Mass Transfer in Catalyst Particles of Non-Traditional Shape

1996 ◽  
Vol 61 (4) ◽  
pp. 564-573
Author(s):  
Jiří Hanika ◽  
Natasha Dropka ◽  
Milan Kubíček
Keyword(s):  
Mass Transfer ◽  
Partial Differential Equations ◽  
Numerical Solution ◽  
Reaction Rate ◽  
Concentration Field ◽  
Order Reaction ◽  
Favourable Effect ◽  
Diffusion Region ◽  
Problem Solution ◽  
First Order

The numerical solution of a system of partial differential equations describing the reacting component transfer in catalyst particles of non-traditional shapes, in extrudates of the starcat and starring types, facilitates the concept of concentration field in a catalyst and of the effectiveness factor of internal diffusion which determines the total reaction rate and thus the catalyst performance. The problem solution was carried out for the first-order reaction of infinite long extrudate and for the particles of star-shaped catalyst of finite length. The favourable effect was confirmed of the catalyst extrudate shaping on its performance as far as the rection takes place in the diffusion region.

Leaching Kinetics of Atrazine and Inorganic Chemicals in Tilled and Orchard Soils

2014 ◽  
Vol 28 (2) ◽  
pp. 231-237 ◽  
Author(s):  
Lech W. Szajdak ◽  
Jerzy Lipiec ◽  
Anna Siczek ◽  
Artur Nosalewicz ◽  
Urszula Majewska
Keyword(s):  
Reaction Rate ◽  
Inorganic Compounds ◽  
Model Performance ◽  
Order Reaction ◽  
First Order Reaction ◽  
Order Kinetic ◽  
Time Data ◽  
First Order ◽  
Concentration Changes ◽  
Reaction Constants

Abstract The aim of this study was to verify first-order kinetic reaction rate model performance in predicting of leaching of atrazine and inorganic compounds (K+1, Fe+3, Mg+2, Mn+2, NH4 +, NO3 - and PO4 -3) from tilled and orchard silty loam soils. This model provided an excellent fit to the experimental concentration changes of the compounds vs. time data during leaching. Calculated values of the first-order reaction rate constants for the changes of all chemicals were from 3.8 to 19.0 times higher in orchard than in tilled soil. Higher first-order reaction constants for orchard than tilled soil correspond with both higher total porosity and contribution of biological pores in the former. The first order reaction constants for the leaching of chemical compounds enables prediction of the actual compound concentration and the interactions between compound and soil as affected by management system. The study demonstrates the effectiveness of simultaneous chemical and physical analyses as a tool for the understanding of leaching in variously managed soils.

scholarly journals Determination of exothermic batch reactor specific model parameters

2019 ◽  
Vol 292 ◽  
pp. 01063
Author(s):  
Lubomír Macků
Keyword(s):  
Rate Constant ◽  
Reaction Rate ◽  
Batch Reactor ◽  
Specific Model ◽  
Reaction Rate Constant ◽  
Order Reaction ◽  
First Order Reaction ◽  
Model Parameters ◽  
Reactor Model ◽  
First Order

An alternative method of determining exothermic reactor model parameters which include first order reaction rate constant is described in this paper. The method is based on known in reactor temperature development and is suitable for processes with changing quality of input substances. This method allows us to evaluate the reaction substances composition change and is also capable of the reaction rate constant (parameters of the Arrhenius equation) determination. Method can be used in exothermic batch or semi- batch reactors running processes based on the first order reaction. An example of such process is given here and the problem is shown on its mathematical model with the help of simulations.

Heat/mass transport in shear flow over a heterogeneous surface with first-order surface-reactive domains

2015 ◽  
Vol 782 ◽  
pp. 260-299 ◽  
Author(s):  
Preyas N. Shah ◽  
Eric S. G. Shaqfeh
Keyword(s):  
Mass Transfer ◽  
Shear Rate ◽  
Shear Flow ◽  
Reaction Rate ◽  
Patch Size ◽  
Patch Area ◽  
First Order ◽  
Effective Boundary ◽  
Order Surface ◽  
Slip Distance

