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The oxidative depolymerization of alkali lignin can be achieved by using Keggin structure polyoxometalate-ionic liquid (POM-IL) as catalyst under aerobic conditions. The effects of catalysts such as [HC 4 im] 3 PMo 12 O 40 , [HC 4 im] 5 PV 2 Mo 10 O 40 , [HC 2 im] 5 PV 2 Mo 10 O 40 , and [HC 4 im] 4 SiMo 12 O 40 (abbreviated as POM-IL1, POM-IL2, POM-IL3, and POM-IL4, respectively), the acidity of aqueous IL solutions on lignin conversion, and aromatic product distribution were investigated. Under optimized conditions, phenolic products (mainly m (p)-cresol, veratrole, vanillin) had the highest yield and the selectivity was as high as 75.0% using POM-IL1 as the catalyst. POM-IL2 and POM-IL3 were used as the catalysts, the highest conversion of 76.0% of lignin was achieved, and the overall yield of ketone products were higher on lignin samples, in which the main products include acetovanillone, 3-methoxyphenol, and 4-methylcatechol, and the highest selectivity of ketone products was 76.8%. The results show that the lignin fragments could be successfully oxidized into platform compounds in aqueous acidic ILs (AILs) solutions catalyzed by Keggin structure POM-IL. In addition, the role of AILs and POM-ILs in the oxidative depolymerization of alkaline lignin was analyzed, and the possible reaction mechanism between AIL-water/POM-IL/lignin system was speculated. [Display omitted] • Oxidative depolymerization of AL in aqueous ILs/POM-ILs was investigated. • AL conversion of 76.0%. was achieved under O 2 pressure of 2.2 MPa at 150 °C. • A cooperative catalytic effect between acidic IL and POM-IL can be found. • Cation and anion types of POM-ILs and acidic ILs affected product distributions. [ABSTRACT FROM AUTHOR]

The treatment of enzymatically hydrolyzed lignin (EHL) in dialkylimidazolium-based ionic liquid (IL)–water mixtures (50–100 wt% IL content) was investigated at 150 °C for 3 h. pH, IL type, and IL content were found to greatly influence the degradation of lignin and the structure of regenerated lignin. 1-Butyl-3-methylimidazolium methylsulfonate–water mixtures with low pH facilitated lignin depolymerization but destroyed the regenerated lignin substructure. Regenerated lignin with low molecular weight and narrow polydispersity index (2.2–7.7) was obtained using a 1-butyl-3-methylimidazolium acetate-based system. Water addition inhibited lignin depolymerization at 50–100 wt% IL content, except for 70 wt% 1-butyl-3-methylimidazolium chloride–water mixture. Compared with pure IL treatment, obvious differences were observed in the breakdown of inter-unit linkages and ratio of syringyl to guaiacyl units in regenerated lignin with IL–water treatment. [ABSTRACT FROM AUTHOR]

Abstract: An ionic liquid (IL)–water mixture employed to treat lignocellulosic biomass is promising. The addition of water decreases viscosity and process cost so as to improve the IL practical application. In this work, effects of temperature (50–170°C), water content (0–80wt%), treating duration (0.5–4h) and pressure (0.1–3.2MPa) on treating legume straw process using a 1-butyl-3-methylimidazolium chloride ([C4mim]Cl)–water mixture were experimentally investigated. Legume straw was found to be partially dissolved, and the dissolved substances can be flocculated by adding the coagulating agent—water (equal to volume of the solution). For this process at 0.1MPa, the maximum 29.1wt% legume straw is dissolved in the [C4mim]Cl–water mixture with water content of 20wt% at 150°C during 2h, which is much higher than 9.8wt% using pure [C4mim]Cl. A hemicellulose-free lignin-rich material (64.0wt% lignin and 35.3wt% cellulose) is obtained by adding the water. Even for 0.5h, 22.3wt% of legume straw is dissolved in the case of water content of 20wt%, 150°C and 0.1MPa. High pressure favors the dissolution of legume straw but lignin content in the residue has no obvious change. The addition of proper amount of water facilitates the dissolution of legume straw and a relative rapid dissolving rate can be achieved in a [C4mim]Cl–water mixture. There are great differences in chemical and physical properties between legume straw and the obtained samples (residue and floc) due to the dissolution and reconstitution. [Copyright &y& Elsevier]

