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"Sint Annaland, Martin van"
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Recent Advances in Pd-Based Membranes for Membrane Reactors
Palladium-based membranes for hydrogen separation have been studied by several research groups during the last 40 years. Much effort has been dedicated to improving the hydrogen flux of these membranes employing different alloys, supports, deposition/production techniques, etc. High flux and cheap membranes, yet stable at different operating conditions are required for their exploitation at industrial scale. The integration of membranes in multifunctional reactors (membrane reactors) poses additional demands on the membranes as interactions at different levels between the catalyst and the membrane surface can occur. Particularly, when employing the membranes in fluidized bed reactors, the selective layer should be resistant to or protected against erosion. In this review we will also describe a novel kind of membranes, the pore-filled type membranes prepared by Pacheco Tanaka and coworkers that represent a possible solution to integrate thin selective membranes into membrane reactors while protecting the selective layer. This work is focused on recent advances on metallic supports, materials used as an intermetallic diffusion layer when metallic supports are used and the most recent advances on Pd-based composite membranes. Particular attention is paid to improvements on sulfur resistance of Pd based membranes, resistance to hydrogen embrittlement and stability at high temperature.
Journal Article
Mixed Ionic-Electronic Conducting Membranes (MIEC) for Their Application in Membrane Reactors: A Review
Mixed ionic-electronic conducting membranes have seen significant progress over the last 25 years as efficient ways to obtain oxygen separation from air and for their integration in chemical production systems where pure oxygen in small amounts is needed. Perovskite materials are the most employed materials for membrane preparation. However, they have poor phase stability and are prone to poisoning when subjected to CO2 and SO2, which limits their industrial application. To solve this, the so-called dual-phase membranes are attracting greater attention. In this review, recent advances on self-supported and supported oxygen membranes and factors that affect the oxygen permeation and membrane stability are presented. Possible ways for further improvements that can be pursued to increase the oxygen permeation rate are also indicated. Lastly, an overview of the most relevant examples of membrane reactors in which oxygen membranes have been integrated are provided.
Journal Article
Fluidized Bed Membrane Reactors for Ultra Pure H2 Production—A Step forward towards Commercialization
In this research the performance of a fluidized bed membrane reactor for high temperature water gas shift and its long term stability was investigated to provide a proof-of-concept of the new system at lab scale. A demonstration unit with a capacity of 1 Nm3/h of ultra-pure H2 was designed, built and operated over 900 h of continuous work. Firstly, the performance of the membranes were investigated at different inlet gas compositions and at different temperatures and H2 partial pressure differences. The membranes showed very high H2 fluxes (3.89 × 10−6 mol·m−2·Pa−1·s−1 at 400 °C and 1 atm pressure difference) with a H2/N2 ideal perm-selectivity (up to 21,000 when integrating five membranes in the module) beyond the DOE 2015 targets. Monitoring the performance of the membranes and the reactor confirmed a very stable performance of the unit for continuous high temperature water gas shift under bubbling fluidization conditions. Several experiments were carried out at different temperatures, pressures and various inlet compositions to determine the optimum operating window for the reactor. The obtained results showed high hydrogen recovery factors, and very low CO concentrations at the permeate side (in average <10 ppm), so that the produced hydrogen can be directly fed to a low temperature PEM fuel cell.
Journal Article
Numerical Investigation of the Influence of Temperature on Fluidization Behavior: Importance of Particle Collision Parameters and Inter-Particle Forces
Fluidized bed reactors (FBRs) are integral to various industries due to their exceptional capability in facilitating efficient gas–solid interactions, resulting in superior mixing and heat and mass transfer. This research delves into the impact of temperature on fluidization dynamics, particularly focusing on the collisional properties of particles within the bed. The investigation builds upon foundational research, notably Geldart’s classification of fluidization regimes and recent advancements in high-temperature experimental techniques, such as High-Temperature Endoscopic-Laser particle image velocimetry/digital image analysis. To explore these temperature effects, a coupled Discrete Element Method and Computational Fluid Dynamics (cfd–dem) model was employed. This approach enables a detailed examination of gas–particle and particle–particle interactions under varying temperature conditions. The simulations in this study explore the friction coefficient, as well as changes in both tangential and normal restitution coefficients, which affect the fluidization behavior. These changes were systematically analyzed to determine their influence on minimum fluidization velocity and bubble formation. The numerical results are compared with experimental data from high-temperature fluidization studies, highlighting the necessity of incorporating inter-particle forces to fully capture the observed phenomena. The findings underscore the critical role of particle collisional properties in high-temperature fluidization and suggest the potential increasing role of inter-particle forces. Overall, this paper provides new insights into the complex dynamics of fluidized beds at elevated temperatures, emphasizing the need for further experimental–numerical research to enhance the reliability and understanding of these systems in industrial applications.