Surfaces that include heterogeneous mass transfer at the microscale are ubiquitous in nature and engineering. Many such media are modelled via an effective surface reaction rate or mass transfer coefficient employing the conventional ansatz of kinetically limited transport at the microscale. However, this assumption is not always valid, particularly when there is strong flow. We are interested in modelling reactive and/or porous surfaces that occur in systems where the effective Damköhler number at the microscale can be $O(1)$ and the local Péclet number may be large. In order to expand the range of the effective mass transfer surface coefficient, we study transport from a uniform bath of species in an unbounded shear flow over a flat surface. This surface has a heterogeneous distribution of first-order surface-reactive circular patches (or pores). To understand the physics at the length scale of the patch size, we first analyse the flux to a single reactive patch. We use both analytic and boundary element simulations for this purpose. The shear flow induces a 3-D concentration wake structure downstream of the patch. When two patches are aligned in the shear direction, the wakes interact to reduce the per patch flux compared with the single-patch case. Having determined the length scale of the interaction between two patches, we study the transport to a periodic and disordered distribution of patches again using analytic and boundary integral techniques. We obtain, up to non-dilute patch area fraction, an effective boundary condition for the transport to the patches that depends on the local mass transfer coefficient (or reaction rate) and shear rate. We demonstrate that this boundary condition replaces the details of the heterogeneous surfaces at a wall-normal effective slip distance also determined for non-dilute patch area fractions. The slip distance again depends on the shear rate, and weakly on the reaction rate, and scales with the patch size. These effective boundary conditions can be used directly in large-scale physics simulations as long as the local shear rate, reaction rate and patch area fraction are known.

scholarly journals The alcoholysis of 1,2,2-trimethylpropyl-methylfluorophosphonate

2000 ◽  
Vol 65 (12) ◽  
pp. 857-866
Author(s):  
Mladjen Micevic ◽  
Slobodan Petrovic
Keyword(s):  
Kinetic Data ◽  
Reaction Rate ◽  
Frequency Factor ◽  
Reaction Rate Constant ◽  
Order Reaction ◽  
Activation Entropy ◽  
Second Order Reaction ◽  
Third Order ◽  
First Order ◽  
Kinetics Of

The alcoholysis of 1,2,2-trimethylpropyl-methylfluorophosphonate (soman) was examined with a series of alkoxides and in corresponding alcohols: methanol, ethanol, 1-propanol, 2-propanol, 2-methoxyethanol and 2-ethoxyethanol. Soman reacts with the used alkoxides in a second order reaction, first order in each reactant. The kinetics of the reaction between 1,2,2-trimethylpropyl-methylfluorophosphonate and ethanol in the presence of diethylenetriamine was also examined. A third order reaction rate constant was calculated, first order in each reactant. The activation energy, frequency factor and activation entropy were determined on the basis of the kinetic data.

Enhancement of decomposition of 2-chlorophenol with ultrasound/H2O2 process

1996 ◽  
Vol 34 (9) ◽  
pp. 41-48 ◽  
Author(s):  
Jih-Gaw Lin ◽  
Cheng-Nan Chang ◽  
Jer-Ren Wu ◽  
Ying-Shih Ma
Keyword(s):  
Ionic Strength ◽  
Reaction Rate ◽  
Order Reaction ◽  
Pseudo First Order Reaction ◽  
Initial Concentration ◽  
First Order ◽  
Toc Removal ◽  
Cp Decomposition ◽  
Effects Of Ph ◽  
Pseudo First Order

We investigated the effects of pH, ionic strength, catalyst, and initial concentration on both decomposition of 2-chlorophenol (2-cp) and removal of total organic carbon (TOC) in aqueous solution with ultrasonic amplitude 120 μm and H2O2 (200 mg/l). When the initial concentrations of 2-cp was 100 mg/l and the pH was controlled at 3, the rate of 2-cp decomposition was enhanced up to 6.6-fold and TOC removal up to 9.8-fold over pH controlled at 11. At pH 3, the efficiency of decomposition of 2-cp was 99% but the removal of TOC was only 63%; a similar situation applied at pH 7 and 11. Hence intermediate compounds were produced and 2-cp was not completely mineralized. When the concentration of ionic strength was increased from 0.001 to 0.1 M, the rate of 2-cp decomposition was enhanced only 0.3-fold, whereas the TOC removal was not enhanced. In comparison of the effects of pH and ionic strength, pH had greater influence on both 2-cp decomposition and TOC removal than ionic strength. The effect of a catalyst (FeSO4) on decomposition of 2-cp was insignificant comparing with direct addition of H2O2. The reaction rate at a smaller initial concentration of 2-cp (10 mg/l) was more rapid than at a greater one (100 mg/l). The rate of 2-cp decomposition and TOC removal appeared to follow pseudo-first-order reaction kinetics.

