Power Law Kinetic Model Research Articles

Catalytic performance of structured packages coated with perovskite-based nanocomposite in the methane steam reforming reaction

A conventional Ni + YSZ/YSZ anode half-cell (the Research Center Jülich) and the Ni + YSZ/YSZ planar half cell washcoated by a layer of the Ru + Ni-doped perovskite-based nanocomposite (Ru + Ni/LaPrMnCr/YSZ) were compared in terms of their activities and selectivities in the steam reforming of methane. The kinetic measurements were carried out in a laboratory scale plate-type reactor, and results were interpreted using computational models. A power-law kinetic model was verified against the experimental data, and parameters were estimated. Both numerical prediction and experimental testing indicate that the nanocomposite coated Ni + YSZ/YSZ plate shows much better catalytic performance under the middle-temperature operating conditions. CFD simulations show that for the high activity of thermally conductive catalytic plates, superior heat transfer performance is observed in the lab-scale reactor. The lab-scale data were successfully up-scaled for the case of steam reforming of natural gas on a structured catalyst at realistic operation conditions. Up to 700 °C, the pilot test data obtained with the structured catalyst comprised of three stacked parallel Ni–Al plates (50 × 50 × 1 mm) coated with perovskite-based nanocomposite correlate quite good with the 1-D plug-flow reactor model predictions assuming the proposed kinetics.

Functionalization of halloysite nanotubes by enlargement and hydrophobicity for sustained release of analgesic

A novel hydrophobic organic–inorganic hybrid nanocomposite was prepared for sustained release of analgesic. Using enlarged halloysite nanotubes (EHNTs) as nanocontainer and organosilane (OS) as the hydrophobic layer, nanocomposite denote as [email protected] was readily prepared with a mild reaction. Then the [email protected] was characterized by Fourier transform infrared spectroscopy, transmission electron microscopy, energy dispersive X-ray analysis, and high-performance liquid chromatography. The hydrophobic layer composed of tetraethoxysilane and octyltriethoxysilane made a difference on the wettability of the [email protected] It was proved that the nanocomposite exhibited excellent hydrophobicity with a water contact angle of 132°. Moreover, an enhanced capacity for adsorption (25%) and the sustained-release performance (100 h) of the [email protected] toward IBU were demonstrated and it followed the power law kinetic model. In conclusion, the drug-release platform explored in this work is suitable for other drugs and shows further comprehensive application prospect.

Intrinsic Kinetics of Coking Crude Benzene Hydrodesulfurization on a Ti Modified Co-Mo-P/γ-Al<sub>2</sub>O<sub>3</sub> Catalyst

With different content of thiophene in coking crude benzene, the Orthogonal design experiments of thiophene hydrodesulfurization on a Ti modified Co-Mo-P/γ-Al2O3 catalyst were carried out in a micro-reactor under the reaction conditions of 2.3~2.7MPa,275~335°C, 0.5h-1LHSV and H2/Oil 600~750. The kinetic parameters and the intrinsic kinetics were acquired by 4-order Runge-Kutta method and the modified Simplex method. The power-law type kinetic model was established and consistent with the experiment data and highly acceptable and reliable.

Discrimination of Three Different Power-law Kinetic Models for Hydrocracking of Asphaltenes by Periodic Operation

The three different power-law kinetic models proposed by Trejo et al. (2007) for the hydrocracking of asphaltenes are discriminated under periodic operation. In the present work, the analysis of a plug flow reactor for these three models can be shown to have identical conversion of asphaltenes under conventional steady state operation. The behavior of the models under the periodic operation in the feed concentration cycling in asphaltenes and/or hydrogen concentration is evaluated for the average conversion of asphaltenes. The effect of different feed concentration cycling modes is also evaluated.

