(531d) Enhancing H2-Permselectivity of High-Flux Hollow Fiber Membrane Via in-Situ Layer-By-Layer Surface Treatment

A primary challenge for realizing a hydrogen economy is the production of inexpensive and high purity hydrogen. Current techniques for the purification of hydrogen such as Pressure Swing Adsorption or cryogenic distillation are costly, energy intensive and complex in operation. Polymeric gas membranes with low production cost, improved mechanical properties, and high selectivity have the potential to replace current state of art technologies. Membranes have already found widespread application at industrial scale for the separation of nitrogen, air enrichment and the removal of CO₂ from synthesis gas. However, these size selective membranes have a tradeoff between permeability and selectivity.

Our previous work demonstrated layer-by-layer (LbL) deposition of thin functional films as a robust, low-cost method to introduce size-selective functionality to a membrane substrate [1]. Current industrial polymeric membranes generally employ high-flux, low-cost and low-selectivity Hollow Fiber membranes for light gas (H₂, CO₂, CH₄) separations. In this work, we demonstrate that LbL deposition of sub-micron conformal coating on a highly selective membrane with competitive permeability on hollow fibers (HF) for enhanced light gas separation. For the first time, we show increase in the H₂ selectivity of high flux HF membranes by addition of Polyethylenimine (PEI)/polyacrylic acid (PAA) bi-layers.

Polyamide imide (Torlon) Hollow fibers were provided by collaborators at NETL. These HFs were first potted in a tube and shell assembly followed by passing PEI and PAA solution alternatively. The optical microscopic images of these membranes indicated a thickness of 5 microns. These membranes showed high degree of ‘ionic-crosslinking’ achieved high selectivities of H2: CO2 (>200:1) and H2: N2 (>2000:1) at 40 Barrers of H₂ permeability exceeding the Robeson upper bound for homogenous polymer films [2]. The deposition of a low-cost, water-based polymers and easy to fabricate LbL membranes on conventional HF has potential use at industrial scale for hydrogen separation.

1. Kim, D., et al., Highly size-selective ionically crosslinked multilayer polymer films for light gas separation. Adv Mater, 2014. 26(5): p. 746-51.
2. Robeson, L.M., The upper bound revisited. Journal of Membrane Science, 2008. 320(1-2): p. 390-400.