Effect of acid–base interaction on the sorption characteristics of liquids in poly(vinylidene fluoride)

The sorption characteristics of various liquids in poly(vinylidene fluoride) (PVDF) were investigated in relation to the Lewis acid–base interaction between the liquids and the polymer. The sorption amount of various liquids and the sorption selectivity of binary mixtures in PVDF were measured and their characteristics were found to be significantly affected by acid–base interaction. The acid–base interaction was evaluated from the Drago constants of PVDF, which were obtained by extending the Fowkes' method observing the shift of stretching frequency of the carbonyl bond of ethylacetate sorbed in PVDF. The partial molar enthalpy change of mixing at infinite dilution was estimated using the Drago constants of PVDF and used as a parameter explaining the sorption characteristics of liquids in PVDF. © 1992 John Wiley & Sons, Inc.     

Rate multiplicity due to interactions between adsorbed species

A generalized Langmuir-Hinshelwood mechanism for the reaction A + 1 /2B₂ ⇌ C has been studied. Lateral (nearest neighbor) interactions between the adsorbed species have been considered to analyze the multiple steady-states in the chemical reaction. Forward and reverse reaction rate constants have been evaluated via the lattice-gas model with the absolute rate theory. The simulation by the proposed model can predict multiple steady-states and hysteresis. Experimental correlation was made for the rate multiplicity observed by Sung [3] on CO oxidation reaction.     

Model for attachment of active species onto gelular polymer bead

Equations for the equilibrium between the stresses and the degree of swelling, and also for the mass balance of substrate and functional groups, are proposed in order to analyze the attachment of active species onto gelular polymer bead. The asymptotic expansion technique was used to solve these equations when the relaxation rate of polymer in solvent is higher than the reaction rate and the reaction rate is much faster than the diffusion rate. It was shown that the interaction between solvent and polymer with attachment can be explained from the simulation. The equations proposed can be utilized to better understand the control of active species distributions in the polymer bead. © 1992 John Wiley & Sons, Inc.     

STATISTICAL THERMODYNAMIC ANALYSIS ON THE SORPTION SELECTIVITY FOR A BINARY LIQUID MIXTURE ON THE SOLID SURFACE

The nonideal concentration dependent sorption selectivity for the liquid-solid interface was analyzed by introducing the admolecular interaction in the statistical thermodynamic approach. The quasi-chemical and Bragg-Williams approximations together with the maximum term condition result in the desired expression for the adsorption isotherm. Experiments were carried out for the adsorption of the binary (xylene/toluene) mixture on the Y-zeolite as a nonideal system. The derived isotherms were correlated with both the ideal system reported by Sircar and Myers and the present nonideal adsorption data.     

Local structure and photocatalytic activity of B2O3–SiO2/TiO2 ternary mixed oxides prepared by sol–gel method

The local structure and the photoactivity of B₂O₃–SiO₂/TiO₂ ternary mixed oxides (SiO₂ content was fixed as 30 at.% with respect to TiO₂) was investigated by using XRD, FT-IR, BET, UV-vis spectra, and electron paramagnetic resonance (EPR) measurement. In FT-IR analysis, boron was incorporated into the framework of titania matrix with replacing Ti---O---Si with Si---O---B or Ti---O---B bonds. Also, paramagnetic species such as O⁻ and Ti³⁺ defects were formed by the boron incorporation. In SiO₂/TiO₂ mixed oxides, a blue shift in the light absorption band was observed due to the quantization of band structure. All B₂O₃–SiO₂/TiO₂ samples had pure anatase phase and no rutile phase was formed even though the calcination temperature was over 900 °C. Incorporating boron oxides of more than 10% enlarges the grain size of anatase phase and causes a red shift of the light absorption spectrum. The surface area was monotonically decreased with increasing the content of boron content. As a result, the photoactivity of B₂O₃–SiO₂/TiO₂ ternary mixed oxides was greatly influenced by the content of boron oxide. The highest photoactivity (g moles/min l) was obtained when the boron content was 5% and seven times higher than that of silica/titania binary mixed oxide. In addition, the specific photoactivity (g moles/m² l) was maximum still at 5%. It was concluded that the large reduction of surface area, the change of band structure, and more formation of bulk Ti³⁺ sites are responsible for the deterioration in the photoactivity of B₂O₃–SiO₂/TiO₂ ternary mixed oxides when the content of boron is over 10%, although their crystallinity was enhanced by increasing the calcination temperature with keeping anatase phase.     

