Deep eutectic solvents based on choline chloride–carboxylic acids, as a low-cost effective bifunctional catalyst, were successfully used to catalyze epoxidation of soybean oil with peroxyformic acid as the oxygen supplier under solvent-free conditions. The influence of reaction temperature and time on the epoxidation process evaluated by 1H nuclear magnetic resonance (NMR) quantitative analysis was extensively investigated. The optimal mild conditions were 50 °C and 8 h for choline chloride–oxalic acid dihydrate with 88.80% conversion of double bonds and a high selectivity of 93.86%. Meanwhile, choline chloride–malonic acid at 50 °C for 10 h exhibited better catalytic performance, 90.87% selectivity versus only 83.52% in the choline chloride–citric acid monohydrate system for 8 h. The epoxy products analyzed simultaneously by 1H NMR and the titration method were characterized in Fourier transform infrared, 13C NMR, and thermogravimetric analysis. The results suggested choline chloride–oxalic acid dihydrate with a favorable recyclability was more efficient for the promotion of epoxidation of soybean oil.

•Upgrading bio-oil by esterification and alkylation with azeotropic water removal is investigated.•Sugars and their derivatives can separate from upgraded bio-oil by H2O/CH2Cl2 extraction.•Upgraded bio-oil has great properties as stable oxygenated liquid fuel.Due to the negative effects of acids and aldehydes, crude bio-oil has to be upgraded before its application as a high-graded fuel. A novel method for bio-oil upgrading by simultaneous catalytic esterification and alkylation with azeotropic water removal using n-butanol and 2-methylfuran was investigated in this work. Under the optimum upgrading conditions, water content was evidently decreased from 27.82% to 3.21%, and acid number was reduced from 41.12 mg NaOH/g to 6.17 mg NaOH/g. High heating value of upgraded bio-oil was more than 2 times higher than crude bio-oil and the other properties were also improved significantly. GC-MS analysis indicated that labile acids, aldehydes, ketones and lower alcohols were transformed to stable target products. The introduction of 2-methylfuran effectively suppressed acetalization reactions and the yields of more stable alkylation products were higher than acetals. In addition, oxygenated liquid fuel and sugars and their derivatives could be effectively separated from upgraded bio-oil by H2O/CH2Cl2 extraction. The main product in crude sugars part was butyl-β-D-glucopyranoside, which was formed by means of hydrolysis of levoglucosan and the following glycosidation.

Ionic liquid/ethanol was used in bamboo hydrolysis residue (BHR) to separate lignin and cellulose. The optimal dissolution conditions were as follows: 160 °C, 150 min, 1 : 1 of volume ratio of [AMIM]Cl to ethanol, 1 : 10 of mass ratio of solid to liquid, when the dissolution rate was 41.7%, the purity of crude lignin was 86.7%, while that of cellulose product was 92.0%. Additionally the recycling effect of [AMIM]Cl/ethanol was ideal. The crystal structure of cellulose had not been destroyed; its crystallinity increased. Cellulose enzymatic saccharification was investigated, and the optimum process conditions were as follows: 50 °C, 48 h, 2 g L−1 of cellulase concentration, pH = 4.5, when the saccharification yield reached 83.7%. The cellulose crystal structure was destroyed and its degree of crystallinity was decreased after saccharification. Then the monosaccharide was used to convert to 5-hydroxymethylfurfural (5-HMF) under Brønsted acids or Lewis acids catalysis in [AMIM]OAc. It was found that the catalytic effect of Lewis acids was much better than that of Brønsted acids investigated, especially CrCl3. Choosing CrCl3 as catalyst, the optimum process conditions were as follows: 1 : 10 of mass ratio of solid to liquid, 10 mol% (based on monosaccharide) CrCl3, 160 °C, 3 h, when the 5-HMF yield reached 56.8%.

