo was used for enzymatic hydrolysis and ethanol fermentation, with glucose yield and ethanol production of 76.13 % and 16.17 g/L, which was significantly improved by 30 % and 48 % compared to bamboo treated with corresponding binary TEAC/OA. The characterization of trinary pretreated bamboo revealed that the addition of polyols helped to protect the β-O-4 substructure of lignin, reduce the recondensation of lignin fragments, and thus enhance enzyme digestibility. Furthermore, 37.9% of lignin with high purity and highly active hydroxyl substructures was recovered. The proposed novel TEAC/OA-BDO DES mixture has great potential as an effective pretreatment solvent for future bamboo biorefinery.

Valorization of wheat straw through enhancement of cellulose accessibility, xylan elimination and lignin removal by choline chloride:p-toluenesulfonic acid pretreatment

Different molar ratio of choline chloride (ChCl) and p-toluenesulfonic acid (p-TsOH) (2:1, 1:1 and 1:2, mol:mol) were used to prepare deep eutectic solvents (ChCl:p-TsOH) for pretreating cellulose fibers to elevate cellulose accessibility, enhance xylan elimination, increase lignin removal and promote enzymatic digestion. ChCl:p-TsOH (1:1, mol:mol) could effectually destroy the dense layout of wheat straw (WS) at 80 °C for 60 min. Cellulose crystallinity declined from 43.4 % to 25.5 %, and the lignin surface area and hydrophobicity were reduced to 182.6 m2/g and 3.2 L/g, respectively. While cellulose accessibility in WS was significantly improved to 523.9 mg/g. The delignification and xylan removal reached 72.4 % and 90.5 %, respectively. The enzymatic digestibility reached 89.3 %. Furthermore, molecular dynamics simulation and quantum chemistry calculation were conducted on the lignocellulose model. The van der Waals interaction between ChCl:p-TsOH and lignin and the dispersion interaction between ChCl and lignin were identified. Accordingly, the interaction between biomass and ChCl:p-TsOH was elucidated at the molecular level. It provided a comprehensive understanding of lignocellulosic biomass valorization through the highly efficient pretreatment by ChCl:p-TsOH.

Valorization of rapeseed straw through the enhancement of cellulose accessibility, lignin removal and xylan elimination using an n-alkyltrimethylammonium bromide-based deep eutectic solvent

n-Alkyltrimethylammonium bromide (CnTAB)-based deep eutectic solvent (DESs) has potential in the efficient delignification and utilization of carbohydrates in biomass. In this research, DESs containing Brønsted acid and Lewis acid were prepared with CnTAB (alkyl-chain length 12-18), organic acids and metal chlorides, and the optimal treatment conditions were acquired by pretreatment optimization. Through the pretreatment with TTAB/LCA/Fe3+ (1:4:0.0111, mol:mol:mol) (162.5 °C, 61.7 min), lignin (89.2 %) and xylan (77.9 %) were effectively eliminated, and the hydrophobicity of rapeseed straw substantially declined from 4.62 to 2.09 m2/g, acquiring the highest enzymatic saccharification efficiency of 92.5 %. The relationship of DES properties and enzymatic saccharification efficiency was explored. Additionally, hemicellulose in rapeseed straws could be efficiently transformed into furfural (3.75 g/L) and xylo-oligosaccharides (3.64 g/L). To clarify the structural and property changes brought by pretreatment, rapeseed straws were testified by FT-IR, SEM and CLSM and deeply discussed. The interaction between lignocellulose and TTAB/LCA/Fe3+ was elucidated by molecular dynamics simulations and quantum chemical calculations, explaining the effectual treatment performance and hemicellulose upgrading at the molecular level. Eventually, a potential pretreatment mechanism of TTAB/LCA/Fe3+ was proposed. This established TTAB/LCA/Fe3+ treatment holds great promise for valorization of biomass into biofuels and biobased chemicals.

