The specific heat capacities (Cp) of four absorbents (1,1,3,3-tetramethlylguanidinium lactate, monoethanolammonium lactate, betaine-ethylene glycol, and l-carnitine-ethylene glycol), which can chemically absorb sulfur dioxide (SO2) with low concentrations, were measured by a Calvet BT 2.15 calorimeter in a temperature range of 318.15 K–363.15 K. The measured specific heat capacities as a function of temperature were correlated with a second-order empirical polynomial equation. The result indicates that the equation can accurately fit the measured specific heat capacities. All the measured specific heat capacities increase with increasing temperature. 1,1,3,3-Tetramethlylguanidinium lactate has the lowest specific heat capacity. The measured specific heat capacities of the four absorbents are lower than that of water, which is beneficial to the desulfurization process.

A novel absorbent sodium lactate (NaLa) aqueous solution (aq) for SO2 absorption is reported. SO2 in simulated flue gas is reversibly absorbed in NaLa aq. The absorption capacity of SO2 in the absorbent increases with increasing NaLa content and SO2 concentration, and decreasing temperature. Compared with the absorbents reported in the literature, the absorption capacity of SO2 in NaLa aq. is much high, for example, 50 wt % NaLa aqueous solution can absorb 0.130 g SO2/g absorbent at a SO2 concentration of 2.5 vol % and 40 °C. Importantly, NaLa (aq) exhibits high reversibility and long-term stability, indicating a promise for the desulfurization of flue gas. The absorption mechanism is proposed to be the replacement of lactic acid (HLa) by sulfurous acid (H2SO3), which is generated by dissolving SO2 in water.

Task-specific ionic liquids (TSILs) have been widely observed to effectively absorb low-concentration SO2 from flue gas by chemical interaction. However, the interaction between SO2 and TSILs is still unclear. The addition of solvents can decrease the viscosity of TSILs and promote mass transfer, but whether the solvents have an impact on absorption is unknown, as is the effect on absorption mechanism. To solve these issues, we synthesized several types of TSILs containing carboxylate anion to capture SO2 from simulated flue gas. The mechanism of absorption of SO2 by the TSILs was investigated in detail using Fourier transform infrared (FT-IR), 1H nuclear magnetic resonance (NMR), and 13C NMR. The results show that chemical interactions can be found between the carboxylate anions of TSILs and SO2. Simultaneously, the effect of several solvents on SO2 absorption capacity of TSILs was studied. The results indicate that ethylene glycol (EG) in TSILs has a strong influence on SO2 absorption by guanidinium- and alkanolaminium-based TSILs, but for quaternary ammonium-based TSILs, EG has no effect. Finally, the interaction between EG and TSILs was investigated by FT-IR, and the absorption mechanism was studied. It has been found that the addition of EG can improve the basicity of guanidinium- and alkanolaminium-based TSILs to increase the absorption capacity.

Carboxylic acids are widely used in industry and are considered an important type of chemicals. The production of carboxylic acids through oxidation of lignite is very promising. The traditional alkali−oxygen oxidation of lignite can produce high yields of carboxylic acids, but the process consumes a great deal of alkali and acids and the high reaction temperature increases the energy consumption. In the present work, we found that carboxylic acids, including small-molecule fatty acids and benzene poly(carboxylic acid)s, could be obtained by catalytic oxidation of lignite in NaVO3/H2SO4 aqueous solution with molecular O2. The effects of NaVO3/coal mass ratio, H2SO4 content, reaction temperature, initial O2 pressure and reaction time on the conversion of lignite and yield of carboxylic acids were investigated. In the process of reaction, lignite is first converted into water-soluble intermediates, which are then converted into carboxylic acids. The second step is the rate controlling step. It has been found that in the catalytic system, sulfuric acid not only promotes the degradation of lignite, but also changes the activity of vanadium species. Vanadium species promote both the conversion of lignite and the generation of carboxylic acids. The presence of oxygen makes vanadium species complete redox cycle, keeping the reaction ongoing. Compared with the alkali–oxygen oxidation, this catalytic oxidation method can reduce the usage of acid and alkali, and lower reaction temperature, while keeping the same yield. The catalytic system was reused four times without decline in activity.

Carboxylic acids (CAs) are considered as an important group of chemicals and are widely used in the chemical industry. The production of CAs via oxidation of lignite is a promising industrial process. In the present work, we found that H5PV2Mo10O40 (HPA) was beneficial to catalytic oxidation of lignite by O2 in aqueous H2SO4 solutions to produce CAs. The effects of HPA concentration, H2SO4 concentration, reaction temperature, initial O2 pressure, and reaction time on lignite conversion and CA yield were studied. The catalytic oxidation of lignite in aqueous HPA/H2SO4 solutions with O2 can yield 56.9 wt % CAs, including 33.5 wt % formic acid, 14.4 wt % acetic acid, 1.5 wt % succinic acid, 1.1 wt % oxalic acid, and 6.4 wt % benzene carboxylic acids (BCAs, including 12 types) at 170 °C and 3 MPa for 60 min. In this catalyst system, the existence of H2SO4 can change the catalytic activity of HPA, and the synergistic effect of HPA and H2SO4 can significantly promote the production of CAs. VV can oxidize lignite or intermediates to form VIV, which can be reoxidized by O2 to complete a redox cycle. In the catalytic oxidation, lignite was converted into water-soluble intermediates at first, and then the water-soluble intermediates were converted to CAs. The catalyst system was reused four times without significant decline in activity. Compared with the traditional alkali-oxygen oxidation, this method can decrease the usage of mineral acid and alkali and lower reaction temperatures.

•Quaternary ammonium salts (QASs) can form deep eutectic solvents (DESs) with phenols.•The mass transfer coefficients and extraction rates of phenol were determined.•Effects of stirring rate, temperature, specific area and QASs on extraction rates.•The mass transfer of phenol in the extraction is controlled by diffusion.•Phenol diffusion in the DES phase is the slow extraction rate-determining step.The separation of phenols from oil mixtures with quaternary ammonium salts (QASs) via forming deep eutectic solvents (DESs) is efficient, which avoids using alkali and acid and producing phenol-contained wastewater. In order to understand deeply the extraction process, the extraction kinetics of phenol in a model oil/DES system was studied using a constant-interface Lewis cell technique. The mass transfer coefficients and extraction rates of phenol were determined and the effects of stirring rate, temperature, specific area and QASs on the extraction were investigated. The results show that when using choline chloride as extractant, the extraction rate and mass transfer coefficient of phenol increase with increases of stirring rate and temperature. In the extraction process, the apparent active energy is 8.85 kJ mol−1. The mass transfer of phenol is controlled by diffusion, and the phenol diffusion in the DES phase is the slow extraction rate-determining step.

•Two kinds of zwitterionic alkaloids are biodegradable, environmentally benign and free from halogen anion.•Effect of temperature and dosage of zwitterionic alkaloids were investigated.•Zwitterionic alkaloids can separate phenol from oil with high selectivity.•It can provide important information for designing separation processes as well as their simulation and optimization.Phenols are important materials for the organic chemical industry. They mainly come from coal liquefaction oil, coal tar, petroleum and biomass pyrolysis oil, making the separation of phenols from oil mixtures of great commercial value. Two zwitterionic alkaloids, betaine and L-carnitine, biodegradable and environmentally benign ionic compounds, can efficiently separate phenols from oils by forming deep eutectic solvents (DESs). In this work, the phase equilibria of two ternary systems of toluene + phenol + betaine and toluene + phenol + L-carnitine were measured at 25.0 °C, 45.0 °C and 65.0 °C under atmospheric pressure. The phase behaviors of the two ternary systems were studied, which indicated that there were three kinds of phase regions: liquid, liquid-liquid, and liquid-liquid-solid. The separation of phenol from oil mixtures occurs at the latter two phase regions. Effects of temperature, zwitterionic alkaloid type and its dosage on the phase equilibrium were investigated. With decreasing temperature, the distribution and selectivity coefficients increase. L-carnitine shows better performance in separating phenol from oils via forming DES than betaine.