Adding water obviously enhanced the thermal stability of alkylimidazolium-acetate at 150 °C. In this case, the cationic type of IL and water content have obvious effects on the depolymerization of enzymatically hydrolyzed lignin and the structure of regenerated lignin. Unlabelled Image • Water addition obviously enhanced thermal stability of acetate ILs. • Lignin treatment with acetate IL-water mixtures (50–90 wt%) were investigated. • Lignin degradation was more affected by cation type than IL content and pH value. • Adding water affected the cleavage of inter-unit lignin linkages. Water addition was found to enhance the thermal stability of alkylimidazolium–acetate ionic liquids (ILs). Especially in the case of high water content (30–50 wt%), few decomposition products can be observed in the 1H NMR spectra even after treatment for 24 h at 150 °C. On the basis of this finding, lignin treatment of water and acetate IL mixtures (50–90 wt% IL content) were investigated at 150 °C. The addition of water, as opposed to pure IL treatment, can inhibit the lignin depolymerization into small fragments. Lignin degradation and the structure of regenerated lignin are more affected by cation types of ILs rather than the IL contents and pH values. In the case of 50–70 wt% 1-ethyl-3-methylimidazolium acetate–water system, the specific inter-unit linkages of lignin can be broken down, and regenerated lignin with a narrow polydispersity index (5.0–9.6) can be obtained. [ABSTRACT FROM AUTHOR]

Lignin dissolution in dialkylimidazolium-based ionic liquid (IL)–water mixtures (40 wt%–100 wt% IL content) at 60 °C was investigated. The IL content and type are found to considerably affect lignin solubility. For the IL–water mixtures except 1-butyl-3-methylimidazolium tetrafluoroborate ([C 4 C 1 im]BF 4 ), the maximum lignin solubility can be achieved at 70 wt% IL content. Lignin solubility in IL–water mixtures with different cations follows the order 1-butyl-3-methylimidazolium ([C 4 C 1 im] + ) > 1-hexyl-3-methylimidazolium ([C 6 C 1 im] + ) > 1-ethyl-3-methylimidazolium ([C 2 C 1 im] + ) > 1-octyl-3-methylimidazolium ([C 8 C 1 im] + ) > 1-butyl-3-ethylimidazolium ([C 4 C 2 im] + ) > 1-butyl-3-propylimidazolium ([C 4 C 3 im] + ). For IL mixtures with different anions, lignin solubility decreases in the following order: methanesulfonate (MeSO 3 − ) > acetate (MeCO 2 − ) > bromide (Br − ) > dibutylphosphate (DBP − ). Evaluation using the theory of Hansen solubility parameter (HSP) is consistent with the experimental results, suggesting that HSP can aid in finding the appropriate range of IL content for IL–water mixtures. However, HSP cannot be used to evaluate the effect of IL type on lignin solubility. [ABSTRACT FROM AUTHOR]

Ammonia is considered as a promising hydrogen or energy carrier. Ammonia absorption or adsorption is an important aspect for both ammonia removal, storage and separation applications. To these ends, a wide range of solid and liquid sorbents have been investigated. Among these, the deep eutectic solvent (DES) is emerging as a promising class of ammonia absorbers. Herein, we report a novel type of DES, i.e. , metal-containing DESs for ammonia absorption. Specifically, the NH 3 absorption capacity is enhanced by ca. 18.1–36.9% when a small amount of metal chlorides, such as MgCl 2 , MnCl 2 etc. , are added into a DES composed of resorcinol (Res) and ethylene glycol (EG). To our knowledge, the MgCl 2 /Res/EG (0.1:1:2) DES outperforms most of the reported DESs. The excellent NH 3 absorption performances of metal–containing DESs have been attributed to the synergy of Lewis acid–base and hydrogen bonding interactions. Additionally, good reversibility and high NH 3 /CO 2 selectivity are achieved over the MgCl 2 /Res/EG (0.1:1:2) DES, which enables it to be a potential NH 3 absorber for further investigations. [Display omitted] • Metal-based deep eutectic solvents (MDESs) were prepared for ammonia absorption. • MDESs significantly improve ammonia absorption capacity. • MgCl 2 /Res/EG possesses a high NH 3 capacity up to 0.239 g NH3 /g DES at 313 K. • MgCl 2 /Res/EG exhibits a good recycling performance. • MDESs are potential NH 3 absorbers for further investigations. [ABSTRACT FROM AUTHOR]

