Adsorption processes in highly porous materials play a key role in numerous technical procedures nowadays. These include gas storage and separation, thermally driven heat pumps and chillers, heterogeneous catalysis and sensors. These procedures tend to use activated carbon, silica gels and zeolites.
Research on sorption materials is currently focused on the new material class of metal organic frameworks (MOFs). These crystalline compounds are based on a unique modular chemical system, creating a higher chemical variability than ever before, sometimes with a huge inner surface (SBET > 4000 m²/g) and an accessible pore volume (> 1 cm3/g).
These high-efficiency adsorbents increase heat and material transport requirements, particularly in cyclic applications such as adsorption heat pumps and chillers. The refrigerant (e.g. water or alcohol) must have good access to the surfaces and therefore the adsorption centers. In addition, a high thermal coupling is required in order to be able to quickly dissipate the resulting heat.
Experts at Fraunhofer ISE have managed to ideally fulfill these requirements by synthesizing compounds from the class of MOFs and developing two complementary coating processes, for which a patent has already been taken out. Heat-transfer structures coated in a sorption process with MOFs or classic sorbents are the perfect choice for numerous applications.