Heterogeneous Catalytic Reaction Model Research Articles

Flow behaviors, reaction kinetics, and optimal design of fixed- and fluidized-beds for CO2 methanation

The performances of three catalytic reactors for CO2 methanation, i.e., single fixed-bed (1FxB), two-stage fixed-bed (2FxB), and bubbling fluidized-bed (BFB), were evaluated at a feed flow rate of 166.5 Nm3/h. A heterogeneous catalytic reaction model (HCRM) combining the one-dimensional plug-flow model on the reactor scale and the reaction–diffusion model on the particle scale was used for 1FxB and 2FxB. A two-phase reaction model (TPRM), including the mass transfer between the bubble and emulsion phases and axial dispersion, was proposed for the BFB. The results from HCRM and TPRM were in good agreement with experimental and modeling data. The 1FxB, 2FxB, and BFB were optimized via the parametric study considering the hot spot temperature, operating temperature and pressure, space velocity, flue gas recirculation ratio, and operational stability. The catalyst weights of 1FxB, 2FxB, and BFB required for a 90% CO2 conversion were 191, 40, and 34 kg, respectively. The proposed models were able to identify the flow behaviors, mass transfer, and reaction kinetics of the fixed- and fluidized-beds, which are useful for the optimal design of CO2 methanation reactors.

Non-equilibrium thermodynamics as a tool to compute temperature at the catalyst surface.

The surface temperature is computed for a heterogeneous catalytic reaction model, namely the oxidation of carbon monoxide on platinum. The surface temperature was found using non-equilibrium thermodynamic theory, a theory which provides the proper dependencies between heat and mass fluxes and the reaction rate. The theory predicts a possible coupling between the reaction rate and the thermal driving force and can help extend classical reaction kinetics. In the absence of direct measurements, we explore the coupling numerically. The results are able to capture experimental data reported in the literature, and give new insights into why Arrhenius plots may turn out to be non-linear.

Hydrogen production in an environmental-friendly process by application of chemical looping combustion via Ni- and Fe-Based oxygen carriers

In this research, application of chemical looping combustion (CLC) instead of furnace in a conventional steam reformer (CSR) assisted by Pd/Ag membranes for hydrogen production has been analyzed. Ni- and Fe-based oxygen carriers have been employed in CLC for carbon dioxide capture. A steady state one dimensional heterogeneous catalytic reaction model is applied to analyze the performance and applicability of proposed CLC-SRM configuration via different oxygen carriers. Simulation results show that for all types of used oxygen carriers combustion efficiency reaches to 1 in the fuel reactor (FR) part of CLC-SRM. In CLC-SRM, methane conversion increases from 26% in CSR to 33.7% and 30.87 with employing Ni- and Fe- based oxygen carriers respectively. In addition, hydrogen production increases from 3380 kmol h–1 in CSR to 4258 and 3948 kmol h–1 in CLC-SRM with employing Ni- and Fe-based oxygen carriers respectively. Increasing FR feed temperature in CLC-SRM via all types of oxygen carriers shows enhancement of methane conversion and hydrogen production in the SR side. By increasing FR feed temperature from 800–1000 K, hydrogen production can increases 41.36 and 33.08% by using Ni- and Fe- based oxygen carriers in comparison with CSR respectively.

Synthesis gas production with simultaneous CO2 capturing and consuming: Application of chemical looping combustion by employing Fe45‐Al2O3 and Mn40/Mg–ZrO2 oxygen carriers

In this study, thermal coupling of chemical looping combustion (CLC) and dry reforming of methane (DR) via employment of Fe45‐Al2O3 and Mn40/Mg–ZrO2 oxygen carriers (OCs) were investigated. The main aim of this configuration (CLC‐DR) is the prevention of large CO2 emissions to the atmosphere by CLC and simultaneous consumption of the captured gas to synthesis gas through a DR reaction. For this purpose, a steady state one‐dimensional heterogeneous catalytic reaction model is applied to analyze the performance and applicability of the proposed CLC‐DR configuration using both OCs. Simulation results indicate that for both OCs, combustion efficiency reaches 1 in the fuel reactor (FR) of CLC‐DR. Additionally, results illustrate that CH4 conversion in the DR side of CLC‐DR reaches 0.7235 and 0.7213 with Fe45‐Al2O3 and Mn40/Mg–ZrO2 OCs respectively.Results show that application of CLC‐DR employing Fe45‐Al2O3 and Mn40/Mg–ZrO2 OCs produces 8611 and 8585 kmol h−1 of synthesis gas, respectively. Synthesis gases with H2/CO mole ratios of 0.9519 and 0.9612 are achieved using Fe45‐Al2O3 and Mn40/Mg–ZrO2 OCs respectively. In addition, results demonstrate that by increasing the feed temperature of CLC‐DR from 800 to 1000 K, synthesis gas production reaches 11 210 and 11 340 kmol h−1 when using Fe45‐Al2O3 and Mn40/Mg–ZrO2, respectively.Finally, thermal and molar behaviours of CLC‐DR configuration indicate that it is applicable, and by utilization of this configuration 547.8 tonne day−1 can be captured and converted to synthesis gas.

