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).     

Hydrogen production by methanol steam reforming carried out in membrane reactor on Cu/Zn/Mg-based catalyst

The methanol steam reforming (MSR) reaction was studied by using both a dense Pd-Ag membrane reactor (MR) and a fixed bed reactor (FBR). Both the FBR and the MR were packed with a new catalyst based on CuOAl₂O₃ZnOMgO, having an upper temperature limit of around 350 °C. A constant sweep gas flow rate in counter-current mode was used in MR and the experiments were carried out by varying the water/methanol feed molar ratio in the range 3/1–9/1 and the reaction temperature in the range 250–300 °C. The catalyst shows high activity and selectivity towards the CO₂ and the H₂ formation in the temperature range investigated. Under the same operative conditions, the MR shows higher conversions than FBR and, in particular, at 300 °C and H₂O/CH₃OH molar ratio higher than 5/1 the MR shows complete methanol conversion.     

Poly-dimethylsiloxane (PDMS) based micro-reactors for steam reforming of methanol

A miniaturized methanol steam reformer with a serpentine type of micro-channels was developed based on poly-dimethylsiloxane (PDMS) material. This way of fabricating micro-hydrogen generator is very simple and inexpensive. The volume of a PDMS micro-reformer is less than 10 cm³. The catalyst used was a commercial Cu/ZnO/Al₂O₃ reforming catalyst from Johnson Matthey. The Cu/ZnO/Al₂O₃ reforming catalyst particles of mean diameter 50-70 μm was packed into the micro-channels by injecting water based suspension of catalyst particles at the inlet point. The miniaturized PDMS micro-reformer was operated successfully in the operating temperatures of 180-240 °C and 15%-75% molar methanol conversion was achieved in this temperature range for WHSV of 2.1-4.2 h⁻¹. It was not possible to operate the micro-reformer made by pure PDMS at temperature beyond 240 °C. Hybrid type of micro-reformer was fabricated by mixing PDMS and silica powder which allowed the operating temperature around 300 °C. The complete conversion (99.5%) of methanol was achieved at 280 °C in this case. The maximum reformate gas flow rate was 30 ml/min which can produce 1 W power at 0.6 V assuming hydrogen utilization of 60%.     

Characterization of CuMn-spinel catalyst for methanol steam reforming

CuMn-spinel oxide (CuMn(S)) and non-spinel CuMn (CuMn(NS)) oxide have been obtained by calcining the same precursor at 900 °C and 300 °C, respectively. CuMn(S) was composed of Cu_1.5Mn_1.5O₄ spinel and Mn₃O₄, while CuMn(NS) consisted of CuO and Mn₃O₄. XRD, EXAFS, and TEM measurements of the samples reduced in hydrogen revealed that both CuMn(S) and CuMn(NS) were reduced to Cu metal dispersed on MnO and that the particle size of Cu metal from the CuMn(S) was smaller than that from CuMn(NS). In methanol steam reforming, the spinel derived catalyst showed higher activity than the non-spinel due to the higher dispersion of the Cu metal.     

Micro-channel reactor for steam reforming of methanol

Micro-channel reactor for steam reforming of methanol seems to be attractive for portable application as one part of fuel processor in fuel cell. In the present study, steam reforming of methanol was performed in one stainless steel micro-channel reactor coated with commercial catalyst. The different sols (alumina, zirconia and mixed sol of alumina and zirconia) as a binder for the catalyst were applied to compare the stability and performance. Among the different sols, mixed sol of alumina and zirconia comparatively produced better stability and performance.     

