Post-synthesis defect abatement of inorganic membranes for gas separation

The opportunity of membrane technology for hydrogen purification in the power to hydrogen (P2H) roadmap: a review

The global energy market is in a transition towards low carbon fuel systems to ensure the sustainable development of our society and economy. This can be achieved by converting the surplus renewable energy into hydrogen gas. The injection of hydrogen (⩽10% v/v) in the existing natural gas pipelines is demonstrated to have negligible effects on the pipelines and is a promising solution for hydrogen transportation and storage if the end-user purification technologies for hydrogen recovery from hydrogen enriched natural gas (HENG) are in place. In this review, promising membrane technologies for hydrogen separation is revisited and presented. Dense metallic membranes are highlighted with the ability of producing 99.9999999% (v/v) purity hydrogen product. However, high operating temperature (⩾300 °C) incurs high energy penalty, thus, limits its application to hydrogen purification in the power to hydrogen roadmap. Polymeric membranes are a promising candidate for hydrogen separation with its commercial readiness. However, further investigation in the enhancement of H₂/CH₄ selectivity is crucial to improve the separation performance. The potential impacts of impurities in HENG on membrane performance are also discussed. The research and development outlook are presented, highlighting the essence of upscaling the membrane separation processes and the integration of membrane technology with pressure swing adsorption technology.

Applying Alkyl-Chain Surface Functionalizations in Mesoporous Inorganic Structures: Their Impact on Gas Flow and Selectivity Depending on Temperature

Porous inorganic capillary membranes are prepared to serve as model structures for the experimental investigation of the gas transport in functionalized mesopores. The porous structures possess a mean pore diameter of 23 nm which is slightly reduced to 20 nm after immobilizing C₁₆-alkyl chains on the surface. Gas permeation measurements are performed at temperatures ranging from 0 to 80 °C using Ar, N₂, and CO₂. Nonfunctionalized structures feature a gas transport according to Knudsen diffusion with regard to gas flow and selectivity. After C₁₆-functionalization, the gas flow is reduced by a factor of 10, and the ideal selectivities deviate from the Knudsen theory. CO₂ adsorption measurements show a decrease in total amount of adsorbed gas and isosteric heat of adsorption. It is hypothesized that the immobilized C₁₆-chains sterically influence the gas transport behavior without a contribution from adsorption effects. The reduced gas flow derives from an additional surface resistance caused by the C₁₆-chains spacially limiting the adsorption and desorption directions for gas molecules propagating through the structure, resulting in longer diffusion paths. In agreement, the gas flow is found to correlate with the molecular diameter of the gas species (CO₂ < Ar < N₂) increasing the resistance for larger molecules. This affects the ideal selectivities with the relation [Formula: see text]. The influence on selectivity increases with increasing temperature which leads to the conclusion that the temperature induced movement of the C₁₆-chains is responsible for the stronger interaction between gas molecules and surface functional groups.

On a Rational Performance Evaluation for the Development of Inorganic Membrane Technology in Gas Separation and Membrane Reactors

Inorganic membranes can be made of different materials. However, there have been only few reports on membrane evaluation to convert lab-scale membranes into a prototype for industrial applications. In order to fill this significant gap, new approaches for the development and optimization of membrane products are required. This work focuses on the different aspects related to the performance assessment of membranes used for gas separation and membrane reactors. This approach can be visualized as an algorithm consisting of three specific loops involving different aspects of the overall membrane evaluation. Several factors that have an impact on membrane performance are discussed. These factors are divided into two categories: directly affecting the measurements (setup leakage, concentration polarization, repeatability, pressure gradient) and related to the intrinsic characteristics of permeation flux across the membrane (single and mixture permeation, transport modeling, defect flux, microstructure flexibility). This evaluation protocol includes a literature review with the most recent breakthroughs in this research area.

Bendable Zeolite Membranes: Synthesis and Improved Gas Separation Performance

Separation and sequestration of CO2 emitted from fossil energy fueled electric generating units and industrial facilities will help in reducing anthropogenic CO2, thereby mitigating its adverse climate change effects. Membrane-based gas separation has the potential to meet the technical challenges of CO2 separation if high selectivity and permeance with low costs for large-scale manufacture are realized. Inorganic zeolite membranes in principle can have selectivity and permeance considerably higher than polymers. This paper presents a strategy for zeolite growth within the pores of a polymer support, with crystallization time of an hour. With a thin coating of 200-300 nm polydimethylsiloxane (PDMS) on the zeolite-polymer composite, transport data for CO2/N2 separation indicate separation factors of 35-45, with CO2 permeance between 1600 and 2200 GPU (1 GPU = 3.35 × 10(-10) mol/(m(2) s Pa)) using dry synthetic mixtures of CO2 and N2 at 25 °C. The synthesis process results in membranes that are highly reproducible toward transport measurements and exhibit long-term stability (3 days). Most importantly, these membranes because of the zeolite growth within the polymer support, as contrasted to conventional zeolite growth on top of a support, are mechanically flexible.

Zeolite membranes – a review and comparison with MOFs

The latest developments in zeolite and MOF membranes are reviewed, with an emphasis on synthesis techniques. Industrial applications, hydrothermal stability, polymer-supported and mixed matrix membranes are some of the aspects discussed.

Separation membranes. Interfacial microfluidic processing of metal-organic framework hollow fiber membranes

Molecular sieving metal-organic framework (MOF) membranes have great potential for energy-efficient chemical separations, but a major hurdle is the lack of a scalable and inexpensive membrane fabrication mechanism. We describe a route for processing MOF membranes in polymeric hollow fibers, combining a two-solvent interfacial approach for positional control over membrane formation (at inner and outer surfaces, or in the bulk, of the fibers), a microfluidic approach to replenishment or recycling of reactants, and an in situ module for membrane fabrication and permeation. We fabricated continuous molecular sieving ZIF-8 membranes in single and multiple poly(amide-imide) hollow fibers, with H2/C3H8 and C3H6/C3H8 separation factors as high as 370 and 12, respectively. We also demonstrate positional control of the ZIF-8 films and characterize the contributions of membrane defects and lumen bypass.