Characterization of silica-PEG-CaCl2composite sorbents in an open thermochemical heat storage reactor

Composite sorbents based on silica, polyethylene glycol (PEG) and containing calcium chloride were successfully synthetized using the sol-gel method. Their heat storage performance was investigated in a lab-scale open fixed-bed reactor. The silica/PEG matrix managed to stabilize hydrated calcium chloride when the salt content was equal to 32 wt% despite partial salt deliquescence. The presence of a crystallized phase CaCl2/PEG resulting from the complexation of the salt by the polymer may indeed prevent salt leakage, which was observed only when the salt content was increased to 42 wt%. Comparative experiments with a PEG-free control sample confirmed that the polymer enhances material stability. With a regeneration temperature of 130 °C, the best performing composite sorbent exhibited an average water sorption capacity of 0.37 gH2Og−1of dehydrated material and an energy density of 782 kJ kg−1over four successive sorption cycles at 30 °C and 42 % relative humidity. The dispersion and accessibility of the salt was enhanced after its first dissolution in the reactor. Compared to zeolite 13X, the sorption kinetics of the composite is much slower, resulting in a halved generated power. Still, the mass energy density of the composite is 70 % higher than that of zeolite, which makes it a promising material for heat storage applications with moderate required power outputs.