•Selective dissolution of lignin via ionic liquid–ethanol–water mixture.•Low-boiling point anti-solvents employed for lignin precipitation.•High-purity and low-molecular weight lignins get fractionated.This study focused on the anti-solvents precipitation process of lignin fractionation. Eucalyptus globulus wood was pretreated by ionic liquid–ethanol–water mixture before anti-solvents precipitation experiments. The influence of potential anti-solvents on lignin fractionation was extensively studied. Water, methanol, dichloromethane and iso-propanol were proven effective for lignin fractionation by the formation of precipitation. Lignin fractionation performance (yield and purity) was significantly affected by temperature and anti-solvents dosage. The purity of fractionated lignins increased with growing anti-solvents dosage and temperature. While the yield of fractionated lignins decreased as temperature rose. An increase in anti-solvents dosage could dramatically improve lignin yield. Lignin yield increased to a maximum value, but decreased when the anti-solvents dosage increased further. For different anti-solvents, the sequence on lignin yield was: iso-propanol > water > dichloromethane > methanol. While the sequence of anti-solvents on lignin purity displayed in reverse with lignin yield. Lignins fractionated by different anti-solvents were characterized by FT-IR and GPC. Results showed that the fractionated lignins were G–S type, of low molecular weight, with narrow distribution range (450–2250 g/mol) and extremely low polydispersity (Mw/Mn) value (1.12–1.13). These fractionated lignins could be promising materials for the production of high value chemical and fuels.

This paper reports a simultaneous catalytic esterification of acetic acid and alkylation of acetaldehyde using a silica sulfuric acid catalyst from 40 to 140 °C. The results show that the esterification of acetic acid and acetalization of acetaldehyde with 1-butanol took place simultaneously, and both reactions were strongly affected by the temperature and catalyst dosage. The esterification of acetic acid was restrained by acetalization of acetaldehyde at a relatively low temperature (e.g., 90 °C). The increase of the reaction temperature, however, would result in the decomposition of acetals (1,1-dibutoxyethane). To solve these problems, 2-methyl furan, which can react with acetaldehyde, was introduced. Further work shows that the decomposition of 1,1-dibutoxyethane was successfully resolved by the alkylation reaction of acetaldehyde, and yields of the ester (butyl acetate) decreased with the increase of the water content. The maximum yields of alkylation products [2,2′-ethylidenebis(5-methylfuran)] and butyl acetate were 84.5 and 74.4%, respectively.

Novel nanoporous magnetic cellulose–chitosan composite microspheres (NMCMs) were prepared by sol–gel transition method using ionic liquids as solvent for the sorption of Cu(II). The composite microspheres were studied by scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FTIR), thermogravimetric analysis (TGA), X-ray diffraction (XRD), and vibrating sample magnetometry (VSM). Subsequelty, the adsorption of Cu(II) to NMCMs was investigated systematically with varried parameters such as pH, contact time, and initial concentration. Results revealed that the composite microspheres exhibited efficient adsorption capacity of Cu(II) from aqueous solution, due to their favorable chelating groups in structure. The adsorption process was best described by a pseudo-second-order kinetic model, while isotherm modeling revealed that the Langmuir equation better describe the adsorption of Cu(II) on NMCMs as compared to Freundlich model. Moreover, the loaded NMCMs can be easily regenerated with HCl and reused repeatedly for Cu(II) adsorption up to five cycles. The environmental friendly microspheres were expected to be a promising candidate for future practical use in heavy metal ions removal.

Amorphous carbon-based sulfonated catalysts were generated from four kinds of biomass (lignin, cellulose, wood meal and D-xylose) by hydrothermal carbonization at various temperatures (225, 245 and 265 °C) followed by sulfonation, with a yield of 36–56%. All of these catalysts showed aromatic structure, hydroxyl and carboxyl groups, with a density of SO3H groups between 0.56 and 0.87 mmol g−1. 5-Hydroxymethylfurfural (HMF) was produced from inulin in ionic liquids (ILs) in one step with the addition of carbon-based sulfonated catalysts, with a factual yield of 47–65% at 100 °C, 60 min. Moderate extension of reaction time (from 30 to 90 min) and increase of temperature (from 80 to 120 °C) promoted HMF production. Ethyl acetate was used as extractant, and about 39–55% of HMF can be recovered from ILs. One problem with these carbon-based sulfonated catalysts was that they would be partly deactivated in ILs for separate reuse, however, they can be easily regenerated by dilute sulfuric acid treatment. The carbon-based sulfonated catalysts exhibited good catalytic activity compared with traditional solid acid catalysts, and the carbon-based sulfonated catalyst/ILs reaction system showed high reusability. In consideration of the renewable as well as the high catalytic activity abilities, these biomass derived carbon-based sulfonated catalysts would be promising for industrial application.

