A “free volume” model of permeation of gas and liquid mixtures through polymeric membranes

A recent “free volume” model of gas permeation (3) has been extended to the transport of gas mixtures through nonporous polymeric membranes. The present model assumes that the rates of transport of the components of a mixture depend on the free volume of the gas-polymer system, and that the effect of these components on the free volume is additive. The latter assumption limits the model to relatively dilute systems, with total penetrant concentrations of perhaps less than 0·2 volume-fraction. The prediction of permeation fluxes and permeability coefficients requires the knowledge of specified free-volume parameters which can be determined from measurements of diffusion coefficients and viscosities of the pure penetrant-polymer systems. When the systems are sufficiently dilute to obey Henry's law, the permeability coefficients for the components of a gas mixture can be predicted using only permeability measurements with the pure components. The extended free-volume model can be applied also to the permeation of liquid mixtures. The theoretical predictions are compared with the results of several experimental studies, and the potential usefulness and limitations of the model are discussed.     

Compression characteristics of pharmaceutical powder mixtures

A study has been made of the compression characteristics of binary, ternary and quaternary mixtures of the ingredients of a typical griseofulvin tablet formulation. The results have been analysed in terms of the compression equations of Heckel and of Cooper and Eaton and in terms of Cheng's equation for tensile strength.The terms in these equations vary systemactically with the composition of the mixtures and they can be employed as a measure of the hardness and compressibility of the different mixtures.     

Ternary liquid—liquid equilibria: the van laar equation

The capabilities of the three suffix van Laar equations in predicting the more complex types of ternary liquid—liquid phase diagrams have been examined. While the limitations enforced by thermodynamic consistency on the binary parameters seriously affect the quantitative accuracy with which correlations can be achieved, the van Laar equations are capable of describing qualitatively a variety of complex phenomena. In the system water, n-hexane, phenol, the eruption of a three liquid phase region inside a binodal curve as temperature is decreased is accounted for by the van Laar equation. The similar eruption of a three liquid phase region inside a band in the system glycol, lauryl alcohol, nitroethane is also described. A variety of other types of computed phase diagrams, all of which (save one) have experimental counterparts, are presented. It is also shown that the van Laar equation is capable of quantitatively correct correlation of data for some selected simple systems.     

Mechanism of fibrillation in the flow of molten polymer mixtures

Experiments on the flow of melts of mixtures of thermodynamically incompatible polymers show that ultra-fine fibrils of one of the polymers form in the matrix of the other in the entrance to the extrusion orifice.     

On shape normalization for non-uniformly active catalyst pellets

The possibility of shape normalization of catalyst pellets with non-uniform catalytic activity profiles is examined. A first order isothermal reaction occurring in slab or spherical catalyst pellets, with a variety of activity profiles, is considered. Analytic solutions for the effectiveness factor are reported in all cases. When the catalytic activity at the external surface of the pellet is non-zero, a physically significant normalization of the Thiele modulus is suggested which makes the asymptotic behavior of the effectiveness factor identical for all pellet shapes and all activity profiles. For an operational range intermediate between kinetic and diffusion control, however, the normalization can lead to significant errors. No such normalization exists when the surface catalytic activity is zero.     

Changes in physicochemical properties of active carbon within a grain

Commercial active carbons were subjected to abrasion in a spouted bed and as a result, active carbons, with external layers removed to different degrees, were obtained. For active carbons so obtained, physicochemical properties were determined from densimetric and adsorption investigation.It was found that radial changes in the properties of active carbons resulted from the nature of the activation reaction.It seems that the method of working by abrasion in spouted beds can also be used for investigating other processes taking place in fluid—solid system.     

The effect of catalyst temperature zoning on hydrotreating a coal-derived liquid

The effect of catalyst temperature zoning on hydrotreating reactions, coke formation, and changes in catalyst surface area and pore volume was examined. A coal liquid was hydrotreated with the top zone operated in the range of 400–500° C (752–932° F) while the lower zone was maintained at 400° C (752° F). Increasing the top zone from 400° C (752° F) to 450° C (842° F) had beneficial effects on hydrogenation, HDN, and HDM at no cost of increased catalyst coke content. A further temperature increase was detrimental because of excessive coking and possible thermodynamic equilibrium limitations.     

Acidization III—The kinetics of the dissolution of sodium and potassium feldspar in HF/HCl acid mixtures

The dissolution of a potassium and a sodium feldspar in hydrochloric-hydrofluoric acid mixtures was studied in a rotating disk system at 25 and 100°C under a pressure of 40 psig. Under these conditions, the dissolution rate is limited by the rate of reaction of the acids with the solid surface.The rate of dissolution may be described by the following type of rate law:

The parameters a and b for potassium feldspar have the values 0·4 and 1·2, respectively, whereas for sodium feldspar both have a value of 1·0. A mechanism for the dissolution reaction is proposed which is consistent with experimental observation. The analysis suggests that the dissolution is limited by the rate at which the hydrofluoric acid reacts with the solid surface and that the strong influence of the hydrochloric acid on the dissolution rate is due to the adsorption of hydrogen ions on the mineral surface.     

