Demonstration of a packed bed membrane reactor for the oxidative dehydrogenation of propane

An experimental demonstration of the oxidative dehydrogenation of propane (ODHP) in a lab-scale packed bed membrane reactor has been performed. Experiments were carried out with both premixed and distributed oxygen feed over a Ga₂O₃/MoO₃ catalyst and compared, and the influence of the gas composition, flow rate and the extent of dilution was investigated. The experimental results were found to compare very well with detailed reactor simulations. The results revealed that, in comparison with conventional reactor concepts for the ODHP (fixed bed with premixed reactants feed), a significantly higher propylene yield can be achieved at higher propane conversions in a packed bed membrane reactor.     

Partial oxidation of methane to synthesis gas on a Rh/TiO2 catalyst in a fast flow porous membrane reactor

The partial oxidation of methane to synthesis gas has been studied over a 3% Rh/TiO₂ catalyst in a fixed bed and a novel membrane reactor under autothermal conditions using O₂ as oxidant. The membrane reactor allows the partial oxidation reaction to be performed without premixing the reactants reducing the risk of explosion even at low methane/oxygen ratios. The membrane reactor can operate autothermally and at millisecond residence time. Methane conversions of up to 65% with CO and H₂ selectivities of 90 and 82% respectively have been achieved. The low methane oxygen ratio and the high flow rates are the key factors to attain autothermal behavior. The most sensitive factor to attain high conversion and selectivities appears to be short contact time but high temperature. A kinetic model was used to interpret the experimental results. This revised version was published online in July 2006 with corrections to the Cover Date.     

A novel continuous reactor for catalytic reduction of NOx—fixed bed simulations

A novel dual‐zone fluidized bed reactor was proposed for the continuous adsorption and reduction of NO_x from combustion flue gases. The adsorption and reaction behaviour of such a reactor has been simulated in a fixed bed reactor using Fe/ZSM‐5 catalyst and propylene reductant with model flue gases. Fe/ZSM‐5 exhibited acceptable activity at T = 350°C and GHSV = 5000 h^?1 when O₂ concentration was controlled at levels lower than 1% with a HC to NO molar ratio of about 2:1. XPS and BET surface area measurement revealed the nature of the deactivation of the catalyst. Those performance data demonstrated the feasibility of a continuous dual‐zone fluidized bed reactor for catalytic reduction of NO_x under lean operating conditions.     

A priori modelling of an adiabatic spouted bed catalytic reactor

An a priori reactor model for an adiabatic spouted bed reactor has been developed. This model uses first-principles mass and energy balances to predict the concentration and temperature profiles in the spout, annulus and fountain regions of the reactor. The particle circulation and voidage profiles in the spout are calculated using previously developed analytical techniques. Particle circulation patterns in the annulus are determined by a minimum path-length analysis. The spout and fountain are shown to contribute significantly to the overall conversion in the bed. Predicted and experimental conversions at flowrates up to 1.2U_ms show that extension of the fountain reaction zone and increased particle circulation with increasing inlet flow makes up for the higher average voidage in the spout and fountain. Experimental data confirm the calculated results for a stably spouting bed with CO oxidation over a Co₃O₄/αAl₂O₃ catalyst. The effects of flowrate and inlet reactant concentration are confirmed.     

Thermodynamic Analysis for Quantifying Fuel Cell Grade H2 Production by Methanol Steam Reforming

Steam reforming of methanol in fixed‐bed and hybrid reactors, namely, traditional fixed‐bed reactor (FBR1), fixed‐bed reactor with H₂‐selective membrane (FBR2), and fixed‐bed reactor with CO₂ adsorption (FBR3) is thermodynamically analyzed. The performance of these reactors is compared in terms of quality and quantity of H₂ production for fuel cell application. In FBR2 and FBR3, the contents of undesired products CO, CH₄, and carbon are highly reduced.     

Catalytic oxidation of hydrogen chloride in a fluid bed reactor

The Deacon reaction (HCI + 1/4 O₂ ⇋ 1/2 Cl₂ + 1/2 H₂O) was studied in a catalytic fluid bed reactor. Reaction rates found from measurements in differential and integral reactors were represented by the Langmuir-Hinshelwood type rate equation. Considering the effect of catalysts in the dilute phase, it was found that conversions in a fluid bed reactor can be calculated without any modifying parameters. It is pointed out that the wake fraction, which has been necessary to consider for fast reactions in a fluid bed reactor, is attributed to the dilute phase effect.     

