Preparation and thermal properties of zeolite 13X/MgSO4-LiCl binary-salt composite material for sorption heat storage

Abstract

Thermal energy storage can play a pivotal role in waste heat recovery and solar energy thermal utilization by balancing the time and space-mismatch between supply and demand of energy. Thermochemical sorption heat storage technology has gained the enormous interest for its ability to make use of the low-grade thermal energy. However, the slow sorption reaction kinetics of sorbents remains an obstacle for the large-scale industrial applications of thermochemical sorption heat storage technology. In this study, a new type of zeolite 13X/MgSO4-LiCl composite sorbent material has been fabricated by impregnating zeolite 13X with the mixed solution of MgSO4 and LiCl. The structural characteristics and sorption heat storage performance of composite adsorbents with different mass ratios of MgSO4 and LiCl were studied experimentally by scanning electron microscopy (SEM), full-automatic specific surface area and pore analyzer (ASAP), and thermogravimetry analysis-differential scanning calorimetry (TGA-DSC). The results indicate that binary-salt sorbents show the faster sorption kinetics and higher water sorption capacity compared to single salt sorbents. When the mass ratio of MgSO4 and LiCl is 2:1, the zeolite 13X/MgSO4-LiCl composite sorbent (XML-2/1) has the best sorption heat storage performance. Under the sorption temperature of 25 °C and relative humidity (RH) of 60 %, the maximum sorption capacity is 0.24 g/g, and the corresponding heat storage density of 458.3 kJ/kg can be achieved. The results indicate that the zeolite 13X/MgSO4-LiCl composite adsorbent can improve the sorption rate and heat storage density. Compared with pure zeolite 13X and zeolite 13X/MgSO4 composite sorbents, the addition of LiCl can effectively improve the sorption rate and sorption heat storage capacity. The findings of this investigation could promote the growing body of research on the mixed salt (binary-salt or multiple-salt) composite materials and new insights can be offered by broadening the application of zeolite-based composite materials in low-grade thermal energy storage for space heating, which can guide further research and development in this field and ultimately help facilitate the transition toward the clean energy.