Cloud Point Method Research Articles

Liquid–Liquid Equilibrium for Ethanolysis Systems of Fish Oil

Enzymatic alcoholysis of fish oil can produce monoacylglycerols rich in polyunsaturated fatty acids at atmospheric pressure and low temperature. Biocatalysis in organic solvents helps to create a homogeneous reaction system for the reactants, ethanol and fish oil. This work presents liquid–liquid equilibrium at two different temperatures (303.2 K and 323.2 K) and at atmospheric pressure for two solvent-systems in the ethanolysis of fish oil: ethanol + oil + tert-pentanol and ethanol + oil + hexane. Experimental solubility (binodal) curves were obtained by the cloud point method and tie-line composition was obtained by density and high-temperature gas chromatography. The consistency of experimental tie-line data was checked by using the Othmer–Tobias equation. The experimental liquid–liquid data were correlated satisfactorily by the nonrandom two liquid model for activity coefficient calculations.

LLE for the systems ethyl palmitate (palmitic acid)(1) + ethanol(2) + glycerol (water)(3)

This work reports a new experimental set of liquid–liquid equilibrium measurements for the systems ethyl palmitate(1)+ethanol(2)+glycerol(3) and ethyl palmitate(1)+ethanol(2)+water(3) at atmospheric pressure and at 298.15K and 313.15, and for the system palmitic acid(1)+ethanol(2)+water(3) at 338.15K. The liquid-phases compositions were measured by determining their refractive index and densities. Solubility curves (binodal) were also obtained by cloud-point method for ternary systems. The experimental data were satisfactorily correlated by NRTL and UNIQUAC equations. A comparative analysis was performed using the UNIFAC-LL and UNIFAC-Dortmund group contribution method. Interesting results from thermodynamics models were obtained for the systems studied in this work.

Poly(N-isopropylacrylamide-co-hydroxyethylacrylamide) thermosensitive microspheres: The size of microgels dictates the pulsatile release mechanism

Poly(N-isopropylacrylamide-co-N-hydroxyethylacrylamide) (poly(NIPAAm-co-HEAAm)) was prepared as a new thermosensitive copolymer possessing a sharp phase transition around the human body temperature. The effect of the copolymer concentration on the lower critical solution temperature (LCST) was determined under physiological conditions by cloud point (CP) and differential scanning calorimetric (DSC) methods. Then, thermosensitive microspheres were prepared from preformed copolymers by chemical cross-linking of hydroxyl groups with glutaraldehyde at a temperature situated slightly below LCST of the copolymer solution. The volume phase transition temperature (VPTT) of corresponding cross-linked microspheres was determined from swelling degree-temperature curve. The microspheres were loaded with model drug indomethacin by the solvent evaporation method. The DSC analysis proved that the drug is molecularly dispersed in the polymer network. Finally, the influence of the microsphere size on drug release was investigated. It was established that microspheres with the diameter ranging between 5 and 60μm release the drug with almost the same rate below (in the swollen state) and above the VPTT (in the collapsed state). On the contrary, microspheres with the diameter ranging between 125 and 220μm release a significantly higher amount of indomethacin below than above the VPTT. This different behavior is enough to assure a pulsatile release mechanism when the temperature changes cyclically below and above the VPTT. However, both small and large microspheres release a large amount of the drug during the collapsing process.

Thermophysical properties of biodiesel and related systems: (Liquid + liquid) equilibrium data for castor oil biodiesel

This work reports new liquid–liquid solubility values (binodal curves) as well as (liquid+liquid) equilibrium data for, ternary and quaternary systems containing fatty acid methyl esters (FAME) and fatty acid ethyl esters (FAEE) from castor oil, water, glycerol, methanol and anhydrous ethanol at T=(303.15, 318.15, and 333.15)K. Solubility curves (binodal) were also obtained by the cloud-point method for binary systems containing FAME, FAEE, water, or glycerol. All results obtained can be considered of good quality. The experimental values were correlated using the UNIQUAC model, whose results presented good performance and satisfactory fitting of equilibrium values.

