Exploring the Mechanism of Ionic Liquids to Improve the Extraction Efficiency of Essential Oils Based on Density Functional Theory and Molecular Dynamics Simulation

Highlights

• According to the design of the experiment (DoE), multivariate analysis models were used to optimize the critical process parameters combined with multi-objective optimization.
• Based on the optimized operating conditions, the MILT-HD method not only enhances the extraction efficiency from Amomi fructus but also reduces energy demands and CO₂ emissions.
• Based on the density functional theoretical (DFT) and molecular dynamics (MD) simulations, the mechanisms for ionic liquids (ILs) to improve the extraction efficiency of essential oil was comprehensively revealed.

AbstractIn this paper, Amomi fructus (Latin) was used to explore the mechanism of ionic liquids (ILs) in improving the extraction efficiency of essential oils. Microwave assisted ionic liquid treatment followed by a hydro-distillation (MILT-HD) process for isolating Amomi fructus essential oil was optimized by multi-objective optimization. Under optimum operating conditions, the IL-assisted extraction method not only enhances extraction efficiency but also reduces energy demands and CO₂ emissions. Since the hydrogen bond structure network of cellulose in the cell wall is an important reason for hindering diffusion of essential oils, the mechanism of ILs was explored by density functional theoretical (DFT) and molecular dynamics (MD) simulations. According to DFT calculations, ILs can facilitate the cleavage of cellulose chains and have strong non-covalent interactions with cellulose. Based on the MD simulations, the degree of destruction of the cellulose hydrogen bond structure was explored. According to the DFT and MD simulations, the ILs can significantly destroy cellulose structure, thereby promoting essential oil release from the plant. These results were confirmed by scanning electron microscopy (SEM) and Fourier transform infrared spectroscopy (FTIR). This work is conducive to better understand the MILT-HD process for isolating essential oil and comprehensively understand the mechanism of ILs in the extraction process.     

关于限域离子液体吸附CO_2的密度泛函理论(DFT)的研究

近年来,温室效应日趋严重,因此吸收CO_2的材料受到了广泛的关注.采用了密度泛函理论(DFT)研究以SiO_2为载体的限域离子液体对CO_2的吸附.对比纯净离子液体(ILs)以及限域离子液体与CO_2的相互作用情况,在这两种状态下两种体系的吸附情况大不相同.从几何结构、相互作用以及电荷分析等方面对ILs、 SiO_2以及ILs/SiO_2复合结构进行研究.计算结果表明,载体、离子液体和CO_2之间都存在较强的相互作用.离子液体的负载不仅改变了SiO_2载体的结构,而且受载体的影响阴阳离子之间的相互作用力也发生了改变.计算结果为进一步深入限域离子液体对CO_2的吸附打下了理论基础.     

A Novel Mechanism for the Extraction of Metals from Water to Ionic Liquids

We present a novel mechanism for the extraction of metals from aqueous phases to room-temperature ionic liquids (ILs) by use of a high-temperature salt as an extraction agent. The mechanism capitalizes on the fact that charged metal complexes are soluble in ILs; this allows for extraction of charged complexes rather than the neutral species, which are formed by conventional approaches. The use of a well-chosen extraction agent also suppresses the competing ion-exchange mechanism, thus preventing degradation of the ionic liquid. The approach permits the use of excess extractant to drive the recovery of metals in high yield. This work presents both a thermodynamic framework for understanding the approach and experimental verification of the process in a range of different ILs. The method has great potential value in the recovery of metals, water purification and nuclear materials processing.     

Theoretical Explanation for How SO3H‐Functionalized Ionic Liquids Promote the Conversion of Cellulose to Glucose

While the catalytic transformation of cellulose to glucose by functionalized ionic liquids (ILs) has been achieved successfully under mild conditions, insight into the fundamental molecular mechanism is still lacking. The present work presents the first attempt to address the fundamental reaction chemistry of the catalytic transformation. An enzyme‐like catalytic mechanism of ILs, in which glycosidic bond hydrolysis proceeds through a retaining mechanism and/or an inverting mechanism, is proposed. DFT calculations show that both mechanisms involve moderate barriers (<30 kcal mol^?1), which is consistent with the catalytic performance of the ILs under mild conditions (<100 °C). The “biomimetic” mechanism model proposed herein is expected to be viable for understanding the unique catalytic activity of ILs under mild conditions.     

