New Composite Water Sorbents CaCl₂-PHTS for Low-Temperature Sorption Heat Storage: Determination of Structural Properties.

Alenka Ristić,Nataša Zabukovec Logar

doi:10.3390/nano9010027

Alenka Ristić, Nataša Zabukovec Logar

Open Access

https://doi.org/10.3390/nano9010027

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Abstract

Sorption heat storage, as one of low-energy consuming technologies, is an approach to reduce CO2 emissions. The efficiency of such technology is governed by the performance of the applied sorbents. Thus, sorbents with high water sorption capacity and regeneration temperature from 80 to 150 °C are required. Incorporation of hygroscopic salt such as calcium chloride into porous materials is a logical strategy for increasing the water sorption capacity. This work reports the study on the development of composites with PHTS (plugged hexagonal templated silicate) matrix with an average pore size of 5.7 nm and different amounts of calcium chloride (4, 10, 20 wt.%) for solar thermal energy storage. These composites were prepared by wetness incipient impregnation method. Structural properties were determined by X-ray diffraction (XRD), nitrogen physisorption, scanning electron microscopy (SEM) and transmission electron microscopy (TEM). CaCl2 was confined in micro- and mesopores of the matrix. The resulting CaCl2-PHTS materials were used for water sorption at 40 °C, showing an increase of maximal water uptake with higher amount of calcium chloride from 0.78 g/g to 2.44 g/g of the dry composite. A small reduction in water uptake was observed after 20 cycles of sorption/desorption between temperatures of 140 °C and 40 °C, indicating good cycling stability of these composites under the working conditions.

Highlights

Thermal energy storage (TES) is becoming a crucial technology in enabling more efficient use of renewable energy and contributing to the reduction of our dependency on fossil fuels
The synthesis procedure of the SBA-15 was modified in order to synthesize the Plugged hexagonal templated silicate (PHTS) matrix with average pore size of 5.7 nm with the aim to confine CaCl2 in the pores of this matrix
Three diffraction peaks were still present and their 2θ values were only slightly shifted, indicating that thatchannels the channels with order goodwere order were maintained during the preparation of the the with good maintained during the preparation procedureprocedure of the composite

Summary

Introduction

Thermal energy storage (TES) is becoming a crucial technology in enabling more efficient use of renewable energy and contributing to the reduction of our dependency on fossil fuels. It can be divided into three main categories according to how energy is stored: sensible heat (e.g., water tanks, underground storage), latent heat (e.g., ice, phase change materials), and thermochemical heat storage [1]. The main criteria for the selection of a proper sorbent for sorption thermal energy storage are high sorption capacity, low desorption temperature, and high temperature level of released heat of adsorption [4]. The most versatile class of sorbents are the two-component sorbents or composite salt in porous inorganic matrix (CSPM) [7] which combine the advantages of the pure porous matrix and hygroscopic salt hydrates for the enhancement of water sorption capacity, heat, and mass transfer

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