Standard potentials of the silver—silver bromide electrode in dioxane—water mixtures and related thermodynamic functions

The standard potentials of AgAgBr electrode in eighteen dioxane + water solvent mixtures containing up to 90 wt % dioxane, have been evaluated from the emf measurements of the cell Pt, H₂ (g, 1 atm); HBr (m), X % dioxane, Y % water: AgBr, Ag at nine different temperatures in the range 15–55°C. The standard molal potentials in each solvent have been represented as a function of temperature. The standard thermodynamic functions for the cell reaction, the primary medium effects of various solvents upon HBr and the standard thermodynamic quantities for the transfer of one mole of HBr from water to the respective dioxane + water media have been computed and discussed in the light of ion—solvent interactions as well as the structural changes of the solvents.     

Thermodynamic studies of sodium bromide in 2-propanol—water mixtures (10, 30 and 50 wt.%) from electromotive force measurements

The emf of the cell: Pt|Na(Hg)|NaBr(m), w wt.% 2-propanol—water mixture|AgBr, Ag has been measured with w = 10, 30 and 50 at temperatures of 293.15, 303.15 and 313.15 K in the molality range of NaBr from 0.04 to 0.18 mol kg^?1. From these data the standard emf of the cell has been obtained and by utilizing data from the literature for the E⁰ of Ag/AgBr electrode the standard potential of sodium amalgam electrode has been determined. Mean activity coefficients of NaBr and thermodynamic functions ΔG⁰_t, ΔH⁰_t and ΔS⁰_t for transfer of NaBr from water to 2-propanol—water mixtures have also been calculated. Thermodynamic quantities of transfer have been compared to those for the HBr electrolyte.     

Selective solvation of silver(I) bromate in methanol—acetonitrile and ethanol—acetonitrile mixtures at 30°C

The selective solvation of silver(I) bromate in the binary solvent mixtures of methanol + acetonitrile and ethanol + acetonitrile has been studied at 30°C by solubility and emf measurements. The solubility of the salt increases with the addition of acetonitrile up to a mole fraction (X_AN) of 0.6 and 0.7 in the case of methanol + acetonitrile and ethanol + acetonitrile respectively and then decreases with further addition of the same. The transfer free energy of the silver ion (molal scale) decreases continuously with the addition of acetonitrile in both the mixtures. The transfer free energies of bromate ion (molal scale) are found to be quite small up to X_AN ≈ 0.7 in both methanol + acetonitrile and ethanol + acetonitrile mixtures and then increase. The solvent transport number Δ, of acetonitrile is positive with a maximum at X_AN = 0.55 (Δ = 2.7) and at X_AN = 0.45 (Δ = 2.2) for methanol + acetonitrile and ethanol + acetonitrile systems respectively. These results have been interpreted as arising due to a heteroselective solvation of the salt with the silver ion being preferentially solvated by acetonitrile and the bromate ion by the amphiprotic component which is marked especially at higher compositions.     

Walden product, ion-solvent interactions and solvent structure in water-rich mixtures ionic conductances in water-sulfolane, water-acetonitrile and water-dimethylsulfoxide

Conductance measurements are reported for several salts in binary aqueous mixtures containing up to 60 mole % sulfolane, 20 mole % acetonitrile and 20 mole % dimethylsulfoxide. The variations of R = (λ^±₀η₀)_s/(λ^±₀η₀)_w with solvent composition have been compared with those observed in other water-rich mixtures. Alkali cations show R values greater than one with maxima in all the solvent mixtures. This behaviour has been discussed in terms of “sorting”, “averaging” and “steric” effects. Contrary to what happens to alkali cations, halide ions show R values greater or lesser than one according to whether the organic solvent respectively increases or decreases water structure. On these bases we suggest that conductometric behaviour of the halide ions may be indicative of the effect of the cosolvent on the water structure in water-rich mixtures and that DMSO is a water structure breaker.     

The electrochemical oxidation of lead in various H2OH2SO4 mixtures—II. Ring-disc electrode study

The rotating ring-disc electrode technique was used to study the generation of soluble Pb(II) species during the anodic oxidation of the lead electrode in various H₂OSO₄ media. The concentration range extended from 0.06 to 10.3 M H₂SO₄. For every concentration it was possible to detect a small cathodic ring current variation which was attributable to the reduction of Pb(II) to Pb. Quantitative measurements of the collection efficiency showed that the small cycle life of the lead-acid battery in 5.6 M H₂SO₄ cannot be ascribed to the dissolution step.     

