Solubility of CF4 in lower alcohols

This work is inserted in a research program that consists mainly in the experimental and theoretical study of the effect of association/solvation between solute and solvent molecules in the solubility of gases in liquids. The solubilities of tetrafluoromethane in lower alcohols (methanol, ethanol, 1-propanol, 1-butanol) have been determined in the temperature range of 288–308 K, at atmospheric pressure, using an automated apparatus recently assembled in our laboratory. An accuracy of 0.6% and a precision of the same order of magnitude was achieved. The solubility is the lowest in methanol which is the highest associated alcohol and increases with the C-content of the alcohol. The molar Gibbs energy, enthalpy and entropy of solution were calculated from the experimental results (at 1 atm partial pressure of the gas and 298 K). A semiempirical correlation between the solubility of CF₄ in alcohols at 298 K and the Gutmann acceptor number (AN) of the solvents has been developed.     

Excess molar enthalpies of methylformate + (1-propanol, 2-propanol, 1-butanol, 2-butanol and 1-pentanol) at T = 298.15 K, p = (5.0, 10.0) MPa, and methylformate + 1-propanol at T = 333.15 K, p = 10.0 MPa

A high pressure flow-mixing isothermal calorimeter is used to determine the excess molar enthalpies of methylformate + (1-propanol, 2-propanol, 1-butanol, 2-butanol and 1-pentanol) at T = 298.15 K and p = (5.0, 10.0) MPa, and methylformate + 1-propanol at T = 333.15 K and p = 10.0 MPa. The Redlich-Kister equation is fit to the experimental results.     

Self-assembly of inner skin hollow fiber polyelectrolyte multilayer membranes by a dynamic negative pressure layer-by-layer technique

In the past studies, electrostatic layer-by-layer (LbL) adsorption of oppositely charged polyelectrolytes has proven to be a promising method for the preparation of polyelectrolyte multilayer membranes (PEMMs). Till now, this method was mainly used to assemble flat sheet and tubular membranes. Since hollow fiber membrane has some advantages such as high-packing density, self-contained mechanical support and hence the consequent economical superiority, this study therefore seeked to assemble inner skin hollow fiber PEMMs by using a dynamic LbL adsorption technique. The assembly process was successfully accomplished by alternatively dynamically filtrating polyacrylic acid (PAA) and polyethyleneimine (PEI) on a hydrolyzed hollow fiber polyacrylonitrile (PAN) membrane under a negative pressure condition. In the case of pervaporation separation of 95 wt.% ethanol–water mixture (50 °C), the membrane obtained with only 4.5 and 6.5 bilayers had separation factor of 245 and 1338 while the permeate fluxes were 290 and 120 g/(m² h), respectively. The pervaporation separation behavior of various alcohol/water mixtures with the alcohols being t-butanol, 2-propanol and ethanol were also investigated. Finally, scanning electron microscopy and atomic force microscopy clearly confirms a uniform and defect-free layer formed on the inner surface of hollow fiber support. Since different polyelectrolyte pairs could be used to assemble PEMMs for different uses, it was expected that the dynamic negative pressure LbL adsorption technique could also potentially be used to prepare many types of PEMMs in other fields.     

Anti-trade-off in dehydration of ethanol by novel PVA/APTEOS hybrid membranes

Novel organic–inorganic hybrid membranes were prepared through sol–gel reaction of poly(vinyl alcohol) (PVA) with γ-aminopropyl-triethoxysilane (APTEOS) for pervaporation (PV) separation of ethanol/water mixtures. The membranes were characterized by FTIR, EDX, WXRD and PALS. The amorphous region of the hybrid membranes increased with increasing APTEOS content, and both the free volume and the hydrophilicity of the hybrid membranes increased when APTEOS content was less than 5 wt%. The swelling degree of the hybrid membranes has been restrained in an aqueous solution owing to the formation of hydrogen and covalent bonds in the membrane matrix. Permeation flux increased remarkably with APTEOS content increasing, and water permselectivity increased at the same time, the trade-off between the permeation flux and water permselectivity of the hybrid membranes was broken. The sorption selectivity increased with increasing temperature, and decreased with increasing water content. In addition, the diffusion selectivity and diffusion coefficient of the permeants through the hybrid membranes were investigated. The hybrid membrane containing 5 wt% APTEOS has highest separation factor of 536.7 at 50 °C and permeation flux of 0.0355 kg m⁻² h⁻¹ in PV separation of 5 wt% water in the feed.     