Simultaneous syngas production with different H2/CO ratio in a multi-tubular methane steam and dry reformer by utilizing of CLC

For syngas production, the combustion of fossil fuels produces large amounts of CO2 as a greenhouse gas annually which intensifies global warming. In this study, chemical looping combustion (CLC) has been utilized for the elimination of CO2 emission to atmosphere during simultaneous syngas production with different H2/CO ratio in steam reforming of methane (SR) and dry reforming of methane (DR) in a CLC-SR-DR configuration. In CLC-SR-DR with 184 reformer tubes (similar to an industrial scale steam reformer in Zagros Petrochemical Company, Assaluyeh, Iran), DR reaction occurs over Rh-based catalysts in 31 tubes. Also, SR reaction is happened over Ni-based catalysts in 153 tubes. CLC via employment of Mn-based oxygen carriers supplies heat for DR and SR reactions and produces CO2 and H2O as raw materials simultaneously. A steady state heterogeneous catalytic reaction model is applied to analyze the performance and applicability of the proposed CLC-SR-DR configuration. Simulation results show that combustion efficiency reached 1 at the outlet of fuel reactor (FR). Therefore, pure CO2 and H2O can be recycled to DR and SR sides, respectively. Also, CH4 conversion reached 0.2803 and 0.7275 at the outlet of SR and DR sides, respectively. Simulation results indicate that, 3223 kmol·h−1 syngas with a H2/CO ratio equal to 9.826 was produced in SR side of CLC-SR-DR. After that, 1844 kmol·h−1 syngas with a H2/CO ratio equal to 0.986 was achieved in DR side of CLC-SR-DR. Results illustrate that by increasing the number of DR tubes to 50 tubes and considering 184 fixed total tubes in CLC-SR-DR, CH4 conversions in SR and DR sides decreased 2.69% and 3.31%, respectively. However, this subject caused total syngas production in SR and DR sides (in all of 184 tubes) enhance to 5427 kmol·h−1. Finally, thermal and molar behaviors of the proposed configuration demonstrate that CLC-SR-DR is applicable for simultaneous syngas production with high and low H2/CO ratios in an environmental friendly process.

Simultaneous production of methanol, DME and hydrogen in a thermally double coupled reactor with different endothermic reactions: Application of cyclohexane, methylcyclohexane and decalin dehydrogenation reactions

Three different units of a multi-tubular reactor with 2962 three concentric tubes have been investigated as a thermally double coupled reactor (TDCR) in co-current mode. Exothermic reactions are same for all three units and are occurred in the inner (methanol synthesis) and outer tubes (direct DME synthesis from syngas) while endothermic reaction is different for each unit. Three endothermic dehydrogenation reactions of cyclohexane (CH), methylcyclohexane (MCH) and decalin (DC) have been considered for middle tube side of each unit. A steady-state heterogeneous catalytic reaction model is applied to evaluate the performance of TDCR for simultaneous production of methanol, hydrogen and dimethylether (DME) in one reactor. The simulation results of each unit are compared with others that operated at the same feed conditions. Results show that conversion of CH, MCH and DC reaches to 67%, 56% and 77% at the output of each unit respectively. Output methanol yield with application of CH and MCH dehydrogenation as endothermic reactions are same equal to 0.37. Also, methanol yield for DC unit is 0.33. In addition, conversion of monoxide at the output of DME synthesis side reaches to 64%, 65% and 62% for CH, MCH and DC units, respectively.

Methane dry reformer by application of chemical looping combustion via Mn-based oxygen carrier for heat supplying and carbon dioxide providing

In this study, the production of H2 utilizing chemical looping combustion (CLC) in a methane dry reformer assisted by H2 perm-selective membranes in a CLC-DRM configuration has been investigated. CLC via employment of a Mn-based oxygen carrier generates large amounts of heat in addition to providing CO2 as the raw material for the dry reforming (DR) reaction. The main advantage of the CLC-DRM configuration is the simultaneous capturing and consuming of CO2 as a greenhouse gas for H2 production.A steady state one dimensional heterogeneous catalytic reaction model is applied to analyze the performance and applicability of the proposed CLC-DRM configuration. Simulation results show that CH4 is completely consumed in the fuel reactor (FR) of the CLC-DRM and pure CO2 is captured by condensation of H2O. Also, CH4 conversion and H2 yield reach 73.46% and 1.459 respectively at the outlet of the DR side in the CLC-DRM. Additionally, 4562kmolh−1 H2 is produced in the DR side of the CLC-DRM.Finally, results indicate that by increasing the FR feed temperature up to 880K, CH4 conversion and H2 production are enhanced to 81.15% and 4790kmolh−1 respectively.

