A comparison of liquid–liquid porosimetry equations for evaluation of pore size distribution

This paper reviews and numerically tests many of the methods for the determination of pore size distribution of liquid membranes by liquid–liquid porosimetry. The flux through membranes was defined for flow of two immiscible liquids when drops or a liquid jet is formed, as well as the case when the interface is forced out by sufficient pressure. Several methods from literature for the determination of pore size distribution, some variations of these, and one new method are presented with a consistent theoretical basis. Using numerical tests it was found that all methods were very sensitive to measurement noise as low as ±0.1%, and that some form of data smoothing, such as a smoothing spline, was required to obtain a satisfactory distribution. The effects of elastic and permanent membrane compression were tested and a method was proposed to reduce the resulting error. A method based on the ratio of flux liquids with and without a liquid–liquid interface was recommended as it was less sensitive to the effects of compression in some cases and it provides a check when compression is not repeatable.     

Are pore size distributions in microfiltration membranes measurable by two-phase flow porosimetry?

The issue of evaluating equivalent pore diameter distributions in membrane microfilters from gas-liquid (g-l) porosimetry data has been critically examined. Experiments performed with one isotropic and one composite anisotropic membrane in both possible orientations revealed conspicous dependence of the obtained (g-l) porosimetry peaks on imposed pressure ramp rates, p. Interference of this kinetic effect can be eliminated from the measured data by extrapolation to p = 0. The ramp rate effect is most likely caused by tortuous pore length distribution, and relatively long times required for liquid expulsion. For two experiments, the observed effects of p could be reconciled with predictions of the Schlesinger-Bechhold theory [Bechold et al., Kolloid Z., 55 (1931) 172–198]. The data obtained with the thin top layer of the composite membrane facing intruding air directly did deviate somewhat from the theory. Pores characterized by (g-l) porosimetry are likely of the “throat type”, and their size distribution is considerably more narrow than that obtained for the “node-type” pores by SEM-image analysis [Zeman and Denault, J. Membrane Sci., 71 (1992) 221–231]. A single bivariate distribution function was constructed for these two distinct pore populations. Flow-weighted or number fraction distributions can be calculated from the extrapolated porosimetry data. For narrow ranges of “throat” diameters, these distributions are fairly similar.     

Revision of the volumetric method for measurements of liquid–liquid equilibria in binary systems

A theoretical analysis of the accuracy of the volumetric method for the determination of liquid–liquid equilibrium was carried out. The results show that, under certain conditions, this method can be used to investigate systems showing relatively small mutual solubilities. Relations were derived to estimate standard deviations of the equilibrium compositions determined by the volumetric method.

In the experimental part of the work, an apparatus for measurements of mutual solubilities of liquids was constructed. A procedure that enabled us to determine precisely volumes of liquid phases was developed. This procedure and apparatus present the advantage that relatively small amounts of samples are required (approximately 2 × 20 ml). Theoretical conclusions concerning the applicability of the volumetric method were checked by measuring mutual solubilities at 303.15 K in systems methylcyclohexane + N,N-dimethylformamide, 1-butanol + water and dimethyl phthalate + water. Further, the method was used to measure systematically the liquid–liquid equilibrium in systems ethyl acetate + ethylene glycol and phenyl acetate + ethylene glycol at temperatures from 293 to 323 K. Data for these systems were acquired by means of other methods as well and a good agreement was observed on comparison.     

Modified liquid displacement method for determination of pore size distribution in porous membranes

A new method called constant pressure liquid displacement method (CPLM) was developed and tested to measure the pore size distribution of porous membranes. The permeability, defined as a ratio of the flow rate to the pressure applied, used to be assumed constant either for a conventional liquid displacement method or for a bubble point method, leading to the erroneous interpretation of the pore size distribution. However, it was possible to eliminate such an assumption by measuring the flow rates experimentally at a standard low pressure through the pores penetrated with a permeating liquid according to the proposed method. The pore size distribution for a hydrophobic PVDF membrane was successfully measured by the CPLM and compared with those measured by two different methods such as the conventional liquid displacement method and the mercury intrusion method.     

