Kinetic Model of Gas‐Liquid‐Liquid Reactive Extraction for Production of Hydrogen Peroxide

The kinetic aspects of the gas‐liquid‐liquid reactive extraction process for the production of hydrogen peroxide were investigated in a batch reactor. It was observed that the gas‐liquid reaction rate is strongly affected by mass transfer of oxygen across the liquid film and the reaction can be simplified to pseudo‐first order. The extraction rate is governed by both reaction and liquid‐liquid mass transfer, and is slightly lower than the reaction rate. In addition, a kinetic model of the reactive extraction process for the production of hydrogen peroxide was developed. Kinetic parameters under different conditions were determined by experiments. The data calculated from the kinetic model match experimental data well under different conditions for hydrogen peroxide production in gas‐liquid‐liquid reactive extraction.     

Comparison of Mechanistic Models for the Catalytic Oxidation of Trichloroethylene over Cr/Al2O3 and Al‐Cr/Porous Glass Catalysts

In this study the catalytic oxidation of trichloroethylene was investigated in a fixed bed tubular reactor system that consisted of a 50 cm long and 3 cm inner diameter quartz glass tube packed with the catalyst. The Cr/Al₂O₃ catalyst (Cat. I) contains 3.8 w/o Cr and the Al‐Cr/porous glass catalysts (Cat. II) contain in one set 5.5 w/o Al and 9.6 w/o Cr and in the other set 6.2 w/o Al and 11.7 w/o Cr. The two types of catalysts were prepared by impregnation procedure. A number of kinetic rate expressions were evaluated for their ability to fit the experimental data to the integral reactor equation using SimuSolv packet program. The temperature influence on the reaction rate constants and the adsorption equilibrium constants were correlated simultaneously using Arrhenius and van't Hoff equations, respectively. The kinetic rate expression, based on Rideal‐Eley type model, describes well the integral conversion data for Cat. I while Langmuir‐Hinshelwood/Hougen‐Watson type model describes well the integral conversion data for Cat. II over the range of conditions investigated.     

Performance Enhancement by Unsteady‐State Reactor Operation: Theoretical Analysis for Two‐Sites Kinetic Model

Theoretical analysis of the reactor performance under unsteady‐state conditions was carried out. The reactions are described by two kinetic models, which involve the participation in catalytic reaction of two types of active sites. The kinetic model I assumes the blocking of one of the active sites by a reactant, and the kinetic model II suggests a transformation of active sites of one type into another under the influence of the reaction temperature. The unsteady‐state conditions on the catalyst surface are supposed to be created (i) by forced oscillations of temperature and concentration in the reactor inlet (periodic operation of reactor) and (ii) by catalyst circulation between two reactors in a dual‐reactor system (spatial regulation). The influence of various parameters like concentration of reactant, cycle split, length of period of forced oscillations, temperatures and the ratio of catalyst volumes in the dual‐reactor was investigated with respect to the yield of the desired product. It is shown that for both cases of unsteady‐state conditions (periodic reactor operation as well as in a dual‐reactor system), a mean reaction rate predicted by the kinetic model I was up to two times higher than the steady‐state value. The kinetic model II shows a 20 % increase of the selectivity towards the desired product.     

Kinetics of Liquid‐Phase Hydrogenation of Iso‐valeraldehyde to Iso‐amyl Alcohol Over A Ru/Al2O3 Catalyst

The liquid‐phase catalytic hydrogenation of iso‐valeraldehyde to iso‐amyl alcohol was studied in a slurry reactor. The kinetics of liquid‐phase hydrogenation of iso‐valeraldehyde over a 5% Ru/Al₂O₃ catalyst was studied in the range of temperature 373‐393 K and H₂ pressure 0.68‐2.72 MPa using 2‐propanol as the solvent. The selectivity to iso‐amyl alcohol was 100%. The kinetic data were analyzed using a simple power law model. A single site Langmuir‐Hinshelwood type model suggesting dissociative adsorption of hydrogen and surface reaction as the rate‐controlling step provided the best fit of the experimental data. The catalyst could be reused thrice without any loss in activity.     

