Hydrodynamic properties of coal in turbulent fluidized beds

Hydrodynamic properties in turbulent fluidized beds of three different sizes of coal (d _p = 0.507, 0.987, 1.147 mm) have been determined from the pressure fluctuations in a 0.1 m-ID × 3.0 m high Plexiglas column. The transition velocity from the slugging to turbulent flow regimes can be determined from the statistical analysis of pressure fluctuations such as mean amplitude, standard deviation and skewness, the pressure wave velocity, and the bed expansion with gas velocity. The bed expansion in the slugging and turbulent flow regimes cannot be estimated from the two-phase theory. The voids rise velocity and the bed expansion ratio (H/H _mf ) in the turbulent flow regime have been correlated with the relevant dimensionless and operating parameters The ransition velocity to the turbulent flow regime has been determined based on the slug breakdown caused by the inertial force of an upflowing maximum stable slug which overcomes the gravitational force induced by solid refluxing as:      

n‐butane isomerization on sulfated zirconia: isotopic transient kinetic analysis of reaction at the site level

By using SSITKA (steady‐state isotopic transient kinetic analysis), n‐butane (n‐C₄) isomerization on sulfated zirconia (SZ) has been studied for the first time at the site level. Accurate measures of the average residence time and the concentration of the most active surface intermediates leading to isobutane (iso‐C₄) were able to be determined. As has previously been observed, a fast initial deactivation of the catalyst followed by a slow steady‐state deactivation was observed over 400 min time‐on‐stream (TOS). It was shown that even though a large amount (∼100 μmol/g) of n‐C₄ was adsorbed on the catalyst, the concentration of active surface intermediates leading to iso‐C₄ was only ∼10 μmol/g at 30 min TOS. The continuous decrease in indicated that the decrease in catalytic activity was due to loss of active sites. An increase in the average residence time of active surface intermediates leading to iso‐C₄ was observed only between 30 and 100 min TOS. This suggests a possible presence of two types of active sites for n‐C₄ isomerization on SZ under the reaction condition studied. It is suggested that the more‐active sites contributed to the high initial activity, while the majority of active sites after 100 min TOS were the less active sites. This revised version was published online in July 2006 with corrections to the Cover Date.     

Flow directions in gas assisted injection molding when cavities of square flat plates and pipes are involved 1. Theory of flow model and its criterion

In such a complex situation as the cavity of two square plates connected to cavities composed of four pipes with same length and different diameter connected in series and parallel, the resistance of cavity of two square plates should be combined with that of pipes to determine the gas direction in gas assisted injection molding (GAIM). The flow model of Newtonian fluid was previously suggested under the fan-shaped geometry incuding relatively thin cavity of two square plates when , and (H/R₀)².However, one may frequently encounter the problem of relatively thick fan-shaped cavity between two square plates where (H/R₀)² is around 10^-1 and is the order of one. The rule of thumb containing a first order-approximated flow model by perturbation technique was introduced to show, in qualitative way, whether the resistance of the relatively thick cavity of two square plates may affect the gas direction in GAIM under the fore-said geometry. Subsequently, various simulations were performed under the conditions that all dimensions of cavity of two square plates and pipes were fixed except for the diameters of pipes. The results of simulation were compared with the results of the rule of thumb (RT1) containing the approximated flow model as well as those of another rule of thumb (RT2) without the resistance of the relatively thick cavity of two square plates. The results of simulations were generally consistent with the former in qualitative way to determine gas directions in gas assisted injection molding even though a relatively large value of 0.36 was applied as the value of ε to describe a relatively thick cavity of two square plates. In addition, the situation was treated when cavities of pipes and runners were involved in configuration. The rule of thumb was used for the ratio of initial velocities to be recalculated at the first coming change of diameters when the ratio was close to unity and it was quite consistent to the results of simulation.     

