Multicomponent gas separation by an asymmetric permeator containing two different membranes

A numerical analysis of an asymmetric permeator containing two different kinds of membranes and capable of separating a ternary feed gas mixture into three product streams has been carried out. For negligible axial pressure drops in the gas streams, equations have been developed and calculation methods illustrated for four flow patterns: cross, parallel, countercurrent and perfectly mixed. The main parameters used in the analysis are pressure ratios, the ratio of the two membrane areas and the permeabilities. Results have been presented for a 50% H₂10% CO₂40% N₂ feed with a permeator having one cellulose acetate (CA) type membrane and one silicone membrane. For both permeate streams, countercurrent achieves highest permeate qualities and requires least membrane area amongst all four flow patterns. The presence of a silicone membrane produces a richer H₂ permeate from the CA membrane than that from a CA-membrane-alone configuration. Simultaneously, an enriched CO₂ permeate is obtained from the silicone membrane. Under the ideal condition of zero pressure ratios, the asymmetric permeator has also been evaluated against the series configuration of a permeator containing a CA membrane only followed by a permeator containing only a silicone (S) membrane. The asymmetric configuration usually performs better than this series configuration for the chosen range of parameters.     

The behaviour of ruthenium anodes in base

Cyclic voltammograms were recorded for ruthenium metal in base as a function of sweep limit and hydroxide ion concentration. A variety of both soluble and insoluble corrosion products were observed and an attempt was made to identify the various processes taking place on the basis of known data for this system. The development of a charge storage film under potential cycling conditions, as on iridium and rhodium, was noted. Current flow under potentiostatic conditions below 2.2 V was attributed largely to metal corrosion, the overpotential for oxygen evolution, which was observed only at higher values, being unusually high under these conditions. The vast difference in corrosion behaviour and rates of oxygen evolution between thermally and anodically prepared ruthenium oxide films was attributed to stronger bonding of surface ruthenium ions in the case of the thermally treated lattice. The pronounced effect of stirring on the anodic reactions of the metal in base was attributed to rapid removal of the weakly adherent surface oxide layer.     

Discrete resistance changes in thin lipid membranes

Semispherical membranes were formed using a mixed lipid preparation extracted from beef brain gray matter. The membrane obtained had a thickness between several hundred angstroms and about one thousand angstroms as determined by the interference color of reflected light. The initial thick membrane and newly formed primary black membrane had a resistance greater than 10¹⁰ ohms, similar to that of the bulk lipid phase. However, when a small (< 15 mV) transmembrane potential was applied, the resistance decreased in a stepwise fashion to a final resistance of about 10⁵10⁶ ohms. The resultant thin membrane exhibited stepwise temperature-dependent fluctuations in conductance similar to those obtained with membranes to which substances such as the “excitability-inducing material” of Mueller and Rudin and certain ionophores have been added. Further, the membrane showed rectification when calcium was present on only one side of the membrane.     

An analysis of carrier-mediated photodiffusion membranes

Reversible photochromic reactions can be combined with carrier-mediated transport in partially illuminated membranes to achieve very high degrees of flux enhancement. Transport across these membranes can be achieved even against a concentration gradient. Coupled systems of non-linear diffusion-reaction equations for these membranes were solved using the technique of orthogonal collocation on finite elements to study and optimize the transport across them. The results indicate that the efficiency of light utilization is maximum for thin membranes at low degrees of illumination. Carrier-mediated photodiffusion membranes in combination with a fuel cell can be used for the storage of solar energy.     

Phase inversion sulfonated polysulfone membranes

The use of two nonsolvents serving as a cosolvent system, replacing the traditional volatile solvent plus less volatile nonsolvent system, in the formation of asymmetric phase inversion membranes was investigated. Specifically, asymmetric membranes of sulfonated polysulfone were cast from a cosolvent system consisting of tetrahydrofuran and formamide. The nonsolvents and the proportions in which they are mixed to produce the cosolvent system, as well as the gelation medium isopropyl alcohol, were selected based on the three-component solubility parameter concept of Hansen. The structure of each membrane was evaluated using scanning electron microscopy; the performance was evaluated for use in pressure-driven membrane separation processes. The membranes were found to be dependent on the composition of the original casting solution and the composition of the nascent membrane at the instant of gelation. These ideas are clearly represented through the use of a triangular polymer solubility diagram.     

Quantitative description of the rejection of polymeric catalysts by ultrafiltration membranes

The rejection capability of ultrafiltration membranes for polymeric catalysts like enzymes was measured under well defined conditions. A simple model has been developed to describe the course of retention during continuous operation. Even at very low concentrations of the polymer, a significant influence of concentration polarization on the retention could be found. The course of retention could be described numerically simply by using distribution parameters for the pore size of the membrane and the particle size of the polymeric catalyst.     

