低共熔溶剂的分子结构及物性估算的研究进展

低共熔溶剂具有熔点低、不挥发、不易燃、溶解性良好、易合成、廉价、低毒、腐蚀性低、生物降解性好等特点,常被作为"绿色"溶剂应用于金属加工和合成反应中。然而,目前对低共熔溶剂的结构和性质的研究只限于少部分具体的低共熔溶剂,没有形成系统全面的理论体系。简述了低共熔溶剂的合成与分类、分子结构和形成机理的研究进展,归纳了低共熔溶剂的物性估算方法,并指出了一些关于低共熔溶剂研究中存在的问题,提出了可能的解决方案。     

低共熔溶剂在化工分离过程中的应用及研究进展

近年来,低共熔溶剂由于具有廉价、原材料易得、蒸汽压低且更加环境友好的合成过程等特点,越来越成为绿色化学领域的研究热点,特别是低共熔溶剂作为萃取剂在化工分离过程中的应用引起广泛关注。本文主要介绍了低共熔溶剂的组成、性质以及在分离过程中的一些应用和研究进展,最后对其未来的研究方向和存在的问题进行了讨论。     

Improved Production of 5-Hydroxymethylfurfural in Acidic Deep Eutectic Solvents Using Microwave-Assisted Reactions

Hydroxymethylfurfural (5-HMF) is a key platform chemical, essential for the production of other chemicals, as well as fuels. Despite its importance, the production methods applied so far still lack in sustainability. In this work, acidic deep eutectic solvents (DES), acting both as solvent and catalyst, were studied for the conversion of fructose into 5-HMF using microwave-assisted reactions. These solvents were screened and optimized by varying the hydrogen bond donor (HBD) and hydrogen bond acceptor (HBA). The bio-based solvent γ-valerolactone (GVL) was also applied as additive, leading to a boost in 5-HMF yield. Then, a response surface methodology was applied to further optimize operating conditions, such as reaction time, temperature and wt.% of added GVL. The highest 5-HMF yield attained, after optimization, was 82.4% at 130 °C, in 4 min of reaction time and with the addition of 10 wt.% of GVL. Moreover, a process for 5-HMF recovery and DES reuse was developed through the use of the bio-based solvent 2-methyltetrahydrofuran (2-Me-THF), allowing at least three cycles of 5-HMF production with minimal yield losses, while maintaining the purity of the isolated 5-HMF and the efficacy of the reaction media.     

Computer Simulations of Deep Eutectic Solvents: Challenges,Solutions, and Perspectives

Deep eutectic solvents (DESs) are one of the most rapidly evolving types of solvents, appearing in a broad range of applications, such as nanotechnology, electrochemistry, biomass transformation, pharmaceuticals, membrane technology, biocomposite development, modern 3D-printing, and many others. The range of their applicability continues to expand, which demands the development of new DESs with improved properties. To do so requires an understanding of the fundamental relationship between the structure and properties of DESs. Computer simulation and machine learning techniques provide a fruitful approach as they can predict and reveal physical mechanisms and readily be linked to experiments. This review is devoted to the computational research of DESs and describes technical features of DES simulations and the corresponding perspectives on various DES applications. The aim is to demonstrate the current frontiers of computational research of DESs and discuss future perspectives.     

Effective Release of Intracellular Enzymes by Permeating the Cell Membrane with Hydrophobic Deep Eutectic Solvents

An efficient and green method is crucial for the recovery of intracellular biological products. The major drawbacks of the conventional cell disruption method are nonselectivity and enzyme denaturation. The permeability of hydrophobic deep eutectic solvents (DESs) to the cell membrane was studied, for the first time, and then hydrophobic DESs were innovatively applied to release intracellular enzymes from recombinant Escherichia coli. After optimization, a DES suspension of l -menthol/oleic acid (0.5 %, v/v) showed the highest release yield of intracellular enzyme. Compared with that released by sonication, a release yield of phospholipase D (PLD) of up to 114.58 % was achieved, and the specific activity was increased by 1.96 times. The microstructure of the cell membrane under different treatments was observed by using an electron microscope to understand the permeation of DESs to the cell membrane. The feasibility and applicability of the proposed release method in industrial applications were also demonstrated. The effective and green release method of intracellular enzymes developed herein has bright prospects for industrial application to replace traditional cell disruption methods. A preliminary study on the permeability of hydrophobic DESs to the cell membrane showed that there would be a potential application prospect of hydrophobic DESs not only in releasing intracellular contents, but also in seeking new green penetrating agents.     