Solubility and tie line data of the water–phosphoric acid–solvents at T = 303.2, 313.2, and 323.2 K: An experimental and correlational study

Experimental solubility and tie-line data for (water+phosphoric acid+1-decanol or 1-dodecanol or 1-dodecanethiol) ternary systems were obtained at T=303.2, 313.2, and 323.2K and atmospheric pressure for the first time. The investigated systems display two types of LLE behavior. The systems consisting of the heavy alcohols exhibit type-1 LLE behavior, while, a type-2 behavior is exhibited by the other system. Cloud point method was used to obtain the solubility data and the Karl-Fischer, acidimetric titration, and refractive index methods were used to determine the tie-line data. The Othmer–Tobias and Hand correlations equations were used to ascertain the quality of the LLE data. Distribution coefficients and separation factors were determined to evaluate the extracting capability of the solvents. The experimental LLE data were regressed and adequately correlated with the UNIQUAC and NRTL models.

Ternary liquid–liquid equilibrium data for the (water + butyric acid + n-hexane or n-hexanol) systems at T = (298.2, 308.2, and 318.2) K

In this study, liquid–liquid equilibrium (LLE) values for the (water+butyric acid+n-hexane) and (water+butyric acid+n-hexanol) ternary systems were experimentally obtained at T=(298.2, 308.2, and 318.2) K and atmospheric pressure for the first time. The cloud point method was used to determine the solubility data. The concentration of each phase was determined by acidimetric titration, the Karl-Fischer technique, and refractive index measurements. Both the ternary systems exhibit type-1 behaviour of LLE. The experimental tie-line data were correlated using the UNIQUAC and NRTL models. The Othmer–Tobias and the Hand correlation equations were used to check the consistency of the obtained tie-line data for each system. Distribution coefficients and separation factors were calculated over the immiscibility regions. Finally, the Katritzky LSER multi-parameter equation was used to correlate the separation factors.

Functional oligo(vinyl acetate) bearing bipyridine moieties by RAFT polymerization and extraction of metal ions in supercritical carbon dioxide

A novel method is developed to functionalize the oligo(vinyl acetate) (OVAc) via a bipyridine (bpy) moiety. A bifunctional xanthate bis[2-(2-(O-ethyl dithiocarbonate)propionate ethoxy)-4,4′-dicarbonyl-2,2′-bipyridine] (X-bpy-X) was synthesized as a RAFT/MADIX agent to control vinyl acetate (VAc) polymerization, and then the bpy moiety was introduced into the OVAc chain successfully. A series of oligo(vinyl acetate)-bipyridine-oligo(vinyl acetate) (OVAc-bpy) with a PDI of 1.5 and a molecular weight range of 1000–3500 were obtained. The phase behaviour of OVAc-bpy in supercritical carbon dioxide (sc-CO2) was determined by the cloud point method. Compared with OVAc homopolymers with a similar degree of polymerization (DP), OVAc-bpy has lower solubility due to the existence of bpy moieties. The lowest cloud point pressure was achieved in sc-CO2 at Mn,GPC = 1900. OVAc-bpy was used as a ligand to extract the metal ions by using sc-CO2 as the solvent. The extraction rate can be as high as 98% (for Ni2+) and reasonably good for other metal ions (Cu2+ and Co2+) without using any additive.

Unusual LCST-type behaviour found in binary mixtures of choline-based ionic liquids with ethers

The fluid phase equilibria of binary mixtures of three cholinium-based ionic liquids-N-alkyl-N,N-dimethylhydroxyethylammonium bis(trifluoromethane)sulfonylimide, [N1 1 n 2OH][Ntf2]– with nine different ethers have been investigated. The experiments were conducted at atmospheric pressure between 200 K and 360 K using the cloud-point method. Most of the systems exhibit unusual liquid–liquid demixing behavior characterized by the existence of lower critical solution temperatures (LCSTs). To the best of our knowledge this is the first report on a functionalized ionic liquid plus ether system exhibiting a LCST behavior. The mutual solubilities of the ionic liquids and ethers are larger (higher LCST values) for ionic liquids with longer alkyl side chains attached to the cations. On the other hand, the solubility of the ethers is defined by the exposure of the corresponding C–O–C dipole and the extension/compactness of the alkyl residues surrounding the ether function. Auxiliary ab initio calculations and Molecular Dynamics simulations were used to rationalize the experimental results at a molecular level.

