Sorption Of Mixtures Research Articles

Sorption of binary mixtures of toluene + lower aliphatic alcohols C1 – C6 in low‐density polyethylene

AbstractSorption gravimetric and volumetric techniques performed at 25°C and at atmospheric pressure were employed to study the preferential and total sorptions from binary liquid mixtures of toluene + lower aliphatic alcohols (C1 – C6) in a high‐pressure low‐density polyethylene membrane and the volume of the swollen membrane. Toluene was preferentially sorbed in all six systems. The total sorbed amount increased from pure alcohol to pure toluene. The experimental volume of the swollen membrane was compared with that calculated under the assumption that interactions between the polymer and liquid mixture were negligible. The composition of the binary liquid mixture sorbed in the polymer as a function of the composition of the bulk solution surrounding the membrane is presented. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2011

Effects of cell condition, pH, and temperature on lead, zinc, and copper sorption to Acidithiobacillus caldus strain BC13

This study describes the effects of cell condition, pH, and temperature on lead, zinc, and copper sorption to Acidithiobacillus caldus strain BC13 with a Langmuir model. Copper exhibited the highest loading capacity, 4.76±0.28mmolg−1, to viable cells at pH 5.5. The highest kL (binding-site affinity) observed was 61.2±3.0Lmmol−1 to dehydrated cells at pH 4.0. The pHs that maximized loading capacities and binding-site affinities were generally between 4.0 and 5.5, where the sum of free-proton and complexed-metal concentrations was near a minimum. Of additional importance, lead, zinc, and copper sorbed to viable cells at pH values as low as 1.5. Previous studies with other acidithiobacilli did not measure viable-cell sorption below pH 4.0. In separate experiments, desorption studies showed that far less copper was recovered from viable cells than any other metal or cell condition, suggesting that uptake may play an important role in copper sorption by At. caldus strain BC13. To reflect an applied system, the sorption of metal mixtures was also studied. In these experiments, lead, zinc, and copper sorption from a tertiary mixture were 40.2±4.3%, 28.7±3.8%, and 91.3±3.0%, respectively, of that sorbed in single-metal systems.

In-situ neutron diffraction study of magnesium amide/lithium hydride stoichiometric mixtures with lithium hydride excess

The hydrogen sorption of mixtures of magnesium amide (Mg(NH 2) 2) and lithium hydride (LiH) with different molecular ratios have been investigated using in-situ neutron diffraction; the experiments were performed at D20/ILL and SPODI/FRMII. The results reveal a common reaction pathway for 1:2, 3:8 and 1:4 magnesium amide: lithium hydride mixtures. Intermediate reaction steps are observed in both ab- and desorption. The thermodynamic properties of the system at 200 °C are not changed by the addition of excess lithium hydride. This finding has important implications for the tailoring the characteristics of this promising hydrogen storage material.

Simulating Microwave-Heated Open Systems: Tuning Competitive Sorption in Zeolites

We have developed a new grand canonical molecular dynamics (GCMD) algorithm to study microwave (MW) heating effects on competitive mixture sorption and have applied the method to methanol and benzene in silicalite zeolite. The new algorithm combines MW-driven molecular dynamics with grand canonical Monte Carlo (GCMC), the latter modeling adsorption/desorption processes. We established the validity of the new algorithm by benchmarking single-component isotherms for methanol and benzene in silicalite against those obtained from standard GCMC, as well as against experimental data. We simulated single-component and mixture adsorption isobars for conventional and MW-heated systems. In the case of the single-component isobars, we found that for dipolar methanol, both the MW and conventional heated isobars show similar desorption behavior, displaying comparable loadings as a function of molecular temperature. In contrast, nonpolar benzene showed no desorption upon exposure to MWs, even for relatively high field strengths. In the case of methanol/benzene mixtures, the fact that benzene is transparent to the MW field allows the selective desorption of methanol, giving rise to loading ratios not reachable through conventional heating.

Competitive sorption of tungstate, molybdate and phosphate mixtures onto goethite

Competitive sorption of tungstate, molybdate and phosphate mixtures onto goethite

Classification and regression trees (CARTs) for modelling the sorption and retention of heavy metals by soil

The sorption and retention of mixtures of heavy metals by soil is a complex process that depends on both soil properties and competition between metals for sorption sites. In this study, the sorption and retention of mixtures of Cd, Cr, Pb, Cu, Zn and Ni by a representative sample of soils from Galicia (N.W. Spain) was reproduced considerably more precisely by binary decision-tree regression models constructed using the CART algorithm than by linear regression models. Of the six metals competing for sorption sites in these experiments, Pb, Cu and Cr were sorbed and retained to a greater extent than Cd, Ni and Zn. Non-linear tree regression models constructed with CART fitted the data better than linear models, especially for Cd, Ni and Zn; and with both kinds of model the data for Pb, Cu and Cr were fitted better than those for Cd, Ni and Zn (the difference being much more marked for linear models), suggesting that the influence of soil properties on the sorption and retention of the latter three metals was limited by the preferential binding of the former three.

