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Reactant Concentration (reactant + concentration)
Kinds of Reactant Concentration Selected AbstractsPolydisperse Spindle-Shaped ZnO Particles with Their Packing Micropores in the Photoanode for Highly Efficient Quasi-Solid Dye-Sensitized Solar CellsADVANCED FUNCTIONAL MATERIALS, Issue 3 2010Yantao Shi Abstract In this paper, a novel hierarchically structured ZnO photoanode for use in quasi-solid state dye-sensitized solar cells (DSCs) is presented. The film is composed of polydisperse spindle-shaped ZnO particles that are prepared through direct precipitation of zinc acetate in aqueous solution. Without additional pore-forming agents, the microporous structure is well constructed through the packing of polydisperse ZnO particles. In the film, small ZnO particles are able to improve interparticle connectivity and offer a large internal surface area for sufficient dye-adsorption; on the other hand, particles of larger size can enhance the occurrence of light-scattering and introduce micropores for the permeation of quasi-solid state electrolytes. Meanwhile, morphologies, particle size, and specific areas of the products are controlled by altering the reactant concentration and synthetic temperature. Combined with a highly viscous polymer gel electrolyte, a device based on this ZnO photoanode shows high conversion efficiencies, 4.0% and 7.0%, under 100 and 30,mW cm,2 illumination, respectively. Finally, the unsealed device is demonstrated to remain above 90% of its initial conversion efficiency after 7 days, showing excellent stability. [source] Characterization of a photocatalytic reaction in a continuous-flow recirculation reactor systemJOURNAL OF CHEMICAL TECHNOLOGY & BIOTECHNOLOGY, Issue 6 2006Fumihide Shiraishi Abstract A continuous-flow recirculation mode, generally called a recycle mode, is known to be practically meaningless except when the reactant is separated from the product at the reactor exit or when the reaction is autocatalytic, because when simply circulating a small amount of the fluid containing a reactant, the reactant concentration in this mode is lowered due to mixing of the fluid at the reactor entrance, leading to a decrease in the conversion at the reactor exit. This mode may, however, be meaningful in photocatalytic reactions with very large film-diffusional resistance. To indicate the validity of this estimation, therefore, characteristics of a continuous-flow recirculation reactor have been investigated both theoretically and experimentally. As a result, it is found that by increasing the circulation flow rate the conversion and productivity in this reactor is higher than that in a continuous-flow reactor because the film-diffusional resistance is remarkably reduced. Copyright © 2006 Society of Chemical Industry [source] Performance of fractionating reactors in the absence of rate limitationsJOURNAL OF CHEMICAL TECHNOLOGY & BIOTECHNOLOGY, Issue 9 2004Jeroen L den Hollander Abstract A fractionating reactor for equilibrium-limited reactions is studied theoretically. Reactant A is fed in the center of the countercurrent fractionating system. Product P is effectively transported with the auxiliary phase, while product Q is effectively transported with the main phase, in which the reaction takes place. Model calculations were based on partition and reaction equilibrium at all stages. These show that if the initial reactant concentration and the flow rates are properly selected, the extent of conversion will significantly exceed the corresponding batch conversion. To approach complete conversion in the fractionating reactor, and to recover both products in a pure form, net transport of reactant in either of the countercurrent directions should be prevented. However, irrespective of the number of equilibrium stages, this situation cannot be fully reached when the reactant feed stream is too large (compared with the main and auxiliary streams). Nonetheless, one of the two products may be recovered in a pure form even for such large feed streams. Copyright © 2004 Society of Chemical Industry [source] Thermal and mass transients in the developing region of a homogeneous tubular chemical reactorAICHE JOURNAL, Issue 3 2010Mohammad K. Alkam Abstract The current investigation presents a finite difference simulation of a homogeneous tubular reactor under laminar flow conditions. The present simulation considers the unsteady operation where transients in flow hydrodynamics, temperature field, and species concentrations have been considered. Flow development in the entrance region of the present reactor has been considered. Present results exhibit reactant concentration and mixing cup temperature profiles for a variety of operating conditions. Effects of several parameters on the performance of the current reactor have been examined, including, reaction parameter, order of reaction, and Schmidt number. © 2009 American Institute of Chemical Engineers AIChE J, 2009 [source] Miscible displacements with a chemical reaction in a capillary tubeAICHE JOURNAL, Issue 3 2008Yuichiro Nagatsu Abstract Miscible displacement of a