Hydrogen generation in a Pd membrane fuel processor: Productivity effects during methanol steam reforming

Performance analyses are carried out for the palladium membrane fuel processor for catalytic generation of high purity hydrogen. The reactor model includes detailed particle-scale multi-component diffusion, multiple reversible reactions, flow, and membrane transport. Using methanol steam reforming on Cu/ZnO/Al₂O₃ catalyst as the test reaction, a systematic examination of the effects of operating and reactor design parameters on key performance metrics is presented. Single particle simulations reveal a complex interplay between nonisobaric transport and the reversible reactions (methanol reforming and decomposition, and water-gas shift), which impact overall reactor performance. An analysis of characteristic times helps to identify four different productivity controlling regimes: (i) permeation control, encountered with thick membranes and/or insufficient membrane area; (ii) catalyst pore diffusion control encountered with diffusion of reacting species in larger particles; (iii) reaction control, encountered when intrinsic catalytic rates are too low because of inadequate activity or catalyst loading; and (iv) feed control, encountered when the limiting reactant feed rate is inadequate. The simulations reveal that a maximum in the hydrogen productivity occurs at an intermediate space velocity, while the hydrogen utilization is a decreasing function of space velocity, implying a trade-off between productivity and hydrogen utilization. The locus of productivity maxima itself exhibits a maximum at an intermediate membrane surface to volume ratio, the specific value of which is dependent on the particle size, membrane thickness and reaction conditions. At moderate temperature and total pressure (, 10 bar), particles smaller than 2 mm diameter, Pd membranes with thickness less than , and membrane surface to volume ratio exceeding are needed to achieve viable productivity . A comparison between the packed-bed membrane reactor and conventional packed-bed reactor indicates a modest improvement in the conversion and productivity due to in situ hydrogen removal.     

Hydrogen production from methanol by oxidative steam reforming carried out in a membrane reactor

The aim of this work is to study from an experimental point of view the oxidative steam reforming of methanol by investigating the behaviour of a dense Pd/Ag membrane reactor (MR) in terms of methanol conversion as well as hydrogen production. The main parameters considered are the operating temperature and the O₂/CH₃OH feed ratio. This is a pioneer work in the application of MR to this kind of reaction, whose goal should be to produce a CO-free hydrogen stream suitable for hydrogen fuel cell applications. The experimental results show that the MR gives methanol conversions higher than traditional reactors (TRs) at each temperature investigated, confirming the good potential of the membrane reactor device for this interesting reaction system.     

Preparation and characterization of Ir-based catalysts on metallic supports for high-temperature steam reforming of methanol

Ir-based catalysts on heat-resisting foil supports with different washcoats were investigated for hydrogen production by high-temperature steam reforming of methanol. Al₂O₃, Ce_0.8Zr_0.2O₂–Al₂O₃, Ce_0.8Zr_0.2O₂/Al₂O₃ and Ce_0.8Zr_0.2O₂ coatings were prepared on the metallic supports and iridium was deposited on them as the active component. The samples were characterized by X-ray powder diffraction (XRD), ultrasonic vibration test, scanning electron microscope (SEM) and temperature-programmed reduction (TPR). The performance of the catalysts for steam reforming of methanol was evaluated with a fixed-bed reactor. It was found that the phase structure, the shape of the surface particles and the coating adherence were different from each other for the four kinds of coatings. The activities, selectivities and stabilities of these Ir-based catalysts on metallic supports were compared to select the optimal one for use in high-temperature methanol steam reforming. The results indicated that the Ir/Ce_0.8Zr_0.2O₂/Al₂O₃/FeCrAl catalyst showed better performance than the other catalysts, which is a promising candidate for hydrogen production via the methanol steam reforming process in Pd membrane reactors.     

Highly selective supported Pd catalysts for steam reforming of methanol

Steam reforming of methanol, CH₃OH + H₂O 3H₂ + CO₂, was carried out over various Pd catalysts (Pd/SiO₂, Pd/Al₂O₃, Pd/La₂O₃, Pd/Nb₂O₅, Pd/Nd₂O₃, Pd/ZrO₂, Pd/ZnO and unsupported Pd). The reaction was greatly affected by the kind of support. The selectivity for the steam reforming was anomalously high over Pd/ZnO catalysts.     