Glycerol‐Reforming Kinetics Using a Pt/C Catalyst

Catalytic steam reforming of glycerol, a by‐product in biodiesel production, represents an attractive route to hydrogen. For the first time, the kinetics of the glycerol steam reforming reaction over a Pt/C catalyst was considered. Kinetic data, i.e., glycerol conversion vs. space time, were obtained experimentally by using a fixed‐bed reactor and were analyzed by the integral method of analysis. It was found that in the studied ranges of temperature from 623 to 673 K and space time from 0.39 to 1.56 g h/mol the investigated reaction is of the first‐order with respect to glycerol. The specific reaction rate constant at 673 K was determined to be 1.1·10⁵ cm³/g_cat h. The values of glycerol conversion predicted by the first‐order kinetic model were in good agreement with those obtained experimentally. The increase in temperature, space time, and initial water/glycerol ratio caused the expected increase in hydrogen yield.     

An experimental investigation on the rate of CO<Subscript>2</Subscript> absorption into aqueous methyldiethanolamine solutions

In this paper, the CO₂ absorption rates into aqueous solutions of Methydiethanolamine (MDEA) at various concentrations of 1, 2, 3 and 4 M and temperatures varying from 293 to 323 K were measured by using a laboratory stirred reactor. The kinetics experiments were conducted under a pseudo first order regime. The data were analyzed by means of chemical absorption theory and the kinetic parameters associated with the reaction, such as the reaction order and the reaction rate constants, were evaluated. The effect of temperature on the reaction rate constant was assessed and the activation energy was evaluated at about 44.12 kJoule/mol.     

Catalytic Hydrocracking of a Bitumen‐Derived Asphaltene over NiMo/γ‐Al2O3 at Various Temperatures

Hydrocracking of a bitumen‐derived asphaltene over NiMo/γ‐Al₂O₃ was investigated in a microbatch reactor at varying temperatures. The molar kinetics of asphaltene cracking reaction was examined by fitting the experimental data. Below a defined temperature, the molar reaction showed the first‐order kinetic feature while at higher temperatures secondary reactions such as coke formation became significant, causing deviation of the reaction behavior from the proposed first‐order kinetic model. Selectivity analysis proved that dominant products varied from gases to liquids to gases with increasing temperature, shifting the dominant reaction from C–S bonds cleavage to C–C bonds cleavage.     

Cure kinetics and thermal stability of micro and nanostructured thermosetting blends of epoxy resin and epoxidized styrene‐block‐butadiene‐block‐styrene triblock copolymer systems

The compatibility of styrene‐block‐butadiene‐block‐styrene (SBS) triblockcopolymer in epoxy resin is increased by the epoxidation of butadiene segment, using hydrogen peroxide in the presence of an in situ prepared catalyst in water/dichloroethane biphasic system. Highly epoxidized SBS (epoxy content SBS >26 mol%) give rise to nanostructured blends with epoxy resin. The cure kinetics of micro and nanostructured blends of epoxy resin [diglycidyl ether of bisphenol A; (DGEBA)]/amine curing agent [4,4′‐diaminodiphenylmethane (DDM)] with epoxidized styrene‐block‐butadiene‐block‐styrene (eSBS 47 mol%) triblock copolymer has been studied for the first time using differential scanning calorimetry under isothermal conditions to determine the reaction kinetic parameters such as kinetic constants and activation energy. The cure reaction rate is decreased with increasing the concentration of eSBS in the blends and also with the lowering of cure temperature. The compatibility of eSBS in epoxy resin is investigated in detailed by Fourier transform infrared spectroscopy, optical and transmition electron microscopic analysis. The experimental data of the cure behavior for the systems, epoxy/DDM and epoxy/eSBS(47 mol%)/DDM show an autocatalytic behavior regardless of the presence of eSBS in agreement with Kamal's model. The thermal stability of cured resins is also evaluated using thermogravimetry in nitrogen atmosphere. POLYM. ENG. SCI., 2012. © 2012 Society of Plastics Engineers     