Elimination of All Free Glycerol and Reduction of Total Glycerol from Palm Oil-Based Biodiesel Using Non-Glycerol Based Deep Eutectic Solvents

Purification of biodiesel prior to utilizing it as an alternative fuel is an essential industrial practice. Low glycerol content is one of the important pointers needed for passing the EN 14214 and ASTM D6751 international biodiesel standards. In this study, choline chloride (ChCl) as salt and ethylene glycol and 2,2,2-Trifluoroacetamide as hydrogen bond donors (HBDs) were employed to synthesize two ammonium salt-non glycerol based Deep Eutectic Solvents (DES). The physical properties of the synthesized DESs were measured and analyzed. These DESs were utilized to remove all the free glycerol from the palm oil-based biodiesel. The results indicated that all the tested DESs were able to remove all free glycerol successfully. The Central Composite Design (CCD) of the Response Surface Methodology (RSM) was used to to experiment design and optimization of total glycerol removal using ethylene glycol-based DESs and 2,2,2-Trifluoroacetamide-based DESs. The maximum total glycerol removal by ethylene glycol-based DESs was obtained at 0.66 ethylene glycol mole fraction and at DES/biodiesel molar ratio of 3 with removal efficiency of 23.85% as well as by 2,2,2-Trifluoroacetamide-based DESs at 0.60 2,2,2-Trifluoroacetamide mole fraction and at DES/biodiesel molar ratio of 2.93 with removal efficiency of 29.29%. The reusability of these DESs for removing free glycerol and total glycerol content from palm oil-based biodiesel was also investigated. This study proves that both ammonium salt-non glycerol based DESs can be successfully employed to remove the glycerol from palm oil-based biodiesel.     

Removal of Dibenzothiophene from Diesels by Extraction and Catalytic Oxidation with Acetamide‐Based Deep Eutectic Solvents

A series of acetamide‐based deep eutectic solvents (DESs) with different proportions were prepared. Extraction and catalytic oxidation desulfurization (ECODS) of the acetamide‐based DESs were investigated and the process was optimized. Such DESs with a molar ratio of acetamide and p‐TsOH of 1/3 (C₂H₅NO/3p‐TsOH) exhibits such a remarkable catalytic activity that the dibenzothiophene (DBT) removal could reach 100 % under optimized conditions. C₂H₅NO/3p‐TsOH was used for the oxidative desulfurization of actual commercial diesel. The sulfur removal of diesel achieved up to 98 %. C₂H₅NO/3p‐TsOH could be recycled six times and the desulfurization activity was slightly decreased. Evaluation of the mechanism indicated that oxidative desulfurization (ODS) was realized via dual activation of acetamide‐based DESs. A novel and effective way for deep desulfurization of diesel is provided.     

Separation of Hydrocarbons by Means of Liquid-Liquid Extraction with Deep Eutectic Solvents

Liquid-liquid equilibria for six ternary systems with choline chloride urea or choline chloride glycerol (molar ratio, 1:2) as selective solvent were experimentally determined at atmospheric pressure and 25°C. Equilibrium data were presented with tie lines. Extraction experiments with three-component systems were performed. The suitability of deep eutectic solvents for the separation of pyridine and toluene from n-hexane, and n-butanol from toluene was evaluated in terms of properties of solvents, solute distribution ratio, and extraction efficiency. Choline chloride glycerol has a better potential for separation of pyridine from its mixture with n-hexane. The equilibrium data were well described with the NRTL model.     

深度共熔溶剂对桉木组分的溶解选择性

制备了不同季铵盐三丁基甲基氯化铵(MTBAC)、四甲基氯化铵(TMAC)、苄基三乙基氯化铵(TEBA)和氯化胆碱(ChCl)分别与DL-乳酸(HL)以摩尔比1:9合成的深度共熔溶剂,并将用于溶解桉木粉中木质素。结果表明,由苄基三乙基氯化铵/DL-乳酸(TEBA/HL)合成的深度共熔溶剂处理桉木粉,在90 ℃下反应10 h,木质素溶解率达92.3wt%,综纤维素溶解率仅为8.3wt%;同时,木质素与综纤维素溶解选择性系数之比K达到158.5,表明TEBA/HL对木质素的溶解选择性最佳。通过红外光谱(FT-IR)分析各分离产物,证明提取物中有木质素特征官能团。通过凝胶渗透色谱(GPC)分析表明分离产物相对分子质量均有所降低。通过固体13C核磁共振谱(CP/MAS 13C NMR)分析90 ℃下TEBA/HL中分离产物结构,证明其结构征符合阔叶材木质素结构特点。     

