Nanocomposite MFI-alumina membranes via pore-plugging synthesis: Specific transport and separation properties

Preparation and Evaluation of Nanocomposite Sodalite/α-Al2O3 Tubular Membranes for H2/CO2 Separation

Nanocomposite sodalite/ceramic membranes supported on α-Al₂O₃ tubular support were prepared via the pore-plugging hydrothermal (PPH) synthesis protocol using one interruption and two interruption steps. In parallel, thin-film membranes were prepared via the direct hydrothermal synthesis technique. The as-synthesized membranes were evaluated for H₂/CO₂ separation in the context of pre-combustion CO₂ capture. Scanning electron microscopy (SEM) was used to check the surface morphology while x-ray diffraction (XRD) was used to check the crystallinity of the sodalite crystals and as-synthesized membranes. Single gas permeation of H₂, CO₂, N₂ and mixture gas H₂/CO₂ was used to probe the quality of the membranes. Gas permeation results revealed nanocomposite membrane prepared via the PPH synthesis protocols using two interruption steps displayed the best performance. This was attributed to the enhanced pore-plugging effect of sodalite crystals in the pores of the support after the second interruption step. The nanocomposite membrane displayed H₂ permeance of 7.97 × 10⁻⁷ mol·s⁻¹·m⁻²·Pa⁻¹ at 100 °C and 0.48 MPa feed pressure with an ideal selectivity of 8.76. Regarding H₂/CO₂ mixture, the H₂ permeance reduced from 8.03 × 10⁻⁷ mol·s⁻¹·m⁻²·Pa⁻¹ to 1.06 × 10⁻⁷ mol·s⁻¹·m⁻²·Pa⁻¹ at 25 °C and feed pressure of 0.18 MPa. In the presence of CO₂, selectivity of the nanocomposite membrane reduced to 4.24.

Highly permeable tubular silicalite-1 membranes for CO2 capture

Membranes represent one of the most promising alternatives for CO₂ separation and capture. Zeolites membranes, in particular, that can withstand high temperatures and pressures, offer energy efficient way to capture CO₂ compared to conventional separation techniques such as amine absorption. In this work, silicalite-1/ceramic composite membranes were prepared on the inner surface of zirconium oxide and/or titanium oxide tubular supports by a pore plugging hydrothermal synthesis. Five types of supports with different pore sizes ranging from 0.14 to 1.4 μm, were studied. The synthesized membranes were characterized by scanning electron microscope (SEM), electron diffraction spectrometer (EDS), x-ray diffraction (XRD), and gas permeation with pure and mixed gas feeds. All membranes showed high concentrations of Si within the active layer of the support, suggesting successful pore-plugging of the membranes. The greater the pore size of the active layer of the support, the greater was the concentration of Si observed. In addition, large coffin-shape crystals, which are characteristics of silicalite-1, were also observed on top of each membrane. The analysis of XRD micrographs revealed that the crystals were mostly oriented with either the a- or b-axes perpendicular to the membrane surface, which is desirable from the point of view of minimizing the resistance to gas transport through the zeolite membrane. Except for the membranes synthesized using the supports with 0.14 μm pores, all membranes were very selective with CO₂/N₂ permselectivities up to 30 at low-pressure differentials. At the same time, the membranes were very permeable with CO₂ permeance in the order of 10^-6 mol m^-2 Pa^-1 s^-1. Assuming the thickness of the selective layer to be equivalent to the thickness of the active layer of the support, all membranes fell above the revised Robeson upper-bound line for CO₂/N₂ separation.

Mixed matrix membranes for hydrocarbons separation and recovery: a critical review

The separation and purification of light hydrocarbons are significant challenges in the petrochemical and chemical industries. Because of the growing demand for light hydrocarbons and the environmental and economic issues of traditional separation technologies, much effort has been devoted to developing highly efficient separation techniques. Accordingly, polymeric membranes have gained increasing attention because of their low costs and energy requirements compared with other technologies; however, their industrial exploitation is often hampered because of the trade-off between selectivity and permeability. In this regard, high-performance mixed matrix membranes (MMMs) are prepared by embedding various organic and/or inorganic fillers into polymeric materials. MMMs exhibit the advantageous and disadvantageous properties of both polymer and filler materials. In this review, the influence of filler on polymer chain packing and membrane sieving properties are discussed. Furthermore, the influential parameters affecting MMMs affinity toward hydrocarbons separation are addressed. Selection criteria for a suitable combination of polymer and filler are discussed. Moreover, the challenges arising from polymer/filler interactions are analyzed to allow for the successful implementation of this promising class of membranes.

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.

Potential Applications of Zeolite Membranes in Reaction Coupling Separation Processes

Future production of chemicals (e.g., fine and specialty chemicals) in industry is faced with the challenge of limited material and energy resources. However, process intensification might play a significant role in alleviating this problem. A vision of process intensification through multifunctional reactors has stimulated research on membrane-based reactive separation processes, in which membrane separation and catalytic reaction occur simultaneously in one unit. These processes are rather attractive applications because they are potentially compact, less capital intensive, and have lower processing costs than traditional processes. Therefore this review discusses the progress and potential applications that have occurred in the field of zeolite membrane reactors during the last few years. The aim of this article is to update researchers in the field of process intensification and also provoke their thoughts on further research efforts to explore and exploit the potential applications of zeolite membrane reactors in industry. Further evaluation of this technology for industrial acceptability is essential in this regard. Therefore, studies such as techno-economical feasibility, optimization and scale-up are of the utmost importance.

Grain Boundary Defect Elimination in a Zeolite Membrane by Rapid Thermal Processing

Microporous molecular sieve catalysts and adsorbents discriminate molecules on the basis of size and shape. Interest in molecular sieve films stems from their potential for energy-efficient membrane separations. However, grain boundary defects, formed in response to stresses induced by heat treatment, compromise their selectivity by creating nonselective transport pathways for permeating molecules. We show that rapid thermal processing can improve the separation performance of thick columnar films of a certain zeolite (silicalite-1) by eliminating grain boundary defects, possibly by strengthening grain bonding at the grain boundaries. This methodology enables the preparation of silicalite-1 membranes with high separation performance for aromatic and linear versus branched hydrocarbon isomers and holds promise for realizing high-throughput and scalable production of these zeolite membranes with improved energy efficiency.