Kinetics of Water Adsorption in Metal-Organic Framework(MOF-303) for Adsorption Cooling Application

Abstract

Adsorption cooling systems (ACS) powered by low-temperature heat offer an energy-efficient and environmentally friendly alternative to traditional vapor-compression systems. The effectiveness of ACS is significantly influenced by the alignment of the adsorbent properties with the operating conditions of the cycle. Metal-Organic Frameworks (MOFs) are considered the next generation of water harvesting and ACS. Many MOFs are synthesized and tested for water harvesting systems, one of these MOFs is MOF-303 which was reported to have very rapid water sorption dynamics under atmospheric conditions. However, MOF-303 has never been tested under the same conditions as ACS (under vacuum). In this study, the isotherms and kinetics of water adsorption on MOF-303, as an efficient adsorbent of water vapor, is experimentally investigated for the ACS using the linear driving force model. The diffusion coefficients across a wide range of relative pressures under two different temperatures were estimated. The study compares the adsorption process of MOF-303 with traditional silica gel (SG) in the context of diffusion kinetics relevant to ACS. Based on the output and at a constant temperature of 25 °C and across all relative pressure ranges, MOF-303 exhibited an average increase of approximately eight times in diffusion kinetics compared to SG. Specifically, within the relative pressure range of 10–30 %, which is optimal for ACS, MOF-303 demonstrated a seven-fold increase in diffusion kinetics over SG. The diffusion values for SG display a clear upward trend with increasing temperature. In contrast, the diffusion values for MOF-303 are subject to fluctuations with temperature changes under investigation. Notably, the isotherm for MOF-303 shows an inflection point at relative pressures between 10–15 %, causing a significant reduction in diffusion at these specific relative pressures compared to other relative pressure values. The findings in this study highlight the potential use of MOF-303 as a highly efficient water adsorbent for the ACS which will enable scientists and engineers to develop sustainable low-grade energy systems.