Structure and Properties of Composite Adsorbents Salt Inside Porous Matrix

Abstract

The chapter is devoted to structure and properties of composite adsorbents ‘salt inside porous matrix'. Characteristics of adsorbents ‘salt inside porous matrix', such as ‘zeolite – crystalline hydrate', ‘vermiculite – crystalline hydrate', ‘silica gel – crystalline hydrate' were analysed. Main advantages of composite adsorbents are shown to be higher adsorptive capacity and lower regeneration temperature as compared with host matrix. Adsorptive capacities of composite materials are shown to be significantly enhanced by introduction of salts in host matrix such as zeolite, vermiculite, or silica gel. Water uptake by composite adsorbent is shown to be increased by rising the salt content in it. The drawback of most of existing impregnation technologies is shown to be impossibility of obtaining composite with salt content more than 40 – 60% along with complexity. Sol gel method is shown to be an alternative for conventional impregnation methods. Properties of adsorbents ‘silica gel – sodium sulphate' synthesized according to sol gel method developed by authors were considered. The composite ‘silica gel – sodium sulphate' composition and structure were studied by IR-spectroscopy and wide-angle x-ray scattering. Adsorptive properties of crystalline Na2SO4 when allocated in silicon oxygen matrix are shown to result from dispersion up to nanoscale. Adsorptive capacities and heat of adsorption of composites ‘silica gel – sodium sulphate' and ‘silica gel – sodium acetate' surpass almost by 30% the value calculated from the linear superposition of the sorption capacities of the sorbent and massive salt. Their adsorption properties are shown to be not a linear combination of properties of silica gel and salt. The formation of a unique structure promoting an increase in the rate of reaction between crystalline hydrates and water vapor in the developed pores of the silicon-oxygen matrix is confirmed. It leads to increasing the heat of adsorption and the heat energy storage density. Strong difference of water sorption kinetic curves of composite ‘silica gel – sodium sulphate' and massive sodium sulphate is revealed. The correlation of their composition, structure, water adsorption kinetic, and operating characteristic as heat storage material is stated.