Carboxylate Ionic Liquids Research Articles

Ionic liquids as oil additives for lubricating oxygen-diffusion case-hardened titanium

Abstract This study attempts to use ionic liquids (ILs) as oil additives to lubricate oxygen-diffusion (OD) case-hardened titanium for improved friction and wear behavior. Four oil-soluble ILs were used as additives in a base oil for boundary lubrication of an OD-treated Ti-6Al-4V surface sliding against a bearing steel ball. The ILs improved the friction behavior to various extents and the two phosphate ILs clearly outperformed the conventional ZDDP. Unlike ZDDP that adversely caused a higher material loss, ILs exhibited excellent wear protection suggesting good material-chemical compatibility. Particularly, the carboxylate IL protected the OD-Ti surface from any measurable wear. The morphology and chemical composition of the worn surfaces and tribofilms were examined to gain insights of the anti-wear mechanism.

Double bond carboxylate ionic liquids for reversible SO2 capture

Abstract Solubility of SO2 in [N2224][Met] was measured at temperature from 313.2 to 333.2 K and pressure up to 1.8 bar. The [N2224][Met] absorbed SO2 at high speed and could be recycled for four times. The Reaction Equilibrium Thermodynamic Model (RETM) was used to correlate the experimental data, Henry’s constant (H), reaction equilibrium constant (K0), and thermodynamic properties ( Δ r H m 0 , Δ r G m 0 , Δ r S m 0 , Δ H phy a n d Δ H chem ) were derived. Considering the absorption capacity and low absorption enthalpy, as well as the fast absorption process, [N2224][Met] is thought to be a promising absorbent to ordinary solvent as a desulfurizer.

Ionic Liquid Stabilized Niobium Oxoclusters Catalyzing Oxidation of Sulfides with Exceptional Activity.

We present here a new class of niobium oxoclusters that are stabilized effectively by carboxylate ionic liquids. These functionalized ILs are designated as [TBA][LA], [TBA][PA], and [TBA][HPA] in this work, in which TBA represents tetrabutylammonium and LA, PA, and HPA refer to lactate, propionate, 3-hydroxypropionate anions, respectively. The as-synthesized Nb oxoclusters have been characterized by use of elemental analysis, NMR, IR, XRD, TGA, HRTEM. It was found that [TBA][LA]-stabilized Nb oxoclusters (Nb-OC@[TBA][LA]) are uniformly dispersed with an average particle size of 2-3 nm and afforded exceptionally high catalytic activity for the selective oxidation of various thioethers. The turnover number with Nb-OC@[TBA][LA] catalyst was over 56 000 at catalyst loading as low as 0.0033 mol % (1 ppm). Meantime, the catalyst also showed the high activity for the epoxidation of olefins and allylic alcohols by using only 0.065 mol % of catalyst (50 ppm). The characterization of 93 Nb NMR spectra revealed that the Nb oxoclusters underwent structural transformation in the presence of H2 O2 but regenerated to their initial state at the end of the reaction. In particular, the highly dispersed Nb oxoclusters can absorb a large amount of polar organic solvents and thus were swollen greatly, which exhibited "pseudo" liquid phase behavior, and enabled the substrate molecules to be highly accessible to the catalytic center of Nb oxocluster units.

Anionic structural effect in liquid–liquid separation of phenol from model oil by choline carboxylate ionic liquids

Phenolic compounds exist in crude oil as pollutants, and their removal is vital important for the refining and further application of oils. In traditional separation approaches, strong acid and strong base have to be used to remove these compounds, which may cause serious environmental problems. In this work, 19 kinds of cholinium ionic liquids have been developed to separate phenol from model oil by liquid–liquid extraction. Structural effect of anions of the ionic liquids in the separation is systematically investigated. It is found that depending on the chemical structure of ionic liquids, phenol can be removed from toluene with single-step removal efficiency from 86 to 99% under optimal conditions. The type of substituent groups and the -CH2 number between two carboxylates have obvious effect on the removal efficiency, and more hydrophilic ionic liquids have a stronger extraction performance for phenol. Furthermore, thermodynamic, 13C NMR, 1H NMR and density functional theory calculations have been performed to characterize the extraction process and to understand the extraction mechanism. It is shown that the extraction of phenol from oil to ionic liquid is a favorable process, and this process is mainly driven by enthalpy change. The formation of the hydrogen bond between anion of the ionic liquid and -OH of phenol is the main driving force for the extraction of phenol from oil to the ionic liquids.

