Vapor–liquid equilibria of selected binary mixtures formed by 2-methylpyrazine at 94.7 kPa

Vapor–liquid equilibria at 94.7?kPa, over the entire composition range are obtained for the binary mixtures formed by 2-methylpyrazine with 1,2-dichloroethane, 1,1,1-trichloroethane, 1,1,2,2-tetrachloroethane, trichloroethylene, tetrachloroethylene, N,N-dimethylformamide and N,N-dimethylacetamide. A Swietoslawski type ebulliometer is used to measure the bubble point temperatures necessary to determine the vapor–liquid equilibria. The Wilson equation is used to represent measured liquid phase composition versus temperature data.     

(Vapor + liquid) equilibria of the binary mixtures of m-cresol with C1-C4 aliphatic alcohols at 95.5 kPa

Bubble point temperatures at 95.5 kPa, over the entire composition range, are measured for the binary mixtures formed by m-cresol with: methanol, ethanol, 1-propanol, 2-propanol, and n-, iso-, sec-, and tert-butanols - using a Swietoslawski-type ebulliometer. The liquid phase composition - bubble point temperature measurements are well represented by the Wilson model. (Vapor + liquid) equilibria predicted from the model are presented.     

Excess Gibbs free energies of the binary mixtures of acetonitrile with butanols at 94.83 kPa

Bubble point temperatures at 94.83 kPa, over the entire composition range, are measured for the binary mixtures of acetonitrile with: n-, iso-, sec- and tert-butanols – using a Swietoslawski type ebulliometer. The liquid phase composition versus bubble point temperature measurements are found to be well represented by the Wilson model. Measured values of the liquid phase mole fraction versus bubble point temperature data are presented along with the computed values of the vapor phase mole fractions, activity coefficients and excess Gibbs free energies and discussed.     

New equipment using a static analytic method for the study of vapour–liquid equilibria at temperatures down to 77 K

A new apparatus designed for the study of vapour–liquid equilibria (VLE) of small molecules at temperatures down to 77 K and pressures up to 40 MPa was built, set-up and used up to 2.8 MPa. It is based on the `static-analytic' method using two pneumatic capillary sampling devices, which allow taking small and reliable in-situ samples and performing direct analyses through gas chromatography. Accurate P, x, y isothermal data obtained for the O₂–N₂ and Ar–N₂ mixtures are well represented by the Soave–Redlich–Kwong equation of state (SRK-EoS). The conclusions which can be drawn from the comparison with literature data are the following: maximum deviations on pressure, temperature and vapour phase composition, between literature experimental data and the calculated ones (using our binary interaction parameters) are not larger than 3.3%, 0.12 K and 4.2%. We also point out inconsistencies in several literature data.     

Effect of Cation Structure in Quinolinium-Based Ionic Liquids on the Solubility in Aromatic Sulfur Compounds or Heptane: Thermodynamic Study on Phase Diagrams

Experimental and theoretical studies on thermodynamic properties of quinolinium-based ionic liquids (ILs) based on bis(trifluoromethylsulfonyl)imide anion (namely N-butyl-quinoloinium bis(trifluoromethylsulfonyl)imide, [BQuin][NTf₂], N-hexylquinoloinium bis(trifluoromethyl-sulfonyl)imide, [HQuin][NTf₂], and N-octylquinoloinium bis(trifluoromethyl-sulfonyl)imide, [OQuin][NTf₂]) with aromatic sulfur compounds and heptane, as a model compound of fuel were examined in order to assess the applicability of the studied ionic liquids for desulfurization of fuels. With this aim, the temperature-composition phase diagrams of 13 binary mixtures composed of organic sulfur compounds (thiophene, benzothiophene, or 2-methylthiophene) or heptane and ionic liquid (IL) were investigated at ambient pressure. A dynamic method was used to determine the (solid–liquid) equilibrium phase diagrams in binary systems over a wide composition range and temperature range from T = 255.15 to 365.15 K up to the fusion temperature of ILs. The immiscibility gap with an upper critical solution temperature (UCST) was observed for each binary system under study. The influence of the alkane chain length of the substituent on the IL cation and of the sulfur compounds (the aromaticity of the solvent) was described. The experimental (solid + liquid) phase equilibrium dataset were successfully correlated using the well-known NRTL equation.     

Bubble point temperatures of the binary mixtures of nitrobenzene with C1–C4 aliphatic alcohols at 94.95 kPa

Bubble point temperatures at 94.95 kPa, over the entire composition range, are measured for the binary mixtures of nitrobenzene with: methanol, ethanol, 1-propanol, 2-propanol and n-, iso-, sec- and tert-butanols – using a Swietoslawski-type ebulliometer. The liquid phase composition – bubble point temperature measurements are well represented by the Wilson model.     

