MOF4AIR main concepts
What are the main technologies used in the MOF4AIR project?
Let’s start with the wide perspective of the project! In MOF4AIR we use MOFs optimised for carbon adsorption to capture CO2 in enhanced carbon capture processes. The captured CO2 can then be valorised through carbon utilisation or stored underground. The figure below shows this strategy.
MOFs optimised for CO2 capture
What are MOFs ? Why are they interesting for CO2 capture?
What are MOFS? MOFs are hybrid porous solids representing a relatively new class of crystallized porous materials. They combine inorganic and organic moieties to build 3D networks exclusively through strong bonds.
The inorganic parts (usually labeled as ‘bricks’) are the ‘nodes’ of the networks which can be made of simple metal ion or assembly of cations such as oxo-clusters, or oxo-chains. The organic ligands represent the link between the ‘nodes’ by means of their peripherical functional groups bearing anionic oxygens (e.g., polycarboxylates, polyphosphonates) or nitrogens (e.g., imidazolates, polypyrazolates, polytetrazolates) donors. The ‘unlimited’ combination between organic and inorganic moieties offers huge number of possibilities in terms of chemical nature as well as pore geometry (e.g., channels, cages) and dimension (e.g., micropores, mesoporous).
Why are MOFs interesting for CO2 capture? Due to their high tunability, the structures of MOFs thus can be adjusted to capture preferably CO2 rather than other components in flue exhaust gases (e.g. N2). Moreover, the thermal and chemical stability of many MOFs has made them even more serious candidates for CO2 capture.
The figure below illustrates the different components of MOFs and their different types
Enhanced carbon capture processes by adsorption
The MOFs presented above are enhanced integrated in carbon adsorption processes
Two CO2 adsorption processes are investigated in the MOF4AIR project: Vacuum Pressure Swing Adsorption (VPSA) and Moving Bed Temperature Swing Adsorption (MBTSA)
PSA: Pressure Swing Adsorption (PSA) is a well-established and commercial gas separation technique, based on physical binding of gas molecules to a solid adsorbent material. Its process uses the effect of alternating high and low pressure/partial pressure to perform either adsorption (binding) or desorption (release).
In MOF4AIR, the desorption is achieved by the aid of vacuum, and so the process is called Vacuum Pressure Swing Adsorption (VPSA). With its low-pressure adsorption step (1-1.25 bars), VPSA avoids the high energy cosumption for compression of flue gas. Moreover, the working capacity of the adsorbent is higher in this case, which ensures better performance of the adsorption process. Check here what the VPSA process looks like.
MBTSA: As its PSA counterpart, TSA is a well-known separation technique used to separate gases with solid absorbents. In the process MBTSA, the flue gas is stripped counter-currently in the “adsorption” section, in contact with a descending solid adsorbent, being shaped spheres with diameters of 0.3-0.7mm.
The great advantage of this technique is that moving adsorbent enables a fast heat transfer and increases the retention time of the solid into the column; hence ensuring that a CO2 capture: equilibrium capacity superior at 90% is achieved. Once the spheres cannot adsorb more CO2 capture, the heat transfer also ensures their regeneration. Check here what the MBTSA process looks like.