Abstract
AbstractIn this work, the influence of the zeolitic imidazolate framework 78 (ZIF‑78) morphology, with 1D pores, on the mixed matrix membrane (MMM) CO2/N2 mixed gas separation performance is investigated as well as the influence of the feed composition and pressure. Low aspect ratio and a high aspect ratio ZIF‑78 particles are synthesized and incorporated in Matrimid with 10 and 20 wt% additive content. High pressure CO2 and N2 sorption measurements show that both the low and high aspect ratio ZIF‑78 metal–organic frameworks (MOFs) exhibit similar sorption behavior. The incorporation of ZIF‑78 into Matrimid results in improved CO2 permeabilities up to 39%, without compromising the selectivity, relative to native Matrimid membranes. Both at low and high CO2 partial pressures, the MMMs containing the different ZIF‑78 morphologies show equal CO2 permeabilities, indicating that the ZIF‑78 morphology and consequently the aspect ratio are insignificant for these particular MMMs, contradicting previous observations in literature. Thus, depending on the MOF/polymer system, the MOF morphology and aspect ratio can be considered as a design aspect. Finally, a clear influence of feed composition and pressure on the MMM solubility coefficient and diffusivity is observed, emphasizing the importance of the mixed gas composition and measurement conditions.
Highlights
In this work, the influence of the zeolitic imidazolate framework 78 (ZIF‐78) mor- organic–inorganic networks exhibit high phology, with 1D pores, on the mixed matrix membrane (MMM) CO2/N2 mixed gas separation performance is investigated as well as the influence of the feed composition and pressure
The X-ray diffraction (XRD) patterns of zeolitic imidazolate frameworks (ZIFs)-78 low aspect ratio (LA) and high aspect ratio (HA) are shown in Figure S1 (Supporting Information) and agree for the majority with literature.[14,19,20,38]
The CO2 permeability increases with increasing ZIF load for both the LA and HA MMMs at all operating conditions, relative to the Matrimid CO2 permeability (Figure 6A,B), which exhibits CO2 permeabilities that lie within the range of reported literature values.[48,51,52,53]
Summary
Before analyzing the MMMs with the two different ZIF-78 morphologies, an analysis of the low aspect ratio (LA) and high aspect ratio (HA) ZIF-78 morphologies is performed to identify their structure and sorption behavior. The absence or presence of certain diffraction peaks or a variation in peak intensity in ZIF-78 as well as other ZIF types is more often observed and can occur due to, e.g., a difference in thermal treatment, used solvent or presence of guest molecules, e.g., an organic base.[19,21,39,40] Both ZIF-78 LA and HA exhibit high thermal stability (Figure S2, Supporting Information). Similar sorption behavior of ZIF-78 with varying aspect ratios was observed elsewhere in literature.[19] Contrary to the BET surface analysis, no significant difference between ZIF-78 LA and HA is observed for high pressure N2 and CO2 sorption
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