Conventional Packed-bed Reactor Research Articles

Integration of Methane Steam Reforming and Water Gas Shift Reaction in a Pd/Au/Pd-Based Catalytic Membrane Reactor for Process Intensification.

Palladium-based catalytic membrane reactors (CMRs) effectively remove H2 to induce higher conversions in methane steam reforming (MSR) and water-gas-shift reactions (WGS). Within such a context, this work evaluates the technical performance of a novel CMR, which utilizes two catalysts in series, rather than one. In the process system under consideration, the first catalyst, confined within the shell side of the reactor, reforms methane with water yielding H2, CO and CO2. After reforming is completed, a second catalyst, positioned in series, reacts with CO and water through the WGS reaction yielding pure H2O, CO2 and H2. A tubular composite asymmetric Pd/Au/Pd membrane is situated throughout the reactor to continuously remove the produced H2 and induce higher methane and CO conversions while yielding ultrapure H2 and compressed CO2 ready for dehydration. Experimental results involving (i) a conventional packed bed reactor packed (PBR) for MSR, (ii) a PBR with five layers of two catalysts in series and (iii) a CMR with two layers of two catalysts in series are comparatively assessed and thoroughly characterized. Furthermore, a comprehensive 2D computational fluid dynamics (CFD) model was developed to explore further the features of the proposed configuration. The reaction was studied at different process intensification-relevant conditions, such as space velocities, temperatures, pressures and initial feed gas composition. Finally, it is demonstrated that the above CMR module, which was operated for 600 h, displays quite high H2 permeance and purity, high CH4 conversion levels and reduced CO yields.

Direct synthesis of propylene oxide in a packed bed membrane reactor

In the present work, the direct synthesis of propylene oxide (PO) in the liquid phase is successfully performed in a packed bed membrane reactor. We show that this engineering device can be implemented under mild reaction conditions (low temperature and pressure) and outside the explosive regime (low hydrogen concentration), making it appealing for industrial applications. The ceramic membrane allows for a separate feed of the reactants, therefore addressing the PO selectivity issue related to the propylene hydrogenation. The reaction is operated in a continuous methanol flow fed with propylene inside the tubular membrane; hydrogen and oxygen are fed through the porous material. We observe that the feeding strategy of the reactants has an important effect on key parameters such as PO selectivity and productivity. By separating propylene from hydrogen, the propane formation was reduced with respect to conventional packed bed reactors. Moreover, the addition of small amounts of NaBr to the reaction medium increases the catalytic activity to PO, but also to propane formation. Therefore, this study provides a good starting point in the design of a membrane reactor device for the direct synthesis of PO where the main limitations such as propylene hydrogenation and water formation can be addressed.

Enhanced i-C5 production by isomerization of C5 isomers in BZSM-5 membrane reactor packed with Pt/ZSM-5 nanocatalyst

In this study, isomerization of C5 was carried out in a combined separation and reaction system using tubular BZSM-5 membrane packed with Pt/ZSM-5 nanocatalyst. The feed mixture is passed over the BZSM-5 membrane and linear n-C5 molecules were separated from branched ones before contacting the catalyst bed. The catalytic performance of the membrane reactor was compared with that of a conventional packed bed reactor with similar dimensions and at comparable operation conditions. These results showed that membrane reactor significantly enhanced i-C5 yield in isomerization of n-C5. The influence of operating conditions on the performance of membrane reactor was evaluated. The membrane reactor displayed a maximum increase in i-C5 yield compared to packed bed reactor of 6300% at 220°C.

Modeling and Optimization of High-Performance Polymer Membrane Reactor Systems for Water–Gas Shift Reaction Applications

In production of electricity from coal, integrated gasification combined cycle plants typically operate with conventional packed bed reactors for the water-gas shift reaction, and a Selexol process for carbon dioxide removal. Implementation of membrane reactors in place of these two process units provides advantages such as increased carbon monoxide conversion, facilitated CO2 removal/sequestration and process intensification. Proposed H2-selective membranes for these reactors are typically of palladium alloy or ceramic due to their outstanding gas separation properties; however, on an industrial scale, the cost of such materials may become exorbitant. High-performance polymeric membranes, such as polybenzimidazoles (PBIs), present themselves as low-cost alternatives with gas separation properties suitable for use in such membrane reactors, given their significant thermal and chemical stability. In this work, the performance of a class of high-performance polymeric membranes is assessed for use in integrated gasification combined cycle (IGCC) units operated with carbon capture, subject to constraints on equipment and process streams. Several systems are considered for use with the polymeric membranes, including membrane reactors and permeative stage reactors. Based upon models developed for each configuration, constrained optimization problems are formulated which seek to more efficiently employ membrane surface area. From the optimization results, the limiting membrane parameter for achieving all carbon capture and H2 production specifications for water–gas shift reactor applications is determined to be the selectivity, α H 2 / C O 2, and thus a minimum value of this parameter which satisfies all the constraints is identified for each analyzed configuration. For a CO2 capture value of 90%, this value is found to be α = 61 for the membrane reactor and the 3-stage permeative stage reactor and α = 62 for the 2-stage permeative stage reactor. The proposed systems approach has the potential to be employed to identify performance limitations associated with membrane materials to guide the development of future polymeric and other advanced materials with desired membrane characteristics for energy and environmental applications.

