Solute Distribution Coefficient Research Articles

The influences of solid-phase organic constituents on the partition of aliphatic and aromatic organic contaminants

The influence of natural organic matter (NOM) constituents on contaminant distribution coefficients was evaluated by determining the K oc values of aromatic and aliphatic organic compounds (solutes) with clays modified with both aromatic- and aliphatic-rich organic constituents. The studied compounds consisted of naphthalene, phenanthrene, n-pentane, and 2,3,4-trimethylmethane; the solid samples comprised two clays with little organic content, kaolinite and Ca-montmorillonite. Two aliphatic surfactants and three aromatic dyes, sorbed to the clays, served as reference NOM constituents. For solutes of comparable water solubilities, the organic-carbon normalized distribution coefficients ( K oc ) of the aliphatic solutes between sorbed aliphatic organic matter and aqueous solution slightly exceed those of the aromatic solutes. By contrast, the aromatic solutes exhibited higher K oc values than did the aliphatic compounds with sorbed aromatic-rich organic matter. The difference in K oc values could be attributed to either comparable solubility parameters or the difference in the chemical structure between nonionic organic solutes and specific components of the simulated NOM. The much higher K oc values observed for the aromatic solutes indicate that the NOM composition is a major factor determining the NOC environmental distribution.

Optimization of a vacuum freezing cool‐thermal storage coupled with wastewater treatment process

AbstractPurification of wastewater by freezing under vacuum in a cool‐thermal storage process is investigated. Mathematical models of heat transfer and mass transfer in this system are developed to describe the thickness and the solute distribution of ice as the cool‐thermal storage process proceeds. A mathematical treatment for determining the optimum solidification thickness and operating time to remove the maximum amount of solute is presented. For the system of constant volumetric rate of vacuum, the suction rate is an important factor in determining the efficiency of the process. The suction rate should be kept within the range of 10,000 to 20,000 m3/m2hr when the solute distribution coefficient is less than 1. When the coefficient is greater than 1, the suction rate should be run within 5000 to 10,000 m3/m2hr. Over the proper range of operation, the optimal operating time is a weak function of suction rate. © 2004 Wiley Periodicals, Inc. Heat Trans Asian Res, 33(3): 189–200, 2004; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/htj.10134

Thermodynamic equilibrium of the solute distribution in size-exclusion chromatography

Our understanding of the nature of solute retention in size-exclusion chromatography (SEC) is predicated upon an equilibrium, entropy-controlled, size-exclusion mechanism. The entropic nature of the separation depends, in turn, upon the solute distribution coefficient ( K SEC) being at (or close to) thermodynamic equilibrium. Classic experiments to confirm this assumption were performed over thirty years ago. Here, we combine information obtained from both flow and static mixing SEC experiments to show that the solute distribution in SEC is in thermodynamic equilibrium over a molar mass range extending one order of magnitude higher than previously measured (from 2×10 3 to 1.1×10 6 Da) using crosslinked polystyrene packing material of identical pore size (10 4 Å). The differences between our observations and previous ones conducted over three decades ago are ascribed, principally, to advances in stationary phase synthesis and column technology for SEC in particular and, secondarily, to improvements in the performance of the various instrumental components of liquid chromatographic systems in general.

Analysis of mass transfer in hollow-fiber membranes

The mixing-cup concentration was investigated under different flow conditions (parabolic flow and plug flow in the lumen side of hollow fibers) and at different values of the concentration-dependent diffusion and solute distribution coefficient. The concentration dependency of both coefficients was defined by two different functions and integrated analytically as examples. The mixing cup concentration was calculated by the numerical method. The mixing cup concentration was plotted as a function of an axial coordinate under different conditions.