Cornstalk lignin was hydrothermally depolymerized at mild conditions in ethanol–water for producing value-added phenolics. The effects of residence time (from 30 min to 180 min), reaction temperature (from 498 K to 573 K) and concentration of ethanol (from 0% to 95% vol.) on yields of liquid products and phenolic compounds were studied in detail. The optimal conditions of 523 K, 90 min and 65% vol. ethanol–water resulted in the highest yield of liquid products (∼70 wt.%). The liquid products were analyzed by gas chromatography–mass spectrometry (GC–MS) to confirm the presence of primarily heterocycle (2,3-dihydrobenzofuran) and phenolics (such as ethylphenol, guaiacol, ethylguaiacol and syringol). Reaction conditions had significant effects on yield and composition of liquid products.Highlights► Lignin was hydrothermally depolymerized in ethanol–water at mild conditions. ► High yield of liquid products was obtained (∼70 wt.%). ► The liquid products were mainly composed of phenolics.

A method for production of high-value-added phenolics by combining organosolv lignin extraction with lignin hydrothermal depolymerization without catalysts under mild conditions was successfully developed. During lignin extraction, the optimal ethanol concentration in mixed solvent is 65 vol %, with which 78% purity (based on Klason lignin) of crude lignin was obtained. High yield of liquid products up to 65.5% was recovered from lignin depolymerization under conditions of 523 K, 90 min, 65 vol % ethanol, and 3% lignin; meanwhile, only 17% solid residue was obtained. The gas chromatography–mass spectrometry (GC–MS) analyses of the obtained liquid products confirmed the presence of value-added phenolics, among which the yields of 4-ethylphenol, 4-vinylphenol, guaiacol, 4-ethylguaiacol, and 4-vinylguaiacol were very high (∼30% of the identified compounds). Gel permeation chromatography (GPC) and Fourier transform infrared (FT-IR) spectroscopy of these liquid products indicated that lignin was really depolymerized to low molecular weight compounds and that the cleavage of ether bonds and decarbonylation were the major reactions during lignin depolymerization.

The mixture of ionic liquid (IL) and aqueous ethanol has been proven to be a promising biomass pretreatment solvent, facilitating the separation of cellulose and faster breakdown of hemicellulose through the disruption of lignin. However, lignin and sugar monomers from the hydrolysis of polysaccharides are soluble in IL and difficult to separate. This complicates the recycling of IL. To address this, CrCl3 and CrCl3·6H2O are used as catalysts for the one-pot conversion of lignin and sugars in the ionic liquid 1-butyl-3-methyl imidazolium chloride ([BMIM]Cl). Furfural resin or humin is produced and separated from IL after the reactions. When catalyzed by CrCl3.6H2O and at a high temperature (≥170 °C), almost all the lignin and sugars are transformed to humin, which leads to the high efficiency of IL recycling. And the mechanisms of the reactions are studied with guaiacylglycerol-beta-guaiacyl ether (GG) and glucose as model compounds.