Methyltriphenylphosphonium carboxylate ionic liquids: Green synthesis, adsorption and aggregation behavior in aqueous solution

In this paper, a series of methyltriphenylphosphonium carboxylate room temperature ionic liquids [Ph3PCH3][CnH2n+1COO] with different alkyl chain length (n = 7, 9, 11, 13, 15, 17) have been synthesized by quaternization of triphenylphosphine (TPP) with dimethyl carbonate (DMC) and followed anion exchange with different carboxylic acids. The synthesis route is not only simple, but also can avoid problems such as toxicity, environmental pollution and equipment corrosion. The structures of these compounds were characterized by FT-IR and 1H-NMR. Meanwhile, their surface adsorption and aggregation behavior in aqueous solution have been investigated by equilibrium surface tension, electrical conductivity and transmission electron microscopy (TEM) measurements. Furthermore, the impact of alkyl chain length on their surface adsorption and aggregation behavior were also investigated. TEM results indicated that methyltriphenylphosphonium carboxylate ionic liquid surfactants could self-assemble into regular spherical aggregates in aqueous solution. The diameter of the spherical aggregates is about 50 ∼ 100 nanometers and does not change much with the change of alkyl chain length.

Wetting, foaming, and emulsification properties of novel methyltriphenylphosphonium carboxylate ionic liquid surfactants

Novel methyltriphenylphosphonium carboxylate ionic liquid (IL) surfactants [Ph3PCH3][CH3(CH2)6COO] (MTPP-O), [Ph3PCH3][CH3(CH2)8COO] (MTPP-D), [Ph3PCH3][CH3(CH2)10COO] (MTPP-L), [Ph3PCH3][CH3(CH2)12COO] (MTPP-M), [Ph3PCH3][CH3(CH2)14COO] (MTPP-P), [Ph3PCH3][CH3(CH2)16COO] (MTPP-S) were synthesized via quaternization triphenylphosphine with dimethyl carbonate and anion exchange with different carboxylic acids successively. The structures of these IL surfactants were confirmed by FT-IR and 1H-NMR. Meanwhile, the wetting, foaming, and emulsification properties of these IL surfactants were studied in this paper. The results revealed that methyltriphenylphosphonium carboxylate IL surfactants have lower foaming properties than quaternary ammonium salts with the same anionic units. And, these IL surfactants show better emulsification ability to soybean oil than that of liquid paraffin. Furthermore, contact angle results indicated that these IL surfactants have different wettability for parafilm and the contact angle increases at a higher concentration for MTPP-L, MTPP-M, and MTPP-P.

Viscosity, Electrical Conductivity, Density and Surface Tension of Methyltriphenylphosphonium Carboxylate Ionic Liquids

Abstract In this paper, three new kinds of phosphonium-based room temperature ionic liquids (ILs) [Ph3PCH3][CH3(CH2)8COO] (MTPP-D), [Ph3PCH3][CH3(CH2)10COO] (MTPP-L), and [Ph3PCH3][CH3(CH2)12COO] (MTPP-M) were synthesized using triphenylphosphine, dimethyl carbonate and carboxylic acids as raw materials. The viscosity, electrical conductivity, density and surface tension of the synthesized ILs were measured in the temperature range from 298.15 K to 333.15 K under ambient pressure. Meanwhile, the effects of temperature and alkyl chain length on their viscosity, electrical conductivity, density and surface tension were also investigated. The molecular volume, standard entropy, lattice energy and isobaric expansivity of the three ILs were calculated at 298.15 K. Experimental results indicate that the viscosity, density and surface tension of the three ILs decrease significantly with the increase of temperature, while the electrical conductivity shows an opposite trend. The longer the alkyl chain, the higher the viscosity, the lower the electrical conductivity, density and surface tension of the ILs. The experimental dynamic viscosity can be well correlated by the Vogel-Fulcher-Tammann (VFT) equation and simple linear equation. The temperature dependence of electrical conductivity can be well fitted by Arrhenius equation and VFT equation. The molecular volume, standard entropy and isobaric expansivity increase with increasing alkyl chain length, while the lattice energy decreases.