Solubilities of nonvolatile solutes in polymers from molecular thermodynamics

AbstractBecause there is no simple, general method for measuring solubilities of nonvolatile solutes in a polymer, this work presents a thermodynamic framework for estimating such solubilities from infinite‐dilution distribution‐coefficient data for aqueous solutions of the solute in equilibrium with the polymer. The experimental infinite‐dilution distribution coefficient is related to that calculated from a molecular‐thermodynamic model (Flory–Huggins). The three binary Flory parameters are obtained from water–solute and water–polymer data, and from the solute's distribution coefficient. Solubilities of 19 nonvolatile aromatic solutes were estimated in three polymers: ethyl‐vinyl acetate copolymer (EVAc) with 33 (EVAc33), 45 (EVAc45) wt. % vinyl acetate content, and poly(vinyl acetate) (PVAc) at 25°C, where most of the solutes are solids. For some of these systems, predicted solubilities are compared with new experimental results. The calculations reported here may be useful for various applications, including the design of membrane processes or drug‐delivery systems, and for packaging technology for foods, chemicals, and pharmaceuticals.

Distribution of solutes between polymer and supercritical fluid by inverse supercritical fluid chromatography

Two methods of inverse supercritical fluid chromatography (ISFC), frontal analysis supercritical fluid chromatography (SFC) and elution SFC, have been compared for the determination of distribution coefficients of solutes between a polymer and a supercritical CO2. The logarithm of the distribution coefficient showed monotonic decrease with the density of the supercritical fluid (SF). The abnormal-maximum behavior of solute sorption in the polymer phase was explained by the fluid and solute properties, ϕ2P/P 2 sat . Interesting open-elliptic shapes of sorption and volume-fraction curves were obtained and explained with the fugacity coefficient. Correction to the capacity factor was employed to eliminate the retention due to the adsorption on the surface of the silica support. A model based on the Flory equation and the Peng-Robinson equation of state (EOS) successfully predicted the phase behavior of the ternary solutesupercritical fluid-polymer systems using only interaction parameters obtained from the binary systems. The solute distribution coefficient at infinite dilution was used to calculate the phase equilibrium at finite concentration using a ternary-phase diagram.

ANALYSIS OF LEAKAGE EFFECT IN COUPLED TRANSPORT THROUGH LIQUID SURFACTANT MEMBRANE

Considerable effort has been directed toward describing, through analysis of mass-transfer resistances for solute diffusion and reaction in an emulsion drop, the permeation mechanism in liquid membrane systems based on the advancing reaction front model. However, very little attention has been paid to the loss of extraction efficiency often encountered in these systems due to rupture of the emulsion globules. In the present study, an unsteady-state mathematical model for batch extraction of monovalent HCrO4 − and divalent CrO4 2− from aqueous solution, through the use of Aliquat 336 as extractant and sodium hydroxide as stripping reagent, is reported. The rate of change of internal-phase volume due to membrane breakage was assumed to be independent of time, and an instantaneous and irreversible reaction between the solute and the internal reagent at the membrane–internal droplet interface was presumed to create a reaction front within the emulsion globule. The leakage coefficient was determined experimentally and was found to be dependent on internal-phase volume fraction. Batch experiments were performed for separation of Cr(VI) from aqueous potassium dichromate solution and the validity of the model was tested through the comparisons of model predictions with experimental data for different internal-phase volume fractions. The effect of external-phase pH on overall extraction in presence of leakage was also studied with semiempirical equations of the solute distribution coefficient that were obtained through experiments.

Ａｌ‐Ｔｉ‐Ｃｒ系三元状態図と（Ａｌ，Ｃｒ）３Ｔｉ合金の凝固組織

The Al-rich region of the Al–Ti–Cr ternary phase diagram was determined on the basis of the experimental results of differential thermal analysis, high temperature isothermal heating, and X-ray micro analysis. The solidification passes of alloys with primary L12–(Al, Cr)3Ti phase were analyzed by using the diagram. The L12 solidus and liquidus at 1250∼1350°C were measured, and solute distribution coefficients for Ti or Cr (kTi, kCr) were derived as functions of liquid composition (CLTi, CLCr). Further, boundaries of liquidus surfaces between L12 phase and the surrounding phases (Cr(Cr2Al), Al17Cr9, Al3Ti, Al7Ti3, TiAl, TiAlCr) were established. Changes of liquid and solid concentrations during solidification of various Al–Ti–Cr alloys were calculated by the progressive solidification equation using the above Al–Ti–Cr diagram and kTi, kCr. The calculated structures agreed well with the experimental results.

