Sizing up the mesh to keep contaminants out

A new membrane can efficiently separate different gases, an essential process in the chemical and energy industries. Membranes are an attractive alternative to traditional energy-intensive approaches if they can offer comparable performance. 

The new membrane incorporates metal–organic frameworks (MOFs) into existing polymer membranes. MOFs can provide highly selective filtration but are challenging to work with, while polymers are easier to handle but are less efficient filters. 

“The combination of MOFs and polymeric membranes into a single system, namely mixed matrix membranes, offers the opportunity to create disruptive membranes with distinctive properties,” says Mohamed Eddaoudi of the King Abdullah University of Science and Technology, Saudi Arabia, who led the study. 

Together with their collaborators at the Georgia Institute of Technology, USA, his team developed a method to incorporate the right MOF into the right polymer, creating an exceptionally effective membrane for separation.

The membrane’s remarkable performance is largely due to the structure of the MOF crystals, which limits access to the pores. The metal clusters are positioned in a cube, with a cluster at each of the cube’s corners and another on each face, a pattern known as face-centred cubic (fcu) MOF.  Linker molecules connect the clusters, forming triangular openings which act as a sieve, the size of which depends on the linker molecule. 

“The triangular windows are the sole entrance to the pore system and thus their size regulates which gases pass through,” explains Eddaoudi.

The mixed matrix membrane outperformed existing membranes, efficiently removing carbon dioxide and hydrogen sulfide from natural gas and even distinguishing the linear and branched isomers of butane. The team tested the membrane not only under lab conditions but also in conditions more relevant to industrial use.

“There is no doubt in my mind that this approach can be expanded to various MOFs and polymers with suitable characteristics for various energy-intensive separations,” says Eddaoudi.

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