Critical and three phase behavior in the carbon dioxide/tridecane system

The PT behavior of the carbon dioxide/normal alkane series exhibits a distinct transition in the CO₂/nC₁₃H₂₈ system. This particular diagram is characterized by two liquid—liquid—vapor (l-l-g) loci, a lower liquid-upper liquid (l-l) critical branch extending from high pressures to the upper critical end point (UCEP) and two liquid—vapor (l-g) critical branches which cross near the lower critical end point (LCEP).An experimental PTx diagram in the vicinity of the CO₂ critical point, LCEP and K point reveals the emergene at the LCEP of a l-l region which increases in size with temperture while the upper liquid—vapor (L₂-g) region diminishes, eventually disappearing at the K point. The l-l-g surface illustrates the compositional changes of each phase with temperture.Detailed Px diagrams at three temperatures between the LCEP and K point are presented and each exhibits two critical points, a l-l-g locus and curves of constant phase volume ratio which show discrete changes in both value and slope at the l-l-g locus. Graphical and numerical methods of determining the phase densities and compositions from three phase volumetric behavior are presented.     

Phosphate and arsenate electro-insertion processes into a N,N,N′,N′-tetraoctylphenylenediamine redox liquid

The electro-insertion of ions is a well-known phenomenon, which allows the transfer of anions or cations across phase boundaries to be monitored and driven electro-chemically. Extremely hydrophilic anions, such as phosphate and arsenate, are not usually observed to undergo electro-insertion. It is shown here that at organic redox liquid|water|electrode triple interfaces these anions can be forced electro-chemically to transfer into organic media.The transfer process of phosphate anions from aqueous buffer solutions into organic microdroplets of the redox liquid N,N,N^′,N^′-tetraoctylphenylenediamine (TOPD) is pH and concentration sensitive. It is shown that phosphate is transferred in the form of PO₄HK⁻ in the presence of phosphate buffer. Two distinct potential regions are identified and attributed to (i) interfacial redox processes at the liquid|liquid interface associated with deprotonation and (ii) bulk redox processes associated with anion transfer from the aqueous to the organic phase.The comparison of phosphate and arsenate electro-insertion processes suggests that arsenate is less hydrophilic and transferred into the organic phase preferentially.     

Phase equilibrium data and thermodynamic modelling of the system (propane + DMF + methanol) at high pressures

Reported in this work are phase equilibrium data at high pressures for the binary and ternary systems formed by {propane + N,N-dimethylformamide (DMF) + methanol}. Phase equilibrium measurements were performed in a high-pressure, variable-volume view cell, following the static synthetic method for obtaining the experimental bubble and dew points transition data over the temperature range of (363 to 393) K, pressures up to 11.5 MPa and overall mole fraction of the lighter component varying from 0.1 to 0.995. For the systems investigated, vapour–liquid (VLE), liquid–liquid (LLE) and vapour–liquid–liquid (VLLE) phase transitions were visually recorded. Results show that the systems investigated present UCST (upper critical solution temperature) phase transition curves with an UCEP (upper critical end point) at a temperature higher than the propane critical temperature. The experimental data were modelled using the Peng–Robinson equation of state with the Wong–Sandler and the classical quadratic mixing rules, affording a satisfactory representation of the experimental data.     

Activity coefficients of the binary mixtures of o-cresol or p-cresol with C1–C4 aliphatic alcohols near ambient pressure

Bubble point temperatures near ambient pressure, for the binary mixtures, formed by o-cresol or p-cresol with – methanol, ethanol, n- and iso-propanols and n-, iso-, sec- and tert-butanols – covering the whole composition range, are measured using a Swietoslawski-type ebulliometer. The liquid phase composition–bubble point temperature measurements are found to be well represented by the Wilson model. Values of the optimum Wilson parameters as well as the computed values of vapor phase mole fractions and activity coefficients are tabulated. The results are discussed in terms of isomerization with reference to the selected set of compounds, constituting the mixtures and the stearic effects in the cresols.     

Thermodynamic representation of ternary liquid–liquid equilibria near-to and far-from the plait point

Common classical expressions for the molar excess Gibbs energy of mixing g^E do not contain a contribution from composition fluctuations that are significant in the vicinity of the plait point for a ternary system. We propose a correction to g^E based on reasonable phenomenological assumptions. This correction requires three ternary constants, but two are obtained from stability relations provided that we know the composition of the plait point. While the method proposed here is not predictive, it provides a consistent thermodynamic procedure for calculating the liquid–liquid phase diagram of a ternary system with a plait point. The proposed method is illustrated for three ternaries. When calculations are based on the classical expressions for g^E alone, calculated results are in serious disagreement with experiment near critical conditions. Inclusion of the proposed correction for g^E provides dramatic improvement.     

