MODELING LIQUID MASS TRANSFER IN HIGEE SEPARATION PROCESS

Correspondence concerning this paper should be addressed to Professor Richard S.H. Mah. Hsien-Hsin Tung is now affiliated with Department of Chemical Engineering, California Institute of Technology

Penetration theory is used to describe the liquid mass transfer in Higee separation process. Within a possible range of effective areas, it is shown that the predicted mass transfer coefficients are in reasonable agreement with the estimated mass transfer coefficients. The estimated coefficients were calculated from the experimental data and the possible effective areas. Hence it is concluded the penetration theory is generally applicable to describe liquid mass transfer in Higee separation process. The comparison also suggests that liquid mixing at the junctions of packing materials may be more complete in Higee process than in traditional process.     

Living cationic polymerization of isobutyl vinyl ether (II): Photoinduced living cationic polymerization in a mixed solvent of toluene and diethyl ether

A new method of preparation of living cationic polymer of isobutyl vinyl ether via photoinduced polymerization in the presence of diphenyliodonium iodide (DPII, initiator) and zinc iodide in a mixed solvent of toluene/diethyl ether, which was irradiated at ?78°C for short period, was completed within 15 min. The reaction was allowed for further reaction in the dark until monomer was fully consumed. It was found that increase in the conversion of monomer to polymer during the irradiation is very limited. Confirmation of the linear dependence of number‐average molar mass of resulting polymer on % conversion together with the fact that polymerization proceeds until monomer consumption, and controllability of number‐average molar mass of resulting polymer, depending on the molar ratio of monomer and initiator, strongly suggests the living nature of this polymerization, unless reaction temperature becomes higher than 0°C, i.e., the absence of chain breaking process. The narrow molar mass distribution, whose polydispersity index values are less than 1.2, reveals that the rate of initiation where irradiation is usually completed within 15 min is much faster than that of propagation in cationic nature in this system. Effect of some major factors, such as solvent polarity and temperature, on the living nature of the polymerization was also investigated. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 101: 3581–3586, 2006     

Effects of pH on rhodopsin photointermediates from lumirhodopsin to metarhodopsin II

Time-resolved absorption difference spectra of membrane suspensions of bovine rhodopsin at pH 5, 6, 7, 8, 9, and 10 were collected in the time range from 1 micro s to 200 ms after laser photolysis with 7-ns pulses of 477-nm light. The data were analyzed using singular value decomposition (SVD) and global exponential fitting. At pH 7 the data agree well with previously obtained data (Thorgeirsson et al. (1993) Biochemistry 32, 13861-13872) with fits improved at all pH's by inclusion of a small component due to an absorbance change caused by rotational diffusion which is detectable even at magic angle polarization. A "square scheme" suggested to best explain the previous data, which involves two branches following decay of the lumi intermediate with pathways (1) lumi --> MI480 right harpoon over left harpoon MII and (2) lumi right harpoon over left harpoon MI380 --> MII, could be confirmed throughout the entire pH range. However, to account for the increased rate of the MII --> MI480 reaction in path 1 for rising pH values, we propose that the MII in the square scheme consists of deprotonated MII and protonated MIIH+ forms in rapid equilibrium with each other, resulting in an extended square scheme and increasing the number of 380-nm products from two to three. In addition to the kinetic processes described by the extended square scheme, above pH 8 fast ( approximately 10 micro s) and slow ( approximately 50 ms) components were found. The fast component was assigned to the decay of a blue-shifted lumi intermediate, and the slow component, resolvable only at pH 10, was assigned to formation of a 450 nm absorbing photoproduct.     

Control of the leakage current in SrTiO3 films by acceptor doping

Stoichiometric SrTiO3 (STO) films doped with Fe or Cr were prepared by r.f. magnetron sputtering technique. The effects of Fe or Cr doping in the SrTiO3 films were studied on the leakage current property which was discussed by defect chemistry. The experimental results can be explained by a model in which oxygen vacancies are the key defects responsible for the leakage current. Acceptor doping, with a small concentration of Fe or Cr, has led to a substantial improvement to 10–9 order in the leakage current density. Above the concentration of 0.010.02 mol% Fe2O3, Cr2O3, however, as the concentration increased, the leakage current increased. These acceptors in Ti4+ site are expected to electrically compensate for donor species such as oxygen vacancies, thereby reducing the concentration of mobile carriers that contribute to electrical conduction. Consequently, acceptor doped STO films have been shown to be superior to undoped films for applications requiring high leakage resistance, such as dynamic random access memory capacitors. © 1998 Chapman & Hall     

Metallic interconnects for solid oxide fuel cell: A review on protective coating and deposition techniques

With the reduction of solid oxide fuel cells (SOFCs) operating temperature to the range of 600 °C–800 °C, metallic alloy with high oxidation resistance are used to replace traditional ceramic interconnects. Metallic interconnects is advantageous over ceramic interconnects; in terms of manufacturability, cost, mechanical strength, and electrical conductivity. To date, promising candidates for metallic interconnects are all Cr-containing alloys, which are susceptible to volatile Cr migration that causes cell degradation. As such, protective coatings have been developed to effectively inhibit Cr migration; as well as maintain excellent electrical conductivity and good oxidation resistance. This article reviews the progress and technical challenges in developing metallic interconnects; different types of protective coatings and deposition techniques for metallic interconnects for intermediate-temperature SOFC applications.     

The ability of zinc to inhibit the sporulation and viability of Clostridium sporogenes and growth of other bacteria

The objective of this study was to investigate the influence of zinc on the sporulation and viability of Clostridium sporogenes and on the growth of other bacteria. When 0.5% ZnCl₂ was added to a sporulation medium, it completely inhibited C. sporogenes (PA 3679) sporulation for up to 3 weeks. At concentrations of 0.5% and 1.0%, ZnCl₂ not only completely inactivated the vegetative cell viability (>7.0 Log reduction) but also significantly reduced the spore viability (<2.1 Log reduction) of C. sporogenes. Taken together, it was concluded that zinc blocks C. sporogenes sporulation by damaging (or killing) vegetative cells and probably by interfering with the biosynthesis of spore components. In addition to the inhibitory effect on the sporulation and viability of C. sporogenes, ZnCl₂ was found to have a broad antimicrobial spectrum against all Gram‐positive and Gram‐negative spoilage and pathogenic bacteria tested. The minimal inhibitory concentration for inhibiting the bacteria ranged between 3.7 and 7.4 mm . Therefore, we expect that this compound or a combination thereof has a potential as a surface‐cleaning agent or disinfectant.     

Peroxodisulfate generation on boron-doped diamond microelectrodes array and detection by scanning electrochemical microscopy

In this work, the electrogeneration of peroxodisulfate from a 1 M H₂SO₄ solution on boron-doped diamond microelectrodes array has been studied. The peroxodisulfate is detected at the vicinity of the boron doped diamond electrode, with the SECM probe, only when the polarization of the microarray is greater than 2.1 V versus AgCl/Ag. The main electrochemical interest of working with microarrays comes from the fact that current densities and efficiencies are comparable to those observed in the peroxodisulfate industrial production. The local Scanning Electrochemical Microscopy studies have shown that the peroxodisulfate reaction is related to a surface mediated oxidation of sulfate anions into peroxodisulfate according to a complex reactional mechanism.