Membrane Reactor For Steam Reforming Research Articles

CO2-permselective membrane reactor for steam reforming of methane

Steam reforming of methane (SRM) for hydrogen production with simultaneous CO2 removal in a CO2-permselective membrane reactor is studied experimentally and analyzed by a mathematical model. The membrane consists of a thick porous BYS (Bi1.5Y0.3Sm0.2O3-δ)-SDC (Sm0.2Ce0.8O2-δ) support layer and a thin, dense SDC-carbonate dual-phase layer (∼150 μm) for CO2 separation. Experimental results of CO2 permeation in the BYS-SDC membrane and SRM reactions in a fixed-bed reactor were conducted to obtain the CO2 permeation and SRM reaction rate parameters for the model. The model's reliability is confirmed by comparing the simulation results with atmospheric pressure experimental data for SRM in the BYS-SDC membrane reactor. Simulation results are presented to show the effects of permeation number (θ) and Damkohler number (Da) (which respectively represent membrane CO2 permeance and SRM reaction rate), feed pressure in the reaction side, and sweep side conditions on the performance of SRM in the membrane reactor. Overall, increasing θ results in an increase of H2 yield, retentate H2 concentration, CO2 recovery, and a decrease of retentate CO concentration, with such effects being enhanced at higher Da and feed pressure or vacuum in the sweep side. CO2 permeance affects CH4 conversion only at high feed pressures. At feed pressure of 5 atm and applying vacuum at the sweep side of the membrane reactor, the simulation results show that the membrane reactor can achieve over 99% CH4 conversion, H2 yield, and CO2 recovery and produce an essentially pure H2 stream with zero CO concentration at Da >10,000 and θ > 1.

Performance assessment of packed bed reactor and catalytic membrane reactor for steam reforming of methane through metal foam catalyst support

A kinetic model for the methane steam reforming has been investigated. The performances are compared between the packed bed reactor and catalytic membrane reactor with metal foam catalyst support. The effects of various variables such as pressure, temperature of the reaction, ratio of methane to steam in feed, thickness of membrane and sweep gas on the total methane conversion and hydrogen production were investigated qualitatively. The comparison between these two types of reactors was carried out in the temperature range of 350 °C–750 °C and pressure range of 2–30 bar. Isothermal modeling has been performed and showed a higher performance of the membrane reactor rather than the packed bed reactor. Methane conversion can be reached 100% for lower temperatures than used with industrial PBR, and better performances are reached with an increase of the operating pressure. The maximum conversion of methane for the CMR is quickly reached while the conversion evolution observed for the PBR is smoother.

Steam reforming of methane and methanol in simulated macro & micro-scale membrane reactors: Selective separation of hydrogen for optimum conversion

Various configurations of membrane reactor for steam reforming of methane and methanol are studied here using mathematical model. Micro-scale membrane reactor is conceptualized as a channel with one wall coated with catalyst material, and the other wall permeating hydrogen through a layer of palladium. The membrane layer helps in removal of hydrogen from the reaction site, thereby shifting the equilibrium conversion. In comparison with macro-scale model, the membrane micro-reactor required a shorter residence time to achieve the same level of conversion. This is primarily because of better removal of hydrogen, and is true even when the dispersed catalyst density remained same in both macro and micro models. Any perturbation in the rate constants of sub-reactions that could be arising from catalyst site rearrangements in the micro-fabricated layer does not significantly affect the conversion. Effects of the thickness of the membrane and operating temperature on the conversion are discussed. The pressure drop along the length of the channel arising from friction, reaction stoichiometry, and permeation of product component was estimated. The ratio of membrane area to the catalytic surface area in the channel as a function of distance from the inlet end should be such that the conversion is maximized. This is observed that with selective placement of membrane and catalyst, a methane conversion of more than 95% can be achieved by considering only 40% of the wall, covered with membrane.