•Alkali-oxygen oxidation of Yilan oil shale could yield 13.6 wt% of 12 benzene carboxylic acids (BCAs).•A new structural model of Yilan oil shale kerogen was constructed based on BCAs information.•The model had a molecular formula of C5322H6322O1355N100S45.•There were two kinds of aromatic clusters, convertible and not convertible to BCAs.•The model can reflect not only the distribution of BCAs, but also the results of all techniques used.Oil shale is an important fossil resource, and the structure of its kerogen is the foundation of application. In this work, we found that 12 benzene carboxylic acids (BCAs) were obtained from oil shale via alkali-oxygen oxidation. However, none of the structural models proposed in the literature can explain the yield distribution of BCAs. Therefore, the structure of Yilan oil shale (YL) kerogen was studied and a new typical structural model of the kerogen was constructed based on the yield distribution of 12 BCAs combined with the results of ultimate analysis, 13C NMR, FTIR, XRD, and XPS of YL kerogen. The alkali-oxygen oxidation of YL kerogen showed that the kerogen was fully converted and total mass yields of BCAs had a maximum of 13.6 wt%. The yield distribution of BCAs and 13C NMR result indicate that aromatic clusters in the kerogen come in two forms: convertible to BCAs and unconvertible to BCAs. The structures of organic heteroatom species (O, N and S) were determined by 13C NMR, FTIR, XPS and ion-exchange method. The structural model constructed based on these results has a molecular formula of C5322H6322O1355N100S45 and a mass-average molecular weight of 94,816 Da, which not only account for the distribution of BCAs, but also the results of all techniques used above.The structure of YL kerogen was studied and a structural model was constructed based on the distribution of benzene carboxylic acids (BCAs) from oxidation of the kerogen, combined with its ultimate analysis, 13C NMR, FTIR, XRD, XPS, analysis of carboxyl and phenolic hydroxyl groups.Download high-res image (372KB)Download full-size image

•The relationship between structural characteristics and kerogens’ humic degree was studied.•The aliphaticity and average methylene chain length decrease with increasing humic degree.•The aromaticity and average aromatic cluster size increase with increasing humic degree.•The existence forms of heteroatom species (O, N and S) in kerogens were determined.•The heteroatom species change regularly with increasing humic degree of kerogens.Elemental analysis, CP/MAS 13C NMR, FTIR, XRD, XPS and ion-exchange experiment were used to study the structural characteristics of Longkou, Huadian and Yilan kerogens in an increasing order of humic degree. The relationship between their humic degree and structural characteristics was studied from three aspects: aliphatic structure, aromatic structure and heteroatom species (O, N and S). The results show that the kerogens are mainly composed of aliphatic structure, dominantly as CH2 chain. Moreover, the ratio of aliphatic carbon (fal, aliphaticity) and average methylene chain length (Cn) decrease with the increase of humic degree. In these kerogens, most of their aromatic clusters are separated by various bridge bonds or many CH2 long chains. Furthermore, the ratio of aromatic carbon (fa, aromaticity) and average aromatic cluster size increase while the substitutive degree of aromatic ring decreases with increasing humic degree. With an increase in humic degree, the content of OCO (carboxyl and ester) decreases and the contents of CO (alcohol, phenol, and ether) increase. Moreover, the content of phenolic hydroxyl groups increases and the content of carboxyl groups decreases with increasing humic degree. The organic nitrogen in the kerogens is distributed as pyridinic nitrogen, amine nitrogen, pyrrolic nitrogen and chemisorbed nitrogen oxides. The contents of pyridinic nitrogen and chemisorbed nitrogen oxides increase while the contents of amino nitrogen and pyrrolic nitrogen decrease with increasing humic degree. In addition, organic sulfur in these kerogens exists as aromatic and aliphatic sulfur, sulfone and sulfoxide. The contents of aromatic sulfur and sulfoxide increase while the contents of aliphatic sulfur and sulfone decrease with increasing humic degree.

•Lignin degradation was first studied in lignocellulose catalytic oxidation.•Intermediates were carefully determined and probable mechanisms were proposed.•Effects of H2SO4, NaVO3 and O2 on lignin degradation were investigated.Catalytic oxidation of lignocellulose in hydrothermal condition catalyzed by vanadium-containing homogeneous catalysts is a promising method to prepare formic acid (FA), a potential material in emerging field of clean energy technologies. The FA production from polysaccharides components of lignocellulose has already been well studied. However, the conversion of lignin component, which quite differs in structure from polysaccharides, has not been studied systematically. In this work, the lignin degradation was studied in NaVO3-H2SO4 aqueous solution with O2 as oxidant. The degradation mechanism was studied in detail. Compared with polysaccharides, lignin can produce a much lower yield of FA with a formation of a larger amount of CO2. H2SO4 can catalyze highly-polymerized lignin to segments by CO bond hydrolytic cleavage, but the conversion is limited. NaVO3 and O2 can accelerate the lignin degradation by weakening the CO bond. In liquid phase, NaVO3 and O2, with a low selectivity on products, lead to different kinds of reactions, mainly including phenolic hydroxyl oxidation to quinone, aliphatic hydroxyl oxidation to ketone/aldehyde, aliphatic CC bond cleavage, intramolecular dehydration and decarboxylation. This study gives a deep understanding of lignin transformation during catalytic oxidation, and provides guidance to the further application of FA production from natural lignocellulose.

•A new method of production of carboxylic acids (CAs) from lignite was proposed.•Lignite was oxidized by O2 with FeCl3/H2SO4 catalyst system to yield 51.7 wt% CAs.•A synergistic effect of FeCl3 and H2SO4 significantly promotes the production of CAs.•The FeCl3/H2SO4 catalyst system shows well reusability.•The method is environmentally benign compared with previous alkali-O2 and V-based oxidations.Carboxylic acids (CAs) are important chemicals widely used in industrial manufacturing. They can be produced with high yields from O2 oxidation of lignite and the process is regarded promising in the future. However, current methods for the process consume a large amount of mineral alkali and acids, or involve catalysts that are harmful to environment and human beings, and require high temperatures. In this work, we have screened various catalysts and found an iron-based catalyst (FeCl3, Fe2(SO4)3) to be beneficial for the process. The products include formic acid, acetic acid, oxalic acid, succinic acid and benzene carboxylic acids (BCAs, including 12 types). The effects of FeCl3 concentration, H2SO4 concentration, reaction temperature, initial O2 pressure and reaction time on lignite conversion and CAs yield are studied. It is found that H2SO4 can change the catalytic activity of FeCl3 resulting in a synergistic effect for CAs production. In the oxidation process, Fe3+ is reduced to Fe2+ by lignite while O2 reoxidizes Fe2+ to Fe3+ to form a redox cycle. The catalyst can be reused without significant decline in activity. The method developed in this work requires no alkali and consumes little H2SO4, and is environmentally benign.

•An anti-extraction method could remove the neutral oil entrained in deep eutectic solvents (DESs).•DESs were formed by quaternary ammonium salts and phenolic compounds from oil mixtures.•Low-carbon alkanes like n-hexane could efficiently extract the neutral oil and not dissolve in DESs.•The purity of phenolic compound product is greatly improved and reaches up to 96.5%.Forming deep eutectic solvents (DESs) by quaternary ammonium salts (QASs) and phenolic compounds to extract phenolic compounds from oil mixtures is effective. However, a small amount of neutral oil is entrained in the DESs. In this work, we proposed an anti-extraction method to remove the neutral oil entrained in DESs. Low-carbon alkanes (LCAs, including n-hexane, cyclohexane, and n-nonane) were added to model DESs to remove neutral oil. We found that the LCAs could effectively remove neutral oil entrained in the DESs. Of the three LCAs, n-hexane showed the best performance, and the removal rate of neutral oil could reach as high as 92.2%. The separation process could complete within 15 min, and the removal rate of neutral oil did not change significantly with temperature. In addition, n-hexane could effectively remove neutral oils in DESs formed by real coal tar and choline chloride. The neutral oil content in the phenolic compound product decreased to only 1.9 wt%, which greatly improves the purity of the phenolic compound product.Download high-res image (72KB)Download full-size image

•The yields of benzene carboxylic acids increase from 18.5% to 51.3% with coal rank.•Low rank coal benefits the generation of BCAs with a high number of carboxyl.•With increasing of coal rank, BCAs with a small number of carboxyl increase.•When the carbon content of coal is > 87%, the structure of coal has a mutation.The oxidation of coal to produce benzene carboxylic acids (BCAs) was widely researched. However, the relationship between coal rank and BCAs from coal is unknown. In this study, 8 kinds of coal with different ranks were investigated and the effect of coal rank on the BCA yield distribution was studied. The results indicate that with the increase of coal rank, the yield of BCAs increases, and the structure of coal becomes more and more difficult to be degraded. In addition, BCA yield distribution varies significantly with the increase of coal rank. The results of 13C NMR show that with increasing coal rank, the fraction of aromatic carbon (fa) and mole fraction of aromatic bridgehead carbon in aromatic carbon (Xb) both are increased gradually, and alkyl-substituted degree of aromatic ring (δ) and average methylene chain length (Cn) both are decreased. More and more parent structures of phthalic acid, trimellitic acid, hemimellitic acid and prehnitic acid exist in the coal with the increase of coal rank. When the carbon content of coal is > 87%, the structure of coal has a mutation property that more and more circular catenations of aromatic rings exist in the structure of coal.

