Tuning carbon molecular sieves for natural gas separations: A diamine molecular approach

Abstract

This article introduces a new postsynthetic modification method for tuning the separation properties of carbon molecular sieve (CMS) membranes. Polymeric hollow fibers of 6FDA/BPDA‐DAM were pyrolyzed to 550°C under inert Argon, and were then exposed to a tetrahydrofuran solution containing PPM levels of paraphenylenediamine dopant. The original goal of the treatment was to modify the morphology in a manner to prevent relaxation of the CMS to suppress physical aging, envisioned to be analogous to that in glassy polymer membranes where reduction of “unrelaxed free volume” causes reduced permeance with a mild increase in selectivity. Results of long‐term CO2 and CH4 permeation experiments of doped fibers showed that aging‐resistant membranes did not result. This fact notwithstanding, results revealed this approach provides a valuable new tuning tool for CMS transport properties. Complementary gas sorption experiments performed suggest the amine dopants tune large ultramicropores, thereby increasing size and shape based diffusion selectivity. © 2016 American Institute of Chemical Engineers AIChE J, 63: 751–760, 2017

Carbon Hollow Fiber‐Supported Metal–Organic Framework Composites for Gas Adsorption

“…The asymmetric hollow fiber spinning was done by a dry‐jet/wet‐quench spinning process using water as a quench bath coagulant. Spun fibers underwent solvent exchange in water for 3 days, followed by methanol and hexane exchange for 1 h each, and then drying in vacuum oven at 130 °C for 3 h. The details of polymer dope composition, the schematic of hollow fiber spinning setup, and Torlon hollow fiber formation have been described in previously . The Torlon hollow fibers used in this study had a length of 5 cm with inner and outer diameters of 300 and 700 μm, respectively.…”

“…Hollow fibers have been shown to be excellent gas–solid contactors for various adsorption‐ and membrane‐based separation processes, mainly due to their unique combination of large surface area and high porosity within a packed volume . While polymeric hollow fibers provide numerous advantages for incorporating inorganic compounds and synthesis of composite materials, they suffer from chemical instability and swelling under various MOF hydrothermal synthesis conditions .…”

“…On the other hand, carbon hollow fibers provide high porosity and their structure remains intact under MOF synthesis conditions. The application of carbon hollow fibers in gas separation processes was pioneered by Koros and co‐workers …”

Molecular sieve membranes for N2/CH4separation

“…20 It has been suggested that these sp 2 -hybridized carbon sheets align into lamellar-like structures, yielding ordered microporous structures. 20 Specifically, these CMS phases display open micropores connected by rigid slit-like ultramicropores to provide high sorption and diffusion coefficients.…”

“…20 It has been suggested that these sp 2 -hybridized carbon sheets align into lamellar-like structures, yielding ordered microporous structures. 20 Specifically, these CMS phases display open micropores connected by rigid slit-like ultramicropores to provide high sorption and diffusion coefficients. 21 Different from the well-defined microporous structures which characterize zeolites and metal organic frameworks, CMS exhibit distributions of micropores and ultramicropores.…”