Chemisorption of hydrogen on nickel–magnesia catalysts. Part I. General kinetic characteristics

1969 ◽  
Vol 47 (16) ◽  
pp. 2933-2941 ◽  
Author(s):  
N. S. Viswanathan ◽  
L. M. Yeddanapalli
Keyword(s):  
Experimental Data ◽  
Nickel Catalysts ◽  
Activation Energies ◽  
Effect Of Temperature ◽  
Hydrogen Chemisorption ◽  
Kinetic Characteristics ◽  
Wide Range ◽  
Elovich Equation ◽  
Kinetics Of

A detailed study of the kinetics of hydrogen chemisorption on 3 different nickel catalysts, supported on magnesia and prepared by coprecipitation, has been made over a wide range of pressures and temperatures. The results have been analyzed in the light of the Elovich equation. Experimental data obtained by variations of pressure and temperature indicate the existence of a number of stages in the chemisorption process and support the multiple kinetic stage hypothesis suggested by Low. The effect of temperature on the parameters has been studied, and relations obtained which have been used to calculate activation energies for each of the stages.

The Kinetics of Austenization Process of T91 Ferritic Heat-Resistant Steel

2011 ◽  
Vol 317-319 ◽  
pp. 42-47
Author(s):  
Li Fang Zhang ◽  
Yong Chang Liu
Keyword(s):  
Experimental Data ◽  
Phase Transformation ◽  
Kinetic Parameters ◽  
Nucleation And Growth ◽  
Transformation Model ◽  
Resistant Steel ◽  
Kinetic Characteristics ◽  
Heat Resistant Steel ◽  
Austenite Grain ◽  
Kinetics Of

By fitting the calculated transformed fraction according to developed phase-transformation model to the experimental data obtained by differential dilatometry, the kinetic characteristics of the austenitization process in T91 steels have been investigated. According to the kinetic parameters fitted, we recognize that the nucleation and growth of austenite grain are mainly controlled by the diffusion of carbon in ferritic and austenite respectively. In addition, by increasing the diffusion active energy of carbon in austenite, carbides hinder the motion of interface and thus refine austenite grain.

scholarly journals Kinetics of Drying and Physical-Chemical Quality of Peach cv. Hubimel

2019 ◽  
Vol 11 (16) ◽  
pp. 223
Author(s):  
Newton C. Santos ◽  
Sâmela L. Barros ◽  
Shênia S. Monteiro ◽  
Semirames do N. Silva ◽  
Victor H. de A. Ribeiro ◽  
...  
Keyword(s):  
Experimental Data ◽  
Mathematical Models ◽  
Effect Of Temperature ◽  
Initial Time ◽  
High Water Content ◽  
Chemical Quality ◽  
Drying Time ◽  
Physical Chemical ◽  
Kinetics Of

The objective of this study was to perform the kinetics of peach drying and to adjust the experimental data obtained to empirical and diffusive mathematical models to evaluate the effect of temperature on the physical-chemical quality of the final product. The drying experiments were performed in an air circulation dryer with a velocity of 1.5 m s-1, the drying kinetics were performed at temperatures of 60, 70 and 80 °C. Among the mathematical models applied, the Page model was the one that best fit the experimental data, because it presents greater efficiency in the description of the drying process. The decrease in the drying rate from the initial time to the end of the process was observed, increasing the temperature of the air caused a reduction in the drying time. It was verified through the analytical solution of the diffusion equation with infinite wall geometry that the increase of the drying temperature caused the increase of the diffusivity and convective coefficient of heat transfer. Through the Biot number, it can be stated that the first-type boundary condition would also describe the process satisfactorily. The fresh peach slices present high water content and water activity and the drying effect caused significant differences in all physical-chemical parameters analyzed.

A Comparison of Rheological Models and Experimental Data of Metallocene Linear Low Density Polyethylene Solutions as a Function of Temperature and Concentration

2016 ◽  
Vol 12 (3) ◽  
pp. 4322-4339
Author(s):  
Salah Hamza
Keyword(s):  
Experimental Data ◽  
Shear Rate ◽  
Rheological Properties ◽  
Power Law ◽  
Low Density Polyethylene ◽  
Effect Of Temperature ◽  
Low Density ◽  
Linear Low Density Polyethylene ◽  
Shear Rates ◽  
Wide Range

