Showing papers on "Permeation published in 1970"

Separation of liquid mixtures by using polymer membranes. II. Permeation of aqueous alcohol solutions through cellophane and poly(vinyl alcohol)

Abstract: The permeation and separation characteristics of four different alcohol—water systems through cellophane and poly(vinyl alcohol) membranes were investigated. The homologous series of linear alcohols n-propanol, ethanol, and methanol as well as isopropanol were studied. A specially designed permeation cell was used to study permeation rates at temperatures ranging from 30° to 50°C. The dependency of both permeation and separation on the molecular size and shape of the permeating species was discussed qualitatively. The temperature dependence of the permeation rate for both pure compounds and binary mixtures was expressed by Arrhenius-type relationships. The rate was found to increase with increasing temperature while the separation decreased. Activation energies of 4–9 kcal/mole were calculated for alcohol—water solutions through cellophane, and of 8–15 kcal/through poly(vinyl alcohol). Departure of permeation rates from the ideal rates were discussed in terms of permeation “enhancement” or “depression.” These phenomena were explained in terms of both the plasticizing action of water and the “clustering” of water molecules within the polymer network.

Isobaric measurement of gas permeability of polymers

Abstract: The principles and design of a gas permeability measuring instrument based on thermal conductivity measurement are described. Since the thermal conductivity of a gas mixture is dependent upon the partial pressure fraction rather than absolute partial pressure of sample gas, and the permeation rate of reference and sample gases through polymer films differe considerably, a pressure-equalizing device is necessary for the accurate measurement of gas permeability. The three types of measurements—integral, differential (flow method), and decay rate measurements—can be used with the instrument. The results of permeability constants and diffusion constants obtained with the methods showed good agreement with the conventional vacuum-type method. With proper selection of methods, the instrument can measure the gas flux through the range of 10−10 to 10−3 cm3 (STP)/cm2 sec cm Hg. Some advantages of the methods are discussed.

A dynamic approach to diffusion and permeation measurements

Abstract: A dynamic method for investigating the mechanism of permeation and diffusion through polymers has been explored. The permeation cell consists of two compartments separated by the membrane. The permeant (gas, vapor, or liquid) is introduced into one compartment; a carrier gas (helium) flows at constant rate through the other and sweeps the permeant which diffuses through the membrane to the thermal conductivity detector. Both compartments are at atmospheric pressure; thus no or little membrane support is required, and leakage problems are minimal. Moreover, the same membrane can be used over a wide temperature range and for diverse permeants. The detector signal is at any instant proportional to the permeation rate. A simple mathematical formalism for deriving the diffusion coefficient from the transient permeation rates has been developed. The measured diffusion and permeability coefficients of CO2, O2, and N2 through low-density polyethylene closely agree with literature values. Permeation of hexane and benzene through polyethylene follows a complex diffusion law, and the rate depends on the thermal history of the system. The dynamic method is particularly suited to the study of transitions in polymers. Changes in permeation rates, usually occurring at transition points, can easily be discovered by slow temperature scanning of the system.

Actual Concentration Profiles in Membrane Permeation

Abstract: The concentration profiles and the concentration dependent diffusion coefficient, at steady-state liquid permeation, were investigated in plastic films by directly measuring the concentration profile. A stacked film packet was developed which permitted peeling of film sections and measuring incremental concentration of permeate. The membrane-permeate systems studied were: nylon 6-water, nylon 6-dioxane, cellulose acetate-water, and polyethylene-dioxane. Membrane thickness was varied from 2 to 53 mil and temperature from 35 to 75°C. Also, poylethylene-benzene and polyethylene–n.-hexane systems were studied at 17 mil and 35°C only. The analysis of the experimental data showed that the exponential model, D = 0 e α C , represented the directly measured concentration profiles to a satisfactory degree. The use of this exponential model leads to a linear variation of the diffusion coefficient with distance within the membrane, but nonlinear as a function of concentration.

Gel-Permeation Properties of Cellulose Part III: Measurement of Pore Structure of Unmodified and of Mercerized Cottons in Fibrous Form

Abstract: The gel permeation technique, initially investigated for measuring the pore structure of cotton cellulose decrystallized by ball-milling, has been adapted for application to the study of cotton in ...

Separation Mechanisms in Gel Permeation Chromatography

Abstract: This paper presents flow rate studies, vacancy chromatography, and a static mixing experiment. Data obtained on an unpacked column (a straight tube) and on a column packed with nonporous glass beads are also reported. The results reveal that peak dispersion in GPC arises mainly from lateral diffusion in the stationary phase (permeation in and out of the porous substrate) and from lateral diffusion in the mobile phase. GPC peak separation is mainly dominated by the process of steric exclusion. Pore size distribution data obtained on Bio-Rad porous glass are shown to illustrate the preference of random coil theories over theories of the equivalent sphere in the interpretation of steric exclusion of flexible polymers. The data are discussed in terms of Herman's diffusion theory and Cassasa's exclusion theory.

