Influence of ionic liquids under controlled water activity and low halide content on lipase activity

Room-temperature ionic liquids (ILs) can be used as reaction media for nonaqueous biocatalysis. However, the purity of ILs should be considered to understand the influence of ILs on enzyme activity. The major impurities in ILs are water and halide. In the transesterification of benzyl alcohol with vinyl acetate, the optimal water activities for lipases in [Omim][Tf₂N] were similar to those in organic solvents. The chloride impurity in [Omim][Tf₂N] seriously influenced the activity of lipase. In this work, the effect of ILs on lipase activity was investigated under controlled initial water activity and low halide content. The activity of lipase was highly dependent upon the anion structure of ILs. The initial reaction rate of lipases followed the order [Tf₂N]⁻>[PF6]⁻>[TfO]⁻>[SbF₆]⁻≈[BF₄]⁻. All tested lipases showed the highest activities in ILs containing [Tf₂N] anion. Particularly, [AAIM][Tf₂N] was shown as a suitable reaction medium for biocatalysis. Lipozyme IM showed the highest activity in this IL among tested ILs. Thermal stability of lipase was also investigated. The higher thermal stability of Novozym 435 was obtained in hydrophobic and water-immiscible ILs such as [Bmim][Tf₂N], [Edmim][Tf₂N], and [Bmim][PF₆].     

Effect of small amount of water on the dynamics properties and microstructures of ionic liquids

A series of systems of 1‐butyl‐3‐methylimidazolium acetate ([Bmim][Ac]), 1‐butyl‐3‐methylimidazolium tetrafluoroborate ([Bmim][BF₄]), and 1‐butyl‐3‐methylimidazolium bis(trifluoromethylsulfonyl)imide ([Bmim][Tf₂N]) with a small amount of water were simulated. Viscosities of systems were obtained by nonequilibrium molecule dynamics simulation and the results show that the viscosities change in different ways: for [Bmim][BF₄] and [Bmim][Tf₂N], viscosities decrease rapidly in the first stage, and then decrease slowly with the increase of water content. But for [Bmim][Ac], the viscosities increase first and then decrease. The unique phenomenon of [Bmim][Ac] can be attributed to the formation of chain‐like structure of anion???water???anion???. Hydrogen bond (HB) interaction between ion pairs is weakened, but the number of HB between water and anions increases with increase of water content. Besides, the microstructures of water in ionic liquids‐water systems were compared and found that the distribution of water is more concentrated in [Bmim][Tf₂N]‐H₂O system, while it is isotropy in [Bmim][Ac]‐H₂O system. © 2016 American Institute of Chemical Engineers AIChE J, 63: 2248–2256, 2017     

Synergistic Extraction of Lanthanides (III) with Mixtures of TODGA and Hydrophobic Ionic Liquid into Molecular Diluent

The extraction of lanthanides(III) from aqueous nitric acid solutions with N,N,N’,N’-tetra(n-octyl)diglycolamide (TODGA) and with mixtures of TODGA and the hydrophobic ionic liquid (IL) [C₄mim][Tf₂N] into 1,2-dichloroethane (DCE) has been investigated. The extraction efficiency of Ln(III) ions was greatly enhanced by the addition of a small amount of IL to an organic phase containing TODGA. The synergistic effect comes from the higher hydrophobicity of Ln(III) extracted species formed by TODGA and the weakly coordinating Tf₂N^? anions compared with those formed by TODGA and NO₃^? ions as the counter-anions. The partition of Tf₂N^? anions between the organic and aqueous phases is the dominant factor governing the extractability of lanthanides(III) with mixtures of TODGA and [C₄mim][Tf₂N]. The extraction of Ln(III) from aqueous nitric acid solutions by TODGA alone and its mixtures with [C₄mim][Tf₂N] into DCE can be described on the basis of the solvation extraction mechanism. However, in the extraction system with added [C₄mim][Tf₂N], the partition of Tf₂N^? between two immiscible phases and the interaction between HTf₂N and TODGA in the organic phase should be taken into account. Possible reasons of the antagonistic effect in the TODGA–[C₄mim][Tf₂N] extraction system are discussed.     