Indirect Synthesis of Bis(2‐PhInd)ZrCl2 Metallocene Catalyst,Kinetic Study and Modeling of Ethylene Polymerization

Bis(2‐phenylindenyl)zirconium dichloride (bis(2‐PhInd)ZrCl₂) catalyst was synthesized via the preparation of bis(2‐phenylindenyl)zirconium dimethyl (bis(2‐PhInd)ZrMe₂) followed by chlorination to obtain the catalyst. Performance of the catalyst for ethylene polymerization and its kinetic behavior were investigated. Activity of the catalyst increased as the [Al]:[Zr] molar ratio increased to 2333:1, followed by reduction at higher ratios. The maximum activity of the catalyst was obtained at a polymerization temperature of 60 °C. The rate‐time profile of the reaction was of a decay type under all conditions. A general kinetic scheme was modified by considering a reversible reaction of latent site formation, and used to predict dynamic polymerization rate and viscosity average molecular weight of the resulting polymer. Kinetic constants were estimated by the Nelder‐Mead numerical optimization algorithm. It was shown that any deviation from the general kinetic behavior can be captured by the addition of the reversible reaction of latent site formation. Simulation results were in satisfactory agreement with experimental data.     

Toward autothermal and hydrogen‐producing sorbent regeneration for calcium‐looping

This paper presents a simulation study on the kinetic performance of combined methane combustion, steam/dry reforming, and limestone calcination for autothermal, hydrogen‐producing, and rapid sorbent regeneration in turbulent fluidized bed reactors. The effects of key operational factors are investigated at reactor pressures of 1 bar to 5 bars, including reactor temperature, CaCO₃/total gas molar feed ratio, and sorbent residence time. The results are compared to those for conventional steam calciners, demonstrating the potential for superior performance of this novel sorbent regeneration technology under certain circumstances. A simple, but effective, design methodology is then suggested to determine the proper range of operating conditions and/or reactor dimensions for limestone calcination using this process.     

Kinetics of the vapour-phase hydrogenation of benzene over a supported nickel catalyst in a stirred-vessel reactor

The catalytic hydrogenation of benzene was investigated over a supported nickel catalyst in a continuous stirred-vessel reactor between 260° and 450°F at atmospheric pressure. The effects of temperature, ratio of hydrogen to benzene and total feed rate (or contact time) on the conversion of benzene and yield of cyclohexane were determined. The use of the stirred reactor helped to eliminate mass transfer limitations. The investigation was carried out using surface-coated catalysts in order to eliminate pore diffusion which might otherwise mask the actual kinetics. Studies of the mixing characteristics of the reactor were carried out under both reacting and non-reacting conditions, by following conversion as a function of stirrer speed and by a tracer (pulse) technique, respectively. The kinetic data were analysed to determine the most probable model to represent the reaction. The Houghen–Watson type analysis was carried out using non-linear least squares instead of the usual linear one. The model that satisfactorily correlated the data over the entire temperature range describes the rate-controlling step as the surface reaction between adsorbed hydrogen and adsorbed benzene, the hydrogen addition being simultaneous. The following Hougen–Watson type equation was proposed: r = k_e K_H ³K_B P_H ³P_B/(1+K_HP_H+K_BP_B+K_CP_C)⁴. The constants in this rate equation were expressed as a function of temperature.     

