New SAPO-34-SPEEK composite coatings for adsorption heat pumps: Adsorption performance and thermodynamic analysis

In this paper, a new adsorbent composite coating by using SAPO-34 filler in a sulfonate polyether ether ketone matrix is proposed for thermally efficient adsorption heat pumps. Composite SAPO-34 zeolite based coatings with 80-95 wt% SAPO-34 content were realized. Preliminary morphological analysis, by scanning electron microscopy, highlighted that the coating microstructure is homogeneous and permeable to water vapor diffusion. Water vapor adsorption isobars were measured at equilibrium for all samples in the temperature range 30-120 °C. The results showed the typical S-shaped trend, which is suitable for adsorption heat pump applications. The highest adsorption value was observed for the coating with highest zeolite filler amount, 95 wt%. This batch exhibited a maximum water uptake of about 29.0 wt%, demonstrating that the S-PEEK matrix does not hinder the SAPO-34 adsorption performance. Finally, starting from obtained experimental data of composite materials adsorption capacities the, a simple energy balance based thermodynamic analysis was performed for air conditioning application by using an aluminum finned-flat tube heat exchanger, as reference. Results highlight that this composite coating technology allows cooling COP up to over 5% higher than that of the conventional loose adsorbent grains configuration, indicating the proposed technology promising for practical application in adsorption heat pumps.