Copolymerization in N-vinylcaprolactam-N-vinylpyrrolidone and N,N-diethylacrylamide-N,N-dimethylacrylamide systems: The effect of composition and spatial structure of copolymers on their thermal sensitivity

Factors that affect the temperature-responsive properties of water-soluble polymers were revealed by studying the copolymerization of two pairs of monomers: N-vinylcaprolactam-N-vinylpyrrolidone and N,N-diethylacrylamide-N,N-dimethylacrylamide. In each pair, the first monomer forms a temperature-responsive polymer and the second gives a polymer soluble in water up to the boiling point. It was found that in all cases, the addition of the second (more hydrophilic) monomer resulted in a monotonous increase in the phase separation temperature in an aqueous copolymer solution, with the temperature rise being comparatively slow in the initial stage and sharply accelerating after the addition of more than 40–50 mol % second monomer. The phase-separation temperature versus copolymer composition curves for N,N-diethylacrylamide-N,N-dimethylacrylamide copolymers of iso-and heterotactic structure synthesized via anionic polymerization are rather similar. At the same time, the copolymers of both types prepared via radical polymerization are characterized by steeper curves, a pattern that may be due to a high content of the syndiotactic structure, however, changes in the copolymer spatial structure have a lesser effect on the phase separation temperature than the presence of units of a more hydrophilic monomer. The addition of a relatively low amount (20–25 mol %) of a less hydrophilic monomer imparts temperature sensitivity to polymers, such as polyvinylpyrrolidone or polydimethylacrylamide, which do not possess this property in the pure form.     

Vapor — liquid and vapor — liquid — liquid phase equilibria of binary and ternary systems of nitrogen,ethene and methanol: Experiment and data evaluation

Zeck, S. and Knapp, H., 1986. Vapor—liquid and vapor—liquid—liquid phase equilibria of binary and ternary systems of nitrogen, ethene and methanol: experiment and data evaluation. Fluid Phase Equilibria, 26: 37–58.VLE and VLLE of three binary and one ternary system containing the components N₂, C₂H₄ and CH₃OH are investigated in a high-pressure phase equilibrium apparatus with vapor recirculation at temperatures 240 < T < 298 K and pressures 4 < p < 100 bar. Immiscibilities in the liquid phase are observed in the binary system C₂H₄CH₃OH with a lower critical end point and in the ternary system N₂C₂H₄CH₃OH.The experimental results are reported and compared with the results of other investigators and of available correlations.     

The synthesis, characterisation, phase behaviour and swelling of temperature sensitive physically crosslinked poly(1-vinyl-2-pyrrolidinone)/poly(N-isopropylacrylamide) hydrogels

Physically crosslinked complexes of polyvinyl pyrrolidinone-poly (N-isopropylacrylamide) (PVP-PNIPAAm) were prepared by photopolymerisation from a mixture of the monomers 1-vinyl-2-pyrrolidinone and N-isopropylacrylamide. IR spectroscopy and calorimetry were used to characterise the resulting xerogels. By alternating the monomer feed ratio, copolymers were synthesised to have their own distinctive lower critical solution temperature (LCST). The transition temperature of the gels was established using cloud point measurement and modulated differential scanning calorimeter (MDSC). This ability to shift the phase transition temperature of the copolymers provides excellent flexibility in tailoring transitions for specific uses. Swelling experiments were performed on the copolymer disks in distilled water at varying temperatures to establish the behaviour of the gels above and below phase transition temperature. The results obtained show that below transition temperature, the gels are water soluble but above this temperature they are slightly less water soluble; significantly less water soluble; or water insoluble; depending on the composition and LCST of the gel.     

Conduction band energy V0 in dense fluids of n- and iso-butane

The conduction band energy V₀ in n- and iso-butane has been measured as a function of the density N in the liquid phase and the supercritical state. Molecular-shape effects on the shape of V₀(N) curves are discussed.     