Thermal Reaction Analysis of Oxidative Coupling of Methane

For more than three decades, the oxidative coupling of methane (OCM) process has been investigated as a promising alternative approach for ethylene production. Simulations of different sets of surface mechanisms over the Na₂WO₄/Mn/SiO₂ catalyst and the gas phase reactions that come along with the OCM reaction were analyzed in a fixed‐bed, membrane, and fluidized‐bed reactor. The results were compared with the experimental data generated in an OCM mini‐plant. It was observed that the gas phase reactions are crucial in reducing the overall selectivity, especially in the fluidized‐bed reactor.     

Increasing ethylene production as a high value hydrocarbon in Fischer-Tropsch (FT) reactor: A concept reactor for combining FT with oxidative coupling of methane

The paper proposes a concept configuration of reactors for coupling OCM and FTS, and presents systematic simulation results. FTS section is a combination of fixed bed and membrane fluidized bed reactor, and feed of the FT reactor is supplied by OCM. The reactor configuration is compared with the consecutive reactors of OCM and one fixed bed FT reactor. Effects of CH₄/O₂ ratio, percent of N₂ in the feed, contact time, and input temperature on the yield of ethylene and valuable hydrocarbons are studied. The results show that compared with one FTS reactor configuration, the dual FTS reactor configuration is more effective and thus gives much higher product yields. Furthermore, a main decrease is observed in the formation of CO₂ and CH₄.     

A novel slurry bubble column membrane reactor concept for Fischer–Tropsch synthesis in GTL technology

Fischer–Tropsch synthesis (FTS) plays an important role in the production of ultra-clean transportation fuels, chemicals, and other hydrocarbon products. In this work, a novel combination of fixed-bed and slurry bubble column membrane reactor for Fischer–Tropsch synthesis has been proposed. In the first catalyst bed, the synthesis gas is partially converted to hydrocarbons in a water-cooled reactor which is fixed bed. In the second bed which is a membrane assisted slurry bubble column reactor, the heat of reaction is used to preheat the feed synthesis gas to the first reactor. Due to the decrease of H₂/CO to values far from optimum reactants ratio, the membrane concept is suggested to control hydrogen addition. A one-dimensional packed-bed model has been used for modeling of fixed-bed reactor. Also a one-dimensional model with plug flow pattern for gas phase and an axial dispersion pattern for liquid-solid suspension have been developed for modeling of slurry bubble column reactor. Proficiency of a membrane FTS reactor (MR) and a conventional FTS reactor (CR) at identical process conditions has been used as a basis for comparison in terms of temperature, gasoline yield, H₂ and CO conversion as well as selectivity. Results show a favorable temperature profile along the proposed concept, an enhancement in the gasoline yield and, thus a main decrease in undesirable product formation. The results suggest that utilizing this type of reactor could be feasible and beneficial. Experimental proof of concept is needed to establish the validity and safe operation of the proposed reactor.     

Hydrogen production by the catalytic steam reforming of methanol: Part 3: Kinetics of methanol decomposition using C18HC catalyst

The rate of catalytic decomposition of methanol in the presence of steam has been studied using a commercial CuO-ZnO-Al₂O₃. low temperature shift catalyst from 150-270°C at one atmosphere pressure in a fixed bed reactor. Mole ratios of steam to methanol of 0.66. 1.0 and 1.5 and catalyst mass to molar feed rate ratios of 25 to 1025 kg. s. mol ^?1 were utilized. The data were correlated and equations developed to successfully predict methanol conversions and carbon monoxide concentrations in the product gas stream over the temperature range studied. No evidence of mass transfer limitations was observed.     