The Sorption of Mixtures of Direct Dyes by Cellulose

The diffuse adsorption model accounts adequately for the adsorption of mixtures of direct dyes by cellulose if no interaction occurs between the dyes in either phase and if allowance is made for ionised carboxyl groups in the cellulose.

Sorption equilibria of CO 2/CH 4 mixture on activated carbon in presence of water

The sorption isotherms of CO 2 + CH 4 mixtures on an activated carbon were collected in the presence of water at a temperature suitable for hydrate formation. The equilibrium composition of both phases was determined. The initial concentration of CO 2 in mixtures was set at 33, 38 and 42%, and the total pressure was up to 10 MPa. CO 2 hydrates were firstly formed following the increase of total pressure, and CO 2 dominates the sorbed phase composition. CO 2 concentration in the sorbed phase begins to decrease when the partial pressure of methane allows for the formation of methane hydrates. Competition for hydrate cavities was observed between CO 2 and CH 4 as reflected in the isotherm shape and phase composition at equilibrium. The formation pressure of hydrates is lower for mixtures than for pure gases, and the highest sorption capacity of each gas decreased in the mixture sorption either.

Effects due to molecular shape and flexibility on the permeability ratio of binary fluid mixtures in a model polymer network via computer simulation

Sorption and diffusion of binary mixtures of small molecules in model polymer networks is studied via computer simulation. Three types of molecules identical in volume but different in shape and flexibility (compact, linear stiff, and linear flexible) are combined into binary mixtures (compact/linear stiff) and (linear stiff/linear flexible). The relative effects of shape and flexibility on separation factor and diffusion coefficient inside random polymer networks are studied using a molecular dynamics/Gibbs-ensemble Monte Carlo hybrid technique. In addition the effects of temperature, pressure, and network strand length are considered. We find that the compact molecules are preferentially absorbed into the network at all strand lengths and temperatures considered here. Flexibility only leads to minor preferential sorption under most conditions. Diffusion coefficients of the competing species inside the network are found to agree within the error bars.

Sorption of binary liquid mixtures in methacrylate‐based biomaterials; Simultaneous determination of the diffusion coefficients and the uptake fraction at equilibrium of the components of ethanol‐water mixtures by a new iterative method

AbstractThe present investigation is concerned with the development of a new iterative method permitting, for a Fickian sorption of a binary liquid mixture in thin polymer sheets, the simultaneous determination of the self‐diffusion coefficients of the components of the mixture, and their uptake fractions at equilibrium. The approach is based on a new equation describing a parallel Fickian sorption of the components of the mixture into thin polymer sheets. The procedure was tested with ideal and Monte Carlo simulated data. The method, applied to ideal simulated data that corresponded to various values of D1, D2 and f, perfectly extracted the desired parameters. The application of the method to Monte Carlo simulated data revealed that this method is fairly applicable even when the simulated data are considerably obscured by “noise”. Finally, the proposed method was successfully applied to the experimental data concerning the sorption kinetics of ethanol–water mixture (75 vol % in EtOH) at 37°C in thin polymeric sheets of triethyleneglycol dimethacrylate (TEGDMA). © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 2008

New instrument to measure the selective sorption of gas mixtures under high pressures

In consideration of the rising crude oil and natural gas prices the use of biogases becomes more and more important for the energy supply worldwide. Typically gases produced from bio-resources consist of high amounts of carbon dioxide and sulphur components besides the burnable gas methane. To establish these biogases in the traditional energy systems of the countries, separation techniques have to be used to remove the inert carbon dioxide and the polluting gases. In literature it is already known, that ionic liquids are sorbens, which can be tailor-made for separation processes. Alkyl sulphate and imidazolium-based ionic liquids are for example very suitable for sorption of carbon dioxide [1]. For the engineering of such gas separation processes sorption isotherms are necessary not only for low pressures but also for pressure ranges where typically natural gas is handled. In this contribution a new experimental technique is presented to measure directly the selective sorption of gas mixtures up to high pressures. For these measurements a method is used which combines the volumetric and gravimetric sorption measuring principle together with a high performance sorptiv gas analysis using fluid density and gas chromatographic measuring technique.