•Distribution of benzene carboxylic acids (BCAs) was obtained with alkali-oxygen oxidation of lignite.•Relationship between distribution of BCAs and lignite structure was studied.•The structural changes of lignite during alkali-oxygen oxidation was investigated with 13C NMR.•The structural properties of residues and humic acids with oxidation time were revealed.Production of carboxylic acids (including 12 types of benzene carboxylic acids (BCAs) and small-molecule fatty acids) from lignite via oxidation has been widely studied, but few studies addressed the relationship between distribution of BCAs and structure of lignite. This work studies alkali-oxygen oxidation of Xiaolongtan lignite and distributions of BCAs with 13C NMR as well as the relationship between the distributions of BCAs and the lignite structures. The results indicate that the dominant aromatic structures in the lignite are naphthalene and benzene with a mole ratio of around 3, and an alkyl-substituted degree of aromatic rings of 0.359. These structure characters determine that the yields of benzene tricarboxylic acids, benzene tetracarboxylic acids, benzene pentacarboxylic acid and mellitic acid are more than those of other BCAs. In the oxidation process, the organic matter of lignite is first converted to humic acids (HAs), then to water soluble acids, and last to carboxylic acids. The last conversion step is the rate-controlling step. Analyses of the residues and HAs indicate that C–O bond of lignite is easily cleaved. The aromatic structures (except condensed aromatic rings) are easily depolymerized from lignite, but the condensed aromatic rings and long alkyl chains are difficult to be oxidized. With an increase in oxidation time, in the residues, the contents of aromatic structures decrease, but the contents of condensed aromatic rings and long alkyl chains both increase. While in HAs, the contents of condensed aromatic rings increase, but the average methylene chain length (Cn) decreases.

•Rice straw was efficiently converted to chemicals in an H2O-SO2 system.•The degradation products in the two-step treatment were prohibited.•The total yield of products by the two-step treatment of rice straw was 41.1%.•Kinetic analysis was performed by Saeman modeling and Arrhenius equation.Rice straw is a renewable, cheap, and abundant resource in agriculture. Due to its controllable and recoverable properties, H2O-SO2 system was studied as a reaction medium to hydrolyze rice straw to produce chemicals by a two-step treatment. The first-step treatment converted hemicellulose to xylose (17.1%), glucose (3.1%) and arabinose (3.5%) at 140 °C. The second-step treatment converted cellulose to glucose (10.9%) at 190 °C. The total yield of products by the two-step treatment of rice straw was 41.1%, which is more than that in the one-step treatment (21.0% at 190 °C). The apparent activation energies for hemicellulose conversion and xylose dehydration were 76.7 and 66.9 kJ/mol, respectively. The degradation products obtained from the two-step treatment are less than that from the one-step treatment.

•The prepared four deep eutectic solvents (DESs) can efficiently capture low-concentration SO2.•Imidazole-based (Im)-glycerol (Gly) DESs are thermostable, cheap and easily prepared.•The absorption of 2000 ppm SO2 in Im-Gly DESs is high up to 0.643 mol SO2/mol Im (0.163 g SO2/g DES).•Im-Gly DES is a promising absorbent for capture and recovery of SO2 from flue gas.Four thermostable functional deep eutectic solvents (DESs) based on imidazole (Im), 2-methylimidazole, 2-ethylimidazole, and 2-propylimidazole as hydrogen bond acceptor (HBA) and glycerol (Gly) as hydrogen bond donor (HBD) were prepared. All prepared DESs can efficiently capture low-concentration SO2. The SO2 solubility increased with decreasing temperature and increasing SO2 concentration and the available absorption of 2000 ppm SO2 in Im-Gly DES was high, up to 0.634 mol of SO2/mol of Im (0.161 g of SO2/g of DES) with nIm:nGly = 1:2 at 40 °C. The regeneration experiments showed that the SO2 absorption capacities in Im-Gly DES did not change after 5 absorption/desorption cycles. Furthermore, the absorption mechanism based on 1H NMR and FTIR analyses indicated that there was an acid–base interaction between SO2 and Im.Download high-res image (84KB)Download full-size image

•Environmentally benign quaternary ammonium-based zwitterions were designed to form DESs.•Separation of phenol from oils via forming DES can avoid environmental pollution.•The zwitterions are free from halogen anion, avoiding its corrosion to steel equipment.•The maximum phenol extraction efficiency is 94.6% by using l-carnitine.•The zwitterions can be regenerated and reused without losses in extraction efficiency and extractant mass.The separation of phenolic compounds from oil mixtures is widely used in the chemical industry. In this research, we found that two types of environmentally benign quaternary ammonium-based zwitterions, betaine and l-carnitine, could be used as new extractants for the separation of phenol from model oils by forming deep eutectic solvents (DESs). The effects of extraction time, temperature, mole ratio of zwitterion to phenol and initial phenol content on the efficiency of phenol separation were investigated. The results indicated that betaine and l-carnitine could form DESs with phenol, and the DESs were insoluble in model oils. Phenol in model oils could be extracted with extraction efficiencies up to 94.6% at an l-carnitine:phenol mole ratio of 0.4 (an l-carnitine:phenol mass ratio of 0.68) and 298.2 K. Phenol in DES could be recovered using an anti-solvent, and betaine and l-carnitine could be regenerated and reused for 4 cycles without obvious decreases in extraction efficiency and extractant mass, and they were not changed in their structures after reuse. The separation mechanism was investigated using FT-IR, which showed that betaine and l-carnitine formed DESs with phenol through hydrogen bonding.

Novel kinds of environmentally benign and stable absorbents, quaternary ammonium inner salts betaine (Bet) and l-carnitine (l-car) in aqueous solution, were designed and applied to efficiently and reversibly capture sulfur dioxide (SO2) in flue gas. The effects of the inner salt concentration, absorption temperature, SO2 concentration, and reuse cycle on the absorption of SO2 by the two absorbents were investigated. The results show that SO2 absorption capacities of the absorbents with 50% inner salt mass fraction were 0.155 mol of SO2/mol of Bet for Bet aqueous solutions and 0.599 mol of SO2/mol of l-car for l-car aqueous solutions, at 40 °C with a SO2 concentration of 2%, and the absorption capacities of absorbents did not change after 5 absorption/desorption cycles. Furthermore, Fourier transform infrared spectroscopy and proton nuclear magnetic resonance results demonstrate that the SO2 absorption follows the law that a strong acid (H2SO3) replaces a weak acid (−COOH). The absorbents could be used for more than 1 week without any change in the structure, indicating the promise for industrial applications in desulfurization of flue gas.

Carboxylic acids are widely used in industry as a kind of important chemical materials, and it is very promising to produce carboxylic acids from lignite. The traditional alkali-oxygen oxidation of lignite does not consider the complex structure of lignite, and the structures with different reactivities are treated under identical and harsh reaction conditions, resulting in a low yield of carboxylic acids. We propose a two-stage oxidation process of lignite to increase the yield and mitigate the harsh reaction conditions. First, lignite was extracted using a NaOH aqueous solution to yield two parts (extract and residue) with different reactivities. The extract and residue then were oxidized separately with alkali-oxygen oxidation under different conditions. In this way, high yields of benzene carboxylic acids (BCAs, 12 types) and small-molecule fatty acids (SMFAs) could be obtained. The extraction conditions and the alkali-oxygen oxidation conditions of the extract and the residue were investigated. Compared with the oxidation of extract, the oxidation of residue requires higher reaction temperature, higher initial O2 pressure, higher alkali concentration, and longer reaction time. The structures of the extract and residue were characterized by 13C nuclear magnetic resonance (13C NMR) and Fourier transform infrared (FT-IR) spectroscopy, which indicates that most of aromatic structures in the extract are single aromatic rings with side chains containing many oxygen-containing functional groups. However, aromatic structures in the residue are mainly condensed aromatic rings with side chains containing many alkyl chains. These differences in their structures result in different yields of carboxylic acids from the extract and residue.