Liquid–liquid and liquid–liquid–solid equilibrium in Na2CO3–PEG–H2O

The phase diagram was determined for the Na₂CO₃–PEG–H₂O system at 25°C using PEG (poly(ethylene glycol)) with a molecular weight of 4000. Compositions of the liquid–liquid and the liquid–liquid–solid equilibria were determined using calibration curves of density and index of refraction of the solutions, and atomic absorption (AA) and X-ray diffraction analyses were made on the solids. The solid phase in equilibrium with the biphasic region was Na₂CO₃·H₂O. Binodal curves were described using a three-parameter equation. Tie lines were described using the Othmer–Tobias and Bancroft correlation’s. Correlation coefficients for all equations exceeded 0.99. The effects of temperature (25 and 40°C) and the molecular weight of the PEG (2000, 3000, and 4000) on the binodal curve were also studied, and it was observed that the size of the biphasic region increased slightly with an increase in these variables.     

Novelties of cyanide displacement reaction in ibuprofen amide process by phase transfer catalysis: Solid–liquid versus solid–liquid (omega)–liquid systems

This work deals with the phase transfer catalysed cyanide displacement reaction on 1-(4-isobutyl phenyl) ethyl chloride to synthesize 2-(4-isobutyl phenyl) propionitrile, which is an intermediate for the synthesis of ibuprofen analogs, belonging to a class of NSAID (nonsteroidal anti-inflammatory drugs). The reaction was studied using solid–liquid phase transfer catalysis (S-L PTC) with trace quantities of water, forming the so-called omega phase at 90 °C. The rates of reaction and selectivity to the product are enhanced in the S-L(org.)-L (ω) PTC in comparison with S-L PTC, which in turn is superior to L-L PTC; the latter suffers from the disadvantage of side reactions in the aqueous phase. In the current work, the effects of various parameters such as catalyst structure, catalyst loading, substrate loading and temperature were studied on the conversion and rates of reaction of 1-(4-isobutyl phenyl) ethyl chloride with solid sodium cyanide under S-L and S-L(ω)-L PTC at 90 °C with toluene as the organic solvent. Tetrabutylammonium bromide (TBAB) was found to be the best catalyst. The role of omega liquid phase in intensification of the S-L PTC was theoretically and experimentally investigated. The kinetic constants have been determined and the apparent activation energy is found as 4.2 kcal/mol, which suggests that the reaction is quite fast, which is likely to bring in mass transfer effects.     

Pore size distribution of unsupported SnO2 membranes prepared by sol-gel process

Unsupported SnO₂ membranes were prepared by sol-gel process and characterized by N₂ adsorption-desorption isotherms and X-ray diffraction. Results show that the texture of dried samples does not change appreciably with the concentration of electrolyte. All of the pore size range used in ultrafiltration process was screened using sintering temperature between 300 and 700°C.     

Development of new extraction method based on liquid–liquid–liquid extraction followed by dispersive liquid–liquid microextraction for extraction of three tricyclic antidepressants in plasma samples

In the present study, a new extraction method based on a three–phase system, liquid–liquid–liquid extraction, followed by dispersive liquid–liquid microextraction has been developed and validated for the extraction and preconcentration of three commonly prescribed tricyclic antidepressant drugs – amitriptyline, imipramine, and clomipramine – in human plasma prior to their analysis by gas chromatography–flame ionization detection. The three phases were an aqueous phase (plasma), acetonitrile and n–hexane. The extraction mechanism was based on the different affinities of components of the biological sample (lipids, fatty acids, pharmaceuticals, inorganic ions, etc.) toward each of the phases. This provided high selectivity toward the analytes since most interferences were transferred into n–hexane. In this procedure, a homogeneous solution of the aqueous phase (plasma) and acetonitrile (water–soluble extraction solvent) was broken by adding sodium sulfate (as a phase separating agent) and the analytes were extracted into the fine droplets of the formed acetonitrile. Next, acetonitrile phase was mixed with 1,2–dibromoethane (as a preconcentration solvent at microliter level) and then the microextraction procedure mentioned above was performed for further enrichment of the analytes. Under the optimum extraction conditions, limits of detection and lower limits of quantification for the analytes were obtained in the ranges of 0.001–0.003 and 0.003–0.010 μg mL⁻¹, respectively. The obtained extraction recoveries were in the range of 79–98%. Intra– and inter–day precisions were < 7.5%. The validated method was successfully applied for determination of the selected drugs in human plasma samples obtained from the patients who received them.     