Pure and mixed gas CH4 and n-C4H10 sorption and dilation in poly(1-trimethylsilyl-1-propyne)

Pure and mixed gas n-C4H10 and CH4 sorption and dilation in poly(1-trimethylsilyl-1-propyne) (PTMSP) are reported at temperatures ranging from −20 to 35°C. The presence of n-C4H10 in the mixture considerably reduces CH4 solubility. For example, CH4 solubility (in the limit of zero CH4 fugacity) at 25°C decreases from 4.0 (pure gas) to 0.78cm3(STP)/(cm3polymeratm) in the presence of n-C4H10 at an activity of 0.60. At −20°C, CH4 solubility decreases by almost an order of magnitude, from 10.2 (pure gas) to 1.22cm3(STP)/(cm3polymeratm) in the presence of n-C4H10 at an activity of 0.61. In contrast, n-C4H10 mixture sorption properties are not measurably affected by the presence of CH4. The dual mode sorption model parameters for CH4 and n-C4H10 in PTMSP were determined from pure and mixed gas sorption measurements, and this model can adequately describe the sorption data. The n-C4H10/CH4 mixed gas solubility selectivity in PTMSP decreases as temperature increases and as n-C4H10 activity increases. For example, at 25°C, the n-C4H10/CH4 solubility selectivity decreases from 250 to 120 as n-C4H10 activity increases from 0.02 to 0.25. At −20°C and an n-C4H10 activity of 0.24, the n-C4H10/CH4 solubility selectivity is 590. Penetrant-induced volume dilation of PTMSP can be adequately modeled by assuming that all swelling is caused by penetrant molecules sorbed in the polymer's dense equilibrium region (i.e., the Henry's law region) during sorption. However, the best fit partial molar volumes in the Henry's law region for the dilation data are considerably lower than the penetrant partial molar volumes in liquids, suggesting that further theoretical efforts are needed to develop predictive models of volume dilation in high free volume glassy polymers.

Sorption of methane and carbon dioxide mixtures in Polish hard coals considered in terms of adsorption-absorption model

The measurements of gas mixture sorption of CO 2 + CH 4 (50%:50%) on hard coals were carried out using an original measurement method. The accuracy of the experimental data was controlled by using a gas chromatograph. Experimental sorption isotherms of individual gases were used for the simulation of sorption of their mixtures. A good agreement was obtained between the simulated and experimental data.

Screening of zeolite adsorbents for separation of hexane isomers: A molecular simulation study

Recent developments in Monte Carlo (MC) simulation techniques have enabled the accurate calculation of sorption isotherms of a variety of molecules in zeolites. Using the example of separation of isomers of hexane we demonstrate the power of MC simulations for screening of zeolite adsorbents for maximum separation selectivity. The simulations underline the exploitation of entropy effects during mixture sorption

Multicomponent mass transport model for the sorption of metal ions on bone char

AbstractThe sorption of binary mixtures of copper/cadmium and copper/zinc ions onto bone char was studied in fixed beds. The effects of solution flow rate, initial dye concentration, and bone char particle size range were investigated. A mass transport model based on film‐surface diffusion and the IAS model for the equilibrium relationship was used to develop theoretical fixed‐bed breakthrough curves. The model incorporates the Sips isotherm for the first time in fixed‐bed predictions, since this isotherm gives an excellent correlation of the experimental equilibrium data. The model was used to determine the optimum surface diffusivities as 7.37 × 10−10 and 2.73 × 10−9 cm2/s for copper and cadmium in the Cu/Cd system; and 1.61 × 10−9 and 2.43 × 10−9 cm2/s for copper and zinc in the Cu/Zn system. © 2004 American Institute of Chemical Engineers AIChE J, 50: 2130–2141, 2004

Plasticized microporous poly(vinylidene fluoride) separators for lithium‐ion batteries. II. Poly(vinylidene fluoride) dense membrane swelling behavior in a liquid electrolyte—characterization of the swelling kinetics

AbstractSome microporous poly(vinylidene fluoride) (PVdF) separators for lithium‐ion batteries, used in liquid organic electrolytes based on a mixture of carbonate solvents and lithium salt LiPF6, were characterized by the study of the swelling phenomena on dense PVdF membranes. Various aspects of the kinetics of the carbonate solvents and the solvent mixture sorption in dense PVdF slabs were studied at different temperatures. Non‐Fickian behavior, characterized by S‐shaped sorption curves, was highlighted, and a salt effect, which resulted in two‐stage sorption, was studied. Diffusion coefficients and activation energies were calculated for the Fickian portions of the sorption curves, that is, at short times and low swelling ratios. A strong influence of the different interaction parameters was shown for the swelling kinetics. This study proved that the swelling of microporous PVdF membranes could be considered instantaneous. © 2003 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 42: 544–552, 2004