Application of ion-exchange reactions between membranes and resins

The separation of a solution of an electrolyte from an ion-exchange resin by an ion-exchange membrane, where the charge sign of the fixed sites is the same, results in a process that is comparable to Donnan dialysis in its overall effect. That is, the counter-ions from the resin can be exchanged for ions of the same charge sign in the electrolyte. The reaction is demonstrated and the efficiency of the process evaluated by monitoring the metathesis of carbonic acid from sodium carbonate. An application of the metathesis of a non-electrolyte to a preconcentration method for ion chromatography is demonstrated.     

Chirality changes in reactions of asymmetric molybdenum complexes

Optical rotatory dispersion and circular dichroism studies have allowed the determination of the changes in configuration at the molybdenum center upon displacement of carbonyl and iodide in neomenthylcyclopentadienyl—Mo(allyl)(NO)X systems. Displacement of carbonyl by iodide occurs with retention of configuration. Replacement of iodide with benzenesulfonate followed by replacement of the sulfonate with iodide occurs stereospecifically with net retention of configuration. In the case of cyclopentadienylMo(cyclooctenyl)(NO)I, the enantiomers were separated via a spontaneous resolution through crystallization of the complex in the space group P2₁2₁2₁. These studies have allowed the correlation not only of the absolute configuration at the metal center with CD studies, but also have established that a long wavelength optically active transition at approximately 400 nm can be correlated with endo-exo isomerism. Comparison of the rates of interconversion suggest that endo to exo isomerization occurs via a clockwise rotation of the allyl in the (R)-isomer. Crystallographic details: (—)-(S)-(NMCp)Mo(allyl)(NO)I crystallizes in the space group P2₁2₁2₁ with a 7.221(1), b 12.686(7), c 21.603(7) Å, Z = 4, V = 1979(2) ų; R₁ = 0.039, R₂ = 0.046; (—)-(S)-(Cp)Mo(cyclooctenyl)(NO)I crystallizes in the space group P2₁2₁2₁ with a 8.466(1), b 10.449(2), c 16.372(2) Å, Z = 4, V = 1448.3(6), R₁ = 0.038, and R₂ = 0.046.     

Electrokinetic phenomena in porous membranes: Determination of phenomenological coefficients and transport numbers

Electrokinetic phenomena in porous membranes were studied in the framework of the linear thermodynamics of irreversible processes. Phenomenological coefficients of two commercial porous membranes were determined. The variation of these coefficients with the different concentrations of NaCl used was also studied. Onsager's reciprocal relationship between cross-coefficients holds within the limits of experimental error.Membrane potentials were measured at concentrations ranging from 10^?3M to 75 X 10^?3M. The apparent transport number of the cation,

, was calculated from the diffusion potential expression. An electrometric method was used to obtain the true cation transport number,

, and the water transport number,

, for different solution concentrations, ranging from 15 x 10^?3M to 75 x 10^?3M. The true transport number of the cation,

, was also determined, taking into account water transport across the membrane. A good agreement was found between

and

values.     

Study of the behaviour of various phenolic compounds in the 4-aminoantipyrine and ultraviolet-ratio spectrophotometric methods without and with distillation

It is customary in industrial analysis in the determination of phenols by the 4-aminoantipyrine (4-AAP) and ultraviolet-ratio spectrophotometric methods to report the total of phenolic compounds as phenol. A study was therefore made of the behaviour of 36 representative phenolic compounds in the 4-AAP and UV-ratio methods, with and without distillation, to ascertain the apparent recoveries relative to that for phenol. The Fisher phenol analyser was used for the UV-ratio method, which depends upon the bathochromic shift (from about 270 to about 290 nm) usually obtained when the solution of the phenol is made alkaline. The apparent recoveries by the 4-AAP method both with and without distillation varied from 0 to 100%. The apparent recoveries by the UV-ratio method without distillation varied from 0 to 148%, and those with distillation varied from 0 to 110%. Sixteen of the compounds tested without distillation gave less than 10% recovery by the 4-AAP method and eleven gave less than 10% recovery by the UV-ratio method. The results after distillation indicated that several of the compounds did not distil completely.     

539—electrochemical behaviour of low-potential electron-transferring proteins at the mercury electrode

This paper reports on a pulse polarographic study of low-potential electron-transferring proteins at the mercury electrode ★. The proteins studied were the negatively charged iron—sulphur cluster containing ferredoxins from spinach, and from Megasphaera elsdenii, the iron-containing rubredoxin and the FMN-containing flavodoxin both from M. elsdenii. Furthermore, the positively charged, four haem-containing cytochrome c₃ from Desulfovibrio vulgaris strain Hildenborough was studied. It was observed that the electrode reaction of these proteins could be made much more efficient when a polymer or surfactant was added, with a charge opposite to the protein. The reduction efficiency of these proteins reaches an optimum when the net charge of the protein times its concentration is about equal to the same amount of opposite charges, which was added as a polymer or surfactant.     

