Composites “lithium chloride/vermiculite” for adsorption thermal batteries: Giant acceleration of sorption dynamics

Abstract

Adsorption thermal batteries have been proposed for storing heat from renewable and waste energy sources. Composites “salt in porous matrix” based on expanded vermiculite have extraordinary methanol sorption and heat storage capacities. However, their practical implementation is restricted by slow desorption, leading to low battery power. This paper aims to accelerate methanol desorption from a composite LiCl/vermiculite through its modification by an aluminum-oxygen containing additive. First, the dynamics of methanol sorption/desorption is studied for a pristine LiCl/vermiculite to reveal the factors braking sorption. Slow heterogeneous nucleation and sluggish growth of crystalline LiCl are shown to dramatically inhibit the methanol desorption from the pristine LiCl/vermiculite composite. To accelerate the nucleation, the vermiculite is modified by 2.5–8.9 wt% of aluminum-oxygen containing additive. Both pristine and modified sorbents are characterized by XRD, SEM, DSC, and BET techniques. The modification allows a giant acceleration of methanol desorption. The characteristic time corresponding to conversion 0.8 reduces by a factor of 2–12 as compared with the pristine composite. The dynamics acceleration affords fourfold increase in the specific power of the heat storage stage of adsorption thermal batteries employing the new composite. In a broader sense, the proposed approach could help accelerate the sorption of methanol, water, and ammonia on composites based on macroporous matrixes and could be advantageous for various adsorption applications.