The use of Nafion-H® as an efficient catalyst for the direct conversion of primary and secondary trimethylsilyl ethers to their corresponding ethers under mild and heterogeneous conditions

Primary and secondary trimethylsilyl ethers were converted to their corresponding ethers in the presence Nafion-H® with good to excellent yields under mild and heterogeneous conditions.     

A thermodynamic analysis on the coincidence of extrema conditions in the sorption equilibrium for ternary polymer systems

Flory-Huggins theory of polymer solutions has been used to express the condition of extrema values in the total sorption, as well as the inversion point in the preferential adsorption parameters for termary polymer systems. Two approaches have been followed, the first considers the binary and ternary interaction parameters independent of polymer concentration and solvent composition. In the second one, this dependence has been introduced. Our attention is focused on the volume fraction of solvent mixture dependence of the above parameters, in order to confirm or not the coincidence between the extrema values and the inversion point. Several cosolvent and cononsolvent ternary polymer systems, have been used to test the validity of the equations obtained. Also, it has been verified, from an experimental point of view, that in cosolvent ternary polymer systems there is coincidence in both compositions while in cononsolvent ternary polymer systems, such coincidence does not appear.     

SYNTHESIS, CHARACTERIZATION, METAL-UPTAKE BEHAVIOR OF BIS（BENZIMIDAZOLE） RESIN SUPPORTED ON EPOXIDE POLYMER

The new chelate resins, abbreviated as PNBMZs and PBBMZs based on epoxide polymer, were synthesized by polycondensation of N,N-diglycidyl-4-glycidyloxyaniline or 1,4-bis（2,3-epoxypropyl）benzene with the primary amine group of 1,3-bis（benzimidazol-2yl）propylamine （BBPAH）. The ion exchangers contain 2.71-3.23 mmol of the ligand contents per gram of the resin. Batch extraction capacities were determined for the metal chloride salts in buffer solutions in the pH range from -1 to 6.0. The chelate resins were very selective for Cu^2＋, Zn^2＋, Cd^2＋ in the presence of other divalent transition metal ions. The maximum uptake capacities of PNBMZ （synthetic molar ratio = 1：1.5） under non-competitive condition were found to be 0.94 mmol/g for Cu^2＋ at pH = 2, 1.3 mmol/g for Cd^2＋ at pH = 1 and 1.75 mmol/g for Zn^2＋ at pH = -1 respectively. While in the case of PBBMZ, it was 1.39 mmol/g for Cd〉 at pH = 1. The metal-uptake behaviors for both of them showed strong pH dependence, and their extraction capacities increase with decreasing pH. The uptake of Cu^2＋ by the resin PNBMZs at pH = 1 was found to be rather fast with t1/2 = 18 min. Metal-uptake experiments under competitive conditions also confirm that the chelate resins have a high selectivity for Cu^2＋, Zn^2＋, Cd^2＋ and the contrary pH dependence.     

Mathematical Modeling of Multicomponent Nonisothermal Adsorption in Sorbent Particles Under Pressure Swing Conditions

A detailed model for nonisothermal sorption of multicomponent mixtures in a single sorbent particle (monodisperse or bidisperse with negligible intracrystalline mass transport limitations) under pressure swing conditions is developed in this study. The dusty-gas model is used to describe the coupling of the molar fluxes, the temperature, the partial pressures and the partial pressure gradients of the components in the pore space of the particle. The variations of the temperature are described by an energy equation in which both convective and conductive modes of heat transport are accounted for. No limitations are imposed on the number of the components in the mixture and on the type of the adsorption isotherm. The model is applied in the investigation of the industrially important air-zeolite 5A system. Two cases with respect to the surrounding gas phase are examined: infinite environment, which is representative for single particle experiments, and finite environment, which is representative for the situation in packed bed adsorbers. It is found that in an infinite environment the external and internal temperature gradients are equally important while in a finite environment the external heat transport limitations are negligible. It is concluded that in modeling the nonisothermal operation of adsorption processes occurring in packed beds it is not necessary to allow for the temperature differences between the gas phase and the surface of the adsorbing particles. Furthermore, if the temperature gradients within the particles can be neglected, only a single temperature equation is needed to describe the energy transport in the bed.     