Gas drying with ionic liquids

The gas drying technology with ionic liquids (ILs) was systematically studied ranging from the molecular level to industrial scale. The COSMO‐RS model was first used to screen the suitable IL and provide theoretical insights at the molecular level. Toward CO₂ gas dehydration, we measured the CO₂ solubility in single [EMIM][Tf₂N] and in the [EMIM][Tf₂N] + H₂O mixture, as well as the vapor‐liquid equilibrium (VLE) of [EMIM][Tf₂N] + H₂O system, to justify the applicability of UNIFAC model. Based on the thermodynamic study, the rigorous equilibrium (EQ) stage mathematical model was established for process simulation. The gas drying experiment with IL was also performed and the water content in gas product can be reduced to 375 ppm. It was confirmed that a less flow rate of absorbent, a higher CO₂ recovery ratio and a much lower energy consumption can be achieved with IL than with the conventional triethylene glycol (TEG). © 2017 American Institute of Chemical Engineers AIChE J, 64: 606–619, 2018     

Ionic liquid mediated surface micropatterning of polymer blends

A polymer of intrinsic porosity (i.e., PIM‐1) has been blended with different ionic liquids (ILs) in order to evaluate the effect of the ILs on the microstructure of the polymer blend. [C₈MIM][Cl], [BMIM][DCa], [BMPyr][DCa], and [BMIM][Tf₂N] have been selected and were mixed with PIM‐1. Polymer blends containing up to 80 wt % of ILs were prepared by a casting method with chloroform as solvent. SEM images show that during the film formation a structuring of the surface appears depending on the nature and the concentration of ILs, with appearance of well‐defined microstructure in the case of [BMIM][Tf₂N] and [BMIM][DCa]. In the case of [BMIM][Tf₂N]/PIM‐1 film, the lower IL concentration induces the denser film with small micropatterns onto the surface. AFM analysis indicates that the ILs are well dispersed on the surface. X‐ray photoelectron spectroscopy, Fourier transform infrared spectroscopy, and water contact angle measurements show that a gradient of IL concentration is observed across the film thickness. It is demonstrated that ILs are versatile co‐solvents for inducing controlled micropatterns in polymer membrane surfaces. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018 , 135, 46109.     

Enhanced stability of <Emphasis Type="Italic">Candida antarctica</Emphasis> lipase B in ionic liquids

The activity and stability of lipase from Candida antarctica were investigated in the kinetic resolution of (R,S)-1-phenylethanol with vinyl acetate using ionic liquids (ILs) as reaction media. Among ILs tested, the highest activity of lipase was observed in [Edmim][Tf₂N]. In hydrophobic ILs such as [Edmim][Tf₂N], [Emim][Tf₂N] and [Pmim] [PF₆], lipase could retain its activity after 5 times reuse, while the activity of lipase in hydrophilic ILs and organic solvents was drastically decreased. The activities of lipase in [Edmim][Tf₂N], [Emim][Tf₂N] and [Pmim][PF₆] were also well maintained after 1 day incubation at 80 °C. The lipase suspended in [Edmim][Tf₂N] could be successfully reused 6 times without loss of activity.     

A new approach of ionic liquid containing polymer sorbents for post-combustion CO2 scrubbing

Room temperature task-specific ionic liquids (TSIL) of 1-(2-hydroxylethyl)-3-methylimidazolium bis(trifluoromethylsulfonyl)imide ([Im₂₁OH][Tf₂N]) or 2-hydroxyethyl(dimethyl)-isopropylammonium bis(trifluoromethylsulfonyl)imide ([N_ip,211OH][Tf₂N]) with superbase, 1,8-diazabicyclo-[5.4.0]undec-7-ene (DBU), has been combined with Torlon^® powders (<106 um) to simulate the potential benefits of integrating equimolar amounts of ionic liquids and superbase into hollow fibers in terms of both sorption uptake and kinetics. Approximately 44 wt% of an equimolar [Im₂₁OH][Tf₂N]-DBU in Torlon^® powders achieved CO₂ sorption uptake of 0.57 mmol CO₂/g at a CO₂ feed pressure of 0.1 atm and at 35 °C. Similar amounts of an equimolar [N_ip,211OH][Tf₂N]-DBU in Torlon^® powders showed CO₂ sorption uptake of 0.45 mmol CO₂/g at the same condition. The half time (time to reach M_t/M_∞ of 0.5) for Torlon^®, Torlon^®(62 mg)/[Im₂₁OH][Tf₂N]-DBU(48 mg) and [Im₂₁OH][Tf₂N]-DBU at low feed pressure (～1.5 psia CO₂) was approximately 4, 55, and 298 s, respectively demonstrating that imbibing an equimolar [Im₂₁OH][Tf₂N]-DBU into polymer powders substantially improved sorption kinetics compared to the neat counterpart. The sorption half time is expected to be even shorter for fibers with smaller characteristic polymer morphology domains. The current study also demonstrates a new experimental approach to characterize CO₂ sorption in an equimolar mixture of ionic liquids and superbase.     

