Israel Cabasso

Separation of liquid benzene/cyclohexane mixtures by perstraction and pervaporation

Abstract The separation of liquid mixtures of benzene and cyclohexane by perstraction and pervaporation was studied and the effectiveness of these two membrane separation processes was compared. The membranes used for this purpose were made from a polymer alloy composed of cellulose acetate and a phosphoryl ester derivative of poly (dimethylphenylene oxide). This alloy has a glass transition temperature of over 200°C and is more permeable to benzene than to cyclohexane. Both the permeability of the alloy membranes and their selectivity for benzene relative to cyclohexane could be significantly enhanced by suitable annealing and conditioning procedures. The permeability of the membranes increased and their selectivity decreased as the benzene concentration in the “feed” mixtures was increased. The same effects were observed by raising the temperature. The permeation rates of the benzene/cyclohexane mixtures were found to be higher in pervaporation than in perstraction, particularly at lower benzene concentrations in the feed mixtures, while the membrane selectivity was the same in the two processes. This comparative study is the first of its kind and provides information on the relative advantages and disadvantages of perstraction and pervaporation.

The permselectivity of ion-exchange membranes for non-electrolyte liquid mixtures. II. The effect of counterions (separation of alcohol/water mixtures with nafion membranes)

The effect of counterions on the transport of alcohol/water mixtures through a Nafion ion-exchange membrane is reported. Correlations between the counterions and the membranes selectivity, permeability and the permeates state of existence in the membrane were established. The membranes selectivity toward water, in steady state pervaporation experiments, is much higher than that recorded in sorption experiments when employing an isopropanol/water azeotropic composition as the feed mixture. The values recorded for the apparent energy of activation are conspicuously low and follow the order Cs >K >Na. For all counterions the membrane exhibits a large fraction of free water (freezing water). A substantial freezing-point depression was recorded following the counterion series H > Li > Na > K ≈ Cs. The Cs+ version exhibits freezing at 0°C. The swollen membrane equilibrated with the feed mixture shows multiple freezing points, indicative of the heterogeneous nature of the membrane.

Surface fluorination of poly (phenylene oxide) composite membranes: Part II. Characterization of the fluorinated layer

Abstract Composite membranes, comprising a selective layer of poly (2,6-dimethyl-1,4-phenylene oxide) on a microporous ceramic support, were surface fluorinated under mild conditions. The treatment parameters, fluorine feed concentration and treatment time, were each varied independently while the other parameter was kept constant. The fluorinated region was characterized using dynamic contact angle analysis and X-ray photoelectron spectroscopy (XPS). The fluorine to carbon ratio increased as a function of treatment time, but showed little variation when the feed concentration was varied. A relatively high oxygen to carbon ratio was observed which showed little change over the range of fluorination conditions. Angle-dependent XPS showed the concentration of fluorine species to be higher at greater depths below the surface. Fluorination times of 5 to 7 min minimized the water contact angle and maximized the total and polar surface free energies. Water contact angles decreased after fluorination but showed no definite trend as a function of feed concentration. The composition of the fluorinated region is discussed in relation to the gas transport properties of membranes fluorinated under similar conditions (Part I of this study).

Modification of asymmetric polysulfone membranes by mild surface fluorination Part II. Characterizationof the fluorinated surface

Abstract Integrally-skinned asymmetric polysulfone (PSF) membranes were surface fluorinated under mild treatment conditions, according to one of two strategies: at fluorination times of 1 to 10 min with a constant fluorine feed concentration of 0.02% F2 (by volume), or at concentrations ranging from 0.02 to 0.15% F2 for a fixed treatment time of 2 min. The fluorinated region was characterized using dynamic contact angle analysis and X-ray photoelectron spectroscopy. It was shown that increasing fluorination times from 1to 5 min resulted in increased F/C and O/C ratios in the fluorinated subsurface region and also increased the polar surface energy contribution (λPa at the surface. Longer fluorination times resulted in an apparent decrease in polarity, possibly due to surface damage. For increasing fluorine concentrations at a constant treatment time, the F/C and O/C atomic ratios in the subsurface region increased up to 0.04% F2 and effectively leveled off at higher feed concentrations. At the surface, λsp decreased after reaching a maximum at 0.06 F2. For both treatment strategies the ideal selectivities for certain gas pairs (He or H2 with N2 or CH4) follow trends similar to that of λps. Decreases in selectivity appear to be associated with fluorination damage (surface roughness and damage to the polymer structure), rather than with a change in the chemical nature of the fluorinated skin region.

Controlled thermal decomposition of aromatic polyethers to attain nanoporous carbon materials with enhanced gas storage

Reported is the development of nanostructured synthetic carbon materials that have been synthesized by thermal-decomposition of aromatic rich polyethers: poly(ether ether ketone) (PEEK) and poly(2,6-dimethyl-1,4-phenylene oxide) (PPO). These polymer based nanostructured carbons are efficacious for gas adsorption and storage and have Brunauer–Emmett–Teller (BET) surface areas of more than 3000 m2 g−1, and average pore diameters of ≤20 A. Surface area, pore characteristics, and other critical variables for selecting porous materials of high gas adsorption capacities are presented. Analysis of the fragments evolved under various carbonization temperatures, and the correlation between the activation and carbonization temperatures provides a mechanistic perspective of the pore evolution during activation. Correlations between gas (N2 and H2) adsorption capacity and porous texture of the materials have been established. The materials possess excellent hydrogen storage properties, with hydrogen storage capacity up to ∼7.0 wt% (gravimetric) and ∼42 g H2 L−1 (volumetric) at −196 °C and 4.5 MPa.

