Identification of thermally stable Pd-alloy composite membranes for high temperature applications

Techno-economic Analysis and Optimization of Intensified, Large-Scale Hydrogen Production with Membrane Reactors

Steam methane reforming (SMR) currently supplies 76% of the world's hydrogen (H2) demand, totaling ∼70 million tonnes per year. Developments in H2 production technologies are required to meet the rising demand for cleaner, less costly H2. Therefore, palladium membrane reactors (Pd-MR) have received significant attention for their ability to increase the efficiency of traditional SMR. This study performs novel economic analyses and constrained, nonlinear optimizations on an intensified SMR process with a Pd-MR. The optimization extends beyond the membrane's operation to present process set points for both the conventional and intensified H2 processes. Despite increased compressor and membrane capital costs along with electric utility costs, the SMR-MR design offers reductions in the natural gas usage and annual costs. Economic comparisons between each plant show Pd membrane costs greater than $25 000/m2 are required to break even with the conventional design for membrane lifetimes of 1-3 years. Based on the optimized SMR-MR process, this study concludes with sensitivity analyses on the design, operational, and cost parameters for the intensified SMR-MR process. Overall, with further developments of Pd membranes for increased stability and lifetime, the proposed SMR-MR design is thus profitable and suitable for intensification of H2 production.

Advances and Perspectives of H2 Production from NH3 Decomposition in Membrane Reactors

Hydrogen is often regarded as an ideal energy carrier. Its use in energy conversion devices does in fact not produce any pollutants. However, due to challenges related to its transportation and storage, liquid hydrogen carriers are being investigated. Among the liquid hydrogen carriers, ammonia is considered very promising because it is easy to store and transport, and its conversion to hydrogen has only nitrogen as a byproduct. This work focuses on a review of the latest results of studies dealing with ammonia decomposition for hydrogen production. After a general introduction to the topic, this review specifically focuses on works presenting results of membrane reactors for ammonia decomposition, particularly describing the different reactor configurations and operating conditions, membrane properties, catalysts, and purification steps that are required to achieve pure hydrogen for fuel cell applications.

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.

Preliminary Equipment Design for On-Board Hydrogen Production by Steam Reforming in Palladium Membrane Reactors

Hydrogen, as an energy carrier, can take the main role in the transition to a new energy model based on renewable sources. However, its application in the transport sector is limited by its difficult storage and the lack of infrastructure for its distribution. On-board H2 production is proposed as a possible solution to these problems, especially in the case of considering renewable feedstocks such as bio-ethanol or bio-methane. This work addresses a first approach for analyzing the viability of these alternatives by using Pd-membrane reactors in polymer electrolyte membrane fuel cell (PEM-FC) vehicles. It has been demonstrated that the use of Pd-based membrane reactors enhances hydrogen productivity and provides enough pure hydrogen to feed the PEM-FC requirements in one single step. Both alternatives seem to be feasible, although the methane-based on-board hydrogen production offers some additional advantages. For this case, it is possible to generate 1.82 kmol h−1 of pure H2 to feed the PEM-FC while minimizing the CO2 emissions to 71 g CO2/100 km. This value would be under the future emissions limits proposed by the European Union (EU) for year 2020. In this case, the operating conditions of the on-board reformer are T = 650 °C, Pret = 10 bar and H2O/CH4 = 2.25, requiring 1 kg of catalyst load and a membrane area of 1.76 m2.

Review of Supported Pd-Based Membranes Preparation by Electroless Plating for Ultra-Pure Hydrogen Production

In the last years, hydrogen has been considered as a promising energy vector for the oncoming modification of the current energy sector, mainly based on fossil fuels. Hydrogen can be produced from water with no significant pollutant emissions but in the nearest future its production from different hydrocarbon raw materials by thermochemical processes seems to be more feasible. In any case, a mixture of gaseous compounds containing hydrogen is produced, so a further purification step is needed to purify the hydrogen up to required levels accordingly to the final application, i.e., PEM fuel cells. In this mean, membrane technology is one of the available separation options, providing an efficient solution at reasonable cost. Particularly, dense palladium-based membranes have been proposed as an ideal chance in hydrogen purification due to the nearly complete hydrogen selectivity (ideally 100%), high thermal stability and mechanical resistance. Moreover, these membranes can be used in a membrane reactor, offering the possibility to combine both the chemical reaction for hydrogen production and the purification step in a unique device. There are many papers in the literature regarding the preparation of Pd-based membranes, trying to improve the properties of these materials in terms of permeability, thermal and mechanical resistance, poisoning and cost-efficiency. In this review, the most relevant advances in the preparation of supported Pd-based membranes for hydrogen production in recent years are presented. The work is mainly focused in the incorporation of the hydrogen selective layer (palladium or palladium-based alloy) by the electroless plating, since it is one of the most promising alternatives for a real industrial application of these membranes. The information is organized in different sections including: (i) a general introduction; (ii) raw commercial and modified membrane supports; (iii) metal deposition insights by electroless-plating; (iv) trends in preparation of Pd-based alloys, and, finally; (v) some essential concluding remarks in addition to futures perspectives.

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.

Hydrogen-induced high-temperature segregation in palladium silver membranes

Growth of Ag-depleted crystallites on PdAg membranes reduces H₂ permeation rates substantially above 823 K but can be reversed in N₂.