Dual layer hollow fiber sorbents: Concept, fabrication and characterization

Hollow fiber sorbents are pseudo-monolithic separations materials created with fiber spinning technology using a polymer ‘binder’, impregnated with high loadings of sorbent ‘fillers’[1]. To increase purified gas recovery during the sorption step and to ensure consistent sorption capacity over repeated cycles, a dense, thin polymer barrier layer on the fiber sorbents is needed to allow only thermal interactions between the sorbate loaded layer and the thermal regeneration fluid. This paper considers materials and methods to create delamination-free dual layer fiber sorbents, with a porous core and a barrier sheath layer formed using a simultaneous co-extrusion process. Low permeability polymers were screened for sheath layer creation, with the core layer comprising cellulose acetate polymer as binder and zeolite NaY as sorbent fillers. Appropriate core and sheath layer dope compositions were determined by the cloud-point method and rheology measurements. The morphology of the as-spun fibers was characterized in detail by SEM, EDX and gas permeation analysis. A simplified qualitative model is described to explain the observed fiber morphology. The effects of core, sheath spin dope and bore fluid compositions, spinning process parameters such as air–gap height, spin dope and coagulation bath temperatures, and elongation draw ratio are examined in detail.

The choice of solvent and liquid–liquid equilibrium for ternary water + 2-methylaziridine + chloroform system: Experimental data and modeling

Based on solvent selection criteria, chloroform was introduced as the most appropriate solvent for the extraction of 2-methylaziridine from aqueous phase. Accordingly, liquid–liquid equilibrium (LLE) data for the ternary water+2-methylaziridine+chloroform system were obtained at different temperatures of 288.2, 298.2 and 313.2K and under ambient pressure. The data for equilibrium composition were determined by cloud point method and conjugate points on tie lines were obtained using the refractive index as a function of composition. Results showed that relative mutual solubility of 2-methylaziridine was higher in aqueous phase than organic phase, and tie line data at each temperature were nicely agree with the Othmer–Tobias correlation. Consequently, extraction capability of chloroform was evaluated with respect to distribution coefficient and separation factor. The NRTL and UNIQUAC models were used to correlate the experimental data and both models showed satisfactorily agreement; however, NRTL exhibited better agreement.

Tie-line data for the aqueous solutions of phenol with organic solvents at T = 298.2 K

Solubility and tie-line data for the (water+phenol+1-octanol), (water+phenol+cyclohexanone), (water+phenol+2-ethyl-1-hexanol), and (water+phenol+isobutyl acetate) ternary systems were obtained at T=298.2K and atmospheric pressure. The solubility data were determined by the cloud point method. The tie-line data were experimentally determined by the Karl-Fischer and refractive index measurement methods. The ternary systems exhibit type-2 LLE behaviour. Distribution coefficients and separation factors were calculated for the immiscibility region to evaluate the extracting capability of the solvents. For each system, the Othmer–Tobias equation was used to ascertain the quality of the LLE results. The experimental values were correlated using the NRTL and UNIQUAC models, and the binary interaction parameters were calculated.

Thermophysical properties of biodiesel and related systems: (Liquid + liquid) equilibrium data for soybean biodiesel

This work reports (liquid+liquid) equilibrium (LLE) data for the systems of interest in soybean biodiesel production. Numerical data for LLE were obtained for binary, ternary and quaternary systems comprising fatty acid methyl esters (FAME) and fatty acid ethyl esters (FAEE) from soybean oil, water, glycerol, methanol, and ethanol at temperatures of (303.15, 318.15, and 333.15)K. Quantification of compounds in equilibrium in both phases was determined by analytical methods whereas solubility curves (binodal) were obtained by the cloud-point method. For all systems investigated, good alignments were obtained between phase compositions and the initial as well as overall compositions hence indicating low deviations from the mass balance. Experimental results were correlated using the UNIQUAC model with satisfactory agreement between experiment and theory.

