Possible dissolution mechanism of alkali lignin in lactic acid-choline chloride under mild conditions

Interpretation of the phenolation and structural changes of lignin in a novel ternary deep eutectic solvent

Deep eutectic solvents (DES) are promising green solvents for depolymerization and reconstruction of lignin. Revealing the transformations of lignin during DES treatment is beneficial for high potential lignin applications. In this study, bagasse lignin was treated with a binary DES and three ternary DESs, respectively. The results showed that net hydrogen bonding acidity(α-β) value of DES was positively correlated to the increment of phenolic hydroxyl of lignin, and the ternary DES of choline chloride-formic acid-oxalic acid (ChCl-FA-OA) exhibited the best phenolation performances. The phenolic hydroxyl content of ChCl-FA-OA treated lignin was increased by 50.4 %, reaching 2.41 mmol/g under optimum conditions (120 °C, 4 h, ChCl-FA-OA = 1:2:1). Moreover, it was found that the cleavage of β-O-4' aryl ether bond and ester bond were dominant reactions during the treatment, accompanied by condensation reactions. Additionally, the obtained lignin oil contained various syringyl and guaiacyl derived phenolic compounds. Especially, the content of acetovanillone in lignin oil reached 29.94 %, much higher than in previous studies. Finally, the degradation mechanism of lignin in ChCl-FA-OA system was proposed. The present work provided insights into the relationship between lignin phenolation and DES properties. The novel ChCl-FA-OA system can achieve efficient lignin depolymerization, and convert lignin biomass into value-added chemical products.

Mechanistic insights into the lignin dissolution behavior in amino acid based deep eutectic solvents

Deep eutectic solvents (DESs) composed by amino acids (L-arginine, L-proline, L-alanine) as the hydrogen bond acceptors (HBAs) and carboxylic acids (formic acid, acetic acid, lactic acid, levulinic acid) as hydrogen bond donors (HBDs) were prepared and used for the dissolution of dealkaline lignin (DAL). The mechanism of lignin dissolution in DESs was explored at molecular level by combining the analysis of Kamlet-Taft (K-T) solvatochromic parameters, FTIR spectrum and density functional theory (DFT) calculations of DESs. Firstly, it was found that the formation of new hydrogen bonds between lignin and DESs mainly drove the dissolution of lignin, which were accompanied by the erosion of hydrogen bond networks in both lignin and DESs. The nature of hydrogen bond network within DESs was fundamentally determined by the type and number of functional groups in both HBA and HBD, which affected its ability to form hydrogen bond with lignin. One hydroxyl group and carboxyl group in HBDs provided active protons, which facilitated proton-catalyzed cleavage of β-O-4, thus enhancing the dissolution of DESs. The superfluous functional group resulted in more extensive and stronger hydrogen bond network in the DESs, thus decreasing the lignin dissolving ability. Moreover, it was found that lignin solubility had a closed positive correlation with the subtraction value of α and β (net hydrogen donating ability) of DESs. Among all the investigated DESs, L-alanine/formic acid (1:3) with the strong hydrogen-bond donating ability (acidity), weak hydrogen-bond accepting ability (basicity) and small steric-hindrance effect showed the best lignin dissolving ability (23.99 wt%, 60 °C). On top of that, the value of α and β of L-proline/carboxylic acids DESs showed some positive correlation with the global electrostatic potential (ESP) maxima and minima of the corresponding DESs respectively, indicating the analysis of ESP quantitative distributions of DESs could be an effective tool for DESs screening and design for lignin dissolution as well as other applications.

Ammonia fiber expansion-assisted deep eutectic solvent treatment for wheat straw fraction separation and bioconversion

In this study, an ammonia fiber expansion (AFEX)-assisted deep eutectic solvent (DES) pretreatment method was developed for the rapid separation of wheat straw fractions, which reduced the pretreatment time for DES and improved the pretreatment efficiency. This study describes the feasibility of the AFEX-assisted DES pretreatment in terms of both progressive and parallel relationships and analyzes the subsequent enzymatic effect in generating glucose from cellulose. Ammonia fiber expansion-assisted DES one-pot pretreatment at 120 °C, for 1.5 h resulted in an enzymatic efficiency of 98.0 ± 3.1 %. Moreover, the enzyme efficiency remained greater than 85 % after three recovery cycle experiments. The comparison between regenerated-lignin (d-lignin) and alkaline-lignin showed that regenerated lignin has a lower molecular weight and belongs to para-hydroxy-phenyl-guaiacyl-syringyl (H-G-S) type lignin. This study developed is a green and efficient pretreatment process with great potential in the separation and utilization of biomass fractions.

