(697c) Natural Gas Sweetening By MOF-Polymer Hybrid Membranes with Tailored Formulation

Natural
Gas Sweetening by MOF-Polymer Hybrid Membranes with Tailored Formulation

Yang
Liu¹, Zhijie Chen², Gongping Liu¹, Youssef
Belmabkhout², Mohamed Eddaoudi^2,*,
William J. Koros^1,*

¹ School of Chemical &
Biomolecular Engineering, Georgia Institute of Technology, 311 Ferst Dr. NW, Atlanta, GA 30332, USA

² Functional Materials Design,
Discovery and Development research group (FMD³), Advanced Membranes
& Porous Materials Center, Division of Physical Sciences and Engineering,
King Abdullah University of Science and Technology, Thuwal
23955-6900, KSA

Worldwide energy consumption has grown
steadily with continuing increases in world population and economic growth of
developing countries. Natural gas is particularly attractive to meet these
energy needs, and consumption of natural gas will continue to rise over the
next several decades. Although CH₄ is the main component of natural
gas, acidic CO₂ and H₂S usually must be removed before
delivery to the pipeline to avoid corrosion of processing and transporting
equipment. Pipeline specifications for H₂S (< 4 ppm in U.S.) are much
stricter than for CO₂ (< 2% in U.S.) because of the additional extremely
toxic nature of H₂S.  Currently, roughly 30% of proven natural gas
resources in the U.S. require treatment due to excessive CO₂ and H₂S
concentration.  In addition, 40% of
worldwide natural gas resources are estimated to be contaminated with high
concentration (up to 20 mol.%) of H₂S. Fortunately, membrane processes
offer potential compact, energy-saving approaches to address such challenges,
as compared to traditional thermally driven gas amine absorption processes. Unfortunately,
organic polymer membranes face a trade-off limit between permeability and
selectivity, while inorganic molecular sieving membranes face a challenge of
reproducibility and economical scale-up. A practical approach to overcome these
drawbacks is to create hybrid mixed matrix materials (MMM) by dispersing a
molecular-sieve phase (filler) in a continuous polymer (matrix). Such hybrids combine
the advantages of both inorganic membranes, e.g. high intrinsic permeability
and selectivity, and organic polymer membranes, e.g. robust processing and
mechanical properties. Here, we report promising features of MMMs based on
metal organic frameworks (MOFs) with tailored internal electrostatic
environments for simultaneous removal of H₂S and CO₂ from
natural gas. Using M-fcu-MOFs
and 6FDA-based polyimides, MOF-polyimide hybrid membranes show extraordinary
performance on H₂S/CH₄ separation under various H₂S
concentrations, well above the trade-off
limit of polymer membranes. Moreover, the membranes maintain high CO₂/CH₄
separation efficiencies. Among the M-fcu-MOFs studied, Zr-fum-fcu-MOF is
considered as the best performing filler with the highest H₂S and CO₂
removal efficiencies. Our interpretation of both sorption and diffusion
behaviors for these hybrids will outline key factors to optimize membrane
performance for such advanced membranes for H₂S and CO₂ removal
for natural gas sweetening.