Carbon dioxide transport through enzymatically active synthetic membranes

The facilitated transport of CO₂ through thin liquid membranes, Millipore filter membranes, and cross-linked protein membranes has been investigated using a tracer ¹⁴CO₂ technique. Both the uncatalyzed reactions and the enzymatic reactions catalyzed by carbonic anhydrase in homogeneous solution and immobilized in several membrane configurations were studied. The steady-state transport data were reduced in terms of an analytical model for simultaneous reaction and diffusion which permitted the direct determination of the diffusional and enzyme kinetic parameters. The experimental method illustrates a powerful technique for measuring rapid reaction kinetics. In addition, a general multi-layer membrane model is developed which is capable of treating membrane kinetic heterogeneities. The multi-layer model yields a useful definition for the reaction boundary layer and provides a comparison among different membrane kinetic configurations for membrane design purposes.     

Adsorption of HCN and H2O vapor mixtures by activated and impregnated carbons

Adsorption isotherms for HCN-H₂O vapor mixtures have been determined on BPL grade activated carbon and on ASC whetlerite (impregnated) carbon. The results show that the adsorption of HCN by carbons which are already in equilibrium with high levels of water vapor is significant. Adsorption of HCN strongly dominates when HCN and H₂O are simultaneously adsorbed from the vapor phase. Adsorbed HCN discourages additional adsorption of water vapor.     

The electrochemical oxidation of lead in various H2OH2SO4 mixtures—I. Linear sweep voltammetry

The linear sweep voltammetry technique was used in order to detect a change in the lead oxidation mechanism around 5 M H₂SO₄. This change could explain the strong decrease in cycle life of the lead-acid battery when increasing H₂SO₄ concentration from 4.7 to 5.6 M. In the concentration range studied (3.6–10 M) no change was detected. The same behaviour was observed when cycling the electrode, when increasing sweep rate and when rotating the electrode.     

Study of Pb(II) in various H2O-H2SO4 mixtures by differential pulse polarography: solubility of lead sulphate,diffusion coefficient of Pb(II) and half-wave potential of Pb(Hg)/Pb(II)

A study of some properties of Pb(II) in solutions of sulphuric acid was carried out by means of differential pulse polarography. The range of concentrations of acid extended from 0.6 to 70 weight % of H₂SO₄ (0.06-11.5 M). Determination of the solubility of lead sulphate was found to be in good agreement with NBS's results in the range of H₂SO₄ concentrations they studied. With increasing concentration in H₂SO₄, the diffusion coefficient was found to decrease more than expected from the Stokes-Einstein equation, while the standard potential of Pb/Pb(II) related to she was found to increase. This led to a more important self-discharge of the negative electrode of the lead-acid battery.     

Conductance measurements of some electrolytes in N, N-dimethylformamide and in binary mixtures of N, N-dimethylformamide containing some organic bases and acetonitrile

Equivalent conductances of Bu₄ NBPh₄ Bu₄ NNO₃ NI, KI, NaBPh₄, Ph₄ PCl and AgNO₃ in N, N-dimethylformamide (DMF) and in binary mixtures of DMF containing 1 mol % of pyridine (Py), α-picoline (α-Pic), β-picoline (β-Pic), γ-picoline (γ-Pic) and acetonitrile (AN) have been measured at 25°C. Limiting ion conductances have been obtained by the method of Fuoss and coworkers [J. Solution Chem. 3, 45 (1974); ibid. 4 (1975)]. The actual solvated radii of ions, calculated using limiting ion conductances show that Ag⁺ possesses very strong preferential solvation by all the bases and by AN, while Na⁺ and K⁺ do not have preferential solvation by these solvents. DMF, though, is more basic than AN, but it does not show preferential solvation for Ag⁺ while AN does.     

A generalized corresponding states method for the prediction of the thermal conductivity of liquids and liquid mixtures

We have recently developed an extension of the three parameter corresponding states principle based on the properties of two non-spherical reference fluids for the viscosity of liquids and liquid mixtures. We extend the method here to the thermal conductivity. We have tested the method for a large number of binary liquid mixtures using the two pure components in each case as our reference fluids. Good agreement between predicted and experimental thermal conductivities was obtained using only the data for the pure components. This agreement becomes excellent if a single binary interaction consta independent of temperature and composition, is used in the mixture calculations. If the pure component reference properties are not available, then the may he obtained from the properties of two similar fluids.     

Studies of the Effects of Particle Size Distribution on the Packing Efficiency of Particles

In the studies of pigment volume effects in paint films, particle packing has been shown to be very important. The effects of particle size distribution on this packing has been known but has received little quantitative consideration. In this paper we consider the packing of real and model continuous distributions of particle sizes. An extension of an algorithm for the calculation of random densest packing is given which applies to continuous distributions. Using a log-normal distribution as a model, the effect of the width of a single distribution on packing is considered. Mixtures of distributions are also considered with the calculation of packing efficiency as a function of mean size ratio and distribution widths. Maxima are shown to occur in the packing efficiency of mixtures of distributions as a function of the volume fractions of the individual distributions. The implications of these packing variations in real systems are then discussed.