Imidazolium Ionic Liquid Cations Research Articles

Synthesis and characterization of imidazolium asphaltenes poly (ionic liquid) and application in asphaltene aggregation inhibition of heavy crude oil

New ionic liquids were synthesized from asphaltene colloids that aggregate in the petroleum sludge precipitated in the storage tanks and transportation petroleum pipeline. The alkyl side chains on the asphaltenes were oxidized to polynuclear aromatic carboxylic acids that catalyzed the formation of imidazolium ionic liquid cations. Heptylamine, glyoxal, and p-hydroxybenzaldehyde were used to prepare 1,3-diheptyl and 1,3-diheptyl-2-hydroxyphenyl imidazolium cations conjugated with asphaltenes carboxylate anions as AsIL and AHIL ionic liquids, respectively. The chemical structure, surface charges, particle sizes, thermal stability and thermal characteristics were assessed. The impact of AsIL and AHIL on the dispersion, solubilization, and inhibition precipitation of asphaltenes in the binary solvents and heavy crude oil was studied. The results demontrate that the prepared ionic liquid containing aromatic (AHIL) acts as an asphaltene dispersing and solubilizing agent to inhibit the asphaltene precipitation more than that containing AsIL.

Microwave-assisted Synthesis of 1-(perfluorohexyl)-3-methylimidazolium iodide

ABSTRACTA perfluorinated ionic liquid, 1-(perfluorohexyl)-3-methylimidazolium iodide, was synthesized via microwave reaction and compared to a non-fluorinated analog. Typically, the synthesis of fluorinated ionic liquids involves long reaction times and multiple steps. We have demonstrated a shortened synthesis and a more straightforward procedure, by using a microwave reactor for the microwave-assisted synthesis of 1-(perfluorohexyl)-3-methylimidazolium iodide. The addition of fluorinated alkyl chains on imidazolium ionic liquid cations increases the molecular free volume of the ionic liquid which is beneficial for increasing CO2 physisorption. Computational and experimental data shows an increased CO2 solubility and capacity for fluorinated ionic liquids. The perfluoroalkyl functionalized ionic liquid is characterized using 1H and 19F NMR spectroscopy, FTIR spectroscopy, and DSC. By DSC, a crystallization onset is near -31 °C and while the onset of the melting point between -30 and -17 °C.

Reversed-phase ion-pair chromatography of hydroxyl functionalized imidazolium ionic liquid cations and its application in analysis of environmental water and measurement of hydrophobicity constants

A reversed-phase ion-pair chromatography with ultraviolet detection method for the determination of 1‑hydroxyethyl‑3‑methyl imidazolium cation ([HOEtMIm]+) and 1‑hydroxypropyl‑3‑methyl imidazolium cation ([HOPrMIm]+) was developed. The method has been applied to the analysis of hydroxyl functionalized imidazolium ionic liquid cations in Songhua River water samples and the determination of hydrophobicity constants. [HOEtMIm]+ and [HOPrMIm]+ were not completely separated in the reversed-phase chromatography, but complete separation was realized in the reversed-phase ion-pair chromatography. The effects of ion-pair reagents, organic solvents, column temperatures and ultraviolet detection wavelengths on the separation and detection of hydroxyl functionalized imidazolium ionic liquid cations in reversed-phase ion-pair chromatography were investigated. Ordinary imidazolium ionic liquids do not interfere with the determination of hydroxyl functionalized imidazolium ionic liquids. The suitable ion-pair reagent was sodium octanesulfonate. Using reversed-phase C18 chromatographic column, the mobile phase consisted of 0.5 mmol/L sodium octanesulfonate solution/methanol (85/15, v/v) with column temperature of 40 °C, ultraviolet detection wavelength of 210 nm and flow rate of 1.0 mL/min, [HOEtMIm]+ and [HOPrMIm]+ can be achieved baseline separation within 20 min. The detection limits were 0.36 and 0.50 mg/L, respectively. The relative standard deviations of peak area and retention time were less than 0.80%. Recoveries of sample addition were between 97.3% and100.5%. The method was simple, accurate, reliable, satisfying the requirement of quantitative analysis, and has good practicability.

