One-dimensional Heterogeneous Model Research Articles

Evaluation of the use of ceramic foams as catalyst supports for reverse-flow combustors

The performance of a silicon carbide foam supported palladium catalyst (Pd/β-SiC) in a reverse flow reactor for the abatement of methane in diluted streams (2700–5400ppm) has been studied in this article. The limits of stable operation for this configuration have been experimentally established, being narrower than the corresponding to particulated and honeycomb monolith beds because of the lower thermal inertial of foamed beds. A heterogeneous one-dimensional model has been developed (including the use of specific correlations for mass transfer and dispersive terms) and experimentally validated for predicting the behaviour of these reactors.Finally, the numerical model has been used for simulating reverse-flow reactors equipped with different catalyst shapes (e.g. Raschig rings, honeycomb monoliths and foams) of equivalent geometry. Results for different superficial velocities (0.25–1.5m/s) are compared in terms of transport properties and performance, concluding that honeycomb monolithic beds are the most appropriate configuration for these devices.

Utilization of cyclohexanol dehydrogenation in a novel thermally coupled reactor for Fischer–Tropsch synthesis in gas to liquid technology

In this study, the dehydrogenation of cyclohexanol (CLL) and its utilization in a novel thermally coupled reactor for Fischer–Tropsch synthesis (FTS) has been investigated. In the new configuration, the produced heat of FTS reactions is removed by the endothermic reaction of CLL dehydrogenation instead of circulating high-pressure boiling water in the conventional reactor (CR). The products of this reaction are hydrogen and cyclohexanone (CLN). Some of the generated hydrogen is utilized in synthesis gas and also in hydro cracking unit for production of GTL products and other is stored and used in some other processes. Gasoline(C5+) – the desirable product – alongside some undesirable products like carbon dioxide and methane are produced in FTS reactions. To demonstrate the superiority and advantages of this new configuration it has been compared with another thermally coupled reactor for FTS in which the dehydrogenation of cyclohexane works as coolant reaction in the endothermic side of the reactor. In order to analyze this novel reactor a one-dimensional heterogeneous model has been applied. After modeling and solving the differential equations, the excellence and advantages of new configuration are clarified. The (C5+) yield is increased and a reduction in the generation of undesirable products like CO2 and CH4 is observed in this new configuration. Moreover, hydrogen and CLN which both are useful products are generated in considerable amounts in the endothermic side of the reactor.

Dynamic modeling of a H2O-permselective membrane reactor to enhance methanol synthesis from syngas considering catalyst deactivation

In this paper, the effect of water vapor removal on methanol synthesis capacity from syngas in a fixed-bed membrane reactor is studied considering long-term catalyst deactivation. A dynamic heterogeneous one-dimensional mathematical model that is composed of two sides is developed to predict the performance of this configuration. In this configuration, conventional methanol reactor is supported by an alumina-silica composite membrane layer for water vapor removal from reaction zone. To verify the accuracy of the considered model and assumptions, simulation results of the conventional methanol reactor is compared with the industrial plant data under the same process condition. The membrane reactor improves catalyst life time and enhances CO2 conversion to methanol by overcoming the limitation imposed by thermodynamic equilibrium. This configuration has enhanced the methanol production capacity about 4.06% compared with the industrial methanol reactor during the production time.

Experimental and Modeling Study of Continuous Catalytic Transesterification to Biodiesel in a Bench-Scale Fixed-Bed Reactor

A 500 h endurance test of continuous catalytic transesterification to biodiesel was conducted in a bench-scale fixed-bed reactor. A designed cylinder shape of KF/Ca–Mg–Al hydrotalcite catalyst was stable through the test with high catalytic activity and mechanical strength, converting palm oil to biodiesel with a conversion of more than 95%. Conditions effects on transesterification under relative high pressure (1.0 MPa) were investigated and a one-dimensional heterogeneous model of a fixed-bed reactor was developed to describe the reaction-mass transfer behaviors of continuous catalytic transesterification in a bench-scale fixed-bed reactor. With the given reactor size, optimum conditions were proposed as a LHSV (liquid hourly space velocity) of 0.76–0.25 h–1, molar ratio of methanol-to-oil of 9.16–13.7, and temperature of 338–347 K.