Thermodynamic Properties and Intermolecular Interactions of a Series of N-Butylammonium Carboxylate Ionic Liquids

A series of new N-butylammonium carboxylate ionic liquids (N-butylammonium formate, N-butylammonium acetate, N-butylammonium propionate, and N-butylammonium butyrate) were synthesized by a one-step method and characterized. The thermodynamic properties such as surface tension, density, electrical conductivity, and dynamic viscosity of the ILs were measured as functions of temperature. Important parameters such as molecular volume, crystal energy, thermal expansion coefficient, standard molar entropy, and the surface properties are estimated by the empirical equations. The Vogel–Fulcher–Tamman (VFT) equation is used to explore the dependence of electrical conductivities and dynamic viscosities on temperature. The relationship between the molar conductivity and the fluidity of the ILs was examined through the use of Walden plots. To describe intermolecular interactions of the N-butylammonium carboxylate ILs, the optimized structures and energetics of ILs are calculated by DFT calculations. The calculated en...

Carboxylate Ionic Liquids with Large Free Volume and Strong Hydrogen Bonding Basicity for Efficient Separation of Butadiene and n-Butene

The separation of 1,3-butadiene (1,3-C4H6) and n-butene (n-C4H8) using ionic liquids (ILs) has received great attention in recent years, but designing an industrially attractive IL that combines large solubility and high selectivity remains challenging. In this work, we prepared several tributylethylphosphonium-based carboxylate ILs featuring large free volume and strong hydrogen bonding basicities through finely tuning the structures of cations and anions for the separation of C4 hydrocarbons. These carboxylate ILs exhibited the highest mass solubility for 1,3-C4H6 yet reported (0.899 and 0.663 mmol/g in [P4442][C17H35COO] and [P4442][HCOO], respectively) and excellent 1,3-C4H6/n-C4H8 selectivity (1.83 in [P4442][HCOO]) at 308.1 K and 100 kPa, which sets a new benchmark for 1,3-C4H6/n-C4H8 separation. Qualitative relationships between the free volume/basicity and their solubility were established. Results revealed that the free volume of unit mass and basicity were positively correlated with the 1,3-C4H6...

Synthesis, self-assembly and micellization characteristics of choline alkanoate ionic liquids in association with a star block copolymer

Herein, alkyl chain dependent self-assembly of choline carboxylate ionic liquids (ILs) and their effect on micellar characteristics of a star block copolymer (Tetronic®T1304) are reported. The ILs showed good aqueous solubility (low Kraft point) and formed spherical micelles. Small angle neutron scattering (SANS) analyses revealed a reduction in the critical micelle concentration (CMC) and elevation in the aggregation number (Nagg) upon increasing alkyl chain length of ILs. More importantly, ILs demonstrated good biocompatibility in murine erythrocytes and A549 cells, irrespective of the chain length.Furthermore, the effect of IL addition on micellar behaviour of T1304 was examined through thermal and scattering studies. We observed alkyl chain dependent increase in the cloud point (CP), critical micellization temperature (CMT), micelle size (Rh, Rc, Rhs) and Nagg. In association with T1304, long chain ILs (n = C12–C18) formed charged mixed micelles with a lower Nagg which showed enhanced solubilization of quercetin, a hydrophobic drug. Mixed micelles, composed with such biocompatible ILs, can further be tuned to explore their drug delivery applications.

Nanostructured Branched-Chain Carboxylate Ionic Liquids: Synthesis, Characterization, and Extraordinary Solubility for Bioactive Molecules

The design of multifunctional ionic liquids (ILs) that integrate different attractive characteristics, such as strong hydrogen-bonding interactions, good lipophilicity, significant nanoscale organization, and low viscosity, in a molecular structure is of great importance for the application of ILs in extraction, biomass conversion, and catalysis but remains challenging. Here, we synthesized a family of novel phosphonium ILs featuring branched chain carboxylate anions with carbon number up to 18 and systematically characterized the physicochemical properties of prepared ILs. The branched chain carboxylate ILs (BCC-ILs) exhibit very strong hydrogen-bond basicity (β = 1.49–1.72, 30 °C) and excellent lipophilicity (π* = 0.73–0.95, 30 °C), and have obvious nanoscale segregation and moderate viscosity (η = 91.8–200.5 mPa, 40 °C). The d value of BCC-ILs ranged from 10.5 to 15.6 A when the length of alkyl chain in anions or cation rose. These nanostructured solvents can undergo self-assembly processes with typica...