CO2 absorption properties of Brønsted acid-base ionic liquid composed of N,N-dimethylformamide and bis(trifluoromethanesulfonyl)amide

The solubilities of CO₂ and the liquid densities in a Brønsted acid-base ionic liquid, [DMFH][Tf₂N], composed of N,N-dimethylformamide (DMF) and bis(trifluoromethanesulfonyl)amide (HTf₂N) have been investigated at high pressures and at different temperatures. The results were compared with those in DMF and a typical 1-butyl-3-methylimidazolium analogue with the same anion, [BMIM][Tf₂N]. The mole fraction scaled solubilities of CO₂ in the three liquids showed a slight increase in the following order, DMF < [DMFH][Tf₂N] < [BMIM][Tf₂N], whereas more remarkable difference was observed in the volume scaled concentrations of CO₂, [BMIM][Tf₂N] < [DMFH][Tf₂N] « DMF, mainly due to the bulkiness of liquid entities.     

Performance and pressure drop of CO2 absorption into task-specific and halide-free ionic liquids in a microchannel

The gas–liquid two-phase flow pattern, absorption rate and pressure drop of CO₂ absorbed into the aqueous solution of the task-specific ionic liquids (1-aminopropyl-3-methylimidazole tetrafluoroborate [Apmim][BF₄] and 1-hydroxyethyl-3-methylimidazole tetrafluoroborate [OHemim][BF₄]) and halide-free ionic liquid 1-butyl-3-methylimidazolium methylsulfate [Bmim][CH₃SO₄] were investigated in a microreactor. The absorption mechanism of the three ionic liquids was analyzed employing the ¹³C NMR spectroscopy. The [Apmim][BF₄] was found to have the best ability of CO₂ capture compared with the other two ionic liquids, as chemical absorption occurred between [Apmim][BF₄] and CO₂, while only physical absorption took place between [OHemim][BF₄]/[Bmim][CH₃SO₄] and CO₂. The sequence of CO₂ absorption rate in three ionic liquids aqueous solutions is: [Apmim][BF₄] > [Bmim][CH₃SO₄] > [OHemim][BF₄]. Furthermore, the effects of gas–liquid flow rate and ionic liquids concentration on CO₂ absorption rate and pressure drop were studied, the pressure drop models based on various flow patterns were proposed.     

Thermal conductivity of the ionic liquid [HMIm][Tf2N] with compressed carbon dioxide

The liquid thermal conductivity of the ionic liquid (IL), 1-hexyl-3-methyl-imidazolium bis(trifluoromethylsulfonyl)amide ([HMIm][Tf₂N]), saturated with compressed vapor and supercritical carbon dioxide was measured over three isotherms (298.15, 323.15, and 348.15 K) and pressures up to approximately 20 MPa using a transient hot-wire technique. Pure [HMIm][Tf₂N] thermal conductivity was also measured over a temperature range of 293.15–353.15 K at ambient pressure and with hydrostatic pressure to approximately 20 MPa. Literature vapor–liquid equilibrium data were used to predict the liquid CO₂ composition at the conditions investigated. Initially, the liquid thermal conductivity slightly decreased with pressure/composition of CO₂ followed by a gradual increase that is mainly attributed to hydrostatic pressure effects. Simple composition-based mixing rules for mixture properties are not qualitatively nor quantitatively accurate. These data could be used to engineer heat transfer equipment required for a variety of proposed IL applications in CO₂ capture, absorption refrigeration, biphasic CO₂/IL reaction platforms, etc.     