Kualitas Kimia dan Profil Serat Bekatul Gandum dengan Kadar Air dan Lama Pemanasan Berbeda

Bekatul gandum (wheat pollard) merupakan hasil samping industri pengolahan gandum yang makin banyak digunakan untuk bahan makanan dan kualitasnya sangat tergantung pada kadar air dan lama pemanasan. Penelitian bertujuan mengkaji pengaruh kadar air dan lama pemanasan yang berbeda terhadap kualitas kimia dan profil serat bekatul gandum. Penelitian menggunakan Rancangan Acak Lengkap faktorial 3 × 2 dengan 3 ulangan. Faktor pertama adalah kadar air 12, 30, dan 60%.  Faktor kedua adalah lama pemanasan 15 dan 30 menit. Kandungan kimia berupa kadar air, abu, lemak kasar, protein kasar, serat kasar, bahan ekstrak tanpa nitrogen (BETN) dan gross energy dianalisis dalam penelitian ini. Demikian juga profil serat (kadar Acid Detergent Fiber (ADF), Neutral Detergent Fiber (NDF), hemiselulosa, selulosa dan lignin.) serta profil serat melalui Scanning Electron Microscope-Energy Dispersive X-Ray (SEM-EDX). Hasil penelitian menunjukkan bahwa tidak ada pengaruh perlakuan kadar air dan pemanasan terhadap kandungan kimia, profil serat bekatul gandum dan profil serat melalui SEM-EDX. Kesimpulan penelitian adalah kadar air dan lama pemanasan tidak menentukan kualitas kimia dan profil serat pada bekatul gandum.Chemical Quality and Fiber Profile Wheat Pollard with Different Water Content and Steaming Durration AbstractWheat bran has known as by product of wheat production which is recently used as food ingredient and its quality could be rely on the water content and heat temperature. The aim of the study was to examine the effect of water content and steaming durration on the chemical quality and fiber profile of wheat bran. The study used a factorial 3 × 2 Completely Randomized Design with 3 replications. The first factor was the water content of 12, 30, and 60%. The second factor was the heating time of 15 and 30 minutes. Moisture content, ash, crude fat, crude protein, crude fiber, nitrogen-free extract material (NFE) and gross energy), fiber profile (Acid Detergent Fiber (ADF) content, Neutral Detergent Fiber (NDF), hemicellulose, cellulose, and lignin.) were analyzed as well as fiber profiles through Scanning Electron Microscope-Energy Dispersive X-Ray (SEM-EDX). The results showed that no remarkable effect of treatment was detected on chemical content, wheat bran fiber profile and fiber profile through SEM-EDX. As conclusion, the water content and heating time did not affect the chemical quality and fiber profile of wheat bran.

Solid acid facilitated deep eutectic solvents extraction of high-purity and antioxidative lignin production from poplar wood

Pure deep eutectic solvents (DESs) system of choline chloride (ChCl)/Lactic acid (Lac) were demonstrated to be an effective strategy for extraction of lignin. In this study, two kinds of different promising solid acid (SA) with DESs were designed to promote the pretreatment of lignocellulose. The SA of phosphotungstic acid (H₃O₄₀PW₁₂) and iron bromide (FeBr₃) were introduced into DESs to extract poplar wood lignin and evaluate the antioxidant activity. It was found that 82.2% and 80.9% of lignin were obtained from poplar wood under H₃O₄₀PW₁₂-ChCl/Lac acid and FeBr₃-choline ChCl/Lac system with 4 h and 8 h, respectively. The lignin fractions with a high purity (>89%), low molecular weight (Mw 1800-2000 g/mol). Besides, the antioxidant activities of lignin fractions were better than butyl hydroxyanisole (BHA). Therefore, DES lignin has prominent antioxidant activity and could developed a potential natural cosmetics and food packaging.