Petroleum Chemistry (v.53, #8)

Percolation of composite poly(vinyltrimethylsilane) membranes with carbon nanotubes by A. M. Grekhov; Yu. S. Eremin; G. A. Dibrov; V. V. Volkov (549-553).
Recent years have seen a flurry of activity in research on the use of nanoparticles to improve the properties of polymeric membranes. It is known that the change in the macroscopic properties of these hybrid materials is associated with the parameters of the cluster of incorporated nanoparticles. The percolation threshold is higher than 15 vol % for the spherical particles and decreases with the increasing aspect ratio of the embedded nanoparticles of another shape. The paper presents the results of study on the permeability of gases (N2, O2, CH4 and C3H8) and a test liquid (ethanol) through hybrid membranes based on the glassy polymer poly(vinyltrimethylsilane) (PVTMS) with embedded multiwall carbon nanotubes (MWCNT) with a concentration of 0.3–3 wt %. It has been found that the permeability of gases and liquids alters at MWCNT concentrations above 0.4 wt %, which corresponds to the percolation threshold for the given particles as proved by calculations. In addition, the gas permeability coefficients measured indicate a change in the transport mechanism and selectivity of the membrane.
Keywords: PVTMS; MWCNT; MMM; hybrid membrane; percolation; diffusion; gas and liquid transport

The Database “Gas Separation Properties of Glassy Polymers,” which was developed at the Topchiev Institute of Petrochemical Synthesis, Russian Academy of Sciences in the late 1990s and updated at regular intervals, is presented in this paper. This database is currently not only an electronic handbook but also a useful tool to search for novel membrane materials with improved properties for solving traditional and new gas-separation problems and for testing various models using a large body of data. To date, the database was also appended with information on the free volumes of polymers measured by positron annihilation lifetime spectroscopy. Permeability coefficients can be calculated for novel polymers by means of a group contribution method using this database. The paper highlights some features of group contribution methods with specific examples.
Keywords: permeability coefficient; diffusion coefficient; selectivity; group contribution method

Controlling the barrier properties of polymer composites containing montmorillonite by N. V. Avagimova; A. Yu. Pulyalina; A. M. Toikka; O. M. Suvorova; A. D. Vilesov; G. A. Polotskaya (559-563).
The barrier and sorption properties of films based on composites of gelatin and siloxane rubber SKTN-A with additives of montmorillonite (MMT) have been studied. The barrier properties of the films have been evaluated from their permeability to dibromomethane and water by vacuum pervaporation. Using the example of these heteropolar liquids, it has been shown that the permeability of the composites can be regulated by introducing up to 7 wt % MMT into the polymer matrix. The barrier characteristics of the gelatin-MMT composites with respect to dibromomethane have been improved by a factor of 3–4 compared with the original polymer. In the case of a hydrophobic polysiloxane matrix, the effect of organomodified MMT* on the barrier properties is less significant.
Keywords: composites; gelatin; polysiloxane; montmorillonite; permeability; sorption

Complexation of ammonia and water with cellulose acetate upon transmembrane transport by I. V. Vorotyntsev; I. I. Grinval’d; I. Yu. Kalagaev; N. A. Petukhova; A. N. Petukhov (564-566).
The mechanism of transmembrane transport of ammonia and water through the cellulose acetate membrane has been determined. The data obtained by FTIR spectroscopy confirm the suggested mechanism of penetrant interaction with the polymeric matrix and provide evidence that complexation by hydrogen bonding involves donor groups, such as C=O, C-O-C, and OH. The sorption of water and ammonia is localized in character and occurs on active sites of the polymeric matrix via the formation of hydrogen bonds with both the hydroxy groups and the ester oxygen atoms of cellulose acetate.
Keywords: FTIR; ammonia; water; cellulose acetate; complexation; transmembrane transport; hydrogen bonds

Concentration history of pervaporation by E. P. Ageev; N. N. Matushkina; N. L. Strusovskaya (567-571).
The permeability and selectivity of the separation of aqueous organic solutions by pervaporation have been studied on semicrystalline poly(ethylene terephthalate) membranes and asymmetric amorphous polyvinyltrimethylsilane membranes in the presence of structural rearrangements initiated by the development of relaxation processes. Attention was focused on the concentration history, which lies in the fact that the permeability and the permeate composition depend on the concentration of the previous solution passed through the membrane at a fixed composition of the feed solution. It has been shown that micropores are formed in both membranes under certain pervaporation conditions and mass transfer occurrs through two competing transport channels. As a result, the oscillatory kinetics of pervaporation and the inversion of separation selectivity in a steady state are observed experimentally.
Keywords: separation processes; selective flux; target component; transport channels

The possibility of creating a vacuum in a membrane and maintaining the vacuum for many days during the osmotic membrane distillation (OMD) process has been experimentally shown. The limiting parameters of OMD with a vacuum have been evaluated as functions of external pressure, temperature, and temperature differential across the membrane. Equations and plots for calculation of the osmotic pressure and the temperature difference that stops the OMD process are presented.
Keywords: osmosis; osmotic membrane distillation; membrane; vacuum; pore volume; vapor pressure; osmotic pressure; surface curvature; surface tension