Effects arising from the replacement of aprotic dipolar solvents with ionic liquids in the nickel-catalyzed reduction of aryl chlorides

In the work on the example of liquid-phase catalytic processes of the aromatic CCl bonds activation occurring in the presence of nickel complexes under reducing conditions the main effects arising from the replacement of aprotic dipolar solvents with ionic liquids are analyzed. The features of the nickel-catalyzed reaction of aryl chlorides, related to the nature of the anion and cation of the ionic liquid, were observed. It was shown that a high concentration of cations and anions in the ionic liquid affects the process of reduction of the nickel complex to the catalytically active state. In addition, the presence of a reactive hydrogen atom in the imidazolium cation of ionic liquid causes the process of hydrodechlorination of aryl chlorides.

Effect of annealing treatment on crystalline and dielectric properties of PVDF/PEG-containing ionic liquid composites

To investigate the effect of poly(ethylene glycol)-containing ionic liquid (IL) and thermal annealing treatment on crystallization and dielectric relaxation behavior of poly(vinylidene fluoride) (PVDF), a series of PVDF/IL composites have been prepared using a solution-cast method. The interaction between imidazolium cation of ILs and >CF2 groups of PVDF can transfer nonpolar α phase to polar β and γ phase as a template at the primary crystallization, and then the interaction between PEG of ILs and >CF2 groups of PVDF can facilitate the PVDF chains in amorphous region to bring more polar phase and decrease the degree of crystallization for PVDF composites according to the template under thermal annealing treatment. The experimental dielectric data were analyzed within the formalisms of complex permittivity and electric modulus. In the frequency spectra of PVDF composites, dc conductivity, electrode and Maxwell-Wagner-Sillars (MWS) interfacial polarization resulted in high values of dielectric permittivity. The incorporation of ILs into the matrix and thermal annealing treatment can accelerate dc conductivity. The temperature dependence of relaxation time of dc conductivity follows the Arrhenius equation. The effect of annealing treatment on charge carrier movement mechanism was resulted from the increase of ion mobility induced by polymer chain segmental motion and polar phase crystals.

Effect of MWCNTs and P[MMA-IL] on the crystallization and dielectric behavior of PVDF composites

Multiwall carbon nanotubes (MWCNTs) and MWCNTs modified by copolymer (P[MMA-IL]) with 1-vinyl-3-ethyl imidazole bromine ionic liquids (IL) and methyl methacrylate (MMA) were incorporated into polyvinylidene fluoride (PVDF) by solution mixing. MWCNTs modified by P[MMA-IL] exhibit better dispersion than that these modified by PMMA. Modified MWCNTs can promote the Tc and Tm of PVDF because of the appearance of β crystalline phase. XRD and FTIR-ATR results confirm that PMMA and MWCNTs cannot induce the β phase, but P[MMA-IL] and MWCNTs can promote the content of β phase due to the ion-dipolar interaction between the imidazolium cation of IL and the >CF2 of PVDF, and the strong induction is brought by the template of MWCNTs. The experimental dielectric data were analyzed within the formalism of complex permittivity and electric modulus. In the frequency spectra of PVDF/P[MMA-IL]/MWCNTs composite, MWS interfacial polarization and electrode polarization result in high value of dielectric permittivity that is related to the large number of the mobile charge carriers. The conductivity relaxation of PVDF/P[MMA-IL]/MWCNTs composite is thermally activated with the hops of charge carriers because P[MMA-IL]/MWCNTs can improve the hops of charge carriers through amorphous and interphase region by ion-dipolar interaction and dipolar ordering reinforced by the template of MWCNTs.

