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  • The composite water sorbent for heat storage
    Ristić, Alenka ; Henninger, Stefan K. ; Kaučič, Venčeslav
    Thermally stable porous adsorbents have become of increasing interest as storage materials mostly in combination with water as working fluid for application in adsorption heat pumps and ... thermochemical heat storage. Mesoporous materials are such materials with a great potential as water sorbents mostly because of their low charging temperature. Thus, these materials can be used in storages for the application of low temperature heat (e.g. solar energy) and industrial waste heat. Another strategy for the improvement of the sorption capacity has resulted in the preparation of composite (two-component) materials by combining the advantages of hygroscopicsalts with those of the basic mesoporous materials. The salt interacts with water to increase the sorption capacity. The matrix absorbs water and serves as a dispersion medium, which forms a required salt particle size and a high salt surface area, affects the properties of the salt, and provides heat supply through the solid. We report here on the investigation on structural properties of the composite water sorbent with ordered mesoporous silicate (SBA-15) as the matrix and the salt hydrate CaCl2. The water sorption properties were determined. The ordered mesoporous silicate was prepared by a modified preparation with using triblock copolymer P123.3 The composite was obtained by wet impregnation of the ordered mesoporous matrix with 2 M solution of calcium chloride. The maintenance of the matrix framework order upon impregnation of CaCl2 was studied by the analysis of low-angle X-ray powder diffraction patterns, showing the ordered mesoporous structure with 2D-hexagonal pore arrangement. The X-ray diffractograms recorded in the wide-angle range did not show any reflections, since the nanosized dimensions of the deposited CaCl2 particles are not detectable by XRD. This could be explained with the presence of highly dispersed CaCl2 with nanosized dimensions that are located on the surface and within the mesopores.The nitrogen sorption isotherms for the mesoporous matrix and for the composite, containing 4 wt% of CaCl2, were typical type-IV isotherm for ordered mesoporous silicas with 2D-hexagonal pore arrangement. The impregnation of CaCl2 solution on ordered mesoporous matrix led to a decreased mesopore volume (from 0.827 to 0.756 cm3g-1) and pore size (from 10.2 to 9.3 nm), thus evidencing the presence of CaCl2 nanoparticles inside of the pores of the matrix. Water adsorption isotherms measured at 40°C showed typical characteristics of the hydrophobic or weak hydrophilic mesoporous adsorbents. The maximum water upload was high, 0.88 g/g for both materials, but the shape of the uptake curve of the composite was changed evidently. It can be concluded that the presence of CaCl2 in the matrix influenced the hydrophilicity of the composite. The composite water sorbent with mesoporous ordered matrix and CaCl2 was prepared by wet impregnation. With regard to the application within an adsorption heat storage the composite is still too hydrophobic. However, a successful shift of the isotherm to lower relative pressure was achieved. This is a first promising step which showed the principle possibility towards a further optimization of this composite water sorbent.
    Vir: Book of abstracts (Str. 90)
    Vrsta gradiva - prispevek na konferenci
    Leto - 2012
    Jezik - angleški
    COBISS.SI-ID - 5117210

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