Influence of electrolytes on the absorption of nitrogen oxide components N2O4 and N2O3 in aqueous absorbents

The influence of electrolytes, which are dissolved in the aqueous absorbent and do not react with nitrogen oxides, on the absorption kinetics of both these components was investigated experimentally. In addition to demineralized water, various salt solutions of different concentrations as well as sodium hydroxide solution were used as absorbents. The term H \documentclass{article}\pagestyle{empty}\begin{document}$ H\sqrt {k_1 D} $\end{document} for N₂O₄ and N₂O₃, which is important for the design of industrial absorbers, was determined as a function of composition and concentration of the absorbents. In the case of N₂O₄, the chosen measuring and evaluation methods permitted a separate determination of the rate constant k of the pseudo first order reaction and of the solubility H. The diffusion coefficient D of the gas in the absorbent can be obtained only by calculation. Experimental results showed that \documentclass{article}\pagestyle{empty}\begin{document}$(H\sqrt {k_1 D} )\,_{{\rm N}_{\rm 2} {\rm O}_{\rm 4} } $\end{document} decreases with increasing ionic strength I, however, without a clear indication of any ion-specific effects. This decrease does not appear to be caused simply by a reduction in solubility (salting out effect), or in diffusion coefficient, but at least, to the same extent, through a decrease of the rate constant k with increasing electrolyte content in the absorbent. The measurements permitted the determination of the gas-based salting out parameter for N₂O₄. The investigations on the absorption of N₂O₃ in water and in an Na₂SO₄ solution showed no experimentally detectable influence of dissolved salts on \documentclass{article}\pagestyle{empty}\begin{document}$(H\sqrt {k_1 D} )\,_{{\rm N}_{\rm 2} {\rm O}_{\rm 3} } $\end{document}. The numerical value of \documentclass{article}\pagestyle{empty}\begin{document}$(H\sqrt {k_1 D} )\,_{{\rm N}_{\rm 2} {\rm O}_{\rm 3} } $\end{document} is six times that of \documentclass{article}\pagestyle{empty}\begin{document}$(H\sqrt {k_1 D} )\,_{{\rm N}_{\rm 2} {\rm O}_{\rm 4} } $\end{document}.     

The viscosity dependence on concentration,molecular weight and shear rate of xanthan solutions

Summary This paper concerns the viscosity dependence of Xanthan as a function of polymer concentration, shear rate and molecular weight in the ordered conformation. The different samples with various molecular weights are obtained by ultrasonication. A unique curve is obtained for the reduced specific viscosity ( ) as a function of γ · γ _r ⁻¹ for the different molecular weight samples and polymer concentrations below an overlap concentration C [η]₀⩽ 1.5. The master curve giving the relation as a function of C [η]₀ is drawn and compared with that of polystyrene in good solvent. The largest increase of in semidilute solution may be due to larger interchain interactions and to larger stiffness of the Xanthan molecule.     

Modified response surface methodology (MRSM) for phase equilibrium-application

Attempts are being made to predict multicomponent azeotropic mixtures from the physical property of pure component and compositions of the constituting binary combination pairs. A modified response surface methodology (MRSM) model has been proposed which correlates boiling temperatures of binary, ternary and quaternary mixtures directly with the compositions of vapor and liquid phases. The generalized MRSM-2 models for liquid and vapor phases are proposed as follows: (for liquid phase) (for vapor phase) These models require normal boiling point of the pure components, T, and group-group parameters A_ij B_ij & C_ij which can be estimated by the group-group concepts of the constituent components. Therefore, this methodology is applied for the system of three and four components by the computer simulation. No experimental data is required for seeking of composition and temperature of the multicomponent azeotropic mixtures. By means of this methodology, MRSM, it is possible to depict an isothermal line map, temperature contours of the individual phase of the constituting ternaries for each quaternary system. Furthermore, it is possible to predict the azeotropic behaviors, maximum, minimum, saddle or any other type of azeotropic mixtures by examining the graphic contours obtained by computer graphics in the triangular coordinate for ternary and tetrahedron for quaternary. The proposed methodology (MRSM model) has been tested and compared successfully with previously reported azeotropic data in various journals for several ternary and quaternary multicomponent systems. Two azeotropic mixtures are newly found for each of two different quaternary tetrahedrons. The composition, temperature and type of the newly found azeotropes are reported.     