Gas Permeation Characteristics across Nano-Porous Inorganic Membranes

Abstract: An overview of parameters affecting gas permeation in inorganic membranes is presented. These factors include membrane physical characteristics, operational parameters and gas molecular characteristics. The membrane physical characteristics include membrane materials and surface area, porosity, pore size and pore size distribution and membrane morphology. The operational parameters include feed flow rate and concentration, stage cut, temperature and pressure. The gas molecular characteristics include gas molecular weight, diameter, critical temperature, critical pressure, Lennard-Jones parameters and diffusion volumes. The current techniques of material characterization may require complementary method in describing microscopic heterogeneity of the porous ceramic media. The method to be incorporated in the future will be to apply a stochastic model and/or fractal dimension. Keywords: Inorganic membrane, surface adsorption, Knudsen diffusion, Micro-porous membrane, permeation, gas separation.

Permeation separation membranes

Abstract: A MEMBRANE FOR THE SELECTIVE PERMEATION SEPARATION OF AQUEOUS MIXTURES, WHICH IS A THIN FILM OR HOLLOW FILAMENT OF A LINEAR ALIPHATIC POLYAMIDE RESIN CONTAINING A HYDROLYZABLE TANNIN.

Gel Permeation Properties of Cellulose: II: Comparison of Structures of Decrystallized Cotton Cross . Linked With Formaldehyde by Various Processes

Abstract: Application of gel permeation chromatography, which has been shown to be an effective means of measuring changes produced in the accessibility of decrystallized cotton cellulose by one form of form...

The permeation of gases through modified polymer films. II. Gas permeability and separation characteristics of gamma ray‐irradiated polyethylene

Abstract: A study has been made of the diffusion, solubility, and separation of nitrogen and methane gases in a series of air-and vacuum-irradiated polyethylene films in the temperature range of 15° to 50°C. Samples were air irradiated to 90 Mrads and vacuum irradiated to 80 Mrads. The major structural differences between the modified films were the presence of oxygenated species in the air-irradiated samples. The oxidation of these samples reduced the amount of crosslinking normally found in vacuum-irradiated samples. Diffusion and permeability coefficients for both gases decreased with irradiation dose. The solubility coefficients for the air-irradiated samples increased with increasing irradiation dose while little change was observed for vacuum-irradiated film. The gas mixture permeabilities could be predicted from the pure component permeabilities, and the methane–nitrogen separation factor decreased with increasing irradiation dose.

Evaluating dispersion in gel chromatography - Dispersion due to permeation

Abstract: Dispersion /peak broadening/ in gel chromatography measured with nonporous and porous column packings, suggesting diffusion controlled separation with linear permeation isotherm

Studies of Ion Exchange Membranes. XXXI. The Hydrogen Peroxide Treatment of the Cation Exchange Membrane of Ferric Ion Form

Abstract: Neosepta CL-2.5T, the cation-exchange membrane prepared by the “Paste Method,” of the ferric-ion form was treated with hydrogen peroxide, and the changes in the membrane properties (the thickness, the water content, and the ion-exchange capacity) were measured. The porous membrane, having no ion-exchange capacity, was obtained by the treatment with hydrogen peroxide and the water permeation through the membrane was measured. Assuming the capillary model, the water-permeability data of this membrane suggested that the apparent pore radius of this membrane was 15–17 mμ and that the apparent pore distance was about 40 mμ. This suggests that Neosepta CL-2.5T contains a minute and continuous heterogeneity; i.e., there is a localized distribution of the ion-exchange resin component within the membrane.

Liquid membrane separation process

Abstract: A PROCESS FOR SEPARATING COMPONENTS OF A HYDROCARBON MIXTURE BY SELECTIVE PERMEATION THROUGH A LIQUID SURFACTANT MEMBRANE CONTAINING A POLAR ADDITIVE.

Fast Gel Permeation Chroma tog raphy

Abstract: A systematic study of the major factors influencing fast analysis by gel permeation chromatography is presented. The study included the effects of (a) solvent flow rate [1–35 ml/min], (b) sample concentration [0.05–0.5%], (c) sample molecular weight [41–411,000 mol wt] and (d) particle size of column packing [10–42μ]. The effect of the operating temperature at the high flow rates was also investigated.

Enhancing the permeation characteristics of polyethylene by membrane irradiation in the fully swollen state.

Abstract: Fully swollen, low-density polyethylene films were irradiated, vacuum dried, reswollen, and subsequently permeability tested using tritiated toluene and benzene as penetrants. The treatment improved the permeability of polyethylene up to 88%, with the enhancement strongly dependent on the choice of the irradiation solvent. These results suggest a potentially practical process for improving the performance of semipermeable membranes.

Fractionation of Residuals by Gel Permeation Chromatography

Abstract: Gel permeation chromatography has been effectively used for the fraction-ation of residuals. The preparative-scale gel permeation chromatograph employed for these studies is described along with selected operating parameters. The instrument has been used to fractionate a shale oil residue, 50% reduced crude, and 25% reduced crude, into fairly narrow molecular weight fractions. The individual cuts from each residual have been analyzed and the elemental distribution established. The trends of heteroatom distribution, i.e., nitrogen, sulfur, nickel, and vanadium, as a function of molecular weight for the various residuals are discussed.