High-performance carbon molecular sieve membranes for ethylene/ethane separation derived from an intrinsically microporous polyimide

Abstract

High-performance carbon molecular sieve membranes for ethylene/ethane separation derived from an intrinsically microporous polyimide, Journal of Membrane Science, http://dx.doi.org/10.1016/j.memsci. 2015.11.013 This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting galley proof before it is published in its final citable form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain. AbstractAn intrinsically microporous polymer with hydroxyl functionalities, PIM-6FDA-OH, was used as a precursor for various types of carbon molecular sieve (CMS) membranes for ethylene/ethane separation. The pristine polyimide films were heated under controlled N 2 atmosphere at different stages from 500 to 800 °C. All CMS samples carbonized above 600 °C surpassed the polymeric ethylene/ethane upper bound. Pure-gas selectivity reached 17.5 for the CMS carbonized at 800 °C with an ethylene permeability of about 10 Barrer at 2 bar and 35 °C, becoming the most selective CMS for ethylene/ethane separation reported to date. As expected, gravimetric sorption experiments showed that all CMS membranes had ethylene/ethane solubility selectivities close to 2 one. The permselectivity increased with increasing pyrolysis temperature due to densification of the micropores in the CMS membranes, leading to enhanced diffusivity selectivity. Mixed-gas tests with a binary 50:50 v/v ethylene/ethane feed showed a decrease in selectivity from 14 to 8.3 as the total feed pressure was increased from 4 to 20 bar. The selectivity drop under mixed-gas conditions was attributed to non-ideal effects: (i) Competitive sorption that reduced the permeability of ethylene and (ii) dilation of the CMS that resulted in an increase in the ethane permeability.

Carbon molecular sieve membrane from a microporous spirobisindane-based polyimide precursor with enhanced ethylene/ethane mixed-gas selectivity

“…Similar to PIM-6FDA-OH, 35 increasing the pyrolysis temperature resulted in less permeable but highly C 2 H 4 /C 2 H 6 selective CMS membranes made from PIM-6FDA, as shown in Fig. 4.…”

“…[34][35][36][37][38] The CMS membrane formed at 800 C from the prototype ladder polymer of intrinsic microporosity, PIM-1, demonstrated signicant densication upon formation of its CMS structure with a dominant crosslinking/sintering effect, resulting in a $1000-fold reduction in the ethylene permeability compared to the pristine PIM-1 from 1640 to 1.3 Barrer. The PIM-1-derived CMS membrane had a pure-gas C 2 H 4 /C 2 H 4 selectivity of 13, similar to that reported for a CMS made from low-freevolume Matrimid® polyimide at 675 C. 16 In another study, a CMS membrane derived from a hydroxyl-functionalized PIM polyimide at 800 C, PIM-6FDA-OH, showed an ideal pure-gas C 2 H 4 /C 2 H 6 selectivity of $18 measured at 2 bar.…”

“…The PIM-1-derived CMS membrane had a pure-gas C 2 H 4 /C 2 H 4 selectivity of 13, similar to that reported for a CMS made from low-freevolume Matrimid® polyimide at 675 C. 16 In another study, a CMS membrane derived from a hydroxyl-functionalized PIM polyimide at 800 C, PIM-6FDA-OH, showed an ideal pure-gas C 2 H 4 /C 2 H 6 selectivity of $18 measured at 2 bar. 35 When tested under mixed-gas conditions with an equimolar feed at a pressure of 20 bar and 35 C, the C 2 H 4 /C 2 H 6 selectivity dropped to 8.3 with a C 2 H 4 permeability of 9.6 Barrer. 35 The CMS precursor polyimide, PIM-6FDA-OH, contained hydroxyl groups in ortho position to the imide linkages.…”

“…35 When tested under mixed-gas conditions with an equimolar feed at a pressure of 20 bar and 35 C, the C 2 H 4 /C 2 H 6 selectivity dropped to 8.3 with a C 2 H 4 permeability of 9.6 Barrer. 35 The CMS precursor polyimide, PIM-6FDA-OH, contained hydroxyl groups in ortho position to the imide linkages. Consequently, its pyrolysis process proceeded in three major stages: (i) transformation of the o-OH-functionalized polyimide to the corresponding polybenzoxazole (PBO) by thermal rearrangement at $400 C (Fig.…”

“…1d), was used to ne-tune the morphology of high-performance CMS membranes for C 2 H 4 /C 2 H 6 separation. Pure-and mixed-gas permeation tests were conducted with an equimolar feed up to 20 bar and 35 C for the 800 C CMS membrane derived from PIM-6FDA to determine its potential for industrial ethylene/ethane separation.…”