Hydrodynamics of a thermopervaporation flow membrane module with cylindrical spacers by V. A. Kirsh; I. L. Borisov; V. V. Volkov (578-584).
The influence of hydrodynamic flow of a butanol-water mixture on the thermopervaporation (TPV) permeate flux and the separation factor has been theoretically and experimentally studied. A possibility of enhancement of thermopervaporation with cylindrical spacers placed in the feed channel or with pulsating feed flow is illustrated by the example of thermopervaporation of a dilute 1-butanol aqueous solution through a PTMSP membrane in a plate-and-frame module. The flow and concentration fields in the planeparallel channel with cylindrical spacers arranged normally to the flow direction have been obtained by numerical solution of the Navier-Stokes and convection diffusion equations. The pressure drop in the channel and the normal diffusion flux of the target component at the feed side of the membrane, depending on the feed flow rate, have been calculated. It has been shown that even two cylindrical spacers can noticeably increase the diffusion flux to the membrane. It has been found that the spacer cross section shape (circular, elliptic, or rectangular) has a minor effect on the mass transfer and pressure drop in the channel. Multifilament highly porous spacers (fiber bundles), which advantageously exhibit a significantly lower resistance to flow compared with impermeable spacers with the same cross section, have been found to provide the maximum enhancement of the diffusion flux.
Keywords: thermopervaporation; spacers; plane-parallel flow module; PTMSP; butanol

A new approach to the separation of oil-in-water emulsions using coalescing filtration and membrane separation has been studied. The problem of membrane fouling during emulsion separation and fouling control methods are considered. A hybrid technology of separation of dilute fine oil-in-water emulsions has been developed. The membrane fouling reduction by coalescing filtration has been evaluated.
Keywords: coalescing filtration; oil in water; petroleum products; oil-in-water emulsion; microfiltration; ceramic membranes; fouling

An NMR study of a water-methanol solution sorbed in MF-4SK sulfonated cation-exchange membranes by D. A. Kritskaya; A. V. Chernyak; S. G. Vasil’ev; E. F. Abdrashitov; V. Ch. Bokun; A. N. Ponomarev; A. S. Dmitruk; V. I. Volkov (590-595).
Concentration dependences of self-diffusion coefficients (SDCs), self-diffusion activation energies for water and methanol, and chemical shifts of the protons of the hydroxyl groups δOH simultaneously in an external water-methanol solution and the solution sorbed in MF-4SK membranes have been studied by NMR. It has been revealed that the SDC of pure methanol and pure water sorbed in an MF-4SK membrane is 3–5 times lower than that outside the membrane. It has been found that, in the presence of a small amount of methanol, the SDC of water in the membrane is 1.5–2 times higher than the SDC of pure sorbed water. At a solution concentration of 0.1–0.5 mole fraction, the SDC values of water and methanol in the membrane vary only slightly and are about 6 × 10−6 and 4 × 10−6 cm2/s, respectively. It has been determined that the δOH value in the membrane is 100–200 Hz higher than that in the external solution. The observed increase in δOH and decrease in SDC in the membrane suggest that the state of the solution in the MF-4SK sulfonated cation-exchange membrane has significantly changed compared to the external solution. The effect of the implanted carbon phase (CP) on the SDC of water and methanol and δOH of the solution sorbed in the MF-4SK membranes containing the CP has been studied. It has been revealed that at a methanol mole fraction of up to 0.5, the introduction of 23 wt % CP decreases the SDC of the solution components by no more than 10–20%. At a methanol mole fraction of 0.25–0.5, the self-diffusion activation energies for methanol and water in the external and membrane solutions decrease by 5–7 kJ/mol.
Keywords: proton-exchange membranes; self-diffusion; pulsed field gradient (PFG) NMR

Structure and gas permeability of nanoporous metal oxide coatings produced by the alkoxide method by N. I. Lukyanova; A. A. Kirsankin; M. V. Tsodikov; V. V. Teplyakov (596-608).
Peculiarities of the preparation of selective nanoporous metal oxide coatings on the surface of macroporous rutile support (pore size 0.1 μm and mixed aluminum and titanium oxides (pore size 0.05 μm) are presented. Gas selective coatings of empirical formula of P x Ti1 − 0.5x O2 ± δ with uniform distribution of nanosized pores have been obtained with the alkoxide method using titanium alkoxide and ettriol phosphite (precursor of the phosphorous-containing component) at their various total concentrations. Surface morphology of the obtained membranes has been investigated and major parameters of gas selective coatings have been determined. It has been shown that the dependences of the He, N2, CO2, and C3H8 gas permeability on temperature and pressure drop are consistent with the molecular regime of gas flow. The reproducible effect of permeability anisotropy of ∼502?60% is observed when the integral vacuum method is used.
Keywords: nanoporous inorganic membranes; membrane surface morphology; gas separation; membrane catalysis