Kinetic and thermodynamic investigations of non-isothermal decomposition process of a commercial silver nitrate in an argon atmosphere used as the precursors for ultrasonic spray pyrolysis (USP): The mechanistic approach

The non-isothermal decomposition process of commercial silver nitrate used as the precursor for the USP procedure was investigated by simultaneous TGA–DTA measurements at different heating rates, in an argon atmosphere. Detailed kinetic and thermodynamic analyses, with special emphasis on the formation of a complete mechanistic scheme of the process were performed. It was found that the process under study can be described by the acceleratory power law kinetic model (P2), in the range of the extent of conversion (α) values (0.15≤α≤0.85), where the value of the apparent activation energy (Ea) can be considered as the constant (141.3kJmol−1). The kinetic prediction analysis was shown that only the power law kinetic model (f(α)=2α1/2) gives the value of Ea which is consistent with the value obtained from the isothermal conditions. The critical temperature (Tc) of decomposition process was determined. The resulting value of Tc was in fairly good agreement with the starting temperature of thermal decomposition of silver oxide (Ag2O). The thermodynamic functions of decomposition process are calculated by the activated complex theory and showed that the silver–oxygen bond secession can be interpreted as a “slow” stage of the decomposition process.

Development and characterization of a matrix suitable for extended release systems - release studies with the herbicides atrazine and diuron

This study aimed to produce and characterize a novel material from fish scales and chitosan for use as a medium for the extended release of herbicides. The mechanism of release for the herbicides atrazine and diuron was influenced by diffusion and swelling according to the power law kinetic model. The atrazine release time was seven days, while that of diuron was four days. The results of this study will contribute to the development of environmental matrices for herbicide release systems.

Simplified kinetic model for steam reforming of ethanol on a Ni/Al2O3 catalyst

AbstractEthanol steam reforming is a promising method for hydrogen production. Kinetic studies are carried out over a nickel‐based catalyst from 200 to 600°C. A simplified Langmuir–Hinshelwood–Hougen–Watson (LHHW) kinetic model was proposed with nine parameters, where the surface decomposition of methane is assumed as the rate determining step (RDS), and while all other reaction steps are set as reversible. It is postulated that the velocity of the backward reaction step of the dissociative methane adsorption is similar to all other equilibrium reactions proposed, while the forward reaction step is set as the RDS. In addition, the formation of adsorbed carbon species is excluded due to the fact that SRE experiments were performed with excess water, suggesting that OH species, excluding O species formation, stick better on active Ni surface than methane. In addition, a power law kinetic model was used for analysis; the activation energy was 31.8 kJ/mol, and the reaction order of ethanol pressure was 1.52. Experimental results were successfully demonstrated by both kinetic models. The purpose of this work was to develop a simplified mechanistic model to replace empirical models (power rate model) and other proposed kinetic models that are too complex for an applied kinetic process. It was found that the simplified LHHW kinetic model has a better fit than that of the power law model. The proposed kinetic model works well over a wide temperature range (200–600°C).

Removal of selected chlorinated micropollutants by ozonation

AbstractFeasibility of ozone oxidation for the elimination of selected dissolved organic micropollutants from water and wastewaters was studied. Five organochlorine pesticides, i.e. hexachlorobutadiene, pentachlorobenzene, hexachlorobenzene, lindane, and heptachlor, were used as organic contaminants of model water. The first four of them are classified as priority hazardous substances. The oxidation treatment process was performed in a jet loop reactor. Ozone was prepared from pure oxygen. Quantification of the organochlorine pesticides in water was achieved by the gas chromatographic method after liquid-liquid extraction. Significant contribution of stripping to the removal of the investigated compounds during the ozonation treatment was also proven by the results. Effective ozonation time with regard to treatment efficiencies was 30 min, which corresponds to the ozone input of 317 mg per liter of active volume of the ozonation reactor. Single power law kinetic models were used to describe experimental data and kinetic parameters were estimated. The best fit of the experimental degradation data of all studied pollutants was obtained by the second order kinetic model. It can be concluded, based on the results obtained, that the applied ozonation process is a promising procedure for the removal of the investigated pesticides from aquatic environment.

