(497e) Precise Selective Layer Engineering of Carbon Molecular Sieve (CMS) Hollow Fiber Membranes for Improved Separation Performance

In my presentation, I will describe a Carbon Molecular Sieve (CMS) hollow fiber membrane system, working in conjunction with a Bubbling Fluidized Bed (BFB), aimed at producing high purity (99%) H₂. As part of this overall project, a series of BFB reactors have been constructed utilizing a biomass gasification process, to produce a hydrogen-rich syngas stream. The product stream from these reactor series represents a complex gas mixture consisting of H₂, CO, CO₂, CH₄, and H₂O vapor. CMS membranes have shown high selectivities between similar-sized penetrants and in this work, they are used to selectively permeate H₂ (0.289 nm), while rejecting the remaining gas molecules (CO₂ – 0.33 nm ; CH₄ – 0.38 nm and CO – 0.375 nm), to ultimately produce high-purity H₂ (fuel cell grade ~ 99.98%). Unlike other rigid molecular sieving materials, CMS membranes have the advantage of being processed into scalable hollow fiber formats which retain the excellent separation performance of the symmetric dense films. For the purpose of this work, we use polyimide-derived CMS hollow fiber membranes produced via high temperature (>500 ) pyrolysis of the precursor hollow fiber.

A specific focus of my work is the selective layer engineering technique of these CMS membranes, which employs a strategy similar to a defect curing technique involving an amine-acyl chloride reaction. In my talk, I will demonstrate how tuning the composition of this curing mixture and changing simple process parameters could increase the selectivity of CMS membranes. Controlled cross linking of the polyimide precursors is envisioned to result in strands of different dimensions compared to regular CMS. This controlled cross linking strategy combined with pyrolysis condition tuning, could lead to membranes with highly desirable permeance and selectivity tradeoffs. A fundamental vision of the effects of this strategy on the CMS microstructure will be presented.