Hydrothermal carbonization of cellulose, lignin, d-xylose (substitute for hemicellulose), and wood meal (WM) was experimentally conducted between 225 and 265 °C, and the chemical and structural properties of the hydrochars were investigated. The hydrochar yield is between 45 and 60%, and the yield trend of the feedstock is lignin > WM > cellulose > d-xylose. The hydrochars seem stable below 300 °C, and aromatic structure is formed in all of these hydrochars. The C content, C recovery, energy recovery, ratio of C/O, and ratio of C/H in all of these hydrochars are among 63–75%, 80–87%, 78–89%, 2.3–4.1, and 12–15, respectively. The higher heating value (HHV) of the hydrochars is among 24–30 MJ/kg, with an increase of 45–91% compared with the corresponding feedstock. The carbonization mechanism is proposed, and furfural is found to be an important intermediate product during d-xylose hydrochar production, while lignin hydrothermal carbonization products are made of polyaromatic hydrochar and phenolic hydrochar. The formation of microspheres on the surface of cellulose and WM hydrochars is discussed, and transformation of the hemicellulose should be the reaction for WM microsphere production.

A new method for selective separation of wood components is presented. Based on Hansen’s theory of solubility, ionic liquid (IL) 1-butyl-3-methylimidazolium bromine ([Bmin]Br) was mixed with aqueous ethanol. HBr the acid catalyst in the degradation of wood components, was found to form in situ by ion exchange between IL and organic acid. The hydrogen bonding capacity of the mixture was enhanced as the presence of IL, which led to the promotion of the solubilization of lignin and other products from carbohydrates hydrolysis. The data showed that, variations of the IL concentration caused cellulose to be separated from pine wood with a purity of more than 94%, or to be hydrolyzed and converted into saccharides together with hemicellulose. Because of the complete hydrolysis of hemicellulose, the cross-linked matrix of lignin and hemicellulose was destroyed, which led to the isolation of lignin with a high purity of about 93%.

Alkaline lignin was liquefied under hydrothermal conditions, and the liquefied products were effectively separated into four main types of substances: benzenediols, monophenolic hydroxyl products, weak-polar products, and water-soluble products (low-molecular-weight organic acids, alcohols, etc.). The production process and yield of each classified products are discussed. More than half of the yields of the oil products consisted of phenolics. A mechanism for phenolic production from lignin liquefaction is proposed. It suggests that the decomposition of lignin under hydrothermal conditions occurs mainly by three steps: hydrolysis and cleavage of the ether bond and the C–C bond, demethoxylation, and alkylation.

Bio-oil was upgraded by catalytic esterification over the selected catalysts of 732- and NKC-9-type ion-exchange resins. The determination of the acid number by potentiometric titration was recommended by the authors to quantify the total content of organic acids in bio-oil and also to evaluate the esterification degree of bio-oil in the process of upgrading. We analyzed the measurement precision and calibrated the method of potentiometric titration. It was proven that this method is accurate for measuring the content of organic acids in bio-oil. After bio-oil was upgraded over 732 and NKC-9, acid numbers of bio-oil were lowered by 88.54 and 85.95%, respectively, which represents the conversion of organic acids to neutral esters, the heating values increased by 32.26 and 31.64%, and the moisture contents decreased by 27.74 and 30.87%, respectively. The accelerated aging test and aluminum strip corrosion test showed improvement of stability and corrosion property of bio-oil after upgrading, respectively.

AbstractUpgradation of bio-oil before utilization is desirable to obtain high grade fuel because of its drawbacks like high viscosity, low heating value, poor stability and high corrosiveness. Organic acids in bio-oils can be converted to their corresponding esters by catalytic esterification and this greatly improved quality of bio-oils. We selected 732 and NKC-9 type ion exchanger resins as esterification catalysts for upgrading bio-oil. The catalytic activity was first investigated by model reaction. The esterification of bio-oil with methanol was conducted in a batch reactor. Acid numbers of upgraded bio-oil on 732 resin and NKC-9 resin were lowered by 88.54% and 85.95%, respectively, which represents the conversion of organic acids to neutral esters; the heating values increased by 32.26% and 31.64%, respectively; the H2O contents decreased by 27.74% and 30.87%, respectively; the densities were lowered by 21.77% for both and the viscosities fell by approximately 97%. A fixed bed reactor was used for continuous catalytic esterification of bio-oil on 732 resin, and the acid number remarkably decreased by 92.61%. The accelerated ageing test showed improvement of stability, and the aluminum strip corrosion test showed reduced corrosion rate of bio-oil after upgradation.