咪唑类离子液体高效吸收二氯甲烷

合成了一系列常规离子液体1-丁基-3-甲基咪唑四氟硼酸盐([Bmim][BF4])、1-丁基-3-甲基咪唑六氟磷酸盐([Bmim][PF6])、1-丁基-3-甲基咪唑双三氟甲磺酰亚胺盐([Bmim][NTf2])、1-丁基-3-甲基咪唑双氰胺盐([Bmim][DCA])、1-丁基-3-甲基咪唑硫氰酸盐([Bmim][SCN])、1-乙基-3-甲基咪唑硫氰酸盐([Emim][SCN])和N-丁基吡啶硫氰酸盐([BPy][SCN]),用智能重量分析仪(IGA)测定不同温度和分压下离子液体吸收二氯甲烷(DCM)的容量。结果表明,[Bmim][SCN]具有最高的二氯甲烷吸收容量(1.46 g/g, 303.15 K, 60 kPa),5次循环后吸收能力无明显下降,[Bmim][SCN]基本可完全再生,能循环使用。量化计算结果表明[SCN]?可与二氯甲烷形成氢键,增强其对二氯甲烷的吸收能力。     

Gold-ionic liquid nanofluids with preferably tribological properties and thermal conductivity

Gold/1-butyl-3-methylimidazolium hexafluorophosphate (Au/[Bmim][PF₆]) nanofluids containing different stabilizing agents were fabricated by a facile one-step chemical reduction method, of which the nanofluids stabilized by cetyltrimethylammonium bromide (CTABr) exhibited ultrahighly thermodynamic stability. The transmission electron microscopy, UV-visible absorption, Fourier transform infrared, and X-ray photoelectron characterizations were conducted to reveal the stable mechanism. Then, the tribological properties of these ionic liquid (IL)-based gold nanofluids were first investigated in more detail. In comparison with pure [Bmim][PF₆] and the nanofluids possessing poor stability, the nanofluids with high stability exhibited much better friction-reduction and anti-wear properties. For instance, the friction coefficient and wear volume lubricated by the nanofluid with rather low volumetric concentration (1.02 × 10^-3%) stabilized by CTABr under 800 N are 13.8 and 45.4% lower than that of pure [Bmim][PF₆], confirming that soft Au nanoparticles (Au NPs) also can be excellent additives for high performance lubricants especially under high loads. Moreover, the thermal conductivity (TC) of the stable nanofluids with three volumetric fraction (2.55 × 10^-4, 5.1 × 10^-4, and 1.02 × 10^-3%) was also measured by a transient hot wire method as a function of temperature (33 to 81°C). The results indicate that the TC of the nanofluid (1.02 × 10^-3%) is 13.1% higher than that of [Bmim][PF₆] at 81°C but no obvious variation at 33°C. The conspicuously temperature-dependent and greatly enhanced TC of Au/[Bmim][PF₆] nanofluids stabilized by CTABr could be attributed to micro-convection caused by the Brownian motion of Au NPs. Our results should open new avenues to utilize Au NPs and ILs in tribology and the high-temperature heat transfer field.     

Liquid‐liquid phase split in ionic liquid + toluene mixtures induced by CO2

High pressure carbon dioxide was dissolved in ionic liquid + toluene mixtures to obtain the conditions of pressure and composition where a liquid‐liquid phase split occurs at constant temperature. Ionic liquids (ILs) with four different cations paired with the bis(trifluoromethylsulfonyl)imide ([Tf₂N]^?) anion were selected: 1‐hexyl‐3‐methylimidazolium ([hmim]⁺), 1‐hexyl‐3‐methylpyridinium ([hmpy]⁺), triethyloctylphosphonium ([P₂₂₂₈]⁺), and tetradecyltrihexylphosphonium ([P₆₆₆₁₄]⁺). The solubility of CO₂ was measured in the liquid mixtures at temperatures between 298 and 333 K and at pressures up to 8 MPa, or until the second liquid phase appeared, for initial liquid phase compositions of 0.30, 0.50, and 0.70 mole fraction of IL. Ternary isotherms were compared with the binary solubility of CO₂ in each IL and pure toluene. The lowest pressure for separating toluene in a second liquid phase was achieved by decreasing the temperature of the system, increasing the amount of toluene in the initial liquid mixture and using [hmim][Tf₂N]. © 2015 American Institute of Chemical Engineers AIChE J, 61: 2968–2976, 2015     