Hydrogenation of olefins over palladium(II) complexes supported on a modified macroporous polymer bead

Gellular and macroporous polymer supports have been prepared. A modified polymer support has also been prepared by coating the internal pore wall of macroporous poly(styrene-co-divinylbenzene) with lightly crosslinked polymer containing functional groups. The supports were phosphinated and PdCl₂ was supported on them. The supports and catalysts were characterized using scanning electron microscopy and Fourier transform infrared spectroscopy. The polymer-supported Pd catalysts were used in the hydrogenation of olefins. The effects of the support structure and solvent were also studied. ©1997 SCI     

Sorption selectivity of NaY- and KY- zeolites for xylene and toluene

The selective adsorption capacities of NaY- and KY-zeolites for xylene isonners and toluene were investigated by measuring the rate of unidirectional diffusion in a batch adsorber and the breakthrough behavior in a fixed-bed column. The sequence of sorption selectivity was found as m-xylene> toluene > p-xylene with NaY-zeolites and as the converse with KY-zeolites. The reversal of selectivity could not be explained by the molecular sieving effects but by the interactions between adsorbing molecules and cation as well as among adsorbing molecules themselves.     

Polymerization of norbornene using novel palladium carboxylate/boron trifluoride etherate catalyst system

The vinyl polymerization of norbornene with Pd(carboxylate)₂/BF₃OEt₂ catalyst system has been investigated by varying the molar cocatalyst/metal ratio, the norbornene/metal ratio, the metal concentration and the reaction temperature. The effects on the catalyst activity were explained on the basis of complexation equilibrium for the active homogeneous complex. A “particular” activity of 154 100 kg NB per mole Pd for an hour has been achieved at B/Pd = 25 and 25 °C. The molecular weights M_w from 77 700 to 293 800 g/mol and glass transition temperatures T_g from 240 to 262 °C were observed for the representative samples of polynorbornene. The molar mass distribution indicates a single-site, highly homogeneous character of the active catalyst species. Catalytic activity and polymer molecular weight can be controlled by varying the reaction parameters over a wide range. NMR and IR spectroscopic studies of the polymer showed 2,3-enchained repeating units of polymer backbone with low diisotacticity. The simplicity of catalyst system composition might be of industrial importance.     

Effect of active site distribution on liquid-phase olefin hydrogenation over polymer-supported palladium complex

Chloromethylated polystyrene beads with different distributions have been prepared and phosphinated. PdCl₂ was supported on the phosphinated supports to give polymer-supported Pd complex catalysts with different active site distributions. The effect of active site distribution on catalytic activity was investigated in the hydrogenation of olefins.     

Deactivation phenomena of supported platinum catalysts during the hydrogenation of cyclopropane

Cyclopropane hydrogenation reaction was performed in a differential reactor operating at atmospheric pressure, 50‡C and H₂/C₃H₆ ratio of 9, and the deactivation of the catalysts during the reaction was investigated by observing the effects of the supports and the size of platinum crystallites, Owinglo the accumulation of the carbonaceous materials the platinum catalysts dispersed on the acidic supports such as γ-Al₂O₃, SiO₂-Al₂O₃ and Y-zeolite deactivated significantly, while no detectable deactivation was observed for the catalysts on the non-acidic supports of SiO₂ and active carbon. In addition smaller platinum particles on acidic supports were morevulnerable to the catalyst deactivation.