Cationic effect of imidazolium-based ionic liquid on the stability of myoglobin

Abstract The conformational change of myoglobin (Mb) during guanidine hydrochloride (GuHCl)-induced protein unfolding in the presence of various ionic liquids (ILs) in phosphate buffer was investigated using both the Soret band absorption and the fluorescence of tryptophan measurements. The GuHCl-induced denaturation midpoints of Mb derived from the absorption and fluorescence spectra were almost similar in the presence of 150 mM ILs with the same cation 1-butyl-3-methylimidazolium (Bmim + ) but different anions (BF 4 − , NO 3 − , Cl − , and Br − ) in phosphate buffer. In addition, the denaturation midpoints of Mb in the presence of ILs were little lower than those in the absence of ILs in phosphate buffer. For the sake of clarity and comparison, we also measured the GuHCl-induced denaturation midpoints of Mb in the presence of 150 mM sodium salts with different anions (BF 4 − , NO 3 − , Cl − , and Br − ) in phosphate buffer and found that their corresponding denaturation midpoints of Mb were almost similar to those observed in the absence of sodium salts in phosphate buffer. These experimental data indicate that Bmim + cation can promote the unfolding of Mb. Further experiments revealed that the denaturation ability of ILs increases with increasing alkyl chain length of imidazolium cation of ILs and that hydroxyl-substituted imidazolium cation could also promote the unfolding of Mb.

Aggregation behaviors of mixed systems for imidazole based ionic liquid surfactant and Triton X-100

Abstract The adsorption and aggregation of mixed systems for ionic liquid (ILs) surfactants (1-decyl-3-methylimidazolium bromide, C 10 mimBr, 1-dodecyl-3-methylimidazolium bromide, C 12 mimBr, 1-hexadecyl-3-methylimidazolium bromide, C 16 mimBr) and non-ionic surfactant Triton X-100 in aqueous media have been investigated by surface tension measurements, electrical conductivity, 1 H NMR and FTIR technologies. Surface properties have been determined such as critical micelle concentration (CMC), surface saturation adsorption ( Γ max ), minimum surface area per surfactant molecule ( A min ), surface tension at the CMC (γ CMC ), adsorption efficiency ( pC 20 ), and surface pressure at the CMC ( Π CMC ) as well as thermodynamic parameters of micellization. The surface tension measurements revealed that the addition of Triton X-100 into ILs can decrease CMC of ILs, suggesting that it is beneficial to the mixed micelle formation. Consistent with the results of surface tension, electrical conductivity measurement demonstrate a small degree of counter-ion binding to form mixed micelles, which may increase with the addition of TX-100. The 1 H NMR data and FT-IR analysis demonstrated the presence of hydrogen-bond between the imidazolium cation of ILs and the PEO units of Triton X-100 and hydrophobic interactions between the alkyl chain of the imidazolium cation and the hydrophobic chain with phenyl of Triton X-100.

Ion Chromatography of Tri-Substituted Imidazolium Ionic Liquid Cations: Method and Application for Octanol–Water Partition Coefficient (KOW) Determination

A method was developed for simultaneous determination of four trisubstituted imidazolium ionic liquid cations (1-ethyl-2,3-dimethylimidazolium, 1-propyl-2,3-dimethylimidazolium, 1-butyl-2,3-dimethylimidazolium, 1-pentyl-2,3-dimethylimidazolium) by ion chromatography using a carboxylic acid cation exchanger bonded to a silica-based column and direct (nonsuppressed) conductivity detection. The effects of the type of eluents, organic acid concentration, acetonitrile volume fraction, and column temperature on the cations retention were investigated. The optimal conditions for the method were 5 mmol L−1 methanesulfonic acid +10% acetonitrile as an eluent, 1.0 mL min−1 flow rate, and a column temperature of 30°C. The detection limit (S/N = 3) were 0.82–2.39 mg L−1 for the cations. The method was validated, accurate, and reproducible. This method was successfully applied to determine trisubstituted imidazolium ionic liquid cations in spiked tap water. The octanol–water partition coefficients (Kow) of these four trisubstituted imidazole substances were also reported in this study.

Fabrication and characterization of phosphoric acid doped imidazolium ionic liquid polymer composite membranes

Phosphoric acid (PA) doped imidazolium ionic liquid polymer composite membranes were fabricated using the approach of immersing the membranes based on imidazolium ionic liquids and polymers of sulfonated poly (ether ether) ketone (SPEEK) or polyvinylidenefluoride (PVDF) into pure phosphoric acid at room temperature. Imidazolium ionic liquids of 1-butyl-3-methylimidazolium hexafluorophosphate (BMIMPF6) or 1-butyl-3-methylimidazolium dihydrogenphosphate (BMIMH2PO4) link phosphoric acid molecules to polymer matrix. SPEEK is suitable to capture imidazolium ionic liquids owing to the strong interaction between imidazolium ionic liquid cations (BMIM+) and sulfonic acid group (SO3−). So the composite membranes based on SPEEK show promise as high temperature proton exchange membranes. Although all the components influence the conductivity values of these composite membranes, phosphoric acid molecular chains play a dominant role in the proton conduction. Proton conductivity of SPEEK/50%BMIMPF6/4.6PA membrane at a level of 3.0×10−2Scm−1 was achieved at 160°C under anhydrous conditions. Although the tensile stress at break decreased from 3.12MPa to 0.10MPa when the temperature increased from room temperature to 160°C, SPEEK/50%BMIMPF6/4.6PA membrane still possesses a stable conductivity of 2.0×10−2Scm−1 more than 600h at 160°C.