CO2 Absorption Mechanism by the Deep Eutectic Solvents Formed by Monoethanolamine-Based Protic Ionic Liquid and Ethylene Glycol

Deep eutectic solvents (DESs) have been widely used to capture CO₂ in recent years. Understanding CO₂ mechanisms by DESs is crucial to the design of efficient DESs for carbon capture. In this work, we studied the CO₂ absorption mechanism by DESs based on ethylene glycol (EG) and protic ionic liquid ([MEAH][Im]), formed by monoethanolamine (MEA) with imidazole (Im). The interactions between CO₂ and DESs [MEAH][Im]-EG (1:3) are investigated thoroughly by applying ¹H and ¹³ C nuclear magnetic resonance (NMR), 2-D NMR, and Fourier-transform infrared (FTIR) techniques. Surprisingly, the results indicate that CO₂ not only binds to the amine group of MEA but also reacts with the deprotonated EG, yielding carbamate and carbonate species, respectively. The reaction mechanism between CO₂ and DESs is proposed, which includes two pathways. One pathway is the deprotonation of the [MEAH]⁺ cation by the [Im]⁻ anion, resulting in the formation of neutral molecule MEA, which then reacts with CO₂ to form a carbamate species. In the other pathway, EG is deprotonated by the [Im]⁻, and then the deprotonated EG, HO-CH₂-CH₂-O⁻, binds with CO₂ to form a carbonate species. The absorption mechanism found by this work is different from those of other DESs formed by protic ionic liquids and EG, and we believe the new insights into the interactions between CO₂ and DESs will be beneficial to the design and applications of DESs for carbon capture in the future.     

Modeling Alcohol Dehydrogenase Catalysis in Deep Eutectic Solvent/Water Mixtures

The use of oxidoreductases (EC1) in non-conventional reaction media has been increasingly explored. In particular, deep eutectic solvents (DESs) have emerged as a novel class of solvents. Herein, an in-depth study of bioreduction with an alcohol dehydrogenase (ADH) in the DES glyceline is presented. The activity and stability of ADH in mixtures of glyceline/water with varying water contents were measured. Furthermore, the thermodynamic water activity and viscosity of mixtures of glyceline/water have been determined. For a better understanding of the observations, molecular dynamics simulations were performed to quantify the molecular flexibility, hydration layer, and intraprotein hydrogen bonds of ADH. The behavior of the enzyme in DESs follows the classic dependence of water activity (a_W) in non-conventional media. At low a_W values (<0.2), ADH does not show any activity; at higher a_W values, the activity was still lower than that in pure water due to the high viscosities of the DES. These findings could be further explained by increased enzyme flexibility with increasing water content.     

Rheological,Thermodynamic, and Gas Solubility Properties of Phenylacetic Acid‐Based Deep Eutectic Solvents

Choline chloride + phenylacetic acid‐based deep eutectic solvents are studied. Their most relevant experimental physicochemical properties at different mixing ratios together with the CO₂ solubility data obtained in wide pressure and temperature ranges are reported. The presented materials exhibit a significant CO₂ capture performance with low corrosion effect when compared with the most common amine‐based CO₂ capture agents. Detailed rheological measurements are carried out and various models are applied to describe the dynamic flow behavior of the solvents. The CO₂ absorption mechanism is evaluated by studying the behavior of the liquid gas and interface. Due to the advantages of low cost, nontoxicity, and favorable physical properties, these solvents are an environmentally promising alternative for effective CO₂ capture technological applications.     

Deep Eutectic Solvent as Green Solvent in Extraction of Biological Macromolecules: A Review

Greater awareness of environmental sustainability has driven many industries to transition from using synthetic organic solvents to greener solvents in their manufacturing. Deep eutectic solvents (DESs) have emerged as a highly promising category of green solvents with well-demonstrated and wide-ranging applications, including their use as a solvent in extraction of small-molecule bioactive compounds for food and pharmaceutical applications. The use of DES as an extraction solvent of biological macromolecules, on the other hand, has not been as extensively studied. Thereby, the feasibility of employing DES for biomacromolecule extraction has not been well elucidated. To bridge this gap, this review provides an overview of DES with an emphasis on its unique physicochemical properties that make it an attractive green solvent (e.g., non-toxicity, biodegradability, ease of preparation, renewable, tailorable properties). Recent advances in DES extraction of three classes of biomacromolecules—i.e., proteins, carbohydrates, and lipids—were discussed and future research needs were identified. The importance of DES’s properties—particularly its viscosity, polarity, molar ratio of DES components, and water addition—on the DES extraction’s performance were discussed. Not unlike the findings from DES extraction of bioactive small molecules, DES extraction of biomacromolecules was concluded to be generally superior to extraction using synthetic organic solvents.     

