Impeded physical aging in PIM-1 membranes containing graphene-like fillers

Abstract

Physical aging of polymer of intrinsic microporosity PIM-1 is one of the major obstacles for its application as a commercial membrane material for gas separation. In this work, physical aging of PIM-1 and matrices of this same polymer containing graphene-like materials were studied.Graphene-like fillers resulted from the functionalization of graphene oxide (GO) with two alkyl chains of different lengths, using octylamine (OA) and octadecylamine (ODA), and further chemical reduction. Extents of membrane aging were evaluated through changes in gas permeability over time;the separation of gas mixtures comprising carbon dioxide and methane, which are of great interest for industrial applications such as the production of biogas or the purification of natural gas, was carried out. 50:50 vol. % CO 2 /CH 4 mixtures were used as feed and separation performance analysed for fresh membranes and at intervals of approximately a month up to 155 days. At the end of this testing period, aged PIM-1 membranes showed a CO 2 permeability of (2.0± 0.7) x 10 3 Barrer, which corresponds to a CO 2 permeability reduction of 68 % from the value obtained right after their fabrication. The addition of alkyl-functionalized GO is shown to be an efficient strategy to retard the physical aging of PIM-1 membranes; filler loadings as low as 0.05 wt.% of reduced octylfunctionalized GO showed a CO 2 permeability of (3.5 ± 0.6) x 10 3 Barrer after 5 months, which is almost three quarters higher than that of pure PIM-1 membrane aged for the same time period and represents a reduction of just 39% from its initial value. Moreover, the addition of graphene-like materials to PIM-1 does not affect its mechanical properties. Highlights Physical aging of mixed matrix membranes (MMMs) composed of PIM-1 and graphene-like materials was investigated. A binary CO 2 /CH 4 (50:50 vol.%) gas mixtures was used. Physical aging was reduced by the incorporation of reduced alkyl-functionalized graphene oxide nanosheets into PIM-1 matrices. Low filler loadings led to higher reduction in physical aging.

Correlating Gas Permeability and Young’s Modulus during the Physical Aging of Polymers of Intrinsic Microporosity Using Atomic Force Microscopy

“…Repeated measurements at different points of the sample result in a narrow distribution ofYoung's modulus around the average value. The value of the fresh sample (dark blue) is in good agreement with the data available in the literature from different techniques (1 -1.7 GPa)32,35,52,53…”

Intrinsically Microporous Polymer Nanosheets for High‐Performance Gas Separation Membranes

“…a) CO 2 permeability (), CH 4 permeability (), and CO 2 /CH 4 selectivity () for methanol‐treated membranes with various loadings of network‐PIM‐1 in PIM‐1; measurements were carried out with a mixed gas CO 2 /CH 4 (1:1, v/v) feed at a temperature of 25 °C and transmembrane pressure of 2 bar; each data point is an average for three membrane samples and the standard deviation is indicated by the error bars. b) Double logarithmic plot of CO 2 /CH 4 selectivity against CO 2 permeability showing 1991 (), 2008 (), and 2019 () upper bounds, with data from this work for PIM‐1 () and MMMs with 0.5 wt% () and 10 wt% () network‐PIM‐1 3 days after methanol treatment, and for PIM‐1 () and the MMM with 0.5 wt% network‐PIM‐1 () after 7 months aging; also shown are data from the literature for MMMs of PIM‐1 with 24.2 wt% ZIF‐8 (▸), 0.5 wt% f‐MWCNT (⬤), 2 wt% SNW‐1 (◂), and 0.126 wt% rGO‐OA (▾) …”

“…It is significant that a change in polymer topology from linear to network can have such a pronounced effect, and this is being explored further in ongoing research. For comparison, representative data from the literature are also shown for MMMs of PIM‐1 with the zeolitic imidazolate framework ZIF‐8, functionalized multi‐walled carbon nanotubes (f‐MWCNT), the covalent organic framework SNW‐1, and octyl‐functionalized reduced graphene oxide (rGO‐OA) …”

Fine-tuning the molecular structure of binaphthalene polyimides for gas separations

“…PIM-1 achieved a remarkable combination of a CO2 permeability of 2300 barrer with a CO2/CH4 selectivity of 18. [16] Since then, many PIM derivatives have been developed such as KAUST-PI-1 which introduced bulky iptycenes [21,22], TPE-PIM which used a comonomer with a slightly less rigid structure, leading to decreased permeability and increased selectivity [23], a mixed matrix PIM to decrease physical aging [24], PIM-SBF-1 which used a spirobifluorene unit with even higher rigidity than found in PIM-1, resulting in similar permeability with greater selectivity [25][26][27] and PIM-PI-1 which combined PIMs with polyimides [28]. Introducing rigid and contorted structures into polyimides is a powerful idea as it broadens the scope of the 'PIM concept' to the already established and extremely varied polyimide chemistry.…”