Dynamic modeling and simulation of hydrotreating of gas oil obtained from heavy crude oil

This paper describes a dynamic heterogeneous one-dimensional model of trickle-bed reactor used for catalytic hydrotreating of oil fractions. The model takes into consideration the main reactions occurring in the hydrotreating process: hydrodesulfurization, hydrodenitrogenation, hydrodearomatization (mono-, di-, and polyaroamatics), olefins hydrogenation, and mild hydrocracking (gas oil, naphtha, and gases). Kinetic parameters were determined from experimental data obtained in an isothermal bench-scale reactor during hydrotreating of atmospheric gas oil coming from a heavy crude oil over a commercial CoMo catalyst. The developed model was used to predict the dynamic behavior of an industrial hydrotreating reactor within a wide range of reaction conditions. Changes in concentration, partial pressure, and temperature profiles are simulated and discussed as a function of reactor axial position and time. The simulation results obtained with the proposed dynamic model showed good agreement with experimental data.

Modeling and simulation of an industrial secondary reformer reactor in the fertilizer plants

In this paper, the industrial secondary reformer reactor has been modeled and simulated at steady-state operation conditions. It aims to modify a complete mathematical model of the secondary reformer design. The secondary reformer is a part of a subprocess in a higher scale unit of ammonia synthesis. It is located after the primary reformer in the ammonia plant where it is used in the synthesis of ammonia. The reactions in the secondary reformer reactor are assumed to be carried inside two reactors in series. The first reactor, upper section, is the combustion zone, while the second reactor, bottom section, is the catalyst zone with nickel catalyst based on the alumina. In order to create a reactor design model for the secondary reformer in the industrial ammonia plant, combustion and catalyst zones have been studied. The temperature and compositions of gas in the combustion zone are predicted using the atomic molar balance and adiabatic flame temperature model. In the catalyst zone, the temperature and composition profiles along the axial distance are predicted using a one-dimensional heterogeneous catalytic reaction model with the assumption that the reactions are first order in methane partial pressure.

Evaluation Performance of Different Types Catalysts of an Industrial Secondary Reformer Reactor in the Ammonia Plants

In this paper, the effect of catalyst shape and characteristics has been investigated where five types of a catalyst were examined under the same operation conditions, where catalysts are similar in the chemical properties (Ni/MgOAl2O3) but it's different in their physical properties in the catalyst section of secondary reformer. The secondary reformer involves continuation of the methane reforming reaction that began in the primary reformer to produce Nitrogen and Hydrogen in the ammonia plant. In order to evaluate performance of various types of catalysts in the secondary reformer reactor, mathematical model have been created. The mathematical model covers all aspects of major chemical kinetics, heat and mass transfer phenomena in the secondary reformer in the ammonia plant at steady state conditions. It aims to optimize the best catalyst from five types of catalyst of the secondary reformer reactor in the State Company of Fertilizers South Region in the Basra/Iraq. The mathematical model allows calculating the axial variations of compositions, temperature and pressure of the gases inside two reactors in series by using the atomic molar balance and adiabatic flame temperature in the combustion section while, in the catalyst section, they are predicted by using a one-dimensional heterogeneous catalytic reaction model. The analysis evaluation performance of the catalyst (RKS-2-7H') have good results than other the catalyst types (RKS - 2, ICI 54 - 2, RKS-2-7H”, RKS-2-7H”’) in catalyst zone of the secondary reformer.

Methanol production in an optimized dual-membrane fixed-bed reactor

Coupling reaction and separation in a membrane reactor improves the reactor efficiency and reduces purification cost in the following stages. This paper focuses on modeling and optimization of methanol production in a dual-membrane reactor. In this configuration, conventional methanol reactor is supported by Pd/Ag membrane tubes for hydrogen permeation and alumina–silica composite membrane tubes for water vapor removal from the reaction zone. A steady state heterogeneous one-dimensional mathematical model is developed to predict the performance of this novel configuration. In order to verify the accuracy of the model, simulation results of the conventional reactor is compared with available industrial plant data. The main advantages of the optimized dual-membrane reactor are: higher CO 2 conversion, the possibility of overcoming the limitation imposed by thermodynamic equilibrium, improvement of the methanol production rate and its purity. Genetic algorithm as an exceptionally simple evolution strategy is employed to maximize the methanol production as the objective function. This configuration has enhanced methanol production rate by 13.2% compared to industrial methanol synthesis reactor.