Novel simulated moving-bed method for reduced solvent consumption

Simulated moving-bed (SMB) chromatography is attractive for reducing sorbent and solvent consumption relative to fixed-bed systems. In this contribution, we describe a novel and versatile method for further reducing solvent consumption in the case of reversed-phase chromatography. The method is based on the variation of the distribution coefficients of solutes to be separated upon varying the composition of a multi-component mobile phase. If the solvent strength of the desorbent is set higher than the solvent strength of the feed, the components will have smaller distribution coefficients in the extraction section of the SMB and hence will be more easily eluted. This will result in a lower desorbent flow and possibly also in a shorter desorbent zone, and, ultimately, in more concentrated products. The so-called “Triangle-method” by Storti et al. [AIChE J., 39 (1993) 471] to obtain the region of complete separation, is extended for this novel SMB method. Theoretical evaluation of the proposed methodology supports the anticipated solvent reduction relative to fixed-bed RP-HPLC for the cases of the purification of the polyketide antibiotic nystatin and the separation of bovine insulin from porcine insulin.

Distribution of solute at solid–liquid interface during solidification of melt

A model for predicting a distribution coefficient (ki) of solute at the solid–liquid (S–L) interface, when the solid layer is growing, is proposed. The interfacial distribution coefficient is expressed as a function of two gradients of the liquid concentration and equilibrium concentration at the S–L interface. The model is applied to the solidification of a simple eutectic binary liquid of lauric acid and myristic acid in an enclosed rectangular box in which a vertical wall is cooled. The impurity-concentration profile in solid is predicted from the direct numerical computations.

Directional solidification of Ni [sbnd]Al [sbnd]Cr [sbnd]Fe alloy

During directional solidification of engineering alloys, the formation of cellular and dendritic structures with concomitant microsegregation and microporosity is of great interest since these solidification features significantly influence mechanical properties. The critical growth rate V{sub c} at which the planar solid-liquid interface reorganizes to a periodic array of cells can be well predicted by the linear analysis of Mullins and Sekerka. This analysis was recently extended by Trivedi and Kurz for high thermal Peclet number conditions and concentrated alloys. Several theoretical models were also reported on the cellular and dendritic spacings in binary systems. According to the model of Hunt, the cellular spacing sharply increases from zero to a maximum as the growth rate increases from V{sub c} to 2V{sub c}. At higher growth rates, the cellular spacing decreases with increasing the growth rate and no discontinuity in spacing occurs at the cellular-dendritic transition. The Kurz and Fisher`s model predicts a minimum in cellular spacing near the cellular-dendritic transition that is expected to occur at the transition growth rate V{sub t} = V{sub c}/k, where k is the solute distribution coefficient. At the growth rates V > V{sub c}/k, the primary dendrite arm spacing {lambda}{sub 1} varies with the growthmore » rate and temperature gradient G according to the relationship {lambda}{sub 1} {proportional_to} V{sup {minus}0.25} G{sup {minus}0.5}. On the contrary, the model of Trivedi predicts a maximum in cellular spacing to occur near the cellular-dendritic transition and cellular structures are found to grow with smaller spacings than dendritic structures under identical growth conditions. The aim of this paper is to investigate the influence of directional solidification on the microstructure evolution in Ni-12.7Al-6.8Cr-1.8Fe (at.%) alloy. Experiments have been carried out at a constant temperature gradient over a wide range of growth rates.« less

The Sorption of Pyrene and Anthracene to Humic Acid‐Mineral Complexes: Effect of Fractional Organic Carbon Content

