Phase Behaviour, Interactions, and Structural Studies of (Amines+Ionic Liquids) Binary Mixtures

We present a study on the phase equilibrium behaviour of binary mixtures containing two 1-alkyl-3-methylimidazolium bis{(trifluoromethyl)sulfonyl}imide-based ionic liquids, [Cnmim] [NTf2] (n=2 and 4), mixed with diethylamine or triethylamine as a function of temperature and composition using different experimental techniques. Based on this work, two systems showing an LCST and one system with a possible hourglass shape are measured. Their phase behaviours are then correlated and predicted by using Flory–Huggins equations and the UNIQUAC method implemented in Aspen. The potential of the COSMO-RS methodology to predict the phase equilibria was also tested for the binary systems studied. However, this methodology is unable to predict the trends obtained experimentally, limiting its use for systems involving amines in ionic liquids. The liquid-state structure of the binary mixture ([C2mim] [NTf2]+diethylamine) is also investigated by molecular dynamics simulation and neutron diffraction. Finally, the absorption of gaseous ethane by the ([C2mim][NTf2]+diethylamine) binary mixture is determined and compared with that observed in the pure solvents.

The phase behaviour of 1-alkyl-3-methylimidazolium tetrafluoroborates; ionic liquids and ionic liquid crystals

Air- and water-stable 1-alkyl-3-methylimidazolium tetrafluoroborate salts with the general formula [C-mim][BF] (n = 0-18) have been prepared by metathesis from the corresponding chloride or bromide salts. The salts have been characterised by H NMR and IR spectroscopy, microanalysis, polarising optical microscopy and differential scanning calorimetry. Those with short alkyl chains (n = 2-10) are isotropic ionic liquids at room temperature and exhibit a wide liquid range, whereas the longer chain analogues are low melting mesomorphic crystalline solids which display an enantiotropic smectic A mesophase. The thermal range of the mesophase increases with increasing chain length and in the case of the longest chain salt prepared, [C-mim][BF], the mesophase range is ca. 150°C.

Continuous flow hydroformylation using supported ionic liquid phase catalysts with carbon dioxide as a carrier.

A supported ionic liquid phase (SILP) catalyst prepared from [PrMIM][Ph2P(3-C6H4SO3)] (PrMIM = 1-propyl-3-methylimidazolium), [Rh(CO)(2)(acac)] (acacH = 2,4-pentanedione) [OctMIM]NTf2 (OctMIM = 1-n-octyl-3-methylimidazolium, Tf = CF3SO2) and microporous silica has been used for the continuous flow hydroformylation of 1-octene in the presence of compressed CO2. Statistical experimental design was used to show that the reaction rate is neither much affected by the film thickness (IL loading) nor by the syngas: substrate ratio. However, a factor-dependent interaction between the syngas: substrate ratio and film thickness on the reaction rate was revealed. Increasing the substrate flow led to increased reaction rates but lower overall yields. One of the most important parameters proved to be the phase behaviour of the mobile phase, which was studied by varying the reaction pressure. At low CO2 pressures or when N-2 was used instead of CO2 rates were low because of poor gas diffusion to the catalytic sites in the SILP. Furthermore, leaching of IL and Rh was high because the substrate is liquid and the IL had been designed to dissolve in it. As the CO2 pressure was increased, the reaction rate increased and the IL and Rh leaching were reduced, because an expanded liquid phase developed. Due to its lower viscosity the expanded liquid allows better transport of gases to the catalyst and is a poorer solvent for the IL and the catalyst because of its reduced polarity. Above 100 bar (close to the transition to a single phase at 106 bar), the rate of reaction dropped again with increasing pressure because the flowing phase becomes a better and better solvent for the alkene, reducing its partitioning into the IL film. Under optimised conditions, the catalyst was shown to be stable over at least 40 h of continuous catalysis with a steady state turnover frequency (TOF, mol product (mol Rh)(-1)) of 500 h(-1) at low Rh leaching (0.2 ppm). The selectivity of the catalyst was not much affected by the variation of process parameters. The linear: branched (1:b) ratios were ca. 3, similar to that obtained using the very same catalyst in conventional organic solvents.

Liquid-liquid miscibility and volumetric properties of aqueous solutions of ionic liquids as a function of temperature

The volumetric properties of seven {water + ionic liquid} binary mixtures have been studied as a function of temperature from (293 to 343) K. The phase behaviour of the systems was first investigated using a nephelometric method and excess molar volumes were calculated from densities measured using an Anton Paar densimeter and fitted using a Redlich-Kister type equation. Two ionic liquids fully miscible with water (1-butyl-3-methylimidazolium tetrafluoroborate ([CCIm][BF]) and 1-ethyl-3-methylimidazolium ethylsulfate ([CCIm][EtSO])) and five ionic liquids only partially miscible with water (1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide ([CCIm][NTf]), 1-butyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide ([CCIm][NTf]), 1-butyl-3-methylimidazolium hexafluorophosphate ([CCIm][PF]), 1-butyl-3-methylpyrrolidinium bis(trifluoromethylsulfonyl)imide ([CCPyrro][NTf]), and butyltrimethylammonium bis(trifluoromethylsulfonyl)imide ([N][NTf])) were chosen. Small excess volumes (less than 0.5 cm · mol at 298 K) are obtained compared with the molar volumes of the pure components (less than 0.3% of the molar volume of the pure ionic liquid). For all the considered systems, except for {[CCIm][EtSO] + water}, positive excess molar volumes were calculated. Finally, an increase of the non-ideality character is observed for all the systems as temperature increases. © 2009 Elsevier Ltd. All rights reserved.