Kinetics and Mechanism of Oxidation of Selenium(IV) by Permanganate Ion in Aqueous Perchlorate Solutions

1993 ◽  
Vol 58 (3) ◽  
pp. 538-546 ◽  
Author(s):  
Refat M. Hassan ◽  
Sahr A. El-Gaiar ◽  
Abd El-Hady M. El-Summan
Keyword(s):  
Reaction Mechanism ◽  
Reaction Rate ◽  
Oxidation Process ◽  
Selenium Dioxide ◽  
Order Reaction ◽  
Acid Solutions ◽  
First Order ◽  
Acid Catalyzed ◽  
Mechanism Of Oxidation ◽  
Kinetics Of

The kinetics of permanganate oxidation of selenium dioxide in perchloric acid solutions at a constant ionic strength of 2.0 mol dm-3 has been investigated spectrophotometrically. A first-order reaction in [MnO4-] and fractional order with respect to selenium(IV) were observed. The reaction rate was found to be pH-independent at lower acid concentrations ([H+] < 0.5 mol dm-3) and was acid-catalyzed beyond this range. Addition of Mn2+ and F- ions leads to the prediction that MnO4- is the sole reactive species in the oxidation process. A tentative reaction mechanism consistent with the reaction kinetics has been proposed.

scholarly journals Occurrence and Some Characterization Studies of Invertase in the Green Plantain Fruit (Musa parasidiaca)

1969 ◽  
Vol 46 (2) ◽  
pp. 120-126
Author(s):  
Betty G. García
Keyword(s):  
Crude Protein ◽  
Reaction Rate ◽  
Order Reaction ◽  
Zero Order ◽  
Optimum Temperature ◽  
First Order ◽  
Sucrose Solutions ◽  
Optimum Ph ◽  
Characterization Studies ◽  
Substrate Concentrations

The crude-protein fraction of green plantains was isolated and found to cause an inversion of sucrose solutions. The rate of inversion of sucrose by the invertase of the green plantain is proportional to the concentration of enzyme. The inversion of sucrose, when catalyzed by green-plantain invertase, appears to follow a first-order reaction rate at low substrate concentrations (below 6 percent). As the concentration of sucrose exceeds 6 percent the rate of the reaction changes to zero order. An optimum pH of 4.15 and an optimum temperature of 44.4° C. were obtained for the activity of green-plantain invertase.

Cementation kinetics of copper on a rotating zinc cylinder

1987 ◽  
Vol 52 (5) ◽  
pp. 1204-1210 ◽  
Author(s):  
Vladimír Glaser ◽  
Jan Vídenský ◽  
Miroslav Kužela
Keyword(s):  
Experimental Data ◽  
Mass Transfer ◽  
Kinetic Equation ◽  
Rate Equation ◽  
Diffusion Region ◽  
First Order ◽  
Proportionality Constant ◽  
Zinc Surface ◽  
Reaction Proceeds ◽  
Kinetics Of

The authors followed the course of cementation of copper from sulphate solutions on a rotating zinc cylinder. Treatment of experimental data revealed that the coefficient of proportionality in the kinetic equation is not influenced by the Cu layer deposited on the zinc surface and is independent of the concentration of Cu(II) ions, but decreases with increasing concentration of ZnSO4 in solution. The cementation reaction proceeds in the diffusion region and is of the first order with respect to the concentration of Cu(II) ions; the proportionality constant in the rate equation corresponds to the mass transfer coefficient.

Kinetics of Methylation of Methyl 5-Deoxy-α/β-D-xylofuranosides

2004 ◽  
Vol 69 (10) ◽  
pp. 1877-1888
Author(s):  
Mária Oščendová ◽  
Jitka Moravcová
Keyword(s):  
Sodium Hydroxide ◽  
Methyl Iodide ◽  
Rate Constants ◽  
Reaction Rate ◽  
Steric Effect ◽  
Order Reaction ◽  
Half Time ◽  
First Order ◽  
Consecutive Reactions ◽  
Kinetics Of

The kinetics of methylation of methyl 5-deoxy-α-D-xylofuranoside (1), methyl 5-deoxy-β-D-xylofuranoside (2) and their partly methylated derivatives with methyl iodide in the presence of sodium hydroxide in acetonitrile was studied. The reaction rate was independent of the base concentration during the first half-time only and the methylation proceeded as a first-order reaction. The rate constants of all side and consecutive reactions were calculated and the influence of both polar and steric effect is discussed. The methylation of 1 was highly regioselective giving almost exclusively 5-deoxy-2-O-methyl-α-D-xylofuranoside.

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