Study on thermo physical and excess molar properties of binary systems of ionic liquids. I: [Cnmim][PF6] (n = 6, 8) and alkyl acetates

The measurements of densities, ρ, speeds of sound, u and refractive indices, nD for binary mixtures containing 1-hexyl-3-methylimidazolium hexafluorophosphate ([C6mim][PF6]) and 1-octyl-3-methylimidazolium hexafluorophosphate ([C8mim][PF6])+ethyl acetate (EA) and butyl acetate (BA) were reported over full range of concentrations. The measurements were performed at atmospheric pressure and seven different temperatures of five degree intervals between (293.15 and 323.15)K. The excess properties on mixing were derived from measured values of these properties. The values of density were utilized to obtain excess molar volumes, VmE, speeds of sound to obtain excess molar isentropic compressibilities, κS,mE and refractive index to get refractive index deviations, ΔφnD. The binary co-efficients of excess properties were obtained by Redlich–Kister polynomial equation. The influences of temperature and addition of –CH2 group in imidazolium cation of ionic liquids as well as acetate on excess properties have been discussed. The VmE and κS,mE are negative and decease with increase in temperature while ΔφnD are positive and increase with increase in temperature. For common acetate, The VmE increases with each increment of –CH2 group in imidazolium cation of IL and similar is true when –CH2 group increases in alkyl acetate for common IL. The deviation in VmEwas investigated by employing Prigogine–Flory–Patterson theory.

RAPID METHOD FOR DETERMINATION OF HOMOLOGUE IMIDAZOLIUM IONIC LIQUID CATIONS BY ION-PAIR CHROMATOGRAPHY USING A MONOLITHIC COLUMN

A fast and gradient ion-pair chromatographic method was developed for determination of five homologue imidazolium ionic liquid cations using a silica-based monolithic column and ultraviolet detection. Chromatographic separations were performed on a Chromolith Speed ROD RP-18e column with 1-heptanesulfonic acid sodium aqueous solution (pH adjusted by citric acid)–acetonitrile as the mobile phase. The effects of chromatographic column, mobile phase, flow rate, and column temperature on retention and separation of the cations were investigated. The retention rules of homologue imidazolium cations were discussed. The results showed that the analysis time could be significantly reduced owing to the application of monolithic column. Simultaneous and fast separation of five imidazolium cations was achieved under the optimum chromatographic conditions. Detection limits (S/N = 3) for the cations were 0.26–1.61 mg/L. Relative standard deviations (n = 5) for peak areas and retention times were less than 0.8%. The method has been successfully applied to the determination of two ionic liquids synthesized by chemistry lab. Recoveries of the cations after spiking were 96.8–101.9%.

Determination of Homologue Imidazolium Ionic Liquid Cations by Ion Chromatography Using a Carboxyl Acid Cation-Exchange Column with Direct Conductivity Detection

An investigation into the determination of four imidazolium ionic liquid cations by ion chromatography using a carboxyl acid cation exchange column and direct conductivity detection was carried out. This research has developed a simple, selective, and accurate ion chromatographic method for separation of imidazolium ionic liquid cations. Detection limits (S/N = 3) for the cations were 3.2–24.3 mg/L. Relative standard deviations (RSD, n = 5) for peak areas were less than 1.6%. The method has been successfully applied to the determination of two ionic liquids synthesized by organic chemistry lab.

