(784f) ZIF/Polyimide Asymmetric Mixed-Matrix Hollow Fiber Membranes With Significantly Enhanced Hydrocarbon Separation Performance

ZIF/Polyimide
Asymmetric Mixed-Matrix Hollow Fiber Membranes with Significantly Enhanced Hydrocarbon
Separation Performance

Chen Zhang, William J. Koros

School of Chemical and Biomolecular
Engineering, Georgia Institute of Technology

Asymmetric
hollow fibers are the most industrially practical geometry for gas separation
membranes in terms of productivity and membrane packing efficiency. However, studies
on polymer-based mixed-matrix membranes in the past two decades have been mostly
limited to the geometry of films with only a few extended to the geometry of
asymmetric hollow fibers due to many technical challenges. For those few examples^1-3 in which selectivity enhancements were
observed in mixed-matrix hollow fiber membranes, defect-sealing post-treatments
(e.g. PDMS coating) were required in most cases to realize the enhanced selectivity.

This study
reports successful formation of high performance asymmetric mixed-matrix hollow
fiber membranes using a zeolitic imidazolate framework (ZIF) and a high T_g
(glass transition temperature) polyimide, in which a significant propylene/propane
selectivity enhancement was realized without any defect-sealing post-treatments.
Spinning dope compositions and spinning parameters were optimized to form
mixed-matrix hollow fiber membranes with desirable properties using the dry-jet/wet-quench
technique. Propylene/propane gas mixture permeation showed that adding ZIF molecular
sieve particles (~17 wt%) in the hollow fiber sheath layer significantly
enhanced propylene/propane selectivity over pure polyimide dense film membrane
by over 70% while maintaining attractive propylene permeance. The intrinsic
compatibility of hydrophobic ZIF particles with the polyimide matrix as well as
the optimized spinning dope compositions were keys for success of this study.

To our best
knowledge, this is the first study in the open literature that reports successful
spinning of asymmetric mixed-matrix hollow fiber membranes showing remarkably
enhanced gas separation selectivity without any defect-sealing post-treatments.
The current study, therefore, has significant impacts on the development of polymer-based
gas separation membranes. An application of ZIF/polyimide mixed-matrix hollow
fiber membrane described in this study is to pre-purify the feed stream of C₃
splitters in olefin plants to reduce the energy cost for producing
polymer-grade propylene.

References:

(1) Husain, S.;
Koros, W. J.: Mixed matrix hollow fiber membranes made with modified HSSZ-13
zeolite in polyetherimide polymer matrix for gas separation. Journal of
Membrane Science 2007, 288, 195-207.

(2) Dai, Y.; Johnson, J. R.;
Karvan, O.; Sholl, D. S.; Koros, W. J.: Ultem®/ZIF-8 mixed matrix hollow fiber
membranes for CO2/N2 separations. J. Membr. Sci. 2012, 401¨C402, 76-82.

(3)
Ekiner, O. M.; Kulkarni, S. S.: Process for Making Hollow Fiber Mixed Matrix
Membranes. US Patent 6663805, 2003.