Organobismuth polymers as X-ray contrast materials: synthesis, characterization and properties

Abstract Organobismuth monomers containing the Ph3Bi moiety were synthesized and polymerized to obtain homogeneous X-ray constrast polymers. Styryldiphenylbismuth (I), α-methylstyryldiphenylbismuth (II), tris(α-methylstyryl) bismuth (III) and (p-diphenylbismuthphenyl)vinyldimethylsilane (IV) were prepared via a Grignard reaction with BiPh2Cl. Monomers I and II are contaminated with significant amounts of Ph3Bi and divinyl compounds. Monomer I can be homo- and copolymerized radically and anionically, II can only be copolymerized, while IV did not polymerize at all. In anionic polymerization the carbanion also attacks the PhBi bond of I and II. Glass transition temperatures were determined as a function of bismuth comonomer content for styrene and acrylate copolymers, and the thermal decomposition was also studied. Radiopacities in millimetres of aluminium per millimetre of polymer were found to be proportional to the molar bismuth content of the transparent copolymer specimens.

Synthesis and characterization of carbamoylphosphonate monomer and its copolymer with styrene. II

A monomer, diethyl α,α-dimethyl-m-isopropenylbenzyl carbamoylphosphonate, has been prepared by the base-catalyzed reaction of the isocyanate m-TMI (α,α-dimethyl-m-isopropenylbenzylisocyanate) with diethyl phosphite. The structure of the carbamoylphosphonate monomer and its styrene copolymer was confirmed spectroscopically, and the nature of the hydrogen bondings in the NHC(O)P(O)(OR)2 unit in the monomer and copolymer is discussed in detail. A bulk polymerization of the carbamoylphosphonate is very slow and tends to yield a crosslinked product, but a solution polymerization produced the soluble copolymers. The Tg(midpoint) of the homo-polymer is low, 67°C, and its capacity to complex UO2(NO3)2 is very high, 28 wt % (19 mol %).

Electrosynthesis of Oligo- and Polysilanes Using a Modified Gas Diffusion Hydrogen Anode

A modified gas diffusion hydrogen anode (GDHA) was developed for electropolymerization of dichlorosilianes. This GDHA consists of three layers: an H 2 dispersion layer made of a fine glass frit, a Teflon-bound electrical conductive carbon layer, and a Pt/carbon catalyst layer. The performance of this H 2 electrode configuration, having different Pt loadings, was evaluated by electropolymerizing MePhSiCl 2 at different monomer concentrations, current densities, and supplied electricities. The modified hydrogen anode is reported to yield polymethylphenylsilane with Mw = ∼11000. The product yield, using this hydrogen electrode, approaches 99% (i.e., oligomer + polymer).

X-ray contrast polymers of p-styryldi(p-tolyl)bismuth: synthesis and properties

Abstract The radiopacifying organobismuth monomer p-styryldi(p-tolyl)bismuth was synthesized in 40% yield by means of a three-step process using 4-bromotoluene, 4-bromostyrene and bismuth trichloride as starting compounds. The product is a crystalline solid of at least 95% purity, unlike the earlier reported styryldiphenylbismuth which could only be obtained in a very impure form. Radical or anionic polymerization yields a soluble homopolymer, and copolymers were made with styrene and methyl methacrylate. The products were characterized by standard techniques. Data are reported on their solubility, blending and radiopacity. The latter property, expressed in mm of aluminium per mm resin, is a linear function of the molar bismuth concentration in the polymer specimens.

Synthesis and characterization of fluorinated polyionomers. Part I: polyperfluoro-sulfonylethoxy propylene vinyl ether sulfonimides containing aryl sulfonic acids

The synthesis and chemistry associated with the preparation of polysulfonimide polyionomers containing aryl sulfonic acids with high charge densities and various solubilities is reported. Homopolymers of perfluoro-sulfonylethoxy propylene vinyl ether (PSEPVE) are prepared by free radical polymerization and functionalized with sulfonyl chlorides of benzene, terphenyl, and triphenylene. The nature of the pendant group has been found to have a substantial impact on solution properties. In particular, water solubility is easily attained in the poly(PSEPVE) benzene sulfonimide, while the incorporation of bulky, rigid aromatic groups in the poly(PSEPVE) triphenylene sulfonimide disulfonic acid product allowed it to retain water insolubility with high charge density (∼2 meq. H+ per g). Perfluoropolysulfonimide gel network polymers are also prepared utilizing similar chemistry. Thermal stabilities upon boiling in an aqueous solution are established by monitoring charge density and changes in the 19F NMR spectra of the ionomers.