New catanionic surfactants based on 1-alkyl-3-methylimidazolium alkylsulfonates, [C(n)H(2n+1)mim][CmH2m+1SO3]: mesomorphism and aggregation

Anionic and cationic alkyl-chain effects on the self-aggregation of both neat and aqueous solutions of 1-alkyl-3-methylimidazolium alkylsulfonate salts ([C(n)H(2n+ 1)mim][CmH2m+1SO3]; n = 8, 10 or 12; m = 1 and n = 4 or 8; m = 4 or 8) have been investigated. Some of these salts constitute a novel family of pure catanionic surfactants in aqueous solution. Examples of this class of materials are rare; they are distinct from both mixed cationic-anionic surfactants (obtained by mixing two salts) and gemini surfactants (with two or more amphiphilic groups bound by a covalent linker). Fluorescence spectroscopy and interfacial tension measurements have been used to determine critical micelle concentrations (CMCs), surface activity, and to compare the effects of the alkyl-substitution patterns in both the cation and anion on the surfactant properties of these salts. With relatively small methylsulfonate anions (n = 8, 10 and 12, m = 1), the salts behave as conventional single chain cationic surfactants, showing a decrease of the CMC upon increase of the alkyl chain length (n) in the cation. When the amphiphilic character is present in both the cation and anion (n = 4 and 8, m = 4 and 8), novel catanionic surfactants with CMC values lower than those of the corresponding cationic analogues, and which exhibited an unanticipated enhanced reduction of surface tension, were obtained. In addition, the thermotropic phase behaviour of [C(8)H(18)mim][C8H18SO3] (n = m = 8) was investigated using variable temperature X-ray scattering, polarising optical microscopy and differential scanning calorimetry; formation of a smectic liquid crystalline phase with a broad temperature range was observed.

Pinning down the solid-state polymorphism of the ionic liquid [bmim][PF6]

The solid-state polymorphism of the ionic liquid 1-butyl-3-methylimidazolium hexafluorophosphate, [bmim][PF6], has been investigated via low-temperature and high-pressure crystallisation experiments. The samples have been characterised by single-crystal X-ray diffraction, optical microscopy and Raman spectroscopy. The solid-state phase behaviour of the compound is confirmed and clarified with respect to previous phase diagrams. The structures of the previously reported gamma-form, which essentially exhibits a G'T cation conformation, as well as those of the elusive beta- and alpha-forms, are reported. Crystals of the beta-phase are twinned and the structure is heavily disordered; the cation conformation in this form is predominantly TT, though significant contributions from other less frequently encountered conformers are also observed at low temperature and high pressure. The cation conformation in the alpha-form is GT; the presence of the G'T conformer at 193 K in this phase can be eliminated on cooling to 100 K. Whilst X-ray structural data are overall in good agreement with previous interpretations based on Raman and NMR studies, they also reveal a more subtle interplay of intermolecular interactions, which give rise to a wider range of conformers than previously considered.

Tunable thermomorphism and applications of ionic liquid analogues of Girard's reagents

A series of ionic liquids based on Girard's reagents was synthesised. Their tunable thermomorphic behaviour with water was demonstrated, and slight modifications in the cationic structure led to drastic changes in their water miscibility. Their phase behaviour, involving monophasic–biphasic transitions, drove a number of practical applications, including scavenging water-soluble dyes and the extraction of metals from water.

Crystallization and phase transformation behaviour of electroless nickel-phosphorus deposits with low and medium phosphorus contents under continuous heating

Electroless nickel-phosphorus deposits with 5-8 wt% P and 3-5 wt% P were analysed for the effects of continuous heating on the crystallization kinetics and phase transformation behaviour of the deposits. The as-deposited coatings consist of a mixture of amorphous and microcrystalline nickel phases, featuring in their X-ray diffraction patterns. Continuous heating processes to 300C-800C at 20C/min were carried out on the deposits in a differential scanning calorimetric apparatus. The subsequent X-ray diffraction analyses show that the sequence of phase transformation process was: amorphous phase + microcrystalline nickel, f.c.c. nickel + Ni3P stable phases. Preferred orientation of nickel {200} plane developed in the deposits after the heating processes. Differential scanning calorimetry of the deposits indicates that the crystallization temperatures increased with decreasing phosphorus content, and increasing heating rate. Crystallization activation energies of the deposits (230 and 322 kJ/mol, respectively) were calculated using the peak temperatures of crystallization process, from the differential scanning calorimetric curves at the heating rates ranging from 5 to 50C/min. It was found that the deposit with lower phosphorus content has higher activation energy.

Influence of molten-state annealing on the phase structure and crystallization behaviour of high impact polypropylene copolymer

The phase structure evolution of high impact polypropylene copolymer (IPC) during molten-state annealing and its influence on crystallization behaviour were studied. An entirely different architecture of the IPC melt was observed after being annealed, and this architecture resulted in variations of the crystallization behaviour. In addition, it was found that the core-shell structure of the dispersed phase was completely destroyed and the sizes of the dispersed domains increased sharply after being annealed at 200 degrees C for 200 min. Through examination of the coarseness of the phase morphology using phase contrast microscopy (PCM), it was found that a co-continuous structure and an abnormal 'sea-island' structure generally appeared with an increase in annealing time. The original matrix PP component appeared as a dispersed phase, whereas the copolymer components formed a continuous 'sea-island' structure. This change is ascribed to the large tension induced by solidification at the phase interface and the great content difference between the components. When the temperature was reduced the structure reverted to its original form. With increasing annealing time, the spherulite profiles became more defined and the spherulite birefringence changed from vague to clear. Overall crystallization rates and nucleation densities decreased, but the spherulite radial growth rates remained almost constant, indicating that molten-state annealing mainly affects the nucleation ability of IPC, due to a coarsened microstructure and decreased interface area. (C) 2011 Elsevier Ltd. All rights reserved.