Simplified Free‐Radical Reaction Kinetics for p‐Xylene Oxidation to Terephthalic Acid

The kinetic models based on complex free‐radical mechanisms always involve lots of parameters, which result in model overparameterization. In this work, on the basis of free‐radical reaction mechanisms, a simplified kinetics for liquid‐phase catalytic oxidation of p‐xylene (PX) to terephthalic acid (TPA) was developed. By assuming that different peroxy radicals have equivalent reactivity, all the initiation rate constants are identical, and the differences in the rates of termination between various peroxy radicals are neglected, the kinetic model is simplified to include only six parameters that are to be determined by experiment. The kinetic model established in this paper was shown to have satisfactory precision in predicting the concentration profiles. The kinetic model proposed is even simpler than the first ‐ order kinetic model because the rate constants concerning chain propagation and termination are independent of temperature within the range investigated.     

Preparation of sorbitol from D‐glucose hydrogenation in gas–liquid–solid three‐phase flow airlift loop reactor

A new process for D ‐glucose hydrogenation in 50 wt% aqueous solution, into sorbitol in a 1.5 m³ gas–liquid–solid three‐phase flow airlift loop reactor (ALR) over Raney Nickel catalysts has been developed. Five main factors affecting the reaction time and molar yield to sorbitol, including reaction temperature (T_R), reaction pressure (P_R), pH, hydrogen gas flowrate (Q_g) and content of active hydrogen, were investigated and optimized. The average reaction time and molar yield were 70 min and 98.6% under the optimum operating conditions, respectively. The efficiencies of preparation of sorbitol between the gas–liquid–solid three‐phase flow ALR and stirred tank reactor (STR) under the same operating conditions were compared. Copyright © 2004 Society of Chemical Industry     

Hydrocracking of Fischer‐Tropsch waxes: Kinetic modeling via LHHW approach

A lumped kinetic model to describe the hydrocracking of complex mixtures of paraffins, such as Fischer‐Tropsch waxes, has been developed. A Langmuir‐Hinshelwood‐Hougen‐Watson approach has been followed, accounting for physisorption by means of the Langmuir isotherm. Finally, a complete form of the rate expression is used, thus introducing the equilibrium constants for dehydrogenation and protonation elementary steps. To minimize the number of model parameters, the kinetic and thermodynamic constants are defined as functions of the chain length. Vapor–liquid equilibrium is calculated along the reactor, and the hydrocarbons concentrations are described by means of fugacity. The model provides quite a good fitting of experimental results and is able to predict the effects of the operating conditions (temperature, pressure, H₂/wax ratio, and WHSV). Outstandingly, the estimated values and trends of the kinetic and thermodynamic constants (activation energies, Langmuir adsorption constants, etc.) are in line with their physical meaning. © 2010 American Institute of Chemical Engineers AIChE J, 2011     

Catalytic removal of phenol from aqueous solutions in a trickle‐bed reactor

The degradation of high concentrations of phenol (1g/dm^?3) in aqueous media at high temperatures (100–190 °C) and pressures (2.0 MPa) has been studied by catalytic wet air oxidation in a trickle‐bed reactor. The effect of reaction temperature, weight hourly space velocity (WHSV) and hydrogen peroxide concentration on phenol concentration, total organic carbon (TOC) and chemical oxygen demand (COD) conversion by using a commercial copper catalyst has been investigated. At 150 °C, TOC removal increased by 28% with the WHSV of 62.5 h^?1. The addition of hydrogen peroxide as a free radical promoter significantly enhanced the depletion rate of phenol. A kinetic study has been carried out leading to the determination of the kinetic constants for the removal of TOC. Copyright © 2005 Society of Chemical Industry     

Kinetics of hydrogenation of 4‐chloro‐2‐nitrophenol catalyzed by Pt/carbon catalyst