Thec logc contribution to the electrolyte conductance and Onsager's reciprocal relation

The differential equations and the boundary conditions for the nonequilibrium binary distribution function of an unsymmetrical binary electrolyte are derived from the Ebeling-Falkenhagen continuity equation. The connection between the Onsager reciprocal relation and the binary distribution functions is shown. Further, Feistel's result for thec logc contribution to the conductance is extended to unsymmetrical binary electrolytes. The reason for the difference between Feistel's and Chen'sc logc term is explained, and the significance of Onsager's reciprocal relation for the calculation ofc logc and higher-concentration contributions of the conductance is discussed.     

ADSORPTION OF 4-METHYLANILINE IN AQUEOUS SOLUTION BY BENZOYL-CONTAINING POLYMERIC ADSORBENTS

New polymeric adsorbents (ZH-02, ZH-03) containing benzoyl group for adsorbing and removing 4-methylaniline from its aqueous solutions were prepared. Studies on the isotherms and the comparison of desorption conditions evidenced through the adsorption of 4-methylaniline in water onto ZH-02 and ZH-03, namely that there are chemisorption‘s transitions at a proper higher temperature. Mini-colunm adsorption studies of 4-methylaniline on XAD-4, ZH-02 and ZH-03 at 288 K show that the breakthrough capacities are 2.39, 2.99 and 3.19 mmol/g and the total capacities are 3.45, 3.92 and 4.35 mmol/g, respectively.     

HPLC of synthetic polymers characterization of polystyrenes by high performance precipitation liquid chromatography (HPPLC)

Summary The advantages and disadvantages of high performance precipitation liquid chromatography have been demonstrated for polystyrene homopolymers. Depending on the mobile phase composition at the dissolution point of the polymeric sample and surface properties of the stationary phase, elution is governed either by a solution process or by adsorption. A contribution by adsorption was noticed on silica as well as on reversed phases based on silica with a normal phase gradient of increasing polarity (heptane to dichloromethane). Elution was solely governed by solubility of the polymers on both types of stationary phase for polystyrenes with a molecular weight above 35 000 and reversed phase gradient of decreasing polarity (methanol to dichloromethane). Under these conditions an identical dependence of elution solvent composition on sample size was found as for turbidity titrations. Due to differences in the velocity of the eluent front and the polymeric sample with porous stationary phases the polymers can be eluted as colloidal solutions Non-porous stationary phases are superior in this respect because the velocities of eluent and solutes are identical.     

Non isothermal heat capacities and chemical reactions using a modulated DSC

An evaluation of measurements of heat capacities by modulated differential scanning calorimetry, MDSC is presented. Heat capacities were obtained from 130 to 550 K by a non isothermal technique in which a periodic modulation was added to the linear heating rate. Effects of amplitude and period of modulation, sample weight, sample type, pan type, and cell imbalance are described. Results are compared with those obtained using the isothermal technique. Heat capacity could be measured well into the decomposition region and separated from the non reversing signal due to chemical reaction (degradation), thus allowing a precise detection of onsets of the thermal degradation. This additional information will aid in the interpretation of the degradation chemistry, a field vital for the petroleum-industry.Dedicated to Professor Bernhard Wunderlich on the occasion of his 65th birthdayPart of this paper was presented at the 23rd Conference of the North American Thermal Analysis Society, Toronto, Canada, September 25–28, 1994.The author (MVN) acknowledges the experimental assistance provided by J. Balogh of Exxon Research and Engineering Company, Linden. Helpful discussions with A. Boller of the University of Tennessee at Knoxville, Dr. Y. Jin, General Electrical, and Dr. S. Sauerbrunn formerly of TA Instruments are also acknowledged.     

Tribromoisocyanuric Acid (TBCA) and Oxone®‐MX Systems as Oxidizing Agents: Oxidative Coupling of Thiols to Their Corresponding Disulfides under Mild and Heterogeneous Conditions

Tribromoisocyanuric acid (TBCA) and Oxone^®‐MX systems were used as effective oxidizing agents for the oxidation of thiols to their corresponding disulfides under mild conditions at room temperature with good to excellent yields.     

一个多元校正的稳健诊断新方法

提出一种新的稳健诊断方法，与最小二乘估计结合进行混合物光谱中非线性点的诊断。文中探讨了该方法的性能，用计算机数字模拟及实际多组分光谱体系夺其进行检验，展示了此诊断方法在分析化学计量学中实际应用的可行性。