•A new structural model of organic matter of Huolinhe lignite was constructed.•The model had a molecular formula of C3942H3666O883N50S11.•The model explain the generation of BCAs in the process of lignite oxidation.•The work provides a new way to study the organic matter structure of coal.Coal is an important fossil energy. In order to improve its use efficiency, the study of its complex structure has drawn much attention all over the world. Since 1942, lots of molecular level models of coal have been proposed. However, they cannot reflect the yield distribution of benzene carboxylic acids (BCAs) that are generated from coal by oxidation. In this work, the organic matter structure of Huolinhe lignite was studied and a new structural model of organic matter of the lignite was constructed based on the yield distribution of BCAs from the oxidation of the lignite. Huolinhe lignite was analyzed via ultimate analysis, FTIR, XPS and 13C NMR to investigate its elemental composition, organic functional groups, and carbons types and quantities. At first, various carbon structural parameters of the lignite were calculated through peak fitting of 13C NMR. Then, combined with BCAs yields, aromatic clusters of the lignite model were built. Finally, a structural model of the lignite organic matter was constructed combined with the results of ultimate analysis, FTIR, XPS, 13C NMR and the contents of carboxyl and phenolic hydroxyl groups. The results showed that the model had a molecular formula of C3942H3666O883N50S11, and a molecular weight of 66,150 amu. The model can not only satisfy the results of ultimate analysis, FTIR, XPS, 13C NMR and the contents of carboxyl and phenolic hydroxyl groups, but also explain the generation of BCAs in the process of lignite oxidation and satisfy the yield distributions of BCAs. The work provides a new way to study and construct the organic matter structural model of coal.

The preparation of formic acid (FA) by catalytic oxidation of sustainable biomass is of significant conceptual and practical interest, because FA is an important chemical and is now produced from non-sustainable fossil fuel. In this work, we found that a binary catalyst of Keggin-type heteropoly acid H5PV2Mo10O40 + H2SO4 was efficient in oxidizing biomass cellulose to FA using oxygen as an oxidant in aqueous solution. In the oxidation, the pH of the aqueous solutions plays a key role, and a decrease in pH improves the transformation. Cellulose was transformed to FA with conversions from 60% to 100% and FA yields from 28% to 61% (based on the carbon atoms in the feedstock) after 5 min of reaction at 180 °C, using H2SO4 as an additive to decrease the pH from 1.79 to 0.56. The influences of the pH on both the catalyst and the reaction pathway were discussed. By decreasing the pH, the oxidation potential and electron affinity were increased due to the formation of protonated H5PV2Mo10O40 and VO2+ species, favoring the reduction of the catalyst and oxidation of the substrate. A reaction pathway for the generation of products was proposed, and the influence of the pH on the reaction pathway was also discussed.

As analogues of ionic liquids, deep eutectic solvents (DESs) have attracted considerable attention in the field of separating aromatics from aromatics/aliphatics mixtures. In this work, the performance of a series of DESs was evaluated for their selective extraction of toluene from toluene/n-heptane mixtures. The results showed that the extraction ability for toluene using DESs was greatly influenced by hydrogen bond acceptors (HBAs) and hydrogen bond donors (HBDs) which formed the DESs. The selectivity of toluene was distinctly enhanced by short side chains, a small central atom of the cation and a large anion of the HBA, together with a suitable position for an alkyl chain and appropriate functional group of the HBD. It was also found that an increase of extraction temperature at the studied range could enhance the selectivity for toluene. This work makes the roles of HBAs and HBDs clear in the extraction of aromatics, providing information for designing more effective DESs for aromatics extraction.

•Phase equilibria for separating phenol in oil with quaternary ammonium salts (QASs).•Phase diagrams of QAS + phenol + toluene ternary mixtures at different temperatures.•Effects of temperatures, QAS type and QAS dosage on phase equilibria are discussed.•Distribution and selectivity in the two phases at different temp. were obtained.•Phenol in oil are separated with QASs via forming deep eutectic solvent in two phases.Phenolic compounds (such as phenol, cresol sand xylenol), which are basic materials for the organic chemical industry, are mainly produced from coal liquefaction oil, coal tar, petroleum, and biomass pyrolysis oil. It has been reported that the separation of phenols from oil with forming deep eutectic solvents based on quaternary ammonium salt (QAS) is an efficient and environmentally friendly method. However, the phase equilibrium of QAS + phenol + oil mixtures has not been reported in the literature. In this work, the phase equilibrium for separating phenol from model oil with 2-hydroxy-N,N,N-trimethyl-ethanaminium chloride (ChCl), N,N,N-triethyl-ethanaminium chloride (TEAC), and N,N,N-trimethyl- methanaminium chloride (TMAC) was studied. Phase equilibria of three ternary systems of toluene + phenol + QAS were measured at 25.0, 40.0 and 65.0 °C, and phase behaviors of the ternary systems were studied. Effects of temperature, type and dosage of QAS on the equilibrium were investigated. The results show that low temperatures are beneficial to extraction of phenol and the phenol removal efficiency decreases with increasing temperature. Among the QASs, TEAC has the strongest ability to separate phenol, but the concentration of toluene entrained in the DES phase is the largest. Only TMAC is dissolved in the oil phase to a small extant, which can cause the loss of extractant. ChCl not only has high phenol removal efficiency, but also causes a small concentration of toluene entrained in the DES phase, which shows that ChCl is an efficient and environmentally friendly extractant.

•Phase equilibria of high pressure CO2+deep eutectic solvents (DESs) were measured.•DESs were formed by phenol and 3 quaternary ammonium salts with 2–4 mol ratios.•Two-phase equilibrium were observed at 313.15–333.15 K and 1.71–13.3 MPa.•CO2 could dissovled in the DES phase and only phenol dissovled in the CO2 phase.Phase equilibria of the binary systems of high pressure CO2 + deep eutectic solvents (DESs) formed by quaternary ammonium salts (QASs, including 2-hydroxy-N, N, N-trimethyl-ethanaminium chloride, ChCl; N, N, N-trimethyl-methanaminium chloride, TMAC; and N, N, N-triethyl-ethanaminium chloride, TEAC) and phenol were measured at temperatures from 313.15 K to 333.15 K, pressures from 1.71 MPa to 13.3 MPa and mole ratios of phenol to QAS from 2.00 to 4.00. It has been found that two-phase equilibrium exists at all the studied conditions. The solubility of phenol in the CO2 phase and the solubility of CO2 in the DES phase at different pressures, temperatures, mole ratios of phenol to QAS have been obtained. Both the solubility of phenol in the CO2 phase and the solubility of CO2 in the DES phase formed by ChCl and phenol shows the largest, while those in the DES phase formed by TEAC and phenol shows the smallest. This work provides phase equilibrium data for phenol extraction and QAS regeneration.

Conversion of cellulose, the most abundant biomass, shows a high selectivity to yield formic acid (FA), when oxidized by O2 in NaVO3–H2SO4 aqueous solution. This conversion involves various reactions including hydrolysis and oxidation. In this work, the relationships between these reactions were studied. There are mainly two hydrolyses and two oxidations occurring in the conversion: initial hydrolysis (from cellulose to monosaccharides) and deep hydrolysis (from monosaccharides to levulinic acid); catalytic oxidation (from monosaccharides to FA) and ordinary oxidation (from levulinic acid to acetic acid). Among these four reactions, catalytic oxidation to FA and deep hydrolysis to byproducts are competitive. The increasing rate of deep hydrolysis is faster than that of catalytic oxidation, when temperature is increased. Catalytic oxidation is promoted and deep hydrolysis is suppressed, when the O2 pressure is increased. Moreover, deep hydrolysis is promoted and catalytic oxidation is suppressed, when H2SO4 concentration is increased. The hydrolysis–oxidation pathway of this conversion was proposed. Thus, the byproducts could be inhibited, and FA-oriented transformation could be realized.