The oxidative depolymerization of alkali lignin (AL) in 1-ethyl-3-methylimidazolium acetate ([C 2 C 1 im]OAc) system without additional catalyst was investigated under mild conditions (initial O 2 pressure of 1.5 MPa, 80 °C–100 °C). Compared with other ionic liquids (ILs), the cooperation of imidazolium cation and acetate anion successfully enhanced AL conversion. Among the investigated imidazolium acetate ILs with ethyl- to octyl-side chains, [C 2 C 1 im]OAc presented the best catalytic capacity for AL oxidative depolymerization. Adding an appropriate amount of water to [C 2 C 1 im]OAc can further improve the reaction efficiency. In the [C 2 C 1 im]OAc system with the addition of 0.10–0.25 mL of water, approximately 77 wt% AL was depolymerized into small molecule soluble products at 100 °C for 2 h. The extracted oil was composed mainly of phenolic derived compounds. With the use of the [C 2 C 1 im]OAc-based system, the specific inter-unit linkages of lignin were broken down, and residual lignin with low molecular weight and narrow polydispersity index (1.88–1.96) was obtained. Compared with that in AL conversion with fresh [C 2 C 1 im]OAc, only a minimal decrease (~3.2%) was observed with the recovered IL until the fifth cycle. These findings revealed that [C 2 C 1 im]OAc–based system is a simple and efficient catalytic system for lignin oxidative depolymerization. Imidazolium cation and acetate anion cooperatively promoted lignin oxidative depolymerization in [C 2 C 1 im]OAc under mild conditions (100 °C, initial O 2 pressure of 1.5 MPa). Adding an appropriate amount of water (0.10–0.25 mL) into [C 2 C 1 im]OAc successfully enhanced the lignin conversion. [Display omitted] • Oxidative depolymerization of AL in alkylimidazolium acetate ILs was studied. • [C 2 C 1 im]OAc was used as both solvent and catalyst without use of other catalysts. • 72% conversion of AL was obtained under O 2 pressure of 1.5 MPa at 100 °C for 2 h. • Adding appropriate amount of water (0.10–0.25 mL) enhanced the conversion of AL. • [C 2 C 1 im]OAc was recycled for 5 times and was stable under reaction conditions. [ABSTRACT FROM AUTHOR]

The esterification reactions that occur between citric acid (CA) and lignin on hydroxyl groups of side chains can inhibit the formation of reactive intermediates in acid-catalyzed pretreatments. The effects of CA on dilute hydrochloric acid (1.0%) pretreatments of corn stalk in hydrated 1,4–dioxane were investigated with sodium hypophosphite (0.5%) as the catalyst at 95 °C for 3.5 h. The resulting cellulose recovery (62.5–80.9%) and lignin removal (72.5–85.0%) after adding CA were significantly higher than those in the pretreatment without CA. Water content influenced pretreatment and delignification when CA was added into the treatment systems. The highest yield of total reducing sugar (97.1%) was achieved during the enzymatic hydrolysis of cellulose-rich materials obtained from the pretreatment with 11.4% water content. Meanwhile, β –O–4′ in the extracted lignin increased from 22.4/100Ar to 41.2/100Ar with increasing water content from 11.4% to 25.9%. These findings implied that CA as a stabilization agent could inhibit the repolymerization of degraded lignin fragments due to the esterification between CA and lignin and then improved the enzymatic saccharification of cellulose. [Display omitted] • Acid pretreatments with CA stabilization were investigated at 95 °C for 3.5 h. • CA stabilization suppressed cellulose acid-hydrolysis and lignin condensation. • Lignin with high β -O-4′ content (22.4–41.2/100Ar) was extracted. • Appropriate amount of water addition favors esterification reaction of CA. • TRS yield of 97.1% was achieved in pretreatment with 11.4% water content. [ABSTRACT FROM AUTHOR]