Methane steam reforming in a Pd-Ru membrane reactor

Methane steam reforming has been carried out in a Pd-Ru membrane reactor at 500–600 ‡C. The membrane reactor consisted of a Pd-6%Ru tube of 100 mm wall thickness and commercial catalysts packed outside of the membrane. The methane conversion was significantly enhanced in the membrane reactor in which reaction equilibrium was shifted by selective permeation of hydrogen through the membrane. The methane conversion at 500 ‡C was improved as high as 80% in the membrane reactor, while equilibrium conversion in a fixed-bed reactor was 57%. The effect of gas flow rate and temperature on the performance of the membrane reactor was investigated and the results were compared with the simulated result from the model. The model prediction is in good agreement with the experimental result. In order to apply the membrane in practice, however, the thickness of the membrane has to be reduced. Therefore, the effect of membrane thickness on performance of the membrane reactor was estimated using the model.     

Steam reforming of methanol over a CuO/ZnO/Al2O3 catalyst part II: A carbon membrane reactor

The reaction of methanol steam reforming was studied in a carbon membrane reactor over a commercial CuO/ZnO/Al₂O₃ catalyst (Süd-Chemie, G66 MR). Carbon molecular sieve membranes supplied by Carbon Membranes Ltd. were tested at 150 °C and 200 °C. The carbon membrane reactor was operated at atmospheric pressure and with vacuum at the permeate side, at 200 °C. High methanol conversion and hydrogen recovery were obtained with low carbon monoxide permeate concentrations. A sweep gas configuration was simulated with a one-dimensional model. The experimental mixed-gas permeance values at 200 °C were used in a mathematical model that showed a good agreement with the experimental data. The advantages of using water as sweep gas were investigated in what concerns methanol conversion and hydrogen recovery. The concentration of carbon monoxide at the permeate side was under 20 ppm in all simulation runs. These results indicate that the permeate stream can be used to feed a polymer electrolyte membrane fuel cell.     

Hydrogen production by oxidative methanol reforming on Pd/ZnO catalyst: effects of Pd loading

Catalytic performances of Pd/ZnO in oxidative methanol reforming reaction were studied as a function of Pd loading. It was confirmed that the formation of Pd–Zn alloy is essential to the selective production of hydrogen. High active Pd/ZnO, comparable to commercial Cu-Zn catalyst, was obtained with higher Pd loading. Selectivity of the reaction was greatly increased by increasing Pd loading on ZnO. At higher Pd loadings (>5%), co-precipitation was superior to impregnation for the catalyst preparation. The catalytic performances were also discussed based on results from X-ray diffraction (XRD) characterization.     

Ethanol steam reforming in a membrane reactor with Pt-impregnated Knudsen membranes

An ethanol reforming membrane reactor (ERMR) with Pt-impregnated Knudsen membranes was investigated to achieve the improvement of ethanol conversion and hydrogen yield. The prepared Pt-impregnated membranes have high permeabilities and reaction activities for the water-gas shift (WGS) reaction. The ethanol reforming-membrane reactor showed ethanol conversion improvement of 7.4–14.4% in comparison with a conventional reactor (CR). Hydrogen yield improvement of 4.2–10.5% was also observed in ERMR with Pt-impregnated SKM in whole reaction temperature range. In addition, CO concentration was considerably reduced via water-gas shift reaction during the permeation.     

Effect of dopants on the performance of CuO–CeO2 catalysts in methanol steam reforming

Steam reforming of methanol was carried out over a series of doped CuO–CeO₂ catalysts prepared via the urea–nitrate combustion method. XRD analysis showed that at least part of the dopant cations enter the ceria lattice. The addition of various metal oxide dopants in the catalyst composition affected in a different way the catalytic performance towards H₂ production. Small amounts of oxides of Sm and Zn improved the performance of CuO–CeO₂, while further addition of these oxides caused a decrease in catalyst activity. XPS analysis of Zn- and Sm-doped catalysts showed that increase of dopant loading leads to surface segregation of the dopant and decrease of copper oxide dispersion. The addition of oxides of La, Zr, Mg, Gd, Y or Ca lowered or had no effect on catalytic activity, but led to less CO in the reaction products. Noble-metal modified catalysts had slightly higher activity, but the CO selectivity was also significantly higher.     

