Abstract
The gas separation properties of 6FDA-DAM mixed matrix membranes (MMMs) with three types of zirconium-based metal organic framework nanoparticles (MOF NPs, ca. 40 nm) have been investigated up to 20 bar. Both NPs preparation and MMMs development were presented in an earlier publication that reported outstanding CO2/CH4 separation performances (50:50 vol% CO2/CH4 feed at 2 bar pressure difference, 35 °C) and this subsequent study is to demonstrate its usefulness to the natural gas separation application. In the current work, CO2/CH4 separation has been investigated at high pressure (2–20 bar feed pressure) with different CO2 content in the feed (10–50 vol%) in the temperature range 35–55 °C. Moreover, the plasticization, competitive sorption effects, and separation of the acid gas hydrogen sulfide (H2S) have been investigated in a ternary feed mixture of CO2:H2S:CH4 (vol% ratio of 30:5:65) at 20 bar and 35 °C. The incorporation of the Zr-MOFs in 6FDA-DAM enhances both CO2 permeability and CO2/CH4 selectivity of this polymer. These MMMs exhibit high stability under separation conditions relevant to an actual natural gas sweetening process. The presence of H2S does not induce plasticization but increases the total acid gas permeability, acid gas/CH4 selectivity and only causes reversible competitive sorption. The overall study suggests a large potential for 6FDA-DAM Zr-MOF MMMs to be applied in natural gas sweetening, with good performance and stability under the relevant process conditions.
Highlights
The acid gas content in raw natural gas varies to the hydrocarbon geo-origins [1,2] and is commonly in the range of 25–55 mol.% for CO2 and below 2 mol.% for H2S (≥5 mol.% in several regions) [3,4]
We present the gas separation performance of the neat 6FDA-DAM membranes and their derived Zr-Metal organic frameworks (MOFs) matrix membranes (MMMs) as a function of feed pressure between 2 and 20 bar
In the previous publication [34], we found very promising performance indicators for several 6FDA-DAM MMMs with Zr-MOFs when tested at low pressure (2 bar), with the best performance observed for membranes that contain 14–16 wt% Zr-MOF
Summary
The acid gas content (carbon dioxide, CO2; hydrogen sulfide, H2S) in raw natural gas varies to the hydrocarbon geo-origins [1,2] and is commonly in the range of 25–55 mol.% for CO2 and below 2 mol.% for H2S (≥5 mol.% in several regions) [3,4]. Due to challenges such as plasticization especially at high-pressure operation and degradation, membrane processes only represents < 5% of the natural gas sweetening market [9,10]. Both plasticization and degradation effects can be suppressed by polymer blending and cross-linking [11,12,13,14,15], but a more promising method is the combination of polymeric and inorganic materials as mixed matrix membranes (MMMs) [16,17,18,19,20]. Yong et al [16] reported the effectiveness of 2 wt% POSS (polyhedral oligomeric silsesquioxane) nanoparticles into the highly permeable PIM-1 to suppress the neat
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