•Deep eutectic solvents (DESs) by levulinic acid and tetrabutylphosphonium bromide•Separation of toluene from toluene/aliphatic mixtures by DESs was developed.•Toluene in DES could be recovered by distillation at 100 °C and DES was reused.•The separation by DESs shows high selectivity and extraction rate.In this work, separation of aromatic hydrocarbons from aromatic/aliphatic mixtures by deep eutectic solvents (DESs) at room temperature was developed. It was found that DES formed by levulinic acid as hydrogen bond donor and tetrabutylphosphonium bromide (TBPB) as hydrogen bond acceptor could efficiently separate aromatic hydrocarbons from aromatic/aliphatic mixtures. Levulinic acid/TBPB mole ratio, DES/toluene mole ratio, toluene mole fraction, and extraction temperature had an influence on the selectivity and extraction rate of toluene. The extraction could be performed at optimal conditions of 6:1 mol ratio of levulinic acid to TBPB and 6.4:1 mol ratio of DES to toluene at room temperature. Toluene in DES could be recovered by distillation of toluene at 100 °C under reduced pressure and DES was reused four times without obvious decrease in weight, selectivity and extraction rate. The work may provide an environmentally friendly method to separate aromatic/aliphatic mixtures, which avoids using a large number of toxic organic solvents.The separation of aromatic hydrocarbons from aromatic/aliphatic mixtures by deep eutectic solvents (DESs) at room temperature was developed. The selectivity and extraction rate of aromatics could be tuned by selecting hydrogen bond donor and hydrogen bond acceptor that form DES. It was found that DES formed by levulinic acid (LA) and tetrabutylphosphonium bromide (TBPB) could efficiently separate aromatic hydrocarbons from aromatic/aliphatic mixtures.

•The solubility of water in oils has a relationship with the content of phenol.•Water in oil can decrease the phenol-separation efficiency.•Water can compete for ChCl with phenol to form DES.•The phenol removal is sensitive to temperature in the presence of water.•Water accumulates in the regenerated ChCl after the reuse of ChCl.Choline chloride (ChCl) was demonstrated to efficiently separate phenols from model oils by forming deep eutectic solvents (DESs). The DES way is a non-aqueous process that avoids the use of mineral alkalis and acids, and prevents the production of wastewater containing phenol. However, real oils, such as coal tar oil and liquefaction oil, consist of a small amount of water, and ChCl is a strong hygroscopic compound, which may influence the removal of phenol in real oil. In this work, the effect of water in mixtures of phenol and toluene (defined as model oils) on the separation of phenol by forming DES with ChCl was studied. The results indicated that water could interact with ChCl to form DES and the interaction between water and ChCl was stronger than that between phenol and ChCl. In the presence of water in model oils, the amount of ChCl should be increased to get the same phenol removal as that without water. Moreover, with water in model oils, the influence of temperature on the phenol removal was more negative. After the reuse of ChCl for four cycles with the presence of water, ChCl accumulated about 23% water and the removal efficiency of phenol decreased from 92% to 87%. To reduce the effect of water on phenol separation, an air drying method could be used to remove water in regenerated ChCl.

The capture of SO2 by ionic liquids (ILs) has drawn much attention. In this work, a series of triethylenetetramine (lactate)n ([TETA]Ln) was synthesized and triethylenetetramine tetralactate ([TETA]L4) was selected to prepare aqueous IL solutions to absorb SO2. It has been found that the aqueous IL solutions can absorb large amounts of SO2; the saturated mole ratio of SO2 to IL in the aqueous IL solution decreases with increasing temperature, and increases with increasing water content of the aqueous IL solution; the density and viscosity of the aqueous IL solution decreases with increasing temperature and water content, and the density and viscosity of aqueous IL solution after SO2 absorption is higher than that before SO2 absorption. The absorption of SO2 by the aqueous IL solution is reversible. Compared with other ILs, [TETA]L4 has many advantages in application, including inexpensive synthetic materials, uncomplicated synthetic procedures, high SO2 capacity, and excellent reversibility.

Because of its controllable and recoverable properties, the H2O–SO2 system was studied as a reaction medium to hydrolyze corn cob to produce chemicals by a two-step treatment. The results indicated that, after the first-step treatment of corn cob, 27.0% xylose, 3.3% glucose, and 3.2% arabinose could be obtained at 140 °C for 1.5 h with 0.024 g/cm3 SO2; after the second-step treatment, 8.6% glucose could be obtained at 190 °C for 0.5 h with 0.048 g/cm3 SO2. The total yield of products by the two-step treatment of corn cob was 48.4%, which was greater than that obtained by the one-step treatment, 32.4% at 190 °C for 0.5 h with 0.048 g/cm3 SO2. Furthermore, the degradation products obtained from the two-step treatment were less than those obtained from the one-step treatment. More importantly, after the reaction, SO2 could be swept by stream stripping and reused.

Because of similar properties and very low volatility, isomers of benzene poly(carboxylic acid)s (BPCAs) are very difficult to separate. In this work, we found that isomers of BPCAs could be separated efficiently by quaternary ammonium salts (QASs) via formation of deep eutectic solvents (DESs). Three kinds of QASs were used to separate the isomers of BPCAs, including the isomers of benzene tricarboxylic acids (trimellitic acid, trimesic acid, and hemimellitic acid) and the isomers of benzene dicarboxylic acids (phthalic acid and isophthalic acid). Among the QASs, tetraethylammonium chloride was found to have the best performance, which could completely separate BPCA isomers in methyl ethyl ketone solutions. It was found that the hydrogen bond forming between QAS and BPCA results in the selective separation of BPCA isomers. QAS in DES was regenerated effectively by the antisolvent method, and the regenerated QAS was reused four times with the same high efficiency.

Electro-oxidation of benzyl alcohol (BA) to benzaldehyde was conducted in homogeneous supercritical CO2/[Bmim][PF6]/MeCN solutions. The study of cyclic voltammetry indicates that electro-oxidation of BA in the solutions is an irreversible reaction, oxidation peak appears at a voltage of 2.7 V, and the electro-oxidation of BA is a diffusion-controlled process. Electrolysis potential, electric quantity, and pressure of the reaction system have great influences on conversion of BA, selectivity towards benzaldehyde, and Faradic efficiency. High selectivities and yields of benzaldehyde can be obtained by tuning electrolysis conditions. Our results have demonstrated that both the selectivity and the yield of benzaldehyde can reach higher than 99.8% at an electrolysis potential of 2.7 V, system pressures of 16–17 MPa and a temperature of 318.15 K.Highlights► A novel electrochemical reaction medium, supercritical CO2 dissolving ionic liquid ► The electro-oxidation of benzyl alcohol to benzaldehyde with a high yield of 99.8% ► The diffusion coefficient of benzyl alcohol in the novel medium is much high

Alkali-oxygen oxidation of coals to produce high-value benzene polycarboxylic acids (BPCAs) is a potential route in the future. Among the coal ranks, lignite has been proved to be easily oxidized due to its low coalification, but the yield of BPCAs obtained from lignite is relatively low because of the low content of aromatic clusters in its structures. However, the aliphatic structures of lignite are relatively rich, which may be served as the mother structures for small-molecule fatty acids (SMFAs). Thus, in the present work, three lignites were oxidized in aqueous alkaline solutions by oxygen. SMFAs were detected and quantified in addition to BPCAs after the reaction. The results show that when the optimal BPCAs yields (18.4–21.5%) are obtained, large amount of SMFAs (39.8–23.2 wt.%) can be obtained simultaneously, including oxalic acid, formic acid, acetic acid, succinic acid and malonic acid. The oxidation of model compounds shows that SMFAs are mainly derived from the oxidation of aliphatic structures as well as the opening of benzene rings in the lignite structure.Highlights► Up to 58% yields of fatty acids and benzene polycarboxylic acids by lignite oxidation ► Fatty acids are derived from aliphatic structures and opening of benzene rings. ► An efficient way has been proposed to convert lignite to valuable chemicals.

The capture of SO2 by ionic liquids (ILs) has drawn much attention due to the unique properties of ILs. Among the ILs, guanidinium- and alkanolaminium-based ILs have been widely studied by many groups experimentally or theoretically. However, the thermal stability of the ILs is low, and the degradation of the ILs may occur during the desorption process of SO2 at high temperatures. In this work, 1-butyl-3-methylimidazolium lactate ([Bmim]L) with high thermal stability was synthesized and was used to absorb SO2. It has been found that the IL can absorb large amounts of SO2 and the solubility of SO2 in the IL decreases with the increase of temperature; the absorption of SO2 by the IL is reversible, and the IL can be reused for the absorption of SO2 without obvious loss of absorption capacity. The comparison of [Bmim]L with other ILs based on lactate anion suggests that the cations of ILs have a significant influence on the absorption and desorption behaviors of SO2 while the length of the alkyl chains has no obvious influence on the solubility of SO2 in imidazolium-based ILs with lactate anion. The imidazolium-based ILs with lactate anion are promising absorbents for the removal of SO2 from the flue gas.

