I. L. Borisov

Simulation of the temperature-driven pervaporation of dilute 1-butanol aqueous mixtures through a PTMSP membrane in a cross-flow module

The selective thermal pervaporation (TPV) of dilute aqueous mixtures of 1-butanol through a hydrophobic poly(1-trimethylsilyl-1-propyne) (PTMSP) membrane in plate-and-frame modules with an air gap has been investigated experimentally and theoretically for the first time. The dependences of the composition and the permeate flow on the temperature and initial concentration of the mixture, the liquid coolant temperature, and the membrane thickness have been measured. It has been shown that a permeate flow across the PTMSP membrane can be achieved in the TPV mode that is not inferior to that of vacuum pervaporation at condensation temperatures of 0.5–15.0°C. The permeation and diffusion activation energies have been estimated from the measured temperature dependences of the partial fluxes. Equations for the TPV process have been derived in terms of the one-dimensional resistance model. The temperature dependences of the diffusion coefficients of 1-butanol and water in the membrane have been determined, and the linear temperature and concentration fields of the components in the module for membranes of different thickness have been calculated from the experimental data using these equations.

Hydrodynamics of a thermopervaporation flow membrane module with cylindrical spacers

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.

A novel hybrid material based on polytrimethylsilylpropyne and hypercrosslinked polystyrene for membrane gas separation and thermopervaporation

To improve the membrane permeability and separation properties in gas separation processes and thermopervaporative (TPV) recovery of butanol from model fermentation mixtures, hybrid membranes based on polymers with an extremely high free fractional volume—polytrimethylsilylpropyne (PTMSP) and hypercrosslinked polystyrene (HCL-PS)—have been first prepared and experimentally studied. The composite membranes have been fabricated using the commercial sorbent Purolite Macronet MN-200 exhibiting high sorption capacity for organic solvents. It has been found that in the hybrid membranes, HCL-PS sorbent particles are nonuniformly distributed throughout the volume: they are located in the surface layer of the membrane. It has been shown that the introduction of a small amount of a modifying component (0.5–1.0 wt %) into the PTMSP matrix improves the time stability of transport properties and increase by a factor of 1.5–2 the permeability coefficients of the material to light gases (N2, O2, CO2, CH4) and butane vapor. It has been found that hybrid PTMSP/HCL-PS membranes have higher separation factors than those of PTMSP membranes in the TPV separation of a butanol/water binary mixture.

Membrane material based on octyl-substituted polymethylsiloxane for separation of C 3 /C 1 hydrocarbons

Novel one-step technique has been proposed for octyl-substituted polymethylsiloxane (POMS) synthesis and vulcanization. The technique makes it possible to prepare С3/С1 selective gas separation membranes. The fact of POMS formation and vulcanization by hydrosilylation reaction involving 1-octene and polymethylhydrosiloxane has been confirmed by IR spectroscopy data. On the basis of the results obtained by measuring permeability of POMS membranes to permanent gases and propane, a preferred modifier to crosslinker ratio at which polymer films with the best gas transport properties can be obtained has been estimated at 95/5. Experimentally determined permeability coefficients for methane and propane (270 and 1560 barrer, respectively) and ideal propane/methane selectivity of 5.8 allow for the conclusion that POMS obtained in the study has transport properties comparable to those of similar membrane materials reported in the literature as obtained via multistep synthesis.

Polydimethylsilalkylene-dimethylsiloxanes as advanced membrane materials for thermopervaporative recovery of oxygenates from aqueous reaction media

Polydimethylsildimethylene-dimethylsiloxane (PSDMS) and polydimethylsiltrimethylenedimethylsiloxane (PSTMS) have been first studied as pervaporation membrane materials for the recovery of butanol from aqueous media. New synthesis procedures that make it possible to obtain the monomers 2,2,5,5-tetramethyl-1-oxa-2,5-disilacyclopentane (1) and 2,2,6,6-tetramethyl-1-oxa-2,6-disilacyclohexane (2) in high yields and with high purity required for subsequent polymerization have been developed. The optimum concentration of the crosslinking agent (tetraethoxysilane (TEOS)) of 5% has been found, which provides the maximum degree of crosslinking without sacrificing high values of separation factor and permeate flux. It has been shown that the permselectivity of PSDMS or PSTMS for butanol–water is higher by a factor of 1.5 or- almost 2, respectively, than the selectivity of the industrial membrane polymer, PDMS, at comparable values of the butanol permeability coefficient.