Effectiveness factor for zeolite catalysed isomerization reactions

We analyze the influence of diffusion on the reversible isomerization reaction A 1↔A 2, occurring within a zeolite catalyst, of spherical, cylindrical, and slab geometries. The intra-crystalline diffusion process is described by the Maxwell–Stefan (M–S) equations. Two different guest–host confinement scenarios are examined. For strongly confined guest molecules, the M–S diffusivities Đ i decrease with loading inside the zeolite. For weakly confined guest molecules, the M–S diffusivities Đ i are independent of the loading. The correlation effects, typical of zeolite diffusion, are described by introducing an exchange coefficient Đ 12 in the M–S diffusion formulation. For facile exchange, D ̵ 12→∞ , correlation effects are washed out. For finite exchange, a logarithmic interpolation formula is used to calculate Đ 12 from the two pure component M–S diffusivities Đ i . Analytic expressions for the effectiveness factor are derived for a variety of confinement and exchange scenarios. In the development of the analytic solution we assume Langmuirian behavior of the pure components and that the mixture sorption loadings can be calculated from the multicomponent Langmuir isotherm. By means of a variety of numerical examples, we stress the various characteristic features of intra-crystalline diffusion influences in zeolite catalysis. The effectiveness factor is found to a strong function of (a) molecular loadings and mixture composition, (b) ratio of diffusivities of the participating species, and (c) the reaction equilibrium constant. Only for the case of low loadings of weakly confined guest molecules and vanishing correlation effects, is the classical formula for the effectiveness factor valid.

Kinetic gravimetric sorption of low volatility gases and vapors in polymers

A kinetic gravimetric sorption apparatus for measuring solubility and diffusivity of low vapor pressure gases and vapors in polymers and other sorbents is described. Sorption and transport data for toluene vapor in poly(dimethyl siloxane) at 25 °C are provided to illustrate the method. These data were obtained by measuring the kinetic uptake of a mixture of carrier gas and toluene vapor and, for comparison, pure toluene vapor at the same thermodynamic activity. Excellent agreement was observed between toluene solubility and diffusivity values obtained from these two different experiments. In the mixture sorption experiments, the type of carrier gas (helium or nitrogen) had no effect on measured toluene solubility and diffusion coefficients.

Analytic solution of the Maxwell–Stefan equations for multicomponent permeation across a zeolite membrane

We develop an analytic solution of the Maxwell–Stefan equations describing steady-state diffusion of n-component mixtures across a zeolite membrane. In the development of the analytic solution we assume Langmuirian behaviour of the pure components and that the mixture sorption can be calculated from the multicomponent Langmuir isotherm. Explicit expressions are derived for calculation of steady-state fluxes and the loading profiles in the membrane. The utility of the developed solution is illustrated by means of two illustrative examples involving permeation of alkane mixtures across an MFI membrane.

Methane and CO 2 sorption and desorption measurements on dry Argonne premium coals: pure components and mixtures

Sorption and desorption behaviour of methane, carbon dioxide, and mixtures of the two gases has been studied on a set of well-characterised coals from the Argonne Premium Coal Programme. The coal samples cover a maturity range from 0.25% to 1.68% vitrinite reflectance. The maceral compositions were dominated by vitrinite (85% to 91%). Inertinite contents ranged from 8% to 11% and liptinite contents around 1% with one exception (Illinois coal, 5%). All sorption experiments were performed on powdered (−100 mesh), dry coal samples. Single component sorption/desorption measurements were carried out at 22 °C up to final pressures around 51 bar (5.1 MPa) for CO 2 (subcritical state) and 110 bar (11 MPa) for methane. The ratios of the final sorption capacities for pure CO 2 and methane (in molar units) on the five coal samples vary between 1.15 and 3.16. The lowest ratio (1.15) was found for the North Dakota Beulah-Zap lignite (VR r=0.25%) and the highest ratios (2.7 and 3.16) were encountered for the low-rank coals (VR r 0.32% and 0.48%) while the ratio decreases to 1.6–1.7 for the highest rank coals in this series. Desorption isotherms for CH 4 and CO 2 were measured immediately after the corresponding sorption isotherms. They generally lie above the sorption isotherms. The degree of hysteresis, i.e. deviation of sorption and desorption isotherms, varies and shows no dependence on coal rank. Adsorption tests with CH 4/CO 2 mixtures were conducted to study the degree of preferential sorption of these two gases on coals of different rank. These experiments were performed on dry coals at 45 °C and pressures up to 180 bar (18 MPa). For the highest rank samples of this sequence preferential sorption behaviour was “as expected”, i.e. preferential adsorption of CO 2 and preferential desorption of CH 4 were observed. For the low rank samples, however, preferential adsorption of CH 4 was found in the low pressure range and preferential desorption of CO 2 over the entire pressure range. Follow-up tests for single gas CO 2 sorption measurements consistently showed a significant increase in sorption capacity for re-runs on the same sample. This phenomenon could be due to extraction of volatile coal components by CO 2 in the first experiment. Reproducibility tests with methane and CO 2 using fresh sample material in each experiment did not show this effect.