Carbon molecular sieve structure development and membrane performance relationships

Abstract

Characterization techniques beyond microscopy, scattering and spectroscopy approaches are needed to understand and improve sub-angstrom discrimination between penetrants in carbon molecular sieve (CMS) membranes. Here we use a method based on molecular scale gas diffusion probes to understand relevant membrane properties at the required level of detail. We further use this method to consider hypotheses about the evolution of structure responsible for fundamental properties of CMS materials derived from a high performance CMS precursor polymer, 6FDA:BPDA-DAM. While 6FDA:BPDA-DAM derived CMS membranes display a ~230 % improvement in CO 2 permeability when compared to Matrimid ® derived CMS formed under the same conditions, the diffusional selectivity for these two materials are very similar at 35 and 38.5, respectively. These results indicate a non-trivial connection between CMS precursor material structure and resulting performance. Linking hypotheses about structural changes likely to occur during pyrolysis with the probe data provides insights regarding transformation of the random coil polyimide into ultra-rigid CMS, with exquisite size and shape diffusion selectivity. The results provide a framework for understanding and tuning properties of this special class of materials with important technological advantages in energy-intensive gas separations.

Hyperaging Tuning of a Carbon Molecular‐Sieve Hollow Fiber Membrane with Extraordinary Gas‐Separation Performance and Stability

“…[6][7][8][9][10][11][12][13][14][15] Optimizing the permeability and selectivity of CMS membranes by tailoring precursors and/or optimizing pyrolysis conditions are accepted approaches. [19,20] These studies led to ad ramatically increased H 2 -vs.-hydrocarbon selectivity.W erefer to this phenomenon as hyperaging,and it is particularly relevant to important cracked-gas cleanup applications for large energy savings.T he hyperaging technique allows pore-size tuning to enhance the selectivity of specific gas pairs.U nlike conventional anti-aging efforts we have explored, hyperaging purposely accelerates the selective aging of CMS membranes,thereby creating CMS hollow fiber membranes with much higher performance for H 2 separation. [19,20] These studies led to ad ramatically increased H 2 -vs.-hydrocarbon selectivity.W erefer to this phenomenon as hyperaging,and it is particularly relevant to important cracked-gas cleanup applications for large energy savings.T he hyperaging technique allows pore-size tuning to enhance the selectivity of specific gas pairs.U nlike conventional anti-aging efforts we have explored, hyperaging purposely accelerates the selective aging of CMS membranes,thereby creating CMS hollow fiber membranes with much higher performance for H 2 separation.…”

“…[21] TheC MS pore morphology includes micropores (7)(8)(9)(10)(11)(12)(13)(14)(15)(16)(17)(18)(19)(20) between the stacks of sheets and smaller ultramicropores (< 7 )within the individual sheets (Supporting Information, Figure S1). [21] TheC MS pore morphology includes micropores (7)(8)(9)(10)(11)(12)(13)(14)(15)(16)(17)(18)(19)(20) between the stacks of sheets and smaller ultramicropores (< 7 )within the individual sheets (Supporting Information, Figure S1).…”

“…CMS membranes are formed by pyrolyzing polymer precursor membranes under controlled conditions to create materials with so-called turbostratic carbon structures.S uch materials comprise disordered, sp 2 -hybridized carbon sheets with bimodal pores formed from packing imperfections. [21] TheC MS pore morphology includes micropores (7)(8)(9)(10)(11)(12)(13)(14)(15)(16)(17)(18)(19)(20) between the stacks of sheets and smaller ultramicropores (< 7 )within the individual sheets (Supporting Information, Figure S1). Theu nique combination of micropores and ultramicropores provides both high flux and high separation efficiency via am olecular sieving function with high permeabilities.…”

Exploiting pyrolysis protocols on BTDA‐TDI/MDI (P84) polyimide/nanocrystalline cellulose carbon membrane for gas separations

“…This is due to the well‐defined pore size distribution that contributes to the molecular sieving mechanism during the gas transport. Although significant research works have been reported as carbon membranes' invention, the need to improve the gas separation properties of these membranes remains tremendously important if they are to become viable for real applications . However, pyrolysis conditions are the main factors that affect both the membrane structure and gas permeation properties.…”

“…Although significant research works have been reported as carbon membranes' invention, the need to improve the gas separation properties of these membranes remains tremendously important if they are to become viable for real applications. 13 However, pyrolysis conditions are the main factors that affect both the membrane structure and gas permeation properties. To this end, as far as the carbon membranes are concerned, the study on pyrolysis atmosphere and thermal soak time is one of the milestones for researchers who are working in this field.…”