Kinetics of liquid phase oxidation of benzyl alcohol with hydrogen peroxide over bio-reduced Au/TS-1 catalysts

In this paper, the kinetics and mechanism of oxidation of benzyl alcohol with H2O2 over heterogeneous bio-reduced Au/TS-1 catalysts have been reported after eliminating mass transfer resistances. Langmuir–Hinshelwood and power-law kinetic models are applied to describe the experimental results of the catalytic oxidation. By fitting the kinetic data using the power-rate law model, the orders of the reaction with respect to benzyl alcohol, H2O2, benzaldehyde and catalyst were found to be 0.55, 0.22, −0.35 and 1.06, respectively, with an activation energy of 38.2kJmol−1 from an Arrhenius plot. These fractional orders indicate that the species were adsorbed on the catalyst surface leading to the product, benzaldehyde. Furthermore, the reaction mechanism derived from the Langmuir–Hinshelwood model is proposed; it gives a reasonable description of the oxidation rate, following a rate expression:.r=0.0119×[BzOH][H2O2](1+2.222×[BzOH]+2.330×[H2O2]+4.769×[BzH])2 (mol L−1 gcat−1 s−1).

Kinetic Study of the Oxidative Dehydrogenation of Cyclohexane over Mg<sub>3</sub>(VO<sub>4</sub>)<sub>2</sub> Catalyst

A Mg3(VO4)2catalyst was synthesized and investigated for the oxidative dehydrogenation of cyclohexane to cyclohexene. Integral measurements were performed to determine the reaction network and products distribution, and differential measurements for kinetic investigations. The kinetic study indicated the oxidative dehydrogenation of cyclohexane to cyclohexene follow a parallel-consecutive network. The power law kinetic model was considered as a rough approximation of the experimental results. The rate constants, which included the activation energies, the pre-exponential factors as well as the orders of cyclohexane and oxygen, were evaluated.

Kinetics of toluene alkylation with methanol catalyzed by pure and hybridized HZSM-5 catalysts

A kinetic study of toluene alkylation with methanol was performed over pure HZSM-5, mordenite/ZSM-5 (hybrid of mordenite and HZSM-5), and ZM13 (composite mixture of HZSM-5 and MCM-41 at pH 13). Experimental runs were conducted using a batch fluidized bed reactor at temperatures of 300, 350 and 400°C and reaction times of 3, 5, 7, 10, 13, 15 and 20s. The rate of toluene methylation and toluene disproportionation were studied on the three catalysts (toluene alkylation is usually accompanied by toluene disproportionation on acid catalyst). Based on the results obtained, a simplified power law kinetic model consisting of three reactions was developed to estimate the activation energies of toluene methylation and disproportionation simultaneously. Coke formation on catalysts was accounted for using both reaction time and reactant conversion decay functions. All parameters were estimated based on quasi-steady state approximation. Estimated kinetic parameters were in good agreement with experimental results. The order of alkylation ability of the catalysts was found to be ZM13>HZSM-5>mordenite/ZSM-5, while the reverse is for toluene disproportionation (mordenite/ZSM-5>HZSM-5>ZM13). Thus, alkylation of toluene is most favorable on ZM13 due to combined effect of mesoporosity induced through its synthetic route and acid content. Toluene/MeOH molar ratio of 1:1 was most suitable for toluene alkylation reaction.