Optimal oxygen feeding policy to maximize the production of Maleic anhydride in unsteady state fixed bed catalytic reactors

The effect of different oxygen feeding scenarios in a fixed bed reactor for the production of Maleic anhydride (MA) is studied. Two reactor configurations were examined. In the first configuration, a cross flow reactor (CFR) with 4 discrete feeding points is considered. Another configuration is the conventional packed-bed reactor (PBR) with a single feed. Nonlinear Model Predictive Controller (NLMPC) was used as optimal controller to operate the CFR in dynamic mode and to optimize the multiple feed dosages in order to enhance the MA yield. The simulation results indicated that different combinations of the four feed ratios can operate the reactor at the best value for the yield provided the first feeding point is kept as low as possible. For the packed bed reactor configuration, a single oxygen feed is considered and is optimized transiently by NLMPC. The simulation outcomes showed that the reactor performance in terms of the produced MA mole fraction can also be enhanced to the same magnitude obtained by CFR configuration. This improvement requires decreasing the oxygen ratio in the reactor single feed by 70%.

Catalytic membrane reactor for the production of biofuels

The H2-distributed feeding concept using Pd/Ag-based membranes and an Ru-based catalyst in a Packed Bed Membrane Reactor (H2-PBMR) for the synthesis of biofuels via the so-called Fischer–Tropsch Synthesis has been demonstrated. The most successful approach resulted when H2-poor syngas (H2/CO=1) typically obtained from the gasification of biomass was fed directly through the reaction chamber, i.e., to the catalyst bed, whereas the H2 needed to reach the proper stoichiometry for the FTS (H2/CO=2) was admitted, and properly distributed, into the catalyst bed through the Pd/Ag-based membrane by flowing H2/He mixtures at the retentate side of the membrane. Under the optimum reaction conditions, the CO conversion measured with the H2-distributed feeding concept is lower than that obtained in a conventional Packed Bed Reactor with H2/CO=2 (37.9 vs 50.7%), but significantly higher than that obtained in a conventional reactor with H2/CO=1 (14.1%). Remarkably, the productivity towards high-molecular hydrocarbons increases by almost 70% and the methane production decreases by one order of magnitude when using the H2-distributed feeding concept in a Packed Bed Membrane Reactor.

CO2 Removal in Packed-Bed Columns and Hollow-Fiber Membrane Reactors. Investigation of Reactor Performance

The CO2 absorption performance of hollow-fiber membranes and conventional packed-bed column reactors under similar operating conditions was evaluated. Two-scale, nonisothermal, steady-state models were used to simulate the reactors behavior. The membrane reactor model accounts for CO2 diffusion in gas-filled membrane pores, CO2 and amine diffusion accompanied by chemical reaction in liquid-filled membrane pores, and CO2 and amine diffusion accompanied by chemical reaction in the liquid film zone surrounding the inside membrane wall. The packed-bed column reactor model interconnects a two-fluid 2D hydrodynamic platform with 2D mass and energy transport equations in the gas and liquid phases and nonlinear differential equations governing diffusion and reaction in the liquid film. In the absence of membrane wetting, the hollow-fiber membrane reactor outperforms the packed-bed column reactor with similar volume and specific surface area. This is not the case under membrane wetting conditions, when at low spec...