Catalyst deactivation and engineering control for steam reforming of higher hydrocarbons in a novel membrane reformer

The catalyst deactivation and reformer performance in a novel circulating fluidized bed membrane reformer (CFBMR) for steam reforming of higher hydrocarbons are investigated using mathematical models. A catalyst deactivation model is developed based on a random carbon deposition mechanism over nickel reforming catalyst. The results show that the reformer has a strong tendency for carbon formation and catalyst deactivation at low steam to carbon feed ratios for high reaction temperatures and high pressures . The trend is similar for the cases without and with hydrogen selective membranes. Based on this preliminary investigation, an engineering control approach, i.e., in-site control with a concept of critical/minimum steam to carbon feed ratio, is proposed and used to determine the carbon deposition free regions for both cases without and with hydrogen membranes. The comparison between the reported data and model simulation shows that the critical steam to carbon feed ratio predicted by the model agrees well with the reported industrial/experimental operating data.     

Reactor design limitations for the steam reforming of methanol

In this paper the limiting mechanisms in the methanol-steam reformation process are analyzed theoretically and compared experimentally as to determine each contribution and limitation to the overall process. Experimental data from steam reformers are presented and analyzed. Models of each mechanism are provided to quantify theoretical times necessary for each process to occur. While the models in this paper are not precise representations of all steam reforming processes, the models do provide enough evidence to conclude that heat transfer is the dominant limiting mechanism in methanol-steam reformation. Further studies quantifying the experimental effects of heat transfer should be pursued with the ultimate goal of properly sizing steam reformers.     

Mixed reforming of heptane to syngas in the Ba0.5Sr0.5Co0.8Fe0.2O3 membrane reactor

Fuel cells are recognized as the most promising new power generation technology, but hydrogen supply is still a problem. In our previous work, we have developed a LiLaNiO/γ-Al₂O₃ catalyst, which is excellent not only for partial oxidation of hydrocarbons, but also for steam reforming and autothermal reforming. However, the reaction needs pure oxygen or air as oxidant. We have developed a dense oxygen permeable membrane Ba_0.5Sr_0.5Co_0.8Fe_0.2O₃ which has an oxygen permeation flux around 11.5 ml/cm² min at reaction conditions. Therefore, this work is to combine the oxygen permeable membrane with the catalyst LiLaNiO/γ-Al₂O₃ in a membrane reactor for hydrogen production by mixed reforming of heptane. Under optimized reaction conditions, a heptane conversion of 100%, a CO selectivity of 91–93% and a H₂ selectivity of 95–97% have been achieved.     

Beneficial effects of the use of a nickel membrane reactor for the dry reforming of methane: Comparison with thermodynamic predictions

The development of a nickel composite membrane with acceptable hydrogen permselectivity at high temperature in a membrane reactor for the highly endothermic dry reforming of methane reaction was the purpose of this work. A thin, catalytically inactive nickel layer, deposited by electroless plating on asymmetric porous alumina, behaved simply as a selective hydrogen extractor, shifting the equilibrium in the direction of a higher hydrogen production and methane conversion. The main advantage of such a nickel/ceramic membrane reactor is the elimination or limitation of the side reverse water gas shift reaction. For a Ni/Al₂O₃ catalyst, containing free Ni particles, normally sensitive to coking, the use of the membrane reactor allowed an important reduction of carbon deposition (nanotubes) due to restriction of the Boudouard reaction. For a Ni–Co/Al₂O₃ catalyst, where the metallic nickel phase was stabilized by the alumina, the selective removal of the hydrogen significantly enhanced both methane conversion (+67% at 450 °C, +22% at 500 °C and +18% at 550 °C) and hydrogen production (+42% at 450 °C, +32% at 500 °C and +22% at 550 °C) compared to the results obtained for a packed-bed reactor. The hydrogen selectivity during the catalytic tests at 550 °C, maintained with constant separation factors (7 for H₂/CH₄, 8 for H₂/CO and 10 for H₂/CO₂), higher than Knudsen values, attested to the high thermal stability of the nickel composite membrane.     