Synthesis and gas separation properties of metathesis poly(5-ethylidene-2-norbornene)

High molecular weight metathesis poly(5-ethylidene-2-norbornene) (PENB) has been synthesized in the presence of the 1st generation Grubbs catalyst at a high monomer/catalyst ratio (3000/1 and higher). The yields of the corresponding polymer have been more than 90% at all monomer/catalyst ratios and molecular weights (Mw) of PENB have been higher than 3 × 105. The gas permeability of different gases (He, H2, O2, N2, CO2, and CH4) through PENB films has been studied, and diffusivity and selectivity coefficients have been determined. It has been found that PENB is more permeable than unsubstituted metathesis polynorbornene and cycloalkyl-substituted polynorbornene dicarboximides, but it is less permeable than some Si-containing polynorbornenes. Despite the fact that PENB is more permeable than metathesis polynorbornene and cycloalkyl-substituted polynorbornene dicarboximides, it is close to these polymers in ideal selectivities for some gas pairs.

Novel Pervaporation Technique Using Permeate Vapor Adsorption for Removal of Chlorinated Organics from Aqueous Media

A novel pervaporation technique has been proposed that makes it possible to selectively remove volatile chlorinated organics (VCO) from contaminated water; to localize them on activated carbon directly in the membrane module; to create a sufficient driving force of the process due to both high sorption capacity of activated carbon and its VCO adsorption selectivity; and to abandon the use of expensive vacuum equipment, thereby minimizing vacuum pump operating costs. The influence of VCO concentration in the solution and the feed flow rate on the efficiency of VCO removal from water has been studied. It has been found that the dominant resistance to VCO flux through the membrane is due to an additional flux resistance associated with diffusion constraints in the boundary liquid layer near the membrane surface. It has been shown that VCO flux values in the case of this pervaporation method (up to 0.47 kg/(m2 h) at 30°C) are several times larger than those for conventional pervaporation approaches. The separation factor can be as high as 380–2400 for a chloroform/water mixture or 400–4800 for a trichloroethylene/water mixture.

Synthesis and metathesis polymerization of fluorine-containing tricyclononenes

Herein the synthesis of a new series of fluorine containing tricyclononenes using [2σ+2σ+2π]-cycloaddition of quadricyclane with fluorine containing alkenes is described. According to the experiment the reactivity of fluorine containing alkenes in [2σ+2σ+2π]-cycloaddition reaction was established. The obtained cycloadducts were successfully involved in ring-opening metathesis polymerization on Ru-based catalytic systems. The obtained polymers were glassy and amorphous. The investigation of gas-transport properties of the new materials with improved selectivity towards different pairs of gases was executed.Herein the synthesis of a new series of fluorine containing tricyclononenes using [2σ+2σ+2π]-cycloaddition of quadricyclane with fluorine containing alkenes is described. According to the experiment the reactivity of fluorine containing alkenes in [2σ+2σ+2π]-cycloaddition reaction was established. The obtained cycloadducts were successfully involved in ring-opening metathesis polymerization on Ru-based catalytic systems. The obtained polymers were glassy and amorphous. The investigation of gas-transport properties of the new materials with improved selectivity towards different pairs of gases was executed.

Sorption selective membranes based on polydimethylsildimethylene- and polydimethylsiltrimethylenedimethylsiloxane

Using cationic and anionic polymerization of 1,1,3,3-tetramethyl-2-oxa-1,3-disilacyclopentane (I) and 1,1,3,3-tetramethyl-2-oxa-1,3-disilacyclohexane (II), α,ω-dihydroxypolydimethylsildimethyleneand α,ω-dihydroxypolydimethylsiltrimethylenedimethylsiloxanes (III and IV, respectively) were synthesized. The polymer materials for the flat membranes MI and MII with stable mechanical properties were produced via crosslinking condensation of tetraethoxysilane and the terminal hydroxyl groups of III and IV. Methane and butane were applied to demonstrate the gas transport properties of these membranes. It was shown that compared to PDMS, the synthesized MI and MII have a higher butane/methane ideal selectivity at high permeability coefficients (7800 and 6600 Barrer, respectively). An increase in butane/methane selectivity is achieved due to the high coefficients of butane solubility in the membrane materials.

Porous hollow fiber membranes with varying hydrophobic–hydrophilic surface properties for gas–liquid membrane contactors

In relation to the demand for asymmetric porous hollow fiber membranes to be used in gas–liquid membrane contactors designed for operation in organic media, polysulfone membranes of this type have been prepared and subsequently modified to impart oleophobic properties to their surface. The structure and properties of the membranes have been characterized using various techniques, such as optical and scanning electron microscopy, and by measuring contact angles and the permeability of helium, carbon dioxide, and hexane. The surface properties of the membranes have been modified by etching with a mixture of hydrogen peroxide and sulfuric acid or coating with a perfluorinated acrylic copolymer. In the latter case, modified membrane samples have shown a significant reduction in wettability with both water and organic liquids. The hexane permeability data indicate the absence of hexane flow through the membrane modified with perfluorinated acrylic copolymer until a gauge pressure of about 1 atm. The results of the study lead to the conclusion that these membranes can find use in gas–liquid membrane contactors, e.g., for the removal of dissolved gases from liquid hydrocarbons.