Tuning catalytic reactivity on metal surfaces: Insights from DFT

Density Functional Theory (DFT) calculations show on two examples how catalytic reactivity qualitatively depends on the environment of the active sites. The example of butadiene selective hydrogenation to butenes on Pt or Pd first illustrates how alloying this catalytically active metal with a non- or less reactive elements (Sn or Au, respectively) allows weaker catalyst–molecule interactions and favors the desorption of butenes. It also shows that, from this weakening of the interactions, new reaction pathways are opened and non-selective pathways through a metallacycle intermediate are disadvantaged. Both effects concur on PtSn for an improved selectivity in butenes, while on the PdAu alloy, the gain in selectivity is explained mainly by the easier butene desorption. The dehydrogenation of ethanol on Rh and Pt surfaces shows how co-adsorbates, as water solvent molecules, can interfere with the catalytic elementary steps, assisting OH bond breaking and disadvantaging CH dissociation. The balance between these two effects is metal dependent. Ethanol interacts by a strong H-bond with the H2O pre-covered surface, in a more stabilizing way than for the simple adsorption on the bare metal. The surface H2O (or surface-OH) complex can hence be seen as the true active site for the reaction. It is hence important to include the influence of the environment, from the surface part or from the reactant part, for an accurate modeling of heterogeneous catalytic reactions.

Enhancement of Hydrogen Production and Carbon Dioxide Capturing in a Novel Methane Steam Reformer Coupled with Chemical Looping Combustion and Assisted by Hydrogen Perm-Selective Membranes

In this novel paper, application of chemical looping combustion (CLC) instead of furnace in a steam reformer assisted by Pd–Ag hydrogen perm-selective membranes (CLC-SRM) for CO2 capture and hydrogen production has been analyzed. NiO18-αAl2O3 particles have been employed as oxygen carriers in CLC-SRM. These particles have shown very high reactivity and allow for working at high temperatures in a CLC process with full methane conversion due to Ni-based oxygen carriers. In the CLC-SRM configuration, the air reactor (AR) and fuel reactor (FR) operate in fast and bubbling fluidization, respectively. In this configuration, reforming tubes are located vertically inside the AR so that methane steam reforming occurs in these fixed bed catalytic tubes that have been covered by the membranes. A steady state one-dimensional heterogeneous catalytic reaction model is applied to analyze the performance of CLC-SRM. Performance of conventional steam reformer (CSR) has been compared with CLC-SRM by investigation of import...

Enhancement of methanol, DME and hydrogen production via employing hydrogen permselective membranes in a novel integrated thermally double-coupled two-membrane reactor

In this paper, a thermally double-coupled two-membrane reactor for simultaneous production of methanol, hydrogen and dimethylether (DME) by employing Pd/Ag membranes in co-current mode has been investigated. In this novel multi-tubular reactor configuration, cyclohexane dehydrogenation as an endothermic reaction has coupled with two exothermic reactions of methanol production and direct DME synthesis from syngas. Two Pd/Ag membranes are used for improving the efficiency of hydrogen production and other products in exothermic sides by separation of hydrogen from unconverted outputs of exothermic sides that are recycled to the reactor. A steady state heterogeneous catalytic reaction model is applied to analyze the performance of thermally double-coupled two-membrane reactor and comparison of the result with corresponding predictions for a conventional methanol reactor, thermally coupled reactor (coupling of methanol synthesis with cyclohexane dehydrogenation only) and thermally double coupled reactor.Modeling results show that by employing this novel configuration, methanol yield reaches to 0.4017 in comparison with 0.3885, 0.3735 and 0.362 for conventional methanol reactor, thermally double coupled reactor and thermally coupled reactor respectively.Also methanol production increases 3.39%, 7.03% and 10.94% compared with conventional methanol reactor, thermally double coupled reactor and thermally coupled reactor respectively. Simulation results illustrate that by using Pd/Ag membranes, DME production raises from 277.24 kmol h−1 in thermally double coupled reactor to 325.3 kmol h−1 in thermally double-coupled two-membrane reactor. Additionally, hydrogen production in endothermic side of thermally double coupled reactor is enhanced from 1076 to 1219 kmol h−1 in thermally double-coupled two-membrane reactor.