In situ evaluation of defect size distribution for supported zeolite membranes

The permporometry measurements are performed with respect to a series of zeolite membranes with different defect sizes, which can be further applied for in situ measurement of the defect size distribution in zeolite membranes. Gas permeation experiments are conducted for CO₂/N₂ gas mixture to test the separation performance of the studied zeolite membranes. By taking into account the “t-layer” on defect walls, a mathematical model and the corresponding procedure are developed so that the defect size distribution in zeolite membranes can be calculated by using the results of permporometry measurements. The defect size distribution and the maximal defect size show a good correlation with the separation performance of CO₂/N₂ gas mixture for zeolite membranes. It is demonstrated that the separation performance of zeolite membranes is mainly determined by large defects. It has been shown that the permporometry-based methodology proposed in this contribution is an effective way for the quality evaluation of zeolite membranes.     

Reaction of benzyl chloride with ammonium sulfide under liquid–liquid phase transfer catalysis: Reaction mechanism and kinetics

The reaction between benzyl chloride and aqueous ammonium sulfide was carried out in an organic solvent – toluene, using tetrabutylammonium bromide (TBAB) as phase transfer catalyst (PTC). Two products, namely dibenzyl sulfide (DBS) and benzyl mercaptan (BM), were identified in the reaction mixture. The selectivity of DBS was maximised by changing various parameters such as NH₃/H₂S mole ratio, stirring speed, catalyst loading, concentration of benzyl chloride, volume of aqueous phase, and temperature. The highest selectivity of DBS obtained was about 90% after 445 min of reaction with excess benzyl chloride at 60 °C. Complete conversion of benzyl chloride could be achieved at the cost of very low selectivity of DBS and very high selectivity of BM. The apparent activation energy for the kinetically controlled reaction was found to be 12.3 kcal/mol. From the detailed study of the effects of various parameters on the reaction, a suitable mechanism was established which could explain the course of the reaction.     

In situ ionic‐liquid‐dispersive liquid–liquid microextraction of Sudan dyes from liquid samples

In situ ionic‐liquid‐dispersive liquid–liquid microextraction was introduced for extracting Sudan dyes from different liquid samples followed by detection using ultrafast liquid chromatography. The extraction and metathesis reaction can be performed simultaneously, the extraction time was shortened notably and higher enrichment factors can be obtained compared with traditional dispersive liquid–liquid microextraction. When the extraction was coupled with ultrafast liquid chromatography, a green, convenient, cheap, and efficient method for the determination of Sudan dyes was developed. The effects of various experimental factors, including type of extraction solvent, amount of 1‐hexyl‐3‐methylimidazolium chloride, ratio of ammonium hexafluorophosphate to 1‐hexyl‐3‐methylimidazolium chloride, pH value, salt concentration in sample solution, extraction time and centrifugation time were investigated and optimized for the extraction of four kinds of Sudan dyes. The limits of detection for Sudan I, II, III, and IV were 0.324, 0.299, 0.390, and 0.655 ng/mL, respectively. Recoveries obtained by analyzing the seven spiked samples were between 65.95 and 112.82%. The consumption of organic solvent (120 μL acetonitrile per sample) was very low, so it could be considered as a green analytical method.     

Liquid–liquid equilibria for pseudoternary systems: isooctane–benzene–(methanol + water)

Liquid–liquid equilibrium data are presented for the pseudoternary systems isooctane–benzene–(90 mass% methanol + 10 mass% water) at 298.15 K and isooctane–benzene–(80 mass% methanol + 20 mass% water) at 298.15 and 308.15 K, under atmospheric pressure. The experimental tie-line data obtained define the binodal curve for each one of the studied systems which depending on the amount of water present show type I or type II liquid–liquid phase diagrams. In order to obtain a general view of the effect of water on the partitioning of methanol and hence on the size of the two-phase region we have also determined experimentally ‘isowater’ tolerance curves for the system isooctane–benzene–methanol at 298.15 K, hence the tie-line data were also obtained for the ternary system. The experimental tie-line data for the four systems studied were correlated with the NRTL and UNIQUAC solution models obtaining a very good reproduction of the experimental behaviour.     

