Ultra-pure hydrogen production via ammonia decomposition in a catalytic membrane reactor

In this work two alternatives are presented for increasing the purity of hydrogen produced in a membrane reactor for ammonia decomposition. It is experimentally demonstrated that either increasing the thickness of the membrane selective layer or using a small purification unit in the permeate of the membranes, ultra-pure hydrogen can be produced. Specifically, the results show that increasing the membrane thickness above 6 μm ultra-pure hydrogen can be obtained at pressures below 5 bar. A cheaper solution, however, consists in the use of an adsorption bed downstream the membrane reactor. In this way, ultra-pure hydrogen can be achieved with higher reactor pressures, lower temperatures and thinner membranes, which result in lower reactor costs. A possible process diagram is also reported showing that the regeneration of the adsorption bed can be done by exploiting the heat available in the system and thus introducing no additional heat sources.     

3D simulation of hydrogen production by ammonia decomposition in a catalytic membrane reactor

Ammonia decomposition in an integrated Catalytic Membrane Reactor for hydrogen production was studied by numerical simulation. The process is based on anhydrous NH₃ thermal dissociation inside a small size reactor (30 cm³), filled by a Ni/Al₂O₃ catalyst. The reaction is promoted by the presence of seven Pd coated tubular membranes about 203 mm long, with an outer diameter of 1.98 mm, which shift the NH₃ decomposition towards the products by removing hydrogen from the reaction area. The system fluid-dynamics was implemented into a 2D and 3D geometrical model. Ammonia cracking reaction over the Ni/Al₂O₃ catalyst was simulated using the Temkin-Pyzhev equation.Introductory 2D simulations were first carried out for a hypothetic system without membranes. Because of reactor axial symmetry, different operative pressures, temperatures and input flows were evaluated. These introductory results showed an excellent ammonia conversion at 550 °C and 0.2 MPa for an input flow of 1.1 mg/s, with a residual NH₃ of only a few ppm. 3D simulations were then carried out for the system with membranes. Hydrogen adsorption throughout the membranes has been modeled using the Sievert’s law for the dissociative hydrogen flux. Several runs have been carried out at 1 MPa changing the temperature between 500 °C and 600 °C to point out the conditions for which the permeated hydrogen flux is the highest. With temperatures higher than 550 °C we obtained an almost complete ammonia conversion already before the membrane area. The working temperature of 550 °C resulted to be the most suitable for the reactor geometry. A good matching between membrane permeation and ammonia decomposition was obtained for an NH₃ input flow rate of 2.8 mg/s. Ammonia reaction shift due to the presence of H₂ permeable membranes in the reactor significantly fostered the dissociation: for the 550 °C case we obtained a conversion rate improvement of almost 18%.     

Single-step synthesized dual-layer hollow fiber membrane reactor for on-site hydrogen production through ammonia decomposition

On-site hydrogen production via catalytic ammonia decomposition presents an attractive pathway to realize H₂ economy and to mitigate the risk associated with storing large amounts of H₂. This work reports the synthesis and characterization of a dual-layer hollow fiber catalytic membrane reactor for simultaneous NH₃ decomposition and H₂ permeation application. Such hollow fiber was synthesized via single-step co-extrusion and co-sintering method and constitutes of 26 μm-thick mixed protonic-electronic conducting Nd_5.5Mo_0.5W_0.5O_11.25-δ (NMW) dense H₂ separation layer and Nd_5.5Mo_0.5W_0.5O_11.25-δ-Ni (NMW-Ni) porous catalytic support. This dual-layer NMW/NMW-Ni hollow fiber exhibited H₂ permeation flux of 0.26 mL cm⁻² min⁻¹ at 900 °C when 50 mL min⁻¹ of 50 vol% H₂ in He was used as feed gas and 50 mL min⁻¹ N₂ was used as sweep gas. Membrane reactor based on dual-layer NMW/NMW-Ni hollow fiber achieved NH₃ conversion of 99% at 750 °C, which was 24% higher relative to the packed-bed reactor with the same reactor volume. Such higher conversion was enabled by concurrent H₂ extraction out of the membrane reactor during the reaction. This membrane reactor also maintained stable NH₃ conversion and H₂ permeation flux as well as structure integrity over 75 h of reaction at 750 °C.     