Modeling and simulations of a reformer used in direct reduction of iron

This paper presents a detailed modeling and simulations of a reformer unit used in the direct reduction of iron (DRI) process. A one-dimensional heterogeneous model for the catalyst tubes which takes into account the intraparticle mass transfer resistance was developed, while the furnace was modeled with bottom firing configuration. Validation against data from a local iron/steel plant showed satisfactory results. The performance variables of the unit were the process gas temperature, wall temperature and conversions of hydrogen, methane and carbon dioxide. The profiles of these output variables along the distance were calculated. The effect of operating parameters such as inlet temperature, natural gas flow rate and gas composition was also determined.

Genetic algorithm strategy (GA) for optimization of a novel dual-stage slurry bubble column membrane configuration for Fischer–Tropsch synthesis in gas to liquid (GTL) technology

In this work, a novel configuration of a cascade double membrane assisted slurry bubble column reactor and hydrogen-permselective membrane reactor is proposed (SDMR) for Fischer–Tropsch synthesis (FTS). A one-dimensional heterogeneous model in first reactor and axial dispersion model (AMD) for both gas and liquid–solid suspension as a homogeneous phase for slurry bubble column reactor has been developed. Subsequently, this novel configuration was optimized. Here, genetic algorithm (GA) method was applied as powerful method for optimization of procedure. The proposed model has been used to compare the performance of an SDMR with a Fluidized-bed membrane dual-type reactor (FMDR) and a conventional reactor (CR). The simulation results show an enhancement in the gasoline production, a main decrease in undesirable product formation and a favorable temperature profile along the proposed concept rather than conventional reactor and even FMDR.

Application of water vapor and hydrogen-permselective membranes in an industrial fixed-bed reactor for large scale methanol production

Coupling reaction and separation in a membrane reactor improves the reactor efficiency and reduces purification cost in the next stages. In this work a novel reactor consisting two membrane layers has been proposed for simultaneous hydrogen permeation to reaction zone and water vapor removal from reaction zone in the methanol synthesis reactor. In this configuration conventional methanol reactor is supported by a Pd/Ag membrane layer for hydrogen permeation and alumina–silica composite membrane layer for water vapor removal from reaction zone. In this reactor syngas is fed to the reaction zone that is surrounded with hydrogen-permselective membrane tube. The water vapor-permselective membrane tube is placed in the reaction zone. A steady state heterogeneous one-dimensional mathematical model is developed for simulation of the proposed reactor. To verify the accuracy of the model, simulation results of the conventional reactor is compared with the available plant data. The membrane fixed bed reactor benefits are higher methanol production rate, higher quality of outlet product and consequently lower cost in product purification stage. This configuration has enhanced the methanol yield by 10.02% compared with industrial reactor. Experimental proof-of-concept is needed to establish the safe operation of the proposed configuration.

Modeling and Simulation of an Industrial Ethylene Oxide (EO) Reactor Using Artificial Neural Networks (ANN)

In the present work, a one-dimensional heterogeneous model was used for dynamic simulation of an industrial fixed-bed catalytic ethylene oxide (EO) reactor in the presence of long-term catalyst deactivation. In order to determine the level of optimum ethylene dichloride (EDC), a multilayer perceptron (MLP) neural network was used. In addition, the effect of inlet gas velocity on EO mole fraction of gas and solid phases was investigated. The model validation was carried out by comparison of model results with corresponding industrial conditions and over a period of three operating years. A good agreement was found between the simulation results of the dynamic model and historical process data. The error of simulation was found to be less than 5%. The results of the artificial neural network (ANN) modeling showed that the maximum selectivity occurs in the range of 0.37–0.42 ppm of EDC. Also, it was observed that with decrease of gas velocity the difference between the EO mole fraction of gas phase and solid phase increases. This behavior was attributed to the distinct resistances of kinetically controlled and the mass transfer resistance of gas film around the catalyst pellets.

