Parameter control in synthesis of Vermiculite-CaCl2 composite materials for thermochemical adsorption heat storage
Yong Zhang, Ziwei Chen, Yanan Zhang, Yuehong Su, Saffa Riffat
Abstract
This study utilised vermiculite as a matrix to explore various impregnation methods for synthesising vermiculite-CaCl2 composite materials (VCMs), focusing on the impact of these methods on the performance of VCMs as thermochemical materials. Results indicate that alternative impregnation methods (e.g., multi-step, vacuum, high pressure, and high temperature) reduce VCM porosity compared to single impregnation, resulting in higher salt content as confirmed by CaCl2 content tests. Multi-step impregnation yields VCMs with an exceptional salt content of 81.37 wt %, surpassing the highest literature value (68 wt %) and the control group VCM-s (51 wt %). Vacuum impregnation notably increases salt penetration, leading to VCM-vac having the lowest porosity. However, this reduced porosity results in lower hydration and dehydration rates. Notably, VCM-vac exhibits the highest energy storage density of 2.05 GJ/m³, which is approximately three times the reported literature values and 1.5 times greater than the study's control group VCM-s. It also exceeds the CaCl2-rich VCM-m by 0.2 GJ/m³. It also demonstrates superior cyclic stability, with most CaCl2 remaining internalised, minimising agglomeration and CaCl2 loss. The energy consumption for vacuum impregnation is estimated at 3.51 kWh/kg(salt), indicating relatively low energy usage. The findings indicate vacuum impregnation emerges as a preferred method for synthesising thermochemical composite materials.