N2O and NO emissions from different N sources and under a range of soil water contents

Emissions of nitrous oxide (N₂O) and nitric oxide (NO) have been identified as one of the most important sources of atmospheric pollution from grasslands. Soils are major sources for the production of N₂O and NO, which are by-products or intermediate products of microbial nitrification and denitrification processes. Some studies have tried to evaluate the importance of denitrification or nitrification in the formation of N₂O or NO but there are few that have considered emissions of both gases as affected by a wide range of different factors. In this study, the importance of a number of factors (soil moisture, fertiliser type and temperature) was determined for N₂O and NO emissions. Nitrous oxide and NO evolution in time and the possibility of using the ratio NO:N₂O as an indicator for the processes involved were also explored. Dinitrogen (N₂) and ammonia (NH₃) emissions were estimated and a mass balance for N fluxes was performed. Nitrous oxide and NO were produced by nitrification and denitrification in soils fertilised with and by denitrification in soils fertilised with . Water content in the soil was the most important factor affecting N₂O and NO emissions. Our N₂O and NO data were fitted to quadratic (r=0.8) and negative exponential (r=0.7) equations, respectively. A long lag phase was observed for the N₂O emitted from soils fertilised with (denitrification), which was not observed for the soils fertilised with (nitrification) and was possibly due to a greater inhibiting effect of low temperatures on microbial activity controlling denitrification rather than on nitrification. The use of the NO:N₂O ratio as a possible indicator of denitrification or nitrification in the formation of N₂O and NO was discounted for soils fertilised with . The N mass balance indicated that about 50 kg N ha⁻¹ was immobilised by microorganisms and/or taken up by plant roots, and that most of the losses ocurred in wet soils (WFPS >60%) as N₂ and NH₃ losses (>55%).     

Simultaneous removal of SO2 and NO X with ammonia absorbent in a packed column

Catalytic oxidation of NO followed by simultaneous removal of SO₂ and NO _X with ammonia is a promising method for control of coal-fired flue gas pollutants. We investigated simultaneous absorption of SO₂ and NO _X in a packed column with ammonia, and found that SO₂ and NO _X could promote absorption with each other in the process of simultaneous removal SO₂ and NO _X . The removal efficiency of SO₂ and NO _X was, respectively, about 98% and 70.9% at pH 5.5, temperature 323.15 K, SO₂ concentration 1,800×10^?6, NO _X concentration 400×10^?6 and ${{m_{NO_2 } } \mathord{\left/ {\vphantom {{m_{NO_2 } } {m_{NO} }}} \right. \kern-0em} {m_{NO} }}$ in our experimental system. The experimental results also show that the formation of sulfite oxidized by reacting with dissolved NO₂ and the molar ratio of sulfite to total sulfur is more than 0.8 in the solution. Accordingly, the energy consumption for sulfite oxidation would be greatly reduced in the process of simultaneous desulfurization and denitrification with ammonia.     

Kinetics of hydrodesulfurization of dibenzothiophene over NiO-MoO3/γ-Al2O3 catalyst

The kinetics of the hydrodesulfurization(HDS) of dibenzothiophene (DBT) has been studied over a NiO-MoO₃/γ-Al₂O₃ catalyst in the temperature range of 473-673 K for partial pressures of DBT from 20 x 10⁵Pa to 70 x 10⁵Pa. A form of the Langmuir-Hinshelwood type rate equation was used to describe the kinetics of the reaction. The reaction was carried out at low conversion level to obtain initial reaction rate data. From this study the rate equation giving the best fit to the data was , which suggests that DBT and hydrogen adsorb on the same type of active sites and that hydrogen adsorbs dissociatively.     