Autothermal Reforming of Methane in a Proton-Conducting Ceramic Membrane Reactor

Endothermic steam reforming of methane for hydrogen production requires heat input with selective oxidation of methane. Dense SrCe 0.75 Zr 0.20 Tm 0.05 O 3-δ perovskite membranes were combined with a reforming catalyst to demonstrate the feasibility of a heat-exchange membrane reactor for steam reforming of methane coupled with selective oxidation of permeated hydrogen. The reforming catalyst used was a prereduced nickel based catalyst supported on γ-Al 2 O 3 . Hydrogen produced via the steam reforming of methane or water gas shift reaction was able to diffuse through the catalyst bed and transport through the membrane. The permeated hydrogen reacted with oxygen (from air) to produce heat for the steam reforming of methane on the other side of the membrane. The membrane reactor avoids the use of an expensive air separation unit to produce pure oxygen. The influence of experimental conditions, such as temperature, gas hourly space velocity, and the steam to carbon (S/C) ratio, on the membrane reactor was investigated. SrCe 0.75 Zr 0.20 Tm 0.05 O 3-δ showed good chemical stability in steam reforming conditions as X-ray diffraction analysis of the membrane surface exposed to steam-reforming conditions for 425 h showed only minor CeO 2 formation. The experimental data demonstrate the feasibility of using a proton conducting ceramic membrane in the heat-exchange membrane reactor for steam reforming of methane coupled with selective oxidation.

Influence of the pre-reformer in steam reforming of dodecane using a Pd alloy membrane reactor

Dodecane, one of the main components in kerosene, was used as a model material to investigate reactions in a palladium membrane reactor for steam reforming of kerosene. The influence of pre-reforming on the performance of the membrane reactor was investigated. A decrease in hydrogen yield caused by coke formation was suppressed through pre-reforming by lowering the concentration of olefins, aromatics and unreacted dodecane in the feed to the membrane reactor. In addition, the proportion of total hydrogen production that permeated the membrane was clearly higher with pre-reforming compared with that without pre-reforming. Pre-reforming prevented deactivation of both the catalyst and the membrane, resulting in efficient separation of hydrogen from the reaction field and therefore achieving a higher hydrogen yield.

Development of Metal-doped Silica Membranes for Increased Hydrothermal Stability and Their Applications to Membrane Reactors for Steam Reforming of Methane

Hydrothermal stability is one of the most important technical challenges for hydrogen separation silica membranes. Metal doping into silica matrix was proposed, and it was found that Ni and Co were effective to improve the hydrothermal stability. Co-doped silica membranes showed a high permeance of 1.8 × 10−7 mol/(m2 · s · Pa) and H2/N2 permeance ratio of 730 with hydrothermal stability (500 °C, steam partial pressure 300 kPa). Using hydrothermally stable silica membranes, permeation properties of helium, hydrogen and water vapor were examined based on the activation energy of permeation. The activation energy of H2 permeation correlated well with the permeance ratio of He/H2. The permeance ratios of H2/H2O of silica membranes are always larger than unity, although the kinetic diameter of hydrogen (0.289 nm) is larger than that of water (0.265 nm). Silica membranes were applied to bimodal catalytic membranes, which consisted of microporous silica top layer for selective permeation of hydrogen and a bimodal catalytic support layer where catalysts such as Ni were impregnated inside a bimodal support consisting of mesopores (γ-alumina) and macropores (α-alumina). Increased performance for production of hydrogen was confirmed by catalytic membranes for steam reforming of methane.

Kinetic simulation of a compact reactor system for hydrogen production by steam reforming of higher hydrocarbons

AbstractA bubbling fluidized bed membrane reactor for steam reforming of higher hydrocarbons is modelled, using n‐heptane as a model component to represent steam reforming of naphtha. The reformer is modelled as a bubbling fluidized bed reactor, consisting of two pseudo phases, a dense phase and a bubble phase, both in plug flow. In situ H2 permselective membranes remove H2 continuously as a pure product, greatly enhancing the H2 yield per mole of heptane fed. A fluidized bed membrane reformer for higher hydrocarbons could give a very compact reactor system combining all the units from the pre‐reformer to the hydrogen purification system in a traditional steam reforming plant into a single unit.

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 ( < 10 ppm CO ) 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 CO 2 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 H 2 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 CH 4 conversion, decreased CO selectivity and higher product yield (H 2 produced/CH 4 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 ( 650 ∘ C ) 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 H 2 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 H 2 permeation.