Pore size distributions in low‐k dielectric thin films from X‐ray porosimetry

X‐ray reflectivity has been used to determine the mass uptake of probe molecules in porous thin films supported on thick silicon wafers. The adsorption occurs by capillary condensation when the films are exposed to probe vapor at controlled partial vapor pressures. The probe solvent partial pressure was varied by mixing saturated air and dry air at constant temperature or by changing sample temperature at a constant vapor concentration. Pore size distribution in the films can be calculated from the probe uptake with typical porosimetric approaches such as the application of the Kelvin equation to convert partial pressure into pore size. For illustration, the pore size distribution of three different nanoporous thin films, the primary candidate of ultra‐low‐k interlevel dielectrics in the next generation of integrated circuit chips, was determined with this technique. These samples represent different generations of low‐k dielectrics developed by industry. © 2002 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 40: 2170–2177, 2002     

Supported liquid membranes (SLM) for recovery of bismuth from aqueous solutions

In this study, the extraction of Bi(III) from synthetic solutions of 2 M H₂SO₄/0.5 M HCl by supported liquid membranes (SLM) using tri-n-octylphosphine oxide (Cyanex 921) as extractant is reported. First, the nature of the Bi(III)/Cyanex 921 solvates extracted to organic phase (in a solvent extraction system) was determined by the slope method. It was found that Bi(III) reacts with 2 molecules of Cyanex 921 to form the solvate BiCl₃·2Cyanex 921. In the recovery of Bi(III) by the SLM system, parameters that influence extraction efficiency were evaluated, including: support, feed solution and stripping solution nature, and extractant concentration in the organic phase which impregnates the support. Results indicate that Cyanex 921 dissolved in kerosene is not able to extract Bi(III) from H₂SO₄ media. Moreover, transfer of H₂SO₄ was observed. HCl addition to the feed solution up to a maximum concentration of 0.5 M increases Bi(III) extraction. Further increase in HCl concentration causes a decrease in Bi(III) transfer. Likewise, the concentration of Cyanex 921 in the SLM organic phase which produced the maximum Bi(III) extraction was found to be 0.3 M. The performance of H₂O and 0.2 M H₂SO₄ as stripping solutions was evaluated, and it was found that only H₂SO₄ enabled Bi(III) transfer.     

Salting‐out assisted liquid–liquid extraction coupled to dispersive liquid–liquid microextraction for the determination of chlorophenols in wine by high‐performance liquid chromatography

A novel procedure of sample preparation combined with high‐performance liquid chromatography with diode array detection is introduced for the analysis of highly chlorinated phenols (trichlorophenols, tetrachlorophenols, and pentachlorophenol) in wine. The main features of the proposed method are (i) low‐toxicity diethyl carbonate as extraction solvent to selectively extract the analytes without matrix effect, (ii) the combination of salting‐out assisted liquid–liquid extraction and dispersive liquid–liquid microextraction to achieve an enrichment factor of 334–361, and (iii) the extract is analyzed by high‐performance liquid chromatography to avoid derivatization. Under the optimum conditions, correlation coefficients (r) were >0.997 for calibration curves in the range 1–80 ng/mL, detection limits and quantification limits ranged from 0.19 to 0.67 and 0.63 to 2.23 ng/mL, respectively, and relative standard deviation was <8%. The method was applied for the determination of chlorophenols in real wines, with recovery rates in the range 82–104%.     

Heat capacity anomalies of associated liquid–alkane mixtures near the liquid–liquid critical point

The isobaric heat capacity for a set of critical binary mixtures composed by an associated liquid and an alkane was measured near the liquid–liquid critical point. From a careful analysis of experimental data, nonuniversal quantities such as critical temperatures and critical amplitudes were obtained. To obtain microscopic parameters that may characterise the critical behaviour of the studied systems, the critical amplitude of the correlation length was determined via two-scale factor universality. Useful insights into the influence of the molecular structure of the alkanes as well as the self-associating capability of the polar liquid on the aforementioned nonuniversal quantities are obtained.     