A comparative simulation analysis of propane dehydrogenation in composite and microporous membrane reactors

Propane dehydrogenation has been simulated for a composite membrane reactor and a microporous membrane reactor using plug‐flow reactor models, in which both were packed with Pt/Al₂O₃ catalyst in the tube‐side. The reaction kinetics employed in the analysis were obtained from experimental data produced in an integral fixed bed reactor with the same catalyst. Comparative studies were carried out to analyse the performances of reactors containing the different membranes in terms of contact time, flow pattern and flow rate of sweep gas, and pressure. In general, the composite membrane reactors gave the better performance for all cases investigated. © 2002 Society of Chemical Industry     

Fluidized bed Claus reactor studies

Fluidized bed studies have been performed on the Claus reaction to determine whether the conversion efficiency of the Claus process could be improved by replacing conventional fixed bed reactors with fluidized bed reactors. Various idealized Claus plants, incorporating fluidized bed technology, were simulated using the equilibrium constant method. The results of the simulation indicated that, for feed gases consisting of pure H₂S, sulphur conversions in excess of 99% are attainable by using a Claus furnace and two fluidized bed reactors in series. To substantiate the theoretical predictions, experimental studies were performed using a single fluidized bed reactor (0.1 m I.D.) containing Kaiser alumina S-501 catalyst. The effects of temperature (150–300°C), flow rates (15–30 l min⁻¹), feed composition (0.06 < H₂S < 18%, 0.03 < SO₂ < 9%, 73 < N₂ < 99.91%) and bed height (0.12, 0.25 m) on the sulphur conversion were examined. The experimental results showed the same general trends as the theoretical predictions but the measured sulphur conversions exceed the theoretical values by up to 8%.     

Compact hollow fibre reactors for efficient methane conversion

In this study, a micro-structured catalytic hollow fiber membrane reactor (CHFMR) has been prepared, characterized and evaluated for performing steam methane reforming (SMR) reaction, using Rh/CeO₂ as the catalyst and a palladium membrane for separating hydrogen from the reaction. Preliminary studies on a catalytic hollow fiber (CHF), a porous membrane reactor configuration without the palladium membrane, revealed that stable methane conversions reaching equilibrium values can be achieved, using approximately 36 mg of 2 wt.%Rh/CeO₂ catalyst incorporated inside the micro-channels of alumina hollow fibre substrates (around 7 cm long in the reaction zone). This proves the advantages of efficiently utilizing catalysts in such a way, such as significantly reduced external mass transfer resistance when compared with conventional packed bed reactors. It is interesting to observe catalyst deactivation in CHF when the quantity of catalyst incorporated is less than 36 mg, although the Rh/CeO₂ catalyst supposes to be quite resistant against carbon formation. The “shift” phenomenon expected in CHFMR was not observed by using 100 mg of 2 wt.%Rh/CeO₂ catalyst, mainly due to the less desired catalyst packing at the presence of the dense Pd separating layer. Problems of this type were solved by using 100 mg of 4 wt.% Rh/CeO₂ as the catalyst in CHFMR, resulting in methane conversion surpassing the equilibrium conversions and no detectable deactivation of the catalyst. As a result, the improved methodology of incorporating catalyst into the micro-channels of CHFMR is the key to a more efficient membrane reactor design of this type, for both the SMR in this study and the other catalytic reforming reactions.     

Effect of Reaction and Permeation Rates on the Performance of a Catalytic Membrane Reactor for Methylcyclohexane Dehydrogenation

Abstract

The effect of the relative rates of reaction and H₂ permeation through palladium-silver (Pd-Ag) membranes upon the performance of a catalytic membrane reactor (CMR) for methylcyclohexane dehydrogenation has been investigated. Mathematical models have been used to identify the conditions at which a membrane reactor gives yields of toluene (TOL) and H₂ significantly in excess of equilibrium values at throughputs of industrial interest. The simulation shows that a catalyst with no product TOL inhibition performs exceptionally well in a CMR, giving conversions considerably above the equilibrium values at favorable operating conditions. Using a membrane unit between two conventional packed-bed reactors to separate the H₂ ex-situ gives significant improvement in performance over the shell-and-tube type CMR, resulting in conversions substantially higher than equilibrium at 633 K, 1.5 MPa, and liquid hourly space velocities of 3–10 volume feed/h/catalyst volumes.

     

Electrochemical methane conversion over SrFeO3−δ perovskite on an yttrium stabilized zirconia membrane

Oxidative methane coupling and the related chemical reactions have been studied in an electrochemical membrane cell of the type: CH₄, (O₂), SrFeO_3– , Au¦8%Y₂O₃:ZrO₂¦Ag, air. The results are compared to a fixed bed study of SrFeO_3– . The C₂₊ selectivity and the alkene/alkane ratio may be higher in the cell reactor than in the fixed bed reactor, but the C₂₊ yield never exceeded fixed bed data. The maximum C₂₊ yield observed in the cell reactor was 3.1%. The electric fields in the cell when electrodes were connected influenced the selectivity to CO₂ in a manner which may be related to the NEMCA effect.     