Characterization of an ammonia decomposition process by means of a multifunctional catalytic membrane reactor

Ammonia decomposition was studied in a multifunctional catalytic membrane reactor filled with Ruthenium catalyst and equipped with palladium-coated membranes. To characterize the system we measured NH₃ conversion, H₂ yield and its partial pressure, the internal and external temperatures of the reactor shell and the electric consumption under several NH₃ flow and pressure conditions. Experimental results showed that the combined effect of Ruthenium catalyst and palladium membranes allowed the reaction to reach the equilibrium in all the conditions we tested. At 450 °C the ammonia conversion resulted the most stationary, while at 7 bar the hydrogen yield was almost independent of both the ammonia flow and temperature. In addition, the experimental system used in this work showed high values of NH₃ conversion and H₂ permeation also without heating the ammonia tank and therefore renouncing to control the feeding gas pressure. When ultra-pure hydrogen is needed at a distal site, a reactor like this can be considered for in situ hydrogen production.     

Direct high-purity hydrogen production from ammonia by using a membrane reactor combining V-10mol%Fe hydrogen permeable alloy membrane with Ru/Cs2O/Pr6O11 ammonia decomposition catalyst

The hydrogen production capabilities of the membrane reactor combining V-10 mol%Fe hydrogen permeable alloy membrane with Ru/Cs₂O/Pr₆O₁₁ ammonia decomposition catalyst are studied. The ammonia conversion is improved by 1.7 times compared to the Ru/Cs₂O/Pr₆O₁₁ catalyst alone by removing the produced hydrogen through the V-10mol%Fe alloy membrane during the ammonia decomposition. 79% of the hydrogen atoms contained in the ammonia gas are extracted directly as high-purity hydrogen gas. Both the Ru/Cs₂O/Pr₆O₁₁ catalyst and the V-10 mol% Fe alloy membrane are highly durable, and the initial performance of the hydrogen separation rate lasts for more than 3000 h. The produced hydrogen gas conforms to ISO 14687–2:2019 Grade D for fuel cell vehicles because the ammonia and nitrogen concentrations are less than 0.1 ppm and 100 ppm, respectively.     

Kinetic and thermodynamic analyses of mid/low-temperature ammonia decomposition in solar-driven hydrogen permeation membrane reactor

It is a promising method for hydrogen generation without carbon emitting by ammonia decomposition in a catalytic palladium membrane reactor driven by solar energy, which could also store and convert solar energy into chemical energy. In this study, kinetic and thermodynamic analyses of mid/low-temperature solar thermochemical ammonia decomposition for hydrogen generation in membrane reactor are conducted. Hydrogen permeation membrane reactor can separate the product and shift the reaction equilibrium forward for high conversion rate in a single step. The variation of conversion rate and thermodynamic efficiency with different characteristic parameters, such as reaction temperature (100–300 °C), tube length, and separation pressure (0.01–0.25 bar), are studied and analyzed. A near-complete conversion of ammonia decomposition is theoretically researched. The first-law thermodynamic efficiency, net solar-to-fuel efficiency, and exergy efficiency can reach as high as 86.86%, 40.08%, and 72.07%, respectively. The results of this study show the feasibility of integrating ammonia decomposition for hydrogen generation with mid/low-temperature solar thermal technologies.     

The impact of ammonia feed distribution on the performance of a fixed bed membrane reactor for ammonia decomposition to ultra-pure hydrogen

In this study, the influence of distribution of ammonia feed along the height of a fixed bed membrane reactor (FBMR) for ammonia decomposition to hydrogen is investigated to understand the leverage of this approach. A rigorous heterogeneous model with verified kinetics is implemented to simulate the reactor. The simulation results indicate that the application of a distributed ammonia feed with equal distribution of injection points resulted in a 17.45% improvement in hydrogen production rate at a low temperature of 800.0 K over a FBMR without feed distribution. In the parameter space of this study, it has been shown that the ammonia conversion is sensitive to the number of distribution points and has an optimal value. It is found that the implication of the optimum number of injection points can substantially reduce the length of the reactor by 75.0% to achieve 100.0% ammonia conversion. The hydrogen reversal permeation phenomenon is observed at a low pressure and the upper part of the reactor. A novel configuration of a FBR and a FBMR with feed distribution is proposed for efficient production of ultra-pure hydrogen at a relatively low pressure. The critical reactor length ratio has been provided for this configuration.     

