Quantitative Analysis of Flow Configuration and Microstructure Effects on Gas Permeation in Multilayer Alumina Ceramic Membranes

This study investigates how flow configuration, pore size hierarchy, and surface wettability jointly influence gas transport in multilayer alumina ceramic membranes. Tubular membranes with nominal pore sizes of 15 nm, 200 nm, and 6000 nm were evaluated using air and CO₂ as probe gases at 100°C and transmembrane pressures between 0.2 and 3.0 bar. Gas flux and permeance were measured under different flow orientations to quantify pressure–flux relationships and identify dominant transport regimes. The results demonstrate that membrane orientation significantly affects permeation behaviour in graded pore structures, with higher flux observed when gas flows from finer to coarser pore layers due to reduced flow resistance and backpressure effects. Transport through the 15 nm membrane was governed by Knudsen diffusion with strong pressure dependence, while the 6000 nm membrane exhibited viscous-dominated flow with pressure-independent permeance; the 200 nm membrane showed transitional behaviour. Contact angle measurements revealed increased hydrophilicity with decreasing pore size, indicating enhanced surface–gas interactions that influence diffusion-dominated transport. SEM-based microstructural analysis confirmed well-defined multilayer architectures with distinct pore morphologies across scales. By quantitatively correlating pore size, wettability, and flow configuration with gas permeation behaviour, this study provides design-oriented guidance for selecting membrane architecture and orientation in porous ceramic membrane modules for gas separation and catalytic applications.