Zeolite-graphene composite adsorbents for next generation adsorption heat pumps

In this study, consolidated composite adsorbents comprising highly porous zeolite of type AQSOA-Z02 and two types of graphene nanoplatelets (GNPs), namely H25-GNPs and M25-GNPs, are developed to enhance the performance of a thermally powered adsorption heat pump. The thermophysical properties such as specific heat capacity, packing density, thermal conductivity, and porosity of the synthesized composite adsorbents are rigorously investigated. The addition of GNPs into zeolite improves the packing density as well as the thermal conductivity significantly. The highest thermal conductivity is observed for 50 wt% H25-GNPs contained composite, which is almost 127 times higher than the parent zeolite. Porous property investigation reveals that the fabricated composites are microporous, like the parent zeolite. Besides, the equilibrium adsorption uptake of water onto the composite adsorbents is measured gravimetrically at three different temperatures, 30, 50, and 70 °C. The experimental uptake data are correlated with the modified Langmuir, Sun and Chakraborty, and Universal models to describe the adsorption process mathematically. It was found that 20 wt% H25-GNPs contained composite provides almost 43% improvement of effective volumetric uptake over the parent zeolite. All the presented findings would carry significant importance for the development of an efficient and compact adsorption heat pump system. Besides, the obtained results would be very supportive for designing zeolite composite based gas separation and storage, desalination, and thermal energy storage systems.