High performance CO₂-perm-selective SSZ-13 membranes: Elucidation of the link between membrane material and module properties

Standard oil synthetic zeolite-13 (SSZ-13) membranes separate CO₂ (0.33 nm) from larger molecules (N₂ (0.364 nm) and CH₄ (0.38 nm)) via micropore (0.37 × 0.42 nm²) size differentiation and function well in humid CO₂-containing feeds, thus allowing effective carbon capture. However, their separation performance in a module configuration is not fully understood. Here, we changed the membrane supports from discs to tubes and investigated the differences in CO₂ perm-selectivities. The resulting hydrophobic SSZ-13 membranes had comparable and high separation factors (~20–30 for CO₂/N₂ and ~130–200 for CO₂/CH₄), while CO₂ permeance increased under wet conditions from ~1.8 × 10⁻⁸ mol∙m⁻² s⁻¹∙Pa⁻¹ (disc) to ~3.0–4.0 × 10⁻⁷ mol∙m⁻² s⁻¹∙Pa⁻¹ (tube). In addition, a long term stability test confirms the robustness of the SSZ-13 membrane under wet conditions. Furthermore, we varied the operating conditions systematically to evaluate the membrane module properties (recovery and purity) in two sizes of permeation cells or single tube modules. Considering the module performance efficiency, approximately, 76% and 59% CO₂ recovery and purity, respectively, were achieved using the tube-supported membrane with respect to a wet CO₂/N₂ mixture (mol:mol = 15:85; simulated for flue gas from coal-fired power plants). In addition, we derived a relationship between mass transport (related to CO₂ molar flux) and feed gas flow properties. Specifically, mass transfer (represented by the Sherwood number) in the feed stream and CO₂ molar flux across the membrane were related to the Reynolds number (a representative parameter of the feed stream). Finally, the Reynolds number was complemented with total feed pressure and CO₂ feed flow rate; the combined parameter described the module performance (CO₂ recovery and purity) well.