AbstractCarbon‐normalized distribution coefficients (Koc) of organic solutes appear to increase as the amount of organic C in a system decreases. This study was conducted to determine the effect of fractional organic C content (foc) on the sorption of anthracene and pyrene. Batch‐sorption experiments were conducted on reagent CaCO3, a geologic calcite, and a montmorillonite to measure anthracene and pyrene sorption. An organic C‐free mineral surface and two surface loadings of humic acid (HA) were evaluated. The Koc of anthracene and pyrene varied with foc as well as with the underlying mineral surface. The sorption of anthracene and pyrene to all HA‐mineral complexes increased with increases in foc, while Koc for the compounds decreased. In higher foc systems (>3 × 10−5), isotherms were C‐type curves indicative of partitioning. In lower foc systems (<3 × 10−5), isotherms were commonly L and S‐type curves indicative of adsorption and condensation. Sources of potential experimental artifact examined were loss of HA from the mineral surface to solution, dissolution of CaCO3 during the experiment, and loss of NOS to experimental glassware or volatilization. None were found to contribute to the observations made. Our results suggest that adsorption‐condensation of pyrene and anthracene created more surface excess than predicted by partitioning alone as evidenced by the large experimental Koc values obtained.

Scale-up of Hollow Fiber Extractors

The performance of a commercial-scale hollow fiber extraction system was investigated by the Separations Research Program (SRP) at the University of Texas at Austin. In this work, hexanol was extracted from water into octanol using a large-scale extraction/distillation system. In the membrane extractor studies, the octanol-rich phase was fed on the tube-side while in the packed column studies, the octanol-rich phase was chosen as the dispersed phase. This chemical system was selected because of its high solute distribution coefficient. As a result, the required solvent to feed ratio was low which creates hydraulic problems for conventional dispersive extractors such as the packed column. Under identical operating conditions, the mass transfer performance of the hollow fiber extractor compared favorably with that of a commercial-scale type 2 structured packing. A height equivalent to a theoretical stage (HETS) of 1.5 meters was obtained with the membrane extractor as compared to 15 meters for the type 2 structured packing. A staged hollow fiber extraction mass transfer model for scale-up was developed and found to agree with data obtained in this work and with data obtained earlier using the n-butanol/succinic acid/water system.

Solvent concentration dependence of solute distribution coefficient

AbstractA simple method for modeling the solvent concentration dependence of solute distribution coefficient is described. Ideal and modified distribution models are proposed based on the mechanism of multicomponent competitive adsorption and the theory of solvent association. The system cresol‐methanol/water‐β‐CD‐silica is tested using the models, which compared with other experimental results show that the ideal distribution model fails at higher water concentrations and that the modified model can describe well the observed solute distribution behavior over the entire concentration range. The relative impact of nonideal factors in the adsorbed phase and the solvent association in the mobile phase on the distribution dependence shows that the limitation of the ideal model at higher water concentrations results mainly from uneven saturation capacities of the solute and solvent components for the system studied here.

Evaluation and Optimization of the Factors Affecting Nonionic Surfactant-Mediated Phase Separations

The technique of extracting and concentrating hydrophobic species from water via nonionic surfactant micelle-mediated phase separations was examined. The effect on extraction efficiency, solute distribution coefficient, and phase volume ratio of pertinent experimental parameters such as surfactant hydrophobicity, pH and ionic strength, equilibration time and temperature, centrifuge time, and analyte and surfactant concentration was systematically evaluated. Surfactant hydrophobicity, which was studied by monitoring the extraction parameters observed for two homologous series of poly(oxyethylene glycol) monoethers, appeared to be the dominant factor along with solution pH for those solutes possessing either an acidic or a basic functionality

Partition and distribution coefficients of solutes and drugs in brush border membrane vesicles

Partition and distribution coefficients (log P, log D) into rat small intestinal brush border membrane (BBM) were measured for a variety of ionizable and non-ionizable drugs and solutes using a novel technique. The log P values were compared with those determined with model solvents, octanol and propylene glycol dipelargonate (PGDP). Non-ionizable solutes with log P values up to 3.0 showed that octanol was a better model for partition into the BBM than PGDP. With one exception, BBM partition coefficients of greater than 3 were not observed, even for solutes with log P values in model solvents that were greater than 5. Liposomes prepared from BBM lipids, or synthetic lipid mixtures of similar composition to BBM, demonstrated similar trends in partition coefficients to the intact BBM. Two cationic drugs, Atenolol ® and Xamoterol ® were investigated for partition into BBM lipid liposomes. An apparent enhancement of log D with respect to octanol was attributed to a “surfactant-like” orientation in the membrane and an interaction of the ionized drug with anionic phospholipid head groups. The anionic drug Proxicromil ® shows the expected decrease in log D with increasing pH, at low NaCl concentrations. Changes in electrophoretic mobility of liposomes after incorporation of Proxicromil into them were consistent with the negative charge of the ionized drug being at the membrane surface. It was concluded that Proxicromil also associates with membranes in a “surfactant-like” orientation and that increased extraction with increasing NaCl concentrations is a result of ionic strength effects. Partition of solutes into BBM vesicles is more complex than into organic solvents and probably represents an important step in overall intestinal permeation of solutes.