Modeling of a Fluidized Bed Membrane Reactor for the Steam Reforming of Methane: Advantages of Oxygen Addition for Favorable Hydrogen Production

A bubbling fluidized bed membrane reactor for steam reforming of methane is mathematically investigated, with the permselective Pd membranes removing hydrogen from the reaction system to enhance the methane conversion. Oxygen fed into the reaction system can decrease the endothermicity of the overall reaction by the combustion of methane, thereby reducing the need of external firing. Operation at low feed steam−carbon ratios is also possible with the steam required for the reforming reaction being provided as a product from the combustion reactions, although problems related to coking also need to be addressed at very low ones. A drop in the reactor temperature at the inlet of the reactor itself due to the high endothermicity and fast kinetics of the steam reforming reactions does not strongly support the idea of a higher feed temperature favoring the reaction conversion. Thereafter, in situ generation of heat by the combustion reactions is a more effective means to give better reactor performance, and a higher feed temperature can be used to supplement this performance. However, since higher oxygen−methane ratios also tend to consume more of the methane itself, this cannot be increased much and an optimum value exists with respect to the favorable production of pure hydrogen from the reactor permeate side.

Thin and dense Pd/CeO 2/MPSS composite membrane for hydrogen separation and steam reforming of methane

A dense Pd/CeO 2/MPSS composite membrane having a thin Pd layer of 13 μm deposited on a macro porous stainless steel (MPSS) tube was prepared using an improved electroless plating method with the commercial activating and plating solutions. The hydrogen permeation behavior of the as-prepared composite membrane under the H 2/H 2 gradient indicated that the hydrogen permeation process may be mainly controlled by the bulk diffusion through the Pd layer. The hydrogen permeability was almost equal to the theoretical value of the pure Pd membrane. In addition, the hydrogen permeation flux as high as 0.275 mol/(m 2 s) was obtained at 823 K under the pressure difference of 200 kPa. However, the operating conditions such as hydrogen feed flux, sweep gas flux, hydrogen pressure, and temperature had a great effect on the permeation flux and resistance when it was operated under the H 2/H 2 + N 2 (sweep gas) gradient. After permeation tests, the catalytic membrane reactor for steam reforming of methane was constructed, appearing a high methane conversion of 97% at 773 K. The membrane stability was proven by steady hydrogen permeation flux, complete hydrogen selectivity versus helium, and unchanged membrane surface morphology after long-term operation.

Experimental Study of Steam Reforming of Methane in a Thin (6 μM) Pd-Based Membrane Reactor

A novel, thin (6 μm), defect-free Pd/MPSS (macroporous stainless steel) composite membrane tube was prepared by using a multidimensional plating mechanism. A high hydrogen permeation flux of 0.260 mol/(m2 s) and complete hydrogen selectivity were obtained at a temperature of 500 °C and a pressure difference of 100 kPa. The catalytic membrane reactor for steam reforming of methane was constructed with the as-synthesized thin Pd/MPSS composite membrane and a commercial Ni−Al2O3 reforming catalyst. Methane conversion, hydrogen extraction ratio, and hydrogen production rate of the membrane reactor were studied in detail under different operating parameters such as temperature, pressure, space velocity, steam-to-methane ratio, and sweep gas flux. Some important effects were found for these operating parameters to the three performance factors. Drastic superiority to the traditional reactor was proved by changing the Pd-based membrane tube to a dense stainless steel tube with the same diameter. Moreover, on com...

Investigation of Methane–Steam Reforming in Fluidized Bed Membrane Reactors

The theme of this work is to investigate the performance of cocurrent and countercurrent fluidized bed membrane reactors for steam reforming of methane. A mathematical model is used to simulate the experimental data and to explore the potential application of high flux membranes to enhance the methane conversion in fluidized bed membrane reactors. It has been shown that complete conversion of methane is achieved by implementing high flux membranes. The influence of some key parameters on the reactors performance has been reported. It was found that in most cases of large bed lengths, the countercurrent configuration is superior to cocurrent configuration and more sensitive to the parameters changes. However, for short bed lengths at relatively low temperatures the cocurrent configuration is superior to countercurrent configuration.

Membrane reactors for hydrogen production

Fuel cell powered vehicles with on board reforming need compact and lightweight components. A membrane reactor, that combines hydrogen permeable membranes with a methanol steam reformer promises considerable weight and space savings. Its dense metal membranes produce high purity hydrogen over a wide range of pressure and load. The selective removal of hydrogen yields methanol- and CO-conversions that are higher than the equilibrium conversion in a conventional reactor. Results with three different metal membranes in a membrane reactor for steam reforming of methanol are presented. A mathematical model accurately describes the measured performance of the membrane reactor and allows predictions for other values of the process parameters.