Effects of protic ionic liquid crystal additives on the water-lubricated sliding wear and friction of sapphire against stainless steel

Additives for water lubrication of a sapphire-stainless steel contact have been developed by adding 1 wt% protic ammonium carboxylate ionic liquid crystals (ILCs) derived from stearic and palmitic fatty acids. Triprotic (2-hydroxyethyl)ammonium stearate, diprotic bis(2-hydroxyethyl)ammonium stearate and bis(2-hydroxyethyl)ammonium palmitate have been studied. In unidirectional, pin-on-disk tests of sapphire against type 316 L stainless steel, the additives reduce the coefficient of friction up to 80%, from the start of the sliding, and reduce or prevent increase of the friction at the lubricated-dry contact transition after water evaporation. The wear rate of the stainless steel is reduced by one order of magnitude. The main mechanism for prevention of surface damage is the reduction of iron oxidation inside the wear track due to adsorption of the ILCs additives. SEM/EDX, TEM, XPS surface analysis, Raman spectroscopy and profilometry results are discussed.

A new insight into pure and water-saturated quaternary phosphonium-based carboxylate ionic liquids: Density, heat capacity, ionic conductivity, thermogravimetric analysis, thermal conductivity and viscosity

Abstract Ionic Liquids (ILs) are task specific materials with tunable properties which may be applied as heat transfer fluids (HTFs) due to their characteristic properties including low vapour pressure, wide liquid range and high thermal stability. This study provides an evaluation of their potential as HTFs from both their physicochemical properties as well as an economic comparison with commonly used materials. The paper presents the thermophysical properties (density, isobaric heat capacity, ionic conductivity, viscosity, thermal stability by TGA, thermal conductivity) and their thermodynamic derivatives (isobaric thermal expansion coefficient, excess molar volume, excess molar heat capacity), as well as the Walden rule of ionicity for a range of hydrophobic ILs based on the trihexyl(tetradecyl)phosphonium, ([P14,6,6,6]+), cation. The ionic liquids studied are trihexyl(tetradecyl)phosphonium acetate ([AcO]−), butanoate ([ButO]−), hexanoate ([HexO]−), octanoate ([OctO]−), and decanoate ([DecO]−), as well as their mixtures with water. It was shown that investigated systems are highly promising materials as HTFs, especially ILs + water mixtures, which may be the solution for many engineering issues.

Absorption of SO2 in Furoate Ionic Liquids/PEG200 Mixtures and Thermodynamic Analysis

Carboxylate ionic liquid (IL) and polyethylene glycol 200 (PEG200) mixtures are suitable for the absorption of acidic SO2 because of their unique properties. In the present work, tetraethylammonium furoate ([N2222][FA]) and choline furoate ([Ch][FA]) were blended with PEG200 to form 40 wt % ILs/PEG200 mixtures as SO2 absorbents. The solubilities of SO2 in these two ILs/PEG200 mixtures were measured at T = (303.15, 313.15, 323.15, and 333.15) K and pressure up to 1.2 bar. [N2222][FA]/PEG200 demonstrated the high SO2 absorption capacity of 7.224 mol per kg absorbent at 303.15 K and 1.0 bar. The chemisorption mechanism of SO2 by mixture was studied by Fourier transform infrared and nuclear magnetic resonance spectra, and the influence of cations on the SO2 absorption capacity was analyzed. Furthermore, the reaction equilibrium thermodynamic model was used to correlate the experimental data, and Henry’s law constant (H), reaction equilibrium constant (K0), and thermodynamic properties (ΔrGm0, ΔrHm0, and ΔrSm0...

Basicity Characterization of Imidazolyl Ionic Liquids and Their Application for Biomass Dissolution

Alkalinity determination is of crucial significance for the applications of basic ionic liquids with imidazolyl. In this work, the ionization constantpKbvalue and acid functionH-values of ionic liquids synthesized were calculated by pH method and UV spectrum-Hammett method. The dissolution ratio of biomass in these ionic liquids was measured at different temperatures. Finally, the relationship between the alkalinity and structure of these ionic liquids was discussed, and the relationship between the alkalinity of ionic liquid and the dissolution mechanism biomass was also discussed. The results show that the basicity of carboxylate ionic liquids is determined mainly by their anions, whereas cations take some finely tuned roles. Furthermore, cations and anions are equally important and are involved in dissolution mechanisms.