PURIFICATION OF HYDROCHLORIC ACID BY ISOOCTANE EXTRACTION

ABSTRACT Removal of organic compounds from hydrocloric acid can be performed by a solvent extraction process followed by a solvent regeneration step by adsorption with sepiolite. The extraction study includes the analysis of the influence of the operating conditions, the determination of the solute distribution coefficient for isooctane and the effect of temperature on the extraction. The adsorption isotherms were calculated to check the technical viability of the method. The obtained efficiency of extraction is close to 90 wt%, whereas that of the solvent regeneration recovery is over 67 wt%

The Effect of Phosphoric Acid Additive on the Porosity and the Distribution Coefficients of Solutes in Cellulose Acetate Particles.

A series of cellulose acetate (CA) particles have been prepared by spraying method from the solutions containing different concentrations of phosphoric acid and CA. The pore sizes of particles obtained have been tested by means of gel chromatography using polyethylene glycol (PEG) with different molecular weights as molecular size probes. It is found that phosphoric acid additive acts as a pore adjusting solvent to from a suitable porosity in CA particles. At low CA concentration (5 wt%) the pore sizes decrease with phosphoric acid in a certain concentration, and at high CA concentration (17 wt%) the pore sizes increase by adding phosphoric acid additive. The water contents of particles and the stationary water contents in chromatographic columns have also been analysized. The results show that both the water contents and stationary water contents for prepared particles are larger than those for original CA powder and increase to a maximum in a certain pore sizes of particles. The equilibrium distribution coefficients (Kd) for aliphatic alcohols, acids and amines have been measured. The Kd values of original CA powder for all these organics are larger than those of prepared CA particles, especially for longer carbon chains of organics. We also found that the structure of prepared particles have some effects on the Kd values for the organics with longer carbon chains, but almost no effects for the organics with short carbon chains.

Retention in field-flow fractionation with secondary chemical equilibria

The application range of field-flow fractionation (FFF) can be extended to low molecular weight solutes, as demonstrated a few years ago by Berthod et al., by taking profit of secondary chemical equilibria (SCE) occurring between the bulk carrier and a retained carrier component. The theory of solute retention in this SCE-FFF method is developed for any value of the solute distribution coefficient and of the retention ratio of the retained carrier component, provided that the Brownian mode of retention applies for this component and that the flow velocity profile is parabolic. This removes some of the limitations of the model previously developed by Berthod and Armstrong and sheds light on the potentialities of the SCE-FFF method for physico-chemical studies about secondary chemical equilibria in colloidal systems. Remaining assumptions in the model are discussed.

The influence of an interface electric field on the distribution coefficient of chromium in LiNbO 3

The effective solute partitioning of chromium was investigated on single crystals of LiNbO 3 grown by the laser-heated pedestal growth (LHPG) technique. Electric field effects at the interface influence this solute partitioning, leading to an electric field-dependent effective solute distribution coefficient, k E. The LHPG technique made it possible to explore these field effects by controllably changing the growth velocity ( V) and the temperature gradient ( G S, G L) near the interface over a wide range. The electric field generated via the temperature gradient is associated with the thermoelectric power while an additional electric field is growth rate associated via a charge separation effect. By applying the Burton-Prim-Slichter (BPS) theory to our experimental data, we found the phase diagram solute partition coefficient to be k 0 ≈ 3.65, while the field-influenced solute partition coefficient ( V = 0) was k′ EO ≈ 8.17 at G L ≈ 11500°C/cm. It is theoretically shown that the same considerations can be applied to all ionic partitioning at a solid-liquid interface.