Hydrogenation of 4‐chloro‐2‐nitrophenol (CNP) was carried out at moderate hydrogen pressures, 7–28 atm, and temperatures in the range 298–313 K using Pt/carbon and Pd/γ‐Al₂O₃ as catalysts in a stirred pressure reactor. Hydrogenation of CNP under the above conditions gave 4‐chloro‐2‐aminophenol (CAP). Dechlorination to form 2‐aminophenol and 2‐nitrophenol is observed when hydrogenation of CNP is carried out above 338 K, particularly with Pd/γ‐Al₂O₃ catalyst. Among the catalysts tested, 1%Pt/C was found to be an effective catalyst for the hydrogenation of CNP to form CAP, exclusively. To confirm the absence of gas–liquid mass transfer effects on the reaction, the effect of stirring speed (200–1000 rpm) and catalyst loading (0.02–0.16 g) on the initial reaction rate at maximum temperature 310 K and substrate concentration (0.25 mole) were thoroughly studied. The kinetics of hydrogenation of CNP carried out using 1%Pt/C indicated that the initial rates of hydrogenation had first order dependence with respect to substrate, catalyst and hydrogen pressure in the range of concentrations varied. From the Arrhenius plot of ln rate vs 1000/T, an apparent activation energy of 22 kJ mol^?1 was estimated. © 2001 Society of Chemical Industry     

Nitration of nitrobenzene at high‐concentrations of sulfuric acid: Mass transfer and kinetic aspects

This article reports studies on mass transfer and kinetics of nitration of nitrobenzene at high concentrations of sulfuric acid in a batch reactor at different temperatures. The effects of concentration of sulfuric acid, speed of stirring, and temperature on mass transfer coefficient were investigated. The kinetics of nitration under homogenized conditions was studied at different sulfuric acid concentrations at these temperatures. The reaction rate constants were determined. The variation of rate constant with sulfuric acid concentration was explained by the M_c function. The activation energies of the reactions were determined from the Arrhenius plots. The regimes of the reactions were determined using the values of the mass transfer coefficients and the reaction rate constants. A model was developed for simultaneous mass transfer and chemical reaction in the aqueous phase. The yields of the three isomers of dinitrobenzene were determined, and the variation of isomer distribution with sulfuric acid concentration and temperature was analyzed. This work demonstrates that more than 90% conversion of nitrobenzene is possible at high‐sulfuric acid concentrations resulting in high yield of the product even at moderate temperatures and at low speeds of stirring. © 2009 American Institute of Chemical Engineers AIChE J, 2010     

Kinetics of o‐Xylene Combustion over a Pt/Alumina Catalyst

o‐Xylene combustion in air over a Pt/γ‐Al₂O₃ catalyst was investigated in a laboratory reactor at low concentrations typical for depollution applications. The results evidenced a slightly negative influence of o‐xylene concentration on combustion rate. A kinetic model of the combustion process was developed by using the Langmuir‐Hinshelwood mechanism, assuming the surface reaction between adsorbed oxygen atoms and adsorbed o‐xylene molecules as controlling step. The rate expression includes the influences of o‐xylene and water adsorption on the active centers of the catalyst. The estimation of rate expression parameters is based on o‐xylene conversion measurements obtained under conditions free of influences of physical steps.     

Reaction rate hysteresis in the hydrotreating of thiophene in wide‐ and narrow‐pore catalysts during temperature cycling

The influence of capillary condensation of reagents in porous catalysts for hydrodesulfurization at temperatures below 195°C and at pressures around 0.95 MPa was investigated experimentally and by modelling. The rate of reaction of thiophene in a solution of n‐heptane was studied in steady and dynamic modes over two Ni‐Mo/γ‐Al₂O₃ mesoporous catalysts with mean pore diameters differing by 2.6‐fold. Pronounced rate hysteresis was observed under thermal cycling for the narrow‐pore catalyst, but less so for the wide‐pore catalyst. The process was modelled for a mixed‐flow reactor under steady and dynamic conditions by means of the Kelvin equation and introducing two kinetic models for liquid and vapour phase to estimate the concentration of reactant in both phases. The model exhibited good agreement with hysteresis results.