INMA researchers design a new membrane capable of separating pollutant gases
The selective removal of harmful gases such as hydrogen sulphide (H2S) and carbon dioxide (CO2) from natural gas (CH4) could become a simple and efficient process using the membrane developed by a multidisciplinary team of scientists from KAUST, CSIC, ShanghaiTech University and the University of Montpellier, in which Álvaro Mayoral, CSIC researcher at the Aragon Nanoscience and Materials Institute, INMA, a joint institute of CSIC and the University of Zaragoza and reference scientist of the LMA, has worked. The research has been published in the prestigious scientific journal Science.
As Álvaro Mayoral comments: “the membrane they have developed is a mixed membrane composed of a polymer and a matrix of a hybrid organometallic material (Mixed Matrix Metal Organic Frameworks, MMMOF). The advantages of the polymeric membrane technology over traditional separation techniques are the efficient use of energy, which leads to lower cost, and simpler operation.
The work is based on the atomic-level understanding of the membrane “filler”; in this case, the high performance of this material is based on the alignment of the nanolayers of organic-inorganic hybrid solids (MOFs) within the polymer and the successful translation of the adsorbent’s separation properties into a processable compound.
Metal Organic Frameworks (MOFs) contain metal centres linked by organic groups to form a three-dimensional porous network. By modifying the pore size, the appropriate material can be obtained that allows the separation of different gases depending on the pore size.
Conventional mixed matrix membranes (MMMs) have randomly oriented channels or pores, making gas separation difficult. To avoid these limitations, the researchers developed MMMOF membranes based on three criteria: (i) a fluorinated MOF (KAUST -8), as a molecular sieve adsorbent that selectively enhances the diffusion of H2S and CO2 while excluding CH4; (ii) tailoring the MOF crystal morphology into nanolayers with a maximally exposed 1D channel, which promotes the interaction between the nanolayer and the polymer; and (iii) in-plane alignment of the nanolayers in the polymer matrix obtaining a uniformly oriented MMMOF membrane.
Compared to conventional MMMs, the MMMOF membrane demonstrates much better separation of H2S and CO2 from natural gas under practical working conditions (e.g. high pressure, high temperature, extended time of 30 days, etc.).
In fact, this centimetre-scale flexible oriented membrane can be considered as a single flexible crystal in which thousands of MOF nanolayers, studied at the atomic scale, are uniformly aligned in a predefined crystallographic direction where the spaces between them are occupied by the polymer.
Reference:
Datta, S. J., Mayoral, A., Bettahalli, N. M. S., Bhatt, P. M., Karunakaran, M., Carja, I. D., Fan, D., Mileo, P. G. M., Semino, R., Maurin, G., Terasaki, O. & Eddaoudi, M. “Rational design of mixed-matrix metal-organic framework membranes for molecular separations”. Science 376, XXX, (2022). DOI: 10.1126/science.abe0192.