Comparative Study on Simultaneous Production of Methanol, Hydrogen, and DME Using a Novel Integrated Thermally Double-Coupled Reactor

The present paper focuses on simulation of a catalytic thermally double-coupled reactor (TDCR) in cocurrent mode. In this novel configuration, the endothermic reaction of cyclohexane dehydrogenation has coupled with two exothermic reactions: methanol production and direct DME synthesis from syngas to improve the heat transfer between the endothermic and the exothermic sides. A multitubular reactor with 2962 three concentric tubes has been considered for TDCR. A steady state heterogeneous catalytic reaction model is applied to analyze the performance of TDCR for simultaneous production of methanol, hydrogen, and dimethyl ether (DME). Simulation results of TDCR have been compared with corresponding predictions for an industrial methanol reactor (CMR) and thermally coupled reactor (coupling of methanol synthesis with cyclohexane dehydrogenation), operated at the same feed conditions. Results showed that by this novel configuration production of methanol and hydrogen increases from 345.48 to 373.21 kmol h–1 and 250.6 to 1066.3 kmol h–1 in comparison with TCR, respectively. In addition, production of DME with a rate of 277.24 kmol h–1 is another superiority of TDCR. In addition, hydrogen production in the endothermic side of TDCR in each of the three concentric tubes (0.1 mol s–1) is higher than hydrogen consumption in methanol synthesis (0.076 mol s–1).

Complexities in modeling of heterogeneous catalytic reactions

Catalysts are omnipresent in the chemical industry. Understanding of catalytic chemical reactions is crucial for a rational development of catalysts. The present paper describes approaches for simulating phenomena in heterogeneous catalysis on a molecular level. Modeling of porous structures and their fractal surfaces will be presented. Simulation of adsorption and diffusion of reactants and products inside the pores by means of various Monte Carlo and Molecular Dynamics algorithms is described, followed by quantum chemical methods for calculating reactions on the active centers. Optimization of pore structures and multiscaling procedures complete the picture.

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.

Existence and uniqueness theorem to a unimolecular heterogeneous catalytic reaction model

A mathematical model for an unimolecular heterogeneous catalytic reaction is considered in the case when the reaction product slowly desorb and then diffuse away from the surface. This model is described by a coupled system of nonlinear parabolic and two ordinary differential equations. The existence and uniqueness theorems of classical solution are proved for this system.

Simulation of Secondary Reformer in Industrial Ammonia Plant

In order to develop a reactor design model for the secondary reformer in the industrial ammonia plant, the effectiveness factor and convection heat transfer coefficient between gas and catalyst surface have been studied. The temperature and composition of inlet gas to the catalyst bed are predicted using the kinetic equations of 32 radical reactions. The effect of oxygen content in air on the product synthesis gas composition and the ratio of synthesis gas to nitrogen have been studied. The effectiveness factor has been calculated with the assumption that the steam methane reforming reaction is first order in methane partial pressure. The catalyst shape is assumed to be spherical with an equivalent volumetric diameter. The temperature and composition profiles along the axial distance are predicted using a one-dimensional heterogeneous catalytic reaction model. The temperatures of both gas and catalyst surface decreased with the axial distance from the top of the bed, while the reactions took place. The temperature difference between gas and catalyst surface also decreased along the axial distance. The predicted temperature and composition by the proposed simulation method have been verified with the data from the industrial plant.

Chemical waves and localized chaos in a model of heterogeneous catalytic reaction in a porous particles

A mathematical model of an oscillatory chemical reaction in a porous catalyst particle is considered. The model describes an oscillatory medium uniformly distributed throughout the volume of a spherical particle. The dynamical interaction of the reaction with the diffusive flow of the gaseous reagent inside the pores generates nonstationary dissipative structures in the oscillatory medium on the surface of the catalyst. Depending on the pressure in the gaseous phase, the model produces specific chemical waves and localized spatio-temporal chaos.

ChemInform Abstract: Mathematical Modeling of Heterogeneous Catalytic Reactions and Processes

AbstractChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.

Mathematical modeling of heterogeneous catalytic reactions and processes

The problems of heterogeneous catalysis are considered using mathematical modeling of catalytic reactions beginning from the atomic and molecular level. Some problems of the nonlinear dynamics of heterogeneous catalytic reactions are discussed. Mathematical models of these systems were designed using a combination of laboratory and computer experiments. The results of simulation of the nonlinear phenomena involved in the reactions NO+CO, NO+H2, and CO+O2, which are important for environmental catalysis, are discussed.

ChemInform Abstract: Modeling of Heterogeneous Catalytic Reactions and Reactors

AbstractChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.