Highly CO2-selective and moisture-resistant bilayer silicalite-1/SSZ-13 membranes with gradient pores for wet CO2/CH4 and CO2/N2 separations

Enhanced capacity in cellulose aerogel for carbon dioxide capture through modified by metal-organic framework

Microporous metal-organic frameworks (MOF) exhibit excellent carbon dioxide (CO2) adsorption performance and selectivity for CO2/N2 separation. However, the challenges associate with the recycling and reuse of MOF powders hinder their practical applications. To address these limitations, a flexible and stable MOF-based composite material was designed by immobilizing UiO-66(Zr)-(OH)2 onto cellulose nanofibers (CNFs) aerogels (MOF-CNFs), which featured high porosity. Experimental results showed that MOF-CNFs exhibited sensitivity to CO2 adsorption at low pressure and achieved a CO2 adsorption capacity of 1.8 mmol/g at 0.15 bar under the 298 K. This represented an 8.8 % improvement compared to the MOF. Ideal adsorbed solution theory (IAST) calculations indicated selectivity for CO2/N2 mixtures (molar ratio 15:85) as high as 66. After eight adsorption-desorption cycles, the CO2 adsorption capacity retained 97 % of its initial value. These results highlighted the significant potential of MOF-CNFs as reusable and highly efficient CO2 separation adsorbents for practical applications, such as flue gas capture.

In Situ Synthesis of Cation-Free Zirconia-Supported Zeolite CHA Membranes for Efficient CO2/CH4 Separation

Cation-free zirconosilicate zeolite CHA and thin zirconia-supported membranes were in situ synthesized in a fluoride-free gel for the first time. The usage of the ZrO₂/Al₂O₃ composite support inhibited the transportation of aluminum from the support into zeolite membranes. No fluorite source was used for the synthesis of cation-free zeolite CHA membranes, indicating the green property of the synthesis. The thickness of the membrane was only 1.0 μm. The best cation-free zeolite CHA membrane prepared by the green in situ synthesis displayed a high CO₂ permeance of 1.1 × 10^-6 mol/(m² s Pa) and CO₂/CH₄ selectivity of 79 at 298 K and 0.2 MPa pressure drop for an equimolar CO₂/CH₄ mixture.

Truly combining the advantages of polymeric and zeolite membranes for gas separations

Mixed-matrix membranes (MMMs) have been investigated to render energy-intensive separations more efficiently by combining the selectivity and permeability performance, robustness, and nonaging properties of the filler with the easy processing, handling, and scaling up of the polymer. However, truly combining all in one single material has proven very challenging. In this work, we filled a commercial polyimide with ultrahigh loadings of a high-aspect ratio, CO₂-philic Na-SSZ-39 zeolite with a three-dimensional channel system that precisely separates gas molecules. By carefully designing both zeolite and MMM synthesis, we created a gas-percolation highway across a flexible and aging-resistant (more than 1 year) membrane. The combination of a CO₂-CH₄ mixed-gas selectivity of ~423 and a CO₂ permeability of ~8300 Barrer outperformed all existing polymer-based membranes and even most zeolite-only membranes.

Small-Pore Zeolite Membranes: A Review of Gas Separation Applications and Membrane Preparation

There have been significant advancements in small-pore zeolite membranes in recent years. With pore size closely related to many energy- or environment-related gas molecules, small-pore zeolite membranes have demonstrated great potential for the separation of some interested gas pairs, such as CO2/CH4, CO2/N2 and N2/CH4. Small-pore zeolite membranes share some characteristics but also have distinctive differences depending on their framework, structure and zeolite chemistry. Through this mini review, the separation performance of different types of zeolite membranes with respect to interested gas pairs will be compared. We aim to give readers an idea of membrane separation status. A few representative synthesis conditions are arbitrarily chosen and summarized, along with the corresponding separation performance. This review can be used as a quick reference with respect to the influence of synthesis conditions on membrane quality. At the end, some general findings and perspectives will be discussed.