Modeling for the catalytic coupling reaction of carbon monoxide to diethyl oxalate in fixed-bed reactors: Reactor model and its applications

A two-dimensional (2D) pseudo-homogeneous reactor model was developed to simulate the performance of fixed-bed reactors for catalytic coupling reaction of carbon monoxide to diethyl oxalate. Reactor modeling was performed using a comprehensive numerical model consisting of two-dimensional coupled material and energy balance equations. A power law kinetic model was applied for simulating the catalytic coupling reaction with considering one main-reaction and two side-reactions. The validity of the reactor model was tested against the measured data from different-scale demonstration processes and satisfactory agreements between the model prediction and measured results were obtained. Furthermore, detailed numerical simulations were performed to investigate the effect of major operation parameters on the reactor behavior of fixed bed for catalytic coupling reaction of carbon monoxide to diethyl oxalate, and the result shows that the coolant temperature is the most sensitive parameter.

Reaction of In-Situ-Gelled Acids With Calcite: Reaction-Rate Study

Summary In-situ-gelled acids have been used extensively in matrix acidizing and acid fracturing for acid diversion and reducing the leakoff rate, respectively. A few studies investigated the rate of dissolution of calcite in polymer-based acids, yet none has addressed in detail the in-situ-gelled acids. Therefore, the aim of this work is to examine the mass transfer and the kinetics of the reaction of 5 wt% HCl in-situ-gelled acids with calcite and determine the effect of Fe crosslinker on the rate of calcite dissolution. The rate of reaction of 5 wt% HCl in-situ-gelled acid was measured using the rotating-disk apparatus. Rock samples of 1.5in. diameter and 1-in. length were used. The effect of temperature (100-250°F) and disk-rotational speed (100-1,800 rev/min) was investigated using Pink Desert limestone rock samples. Calcium concentration was measured in the collected samples and was used to determine the acid-reaction rate. Experimental results showed that the rate of calcite dissolution at 150°F was controlled mainly by the rate of mass transfer of the acid to the surface up to a disk rotational speed of 1,000 rev/min and by the rate of the surface reaction above this value. On the basis of the results obtained, the diffusion coefficient of 5 wt% HCl in in-situ-gelled acid at 150°F; the activation energy; and the reaction rate constant at 150, 200, and 250°F were determined for the first time. A power-law kinetic model was used to determine the kinetics parameters. The presence of Fe3+ crosslinker had a significant effect on the rate of dissolution in comparison with reactions with gelled acid (no crosslinker) at the same condition. The reaction rate decreased by a factor of 2.2 and by a factor of 1.4 when the reaction was conducted at 100 and 1,500 rev/min, respectively. A gel layer, formed on the surface, acted as a barrier between the acid and the rock, which reduced the rate of calcite dissolution.

A Comprehensive Study of Deep Catalytic Oxidation of Benzene, Toluene, Ethyl Acetate, and their Mixtures over Pd/ZSM-5 Catalyst: Mutual Effects and Kinetics

Reaction behaviors and kinetics of catalytic oxidation of benzene, toluene, and ethyl acetate with feed concentrations in the range of 700-5,000 ppm over Pd/ZSM-5 catalyst were investigated. Results for single components show that ethyl acetate (T (50) = 190-200A degrees C) is more easily oxidized than benzene (T (50) = 215-225A degrees C) and toluene (T (50) = 225-235A degrees C). The conversion of ethyl acetate was increased with the increase of its feeding concentration, while the opposite behaviors were observed for benzene and toluene as their conversion rates were decreased with the increase of the inlet concentration. Different behaviors were observed in catalytic oxidation of volatile organic compound (VOC) multi-components, the presence of benzene or toluene inhibits the conversion of ethyl acetate, and the aromatic hydrocarbons inhibit each other in all cases. Ethyl acetate possesses obvious inhibitory effect on benzene oxidation, while it is interesting to note that ethyl acetate has a promotion effect on toluene conversion. The kinetic data were fitted by the Power-law and Mars-van Krevelen kinetic models. The fitting result shows that the Power-law model is more suitable for predicting the conversion of benzene than the other VOCs, and the Mars-van Krevelen model can accurately express the reaction rate of all investigated VOCs.