Current-voltage characteristics of metal-coated track membranes measured in air and vacuum by S. N. Podoinitsyn; T. V. Tsyganova; B. V. Mchedlishvili (609-611).
The current flow through metal-coated track-etched membranes in air and vacuum and its features associated with the presence of field-emission nanostructures on the membrane surface have been studied.
Keywords: track-etched membranes; metal coating; field-emission nanostructures; current-voltage characteristics; breakdown

Permeability of foil based on exfoliated graphite to C1-C6 alkanes by D. A. Syrtsova; E. A. Efimova; V. V. Teplyakov; S. G. Ionov; D. Roizard (612-618).
The results of a study of C1-C4 alkane gas permeability and C5-C6 alkane and methanol vapor permeability through pressed foil based on exfoliated graphite with a density of 1 g/cm3 are presented. It has been found that the permeability of the studied graphite foil to C4-C6 hydrocarbons is higher than calculated values; in particular, reverse selectivity for pairs such as H2/hydrocarbon and N2/hydrocarbon is observed. This can be due to a considerable effect of a surface flow on the total flow through the membrane.
Keywords: nanoporous inorganic membranes; gas separation; vapor separation; hydrocarbons

Elaboration of composite hollow fiber membranes with selective layer from poly[1-(trimethylsylil)1-propyne] for regeneration of aqueous alkanolamine solutions by V. V. Volkov; A. V. Bildukevich; G. A. Dibrov; V. V. Usoskiy; V. P. Kasperchik; V. P. Vasilevsky; E. G. Novitsky (619-626).
The results of research on elaboration of the hollow fiber composite membranes for regeneration of aqueous solutions of alkanolamines in membrane gas-liquid contactor are presented in this work. Asymmetric polysulfone (PSF) hollow fiber UF membranes were used as a porous support, poly[1-(trimethylsylil)-1-propyne] (PTMSP) was employed as a diffusion layer. The influence of PSF hollow fiber casting conditions on hydraulic permeability was studied. Samples of composite membranes were obtained with a defectfree layer of PTMSP and carbon dioxide permeance of 0.26 m3 (STP) (m2 h bar)−1. It was revealed by SEM that the thickness of the PTMSP separation layer is 2.5 microns, where in X-ray spectrometry analysis data and calculations according to resistance-in-series model discovered that the selective layer penetration depth to the pores of the support was 1.4 microns. Calculation by resistance-in-series model showed that 98.6% of resistance to the gas transport is attributed to PTMSP, partially intruded in the pores of the support. Chemical stability of materials which comprise composite membrane makes promising their using for regeneration of aqueous solutions of alkanolamines (pH > 11) from carbon dioxide at a temperature of 100°C and a pressure drop of 10 bar in the membrane gas-liquid contactors.
Keywords: carbon dioxide; membrane contactor-desorber; hollow fiber polymer membranes; composite membranes

Fine purification of silane for removal of chlorosilanes by membrane gas separation by V. M. Vorotyntsev; P. N. Drozdov; I. V. Vorotyntsev; S. N. Manokhina; S. S. Knysh (627-631).
The membrane separation of a silane, dichlorosilane, trichlorosilane, and tetrachlorosilane gas mixture has been theoretically and experimentally studied. The ideal separation factors have been determined experimentally and their values in the separation cell at pressures P 1 and P 2 have been found. The separation factor has been calculated for different ratios of flows in the compartments of a membrane module. The silane cleaning process for the removal of highly penetrating impurities in a radial membrane module and in a membrane module with a feed tank has been calculated.
Keywords: silane; chlorosilanes; membrane; polydimethylsiloxane; gas separation

Asymmetry of ion transport in hybrid MF-4SC membranes with a gradient distribution of hydrated zirconia by E. Yu. Safronova; I. A. Prikhno; G. Pourcelly; A. B. Yaroslavtsev (632-636).
Results of studies of the properties of hybrid MF-4SC membranes with a gradient distribution of hydrated zirconia nanoparticles through the thickness prepared by layer-by-layer casting from a polymer solution are described. The effect of the dopant concentration on the properties of the membranes is studied. At a low oxide concentration, the water uptake and ionic conductivity of the resulting samples increase compared to the original MF-4SC membrane. It is found that the diffusion permeability of HCl and NaCl solutions across these membranes exhibits an asymmetric behavior. It is shown that the diffusion permeability is higher in the case of diffusion of the solutions from the unmodified side of the membrane. The maximum asymmetry coefficient is obtained for a membrane containing 10% ZrO2 in the modified layer for the diffusion of 0.1 M HCl solution (38%). The causes of the diffusion permeability asymmetry are discussed.
Keywords: hybrid membranes; MF-4SC; ion transport; ion transport asymmetry; diffusion permeability