Transport of organic acids through perfluorosulfonate polymeric membranes

Carboxylic acids in aqueous solutions permeate through perfluorosulfonate merebranes. The permeation is significantly enhanced when the sulfonic acid groups are convetted to their sodium salt form. Transport fluxes at atmospheric pressure have been found to vary in the 10^-9—10^-6 mol/cm²-sec range, depending on the nature of the acids. Interesting separation possibilities of carboxylic acids from one another or from nonpolar compounds are discussed.     

The electrochemical behaviour of cobalt in alkaline solutions Part I. The potentiodynamic response in the potential region of the Co/CoO couple

The potentiodynamic response of cobalt in KOH solutions (10^?2M?c?2.5 M) in the potential range of the thermodynamic stability of the Co(II) species reveals two limiting electrochemical behavirours. One of them corresponds to the first potentiodynamic scan and the other is associated with the stabilized E/I profile resulting after a prolonged potential scanning. The former is related to the large contribution of the metal electrodissolution process. The second is explained in terms of reactions taking place at the sandwich-type structured interface. Ageing effects of Co(II) surface species are also considered in the interpretation of results.     

Analytical properties of the amidoxime group: Part VI. Electroanalytical behaviour of ethanediamidoxime

The electroanalytical behaviour of ethanediamidoxime (EDA) has been studied at 0.1 mol l^?1 ionic strength and several pH values (1.75–8.62), using several techniques (dc and DP polarography, chronocoulometry, dc and DP cyclic voltammetry). EDA undergoes an irreversible diffusion-controlled reduction in the entire pH range considered. The best conditions for identification and determination of EDA with the techniques mentioned are also studied.     

Separation of metals by liquid surfactant membranes containing crown ether carboxylic acids

A water-in-oil-in-water emulsion liquid membrane system is used to transport alkali metal and alkaline earth cations from an external alkaline aqueous source phase through an organic membrane containing a crown ether carboxylic acid and into the internal acidic aqueous phase of the emulsion droplet. The influence of varying the crown ether carboxylic acid structure upon the selectivity and efficiency of competitive metal ion transport is examined.     

The thermal behaviour of solid phases in the TeSeO2 system

A comparative study is made of the thermoanalytical stabilities of various tellurium and selenium mixed oxides (TeSeO₄, Te₂SeO₆, Te₃SeO₈, Te₄SeO₁₀ and Te₈SeO₁₈). The observed stabilities are then approximately correlated with data given by a kinetic analysis of the thermal decomposition processes in the non-isothermal regime obtained from TG and DSC by using two calculation methods (Freeman and Carroll and modified Freeman and Carroll).     

Water in polymer membranes. Part III : Water sorption and pore volume in cellulose acetate films

Changes in waveguide properties of several cellulose acetate membranes and one polyimide membrane were measured as a function of their exposure to varying levels of relative humidity. The volume fraction of water in the films and the occupied pore volumes were determined from refractive index and thickness changes. The dependence of the refractive index on water absorption is related to a competition between two processes: one of filling pores with no film expansion and one of “free expansion” where the film expands to completely accommodate the added water volume. The term “pore” is taken to mean a volume with molecular and not macroscopic dimensions. The hydration properties of these dense cellulose acetate membranes were affected by degree of acetylation, casting temperatures and annealing treatments. Annealing CA398 membranes at 180°C decreased film water concentration by reducing the amount of free expansion. Annealed CA398 membranes that were tested in a reverse osmosis cell were found to have high salt rejection compared to unannealed films. The hydration characteristics of a polyimide membrane are compared to cellulose acetate membranes.     

Transport of alkali metal cations across liquid membranes by crown ether carboxylic acids

Competitive alkali metal transport from an alkaline aqueous source phase through a chloroform phase to an acidic aqueous receiving phase facilitated by nine crown ethers with pendant carboxylic acid groups has been investigated. Transport selectivity is controlled by the size of the polyether cavity of the carrier. Increasing the lipophilicity of the carrier, while maintaining a constant polyether cavity size, enhances the total transport rate but does not affect the selectivity. There is poor agreement between the results of competitive transport and the behavior anticipated on the basis of single cation transport studies.     

The phase-separation behaviour of aqueous solutions of polyacrylic acid and its partial sodium salts in the presence of sodium chloride

Phase-separation temperatures have been measured for polyacrylic acid dissolved in aqueous sodium chloride solutions over a range of ionic strengths, degrees of neutralisation, polymer concentrations and molecular weights. The data are used to derive θ-temperatures for this system. The dependence of the θ-points on ionic strength and degree of ionisation is discussed and the results are briefly compared with data for other polyelectrolytes.