The utilization of ammonia for hydrogen storage relies on the implementation of efficient decomposition techniques, and the membrane reactor, which allows simultaneous ammonia decomposition and hydrogen recovery, can be regarded as a promising technology. While Pd-based membranes show the highest performance for hydrogen separation, their applicability for NH₃-sensitive applications, such as proton exchange membrane (PEM) fuel cells, demands relatively thick, and therefore expensive, membranes to meet the purity targets for hydrogen. To address this challenge, this study proposes a solution involving the utilization of a downstream hydrogen purification unit to remove residual ammonia, thereby enabling the use of less selective, therefore more cost-effective, membranes. Specifically, a carbon molecular sieve membrane was prepared on a tubular porous alumina support and tested for ammonia decomposition in a membrane reaction setup. Operating at 5 bar and temperatures ranging from 450 to 500 °C, NH₃ conversion rates exceeding 90% were achieved, with conversion approaching thermodynamic equilibrium at temperatures above 475 °C. Simultaneously, the carbon membrane facilitated the recovery of hydrogen from ammonia, yielding recoveries of 8.2–9.8%. While the hydrogen produced at the permeate side of the reactor failed to meet the purity requirements for PEM fuel cell applications, the implementation of a downstream hydrogen purification unit comprising a fixed bed of zeolite 13X enabled the production of fuel cell-grade hydrogen. Despite performance far from being comparable with the ones achieved in the literature with Pd-based membranes, this study underscores the viability of carbon membranes for fuel cell-grade hydrogen production, showcasing their competitiveness in the field.

A resorcinol-formaldehyde precursor was synthesized to fabricate the CO₂ selective Carbon Molecular Sieve Membranes (CMSMs) developed in this study. The degree of polymerization (DP) was analyzed via Gel Permeation Chromatography (GPC) and its effect on the CO₂/N₂ perm-selectivity and CO₂ permeance was investigated. The membrane that was polymerized at 80 °C (named R80) was selected as the best performing CMSM after a preliminary test. The post treatment with oxidative atmosphere was performed to increase the CO₂ permeance and CO₂/N₂ perm-selectivity on membrane R80. The gas permeation results and Pore Size Distribution (PSD) measurements via perm-porometry resulted in selecting the membrane with an 80 °C polymerization temperature, 100 min of post treatment in 6 bar pressure and 120 °C with an oxygen concentration of 10% (named R80T100) as the optimum for enhancing the performance of CMSMs. The 3D laser confocal microscopy results confirmed the reduction in the surface roughness in post treatment on CMSMs and the optimum timing of 100 min in the treatment. CMSM R80T100 exhibiting CO₂/N₂ ideal selectivity of 194 at 100 °C with a CO₂ permeability of 4718 barrier was performed higher than Robeson’s upper bound limit for polymeric membranes and also the other CMSMs fabricated in this work.

The conceptual design and engineering of an integrated catalytic reactor requires a thorough understanding of the prevailing mechanisms and phenomena to ensure a safe operation while achieving desirable efficiency and product yields. The necessity and importance of these requirements are demonstrated in this investigation in the case of novel membrane-assisted reactors tailored for CO₂ hydrogenation. Firstly, a carbon molecular sieve membrane was developed for simultaneous separation of CO₂ from a hot post-combustion CO₂-rich stream, followed by directing it along a packed-bed of hybrid CuO-ZnO/ZSM5 catalysts to react with hydrogen and produce DiMethyl Ether (DME). The generated water is removed from the catalytic bed by permeation through the membrane which enables reaction equilibrium shift towards more CO₂-conversion. Extra process intensification was achieved using a membrane-assisted reactive distillation reactor, where similarly several such parallel membranes were erected inside a catalytic bed to form a reactive-distillation column. This provides the opportunity for a synchronized separation of CO₂ and water by a membrane, mixing the educts (i.e., hydrogen and CO₂) and controlling the reaction along the catalytic bed while distilling the products (i.e., methanol, water and DME) through the catalyst loaded column. The hybrid catalyst and carbon molecular sieve membrane were developed using the synthesis methods and proved experimentally to be among the most efficient compared to the state-of-the-art. In this context, selective permeation of the membrane and selective catalytic conversion of hybrid catalysts under the targeted operating temperature range of 200–260 °C and 10–20 bar pressure were studied. For the membrane, the obtained high flux of selective CO₂-permeation was beyond the Robeson upper bound. Moreover, in the hybrid catalytic structure, a combined methanol and DME yield of 15% was secured. Detailed results of catalyst and membrane synthesis and characterization along with catalyst test and membrane permeation tests are reported in this paper. The performance of various configurations of integrated catalytic and separation systems was studied through an experimentally supported simulation along with the systematic analysis of the conceptual design and operation of such reactive distillation. Focusing on the subnano-/micro-meter scale, the performance of sequential reactions while considering the interaction of the involved catalytic materials on the overall performance of the hybrid catalyst structure was studied. On the same scale, the mechanism of separation through membrane pores was analyzed. Moreover, looking at the micro-/milli-meter scale in the vicinity of the catalyst and membrane, the impacts of equilibrium shift and the in-situ separation of CO₂ and steam were analyzed, respectively. Finally, at the macro-scale separation of components, the impacts of established temperature, pressure and concentration profiles along the reactive distillation column were analyzed. The desired characteristics of the integrated membrane reactor at different scales could be identified in this manner.

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.