A comparative study of two H2-redistribution strategies along the FT reactor using H2-permselective membrane

In this study, a comparative study of two different hydrogen redistribution strategies along the Fischer-Tropsch synthesis reactor using a Pd-Ag membrane has been carried out. In the first strategy, fresh synthesis gas is flowing in the tube side in co-current mode with reacting material in shell side so that the first segments of reactor use more hydrogen. In the second strategy, fresh synthesis gas is flowing in the tube side in counter-current mode with reacting material in shell side so that last segments of reactor use more hydrogen. A one-dimensional heterogeneous model was developed to compare two strategies from different standpoints. The model was checked using operating data of Fischer-Tropsch synthesis reactor in pilot plant of Research Institute of Petroleum Industry in Iran. Simulation results show an enhancement in the yield of gasoline production, a decrease in undesired products formation (CO3 and CH4) and also a favorable temperature profile along both the configurations of membrane Fischer-Tropsch reactor in comparison with conventional reactor. The comparison between co-current and counter-current configurations in terms of temperature, gasoline (C) and CO2 yields, H2 and CO conversions, and selectivity of components shows the reactor in the co-current configuration operates with lower reactants' conversions and also lower permeation rate of hydrogen. On the contrary, our results demonstrated counter-current-mode decrease CO2 and CH4 as undesired products, better than other kinds of mentioned systems. Copyright © 2010 John Wiley & Sons, Ltd.

A novel water perm-selective membrane dual-type reactor concept for Fischer–Tropsch synthesis of GTL (gas to liquid) technology

Abstract The present study proposes a novel configuration of Fischer–Tropsch synthesis (FTS) reactors in which a fixed-bed water perm-selective membrane reactor is followed by a fluidized-bed hydrogen perm-selective membrane reactor. This novel concept which has been named fixed-bed membrane reactor followed by fluidized-bed membrane reactor (FMFMDR) produces gasoline from synthesis gas. The walls of the tubes of a fixed-bed reactor (water-cooled reactor) of FMFMDR configuration are coated by a high water perm-selective membrane layer. In this new configuration, two membrane reactors instead of one membrane reactor are developed for FTS reactions. In other words, two different membrane layers are used. In order to investigate the performance of FMFMDR, a one-dimensional heterogeneous model is taken into consideration. The simulation results of three schemes named fluidized-bed membrane dual-type reactor (FMDR), FMFMDR and conventional fixed-bed reactor (CR) are presented. They have been compared in terms of temperature, gasoline and CO 2 yields, H 2 and CO conversions and the water permeation rate through the membrane layer. Results show that the gasoline yield in FMFMDR is higher than the one in FMDR. The FMFMDR configuration not only decreases the undesired product such as CO 2 but also produces more gasoline.

Direct dimethyl ether (DME) synthesis through a thermally coupled heat exchanger reactor

Compared to some of the alternative fuel candidates such as methane, methanol and Fischer–Tropsch fuels, dimethyl ether (DME) seems to be a superior candidate for high-quality diesel fuel in near future. The direct synthesis of DME from syngas would be more economical and beneficial in comparison with the indirect process via methanol synthesis. Multifunctional auto-thermal reactors are novel concepts in process intensification. A promising field of applications for these concepts could be the coupling of endothermic and exothermic reactions in heat exchanger reactors. Consequently, in this study, a double integrated reactor for DME synthesis (by direct synthesis from syngas) and hydrogen production (by the cyclohexane dehydrogenation) is modelled based on the heat exchanger reactors concept and a steady-state heterogeneous one-dimensional mathematical model is developed. The corresponding results are compared with the available data for a pipe-shell fixed bed reactor for direct DME synthesis which is operating at the same feed conditions. In this novel configuration, DME production increases about 600 Ton/year. Also, the effects of some operational parameters such as feed flow rates and the inlet temperatures of exothermic and endothermic sections on reactor behaviour are investigated. The performance of the reactor needs to be proven experimentally and tested over a range of parameters under practical operating conditions.