Ionic liquids in electrosynthesis and characterization of a polyazulene-fullerene composite

Polyazulene (PAz) was electrosynthesized in the ionic liquid N,N-butyl-methyl-pyrrolidinium bis(trifluoromethylsulfonyl)imide ([BMP][Tf₂N]) and characterized using electrochemical methods. By using [BMP][Tf₂N] as the electrolyte we obtained films with improved electrochemical and morphological properties compared to films electrosynthesized in an acetonitrile-based electrolyte solution. Composite films consisting of drop cast C₆₀ and electrosynthesized PAz were also investigated in [BMP][Tf₂N] using electrochemical methods, UV–vis and SEM and the results were compared to similar films prepared in acetonitrile. The use of ionic liquids made it possible to study the redox reactions of C₆₀ at room-temperature and in an extended cathodic potential range. In comparison to pure PAz the presence of C₆₀ in the composite film improved the charge storing ability. Electrosynthesis in [BMP][Tf₂N] resulted in composite films with a lower degree of charge trapping compared to composite films synthesized in organic media.     

Insight into the behavior at the hygroscopicity and interface of the hydrophobic imidazolium-based ionic liquids

How to completely remove the water from ionic liquids(ILs) is difficult for researchers because of the hygroscopicity of ILs. In order to study the hygroscopicity of ILs, two kinds of ILs, 1-Butyl-3-methylimidazolium hexafluorophosphate([Bmim][PF_6]) and 1-Butyl-3-methylimidazolium Bis(trifluoromethanesulfonyl)([Bmim][NTf_2]) were investigated by molecular dynamics simulations. Although[Bmim][PF_6] and [Bmim][NTf_2] are hydrophobic, both of the ILs could absorb water molecules from the vapor. In this work, the process of absorbing water from the vapor phase was studied, and the water molecules could disperse into the IL. Aggregation was observed with increasing the water concentration.Although the absorbed water increases obviously, the amount of free water and small cluster in the ILs does not change significantly and always stays at a certain level. The amount of free water and small cluster in [Bmim][PF_6] is more than that in [Bmim][NTf_2], which is consistent with their hydrophobicity. In addition, the liquid-vacuum and liquid–liquid interfaces of the ILs were simulated and analyzed in detail.The number density distribution and angle distribution indicated that [Bmim]+cations arrangement regularly at the IL-vacuum interface. The butyl chain point to the vacuum, while the imidazlium ring is close to the IL phase region and perpendicular to the interface. While at the IL-water interface, the cations and anions are disordered.     

Liquid–liquid extraction of hydroxytyrosol,tyrosol, and oleuropein using ionic liquids

ABSTRACT

Hydroxytyrosol (HT), tyrosol (TY), and oleuropein (OL) are valuable compounds that can be obtained from olive oil production waste. This study implemented liquid–liquid extraction to obtain HT, TY, and OL from model solutions using two organic solvents, namely, ethyl acetate and n-butyl acetate, and three ionic liquids (ILs), namely, [P_6,6,6,14][Tf₂N], [P_6,6,6,14][DCA], and [omim][Tf₂N]. [P_6,6,6,14][DCA] showed the best performance, with extraction efficiencies of 92%, 96%, and 83% for HT, TY, and OL, respectively. [omim][Tf₂N] showed the highest selectivity in the extraction of TY. Comparisons of the results of a proposed mathematical model with experimental data yielded errors lower than 0.5%.     

Efficient recovery of ionic liquid by electrodialysis in the acid hydrolysis process

Electrodialysis (ED) has been recently known as a highly effective technique to remove and recover ionic liquids from aqueous solution. When a conventional electrolyte solution for the ED process containing Na₂SO₄ was used, a recovery ratio of an acidic IL, 1-butyl-3-methylimidazolium hydrogen sulfate ([Bmim][HSO₄]), was 90%. On the other hand, the value clearly increased to 96% when we employed [Bmim][HSO₄] as the electrolyte solution. In an acid hydrolysis of bagasse using the IL under microwave irradiation, the recovery ratio maintains 96%, irrespective of reaction time. This demonstrates the applicability of the proposed ED system in biomass processing.     