Methyl tert-butyl ether decomposition over heteropoly acid catalyst in a cellulose acetate membrane reactor

In this study the methyl tert-butyl ether (MTBE) decomposition over H₃PW₁₂O₄₀ was carried out in a cellulose acetate membrane reactor. The permeability of methanol through the cellulose acetate membrane was about 30 and 300 times higher than that of either isobutene or MTBE, respectively. The isobutene selectivity in the fixed bed reactor was only slightly higher than the methanol selectivity due to the side reaction. In the cellulose acetate membrane reactor, however, the isobutene selectivity in the rejected stream was 68% and the methanol selectivity in the permeated stream was up to 97%. The MTBE conversion in the membrane reactor was about 7% higher than that in the membrane-free fixed bed reactor under the same reaction conditions. The enhanced performance of the membrane reactor in this reversible reaction was mainly due to the selective permeation of methanol which resulted in a methanol-deficient condition suppressing MTBE synthesis reaction.     

NOx removal by selective noncatalytic reduction with urea solution in a fluidized bed reactor

A fluidized bed reactor has been developed to overcome the plugging problem of urea injection by employing a sparger rather than nozzles in the SNCR process for simultaneous removal of SO₂ and NO_x. In a developed fluidized bed reactor, the optimum temperature to remove NO_x is shifted to lower values, the reaction temperature window is widened with the presence of CO in flue gas, and NO conversion is higher than that in a flow reactor. The optimum amount of urea injection in the reactor is found to be above 1.2 based on the normalized stoichiometric molar ratio (NSR) with respect to NO conversion. In the simultaneous removal of SO₂/NO, conversions of SO₂ and NO reach 80–90%, nearly the same values for the individual removal of SO₂ and NO above 850 ‡C.     

Methane steam reforming modeling in a palladium membrane reactor

A mathematical model of a membrane reactor used for methane steam reforming was developed to simulate and compare the maximum yields and operating conditions in the reactor with that in a conventional fixed bed reactor. Results show that the membrane reactor resents higher methane conversion yield and can be operated under milder conditions than the fixed bed reactor, and that membrane thickness is the most important construction parameter for membrane reactor success. Control of the H₂:CO ratio is possible in the membrane reactor making this technology more suitable for production of syngas to be used in gas-to-liquid processes (GTL).     

Catalytic partial oxidation of methane to syngas in a fixed-bed reactor with an O2-distributor: The axial temperature profile and species profile study

Catalytic partial oxidation of methane (CPOM) to syngas has been investigated in a fixed-bed reactor with an O₂-distributor (FR-OD). The axial temperature profile and species profile along the Ni or Rh-based catalyst bed have been measured at different conditions. As the O₂ was distributed radially into the catalyst bed through several rows of holes arranged at the special zone of the OD, a microenvironment maintaining a low O₂/CH₄ ratio (0.10–0.22) was provided in the catalyst bed. The hotspot phenomena appeared at the entrance of the catalyst bed have been effectively controlled. A more uniform temperature profile along the catalyst bed has been given, which is beneficial to the stability of catalyst and the safety of reactor operation.     

Promotion of CO<Subscript>2</Subscript> hydrogénation to hydrocarbons in three-phase catalytic (Fe-Cu-K-Al) slurry reactors

A three-phase slurry reactor has been employed to increase the CO₂ conversion and decrease the selectivity of CO in the direct hydrogénation of CO₂ to hydrocarbons, as it is beneficial for removal of the heat generated due to highly exothermic nature of the reaction. Experiments were conducted over iron-based catalysts (Fe-Cu-K-Al, d_p,=45-75 Μm) in a slurry reactor. It was found that the slurry reactor is preferable to the fixed bed reactor. The productivity and selectivity of hydrocarbons in the slurry reactor appeared to be better than that in the fixed bed reactor for the hydrogénation of CO₂. The CO₂ conversion was increased with increasing reaction temperature (275-300 ‡C), pressure (1-2.5 MPa) or H₂/CO₂ ratio (2-5) in the three-phase slurry reactor. The CO₂ conversion was increased with increasing the amount of CO₂ fed.