Knowledge of rheological properties of polymer and their variation with temperature and concentration have been globally important for processing and fabrication of polymers in order to make useful products. Basheer et al. [1] investigated, experimentally, the changes in rheological properties of metallocene linear low density polyethylene (mLLDPE) solutions by using a rotational rheometer model AR-G2 with parallel plate geometry. Their work covered the temperature range from  to  and  concentration from  to . In this paper, we reconsider Basheer work to describe the rheological behavior of mLLDPE solutions and its dependence on concentration and temperature.Until now, several models have been built to describe the complex behavior of polymer fluids with varying degrees of success. In this article, Oldroyd 4-constant, Giesekus and Power law models were tested for investigating the viscosity of mLLDPE solution as a function of shear rate. Results showed that Giesekus and power law models provide the best prediction of viscosity for a wide range of shear rates at constant temperature and concentration. Therefore, Giesekus and power law models were suitable for all mLLDPE solutions while Oldroyd 4-constant model doesn't.A new proposed correlation for the viscosity of mLLDPE solutions as a function of shear rate, temperature and concentration has been suggested. The effect of temperature and concentration can be adequately described by an Arrhenius-type and exponential function respectively. The proposed correlation form was found to fit the experimental data adequately.

Improved Measurement of the Kinetics of Crystallization in a Batch Experiment

1993 ◽  
Vol 58 (8) ◽  
pp. 1839-1847 ◽  
Author(s):  
Jaroslav Nývlt ◽  
Miloslav Karel
Keyword(s):  
Experimental Data ◽  
Crystal Size ◽  
Evaluation Method ◽  
Potassium Sulfate ◽  
Batch Experiment ◽  
Improved Method ◽  
Short Intervals ◽  
Wide Range ◽  
Kinetics Of ◽  
Single Batch

An improved method is described whereby knowledge of the supersaturation course during a run and measurement of the final product crystal size distribution yield the growth rate of crystals and the nucleation rate in a wide range of supersaturations from only a single batch experiment. The evaluation method is refined by the interpolation of experimental data for short intervals of time. The method is illustrated using potassium sulfate crystallization as an example.

A general mechanism for the high-temperature pyrolysis of alkanes. The pyrolysis of isobutane

1974 ◽  
Vol 337 (1609) ◽  
pp. 199-216 ◽  
Keyword(s):  
Experimental Data ◽  
Computer Modelling ◽  
Single Pulse ◽  
General Mechanism ◽  
Methyl Radical ◽  
Hydrogen Atoms ◽  
Wide Range ◽  
Independent Experimental Data ◽  
Theoretical Considerations ◽  
Kinetics Of

A general mechanism is proposed to predict the kinetics of pyrolysis of alkanes at high temperatures (> 1000 K), based on theoretical considerations and on existing literature data. An experimental investigation of the pyrolysis of isobutane in a single-pulse shock tube over the temperature range 1200–1500 K is reported and the results are used to test the proposed mechanism. Computer modelling demonstrates that the mechanism is adequate to explain the experimental data provided that the following are included: ‘forbidden' isomerization reactions, non-Arrhenius rate constants for the methyl radical abstraction reactions, and the addition of hydrogen atoms to olefins. Although further refinement of the mechanism is to be expected as more data becomes available, it already enables pyrolytic behaviour to be predicted for a wide range of alkanes. The investigation also demonstrates how computer modelling can provide insight into a reaction mechanism even when the number of unknowns exceeds the independent experimental data available.

scholarly journals Catalytic Hydrogenation of Methylacetylene

1967 ◽  
Vol 45 (10) ◽  
pp. 1023-1030 ◽  
Author(s):  
R. S. Mann ◽  
S. C. Naik
Keyword(s):  
Compensation Effect ◽  
Nickel Catalysts ◽  
Hydrogenation Reaction ◽  
Activation Energies ◽  
Reaction Vessel ◽  
Kcal Mole ◽  
Pressure Time ◽  
Wide Range ◽  
Exponential Factors ◽  
Apparent Activation Energies

The reaction between methylacetylene and hydrogen over supported and unsupported nickel catalysts has been investigated in a static constant volume system for a wide range of temperature and reactant ratios. The pressure–time curves consist of two linear portions of different slopes. The reaction over nickel is largely simple hydrogenation, the early stages being principally a selective production of propylene with small yields of reduced polymers of methylacetylene. The orders of the hydrogenation reaction are first and zero with respect to hydrogen and methylacetylene respectively. The overall apparent activation energies for nickel–pumice and nickel–kieselguhr are 16.8 and 14.0 kcal/mole and for unsupported nickel catalysts vary between 17.2 and 20.0 kcal/mole. A satisfactory "compensation effect" exists between the activation energies and logarithmic values of the pre-exponential factors. The unsupported catalysts were not poisoned when methylacetylene was added first to the reaction vessel.