Preparation of a novel bimodal catalytic membrane reactor and its application to ammonia decomposition for COx-free hydrogen production

A novel bimodal catalytic membrane reactor (BCMR) consisting of a Ru/γ-Al₂O₃/α-Al₂O₃ bimodal catalytic support and a silica separation layer was proposed. The catalytic activity of the support was successfully improved due to enhanced Ru dispersion by the increased specific surface area for the γ-Al₂O₃/α-Al₂O₃ bimodal structure. The silica separation layer was prepared via a sol–gel process, showing a H₂ permeance of 2.6 × 10⁻⁷ mol Pa⁻¹ m⁻² s⁻¹, with H₂/NH₃ and H₂/N₂ permeance ratios of 120 and 180 at 500 °C. The BCMR was applied to NH₃ decomposition for CO_x-free hydrogen production. When the reaction was carried out with a NH₃ feed flow rate of 40 ml min⁻¹ at 450 °C and the reaction pressure was increased from 0.1 to 0.3 MPa, NH₃ conversion decreased from 50.8 to 35.5% without H₂ extraction mainly due to the increased H₂ inhibition effect. With H₂ extraction, however, NH₃ conversion increased from 68.8 to 74.4% due to the enhanced driving force for H₂ permeation through the membrane.     

Ammonia for hydrogen storage; A review of catalytic ammonia decomposition and hydrogen separation and purification

Ammonia is of interest as a hydrogen storage and transport medium because it enables liquid-phase hydrogen storage under mild conditions. Although ammonia can be used directly for energy applications, its use in conventional fuel cell electric vehicles necessitates decomposition into nitrogen and hydrogen, and the purification of the hydrogen to the composition required for commercial proton exchange membrane fuel cells. This article provides a review of the material and process considerations for catalytic ammonia decomposition and shows that Ru-based catalysts on conductive support materials are active at < 500 °C, but further understanding around lifetimes and deactivation conditions is required. This review then explores materials and technologies for hydrogen purification from decomposed ammonia gas streams, and our experiments show that defect-free dense-metal membranes are uninhibited by ammonia and can achieve the required product purity.     

Stability of pore-plated membranes for hydrogen production in fluidized-bed membrane reactors

Pd-based membranes prepared by pore-plating technique have been investigated for the first time under fluidization conditions. A palladium thickness around 20 μm was achieved onto an oxidized porous stainless steel support. The stability of the membranes has been assessed for more than 1300 h in gas separation mode (no catalyst) and other additional 200 h to continuous fluidization conditions. Permeances in the order of 5·10⁻⁷ mol s⁻¹ m⁻² Pa⁻¹ have been obtained for temperatures in a range between 375 and 500 °C. During fluidization, a small decrease in permeance is observed, as consequence of the increased external (bed-to-wall) mass transfer resistances. Moreover, water gas shift (WGS) reaction cases have been carried out in a fluidized bed membrane reactor. It has been confirmed that the selective H₂ separation through the membranes resulted in CO conversions beyond the thermodynamic equilibrium (of conventional systems), showing the benefits of membrane reactors in chemical conversions.     

Hydrogen production system combined with a catalytic reactor and a plasma membrane reactor from ammonia

Ammonia is a 1promising raw material for hydrogen production because it may solve several problems related to hydrogen transport and storage. Hydrogen can be effectively produced from ammonia via catalytic thermal decomposition; however, the resulting residual ammonia negatively influences the fuel cells. Therefore, a high-purity hydrogen production system comprising a catalytic decomposition reactor and a plasma membrane reactor (PMR) has been developed in this work. Most of the ammonia is converted to hydrogen and nitrogen by the catalytic reactor. After the product gas containing unreacted ammonia is introduced to the PMR, unreacted ammonia is decomposed and hydrogen is separated in the PMR. Based on these processes, hydrogen with a purity of 99.99% is obtained at the output of the PMR. Optimal operation conditions maximizing the hydrogen production flow rate were investigated. The gap length of the PMR and the gas differential pressure and applied voltage of the plasma influence the flow rate. A pure hydrogen flow rate of ∼120 L/h was achieved using the current operating conditions. The maximum energy efficiency of the developed hydrogen production system is 28.5%.     