Intensification of Mass Transfer in the Extraction Process with a Nanofluid Prepared in a Natural Deep Eutectic Solvent

The phytotoxic residues after olive oil production and residue leaves after pruning contain valuable bioactive compounds. A natural deep eutectic solvent (NADES) and an ethanol-water mixture were used for polyphenol extraction from olive pomace and leaves. Type of solvent, extraction temperature, and particle size of the leaves were optimized. NADES demonstrated better efficiency in the extraction process than conventional solvents; with higher temperature and smaller fraction of olive leaves, a higher yield of polyphenols was obtained from leaves. Extraction with a nanofluid as solvent was carried out. A stable nanofluid was prepared from NADES by adding Al₂O₃ nanoparticles. A higher yield was obtained with nanofluid from leaves, while an improvement of polyphenol extraction was achieved after the removal of oil from olive pomace.     

Performance of Choline-Based Deep Eutectic Solvents in the Extraction of Tocols from Crude Palm Oil

Deep eutectic solvents are emerging green solvents that have potential in many separation processes. This study investigates the performance of choline‐based deep eutectic solvents in the extraction of tocopherols and tocotrienols (collectively known as tocols) from palm oil, a major natural source of tocols. Deep eutectic solvents comprised of choline chloride salt and selected carboxylic acids as hydrogen bond donors were prepared and used in the extraction of tocols from crude palm oil by liquid–liquid extraction. Tocols concentration in the extracted product was at least double that in the control (8671 mg/kg compared to 3285 mg/kg, respectively). Increasing the amount of the deep eutectic solvents increased the tocols concentration in the extracted product up to 18,525 mg/kg, but the yields lowered from 4 % to less than 1 %. The tocols profile was significantly improved by the increase of the tocotrienols fraction in the products from 80.8 to 99.8 %. This study showed that unique interaction between the selected deep eutectic solvents with the tocols make it possible to selectively separate individual tocols in palm oil, where products with fractions rich in tocotrienols and low in tocopherols (particularly α‐tocopherol) are favorable.     

沼气中羰基硫的深度脱除

沼气深度脱硫对于以沼气为制氢原料的分布式燃料电池电站十分重要。采用浸渍法制备了Zn O/γ-Al2O3、Cu O/γ-Al2O3及Cu/γ-Al2O3,实验研究了上述金属氧化物脱硫剂以及商业Fe2O3脱硫剂对沼气中羰基硫(COS)的深度脱除性能。结果表明,Cu基脱硫剂对COS的脱除性能优于Zn O/γ-Al2O3和Fe2O3,其可在250~400℃的温度下将COS脱除到10 ppb以下,能够满足分布式PEMFC电站对脱硫的要求,并达到在其沼气重整器的原料气体预热段完成深度脱硫的目标。Cu O/γ-Al2O3的硫容在250℃达到了最大的0.185 mmol?g?1。对Cu O/γ-Al2O3的脱硫机理进行了分析。固相产物中Cu S的存在说明了COS在Cu O/γ-Al2O3上的吸附为化学吸附,而Cu2O和Cu的存在则说明了沼气中的CH4与CO2在250℃以上的温度下发生了重整反应,Cu2O和Cu为该反应生成的H2和CO的还原产物。气相产物中检测到的H2S,可能是由COS的加氢反应生成的。还考察了沼气中水分对COS深度脱除的影响。Cu基脱硫剂的性能会受到水分的不利影响,但随着温度的升高,该影响呈减小的趋势。     

Deep eutectic solvents: designer fluids for chemical processes

The increasing demand for multi‐task green solvents has spurred the development of next‐generation liquid media such as deep eutectic solvents (DESs), which have recently attracted increased attention. DESs are mixtures of salts and complexing agents, having freezing points lower than those of starting individual components. Similarly to ionic liquids, DESs exhibit distinctive properties such as chemical and thermal stability, biodegradability, non‐flammability, and cost effectiveness. These features account for their wide range of applications, e.g. as extractants, reactants, catalysts, reaction media, additives, and lubricants. This review summarizes the recent research efforts directed at exploring the potential applications of DESs in various chemical processes. With the rapid publication of reports on this new generation of solvents, other roles also are expected to be seen sooner or later. © 2017 Society of Chemical Industry