Fluidised bed membrane reactor for ultrapure hydrogen production via methane steam reforming: Experimental demonstration and model validation

Hydrogen is emerging as a future alternative for mobile and stationary energy carriers in addition to its use in chemical and petrochemical applications. A novel multifunctional reactor concept has been developed for the production of ultrapure hydrogen from light hydrocarbons such as methane for online use in downstream polymer electrolyte membrane fuel cells. A high degree of process intensification can be achieved by integrating perm-selective hydrogen membranes for selective hydrogen removal to shift the methane steam reforming and water-gas-shift equilibriums in the favourable direction and perm-selective oxygen membranes for selective oxygen addition to supply the required reaction energy via partial oxidation of part of the methane feed and enable pure CO₂ capture without costly post-treatment. This can be achieved in a proposed novel multifunctional bi-membrane bi-section fluidised bed reactor [Patil, C.S., van Sint Annaland, M., Kuipers, J.A.M., 2005. Design of a novel autothermal membrane assisted fluidized bed reactor for the production of ultrapure hydrogen from methane. Industrial and Engineering Chemistry Research 44, 9502-9512]. In this paper, an experimental proof of principle for the steam reforming/water-gas-shift section of the proposed novel fluidised bed membrane reactor is presented. A fluidised bed membrane reactor for steam reforming of methane/water-gas-shift on a commercial noble metal-based catalyst has been designed and constructed using 10 H₂ perm-selective Pd membranes for a fuel cell power output in the range of 50-100 W. It has been experimentally demonstrated that by the insertion of the membranes in the fluidised bed, the thermodynamic equilibrium constraints can indeed be overcome, i.e., increased CH₄ conversion, decreased CO selectivity and higher product yield (H₂ produced/CH₄ reacted). Experiments at different superficial gas velocities and also at different temperatures and pressures (carried out in the regime without kinetic limitations) revealed enhanced reactor performance at higher temperatures and pressures (3-4 bar). With a phenomenological two-phase reactor model for the fluidised bed membrane reactor, incorporating a separately developed lumped flux expression for the H₂ permeation rate through the used Pd-based membranes, the measured data from the fluidised bed membrane reactor could be well described, provided that axial gas back-mixing in the membrane-assisted fluidised bed reactor is negligible. This indicates that the membrane reactor behaviour approached that of an ideal isothermal plug flow reactor with maximum H₂ permeation.     

Hydrogen production by glycerol steam reforming with/without calcium oxide sorbent: A comparative study of thermodynamic and experimental work

Thermodynamic analysis and experimental tests of glycerol steam reforming with/without calcium oxide (CaO) as a carbon dioxide (CO₂) sorbent have been performed and compared in this work. Methanol, ethanol, acetaldehyde, acetone and ethylene do not exist in equilibrium conditions according to the equilibrium calculations. Without CaO present, thermodynamic predictions show that a maximum hydrogen concentration of 67% can be obtained at 925 K, with a water to glycerol ratio (WGR) of 9. In the experiments, the Ni/ZrO₂ catalyst fails to catalyze the reactions to thermodynamic equilibrium under the selected conditions as the highest hydrogen concentration obtained is 64%. With the presence of CaO, thermodynamic analysis implies hydrogen purity exceeding 95% can be achieved below 925 K at WGRs of 6 and 9. However, CaCO₃ does not exist at temperatures greater than 1025 K. In the experiments, a hydrogen purity of 95% with only 5% CH₄ as impurity can be reached at 850 K with a WGR of 9. The Ni/ZrO₂ catalyst is not active enough to convert excess CH₄ to hydrogen in glycerol steam reforming as CH₄ concentrations are usually higher than the equilibrium values. The addition of CaO to this system greatly enhances the hydrogen production while reducing the CO concentration.