Power generation from waste heat: Ionic liquid-based absorption cycle versus organic Rankine cycle

Aspen Plus® simulations using the Peng-Robinson (PR-EOS) and the COSMO-SAC models were performed to study absorption power cycles (APCs) using mixtures of R-134a with two ionic liquids, [C₂C₁im][Tf₂N] or [C₆C₁im][Tf₂N], and compared against an R-134a organic Rankine cycle (ORC) operating under similar conditions. The PR-EOS results were in agreement with calculations from a PR model fitted to the R-134a + IL experimental phase equilibrium data. The APCs have similar efficiencies and outperform the ORC by 3%–46%, with the largest differences observed when operating with lower grade (lower T_H) heating sources, lower quality cooling (higher T_L), and lower subcooling in the pump inlet stream. The PR-EOS and the Conductor-like Screening Model Segment Activity Coefficient (COSMO-SAC) results follow similar trends, but numerical discrepancies are observed in the cycle efficiencies and stream flow rates and compositions due to differences in solubilities and enthalpy changes between both models, suggesting that improvements are needed to increase the accuracy of COSMO-SAC for these systems.     

Improving Physical Adsorption of CO2 by Ionic Liquids‐Loaded Mesoporous Silica

CO₂ sorption capacities of the neat and silica‐supported 1‐butyl‐3‐methylimidazolium‐based ionic liquids (ILs) were measured under atmospheric pressure. The silica‐supported ILs were synthesized by the impregnation‐vaporization method and charactrized by N₂ adsorption/desorption and thermogravimeteric analysis (TGA). Evaluation of the effects of influential factors on sorption capacity demonstrated that by increase of the temperature, flow rate, and the weight percentage of ILs in sorbents, the sorption capacity decreases. Among the sorbents, [Bmim][TfO] and SiO₂‐[Bmim][BF₄](50) had the highest capacity. By increasing the IL portion in SiO₂‐[Bmim][BF₄], the selectivity for CO₂ to CH₄ could be improved. The CO₂‐rich sorbents could be easily recycled.     

Microfluidic room temperature ionic liquid droplet generation depending on the hydrophobicity and interfacial tension

We have characterized micro-droplet generation using water immiscible hexafluorophosphate ([PF₆])- and bis(trifluoromethylsulfonyl)imide ([Tf₂N])-based room temperature ionic liquids (RTILs). The interfacial tension between total 7 RTILs and phosphate buffered saline (PBS) was measured using a tensiometer for the first time. PBS is one of the most commonly used buffer solutions in cell-related researches. The measured interfacial tension ranges from 8.51 to 11.62 and from 9.56 to 13.19 for [Tf₂N]- and [PF₆]-based RTILs, respectively. The RTILs micro-droplets were generated in a microfluidic device. The micro-droplet size and generation frequency were determined based on continuous monitoring of light transmittance at the interface in microchannel. The size of RTIL micro-droplets was inversely proportional to the increase of PBS solution flow rate and RTILs hydrophobicity, while droplet generation frequency was proportional to those changes. The measured size of RTILs droplets ranged from 0.6 to 10.5 nl, and from 1.0 to 17.1 nl for [Tf₂N]- and [PF₆]-based RTILs, respectively. The measured frequency of generated RTILs droplets ranged from 2.3 to 37.2 droplet/min, and from 2.7 to 17.1 droplet/min for [Tf₂N]- and [PF₆]-based RTILs, respectively. The capillary numbers were calculated depending on the RTILs, and ranged from 0.51×10^-3 to 1.06×10^-3 and from 5.00×10^-3 to 8.65×10^-3, for [Tf₂N]- and [PF₆]-based RTILs, respectively. The interfacial tension between RTILs and PBS will contribute to developing bioprocesses using immiscible RTILs. Also, the RTILs micro-droplets will enable the high-throughput monitoring of various biological and chemical reactions using RTILs as new reaction media.