An expression for droplet evaporation incorporating thermal effects

2011 ◽  
Vol 667 ◽  
pp. 260-271 ◽  
Author(s):  
K. SEFIANE ◽  
R. BENNACER
Keyword(s):  
Experimental Data ◽  
Thermal Effects ◽  
Droplet Evaporation ◽  
Theoretical Expression ◽  
Dimensionless Number ◽  
Wide Range ◽  
Isothermal Diffusion ◽  
Rate Of Evaporation ◽  
First Time ◽  
Kinetics Of

We propose a general theoretical expression for sessile droplets' evaporation, incorporating thermal effects related to the thermal resistance of the substrate and liquid properties. We develop an expression which accounts for thermal effects associated with evaporative cooling; the latter leads to a reduction in the rate of evaporation, which is not accounted for in the current theories, i.e. ‘isothermal diffusion theories’. The threshold for transition to a regime in which thermal effects start to be significant is identified through a dimensionless number which includes substrate and liquid properties as well as the kinetics of evaporation. The proposed theory is validated against experimental data in a very wide range of conditions and for a variety of systems. The developed expression extends the domain of use of diffusion-based models for droplet evaporation and accurately describes some aspects of the phenomenon which, to the best of our knowledge, are highlighted for the first time.

scholarly journals Kinetics of Grape Seed Oil Epoxidation in Supercritical CO2

Catalysts ◽  
2021 ◽  
Vol 11 (12) ◽  
pp. 1490
Author(s):  
Juan Catalá ◽  
Jesús Manuel García-Vargas ◽  
María Jesús Ramos ◽  
Juan Francisco Rodríguez ◽  
María Teresa García
Keyword(s):  
Supercritical Co2 ◽  
Seed Oil ◽  
Grape Seed ◽  
Effect Of Temperature ◽  
Side Reactions ◽  
Secondary Products ◽  
Yield Data ◽  
Grape Seed Oil ◽  
Wide Range ◽  
Kinetics Of

The epoxidation of grape seed oil in supercritical CO2, to the best of our knowledge, has been only superficially described in the literature, apart from a short communication and our own previous published work on the topic. In this work, a thorough study of the performance of the supercritical epoxidation of grape seed oil is performed in a wide range of conditions, and the kinetic parameters of the supercritical epoxidation of vegetable oils are reported for the first time in the literature. The experimental work has covered a 40–60 °C temperature range at 150 bar, sampling during a period of 48 h. The nature and extent of the side reactions and secondary products obtained have been evaluated, being hydrolysis products and their oligomerization derivatives the major by-products. Reaction rate constants (10−2 h−1 order) and activation energy parameters were finally calculated from the experimental conversion and epoxy yield data to establish the effect of temperature on the kinetics of the process.

THE KINETICS OF HYDROGEN CHEMISORPTION ON AN IRIDIUM CATALYST

1959 ◽  
Vol 37 (5) ◽  
pp. 915-921 ◽  
Author(s):  
Manfred J. D. Low ◽  
H. Austin Taylor
Keyword(s):  
Gas Pressure ◽  
Hydrogen Chemisorption ◽  
Iridium Catalyst ◽  
Elovich Equation ◽  
Kinetics Of

The kinetics of the chemisorption of hydrogen on an iridium catalyst have been studied at various temperatures and pressures. The rate of adsorption is well defined by the Elovich equation. Isothermal anomalies have been observed and were found to be a function of temperature and initial gas pressure.

Kinetics of the Luminescence of Isoelectronic Rare-Earth Ions In III-V Semiconductors

1993 ◽  
Vol 301 ◽  
Author(s):  
H.J. Lozykowski
Keyword(s):  
Experimental Data ◽  
Energy Transfer ◽  
Rare Earth ◽  
Excited States ◽  
Quantitative Agreement ◽  
Host Lattice ◽  
Rare Earth Ions ◽  
Wide Range ◽  
Decay Times ◽  
Kinetics Of

ABSTRACTIn this work we have developed a model for the kinetics of the energy transfer from the host lattice to the localized core excited states of rare earth isoelectronic structured traps (REI-trap). We have derive a set of differential equations for semi-insulating semiconductor governing the kinetics of rare earth luminescence. The numerically simulated rise and decay times of luminescence show a good quantitative agreement with the experimental data obtained for InP:Yb, over a wide range of generation rates.

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