A new oriented mixed-matrix metal-organic framework membrane can effectively remove hydrogen sulfide and carbon dioxide from natural gas in an energy-efficient manner. Image: 2022 KAUST.The selective removal of detrimental gases such as hydrogen sulfide (H2S) and carbon dioxide (CO2) from natural gas (CH4) could become simpler and more effective with a new class of oriented mixed-matrix metal-organic framework (MMMOF) membrane. Developed by researchers at the King Abdullah University of Science & Technology (KAUST) in Saudi Arabia and reported in a paper in Science, this novel class of membrane may allow better use of natural gas.
Compared with traditional separation technologies (e.g., cryogenic distillation and adsorptive separation), membrane technology is more energy-efficient and simpler to operate. Mixed-matrix membranes (MMMs), formed by embedding an adsorbent material in a continuous polymer matrix, offer an appealing combination of the selectivity of adsorbents and the easy processing of polymers.
“Our achievement, in-plane alignment of MOF nanosheets inside the polymer matrix and successful translation of adsorbent distinct separation properties into a processable matrix, is revolutionary,” says Shuvo Datta from KAUST.
MOFs are hybrid organic-inorganic materials that contain metal ions or clusters held in place by organic molecules known as linkers. By varying these components, researchers can create a suitable pore aperture that permits selective sorption and/or diffusion of one gas molecule over another, based on their size.
“These crystalline materials are difficult to process into a defect-free oriented continuous membrane, but we developed a simple solution casting method to process them,” says Mohamed Eddaoudi from KAUST.
Conventional MMMs often undergo nanoparticle-polymer interface incompatibility. This can cause the channels and pores of the adsorbents to become randomly oriented, hampering the gas separation. To avoid those limitations, the MMMOF membranes were conceived and constructed based on three interlocked criteria. These were: using a fluorinated MOF known as KAUST-8 as a molecular sieve adsorbent that selectively enhances H2S and CO2 diffusion while excluding CH4; tailoring MOF crystal morphology into nanosheets with maximally exposed 1D channels and promoting a nanosheet-polymer interaction; and ensuring in-plane alignment of nanosheets in the polymer matrix and attainment of the uniformly oriented MMMOF membrane.
The resulting membrane demonstrated far better H2S and CO2 separation from natural gas under practical working conditions (e.g., high pressure, high temperature, prolonged time of 30 days, etc), compared with conventional MMMs.
“In fact, this centimeter-scale flexible oriented membrane can be regarded as a single piece of a flexible crystal in which thousands of MOF nanosheets are uniformly aligned in a predefined crystallographic direction and the gaps between aligned nanosheets are filled with polymer,” says Datta. “It's the first of its kind.”
“I have no doubt that this discovery will inspire scientists in academia and industry to explore various practical membranes to address numerous industrial energy-intensive separations,” says Eddaoudi.
The team now wants to scale up this procedure to demonstrate its commercial potential. They will also look to apply it to other important industrial gas separation processes.
This story is adapted from material from KAUST, with editorial changes made by Materials Today. The views expressed in this article do not necessarily represent those of Elsevier. Link to original source.