Study on a catalytic membrane reactor for hydrogen production from ethanol steam reforming

Ethanol steam reforming in a membrane reactor with catalytic membranes was investigated to achieve important aims in one process, such as improvement in ethanol conversion and hydrogen yield, high hydrogen recovery and CO reduction. In order to confirm the efficiency of reaction and CO reduction, an ethanol reforming-catalytic membrane reactor with water–gas shift reaction (ECRW) in the permeate side was compared with a conventional reactor (CR) and an ethanol reforming-catalytic membrane reactor (ECR). In comparison with the CR, ethanol conversion improvement of 11.9–19% and high hydrogen recovery of 78–87% were observed in the temperature range of 300–600 °C in the ECRW. Compared with CR and ECR, the hydrogen yield of ECRW increased up to 38% and 30%, respectively. Particularly, the ECRW showed higher hydrogen yield at high temperature, because Pt/Degussa P25 loaded in the permeate side showed catalytic activity for the methane steam reforming as well as WGS reaction. Moreover, CO concentration was reduced under 1% by the WGS reaction in the permeate side in the temperature range of 300–500 °C.     

Performance assessment and evaluation of catalytic membrane reactor for pure hydrogen production via steam reforming of methanol

The steam reforming of methanol was investigated in a catalytic Pd–Ag membrane reactor at different operating conditions on a commercial Cu/ZnO/Al₂O₃ catalyst. A comprehensive two-dimensional non-isothermal stationary mathematical model has been developed. The present model takes into account the main chemical reactions, heat and mass transfer phenomena in the membrane reactor with hydrogen permeation across the PdAg membrane in radial direction. Model validation revealed that the predicted results satisfy the experimental data reasonably well under the different operating conditions. Also the impact of different operating parameters including temperature, pressure, sweep ratio and steam ratio on the performance of reactor has been examined in terms of methanol conversion and hydrogen recovery. The modeling results have indicated the high performance of the membrane reactor which is related to continuous removal of hydrogen from retentate side through the membrane to shift the reaction equilibrium towards formation of hydrogen. The obtained results have confirmed that increasing the temperature improves the kinetic properties of the catalyst and increase in the membrane's H₂ permeance, which results in higher methanol conversion and hydrogen production. Also it is inferred that the hydrogen recovery is favored at higher temperature, pressure, sweep ratio and steam ratio. The model prediction revealed that at 573 K, 2 bar and sweep ratio of 1, the maximum hydrogen recovery improves from 64% to 100% with increasing the steam ratio from 1 to 4.     

Hydrogen production from ammonia by the plasma membrane reactor

A new plasma membrane reactor (PMR) was developed to efficiently produce hydrogen from NH₃ with the use of atmospheric pressure plasma and a hydrogen separation membrane. The generation of high-purity hydrogen from NH₃ was also examined. First, hydrogen gas flowing into the PMR revealed the effect of the PMR on hydrogen separation. Hydrogen separation depends on the partial pressure of hydrogen gas supplied (P_{in, H2}) and permeated (P_{out, H2}) when P_{in, H2}^0.5 − P_{out, H2}^0.5 > 0. Second, NH₃ gas flowing into the PMR revealed its hydrogen production characteristics: the maximum hydrogen conversion rate of a typical plasma reactor (PR) is 13%, whereas the PMR converted 24.4%. Hydrogen obtained by hydrogen separation was approximately 100% pure. A hydrogen generation rate of 20 mL/min was stably obtained.     

Analysis of ammonia decomposition reactor to generate hydrogen for fuel cell applications

In this paper, reaction engineering principles are utilized to analyze process conditions for producing sufficient hydrogen in an ammonia decomposition reactor for generating net power of 100 W in a fuel cell. It is shown that operating the reactor adiabatically results in a sharp decrease in temperature due to endothermic reaction, which results in low conversion of ammonia. For this reason, the reactor is heated electrically to provide heat for the endothermic reactions. It is observed that when the reactor is operated non-adiabatically, it is possible to get over 99.5% conversion of ammonia. The weight of absorbent to reduce ammonia to ppb levels is calculated. An energy balance on the reactor exit gas indicates that there is sufficient heat available to vaporize enough water to achieve 100% relative humidity in the fuel cell. A suitable fuel cell stack is designed and it is shown that this stack is able to provide the necessary power to electrically heat the reactor and produce net power of 100 W.     

