(300b) Design of Flat Sheet Membrane Modules for Gas Separation to Enhance Countercurrent Contacting

High-performance membranes are commonly fabricated as hollow fibers or flat sheets. Hollow fiber modules inherently allow counter-current flow, while standard flat-sheet modules, plate-and-frame or spiral-wound, typically rely on crossflow. As a result, additional design features are required to enable counter-current contacting in flat-sheet modules, and the efficacy of these features in achieving such flow without imposing excessive pressure drops remains poorly understood.

In flat sheet modules, glue lines are often added to direct fluid flow anti-parallel to the retentate flow (i.e., to introduce partial counter-current contacting). Nevertheless, a degree of crossflow is still needed to distribute fluid along the entire leaf. Glue lines also negatively impact membrane performance in two ways: (1) by reducing the membrane area available for permeation, and (2) by introducing extra pressure drop.

This study examines four distinct glue-line configurations, used to modify spiral wound modules, disclosed in the patent literature: (1) multiple glue lines running the full length of the membrane leaf, (2) variations in glue-line shape, (3) changes in glue-line thickness, and (4) placement of the glue line on either the feed side or the permeate side. These configurations are evaluated using COMSOL Multiphysics simulations for O₂/N₂ separation, comparing module stage cuts, feed flow rates, and pressure drops across for a broad range of nitrogen product compositions. The results are presented for both sweep and non-sweep scenarios.

At lower capture rates, the performance differences between configurations are small. However, as capture rates increase, larger discrepancies emerge, driven by imperfect counter-current contacting, additional pressure drop, and lost membrane area. By quantifying these competing factors, this work provides strategies for effectively incorporating glue lines into flat sheet module designs to balance performance and operational penalties.