Methane oxidation over palladium-washcoated foils in the presence of sulphur dioxide

The catalytic oxidation of methane in the presence and absence of SO 2 was investigated on palladium catalysts supported on Al 2O 3 and CeO 2/Al 2O 3 washcoats. The washcoats adhered onto thin stainless steel foils and were investigated under fuel-lean conditions in a stagnation point flow reactor (SPFR). Both palladium-loaded washcoats exhibited hysteresis in the conversion versus temperature profile during heating and cooling. This was attributed to the change in oxidation state of palladium between PdO and Pd. The presence of CeO 2 stabilised PdO, reducing the extent of the conversion discontinuities caused by the PdO ↔ Pd transitions during heating and cooling. However, the Pd/CeO 2/Al 2O 3 catalyst had a lower activity for methane oxidation. The presence of SO 2 in the feed deactivated both catalysts, but unexpected higher conversions following exposure to SO 2 reflected a promotional effect in the thermal decomposition region of PdO. Exposure to 30 ppm SO 2 in the lean methane feed stream eliminated the stabilising effects that CeO 2 had on conversion during the PdO–Pd transition. Frequency factors and activation energies were calculated for a single step reaction mechanism using a power law kinetic model. The numerical code SPIN successfully modelled the conversion curves using the derived kinetic data, providing a means of kinetic validation. The activation energies in absence of SO 2 were 44 ± 1 kJ mol −1 and 58 ± 4 kJ mol −1 for the 3 wt.% Pd/Al 2O 3 and the 3 wt.% Pd/12 wt.% CeO 2/γ–Al 2O 3 catalyst respectively, one of the lowest reported in the literature. The aged catalysts also exhibited relatively low activation energies (49–84 kJ mol −1).

Catalytic Supercritical Water Oxidation for the Destruction of Quinoline Over MnO2/CuO Mixed Catalyst

This article presents the results of the oxidation at supercritical conditions of a nonbiodegradable and highly stable nitrogen containing heterocyclic organic compound (quinoline) over a mixed catalyst in a tubular fixed-bed reactor. The effect of operating conditions namely temperature, pressure, oxygen concentration, and initial quinoline concentration were studied to evaluate their effect on the removal of the organic compound. The results showed that the catalytic reaction depended strongly on temperature and pressure; nevertheless it was very efficient at milder operating conditions close to the critical point of water. A power-law kinetic model was proposed to quantify the catalytic oxidation of quinoline. Three Langmuir−Hinshelwood−Hougen−Watson reaction rates models were also explored to fit the experimental data. However, the kinetic data were better represented by the power-law kinetic model. The catalyst was able to maintain its activity, and thus it can be used as an alternative to reduce the severity of the process.

Oxidation of lean formaldehyde in air over an Au/CeO2 catalyst and its kinetics

The oxidation of low concentration formaldehyde in air over Au/CeO2, prepared by co-precipitation, was investigated. Power-law kinetic models were proposed and the parameters were estimated, which are r = −0.46 × e−14612 / RTCHCHO(303 K < T < 363 K) and r = −295.78 × e−34178 / RTCHCHO (363 K < T < 413 K). The mechanism of the reaction at low temperatures might be different from that at high temperatures.

Kinetics of Methyl Ethyl Ketone Combustion in Air at Low Concentrations over a Commercial Pt/Al2O3 Catalyst

An investigation on the combustion in air of a common volatile organic compound, methyl ethyl ketone (MEK), over a commercial 0.5% Pt/Al2O3 catalyst has been performed. A tubular fixed-bed reactor operating both in the integral (ignition curves) and differential (kinetic study) modes was used at temperatures between 403 and 485 K, MEK partial pressures ranging from 12 to 191 Pa, and space times between 3160 and 25170 kgcat.·min·kmolMEK-1. Water and CO2 were the only reaction products. The apparent reaction orders for MEK given by an empirical power-law kinetic model decreased with reaction temperature from 0.75 at 478 K to 0.44 at 403 K. Several kinetic equations derived from mechanistic considerations have been investigated to account for this fact. The Mars−van Krevelen rate equation described well the kinetics of MEK combustion. However, it has been found that other rate equations derived from the Langmuir−Hinshelwood−Hougen−Watson formalism fit the kinetic data as well as or even better than the Mars−van Krevelen expression.

