(453a) Adsorption-Based Heating and Cooling – Metal-Organic Frameworks over Zeolites?

Increased tangibility of (anthropogenic) climate change and fossil fuel scarcity demand a transition to sustainable energy sources in the near future. The heating and cooling of residential areas requires roughly a third of the worldâ??s primary energy consumption. Thus significantly reducing the energy expenditures for heating and cooling will have a large impact on total energy consumption. Preferably one would like to use sustainable solar or low-grade (< 100 ^oC) waste energy for this purpose. With adsorption heat pumps and chillers (AHP/ACs) this is possible. These devices us the reversible adsorption of a working fluid onto a porous adsorbent to generate heating or cooling and can be operated with sustainable low-grade energy. Furthermore, with water as preferred working fluid, these devices are environmentally benign.

Market penetration of AHP/ACs has been only minor up to now. This because AHP/ACs are currently bulkier and less energy-efficient than their electrically operated vapor-compression counterparts. The moderate performance of AHP/ACs can be largely attributed to poor to moderate adsorptive properties of current state-of-the-art materials (mainly zeolites). To improve performance and thus commercialization of AHP/ACs, we have embarked on a quest to find more suitable adsorbent materials. Especially a relatively novel set of materials, the Metal-Organic Frameworks (MOFs), holds great promises for AHP/ACs. MOFs consist of inorganic clusters linked together by organic ligands to create porous crystalline materials. More than 20.000 MOFs are known currently, spanning a large variety of topologies and material properties. Not surprisingly thus, MOFs have received attention for a plethora of applications.

In this work we critically explore the promise that Metal-Organic Frameworks (MOFs) hold for adsorption heating and cooling by means of a critical comparison to commercially available materials, with special reference to zeolites, using either water [1, 2] or alcohols [1, 3] as working fluid. Based on both experimental and theoretical efforts we conclude that:

(i) MOFs that are sufficiently stable towards water [1, 2] exist.

(ii) Of these subset, multiple MOFs show the desired adsorption behaviour with either water or alcohols as working fluid [1, 2, 3].

(iii) These working pairs (MOF-working fluid) show enhanced energy efficiency and working capacity compared to benchmark materials and require a lower driving temperature.

(iv) The optimal working pair for specific operating windows depends on the MOFâ??s pore structure (adsorption sites and pore size).

(v) MOFs may hold an added benefit for application, as they can be coated (without binder) directly on heat-exchanger surfaces [4, 5].

In short, the future is bright for the application of MOFs in adsorption heat pumps and chillers.

References

[1] De Lange, M.F.; Verouden, K.J.F.M.; Vlugt, T.J.H.; Gascon, J.; Kapteijn, F.; Chemical Reviews, 2015, 115, 12205-1250

[2] Cadiau, A.; Lee, J. S.; Damasceno Borges, D.; Fabry, P.; Devic, T.; Wharmby, M. T.; Martineau, C.; Foucher, D.; Taulelle, F.; Jun, C.-H.; Hwang, Y. K.; Stock, N.; De Lange, M. F.; Kapteijn, F.; Gascon, J.; Maurin, G.; Chang, J.-S.; Serre, C.; Advanced Materials, 2015, 27, 4775-4780.

[3] De Lange, M.F.; Van Velzen, B.L.; Ottevanger, C.P.; Verouden, K.J.F.M.; Lin, L.-C.; Vlugt, T.J.H.; Gascon, J.; Kapteijn, F.; Langmuir, 2015, 31, 12783-12796

[4] De Lange, M. F.; Ottevanger, C. P.; Wiegman, M.; Vlugt, T. J. H.; Gascon, J.; Kapteijn, F.; CrystEngComm, 2015, 17, 281-285

[5] De Lange, M. F.; Zeng, T.; Vlugt, T. J. H.; Gascon, J.; Kapteijn, F.; CrystEngComm, 2015, 17, 5911-5920