Large-scale decomposition of green ammonia for pure hydrogen production

It is acknowledged that Hydrogen has a decisive role to play in insuring a reliable and efficient penetration of renewable electricity in the energy mix. Nonetheless, building a sustainable Hydrogen Economy is faced with numerous challenges across the value chain. Namely, large-scale production and storage are still open issues that need to be addressed. A promising solution is to store renewable H₂ in the form of green ammonia often referred to as Power-to-Ammonia. Thus unlocking all available infrastructure for ammonia to effectively store and export hydrogen in bulk. In this value chain, the missing link is ammonia cracking to recover back hydrogen at high purities. The present work explores a technical solution to recover hydrogen from ammonia at large-scale. Through an exhaustive technoeconomic analysis, we have demonstrated the feasibility of large-scale production of pure H₂ from ammonia. The designed Ammonia-to-H₂ plant operates at a thermal efficiency of 68.5% to produce 200 MTPD of pure hydrogen at 250 bar. Furthermore, this study has established a final estimation of the Levelized Cost of Hydrogen (LCOH) from green ammonia. It was revealed that LCOH is mostly dependent on green ammonia cost, which in turn varies with renewable electricity cost.     

Steam reforming of propane in a fluidized bed membrane reactor for hydrogen production

Steam reforming of propane was carried out in a fluidized bed membrane reactor to investigate a feedstock other than natural gas for production of pure hydrogen. Close to equilibrium conditions were achieved inside the reactor with fluidized catalyst due to the very fast steam reforming reactions. Use of hydrogen permselective Pd₇₇Ag₂₃ membrane panels to extract pure hydrogen shifted the reaction towards complete conversion of the hydrocarbons, including methane, the key intermediate product. Irreversible propane steam reforming is limited by the reversibility of the steam reforming of this methane. To assess the performance improvement due to pure hydrogen withdrawal, experiments were conducted with one and six membrane panels installed along the height of the reactor. The results indicate that a compact reformer can be achieved for pure hydrogen production for a light hydrocarbon feedstock like propane, at moderate operating temperatures of 475–550 °C, with increased hydrogen yield.     

Performance and economics of a Pd-based planar WGS membrane reactor for coal gasification

Conceptual 300 tonne per day (tpd) H₂-from-coal plants have been the subject of several major costing exercises in the past decade. Incorporating conventional high- and low-temperature water-gas-shift (WGS) reactors, amine-based CO₂ removal and PSA-based H₂ purification systems, these studies provide a benchmark against which alternative H₂-from-coal technologies can be compared. The catalytic membrane reactor (CMR), combining a WGS catalyst and hydrogen-selective metal membrane, can potentially replace the multiple shift and separation stages of a plant based on conventional technology. CMR-based shift and separation offers several major advantages over the conventional approach, including greater-than-equilibrium WGS conversion, the containment of the CO₂ at high-pressure and a reduction in the number of unit processes.     

Comparison of experimental and simulation results on catalytic HI decomposition in a silica-based ceramic membrane reactor

In this study, the catalytic decomposition of hydrogen iodide was theoretically and experimentally investigated in a silica-based ceramic membrane reactor to assess the reactor's suitability for thermochemical hydrogen production. The silica membranes were fabricated by depositing a thin silica layer onto the surface of porous alumina ceramic support tubes via counter-diffusion chemical vapor deposition of hexyltrimethoxysilane. The performance of the silica-based ceramic membrane reactor was evaluated by exploring important operating parameters such as the flow rates of the hydrogen iodide feed and the nitrogen sweep gas. The influence of the flow rates on the hydrogen iodide decomposition conversion was investigated in the lower range of the investigated feed flow rates and in the higher range of the sweep-gas flow rates. The experimental data agreed with the simulation results reasonably well, and both highlighted the possibility of achieving a conversion greater than 0.70 at decomposition temperature of 400 °C. Therefore, the developed silica-based ceramic membrane reactor could enhance the total thermal efficiency of the thermochemical process.