Determination of imidazolium ionic liquid cations by ion-pair chromatography using gradient elution

Determination of five imidazolium ionic liquid cations by ion-pair chromatography was carried out using ultraviolet-visible spectrophotometry (UV/VIS) detection. Chromatographic separations were performed on a ZORBAX Eclipse XDB-C18 column with 1-heptanesulfonic acid sodium (adjusted by citric acid to pH 4.0) + acetonitrile as eluent. The effects of ion-pair reagents, acetonitrile concentration and column temperature on retention of the cations were investigated. The retention factor of imidazolium cation on column was increased with the increase of the concentration of 1-heptanesulfonic acid sodium. With the increase of the concentration of acetonitrile, the retention time of imidazolium cation was obviously shortened and the peak shape was improved. Under the optimum conditions, detection limits (S/N = 3) for the cations were 0.05-0.30 mg/L. Relative standard deviations (RSDs) for peak areas were less than 0.1%. The method has been successfully applied to the determination of two ionic liquids by chemically synthesized in laboratory with the recoveries of the cations of 98.6%-102.1% after spiking.

The Presence of Functional Groups Key for Biodegradation in Ionic Liquids: Effect on Gas Solubility

The effect of the incorporation of either ester or ester and ether functions into the side chain of an 1-alkyl-3-methylimidazolium cation on the physico-chemical properties of ionic liquids containing bis(trifluoromethylsulfonyl)imide or octylsulfate anions is studied. It is believed that the introduction of an ester function into the cation of the ionic liquids greatly increases their biodegradability. The density of three such ionic liquids is measured as a function of temperature, and the solubility of four gases-carbon dioxide, ethane, methane, and hydrogen-is determined between 303 K and 343 K and at pressures close to atmospheric level. Carbon dioxide is the most soluble gas, followed by ethane and methane; the mole fraction solubilities vary from 1.8 x 10(-3) to 3.7 x 10(-2). These solubilities are of the same order of magnitude as those determined for alkylimidazolium-based ionic liquids. The chemical modification of the alkyl side chain does not result in a significant change of the solvation properties of the ionic liquid. All of the solubilities decrease with increasing temperature, corresponding to an exothermal solvation process. From the variation of this property with temperature, the thermodynamic functions of solvation (Gibbs energy, enthalpy, and entropy) are calculated and provide information about the solute-solvent interactions and the molecular structure of the solutions.

Determination of Imidazolium Ionic Liquid Cations by Ion-Pair Chromatography Using a Monolithic Column and Direct Conductivity Detection

Determination of four imidazolium ionic liquid cations by ion-pair chromatography was carried out using direct conductivity detection. Chromatographic separations were performed on a silica-based monolithic column with 1-heptanesulfonic acid sodium + acetonitrile + citric acid as eluent. Carbon number rule and influence of acetonitrile on the retention of imidazolium cations were discussed. Detection limits (S/N = 3) for the cations were 2.1–55.9 mg L−1. Relative standard deviations (RSD, n = 5) for peak areas were less than 3.0%. The method has been successfully applied to the determination of two ionic liquids synthesized by organic chemistry lab.

Retention Mechanism of Selected Ionic Liquids On a Pentafluorophenylpropyl Polar Phase: Investigation using RP-HPLC

This study investigated the retention mechanism of a congeneric group of imidazolium ionic liquid cations with alkyl functional groups of different lengths, an aryl substituent, and one pyridinium cation on a pentafluorophenylpropyl silica-based stationary phase. The influence of organic modifier type and content in the mobile phase on the retention mode of alkylimidazolium ionic liquid cations shows a 'U-shaped' relationship. The use of this stationary phase gives excellent linearity and detection limits in the ppt range. The method is also readily applicable to the highly selective analysis of plant extracts previously spiked with ionic liquids.

Capillary electrophoretic separation of cationic constituents of imidazolium ionic liquids

A capillary electrophoretic method for resolving selected imidazolium ionic liquid cations is reported. The method, in which citric buffer is used as the running electrolyte, is simple and reproducible. The separation of a standard mixture is in linear accordance with the relative molecular mass (M(r)) of solutes regardless of the type of substitution (alkyl or aryl). The theoretical prediction of compounds as yet not analyzed is therefore possible; however, cations with identical molecular masses are inseparable with this method. Nevertheless, the method's quantitative analytical performance was excellent. The paper also discusses the applicability of a method for tracking the photodegradation kinetics of an exemplary ionic liquid.