The Ethylbenzene/Styrene Preferential Separation with Ionic Liquids in Liquid–Liquid Extraction

The objective of this work was to explore the feasibility of using ionic liquids (ILs), namely N-ethyl-N-methylmorpholinium dicyanamide, [EMMor][DCA], (3-hydroxypropyl)-1-methylmorpholinium dicyanamide, [N-C₃OHMMor][DCA], 1-(3-hydroxypropyl)-3-methylimidazolium dicyanamide, [N-C₃OHMIM][DCA], 1-(3-hydroxypropyl)pyridinium dicyanamide, [N-C₃OHPy][DCA], (3-cyanopropyl)pyridinium dicyanamide, [N-C₃CNPy][DCA], and (3-cyanopropyl)methylpyrrolidinium dicyanamide, [N-C₃CNMPyr][DCA] for the separation of ethylbenzene and styrene. The liquid–liquid equilibrium (LLE) data in ternary systems of {IL (1)?+?styrene (2)?+?ethylbenzene (3)} at T?=?298.15 K and ambient pressure is presented for the six ILs synthesized by us. The final chromatography analysis of the composition of tie-lines has shown that the studied ILs are not found in the raffinate phase and they show interesting results on the selectivity and solute distribution ratio for styrene extraction. A comparison of different ILs is presented for the studied separation problem. It was observed that the best separation selectivities were found for [N-C₃CNPy][DCA] (S_Av?=?2.38) and [N-C₃OHMMor][DCA] (S_Av?=?2.42) in comparison with other studied ILs in this work and those presented in the literature. While the data presented here are useful from a theoretical standpoint, the possibility of applications for these ILs in technological processes is questionable because of low solute distribution ratios, especially those calculated from the masses [N-C₃CNPy][DCA] (β_MAv?=?0.08) and [N-C₃OHMMor][DCA] (β_MAv?=?0.07). The experimental tie-lines were correlated with the non-random two liquid NRTL model.     

Multiple dual-mode countercurrent chromatography applied to chiral separations using a (S)-naproxen derivative as chiral selector

Countercurrent chromatography (CCC) is a liquid–liquid chromatographic technique without a solid support. Several alternative elution modes can be applied to take advantage of the special nature of the liquid stationary phase. Among these dual-mode (DM) and multiple dual-mode (MDM) consist of switching alternatively between Reversed and Normal Phase operation during the experiment (once for DM and several times for MDM). In this paper, MDM has been applied to the chiral CCC separations of two racemic mixtures, (±)-N-(3,4-cis-3-decyl-1,2,3,4-tetrahydrophenanthren-4-yl)-3,5-dinitrobenzamide and N-(3,5-dinitrobenzoyl)-(±)-leucine, using (S)-naproxen N,N-diethylamide as chiral selector (CS). Although the behaviour of the two analytes differed, improved resolution factors were successfully obtained. Results are rationalized on the basis of the distinct partition behaviour of the CS/enantiomer complexes in the biphasic system.     

Cryopolymerization of N,N-dimethylacrylamide in moderately frozen formamide

The free-radical polymerization of N,N-dimethylacrylamide initiated by the redox pair ammonium persulfate-N,N,N??,N??-tetramethylethylenediamine in moderately frozen and liquid formamides is studied at temperatures 10?C30°C below or above the temperature of crystallization (2.9°C) of the pure solvent at various monomer concentrations in the initial solution. When polymerization is conducted at temperatures below the temperature of crystallization of formamide, the frozen systems, as is evident from their phase diagrams, include the crystallized main bulk of the solvent and the noncrystallizing monomer concentrated in the unfrozen liquid microphase where the reaction occurs. It is found that, in the case of this cryopolymerization variant, the temperature dependences of the yield of the polymer and its viscosity-average molecular mass show an extremum pattern and the positions of maximum points relative to the temperature scale depend on the initial monomer concentration. It is shown that the molecular masses of cryopolymerization products are much higher and their molecular-mass distribution is wider than that of poly(N,N-dimethylacrylamide) samples synthesized through solution polymerization (above the temperature of crystallization of formamide) at the same concentration of the monomer.     

Sorption and selective properties of binary liquid-crystalline sorbent based on 4-Methoxy-4′-ethoxyazoxybenzene and a cetylated β-Cyclodextrin

The mesomorphous, sorption, and selective properties of a binary sorbent based on achiral liquid crystal 4-methoxy-4′-ethoxyazoxybenzene and macrocyclic heptakis(2,3,6-tri-O-acetyl)-β-cyclodextrin (10.25 wt %) are investigated. Macrocyclic additive was found to induce the formation of a helically twisted nematic phase (N*). The standard and excess thermodynamic functions of sorption by binary sorbent from gaseous phase are determined for 29 organic compounds (n-alkanes, cycloalkanes, arenes, monoatomic alcohols, heterocycles, optical isomers of camphene, limonene, and butanediol-2,3). The investigated sorbent is found to have high structural selectivity over the wide temperature range of the N* mesophase (α _p/m = 1.11–1.06, 95–120°C) and moderately expressed enantioselectivity within the narrow region of transition from the solid crystalline state to the N* mesophase (α_+/? = 1.024–1.088, 91–100°C).