Alkali-oxygen oxidation of coals to produce high-value benzene polycarboxylic acids (BPCAs) is a potential substitute for the petroleum route in the future. However, the high amount of alkali consumed in the process stands as a significant obstacle for the practical application of this approach. In the present work, lignite, chosen as the raw material, was oxidized at temperatures higher than those reported so far. The results showed that, as the temperature increased, a gradually shortened reaction time and decreased alkali/coal mass ratio were required to obtain the maximum total yield of BPCAs, which remained about 20%. A total BPCA yield of 20.4% was obtained at conditions of 300 °C, 0.8/1 alkali/coal mass ratio, and 1 min, whereas the traditional method employs the conditions of 240 °C, 3/1 alkali/coal mass ratio, and 30 min to obtain a maximum BPCA yield of 20.5%. The distributions of BPCAs obtained by the two methods were found to be very close to each other. Excess alkali employed in the system can decrease the yield of BPCAs through the salting-out effect, with a more significant effect at higher reaction temperatures. The enhanced salting-out effect induced by excess alkali concentration delays the diffusion of intermediates formed on the lignite surface to the water phase, during which the parent structures for the BPCAs are possibly overoxidized to carbon dioxide. The high-temperature oxidation of lignite dramatically decreases the amount of alkali consumed and improves the production efficiency of BPCAs, which is very important for the industrialization of this process.

As a kind of novel and efficient material, ionic liquids (ILs) are used for capture of acidic gases including SO2 and CO2 from flue gas. Due to very low content of acidic gases in flue gas, it is important to find functional ILs to absorb the acidic gases. However, up to now, there is no criterion to distinguish if the ILs are functional or not before use, which greatly influences the design of functional ILs. In this work, a series of ILs were synthesized and used to determine functional or normal ILs for the capture of acidic gases. It has been found that the pKa of organic acids forming the anion of ILs can be used to differentiate functional ILs from normal ILs for the capture of acidic gases from flue gas. If the pKa of an organic acid is larger than that of sulfurous acid (or carbonic acid), the ILs formed by the organic acid can be called functional ILs for SO2 (or CO2) capture, and it can have a high absorption capacity of SO2 (or CO2) with low SO2 (or CO2) concentrations. If not, the IL is just a normal IL. The pKa of organic acids can also be used to explain the absorption mechanism and guide the synthesis of functional ILs.

Densities and viscosities of 1,1,3,3-tetramethylguanidium lactate ([TMG]L) (1) + H2O (2) with different compositions were determined at temperatures from (303.15 to 328.15) K. Densities of [TMG]L (1) + H2O (2) decrease with the increase of temperature. However, when the mole fraction of water is lower than 0.5, the water content does not have an obvious influence on the density of [TMG]L. When the mole fraction of water is greater than 0.5, the densities of [TMG]L (1) + H2O (2) decrease obviously with further increasing the mole fraction of water. Viscosity of [TMG]L decrease dramatically with the increase of temperature and the water content. Excess molar volumes (VE) and viscosity deviations (Δη) of the binary mixtures were calculated by the experimental data and fitted to the Redlich–Kister equation with four parameters. The result shows that the values of VE and Δη for the binary mixtures are negative over the whole composition range and temperatures from (303.15 to 328.15) K. The negative of the excess properties indicates a strong interaction between the ionic liquid and water. The partial molar volumes (V̅i), excess partial molar volumes (V̅iE), Gibbs energy of activation for viscous flow (ΔG*), and excess Gibbs energy of activation for viscous flow (ΔG*E) of the binary mixtures were also calculated based on the densities and viscosities data. Besides, the Jouyban–Acree model was used to correlate the densities and viscosities of the binary mixtures with respect to the mixture composition and temperature simultaneously.

Novel deep eutectic solvents (DES) based on three different hydrogen-bond donors (HBD), namely phenol, o-cresol, and 2,3-xylenol, and choline chloride (ChCl) were successfully synthesized with different mole ratios of HBD to ChCl. Melting temperature of these DES were measured. Compared with an ideal mixture of the two components, the freezing temperature of the DES depresses greatly from (120 to 127) K. The physical properties, such as density, viscosity, and conductivity of phenol-based and o-cresol-based DES were determined at atmospheric pressure and temperatures from (293.2 to 318.2) K at an interval of 5 K. The results show that the type of HBD, the mole ratio of HBD to ChCl, and temperature have great influences on the physical properties of DES. Densities and viscosities of DES formed by phenol and ChCl decrease with increases of temperature and phenol content. The conductivities of the DES are from (1.40 to 7.06) mS·cm–1, similar to that of room temperature ionic liquids. The conductivities of the DES increase with an increase of temperature, and reach the highest values at phenol to ChCl mole ratios of 4.00 to 5.00. The temperature dependence of densities and conductivities for these DES were correlated by an empirical second-order polynomial with relative deviations less than 0.91 %, and the viscosities were fitted to the VTF equation with relative deviations less than 0.52 %.

Room-temperature ionic liquids (ILs) are widely investigated to capture CO2 from flue gas and can capture a large amount of CO2. However, almost all of the previous studies on the absorption of CO2 by ILs were carried out at low temperatures, less than 60 °C and even at room temperature. When the temperatures reach the real flue gas temperatures, from 110 °C to 140 °C, these ILs might hardly absorb CO2, as high temperatures decrease the CO2 capacity. Therefore, it is necessary to design new task specific ILs to capture CO2 at flue gas temperatures with high absorption capacity. In this work, a new type of polyamine based ILs were developed to absorb CO2 from simulated flue gas at high temperatures and ambient pressure with large absorption capacities up to 0.944 mole ratio or 0.176 mass ratio of CO2 to IL at 110 °C. These ILs could be easily synthesized by neutralization of polyamines and organic acids, and the number of amido groups on the ILs can be easily controlled. The CO2 absorption is influenced by temperature, CO2 volume fraction in the flue gas, and the number of amido groups on the ILs. Also a possible mechanism for the CO2 absorption has been proposed.

Cellulose is the most widely distributed source of biomass, and its efficient conversion to a variety of chemicals is important for a sustainable future. In this work, sulfur dioxide (SO2) dissolved in hot water has been demonstrated to be an efficient catalyst for the selective conversion of cellulose to chemicals such as glucose and levulinic acid. The selectivity of products can be tuned by the SO2 concentration, temperature, and reaction time. SO2 acts both as a supply of H+ ions through ionization of H2SO3 when dissolved in water and as a Lewis acid catalyst that breaks the hydrogen bonds in cellulose. Importantly, SO2 in the reaction mixture can be recovered completely by stream stripping, thus avoiding the formation of acidic wastewater. This work provides a new, efficient, and environmentally benign way to convert cellulose to chemicals.

The oxidation of coal to produce high-valued benzene polycarboxylic acids (BPCAs), which are obtained currently from diminishing petroleum reserves, is a promising industrial process of the future. Up to now, the yield distribution of BPCAs has not been studied in detail and the mechanism of coal oxidation to BPCAs remains unclear. In this study, Huolinhe lignite was oxidized in a batch reactor by alkali-oxygen oxidation. All 12 kinds of BPCAs obtained were quantified by a new established method. Effects of alkali/coal mass ratio, reaction temperature, initial oxygen pressure, and reaction time on the yield distribution of BPCAs were studied for the first time. The results indicate that BPCAs with four or five carboxyls are the predominant products, and BPCAs with one or two carboxyls are formed in a relatively short time; moreover, the formation of BPCAs with more carboxyls is relatively more sensitive to the salting out effect. CP/MAS 13C NMR spectra and oxidation of model compounds show that phenolic, ether-substituted aromatic, ether, and aldehyde groups are easily converted and that water-soluble acids (WSA) are formed rapidly and largely due to the breakage of these bonds. The step from WSA to BPCAs is relatively slow mainly due to the inertia of the aromatic clusters with attached carboxyls or carboxylate. On the whole, the BPCAs are derived from aromatic clusters through the oxidation of condensed benzene rings, bridges, or peripheral groups that are attached to the aromatic clusters. Possible mother units for BPCAs in the lignite are suggested based on the generally agreed lignite structure.

