A bimodal catalytic membrane having a hydrogen-permselective silica layer on a bimodal catalytic support: Preparation and application to the steam reforming of methane

The steam reforming of methane for hydrogen production was experimentally investigated using catalytic membrane reactors, consisting of a microporous silica top layer, for the selective permeation of hydrogen, and an α-alumina support layer, for catalytic reaction of the steam reforming of methane. An α-alumina support layer with a bimodal structure, which was proposed for the enhanced dispersion of Ni catalysts, was prepared by impregnating γ-Al2O3 inside α-Al2O3 microfiltration membranes (1 μm in pore diameter), and then immersing the membranes in a nickel nitrate solution, resulting in a bimodal catalytic support. The bimodal catalytic support showed a large conversion of methane at a high space velocity compared with a conventional catalytic membrane with a monomodal structure. The enhanced activity of Ni-catalysts in bimodal catalytic supports was confirmed by hydrogen adsorption measurements. A bimodal catalytic membrane, i. e., a silica membrane coated on a bimodal catalytic support, showing an approximate selectivity of hydrogen over nitrogen of 100 with a hydrogen permeance of 0.5-1x10-5 m3 m-2 s-1 kPa-1 was examined for the steam reforming of methane. The reaction was carried out at 500 °C, and the feed and permeate pressures were maintained at 100 and 20 kPa, respectively. Methane conversion could be increased up to approximately 0.7 beyond the equilibrium conversion of 0.44 by extracting hydrogen from the reaction stream to the permeate stream

A photocatalytic membrane reactor for VOC decomposition using Pt-modified titanium oxide porous membranes

Porous titanium oxide membranes with pore sizes in the range of 2.5-22 nm were prepared by a sol-gel procedure, and were applied for decomposition of methanol and ethanol as model volatile organic compounds (VOCs) in a photocatalytic membrane reactor, where oxidation reaction occurs both on the surface and inside the porous TiO2 membrane while reactants are permeating via one-pass flow. Methanol was completely photo-oxidized by black-light irradiation to CO2 when methanol at a concentration of 100 ppm was used at a feed flow rate of 500 × 10-6 m3/min, but the conversion decreased when the MeOH concentration in the feed was increased. Pt-modification was carried out by photo-deposition, and led to a decrease in pore diameter. Using Pt-modified membranes, a nearly complete oxidation of methanol up to 10,000 ppm at a feed flow rate of 500 × 10-6 m3/min was observed. Thus, such membranes would be effective for purifying a permeate stream after one-pass permeation through the TiO2 membranes. The decomposition of ethanol is also discussed

Preliminary techno-economic analysis of non-commercial ceramic and organosilica membranes for hydrogen peroxide ultrapurification

Polymeric membrane cascades have demonstrated their technical and economic viability for hydrogen peroxide ultrapurification. Nevertheless, these membranes suffer from fast degradation under such oxidative conditions. Alternative membranes with higher chemical resistance could improve the ultrapurification process. Therefore, this work presents the preliminary techno-economic analysis of two non-commercial membranes (a ceramic one and a hybrid organosilica one). This analysis is complemented with further research regarding the competitiveness of these alternative membranes compared to polymeric ones. The results confirm the technical viability for both membranes, but the ceramic membrane is not appropriate when Na is considered as the limiting impurity (because it has too low rejection coefficient). The economic viability of the proposed ultrapurification processes is also probed, but not under competitive conditions, as the polyamide membrane appears to be the optimal choice. Nonetheless, improvements in the permeability of the hybrid membrane (an increase in the membrane permeability by a factor of 10) or the rejection performance of the ceramic membrane (an increase in the reflection coefficient above 0.85) could transform these non-commercial membranes into the most profitable alternative.This research has been financially supported by the Spanish Ministry of Economy and Competitiveness (MINECO) through CTQ2014-56820-JIN Project, co-financed by FEDER funds. R. Abejón acknowledges the assistance of the Japan Society for Promotion of Science (JSPS) for the award of a Post-Doctoral Fellowship (Short-Term) for North American and European Researchers (PE14057)

Organosilica-Based Membranes in Gas and Liquid-Phase Separation

Organosilica membranes are a type of novel materials derived from organoalkoxysilane precursors. These membranes have tunable networks, functional properties and excellent hydrothermal stability that allow them to maintain high levels of separation performance for extend periods of time in either a gas-phase with steam or a liquid-phase under high temperature. These attributes make them outperform pure silica membranes. In this review, types of precursors, preparation method, and synthesis factors for the construction of organosilica membranes are covered. The effects that these factors exert on characteristics and performance of these membranes are also discussed. The incorporation of metals, alkoxysilanes, or other functional materials into organosilica membranes is an effective and simple way to improve their hydrothermal stability and achieve preferable chemical properties. These hybrid organosilica membranes have demonstrated effective performance in gas and liquid-phase separation

Catalytic Ammonia Decomposition over High-Performance Ru/Graphene Nanocomposites for Efficient COx-Free Hydrogen Production

Highly-dispersed Ru nanoparticles were grown on graphene nanosheets by simultaneously reducing graphene oxide and Ru ions using ethylene glycol (EG), and the resultant Ru/graphene nanocomposites were applied as a catalyst to ammonia decomposition for COx-free hydrogen production. Tuning the microstructures of Ru/graphene nanocomposites was easily accomplished in terms of Ru particle size, morphology, and loading by adjusting the preparation conditions. This was the key to excellent catalytic activity, because ammonia decomposition over Ru catalysts is structure-sensitive. Our results demonstrated that Ru/graphene prepared using water as a co-solvent greatly enhanced the catalytic performance for ammonia decomposition, due to the significantly improved nano architectures of the composites. The long-term stability of Ru/graphene catalysts was evaluated for COx-free hydrogen production from ammonia at high temperatures, and the structural evolution of the catalysts was investigated during the catalytic reactions. Although there were no obvious changes in the catalytic activities at 450 °C over a duration of 80 h, an aggregation of the Ru nanoparticles was still observed in the nanocomposites, which was ascribed mainly to a sintering effect. However, the performance of the Ru/graphene catalyst was decreased gradually at 500 °C within 20 h, which was ascribed mainly to both the effect of the methanation of the graphene nanosheet under a H2 atmosphere and to enhanced sintering under high temperatures

Recent Progress in Silicon Carbide-Based Membranes for Gas Separation

The scale of research for developing and applying silicon carbide (SiC) membranes for gas separation has rapidly expanded over the last few decades. Given its importance, this review summarizes the progress on SiC membranes for gas separation by focusing on SiC membrane preparation approaches and their application. The precursor-derived ceramic approaches for preparing SiC membranes include chemical vapor deposition (CVD)/chemical vapor infiltration (CVI) deposition and pyrolysis of polymeric precursor. Generally, SiC membranes formed using the CVD/CVI deposition route have dense structures, making such membranes suitable for small-molecule gas separation. On the contrary, pyrolysis of a polymeric precursor is the most common and promising route for preparing SiC membranes, which includes the steps of precursor selection, coating/shaping, curing for cross-linking, and pyrolysis. Among these steps, the precursor, curing method, and pyrolysis temperature significantly impact the final microstructures and separation performance of membranes. Based on our discussion of these influencing factors, there is now a good understanding of the evolution of membrane microstructures and how to control membrane microstructures according to the application purpose. In addition, the thermal stability, oxidation resistance, hydrothermal stability, and chemical resistance of the SiC membranes are described. Due to their robust advantages and high separation performance, SiC membranes are the most promising candidates for high-temperature gas separation. Overall, this review will provide meaningful insight and guidance for developing SiC membranes and achieving excellent gas separation performance