Promoted lignocellulose fractionation and improved enzymatic hydrolysis of corn stalks through cationic surfactant combined with deep eutectic solvent pretreatment

The efficient conversion of lignocellulose relies on the implementation of an effective pretreatment strategy. Cationic surfactants combined with deep eutectic solvent ([Betaine][LA] was employed as a novel pretreatment strategy for treating corn stalks. Valuable insights were provided on the impact of the surfactant hydrophobic segment length on pretreatment efficacy. The specific pretreatment conditions were optimized by single factor and orthogonal experiment. Octadecyl trimethyl ammonium bromide (OTAB, 1.5 wt%) with the longest hydrophobic part combined with [Betaine][LA] (Betaine-to-LA molar ratio 1:4) achieved the best pretreatment effect (delignification 92.8 %, xylan elimination 91.1 %) when severity factor reached 4.26, meanwhile, 1.7 g/L xylo-oligosaccharides and 4.4 g/L furfural were detected in pretreatment liquid due to the hydrolysis of hemicellulose in corn stalks with acidic deep eutectic solvent [Betaine][LA]. The relative saccharification activity reached 2.7 times of raw material, while the lignin surface area significantly decreased, leading to enhanced cellulose accessibility. Additionally, molecular perspective provided by molecular dynamics showed the elimination of lignin and xylan was facilitated by strong interaction of hydrogen-bond and van der Waals force between lignin and hemicellulose with [Betaine][LA] + OTAB. Overall, the effectiveness and potential of cationic surfactant combined deep eutectic solvent pretreatment strategy for lignocellulose pretreatment was revealed.

A designed ZrOCl2/ethylene glycol deep eutectic solvent for efficient lignocellulose valorization

Deep eutectic solvents (DESs) hold great potential in biorefining because they can efficiently deconstruct the recalcitrant structure of lignocellulose. In particular, inorganic salts with Lewis acids have been proven to be effective at cleaving lignin-carbohydrate complexes. Herein, a Zr-based DES system composed of metal chloride hydrate (ZrOCl2·8H2O) and ethylene glycol (EG) was designed and used for poplar powder pretreatment. Zr4+-based salts provide sufficient acidity for lignocellulose depolymerization. The acidity of the DES was analysed by the Kamlet-Taft solvatochromic parameter, and the results demonstrated that the acidity can be regulated by the DES composition. Under the optimum conditions (ZrOCl2·8H2O:EG molar ratio of 1:2), the DES pretreatment removes nearly 100 % hemicellulose and 94.7 % lignin. The recovered lignin exhibited a low polydispersity of 1.7. The cellulose residues deliver an efficiency of 94.4 % upon enzymatic digestion. Moreover, the DES can be easily recovered with high yield and purity, and the recycled DES still maintains high delignification and enzymatic hydrolysis efficiencies. The proposed DES pretreatment technology is promising for biomass valorization.

Role of lignin in synergistic digestibility improvement of wheat straw by novel alkaline deep eutectic solvent and tetrahydrofuran pretreatment

A novel efficient pretreatment system containing alkaline deep eutectic solvent (DES) and tetrahydrofuran (THF) was developed in the present study. Under pretreatment conditions of 160 ℃ and 1 h, DES-THF pretreatment was more efficient (81.61%) in cellulose digestibility improvement than DES (choline chloride/monoethanolamine, 67.54%). To further explore lignin structural transformation and lignin-cellulase interaction after pretreatment, milled wood lignin (MWL) was extracted and characterized. Compared with DES-MWL, DES-THF-MWL showed an increased carboxyl group content (24.0%) and decreased condensed phenolic hydroxyl content (9.1%). In DES-MWL, β-O-4 content was 21.79%, while in DES-THF-MWL, β-O-4 accounted for 45.45%, indicating that the addition of THF alleviated cleavage of β-O-4 alkyl ether bonds. Fluorescence emission spectroscopy results showed that quenching mechanism of DES-THF-MWL and cellulase was dynamic, which was different from other lignin. Compared with DES-MWL, decreased Ka between DES-THF-MWL and cellulase indicated decreasing interaction between them. DES-THF pretreatment provides a novel pretreatment method for bioenergy.