Room-temperature ionic liquids (ILs) are widely investigated to absorb SO2 from mixed gases or simulated flue gases and can capture a large amount of SO2, which can be recovered easily by heating and vacuum treatment. However, after many circulations of SO2 absorption from flue gas, the capacity of SO2 in ILs decreases. The main reason may be the oxidation of SO2, and the oxidized SO2 becomes sulfuric acid when water presents in flue gas. Sulfuric acid in the ILs influences the regeneration of ILs and further absorption of SO2 by the ILs. In this work, the effect of sulfuric acid in a task-specific IL, monoethanolammonium lactate ([MEA]L), on the absorption of SO2 and the regeneration of [MEA]L from a mixture containing sulfuric acid were studied. It was found that when sulfuric acid was added into the IL, the absorption capacity of SO2 in [MEA]L decreased greatly. However, when NaOH, CaO, or CaCO3 was added into the mixture of [MEA]L and sulfuric acid, [MEA]L could be regenerated and sulfuric acid was formed into its corresponding salts and precipitated for removal.

The high-pressure phase equilibria of carbon dioxide + benzaldehyde binary system were measured at temperatures from 298.55 to 345.15 K and pressures from 2.20 to 14.96 MPa. The experimental method used in this work was a static-analytical method with liquid and vapor phase sampling. The experimental results are discussed and compared with available literature data. The experimental data were correlated with the Peng–Robinson equation of state (PR EoS) using classical van der Waals (two-parameter conventional mixing rule) mixing rules, which could correlate well the binary phase behavior with an average absolute relative deviation of 3.4%.Graphical abstractHighlights► Phase equilibria of CO2 and benzaldehyde were measured up to 14.96 MPa. ► Experimental data were correlated with PR EoS with van der Waals mixing rules. ► PR EoS could predict well the binary phase behavior with an ARD of 3.4%.

Pretreatment of cellulose to water soluble substances (WSS) can enhance its efficient conversion in water solvent, such as ethanol fermentation. In this work, we found ionic liquid (IL), 1-methyl-3-methylimidazolium dimethylphosphate ([Mmim][DMP]), could convert efficiently cellulose to obtain WSS, and the product WSS and IL mixture could be separated by ethanol anti-solvent way. Effects of ILs, time, temperature and water on cellulose conversion were investigated. NMR, FTIR, XRD and SEM were employed to study the mechanism of cellulose conversion with ILs. The results indicate that [Mmim][DMP] has a greater ability to interact with cellulose than [Bmim][Cl] under the same conditions. Cellulose can be completely converted into WSS in [Mmim][DMP] under all the investigated temperatures from 140 to 160 °C. Increasing temperature is beneficial to the conversion rate of cellulose. But the presence of water can decrease the conversion rate of cellulose. During the treatment by [Mmim][DMP], the hydroxyls of cellulose can form hydrogen bonds with both anion and cation of [Mmim][DMP], and after the treatment the inter- and intramolecular hydrogen bonds of cellulose and the compact structure of cellulose are collapsed.

Densities and viscosities of 1-butyl-3-methylimidazolium tetrafluoroborate ([bmim][BF4]) (1) + N-methyl-2-pyrrolidone (NMP) (2) with w1 = 0.0000, 0.5000, 0.6999, 0.8981, and 1.0000 at T = (298.15 to 318.15) K were measured and fitted to standard equations. The results show that densities and viscosities of the hybrid solvents decrease with the increase of temperature and mass fraction of NMP. A high-pressure variable-volume view cell technique was used to determine the solubility of CO2 in pure solvents and mixtures under elevated pressures up to 6 MPa at temperatures from (298.15 to 318.15) K. The results indicate that the solubility of CO2 in the pure solvents and mixtures increases with the increase of pressure and with the decrease of temperature. The solubility of CO2 in the mixtures increases with the increase of the mass fraction of NMP, but it is very close to that in pure [bmim][BF4] as the mass fraction of NMP is around 0.1019.

Three-dimensional (3D) copper foams have been formed by electrodeposition at different nitrogen pressures and examined by scanning electron microscopy. The results indicate that an increase in system pressure leads to a decrease of the pore size of the copper foam due to the suppressed coalescence of hydrogen bubbles, while the thickness of the copper foam increases with decreasing pressure. Also, the walls around the pores on the copper foam consist of copper dendrites, and the copper dendrites are made up of copper grains with sizes less than 1 μm. The average sizes of the copper grains decrease with increasing system pressure. It has been demonstrated that copper foams with controllable 3D structure formed by electrodeposition at different pressures are comparable to those obtained by electrodeposition at normal pressure in the presence of specific additives.

An extended study on the solubility of glucose in ionic liquid (IL) + antisolvent mixtures has been performed to find a way to separate glucose from ILs. These ILs, commonly used in cellulose conversion processes, are based on combination of cations of 1-methyl-3-alkylimidazolium and anions of chloride, bromide, acetate, and hydrogen sulfate. Effects of temperatures, antisolvents, ILs, mass ratios of antisolvent to IL, and water contents on the solubility of glucose have been investigated in this work. The results demonstrate that the solubility of glucose increases with decreasing mass ratio of antisolvent to IL and elevating temperatures. The solubility of glucose in IL + ethanol mixtures increases in the following order: [emim][Br], [bmim][Cl], [hmim][HSO4], [bmim][CH3COO], and [emim] [CH3COO]. The addition of water can increase the solubility of glucose in IL + antisolvent mixtures. Ethanol can be selected as a better antisolvent to separate glucose from IL than methanol, acetone, and acetonitrile.

Room-temperature ionic liquids (ILs) are widely investigated to absorb SO2 from mixed gases or simulated flue gases and can capture a large amount of SO2, which can be recovered easily by heating and vacuum treatment. However, due to the existence of O2 in flue gases, the oxidation of SO2 may occur. This oxidation might influence the SO2 recovery from ILs and make ILs unable to reuse. This may limit further applications in large-scale desulfurization from mixed gases or flue gases by ILs. In this work, a task-specific IL, monoethanolaminium lactate ([MEA]L), was used to study the absorption of SO2 and oxidation of SO2 by O2 in simulated flue gases with and without ash and activated carbon in [MEA]L. It is found that the presence of O2 in the simulated flue gas does not influence the absorption of SO2 by [MEA]L, but it causes, to a very small extent, the oxidation of SO2. The increase of temperature, time, and the concentration of O2 can increase the oxidation of SO2. Adding in IL ash and activated carbon, which could be captured by IL from flue gases, can also increase the oxidation of SO2. For these problems, we have tried to find some ways to reduce the oxidation of SO2 absorbed by IL.

Task-specific ionic liquids (TSILs) have been experimentally demonstrated to absorb more sulfur dioxide (SO2) than normal ILs from gas mixtures with low SO2 concentrations; however, the differences of SO2 solubilities in the two kinds of ILs at given temperatures and pressures have not been studied systematically. Moreover, the mechanism of the interaction between SO2 and ILs still remains unclear. In this work, the solubilities of SO2 in TSILs (1,1,3,3-tetramethylguanidinium lactate and monoethanolaminium lactate) and normal ILs (1-butyl-3-methylimidazolium tetrafluoroborate and 1-butyl-3-methylimidazolium hexafluorophosphate) were determined. The solubilities of SO2 are correlated by a modified Redlich−Kwong equation of state (RK EoS). The chemical absorption and physical absorption are differentiated, and the absorption mechanism has been proposed with the aid of the modified RK EoS. SO2 absorption capacity in TSILs is contributed from both chemical interaction and physical interaction. Two TSIL molecules chemically absorb one SO2 molecule, and the chemical absorption amount follows the chemical equilibrium. Normal ILs only physically absorb SO2 following Henry’s law. The chemical equilibrium constant, reaction enthalpy, Gibbs energy of reaction, reaction entropy, and Henry’s law constant of SO2 absorbed in ILs have been calculated. The present model can predict SO2 absorption capacity for capture and SO2 equilibrium concentration in IL for recovery.

The solubility of 5-hydroxymethylfurfural (HMF) in supercritical carbon dioxide (scCO2) with and without ethanol (mole fraction of ethanol x3 = 0, 0.025, and 0.050) as a cosolvent was measured by the cloud point at temperatures from (314.1 to 343.2) K and pressures from (8.54 to 19.71) MPa. It is demonstrated that the solubility of HMF increases with the increase of pressure at a fixed temperature but decreases with the increase of temperature at a fixed pressure. When ethanol is added into scCO2 as a cosolvent, the solubility of HMF increases greatly with the increase of the mole fraction of ethanol. The experimental data can be correlated by the Chrastil model and a modified Chrastil model with four adjustable parameters. The correlation results indicate that the association of HMF and CO2 is an endothermic process, and ethanol can reduce the energy of the process.