Hydrodesulfurization of dibenzothiophene on NiMo/γ-Al2O3 washcoated monoliths

Hydrodesulfurization of dibenzothiophene, dissolved in n-hexadecane, was conducted in the temperature range of 548–593K at 10MPa pressure in a conventional packed bed reactor for two different catalyst sizes and on monoliths washcoated with different metal loadings. The monolith catalysts were made by washcoating using NiMo/γ-Al2O3 catalysts prepared by incipient wetness and uniform well-adhered washcoats were obtained by calcination after each dipping–air blowing–drying cycle. The MoO3 loading of the powder catalyst was varied from 12.0 to 24.3wt.%, keeping the MoO3/NiO wt. ratio fixed at 6. With an increase in metal loading, the surface area, pore volume and the concentration of weak acidic sites decreased, whereas the metal particle size and the concentration of acidic sites of intermediate strength increased. The highest conversion was obtained with the catalyst containing 18.6wt.% MoO3 and 3.21wt.% NiO. The effectiveness factor of the larger size catalyst (average size: 1.5mm) varied from 0.61 to 0.71 at 593K. The rate constants (calculated on the basis of metal loading) for the monoliths were in good agreement with those obtained in a packed bed, implying that all the catalyst was utilized in the monoliths. After a 72h run at 593K and 10MPa, the concentration of strong acidic sites increased but there was no change in the activity or product distribution.

Comparative Study of the Performance of Fischer–Tropsch Synthesis in Conventional Packed Bed and in Membrane Reactor Over Iron- and Cobalt-Based Catalysts

A comparative study of Fischer–Tropsch synthesis for synthesizing liquid hydrocarbons from syngas was carried out in a conventional packed bed reactor and in a water perm-selective membrane reactor over iron and cobalt catalysts. The process was performed under different operating conditions, such as inlet syngas feed molar ratio, total pressure, gas velocity, temperature, reactor dimensions and sweep fluid ratio. The main simulation results show that the use of the concept of membrane reactor can improve the process performance compared to that obtained in the case of the conventional packed bed reactor. Furthermore, under certain operating conditions, the process could be intensified by a reduction of carbon monoxide conversion magnitude via the water–gas shift reaction. This is possible by using a hydrophilic membrane. Our findings indicate that the membrane reactor provides a quasi-complete conversion of carbon monoxide over iron- or cobalt-based catalysts.

CuO/ZnO catalysts for methanol steam reforming: The role of the support polarity ratio and surface area

The effect of surface area and polarity ratio of ZnO support on the catalytic properties of CuO/ZnO catalyst for methanol steam reforming (MSR) are studied. The surface area of ZnO was varied changing the calcination temperature, and its polarity ratio was modified using different Zn precursors, zinc acetate and zinc nitrate. It was found that the copper dispersion and copper surface area increase with the surface area of the ZnO support, and the polarity ratio of ZnO strongly influences the reducibility of copper species. A higher polarity ratio promotes the reducibility, which is attributed to a strong interaction between copper and the more polar ZnO support. Interestingly, it was observed that the selectivity of CuO/ZnO catalysts (lower CO yield) increases with the polarity ratio of ZnO carriers. As another key result, CuO/ZnOAc375 catalyst has proven to be more selective (up to 90%) than a reference CuO/ZnO/Al2O3 sample (G66-MR, Süd Chemie).The activity of the best performing catalyst, CuO/ZnOAc-375, was assessed in a Pd-composite membrane reactor and in a conventional packed-bed reactor. A hydrogen recovery of ca. 75% and a hydrogen permeate purity of more than 90% was obtained. The Pd-based membrane reactor allowed to improve the methanol conversion, by partially suppressing the methanol steam reforming backward reaction, besides upgrading the reformate hydrogen purity for use in HT-PEMFC.

Numerical study of heat and mass transfer in the microwave-assisted and conventional packed bed reactors with an irreversible first-order endothermic chemical reaction

This paper presents a numerical study on heat and mass transfer in the microwave-assisted and conventional packed bed reactors with an irreversible first-order endothermic chemical reaction. The numerical simulations have been carried out using one-dimensional heterogeneous reactor models for the both reactors. The obtained results have been compared applying the criterion of the same electrical powers utilized in the reactors. The effects of the inlet gas temperature and microwave power, gas velocity, bed porosity and the heat of reaction on performance of the packed bed reactors have been presented.

A combinatorial chemistry method for fast screening of perovskite-based NO oxidation catalyst.