Enzymatic esterification and phase behavior in ionic microemulsions with different alcohols

The esterification of hexanoic acid and 1-pentanol catalyzed by the lipase fromChromobacterium viscosum was studied at 298.2 K using different Winsor systems as reaction medium. The microemulsion systems consisted of brine and alkane stabilized by the anionic surfactant sodium dodecylsulphate and a short-chained alcohol. The alcohol acts both as a reactant and as a part of the reaction medium. Therefore, it is of great fundamental interest to know the phase behavior of the used microemulsion systems. Partial phase diagrams were determined and the efficiency of different alcohols on the transition from a Winsor I system to a Winsor III or a Winsor IV system with bicontinuous structure and further to a Winsor II system was investigated. The investigated alcohols were 2-methyl-1-propanol, 1-butanol, 2-butanol, 2-methyl-1-butanol, 3-methyl-1-butanol, 1-pentanol, 2-pentanol, 3-pentanol, 2-methyl-1-pentanol, 3-methyl-1-pentanol, 4-methyl-1-pentanol, and 1-hexanol. The aqueous medium consisted of 0.5 m NaCl(aq) or a phosphate buffer (pH=7) and the organic medium of octane or 2,2,4-trimethyl pentane. A long alkyl chain of the alcohol or a branching far from the hydroxyl group gives a more efficient cosurfactant and a transition from Winsor I to Winsor III or Winsor IV at lower alcohol contents. In the Winsor III system the yield of 1-pentyl hexanoate is twice as high as the yield in the bicontinuous Winsor IV system.     

Influence of polypropylene membrane surface porosity on the performance of membrane distillation process

Two kinds of polypropylene capillary membranes were used in the membrane distillation (MD). These membranes exhibited a similar morphology, but one of them has an additional low porosity layer on the internal surface of capillaries. The changes of membrane performance during MD process of tap water were investigated. The presence of low porosity layer (thickness below 1 μm) caused that the air permeability was reduced from 1.365 to 0.863 dm³/m² s kPa, whereas the MD permeate flux was decreased only by 15%. A significantly larger decline of the flux was caused by CaCO₃ deposit formed during distillation of tap water. This deposit was removed every 30–70 h by rinsing the modules with a 2–5 wt.% HCl. Unfortunately, a repetition of this operation several times resulted in a gradual decline of the maximum permeate flux (distilled water as a feed). However, the module efficiency with the membranes covered by a surface layer of low porosity was found to decreases twice as slowly. The investigations revealed that a low surface porosity does not limit the possibility of surface wetting of polypropylene membranes, but hindered the scale formation inside the pores.     

Composite membranes prepared from glutaraldehyde cross-linked sulfonated cardo polyetherketone and its blends for the dehydration of acetic acid by pervaporation

Cardo polyetherketone (PEK-C) composite membranes were prepared by casting glutaraldehyde (GA) cross-linked sulfonated cardo polyetherketone (SPEK-C) or silicotungstic acid (STA) filled SPEK-C and poly(vinyl alcohol) (PVA) blending onto a PEK-C substrate. The compatibility between the active layer and PEK-C substrate is improved by immersing the PEK-C substrate in a GA cross-linked sodium alginate (NaAlg) solution and using water–dimethyl sulfoxide (DMSO) as a co-solvent for preparing the STA-PVA-SPEK-C/GA active layer. The pervaporation (PV) dehydration of acetic acid shows that permeation flux decreased and separation factor increased with increasing GA content in the homogeneous membranes. The permeation flux achieved a minimum and the separation factor a maximum when the GA content increased to a certain amount. Thereafter the permeation flux increased and the separation factor decreased with further increasing the GA content. The PV performance of the composite membranes is superior to that of the homogeneous membranes when the feed water content is below 25 wt%. The permeation activation energy of the composite membranes is lower than that of the homogeneous membranes in the PV dehydration of 10 wt% water in acetic acid. The STA-PVA-SPEK-C-GA/PEK-C composite membrane using water–DMSO as co-solvent has an excellent separation performance with a flux of 592 g m⁻² h⁻¹ and a separation factor of 91.2 at a feed water content of 10 wt% at 50 °C.     