Electrochemical reduction of nitrate ion on various cathodes – reaction kinetics on bronze cathode

Summary The electrochemical reduction of NO ₃ ^- in 0.1 M K₂SO₄ and 0.05 M KNO₃ solution was studied on various electrodes in two different cell configurations, a divided and an undivided one. The products in all cases were NO ₂ ^- , NH₃, N₂ and small amounts of NO₂ and NO. The more efficient cathodes as regards the conversion of NO ₃ ^- to N₂ were Al and the alloy Sn85Cu15, where the selectivity for nitrogen formation was 43 and 35.3% at –1.8 and –2.0 V, respectively. The kinetic analysis of the experimental results was carried out by numerical solution of the resulted differential equations according to the scheme: The rate constants on Sn85Cu15 at –2.0 V for the above reactions were found to be k₁=4.9 × 10^–4 s^–1, k₂=1.76 × 10^–5 s^–1 and k₃=7.66 × 10^–3 l mol^–1 s^–1. At more negative potential more NO ₂ ^- ions reduced and converted either to N2 or NH3. The rate constant of reduction of nitrate was almost the same in the region between –1.7 and –2.0 V, because the reaction is limited by the diffusion. In order to oxidize a part of the undesirable byproducts NO ₂ ^- and NH₃ at the anode of the cell to nitrate and nitrogen respectively, an undivided cell was used. Comparison between the two cell configurations indicated that, although in the undivided cell the % removal efficiency of nitrate was lower than that in the divided one, the selectivities of NO ₂ ^- and NH₃ were 4.8 and 2.2 times lower, respectively.     

NO abatement with CH4 in the presence of O2 on H-ZSM5 with Si/Al=15–200: the dependence of activity on the proton concentration

The abatement of NO with methane in the presence of oxygen was studied on commercial H-ZSM5 samples with Si/Al = 15–200 in a conventional flow apparatus. H-ZSM5 samples were used in the acid form or after exchanging protons with sodium ions to various extents. Their catalytic activity was compared with that of commercial H-mordenite and H-Y. On all H-ZSM5 catalysts, reaction rates R _NO and (molecules s⁻¹ g⁻¹) increased proportionally to the proton concentration, showing that either all protons or a constant fraction of them were equally active. On sodium-exchanged H-ZSM5 samples with Si/Al = 15–17, both R _NO and nearly exponentially increased with the proton concentration. Conversely, on sodium-exchanged H-ZSM5 with Si/Al = 50, both R _NO and linearly increased with the proton concentration. At lower Si/Al ratios, replacing the H-ZSM5 protons with sodium ions partly inactivated the remaining protons. This revised version was published online in July 2006 with corrections to the Cover Date.     

Electrocatalytic activity of copper alloys for \hbox{NO}_{3}^{-} reduction in a weakly alkaline solution Part 1: Copper–zinc

A comparative study of the influence of an addition of Zn to Cu as the basic cathode material on electrocatalytic activity for reduction was performed. Potentiodynamic measurements using a rotating ring-disk electrode were carried out in an artificial solution simulating solution after regeneration of the ion-exchange column for removal in drinking water treatment. The results were verified by batch electrolysis experiments. An enhancement of the electrocatalytic activity was observed. Unfortunately, NH₃ was found to be the main reduction product. The highest electrocatalytic activity was obtained using an electrode containing 41 wt.% Zn.     

Empirical correlation of flow properties of poly(vinyl chloride)

Empirical correlations of flow properties of poly(vinyl chloride) were made using data reported by a number of investigators. Correlation was made by plotting the reduced variable viscosity η/η₀ versus \documentclass{article}\pagestyle{empty}\begin{document}$ (\eta _0 \dot \gamma \bar M_w )/(_\rho RT) $\end{document} or \documentclass{article}\pagestyle{empty}\begin{document}$ (\eta _0 \dot \gamma \bar M_w ^{0.5} )/(_\rho RT) $\end{document} for unplasticized PVC and versus \documentclass{article}\pagestyle{empty}\begin{document}$ (\eta _0 \dot \gamma \bar M_w ^{0.5} )/(_\rho RTW_2 ^a ) $\end{document} with polymer concentration, W₂, for PVC containing plasticizer.     