Design and Implementation of a Simulator for the Hydro Treating Reactor in RTO Development

A computer aided tool is an important part of a real time optimizer. In this paper, a three phase reactor model for describing the hydro desulfurization reactions in a trickle bed reactor was developed. A steady state plug-flow heterogeneous one-dimensional model was employed to implement the HDS simulator. The reactor model considers the main reactions present in the hydro desulfurization process. Simulations were performed for a pilot trickle bed reactor, and the results are discussed in terms of variations with axial position of partial pressure and concentrations in liquid phase. The simulation results show a good agreement with the experimental data.

Performance of reverse flow monolithic reactor for water–gas shift reaction

This work explores the application of monolithic catalysts and reverse flow reactor (RFR) technology for carrying out the water–gas shift reaction (WGS). The performance of both adiabatic fixed-bed reactors (FBR) and RFR operating with particulate or monolith catalysts has been simulated using a heterogeneous one-dimensional model, experimentally validated for other reactions in previous works. Comparisons were made at the same space velocities ( GHSV between 6000 and 12000 h −1) and at previously optimized values of switching time (RFR) and feed temperature (FBR). Results obtained indicate that the operation with monolith catalysts provide better results in terms of wider stability intervals (RFR) and hydrogen yields (both RFR and FBR). When the performances of FBR and RFR are compared, it is observed that, for the same amount of catalyst, the FBR performs better than the FBR, although the difference becomes smaller as the space time increases. So, for high space times, the use of monolithic RFR can be advantageous taking into account the higher energy efficiency of RFR, which may allow operation with no feed heating.

Sensitivity Analysis and Kinetic Parameter Estimation in a Three Way Catalytic Converter

A heterogeneous one-dimensional model is used to simulate a three way catalytic converter (TWC). The mathematical model consists of mass and energy balance equations in the gas and solid phases and accounts for 15 heterogeneous chemical reactions. Langmuir−Hinshelwood type kinetics is used to represent most of the reaction rates. In this work, the kinetic parameters of the various reactions occurring in a TWC are estimated using vehicle data based on a genetic-algorithm-based optimization. The method uses the test data to estimate the reaction kinetic parameters by minimizing the deviation between the model predictions and experimental observations. It is found that the objective function based on the cumulative mass of a species that leaves the reactor until a certain time instant is a preferred performance measure for the optimization. The sensitivity of the exit concentration of various species to various kinetic parameters was found. This is used to identify the subset of reactions which have a significant effect on the various species concentrations in the effluent stream and is used to determine the set of kinetic parameters for optimizing the reactor performance. Single parameter and multiple parameters tuning using genetic algorithm have been demonstrated successfully for a TWC application.

Modeling Temperature Profiles of a Catalytic Autothermal Methane Reformer with Nickel Catalyst

In this work, a one-dimensional heterogeneous model for the autothermal reforming of methane in a catalytic (Ni/Al 2 O 3 catalyst) fixed-bed reactor is proposed. The kinetic model implements an indirect reaction scheme and includes a reduction factor that is dependent on the oxygen concentration. Such a factor delays the reforming and water-gas shift reactions, with respect to the oxidation reactions. Experiments at different steam-to-methane ratios and feed flow rates were conducted in a small-scale reactor to identify and validate the proposed mathematical model. To this end, temperature profiles in the solid phase were measured with an infrared camera. The agreement between experimental data and model predictions is very good for all the investigated operating conditions. In particular, the model predicts the strong separation between the oxidation and the experimentally observed reforming zones well.

Autothermal reforming of methane to synthesis gas: Modeling and simulation

Autothermal reforming (ATR), that is the combination of non-catalytic partial oxidation and adiabatic steam reforming, is an important process to produce synthesis gas (syngas) from natural gas. The main scope of this work is proposing a mathematical model considering an autothermal reformer consisting of two distinct sections; a combustion section and a catalytic bed section. In the combustion section, temperature and composition were predicted using 108 simultaneous elementary reactions considering 28 species. The results were considered as initial conditions for the catalytic bed section. A one-dimensional heterogeneous reactor model was used for kinetic simulation of the second section. Results of the model were compared by ATR process published data.