High preconcentration of ultra-trace metal ions by liquid–liquid extraction using water/oil/water emulsions as liquid surfactant membranes

A high preconcentration method by liquid–liquid extraction using liquid surfactant membranes was developed. The water-in-oil (w/o) emulsion containing dilute hydrochloric acid, 2-ethylhexyl hydrogen 2-ethylhexylphosphonate (PC-88A), liquid paraffin, and kerosene was used for the extraction. In a resulting volume of 1000 cm³ of an aqueous sample solution (pH 5.0) containing less than 1 mg of each metal ion, 2 cm³ of w/o emulsion droplets coated with sorbitan monooleate were dispersed. The analyte metal ions in the outer bulk aqueous phase were extracted into the organic phase to form a complex with PC-88A and successively back-extracted into the inner aqueous phase. The analytes in the resulting inner aqueous phase were determined subsequently by graphite furnace atomic absorption spectrometry applied as a detector. By this procedure, concentration factors of 570, 820, 750, 970, 860, and 880 were achieved for chromium(III), manganese(II), cobalt(II), nickel(II), copper(II), and cadmium(II), respectively, and also the respective detection limits (3σ) of 0.4, 20, 1.2, 18, 18, and 0.7 pg cm⁻³ were obtained.     

Liquid–liquid equilibria of water + ethanol + reformate

Liquid–liquid equilibria (LLE) of the multicomponent system water + ethanol + a synthetic reformate (composed of benzene, n-hexane, 2,2,4-trimethylpentane, and cyclohexane) was studied at atmospheric pressure and at 283.15 and 313.15 K. The mutual reformate–water solubility with addition of anhydrous ethanol was investigated. Different quantities of water were added to the blends in order to have a wide water composition spectrum, at each temperature. We conclude from our experimental results, that this multicomponent system presents a very small water tolerance and that phase separation could result a considerable loss of ethanol that is drawn into the aqueous phase. The results were also used to analyse the applicability of the UNIFAC group contribution method and the UNIQUAC model. Both models fit the experimental data with similar low average root mean square deviations (rsmd ≤ 2.05%) yielding a satisfactory equilibrium prediction for the multicomponent system, although the predicted ethanol (rsmd ≤ 4.6%) compositions are not very good. The binary interaction parameters needed for the UNIQUAC model were obtained from the UNIFAC method.     

Permeability of hydrophilic and hydrophobic Shirasu-porous-glass (SPG) membranes to pure liquids and its microstructure

Morphological properties of hydrophilic and hydrophobic Shirasu-porous-glass (SPG) membranes were investigated over a wide range of mean pore sizes (0.252–20.3 μm) by liquid permeability measurements, scanning electron microscopy and Hg porosimetry. Hydrophobic modification of membrane surface was made by surface coating with silicone resin. The results are discussed using the non-uniform capillary bundle model of membrane permeability. The mean pore tortuosity of 1.28 was kept constant over the whole range of mean pore sizes investigated. The SEM images confirmed that the geometry of pore network was similar for all SPG membranes, irrespective of their mean pore size. The span of pore size distribution ranged from 0.28 to 0.68 and the number of pores per unit cross-sectional membrane area from 10⁹ to 10¹³ m⁻². The membrane resistance was unchanged after surface treatment with silicone resin, which means that the pores were not plugged by the resin, even in the submicron range of mean pore sizes.     

Salt‐assisted liquid–liquid extraction in microchannel

In this study, for the first time, salt‐assisted liquid–liquid extraction was performed in a microchannel system. The proposed design is based on the increase of contact surface area between target analytes and extracting phase during the sample and extracting phase transfer in microchannel. In this method, first sample solution, extracting solvent, and salt were mixed by stirrer and simultaneously delivered into a microchannel using a syringe pump. In order to optimize the influential parameters on the extraction efficiency of the proposed method, zidovudine and tenofovir disoproxil fumarate were selected as model analytes. The main parameters such as extracting solvent and its volume, salt amount, pH of sample solution, and microchannel shape, length, and its inner diameter were investigated and optimized. Under the optimized conditions, the proposed method was linear in the range of 0.1–30 µg/mL and R² coefficients were equal to 0.9922 and 0.9947 for zidovudine and tenofovir disoproxil fumarate, respectively. Extraction efficiency of the proposed method was compared with conventional salt‐assisted liquid–liquid extraction. The results show that the proposed design has higher extraction efficiency than conventional salt‐assisted liquid–liquid extraction. Finally, the proposed method was successfully applied for the determination of zidovudine and tenofovir disoproxil fumarate in plasma samples.