Green and Efficient Processing of Cinnamomum cassia Bark by Using Ionic Liquids: Extraction of Essential Oil and Construction of UV‐Resistant Composite Films from Residual Biomass

There is significant interest in the development of a sustainable and integrated process for the extraction of essential oils and separation of biopolymers by using novel and efficient solvent systems. Herein, cassia essential oil enriched in coumarin is extracted from Cinnamomum cassia bark by using a protic ionic liquid (IL), ethylammonium nitrate (EAN), through dissolution and the creation of a biphasic system with the help of diethyl ether. The process has been perfected, in terms of higher biomass dissolution ability and essential oil yield through the addition of aprotic ILs (based on the 1‐butyl‐3‐methylimidazolium (C₄mim) cation and chloride or acetate anions) to EAN. After extraction of oil, cellulose‐rich material and free lignin were regenerated from biomass–IL solutions by using a 1:1 mixture of acetone–water. The purity of the extracted essential oil and biopolymers were ascertained by means of FTIR spectroscopy, NMR spectroscopy, and GC‐MS techniques. Because lignin contains UV‐blocking chromophores, the oil‐free residual lignocellulosic material has been directly utilized to construct UV‐light‐resistant composite materials in conjunction with the biopolymer chitosan. Composite material thus obtained was processed to form biodegradable films, which were characterized for mechanical and optical properties. The films showed excellent UV‐light resistance and mechanical properties, thereby making it a material suitable for packaging and light‐sensitive applications.     

冠醚-离子液体体系对水相中锶离子的萃取研究

本文研究了以一系列离子液体作为介质时,萃取剂二环己基18冠6（DCH18C6）对水相中Sr^2＋的萃取行为．研究结果表明,DCH18C6／离子液体体系对Sr^2＋的萃取性能优于相应的DCH18C6／JE辛醇萃取体系,一定条件下其萃取Sr^2＋的分配比可达10^3量级．同时,体系对Sr^2＋的萃取性能随着离子液体的结构不同而有所差别．在离子液体萃取体系中,随着水相初始硝酸浓度的增加,对Sr^2＋的萃取性能下降．水相中Na^＋、K^＋等离子的存在也会对体系萃取Sr^2＋产生直接影响．本文还验证了离子液体体系萃取Sr^2＋的机理,即以阳离子交换机理为主实现对Sr^2＋的萃取．     

Understanding the mechanism of cellulose dissolution in 1-butyl-3-methylimidazolium chloride ionic liquid via quantum chemistry calculations and molecular dynamics simulations

While N,N′-dialkylimidazolium ionic liquids (ILs) have been well-established as effective solvents for dissolution and processing of cellulose, the detailed mechanism at the molecular level still remains unclear. In this work, we present a combined quantum chemistry and molecular dynamics simulation study on how the ILs dissolve cellulose. On the basis of calculations on 1-butyl-3-methylimidazolium chloride, one of the most effective ILs dissolving cellulose, we further studied the molecular behavior of cellulose models (i.e. cellulose oligomers with degrees of polymerization n = 2, 4, and 6) in the IL, including the structural features and hydrogen bonding patterns. The collected data indicate that both chloride anions and imidazolium cations of the IL interact with the oligomer via hydrogen bonds. However, the anions occupy the first coordination shell of the oligomer, and the strength and number of hydrogen bonds and the interaction energy between anions and the oligomer are much larger than those between cations and the oligomer. It is observed that the intramolecular hydrogen bond in the oligomer is broken under the combined effect of anions and cations. The present results emphasize that the chloride anions play a critically important role and the imidazolium cations also present a remarkable contribution in the cellulose dissolution. This point of view is different from previous one that only underlines the importance of the chloride anions in the cellulose dissolution. The present results improve our understanding for the cellulose dissolution in imidazolium chloride ILs.     