A fast parallel screening method based on combinatorial chemistry (combichem) has been developed and applied in the screening tests of perovskite-based oxide (PBO) catalysts for NO oxidation to hit a promising PBO formulation for the oxidation of NO to NO2. This new method involves three consecutive steps: oxidation of NO to NO2 over a PBO catalyst, adsorption of NOx onto the PBO and K2O/Al2O3, and colorimetric assay of the NOx adsorbed thereon. The combichem experimental data have been used for determining the oxidation activity of NO over PBO catalysts as well as three critical parameters, such as the adsorption efficiency of K2O/Al2O3 for NO2 (α) and NO (β), and the time-average fraction of NO included in the NOx feed stream (ξ). The results demonstrated that the amounts of NO2 produced over PBO catalysts by the combichem method under transient conditions correlate well with those from a conventional packed-bed reactor under steady-state conditions. Among the PBO formulations examined, La0.5Ag0.5MnO3 has been identified as the best chemical formulation for oxidation of NO to NO2 by the present combichem method and also confirmed by the conventional packed-bed reactor tests. The superior efficiency of the combichem method for high-throughput catalyst screening test validated in this study is particularly suitable for saving the time and resources required in developing a new formulation of PBO catalyst whose chemical composition may have an enormous number of possible variations.

H2 production via water gas shift in a composite Pd membrane reactor prepared by the pore-plating method

In this work, H2 production via catalytic water gas shift reaction in a composite Pd membrane reactor prepared by the ELP “pore-plating” method has been carried out. A completely dense membrane with a Pd thickness of about 10.2 μm over oxidized porous stainless steel support has been prepared. Firstly, permeation measurements with pure gases (H2 and N2) and mixtures (H2 with N2, CO or CO2) at four different temperatures (ranging from 350 to 450 °C) and trans-membrane pressure differences up to 2.5 bar have been carried out. The hydrogen permeance when feeding pure hydrogen is within the range 2.68–3.96·10−4 mol m−2 s−1 Pa−0.5, while it decreases until 0.66–1.35·10−4 mol m−2 s−1 Pa−0.5 for gas mixtures. Furthermore, the membrane has been also tested in a WGS membrane reactor packed with a commercial oxide Fe–Cr catalyst by using a typical methane reformer outlet (dry basis: 70%H2–18%CO–12%CO2) and a stoichiometric H2O/CO ratio. The performance of the reactor was evaluated in terms of CO conversion at different temperatures (ranging from 350 °C to 400 °C) and trans-membrane pressures (from 2.0 to 3.0 bar), at fixed gas hourly space velocity (GHSV) of 5000 h−1. At these conditions, the membrane maintained its integrity and the membrane reactor was able to achieve up to the 59% of CO conversion as compared with 32% of CO conversion reached with conventional packed-bed reactor at the same operating conditions.

Novel Macro-micro Channel Reactor for Reforming Glycerol Produced from Biodiesel Productions

Glycerol is produced as a major byproduct in a biodiesel production process but has been thrown out as a waste. The glycerol byproduct will increase rapidly in amount if the biodiesel commercialization is attainable, so the glycerol reforming technology is required to use as a high value product. In the present study, a novel macro-micro channel reactor for the glycerol reforming was proposed. The reactor consists of a macro channel for the glycerol reforming and micro channels for a catalytic combustion. The macro channel prevents the glycerol reformer from being clogged by the carbon formation. The micro channel improves the heat transfer between the glycerol reformer and the catalytic combustor. The effect of channel configurations, flow conditions and catalyst properties on the heat transfer rate and pressure drop was investigated using a computational fluid dynamics (CFD) analysis. Based on the CFD results, the optimal macro-micro channel reactor was manufactured and its performance was evaluated. The macro-micro channel reactor had a higher glycerol conversion compared to the conventional packed-bed reactor because it had a uniform temperature distribution through the reactor.

Modeling of Dual-Zone Structured Reactors for Natural Gas Steam Reforming

The performance of dual-zone structured catalytic reactors in natural gas steam reforming under typical commercial operating conditions is evaluated by means of detailed Computational Fluid Dynamics (CFD) simulations, including detailed reaction kinetics. A hybrid CFD model is developed, combining a porous medium type description of the reactor core zone and a detailed description of the reactor internals in the near-wall region. The porous medium model parameters are determined from specific pressure drop measurements in a wide mass flow rate range. Additional pressure drop measurements with the complete structure and with pellets serve for CFD model validation. The influence of the flow and catalyst distribution over the different reactor zones and the influence of the catalyst loading are then numerically studied. A comparison with a conventional packed bed reactor is made, and advantages of the dual-zone structured reactors with respect to pressure drop, heat transfer, and catalyst effectiveness are illustrated.