Journal Article
Enhanced Transverse Dispersion in 3D-Printed Logpile Structures: A Comparative Analysis of Stacking Configurations
Three-dimensionally printed logpile structures have demonstrated the tunability of the transverse dispersion behavior, which is relevant in the context of chemical reactor design. The current modeling study aims to further investigate the trade-offs in such structures, extending the range of geometries investigated and addressing the limitations associated with the pseudo-2D nature of previous experiments. The relative transverse dispersion coefficient and pressure drop were determined using computational fluid dynamics simulations in OpenFOAM for structures with different stacking configurations, porosities and scaling of the structures’ unit cell along the secondary transverse axis. The latter could not be varied in previous experiments, but the current results demonstrate that this limitation suppresses vortex shedding in structures with high porosity. These vortices significantly enhance the transverse dispersion. By using a staggered stacking configuration on both transverse axes, an earlier onset of this phenomenon could be realized. Importantly, operation in this regime could be achieved without an equivalent increase in pressure drop, offering a favorable operating trade-off. The findings demonstrate that at low Reynolds numbers, the studied structures consistently outperform randomly packed beds of spheres, highlighting their potential for chemical process intensification.
Journal Article
Auto-Thermal Reforming Using Mixed Ion-Electronic Conducting Ceramic Membranes for a Small-Scale H2 Production Plant
The integration of mixed ionic electronic conducting (MIEC) membranes for air separation in a small-to-medium scale unit for H2 production (in the range of 650–850 Nm3/h) via auto-thermal reforming of methane has been investigated in the present study. Membranes based on mixed ionic electronic conducting oxides such as Ba0.5Sr0.5Co0.8Fe0.2O3-δ (BSCF) give sufficiently high oxygen fluxes at temperatures above 800 °C with high purity (higher than 99%). Experimental results of membrane permeation tests are presented and used for the reactor design with a detailed reactor model. The assessment of the H2 plant has been carried out for different operating conditions and reactor geometry and an energy analysis has been carried out with the flowsheeting software Aspen Plus, including also the turbomachines required for a proper thermal integration. A micro-gas turbine is integrated in the system in order to supply part of the electricity required in the system. The analysis of the system shows that the reforming efficiency is in the range of 62%–70% in the case where the temperature at the auto-thermal reforming membrane reactor (ATR-MR) is equal to 900 °C. When the electric consumption and the thermal export are included the efficiency of the plant approaches 74%–78%. The design of the reactor has been carried out using a reactor model linked to the Aspen flowsheet and the results show that with a larger reactor volume the performance of the system can be improved, especially because of the reduced electric consumption. From this analysis it has been found that for a production of about 790 Nm3/h pure H2, a reactor with a diameter of 1 m and length of 1.8 m with about 1500 membranes of 2 cm diameter is required.
Journal Article
Long-Term Stability of Thin-Film Pd-Based Supported Membranes
Membrane reactors have demonstrated a large potential for the production of hydrogen via reforming of different feedstocks in comparison with other reactor types. However, the long-term performance and stability of the applied membranes are extremely important for the possible industrial exploitation of these reactors. This study investigates the long-term stability of thin-film Pd-Ag membranes supported on porous Al2O3 supports. The stability of five similarly prepared membranes have been investigated for 2650 h, up to 600 °C and in fluidized bed conditions. Results show the importance and the contribution of the sealing of the membranes at temperatures up to 500 °C. At higher temperatures the membranes surface deformation results in pinhole formation and a consequent decrease in selectivity. Stable operation of the membranes in a fluidized bed is observed up to 450 °C, however, at higher temperatures the scouring action of the particles under fluidization causes significant deformation of the palladium surface resulting in a decreased selectivity.
Journal Article
Steam adsorption on molecular sieve 3A for sorption enhanced reaction processes
Steam adsorption enhanced reaction processes are a promising process intensification for many types of reactions, where water is formed as a byproduct. To assess the potential of these processes, adequate models are required that accurately describe water adsorption, particularly under the desired elevated temperatures and pressures. In this work, an adsorption isotherm is presented for H2O adsorption at 200–350 °C and 0.05–4.5 bar partial pressure on molecular sieve (LTA) 3A. The isotherm has been developed on the basis of experimental data obtained from a thermogravimetric analysis and integrated breakthrough curves. The experimental data at lower steam partial pressures can be described with a Generalized Statistical Thermodynamic Adsorption (GSTA) isotherm, whereas at higher steam partial pressures the experimental data can be adequately captured by capillary condensation. Based on the characteristics of the adsorbent particles, a linear driving force relation has been derived for the adsorption mass transfer rate and the apparent micropore diffusivity is determined. The isotherm and mass transport model presented here prove to be adequate for modelling and improved evaluation of steam adsorption enhanced reaction processes.
Journal Article
Microstructure Control of Tubular Micro-Channelled Supports Fabricated by the Phase Inversion Casting Method
Thin-film membrane layers coated onto porous supports is widely considered as an efficient way to obtain high-performance oxygen transport membranes with both good permeability and high mechanical strength. However, conventional preparation methods of membrane supports usually result in highly tortuous channels with high mass transfer resistance. Tubular porous MgO and MgO/CGO supports were fabricated with a simple phase inversion casting method. Long finger-like channels were obtained inside the dual-phase supports by adjusting the ceramic loading, polymer concentration and particle surface area, as well as by introducing ethanol inside the casting slurries. Slurries that exhibit lower viscosity in the zero-shear viscosity region resulted in more pronounced channel growth. These supports were used to produce thin supported CGO membranes for possible application in O2 separation. Similar shrinkage speeds for the different layers during the sintering process are crucial for obtaining dense asymmetric membranes. The shrinkage of the support tube at a high temperature was greatly affected by the polymer/ceramic ratio and compatible shrinkage behaviours of the two layers were realized with polymer/ceramic weight ratios between 0.175 and 0.225.
Journal Article