Application of Polyglycerol Diisostearate Ethoxylates in Microemulsion

Effect of surfactants [polyglycerol diisostearate ethoxylates (PGDIS-E31, PGDIS-E36 and PGDIS-E40) and Tween-80], alcohols (1,2-propandiol, ethanol, 1-propanol, 1-butanol, 2-butanol and 1-pentanol), oils [isopropyl palmitate (IPP), isooctyl palmitate (IOP), dioctyl carbonate (DOC), and dioctyl hexanediate (DOH)], temperature and sodium chloride on the microemulsion formation of the surfactant/alcohol/oil/water system has been investigated by the pseudo-ternary phase diagrams. The capacities of the four surfactants in the microemulsion formation of the surfactant/alcohol/IPP/water system at surfactant/alcohol of 2:1 are in the order of PGDIS-E31 > PGDIS-E36 > Tween-80 > PGDIS-E40, whatever alcohol (ethanol, 1-propanol, and 1-butanol) is used. PGDIS-E31 and 1-butanol exhibit best synergism in the microemulsion formation. In addition, the volume, structure and polarity of oil all influence the microemulsion formation. At the optimum weight ratio 2:1 of PGDIS-E31/1-butanol, the microemulsion region of the PGDIS-E31/1-butanol/IPP/water system is the largest among the studied systems. The microemulsion system of PGDIS-E31/1-butanol/IPP/water is not sensitive to lower temperature such as 40°C. It is also not sensitive to sodium chloride when the concentration of sodium chloride is in the range of 0 to 1.0%.     

High-pressure vapor–liquid equilibria for CO2 + alkanol systems and densities of n-dodecane and n-tridecane

An apparatus based on the static-analytic method was used to measure the vapor–liquid equilibria (VLE) for CO₂ + alkanol systems. Equilibrium measurements for the CO₂ + 1-propanol system were performed from 344 to 426 K. For the case of the CO₂ + 2-propanol system, measurements were made from 334 to 443 K, and for the CO₂ + 1-butanol were obtained from 354 to 430 K. VLE data were correlated with the Peng–Robinson equation of state using the classical and the Wong–Sandler mixing rules. Moreover, compressed liquid densities for the n-dodecane and n-tridecane were obtained via a vibrating tube densitometer at temperatures from 313 to 363 K and pressures up to 25 MPa. The Starling and Han (BWRS), and The five-parameter Modified Toscani-Swarcz (MTS) equations were used to correlate them. The experimental density data were compared with those from literature, and with the calculated values obtained from available equations for these n-alkanes.     

Determination and correlation of the solubility for diosgenin in alcohol solvents

Using a laser monitoring technique, the solubility of diosgenin in ethanol, 1-propanol, 1-butanol, isobutyl alcohol, tert-butanol, 1-pentanol, and iso-octyl alcohol was measured over the temperature range from (290.15 to 330.15) K at atmospheric pressure. Its corresponding (solid + liquid) equilibrium data will provide essential support for industrial design and further theoretical studies. From the experimental results, the solubility of diosgenin in ethanol, 1-propanol, 1-butanol, isobutyl alcohol, tert-butanol, 1-pentanol, and iso-octyl alcohol was found to increase with increasing temperature and decrease with the increase of the polarity of the alcohols solvents. The Apelblat equation, the ideal model and the λh equation were used to correlate the solubility values. The results showed that the three models mentioned above agreed well with the experimental data.     

Cloud point measurements of 1-butyl-2,3-dimethylimidazolium tetrafluoroborate with alcohols

Mutual solubility data of imidazolium-based ionic liquid, 1-butyl-2,3-dimethylimidazolium tetrafluoroborate ([bmmim][BF₄]) with the alcohols, 1-propanol, 2-propanol, 1-butanol, 1-pentanol, and 1-hexanol were obtained by a cloud point method. The upper critical solution temperatures of the ionic liquid and alcohol mixtures were determined from the mutual solubility data. The upper critical solution temperature of the binary mixtures gradually increased as the chain length of the alcohol increased. The mutual solubility data of binary systems ([bmmim][BF₄] + alcohols) have been correlated by the original UNIQUAC model as well as the extended and modified form of the UNIQUAC model. The temperature dependence of the mutual solubility data could be represented in terms of the temperature dependence of the binary energy parameters obtained from the correlation. Additionally the influence of water contamination on the ionic liquid mixture was shown experimentally by adding pure water into the binary mixture ([bmmim][BF₄] + 1-butanol).     