Aggregation behaviour of biocompatible choline carboxylate ionic liquids and their interactions with biomolecules through experimental and theoretical investigations

The self-assembly of long-chain choline carboxylates accompanied by their interaction with BSA protein were investigated with focus on environmental sustainability.

Interfacial sealing and functionalization of polysulfone/SAPO-34 mixed matrix membrane using acetate-based ionic liquid in post-impregnation for CO2 capture

Abstract The CO2 selective ionic liquids (ILs) have been extensively studied in recent years, but their applications are limited by the high viscosity and cost. In this work, acetate-based ionic liquid was used to enhance and functionalize the interface between polysulfone (PSf) and SAPO-34 zeolite in the asymmetric mixed matrix membrane (MMM) prepared via phase inversion. The MMMs were post-modified by immersing the membranes into carboxylate IL solution (1-butyl-3-methylimidazolium acetate). The effects of IL concentration on the membrane morphology and separation performance in CO2 separation were studied. Fourier transform infrared spectra and energy-dispersive X-ray spectra showed that the IL was successfully incorporated into MMM. The post-impregnation of the membrane with IL improved the interface contact between the polymer and zeolite. The interfacial sealing using IL further enhanced the CO2/N2 selectivity of IL-modified MMM, about 818% higher than the CO2/N2 selectivity of unmodified MMM. The maximum selectivity of 39.60 was achieved using PSf membrane incorporated with 5 wt% of SAPO zeolite loading and modified with 0.4 M of IL. This membrane also sustained its separation performance even wet gas was fed.

Structure and Dynamics of Hydroxyl-Functionalized Protic Ammonium Carboxylate Ionic Liquids.

We performed classical molecular dynamics simulations to investigate the structure and dynamics of protic ionic liquids, 2-hydroxy ethylammonium acetate, ethylammonium hydroxyacetate, and 2-hydroxyethylammonium hydroxyacetate at ambient conditions. Structural properties such as density, radial distribution functions, spatial distribution functions, and structure factors have been calculated. Dynamic properties such as mean square displacements, as well as residence and hydrogen bond dynamics have also been calculated. Hydrogen bond lifetimes and residence times change with the addition of hydroxyl groups. We observe that when a hydroxyl group is present on the cation, dynamics become very slow and it forms a strong hydrogen bond with carboxylate oxygen atoms of the anion. The hydroxyl functionalized ILs show more dynamic diversity than structurally similar ILs.

Synthesis of the symmetrical methylene diesters from carboxylic ionic liquids

The reaction between carboxylic ionic liquids and dichloromethane, which provokes the formation of symmetrical methylene diesters, was carried out. The synthesis of these ionic liquid compounds was carried out in a microwave reactor, and the characterization by spectroscopic techniques of methylene diesters (methylene di-2-furoate, methylene di-2-picolinate, methylene dianthranilate, and methylene dioleate) is described and the crystal structures discussed. The crystal packing of methylene dianthranilate is characterized by trimer formation due to hydrogen bonding via interactions between the hydrogen atom of the primary amine group and the oxygen of the carboxylic group.

Long-Chain Carboxylate Ionic Liquids Combining High Solubility and Low Viscosity for Light Hydrocarbon Separations

Ionic liquids (ILs) have been proposed as promising solvents for hydrocarbon separations, but designing an industrially attractive IL combining high solubility and low viscosity remains challenging. Here, we synthesized three new long-chain carboxylate ILs with asymmetric phosphonium cations that had relatively low viscosity and good thermal stability and exhibited very high solubility and excellent selectivity for hydrocarbons with different carbon numbers under ambient conditions. The solubilities of propane, ethane, methane, and nitrogen in these tributylethyl-phosphonium long-chain carboxylate ILs were determined at temperatures of 298.1 to 313.1 K and pressures of 20 to 150 kPa. The effects of molecular structure on the properties of ILs and their absorption performance were investigated. It was found that the introduction of an asymmetric cation with short alkyl chains significantly reduced the viscosity of carboxylate ILs, while an extension on the alkyl chain of carboxylate anions enhanced the sol...