more-viscous liquid by a less-viscous one with a chemical reaction in a capillary tube was investigated experimentally and theoretically. In such a flow field, the less-viscous liquid continuously leaks from the tip of the finger-shaped boundary between the two liquids to form another thin finger depending on flow condition. This is called a "spike." Experimental results show that in the spike product is clearly or scarcely observed when the initial reactant concentration in the less-viscous liquid is sufficiently larger or smaller than the stoichiometry, respectively. On the basis of theoretical results, a model is proposed in which the difference in the reaction plane's location in either the less-viscous liquid or in the boundary (determined by the variation in the initial reactant concentrations) results in a significant difference between the locations of the boundary and the reaction plane, this difference being affected by the spike configuration of the boundary. © 2008 American Institute of Chemical Engineers AIChE J, 2008 [source] Alkylated poly(styrene-divinylbenzene) monolithic columns for ,-HPLC and CEC separation of phenolic acidsJOURNAL OF SEPARATION SCIENCE, JSS, Issue 17 2007Zdenka Ku, erová Abstract Macroporous poly(styrene-divinylbenzene) monolithic columns were prepared in fused silica capillaries of 100 ,m id by in-situ copolymerization of styrene with divinylbenzene in the presence of propan-1-ol and formamide as the porogen system. The monoliths were subsequently alkylated with linear alkyl C-18 groups via Friedel-Crafts reaction to improve the retention and chromatographic resolution of strongly polar phenolic acids. A new thermally initiated grafting procedure was developed in order to shorten the time of the alkylation process. The grafting procedure was optimized with respect to the reaction temperature, time, the grafting reactant concentration, and the solvent used. The type of solvent and the grafting temperature are the most significant factors affecting the hydrodynamic properties, porosity, and efficiency of the columns. While the equivalent particle diameter of the grafted column increased, the capillary-like flow-through pore diameter decreased in comparison to non-alkylated monoliths. The hydrodynamic permeability of the monolith decreased, but the monolithic column still permitted fast ,-HPLC separations. [source] Synthesis of BaTiO3 Particles with Tailored Size by Precipitation from Aqueous SolutionsJOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 1 2004Andrea Testinon Well-defined and stoichiometric spherical particles of BaTiO3 of narrow size distribution were produced at 82° and 92°3C by precipitation from chloride solutions in a strong alkaline environment. The size of the particles can be tailored in the range from ,103 to 70,80 nm by increasing the barium concentration from ,0.07 to 0.7 mol/L. The particles are composed of tight aggregates resulting from the assembly of several nanocrystals. The size of the nanocrystals decreases from 200,300 to 30,40 nm by increasing reactant concentration. At low barium concentration (,0.07 mol/L at 82°3C, ,0.06 mol/L at 92°3C), formation of BaTiO3 is strongly slowed down and nonstoichiometric, Ti-rich powders are produced. Under these conditions, the particles have the tendency to develop a dendritic-like morphology. [source] Two three-dimensional networks in the binary molecular adducts 4-methylimidazolium hydrogen terephthalate and bis(4-methylimidazolium) terephthalateACTA CRYSTALLOGRAPHICA SECTION C, Issue 6 2008Xiang-Gao Meng Both the 1:1 and 2:1,molecular adducts of 4-methylimidazole (4-MeIm) and terephthalic acid (H2TPA) are organic salts, viz. C4H7N2+·C8H5O4,, (I), and 2C4H7N2+·C8H4O42,, (II), respectively. The component ions in (I) are linked by N,H...O and O,H...O hydrogen bonds into continuous two-dimensional layers built from R64(32) hydrogen-bond motifs running parallel to the (100) plane. These adjacent two-dimensional layers are in turn linked by a combination of C,H...O, C,H..., and ,,, interactions into a three-dimensional network. In the crystal structure of (II), with the anion located on an inversion centre, only N,H...O hydrogen bonds result in two-dimensional layers built from R88(42) hydrogen-bond motifs running parallel to the (102) plane. Being similar to those in (I), these layers are also linked by means of C,H...O, C,H..., and ,,, interactions, forming a three-dimensional network. This study indicates that, on occasion, a change of the reactant concentration can exert a pivotal influence on the construction of supramolecular structures based on hydrogen bonds. [source] Investigation of reacting flow fields in miscible viscous fingering by a novel experimental methodAICHE JOURNAL, Issue 3 2009Yuichiro Nagatsu Abstract The reacting flow fields in reactive miscible viscous fingering in a Hele-Shaw cell studied by Nagatsu and Ueda had not been completely elucidated, mainly because one cannot exactly recognize where and when the reaction takes place in the reactive fingering pattern. We developed a novel experimental method that allowed us to identify the reaction region in the