Effects of Cationic Structure on Cellulose Dissolution in Ionic Liquids: A Molecular Dynamics Study

In recent years, great progress has been made in the dissolution of cellulose with ionic liquids (ILs). However, the mechanism of cellulose dissolution, especially the role the IL cation played in the dissolution process, has not been clearly understood. Herein, the mixtures of cellulose with a series of imidazolium‐based chloride ionic liquids and 1‐butyl‐3‐methyl pyridinium chloride ([C₄mpy]Cl) were simulated to study the effect that varying the heterocyclic structure and alkyl chain length of the IL cation has on the dissolution of cellulose. It was shown that the dissolution of cellulose in [C₄mpy]Cl is better than that in [C₄mim]Cl. For imidazolium‐based ILs, the shorter the alkyl chain is, the higher the solubility will be. In addition, an all‐atom force field for 1‐allyl‐3‐methyl imidazolium cation ([Amim]⁺) was developed, for the first time, to investigate the effect the electron‐withdrawing group within the alkyl chain of the IL cation has on the dissolution of cellulose. It was found that the interaction energy between [Amim]⁺ and cellulose was greater than that between [C₃mim]⁺ and cellulose, indicating that the presence of electron‐withdrawing group in alkyl chain of the cation enhanced the interaction between the cation and cellulose due to the increase of electronegativity of the cations. These findings are used to assess the cationic effect on the dissolution of cellulose in ILs. They are also expected to be important for rational design of novel ILs for efficient dissolution of cellulose.     

Understanding cellulose dissolution: effect of the cation and anion structure of ionic liquids on the solubility of cellulose

The effect of ionic liquids (ILs) on the solubility of cellulose was investigated by changing their anions and cations. The structural variation included 11 kinds of cations in combination with 4 kinds of anions. The interaction between the IL and cellobiose, the repeating unit of cellulose, was clarified through nuclear magnetic resonance (NMR) spectroscopy. The reason for different dissolving capabilities of various ILs was revealed. The hydrogen bonding interaction between the IL and hydroxyl was the major force for cellulose dissolution. Both the anion and cation in the IL formed hydrogen bonds with cellulose. Anions associated with hydrogen atoms of hydroxyls, and cations favored the formation of hydrogen bonds with oxygen atoms of hydroxyls by utilizing activated protons in imidazolium ring. Weakening of either the hydrogen bonding interaction between the anion and cellulose, or that between the cation and cellulose, or both, decreases the capability of ILs to dissolve cellulose.     

Ionic liquids enhanced oil recovery from oily sludge-experiment and mechanism

The oily sludge would cause environment pollution, and would cause the heavy oil waste. Therefore, it was vital for us to find novel methods to obtain heavy oil from the oily sludges. In this study, the [C₁₂mim][PF₆] and [C₁₂mim][Br] ionic liquids(ILs) were used to enhance the oil recovery. The toluene could obtain the highest oil recovery, and both the two ILs could increase the oil recovery. Toluene could obtain the highest oil recovery (89.4 wt%), and n-octane could obtain the lowest oil recovery (76.8 wt%). [C₁₂mim] [PF₆] could efficiently increase the heavy oil recovery to 91.2 wt%(by toluene). The [C₁₂mim][Br] could increase the heavy oil recovery further. Both the [C₁₂mim] [PF₆] and the [C₁₂mim][Br] ionic liquids could increase the heavy ois C/H ratio, decrease heavy oil viscosity and increase the sands hydrophilicity. The [C₁₂mim][Br] ionic liquids showed better effect. In addition, the ionic liquids could increase the solvents recovery, and the ionic liquids recovery were high. Therefore, the ionic liquids enhanced oil recovery could be recycled to ten times. The two ionic liquids could effectively decrease the heavy oil interaction force, and when the ionic liquids increased to 200 ppm, the force remained stable. In the end, the ionic liquids enhancing solvent extraction mechanism was put forward.     