[Display omitted] • CoILs were prepared with [C 2 C 1 im]OAc/[B Z C 1 im]TNf 2 of different R IL. • Lignin depolymerization in CoILs was conducted under 1.15 MPa O 2 at 100 °C. • Cooperative effects was found for lignin degradation and product selectivity. • Interactions and microstructure of CoILs influenced catalytic properties. • CoILs can be recycled and reused in the oxidation at least five times. The aerobic oxidation of lignin model 2-phenoxyacetophenone (2-PAP) in cooperative ionic liquid mixtures (CoILs) with 1-ethyl-3-methylimidazolium acetate ([C 2 C 1 im]OAc) and 1-benzyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide ([B Z C 1 im]NTf 2) was investigated. Complete degradation of 2-PAP was achieved with [C 2 C 1 im]OAc/[B Z C 1 im]NTf 2 molar ratio (R IL) of 1/1 and 1/2 at 100 °C for 2 h. The conversion and product yields from CoILs were higher than those in pure ILs, indicating the cooperative effects of [C 2 C 1 im]OAc/[B Z C 1 im]NTf 2 on cleaving aryl–ether bonds. [C 2 C 1 im]OAc promoted the catalytic cleavage of aryl–ether bonds and solvation, and [B Z C 1 im]NTf 2 induced the formation of alkyl radicals and enhanced the product selectivity. Accordingly, the highest conversion of alkali lignin (79.8%) was obtained with R IL of 5/1 at 100 °C for 2 h, and phenol monomers (306 mg/g) were selectively produced. The CoILs exhibited good catalytic capacities for oxidative depolymerization of lignin, which strongly depends on the changes in intermolecular interactions and structural organization with varying R IL. [ABSTRACT FROM AUTHOR]

Highlights: [•] Collagen/cellulose hydrogel beads (CCHBs) reconstituted from a [C4mim]Cl solution. [•] Cu(II) adsorption steeply increases until collagen/cellulose mass ratio exceeds 2/1. [•] The CCHBs have good adsorption properties and reusability. [ABSTRACT FROM AUTHOR]

• FA stabilized lignin was obtained from [C 4 C 1 im]Cl/HCl/FA pretreatment of biomass. • FA stabilization influenced structure feature of lignin fractions. • Lignin with high molecular weight and low S/G ratio was recovered. • FA stabilization changed the compositions of degraded products from lignin. This work investigated the role of formaldehyde (FA) in lignin anti-condensation during corn stalk pretreatment based on 1-butyl-3-methylimidazolium chloride ([C 4 C 1 im]Cl)/hydrochloric acid (HCl). As a result of the aldolization reactions between FA and lignin, the condensation of lignin fragments was inhibited, and lignin remained in soluble fragmental molecules. Characterizations on the compositional and structural changes of lignin and its degraded products during pretreatment (80 °C–100 °C, 2–5 h) with FA addition in comparison with those in DO/HCl/FA or [C 4 C 1 im]Cl/HCl were conducted. Results revealed that the structural features of lignin were affected by FA addition and solvent type. In the [C 4 C 1 im]Cl/HCl/FA system, FA stabilization was unfavorable for the cleavage of β -O-4′ bonds and lignin with low S/G ratio (3.4) and high molecular weight (Mw = 9920 g·mol−1) was extracted. The compositions of degraded products were considerably affected by FA addition. [ABSTRACT FROM AUTHOR]