(401u) Diamine Based Modification of Matrimid® Derived Carbon Molecular Sieve (CMS) Hollow Fiber Membranes for Hydrogen Production from Biomass-Derived Syngas Mixture

In this talk, a selective layer engineering approach is presented, involving the fabrication of Matrimid® polymer hollow fibers via the dry-jet wet-quench method, and its subsequent pyrolysis to form a carbon molecular sieve (CMS) hollow fiber membrane. This membrane system is being designed to be used in conjunction with a 2-stage biomass gasifier, wherein the H₂-rich (~49%) syngas is passed through the membrane system to enrich the final H₂ to 99.98%. For this purpose, a highly selective CMS hollow fiber membrane is being designed and tested under varying temperatures (35 – 100 ) using a synthetic quaternary mixture (25% H₂, 25% CO, 25% CO₂ and 25% CH₄). These membranes are asymmetric in nature, utilizing the silane based modification approach (commonly referred to as V-treatment) [1] which creates hollow fibers with thin (~5 ) selective layers. In our work, we do further modifications to the membranes via the addition of diamine monomers (e.g. Diethyl toluene diamine (DETDA)) to the defect-free selective later of the Matrimid® precursor and pyrolyzing using different pyrolysis temperatures. Such membranes surprisingly raise the H₂ permeance of these membranes with slight increases in H₂/ X selectivities (where X = CO, CO₂ and CH₄). DETDA, a mixed-isomer diamine, was used as the base modifier due to its ability to introduce multiple bonding configurations within the Matrimid® matrix. In parallel, Trimesoyl Chloride (TMC) served as the base acyl chloride crosslinking agent, which in conjunction with DETDA, facilitated further polymer network evolution. Counterintuitively, the addition of TMC , in controlled amounts, further enhances the H₂ permeance. We currently speculate that these selective layer engineering strategies likely disrupt the so-called “hyperskin” formation within CMS membranes during the pyrolysis process. Hyperskin is an ultra-thin, dense portion of the selective layer which is formed by the rapid collapse of the carbon strands near the surface to form micropore-free tight ultramicroporous layer and the presence of such a hyperskin tends to lead to reduced permeances than expected [2]. Sorption analysis on pure Matrimid® -derived and DETDA-modified Matrimid® derived CMS dense films have been performed, which allow the estimation of permeation, diffusion and sorption coefficients for these materials. These fundamental parameters also allow the estimation of the dual mode transport and sorption parameters which provide key insights into the membrane morphologies. A proposed mechanism linking precursor modification to the final CMS microstructure and its eventual impact on the CMS morphology and performance, will be presented in this talk.

References

1. Bhuwania, N.; Labreche, Y.; Achoundong, C. S. K.; Baltazar, J.; Burgess, S. K.; Karwa, S.; Xu, L.; Henderson, C. L.; Williams, P. J.; Koros, W. J. Engineering Substructure Morphology of Asymmetric Carbon Molecular Sieve Hollow Fiber Membranes. Carbon 2014, 76, 417–434. https://doi.org/10.1016/j.carbon.2014.05.008.
2. Sanyal, O.; Hicks, S. T.; Bhuwania, N.; Hays, S.; Kamath, M. G.; Karwa, S.; Swaidan, R.; Koros, W. J. Cause and Effects of Hyperskin Features on Carbon Molecular Sieve (CMS) Membranes. Journal of Membrane Science 2018, 551, 113–122. https://doi.org/10.1016/j.memsci.2018.01.021.