Employing Gutter Layers on Printed Gas Separation Membranes to Improve Membrane Permeance

Upgrading biogas into biomethane using membranes is of increasing interest for small to medium sized anaerobic digesters. While a number of commercial upgrading membranes exist, we note that the thin film composite (TFC) membrane is not commonly employed in this application. Many membranes for gas separations are made using the non-solvent induced phase separation process and result in integrated asymmetric membranes. TFCs offer better control of chemistry and selective layer thickness in order to hit performance targets. To make a good TFC selective layer requires both a method of processing a thin film in combination with a smooth, homogeneous support to achieve the thinnest possible membrane for maximum permeance while preserving selectivity. In this work, we explore the use of an emergent electrospray printed membrane approach to making gas separation membranes while using a gutter layer of a highly permeable polymer to provides a smooth surface for the selective layer and improved distribution of penetrating gases into the support. We discuss methods for making these layers and how we improved compatibility with the selective layer (Pebax). We chose polydimethylsiloxane (PDMS) as a traditional gutter layer material, but we noted that its hydrophobicity prevented good Pebax film formation due to its hydrophobicity. To remedy this, we treat the PDMS gutter layer with plasma to introduce chain defects and increase hydrophilicity. This allows compatibility between the gutter layer and the polar solvent used to print the Pebax and results in a more homogeneous and selective layer.