Effect of impeller blade number on KlA in mechanically agitated vessels

Effects of impeller blade number on gas dispersion and mass transfer rate were thoroughly investigated for mechanically agitated vessels equipped with 2-, 4-, 6- and 8-straight blades disk turbine impellers. The results show that under the same rotational speed, the impeller with more blades always can disperse gas more effectively, which induces a higher value of <K_La>. However, with the same total power consumption, the 4-blade impeller can obtain a higher < K_La> value than the 6- and 8-blade impellers under a lower gassing rate condition (Q_g< 0.5 wm), but if Q_g exceeds 0.5 wm, the 6-blade impeller will perform better than the 4- and 8-blade impellers. To examine the results obtained from the single impeller systems, the same approach is applied to measure < K_La> values for the triple stage 6-blade impeller system (3x6) and quadruple stage 4-blade impeller system (4×4). From the experimental results, it can be found that the 4×4 system gives higher < K_La> value than the 3x6 system under gas completely dispersed conditions. By correlating < K_La> withn _b , N and V_s, the following correlation can be given as:

A simple and efficient oxidation system for the oxidation of alcohols utilizing Oxone® as oxidant catalyzed by polymer-supported 2-iodobenzamide

$\begin{array}{l}{\hbox{R}^1\hbox{R}^2\hbox{CHOH}} \\ {\hbox{RCH}_2\hbox{OH} }\end{array} \dynrightarrow{Oxone}{\hbox{CH}_3\hbox{CN/H}_2\hbox{O}, 70^{\circ}\hbox{C}} \begin{array}{l}{\hbox{R}^1\hbox{R}^2\hbox{CO}} \\ {\hbox{RCOOH}} \end{array} A simple and environmentally friendly procedure for the oxidation of alcohols is presented utilizing Oxone^? (2KHSO₅ · KHSO₄ · K₂ SO₄) as oxidant and polymer-supported 2-iodobenzamide as catalyst in CH₃CN/H₂O mixed solvents.     

Syntheses and Characterization of Diorganotin Derivatives of 2-Mercapto-5-methyl-1,3,4-thiadiazole: X-ray Crystal Structure of Polymeric (C3H3S2N2) [(n-C4H9)6Sn3O(OH)2](C3H3S2N2)

Diorganotin derivatives of 2-mercapto-5-methyl-1,3,4 -thiadiazole, (R = Me 1, n-Bu 2, Ph 3, PhCH₂ 4), have been synthesized and characterized by IR, ¹H, ¹³C and ¹¹⁹Sn NMR spectroscopy. Among them, polymer 2 was also characterized by X-ray crystallography diffraction analysis. This revealed that 2 showed a unique tricyclic structure consisting of a fused five-membered Sn₂ON₂ ring and a four-membered Sn₂O₂ ring. These formed a planar N₂Sn₃O₂ skeleton, with distorted trigonal bipyramidal coordination at the two tin centers and a distorted octahedral coordination at the other tin center. The supramolecular structure of polymer 2 was a 1D zig-zag polymeric chain stabilized by intermolecular O–H...S hydrogen bonds. An erratum to this article can be found at     

Stability of the electrodeposition process for CoPt alloy formation

The stability of the process for electrodeposition of CoPt alloys from ammonium citrate electrolytes containing [Pt(NO₂)₂(NH₃)₂]⁰ as the source of Pt was studied. Voltammetric monitoring of the anodic oxidation of the electrolyte and deposition of CoPt on the cathode showed the effect of the changes of the nature of the Pt complex on the performance of the plating bath. Anodic oxidation of the Pt complex was shown to involve mainly the oxidation of and to some extent NH₃ ligands. The cathodic process is accompanied by reduction of free The reduction of this anion in the bound form is highly inhibited. In contrast, its oxidation at the anode proceeds almost as readily in the bound form as that in the free form.