Liquid–Liquid Equilibrium of Cholinium-Derived Bistriflimide Ionic Liquids with Water and Octanol

The liquid-liquid equilibria of mixtures of cholinum-based ionic liquids (N-alkyl-N,N-dimethylhydroxyethylammonium bis(trifluoromethane)sulfonylimide, [N(11n2OH)][Ntf(2)], n = 1, 2, 3, 4, and 5) plus water or 1-octanol were investigated at atmospheric pressure over the entire composition range. The experiments were conducted between 265 and 385 K using the cloud-point method. The systems exhibit phase diagrams consistent with the existence of upper critical solution temperatures. The solubility of [N(1 1 n 2OH)][Ntf(2)] in water is lower for cations with longer alkyl side chains (larger n values). The corresponding trend in the octanol mixtures is reversed. The ([N(1 1 1 2OH)][Ntf(2)] + water + octanol) ternary system shows triple liquid-liquid immiscibility at room temperature and atmospheric pressure. A combined analytic/synthetic method was used to estimate the corresponding phase diagram under those conditions. Auxiliary molecular dynamics simulation data were used to interpret the experimental results at a molecular level.

Experimental determination and correlation of tie line data for the system (water + butyric acid + methylcyclohexane) at four temperatures

This study demonstrates the experimental solubility and tie line data for (water+butyric acid+methylcyclohexane) system at temperatures of 298.2, 308.2, 318.2, and 328.2K and atmospheric pressure. The cloud-point titration method was used to determine solubility data (binodal curves). The tie line data were determined by acidimetric titration, the Karl–Fischer technique, and refractive index measurements. The investigated ternary system exhibits type-1 behavior of liquid–liquid equilibrium. The thermodynamic models UNIQUAC and NRTL were used to correlate the experimental tie-line data. The consistency of the tie-line data was determined through the Othmer Tobias and Hand correlation equations. Distribution coefficients and separation factors were calculated over the immiscibility regions. A comparison of the extracting capability of the solvent at different temperatures was made with respect to separation factors. The Katritzky multiparameter scale was applied to correlate distribution coefficients and separation factors in this ternary system.

Miscibility of tetrafluoroborate ionic liquids with dihydroxy alcohols

In this paper, we have carried out a study on miscibility of ([bmim]+, [hmim]+, [omim]+)[BF4]− ionic liquids and dihydroxy alcohols: vicinal (1,2-diol) — C2(1,2)(OH)2 to C6(1,2)(OH)2, terminal (1,ω-diol) — C2(1,2)(OH)2 to C5(1,5)(OH)2 and butanediol isomers. Phase diagrams were determined at atmospheric pressure over the temperature range (270 to 340) K using the cloud-point method. LLE data for all 18 binary systems determined show the same behavior, representing phase diagrams with the upper critical solution temperature (UCST). With increasing chain length in C-3 position of the imidazolium cation, the UCST shifts toward higher temperatures for the systems with ethane-1,2-diol. Contrary, for the systems of longer diols with hydroxyl group in 1,2-position (propane-1,2-diol, butane-1,2-diol, pentane-1,2-diol and hexane-1,2-diol) improvement of miscibility was observed. The influence of different characteristics of alcohols and ILs, including cation alkyl chain length, alcohol chain length, and relative position of both OH groups in diol was also studied.

Triton X surfactants to form aqueous biphasic systems: Experiment and correlation

During the last years, the extraction of biomolecules and chemicals by means of Aqueous Biphasic Systems (ABS) has triggered a renewed interest, making it necessary to characterize fully the solubility data of this kind of system. In this study, two surfactants belonging to Triton X series (Triton X-100 and Triton X-102) are proposed as candidates to form ABS, by adding different potassium-based salts (K3PO4, K2HPO4, K2CO3, K2S2O3 and K2SO3) at T=298.15K. Several equations were used to fit the solubility data which were previously obtained by means of the cloud point method. The different phase forming capacities were analyzed in the light of the Hofmeister series, the Effective Excluded Volume (EEV) theory and the molar Gibbs free energy of hydration (ΔhydG). The Othmer–Tobias equation was proposed to correlate the tie-line data.

Liquid–liquid equilibria of water + 2,3-butanediol + isobutanol at several temperatures

(Liquid–liquid) equilibrium (LLE) data for the ternary system of water+2,3-butanediol+isobutanol have been determined at 298.2, 308.2 and 318.2K and atmospheric pressure. Solubility curves were obtained by the cloud point method, while compositions of tie-lines were obtained by gas chromatography. Distribution coefficients and separation factors have been evaluated for the immiscibility region. The reliability of the experimental tie-lines has been confirmed by using Othmer–Tobias correlation. The LLE data of the ternary systems have been correlated by both the NRTL model and UNIQUAC model. Root mean square deviations between experimental and calculated compositions were considered satisfactory.