fingering pattern employed in the previous studies. The novel method involves switching of the less-viscous liquid injected in both the nonreactive and reactive experiments. By using the novel method, we succeeded in showing how the reaction region in the fingering pattern was affected by the initial reactant concentrations, the Péclet number, and time. We propose physical models of the reacting flow field in the cell's gap direction that can explain the obtained experimental results. © 2009 American Institute of Chemical Engineers AIChE J, 2009 [source] Miscible displacements with a chemical reaction in a capillary tubeAICHE JOURNAL, Issue 3 2008Yuichiro Nagatsu Abstract Miscible displacement of a more-viscous liquid by a less-viscous one with a chemical reaction in a capillary tube was investigated experimentally and theoretically. In such a flow field, the less-viscous liquid continuously leaks from the tip of the finger-shaped boundary between the two liquids to form another thin finger depending on flow condition. This is called a "spike." Experimental results show that in the spike product is clearly or scarcely observed when the initial reactant concentration in the less-viscous liquid is sufficiently larger or smaller than the stoichiometry, respectively. On the basis of theoretical results, a model is proposed in which the difference in the reaction plane's location in either the less-viscous liquid or in the boundary (determined by the variation in the initial reactant concentrations) results in a significant difference between the locations of the boundary and the reaction plane, this difference being affected by the spike configuration of the boundary. © 2008 American Institute of Chemical Engineers AIChE J, 2008 [source] Enhanced hydrogenation in a reverse flow chromatographic reactorAICHE JOURNAL, Issue 5 2006Guillermo A. Viecco Abstract An experimental study of the reverse flow chromatographic reactor is carried with the equilibrium limited hydrogenation of 1,3,5-trimethylbenzene (mesitylene, MES) to 1,3,5-trimethylcyclohexane. The reaction is pseudo first-order when carried out in excess hydrogen. A simple experimental setup is used to evaluate the effects of carrier flow, reactant feed concentration, and amount of catalyst on conversion. Conversions exceeding the thermodynamic equilibrium conversion are obtained for a wide variety of switching times, catalyst amounts, carrier flow rates, and reactant concentrations, showing the robustness of the system. While the qualitative features of the process can be predicted for a simple linear adsorption equilibrium model, the experimental results are best fitted by assuming a linear adsorption isotherm combined with an adjusted interfacial mass-transfer resistance. The experimental results are very similar to those reported in previous research of the same reaction in a simulated moving-bed chromatographic reactor. © 2006 American Institute of Chemical Engineers AIChE J, 2006 [source] 17O NMR investigation of phosphite hydrolysis mechanismsMAGNETIC RESONANCE IN CHEMISTRY, Issue 12 2007Sarah K. McIntyre Abstract The use of solution 17O NMR spectroscopy in verifying the mechanism of trialkyl phosphite hydrolysis is presented. Trimethyl phosphite was reacted with 17O-labeled H2O at different temperatures and two reactant concentrations, with the reaction being monitored by 17O NMR. Kinetic details elucidated from the NMR spectra are also discussed. Copyright © 2007 John Wiley & Sons, Ltd. [source] Consideration of the Effect of Irregular Catalytic Active Component Distributions in Mesopores , Extension of a Model for Wall Catalyzed Reactions in Microchannel ReactorsCHEMICAL ENGINEERING & TECHNOLOGY (CET), Issue 7 2003B. Platzer Abstract Data available from the literature and experimental results have shown that the distribution of the catalytic active components can be irregular already for fresh catalysts. The determination of the local concentrations of the catalytic active components using wavelength dispersive X-ray spectroscopy confirms this for microstructured wafers used in microchannel reactors. Considering this nonuniform distribution, the used model gives the relation between the local concentration profiles of the reactants inside the pores and the product yield in the entire pore. These results were used in an equation for the diffusion flux at the pore mouth, which is useful for a microchannel model developed in a recent paper [1]. The theoretical considerations deal with cylindrical pores with known reactant concentrations at the pore mouth and known distribution of the catalytic active component within the pore. Beside numerical results, some analytical solutions with low mathematical expense, applicable to special cases, are discussed. The nonconsideration of the irregular distribution of the catalytic active component can be the reason for difficulties during the extrapolation of experimental results to slightly different conditions and can have a great influence on the reaction results. The regarded examples are typical of wall-catalyzed reactions in microchannel reactors with mesopores. [source] | |||||||||||||