The phase behavior and critical parameters of (CO2 + CH3CO3CH3) have been determined using a high-pressure, variable-volume view cell, and their densities have also been measured in sub- or supercritical regions. The isothermal compressibility, KT, was calculated from the density of the binary mixtures. The transition points, bubble point, dew point, and critical point, have been measured with concentrations of dimethyl carbonate from mole fractions of (0.0242 to 0.1484), temperatures from (308.15 to 337.45) K, and pressures from (6.16 to 16.67) MPa. It is demonstrated that the density and KT are sensitive to the pressure as the pressure gets close to the critical point of the binary mixtures. KT also increases sharply when the pressure approaches the dew points or bubble points at other compositions near the critical composition. When the pressure is much higher than the phase transition pressure or the composition is far from the critical composition, KT is rather small, and the effect of pressure on KT is fairly limited. The phase boundary data of the binary mixtures can be correlated well by the Peng−Robinson equation of state (PR EoS) with two binary parameters.

The solubility of levulinic acid in supercritical carbon dioxide in the absence and presence of ethanol (mole fraction of ethanol x3 = 0.0, 0.027, and 0.051) as a cosolvent was measured with a synthetic method at temperatures from (313.0 to 342.4) K and pressures from (8.0 to 19.0) MPa. It is demonstrated that, at a fixed temperature, the solubility of levulinic acid increases with increasing pressure; at a fixed pressure, it decreases with increasing temperature. When ethanol is added into supercritical carbon dioxide as a cosolvent, the solubility of levulinic acid increases greatly, and it increases with the concentration of the added ethanol. The experimental solubility data can be correlated using the Chrastil model and a modified Chrastil model with four adjustable parameters.

The phase behavior and critical parameters of (carbon dioxide + 1-bromobutane), (carbon dioxide + 1-chlorobutane), and (carbon dioxide + 1-methylimidazole) have been determined using a high-pressure variable-volume view cell, and their densities have also been measured in sub- or supercritical regions. The isothermal compressibility (KT) is calculated from the density of the binary mixtures. The transition points, bubble point, dew point, and critical point, have been measured with concentrations of organic solvent mole fractions from (0.0102 to 0.1495), temperatures from (308.2 to 337.4) K, and pressures from (6.21 to 19.04) MPa. It is demonstrated that the density is sensitive to the pressure as the pressure approaches the critical point of binary mixtures; that is, KT is large and increases significantly. KT also increases sharply when the pressure approaches the dew point or bubble point at other compositions near the critical composition. When the pressure is much higher than the phase transition pressure or the composition is far from the critical composition, KT is rather small, and the effect of pressure on KT is fairly limited. The phase boundary data of the binary mixtures can be correlated well by the Peng−Robinson equation of state (PR EoS) with two binary parameters.

Room-temperature ionic liquids (ILs) which are regarded as environmentally benign solvents are widely used in many research areas. However, the purity of ILs influences the properties of ILs and further applications. The remains of water and organic solvents in ILs not only reduce the purity of ILs but also influence the physicochemical properties and even the results of reactions performed in ILs. In this work, we found a new method, sweeping solvents by N2, to remove quickly the volatile impurity in ILs at mild conditions. The effecting factors of the new method and the comparison with the traditional method have been investigated, and it was found that temperature and N2 flow rate influence the time for removing volatile impurities from four types of ILs. The new method can easily remove the IL’s impurities, including water, ethanol, methanol, acetonitrile, ethyl acetate, and acetone, to a mass fraction as low as 10−3, and the time decreases greatly to just a few hours, even less than 0.5 h. Furthermore, the mechanism of sweeping solvents by blowing N2 has been investigated.

Room-temperature ionic liquids (ILs) have been demonstrated to absorb SO2 efficiently. However, after absorbing a large amount of SO2, the viscosity, the conductivity, and the density of the ILs have not been studied systematically, and the mechanism of the interaction between SO2 and ILs is still being disputed. In this work, two kinds of ILs (task-specific ILs and normal ILs) have been studied to absorb pure SO2 at atmospheric pressure. It is found that the viscosity, the conductivity, and the density show different behaviors between task-specific ILs and normal ILs. For the task-specific ILs to absorb SO2, before a 0.5 mol ratio of SO2 to IL, the viscosity and density increase, and the conductivity decreases with an increase of the mole ratio of SO2 to IL. After that, the conductivity and density increase, and the viscosity decreases with further increasing the mole ratio of SO2 to IL. However, for the normal ILs, the conductivity and density increase and the viscosity decreases with an increase of the mole ratio of SO2 to IL. A new mechanism of ILs absorbing SO2 has been proposed. Task-specific ILs can chemically absorb SO2 when the mole ratio of SO2 to IL is not more than 0.5, and they can physically absorb SO2 when the mole ratio is more than 0.5. The normal ILs can only physically absorb SO2.

The phase equilibria of the carbon dioxide + benzyl alcohol system were measured at 298.15, 306.35 and 313.15 K, under pressures from 1.03 to 16.15 MPa. An upper critical end point (UCEP) of the binary system was identified at 307.45 K and 7.77 MPa and three-phase equilibria were observed along the liquid–liquid–vapor (LLV) equilibrium line between 279.75 and 307.45 K. The experimental data were correlated well by the Peng–Robinson equation of state with two binary parameters. According to the experimental results, the phase behavior of the carbon dioxide + benzyl alcohol system appears to belong to Type-III according to the classification of van Konynenburg and Scott.

Functionalized ionic liquids (ILs) have been demonstrated to absorb SO2 from mixed gases or simulated flue gases efficiently. However, after absorbing a large amount of SO2, the viscosity of the ILs increases greatly, which might limit their eventual applications in large-scale desulfurization from mixed gases or flue gases. In this work, the effect of the presence of water in a simulated flue gas on the absorption of SO2 by a functionalized ionic liquid, 1,1,3,3-tetramethylguanidinium lactate, has been studied at different temperatures. It is found that the presence of water in the simulated flue gas can decrease the viscosity of the IL greatly, and it has no effect on the absorptivity of SO2 from the flue gas. The densities of the IL absorbing SO2 from the flue gas with or without water are also studied. They increase with the increase of the amount of SO2 absorbed from the flue gas in both cases.

The phase behavior of the carbon dioxide + nitrobenzene binary system has been studied in a high-pressure variable-volume view cell using an analytical method. The phase boundaries were measured at temperatures of 298.15, 310.45 and 322.75 K under pressures between 2.76 and 12.83 MPa, and it was found that three-phase equilibria existed over a temperature range from 303.60 to 313.65 K. The experimental data could be correlated with the Peng–Robinson equation of state (PR EoS) and two binary parameters. The phase behavior of the carbon dioxide + nitrobenzene system appears to belong to Type-V according to the classification of van Konynenburg and Scott.

The phase behavior of CO2 and γ-valerolactone (GVL) has been measured using a high-pressure variable-volume view cell and a fiber optic reflectometer. The density of the binary mixture has also been measured, and the isothermal compressibility (KT) of the binary mixture was calculated from the density of the binary mixture. The phase transition points, bubble point, dew point, and critical point, have been measured on the range of GVL mole fraction from 0.01 to 0.15 and temperatures from (308.2 to 550.2) K. The density of the mixture is sensitive to the pressure near the critical point of the mixtures, and KT is also sensitive to the pressure when the pressure is close to the phase transition point, especially close to the critical point. When the pressure is much higher than the phase separation pressure or the composition is far from the critical composition, KT is very small and the effect of pressure on KT is very limited. The phase boundary data of the binary mixture can be correlated well by the Peng−Robinson equation of state (PR EOS) with two interaction parameters.

The phase behavior of the carbon dioxide + 1-methylimidazole binary system has been investigated in a high-pressure variable-volume view cell using an analytical method. Phase equilibrium data for the system carbon dioxide + 1-methylimidazole was measured at 293.15, 309.75 and 323.15 K. The pressure under investigation was between 2.83 and 14.16 MPa. There coexisted three phases (LLV) of the binary system, which were found in a temperature range of 297.85–313.95 K. The densities of the binary mixture at phase transition points were also measured. The experimental data were correlated well by the Peng–Robinson equation of state with two binary parameters. According to the experimental results, the phase behavior of the binary system might be classified to Type-IV or Type-V according to the classification of six principal types of binary phase diagrams.