Aromatic Extraction Using Mixed Ionic Liquids: Experiments and COSMO-RS Predictions

The use of mixed ionic liquids (ILs) as possible alternatives for the removal of aromatics has been studied here via experimentation and predictions. For the IL mixture, a predictive approach such as COSMO (COnductor like Screening MOdel) along with its extension to RS (real solvent) is used in this work. Initially the COSMO-RS model was benchmarked on three different LLE (liquid–liquid equilibria) systems. The binary LLE ([C2mim][NTf2] (1-ethyl-3-methylimidazolium bis{(trifluoromethyl)sulfonyl}amide) + [P66614][NTf2] (trihexyl(tetradecyl)phosphonium bis{(trifluoromethyl)sulfonyl}amide) gave a root-mean-square deviation (rmsd) of 7 %. Thereafter, ternary IL systems [EMIM][ETSO4] + benzene + hexane and [EMIM][MESO4] + benzene + hexane gave a rmsd of 1.68 and 1.86 %, respectively. Further the model was benchmarked on the quaternary IL based system: [BMIM][BF4] + [OMIM][BF4] + toluene + heptane, giving an rmsd of 5.25 %. For experimental benchmarking, the system [EMIM][ETSO4] (1) + benzene (2) and hexane (3) was examined, which gave an rmsd equal to 4.13 % for the NMR technique and 6.32 % via the cloud point method. Further the LLE of the quaternary system [EMIM][ETSO4] + [EMIM][MESO4] + benzene + hexane at T = 298.15 K was determined, and the average rmsd was around 5.25 % for eight tie lines, which is good considering our method to be a priori. Lesser values of selectivity and distribution ratio were obtained for the mixed IL used in this work as compared to a single IL.

The General Phase Behavior of Mixtures of 1‐Alkyl‐3‐Methylimidazolium Bis[(trifluoromethyl)sulfonyl]amide Ionic Liquids with n‐Alkyl Alcohols

The liquid-liquid equilibrium (LLE) phase behavior of mixtures of 1-ethyl-3-methylimidazolium bis[(trifluoromethyl)sulfonyl]amide (C(2)mimNTf(2)) with the n-alkyl alcohols (C(n)OH; 3≤n≤8) is described. By applying the cloud-point method, the LLEs were determined over a temperature range of 275-423 K at ambient pressure. Partial miscibility with upper critical solution temperatures (UCST) was observed. The UCST increase with increasing chain length of the alcohols. The phase diagrams were analyzed numerically by presuming Ising criticality. Concepts for the description of the asymmetry of the phase diagram by presuming the validity of the rectilinear diameter rule or a nonlinear diameter requested by the theory of complete scaling were applied. The results (UCST, critical composition, width and diameter of the phase diagrams) are compared with similar systems and discussed in terms of the corresponding state behavior; they map on a single curve. From at least 45 individual phase diagrams, general aspects of the behavior of this ionic liquid-alcohol mixture type were extracted. A simple empirical relationship was formulated to allow the description of the UCST with an accuracy of about 10 K when taking the ratio of the molar volumes of the alcohol and the 1-alkyl-3-methylimidazolium cation of the ionic liquid into account.

Effect of Aqueous Two-Phase System Constituents in Different Poly(ethylene glycol)–Salt Phase Diagrams

Eight different poly(ethylene glycol) (PEG)/salt aqueous two-phase systems (ATPS's) were characterized at 23 °C. PEGs with different molecular weights (1500 and 8000) were combined with different salts (sodium or potassium citrates and formates) to study the effect of each ATPS constituent in the phase diagram. The binodal curve and several tie-lines were determined for each system using common analytical techniques described in the literature for ATPS's (cloud point method, conductivity, and gravimetric analysis after lyophilization). According to the results, it was found that each ATPS constituent produced a particular effect in the phase diagram. For the salts, changes in the anion produced larger variations in the heterogeneous region size than changes of the cation. Thus, the effect of salt type seems to be largely dependent on the anion, which makes the dominant contribution. The ability to form ATPS's is connected with the Gibbs energy of hydration, ΔGhyd, of the anions: more negative ΔGhyd values facilitate ATPS formation. Changes in the PEG molecular weight affected also the phase diagram: the size of the heterogeneous region increases with the increase in the polymer molecular weight.