Determination of ethanol in ionic liquids using headspace solid-phase microextraction–gas chromatography

The application of ionic liquids (ILs) as nonderivatizing solvents for the pretreatment and regeneration of cellulose is a growing area of research. Here we report the development of a rapid and simple method for the determination of residual ethanol content in two hydrophilic ILs, 1-butyl-3-methylimidazolium chloride and 1-ethyl-3-methylimidazolium acetate. The method utilizes headspace solid-phase microextraction coupled with gas chromatography at elevated extraction temperatures, resulting in rapid equilibration times. The effect of IL water content on the ethanol extraction efficiency is presented. Recovery experiments carried out in real samples gave recoveries ranging from 96.8 to 98.2%.     

Synthesis of Cyclic Carbonate Catalyzed by DBU Derived Basic Ionic Liquids

In this work, 1,8‐diazabicyclo[5.4.0]undec‐7‐ene (DBU), 1,5‐diazabicyclo[4.3.0]‐5‐nonene (DBN), and imidazole (MIM)‐derived bromide ionic liquids (ILs) were synthesized and used to catalyze the cycloaddition reactions of carbon dioxide (CO₂) with several kinds of epoxides to form cyclic carbonates. The DBU derived bromide ionic liquid system was found to have the best catalytic activity among all the tested ILs. The influences of reaction conditions (including temperature, pressure and reaction time) on the reaction of CO₂ to propylene oxide (PO) were studied to show the best conditions of 120 °C, 1 MPa, 2.5 h catalyzed by 2 mol% DBU‐derived bromide ionic liquid, with the conversion of PO and the selectivity of propylene carbonate (PC) reaching 99% and 99%, respectively. Under the optimum reaction conditions, the ionic liquid system could be reused at least five times without decrease in selectivity and conversion. NMR spectroscopy and DFT calculations were used to reveal the hydrogen‐bond interaction between ionic liquids and reagent, based on which the reaction mechanism was proposed.     

Side reaction of cellulose with common 1-alkyl-3-methylimidazolium-based ionic liquids

Ionic liquids with 1-alkyl-3-methyl-imidazolium cations react at C-2 with cellulose at its reducing end, forming a carbon-carbon bond. The reaction is strongly catalyzed by bases, such as the commonly present impurities in ILs, imidazole, and 1-methylimidazole. The direct reaction was verified by means of ¹³C-isotopical labeling and with the help of an IL that carried a fluorescence label which was transferred to cellulose upon the reaction. In solutions of cellulose in alkylmethylimidazolium ILs, both the ionic liquid and the cellulose are evidently not inert.     

基于离子液的超声辅助萃取小蓼叶中的精油及真实溶剂似导体屏蔽模型研究（英文）

Ionic liquids (ILs) based ultrasonic-assisted extract has been applied for the extraction of essential oil from Persicaria minor leaves. The effects of temperature, sonication time, and particle size of the plant material on the yield of essential oil were investigated. Among the different ILs employed, 1-ethyl-3-methylimidazolium acetate was the most effective, providing a 9.55% yield of the essential oil under optimum conditions (70 ℃, 25 min, IL:hexane ratio of 7:10 (v/v), particle size 60-80 mesh). The performance of 1-ethyl-3-methylimidazolium acetate in the extraction was attributed to its low viscosity and ability to disintegrate the structural matrix of the plant material. The ability of 1-ethyl-3-methylimidazolium acetate was also confirmed using the conductor like-screening model for realistic solvents. This research proves that ILs can be used to extract essential oils from lignocellulosic biomass.     

Investigation on the extraction of strontium ions from aqueous phase using crown ether-ionic liquid systems

The extraction of strontium ions using DCH18C6 as the extractant and various ionic liquids (ILs) as solvents has been investigated. The distribution ratio of Sr²⁺ can reach as high as 10³ under certain conditions, much larger than that in DCH18C6/n-octanol system. The extraction capacity depends greatly on the structure of ionic liquids. In IIs-based extraction systems, the extraction efficiency of strontium ions is reduced by increasing the concentration of nitric acid and can also be influenced directly by the presence of Na⁺ and K⁺ in the aqueous phase. It is confirmed that the extraction proceeds mainly via a cation-exchange mechanism.     