Enthalpies of solution in sodium octanoate + water + alcohol mixtures

Enthalpies of solution of sodium octanoate in water, 1-propanol and aqueous mixtures of 1-propanol, 1-butanol, 1-pentanol and 1-hexanol, and of the alcohols in aqueous solutions of sodium octanoate at various concentrations were determined calorimetrically at 35 °C. MostH(soln) values are exothermic and strongly dependent on the solute concentration. The main energetic factor governing the process of dissolution of the surfactant is associated with changes in the water structure caused by the presence of alcohol. That governing the process of the alcohol dissolution in surfactant solutions is due to the effect alcohols have on the CMC of the octanoate. There is no indication of the alcohol being either solubilized in the interior of the aqueous micelle, or becoming part of the micellar film.The solubility at 35 °C of sodium octanoate in water, 1-propanol and their mixtures has also been determined.     

Dependence on molecular parameters of the heat capacity critical behaviour for nitroalkane + alcohol binary systems

Heat capacities per unit volume for a set of nitroalkane + alcohol critical mixtures near their upper consolute point are presented. The selected nitroalkanes were nitromethane and nitroethane whereas the 1-alcohol series from 1-propanol to 1-decanol was studied. The critical anomaly of nitroalkane + non-primary alcohols was also investigated; 2-propanol, 2-pentanol, 3-pentanol and 5-nonanol were chosen to this end. The heat capacity data are obtained at atmospheric pressure as a function of temperature in the homogeneous and heterogeneous regions by means of a differential scanning calorimeter. The exponent and amplitudes that characterises the observed critical anomaly are determined from experimental data, being their values coherent with previous results. In addition, the critical amplitude of the correlation length was calculated using the universality of the two-scale factor. Finally, the changes in the critical parameters as a function of the molecular structure of both nitroalkane and alcohol are analysed.     

Reactions of [CH3]+ and [CD3]+ with alcohols

The reactions of [CH₃]⁺ and [CD₃]⁺ with a number of C₁ to C₅ alcohols were studied at approximately thermal energies (0.1 eV) using a tandem Dempster ion cyclotron resonance mass spectrometer. Branching ratios obtained under single collision conditions are reported for [CH₃]⁺ and [CD₃]⁺ with methanol, perdeutero methanol, ethanol, allyl alcohol, 1-propanol, 2-propanol, perdeutero-2-propanol, 1-butanol, 2-butanol, t-butanol, cyclopentanol and 1-pentanol. The results are examined in terms of the mechanism of reactions and indicate that upon progression to larger alcohols, the formation of a long-lived adduct becomes less important in determining the reaction products.     

Pervaporation dehydration of alcohol–water mixtures: Optimization for permeate flux and selectivity by central composite rotatable design

A central composite rotatable design (CCRD) of response surface methodology was used to analyze pervaporation performance of homogeneous poly(vinyl alcohol) (PVA) membranes. A regression model was developed for the pervaporation flux and selectivity as a function of the operating conditions: temperature, concentration and flow-rate. Dehydration experiments were performed on two different alcohol–water systems: isopropanol–water (IPA–water) and ethanol–water (Et–water) mixtures around their azeotropic concentrations. Based on preliminary experiments and CCRD design, the ranges of values of the operating conditions were selected: temperature 33–67 °C, feed flow-rate 46–114 L/h, and concentration 83–92 wt% for IPA and 93–98 wt% for Et in feed mixtures. A total of 20 pervaporation experiments were conducted for each alcohol–water system. Judged by the lack-of-fit criterion, the analysis of variance (ANOVA) showed the regression model to be adequate. From the regression analysis, the flux and selectivity were expressed with quadratic equations of temperature, feed concentration and flow-rate. The predicted flux and selectivity from the regression model were presented in 3D surface plots. For both alcohol–water systems, quadratic terms of temperature and feed alcohol concentration showed significant (p < 0.0001) influence on the flux and selectivity. A strong interaction effect of temperature and concentration was observed on the selectivity for the Et–water system. However, the interaction of flow-rate with temperature or concentration was found to be less significant. In order to optimize the pervaporation flux and selectivity of azeotropic alcohol–water mixtures, the desirability function approach was applied to analyze the regression model equations by commercial software. For the azeotropic IPA–water mixture (87.5 wt% IPA), the optimized dehydration variables were found to be 50.5 °C and 93.7 L/h for temperature and flow-rate, respectively. For the azeotropic Et–water mixture (95.5 wt% Et), the optimized temperature and flow-rate were found to be 57 °C and 89.2 L/h, respectively. Compared with experiments performed at optimized temperature and flow-rate, the predicted flux and selectivity of the azeotropic mixtures showed errors to be within 3–6%.     