Steam Reforming of Ethanol Using a Commercial Nickel-Based Catalyst

Kinetic study of ethanol steam reforming over a commercial nickel−magnesia−alumina (Ni/MgO/Al2O3) catalyst was conducted in a fixed-bed reactor 15 mm in diameter. The effects of temperature (673−873 K), molar ratio of steam to ethanol in the feed (in the range of 3:1 to 18:1), feed flow rate (W/FEtOH = 46.2−555.25 g-cat min/mol), catalyst particle size (2.25−0.75 mm), and time-on-stream study was studied. Maximum conversion (>95%) was obtained at 873 K, with a molar ratio of steam to ethanol of 12:1 and a W/FEtOH value of >185 g-cat min/mol at atmospheric pressure. A maximum yield of 3.0 moles of hydrogen per mole of ethanol fed was obtained at a temperature of 873 K, a steam-to-ethanol molar feed ratio of 12:1, and a W/FEtOH value of >110 g-cat min/mol. The acquired data was fitted to a power-law kinetic model and the kinetic parameters were evaluated. The activation energy was determined to be 23 kJ/mol. The average absolute deviation (AAD) for the predicted rates of reaction was determined to be 10.2%....

Destruction of methyl ethyl ketone vapor by ozone on activated carbon

This study attempts to combine the technologies of adsorption of volatile organic compounds (VOCs) on activated carbon and the oxidation of the VOCs by ozone (O 3). In the adsorption/oxidation process, the effects of ozone on the adsorption characteristics of methyl ethyl ketone (MEK) vapor on activated carbon are investigated. The kinetic parameters of the reaction for MEK vapor and O 3 on activated carbon are also determined. The results show that the destructive efficiencies of MEK by 1000 ppmv O 3 on activated carbon are from 12.4% to 48.5%. From the power law kinetic model, the apparent kinetic constant, k, is obtained with a value of 0.0438 h −1. Moreover, from the analytical results of the Arrhenius equation, the activation energy, E a, is found to be 5.12 kcal/mol and the value of rate constant, A, is 189.54 h −1. From the Langmuir–Hishelwood model [Escobar, P., Beroy, Q., Iritia, P.P., Huerta, J.H., 2004. Kinetic Study of the Combustion of Methyl–Ethyl–Ketone over α-Hematite Catalyst. Chem. Eng. J. 102, 107] the values of the kinetics parameters k ′ LH and k LH were 0.035 and 0.6183, respectively. Finally, the modified Wheeler equation [Busmundrud, O., 1993. Vapour Breakthrough in Activated Carbon Beds. Carbon 31, 279; Wood, G., Moyer, E.S., 1989. A Review of the Wheeler Equations and Comparison of Its Applications to Organic Vapor Respirator Cartridges Breakthrough Data. Am. Ind. Hyg. Assoc. J. 50, 400; Yoon, Y.H., Nelson, J.J., 1984. Application of Gas Adsorption Kineties I. A Theoretical for Respirator Cartridge Service Life. Am. Ind. Hyg. Assoc. J. 45, 509] in combination with the power law kinetic model or Langmuir–Hishelwood is used to predict the breakthrough curves. The destruction of MEK can be effectively promoted as the bed height of activated carbon and the concentration of ozone increase. When the ozone concentration is increased to 7800 ppmv and the amount of activated carbon is increased to 5 g the destructive efficiency of MEK is still greater than 95% even after a prolonged operational time. From the results of this study, an adsorption process in combination with ozone oxidation shows potential for the control of VOCs and odor.