Membrane technology for gas separation

Scientists at the Instituto de Tecnología Química have made a big step towards the gas separation through membrane technology. It enables the adaptation of the membranes to separate different gases and can have applications in several industrial sectors.

Image by microscopy (FESEM) of the nano-sheets, which are wider (Several micrometers) than thicker (less than 20 nanometers)Scientists at the Instituto de Tecnología Química, a joint center of the CSIC and the Universitat Politècnica de Valencia, have developed a membrane technology to separate gases, which can have many industrial applications.

The membranes are composed of highly porous nanosheets, which are made of metalorganic compounds (also called Metal-Organic-Framework or MOF), and a polymeric matrix onto which the nanosheets have been fixed. The polymer serves as a support of the nanosheets and makes it possible to have a freestanding membrane. 

Avelino Corma, CSIC scientists at the Instituto de Tecnología Química, and main investigator of the project, says: “The tomographic tests we have done by ion beam scanning electron microscopy have shown that the resulting material has excellent properties for gas separation. Also, as it has an unusual and helpful increase in selectivity as pressure increases”.

The researchers have successfully experimented with these membranes for the separation of CO2 from methane. The membranes can be used also for separating other industrially relevant mixtures of gas, such as the mixtures of nitrogen and oxygen or propane and propane.

Custom-made molecular sieves

Francesc Llabrés, scientists at the ITQ, explains that the selectivity and permeability of the membrane can be adapted  modifying the MOF material. “Changing the size of the pores and the chemical composition the nano-sheets can be adapted in order to filter different gases, even in the case of gas mixtures with more than two components. Possibly, they could also be adapted for filtering liquid elements, although we are still working on it”. They are, therefore, molecular sieves that can be custom-made for the application.

The main advantage of this development is that it facilitates applications which were until now very difficult to tackle. For example, nowadays zeolites exist that can separate gases, but they hardly can be added to a polymeric membrane because zeolites don’t adhere well to a polymeric surface. “They badly stick on the polymer and  leave ‘gaps’ between them; through these gaps the gas which has to be filtered can freely ‘escape’”, clarifies Llabrés.

On the contrary, the MOF nanosheets adhere very well to the polymer, without gaps between them, resulting in a better sieves. They open new possibilities in the field of plastic functional barriers, like the ones for food preservation.

Artist's view of the membranes. The MOF nano-sheets (light green) are placed onto the membrane surface. A molecule of CO2 (red and grey) goes through one of these MOF nanosheets but a methane molecule (white and grey) cannot go trough, therefore it is retained on the surface of the membrane.

Besides, they can be used for catalytic processes with membranes. Compared to conventional technologies for gas separation, like cryogenic distillation –which requires liquefaction of the gases, which means an additional and important energy expense-, membrane technology offers an energy saving. It offers also less environmental impact as no solvent is required, whereas the use of amines derivative of ammoniac are used in conventional amine absorption technologies. Also, this new technology enables the construction of smaller equipments for gas separation.

In this study, led by the CSIC, have participated scientists of the Kavli Institute of Nanoscience and the Catalysis Engineering group, both at the Delft University of Technology (The Netherlands), and scientists at the Max Planck Institut für Kohlenforschung (Germany).