P(AA-AMPS)–PVA/polysulfone composite hollow fiber membranes for propylene dehumidification

A series of composite hollow fiber membranes, poly(acrylic acid-co-2-acrylamido-2-methyl-1-propane sulfonic acid) (P(AA-AMPS))–poly(vinyl alcohol) (PVA) membranes as skin layers and polysulfone (PS) hollow fiber membranes as support layers, were prepared for dehumidification of propylene gas. The chemical and physical structures, including inter-components interaction, crystallinity, glass transition temperature and free volume of the membranes, were systematically characterized. Through the sorption experiments, it was found that the membrane exhibited a preferential sorption toward water, and initially the water sorption increased remarkably with P(AA-AMPS) content increasing, afterwards reached the zenith, then decreased rapidly. Dehumidification performance showed that the membrane containing 50 wt.% P(AA-AMPS) exhibited the highest permeance of 363 GPU and an infinite separation factor for 0.5 wt.% water in feed at 298 K. Permeance decreased considerably with increasing operating temperature, but increased considerably with increasing water content.     

Viscosities of dimethyl carbonate with alcohols at several temperatures: UNIFAC-VISCO interaction parameters (OCOO/alcohol)

Viscosities have been determined for the binary mixtures dimethyl carbonate (DMC) + methanol, + ethanol, + 1-propanol, + 2-propanol, + 1-butanol, + 2-butanol, and + 1-pentanol at 293.15, 298.15, 303.15 and 313.15 K and atmospheric pressure. Viscosity deviations for the binary systems were fitted to the Redlich–Kister equation. From the experimental data (DMC or diethyl carbonate with above mentioned alcohols at the same temperatures) the interaction parameters (CH₃OHOCOO) and (OHOCOO) have been determined for their application in the UNIFAC-VISCO method, based on contribution groups, to predict the dynamic viscosities of the binary mixtures. Root-mean-square deviations are also gathered. The group contribution thermodynamic viscosity model GC-UNIMOD has been used to predict the dynamic viscosity of the binary mixtures at 298.15 K and their deviations have been shown.     

Liquid–liquid phase behaviour,liquid–liquid density,and interfacial tension of multicomponent systems at 298 K

Experimental liquid–liquid phase diagrams are presented for the multicomponent systems isooctane–benzene–(80 mass% methanol + 20 mass% water)–5 mass% isobutyl alcohol (2-methyl-1-propanol) and isooctane–benzene–(80 mass% methanol + 20 mass% water)–15 mass% isobutyl alcohol, at 298.15 K. The density and interfacial tension of conjugate phases of concentration located in the isothermal binodal have been determined at 298.15 K for the partially miscible systems: isooctane–benzene–methanol, isooctane–benzene–(80 mass% methanol + 20 mass% water), isooctane–benzene–(80 mass% methanol + 20 mass% water)–5 mass% isobutyl alcohol, and isooctane–benzene–(80 mass% methanol + 20 mass% water)–15 mass% isobutyl alcohol. The experimental tie-line data define the binodal or coexistence curve of the two studied multicomponent systems and depending on the initial isobutyl alcohol concentration the liquid–liquid phase diagram is either of type II, with low alcohol concentration, or type I, with high concentration of alcohol, which is a clear indication that the solubility of the partially miscible systems is greatly enhanced via the co-solvency phenomenon. It is observed that both the density of each conjugate phase and the interfacial tension of each tie-line are valuable indicators of the degree of solubility of the multicomponent systems. Furthermore the experimental tie-lines data were correlated with the NRTL and UNIQUAC solution models with satisfactory quantitative results.