Direct visualization of solution morphology of cellulose in ionic liquids by conventional TEM at room temperature

Taking advantage of the negligible vapor pressure and dissolving features of ionic liquids (ILs), the solution morphology and dissolution process of cellulose in ILs have been visualized directly by conventional transmission electron microscopy (TEM) at room temperature for the first time.     

Elucidation of the Roles of Ionic Liquid in CO2 Electrochemical Reduction to Value-Added Chemicals and Fuels

The electrochemical reduction of carbon dioxide (CO₂ER) is amongst one the most promising technologies to reduce greenhouse gas emissions since carbon dioxide (CO₂) can be converted to value-added products. Moreover, the possibility of using a renewable source of energy makes this process environmentally compelling. CO₂ER in ionic liquids (ILs) has recently attracted attention due to its unique properties in reducing overpotential and raising faradaic efficiency. The current literature on CO₂ER mainly reports on the effect of structures, physical and chemical interactions, acidity, and the electrode–electrolyte interface region on the reaction mechanism. However, in this work, new insights are presented for the CO₂ER reaction mechanism that are based on the molecular interactions of the ILs and their physicochemical properties. This new insight will open possibilities for the utilization of new types of ionic liquids. Additionally, the roles of anions, cations, and the electrodes in the CO₂ER reactions are also reviewed.     

Theoretical study on ionic liquids based on DBUH+: Molecular engineering and hydrogen bond evaluation

The new generation of the ionic liquids (ILs) based on 1,8-diazobicylo [5,4,0] undec-7-ene (DBU) are applied as the solvent in organic reactions. In this work, by using a theoretical procedure, the most probable interactions between the ion pairs of DBUH⁺ based ILs, including 10 functionalized imidazole anions were investigated. For this purpose, the electrostatic potential surfaces were analyzed to detect the most probable interaction sites of DBUH⁺. On the basis of the obtained results, hydrogen bond formation between the anions and DBUH⁺ is influenced by the electronic effect of the substituted functional groups. This means that electron donating groups, such as phenyl has a stabilizing effect on the ion pairs, while electron-withdrawing groups, such as nitro, induces a destabilizing effect. These behaviors are described based on the interaction energy values (ΔE_int). To investigate the dispersion interaction effects in ILs formation, M06-2X-D3 functional was applied in energy analysis. The solvent reaction field was investigated by the polarizable continuum model in ethanol and chloroform as the solvent. The results showed that ethanol has a greater effect on the interaction energy of the ILs. Finally, to have a comprehensive understanding of the charge transfer effect on the stability of the studied ILs and to characterize the most probable interactions, natural bond orbital and quantum theory of atoms in molecules analyses were applied and the obtained results were analyzed.     

离子液体表/界面性质与结构

离子液体与气体、溶剂等物质组成的多相体系为吸收、萃取、两相催化等技术的发展提供了新的平台。离子液体的表/界面性质与结构是含离子液体多相体系的重要科学问题,可在介观尺度下显著影响多相体系反应和分离过程的效率。近年来,离子液体表/界面性质和结构的研究得到了广泛的关注。本文综述了离子液体及其与水、有机溶剂组成的混合物的表/界面张力及结构研究进展,介绍了现有的研究方法、研究对象与研究成果,归纳了离子液体及其混合物表/界面张力及结构的变化规律,分析了表/界面结构与表/界面张力之间的关系,探讨了离子液体表/界面研究存在的问题和未来的发展方向。     

低共熔溶剂在萃取分离中的应用

随着绿色化学的不断发展,如何在分析过程中应用和体现绿色化学特点,避免分析过程对环境产生二次污染及对人员造成危害也得到了关注。开发和使用具有绿色化学特点的溶剂和方法是分析工作者努力的方向之一。在已经出现的新溶剂中,低共熔溶剂(DES)与离子液体(ILs)物理性质相似,并具有环境友好、不可燃、生物降解、价廉、易制备等特点,因而近几年来获得了迅速发展。该文总结了低共熔溶剂的制备、性质及分类,综述了近年来其在萃取和分离中的应用进展。