Effect of Concentration by Thermal Swing Adsorption on the Catalytic Incineration of VOCs

Abstract Among the different processes for elimination of volatile organic compounds (VOCs) from gaseous effluents (mainly air streams), the frequently employed catalytic oxidation is undertaken in this contribution. With the purpose of reducing the amount of catalyst needed for incineration and the surface of recuperative heat exchangers, thermal swing adsorption can be use as a previous step for VOC concentration.By means of simulating the behavior of a conventional packed bed reactor and using kinetic expressions recently developed for the incineration of mixtures of ethyl acetate and ethanol on a laboratory catalyst based on Mn/Cu oxides, it is shown in this paper that the reduction in catalyst volume is significantly larger than the concentration factor, due to the combined effect of the lower flow rate and temperature rise.A second aspect dealt with in this contribution concern the simulation of the packed bed reactor. The intraparticle mass-transfer limitations turn out to be very strong and, consequently, the mass conservation balances of three species inside the particles should be solved numerically and iteratively at each position inside the bed. A precise approximation to circumvent such procedure is developed and shown to reduce computing time in more than one order of magnitude and to avoid convergence troubles otherwise found with the numerical procedure.

Computational Fluid Dynamics in chemical reactor analysis and design: Application to the ZoneFlow™ reactor for methane steam reforming

The ZoneFlow reactor (Tribute Creations, LLC) is a tubular reactor with two types of internals: a core type and adjacent to the wall, a casing type, both covered with a thin layer of catalyst. It aims for higher energy efficiency and lower steam-to-carbon ratios in methane steam reforming by a judicious design of the relative position of the internals and their geometrical characteristics and a higher catalyst effectiveness.The performance of this novel structured catalytic reactor for synthesis gas production by methane steam reforming was simulated using a reactor model accounting in detail for the flow pattern by means of Computational Fluid Dynamics (CFD). A Reynolds Averaged Navier Stokes (RANS) approach was taken. Turbulence, heat transfer by convection and radiation, detailed reaction kinetics including coking, intra-particle diffusion limitations, and the compressibility of the gas phase were accounted for. Simulations were carried out to investigate the ZoneFlow reactor performance under typical commercial operating conditions and compare it with a conventional packed bed reactor using the same Ni catalyst.

Dry reforming of methane has no future for hydrogen production: Comparison with steam reforming at high pressure in standard and membrane reactors

The methane dry-reforming and steam reforming reactions were studied as a function of pressure (1–20 atm) at 973 K in conventional packed-bed reactors and a membrane reactors. For the dry-reforming reaction in a conventional reactor the production yield of hydrogen rose and then decreased with increasing pressure as a result of the reverse water-gas shift reaction in which the hydrogen reacted with the reactant CO2 to produce water. For the steam reforming reaction the production yield of hydrogen kept increasing with pressure because the forward water-gas shift reaction produced additional hydrogen by the reaction of CO with water. In the membrane reactors the methane conversion and the hydrogen production yields were higher for both the dry-reforming and steam reforming reactions, but for the dry reforming at high pressure half of the hydrogen was transformed into water. Thus, the dry-reforming reaction is not practical for producing hydrogen.

Preferential CO oxidation over Cu/CeO 2− x catalyst: Internal mass transport limitation

The effect of internal mass transport limitation on the preferential CO oxidation in hydrogen-rich mixture over copper-cerium oxide catalyst in a form of pellets and washcoat in microchannel reactor is estimated. Internal effectiveness factor η СО >0.8 in the optimum interval of reaction temperature (170–230 °C) is reached if the pellet diameter and washcoat thickness do not exceed 100 and 20 μm, respectively. Compared to conventional packed-bed reactor with catalyst pellets, microchannel catalytic washcoated reactor is more appropriate for practical use.

Monolithic catalysts with high thermal conductivity for the Fischer–Tropsch synthesis in tubular reactors

The adoption of multitubular reactors loaded with washcoated structured catalysts having highly conductive honeycomb supports has been proposed as an alternative to conventional packed-bed reactors in order to approach the ideal plug-flow behaviour while (i) enabling isothermal operation of highly endo- and exo-thermic reactions, (ii) facilitating the intraparticle mass-transfer, and (iii) limiting pressure drop. The potential of such reactors in the low temperature Fischer–Tropsch synthesis is investigated herein by means of a pseudo-continuous, heterogeneous, two-dimensional mathematical model of a single reactor tube. Simulation results indicate that extruded aluminum honeycomb monoliths, washcoated with a Co/Al 2O 3 catalyst, are promising for the application at the industrial scale, in particular when adopting supports with high cell densities and catalysts with high activity. Limited temperature gradients are in fact possible even at extreme process conditions, thus leading to interesting volumetric reactor yields with negligible pressure drop. This result is achieved without the need of cofeeding to the reactor large amounts of liquid hydrocarbons to remove the reaction heat, as opposite to existing industrial Fischer–Tropsch packed-bed reactors.