Effect of NaOH addition on the thermochemical heat storage capacity of nanoporous molecular sieves

Abstract

SUMMARY The water vapor sorption capacity and corresponding generated heat amount are the most important properties for adsorbents in thermochemical heat storage systems. In order to understand the adsorption/desorption behavior of three nanoporous molecular sieves such as 5A, mordenite and natural clinoptilolite (with different structures, Si/Al ratios and balancing cations), the pure zeolites and their composites (obtained by depositing NaOH onto the molecular sieves) were characterized in their structural and surface properties by using appropriate techniques (N2 adsorption isotherms at −196 °C, XRD and (MAS) NMR). The adsorption of water was performed using a Setaram TG‐DSC 111 apparatus. Three successive cycles of hydration (at 20 °C)/dehydration (at 150 °C) were carried out to check the stability of the system in conditions close to those used in adsorption heat pumps. The measured heats of dehydration vary in the 183–614 kJ kg−1sample range for the various samples that present also different water vapor sorption capacities (from ≈ 0.08 to ≈ 0.14 kgH2O kg−1sample). The water adsorption/desorption behavior of the zeolites was mainly related to the porous structure and to the Si/Al ratio, that drive the affinity of zeolite to water. The experimental results showed that the impregnation of the three kinds of nanoporous zeolites with different amounts of sodium hydroxide negatively affects the sorption characteristics of the composites. The blockage of zeolite pores (that limits the access to water molecules), the slight amorphization of the zeolite structure and the formation of carbonates are some of the phenomena identified to influence the water sorption onto NaOH‐containing composites. Copyright © 2016 John Wiley & Sons, Ltd.

Water sorption and heat storage in CaCl2 impregnated aluminium fumarate MOFs

“…In terms of heat released per mol of water, an increase is also obtained after aluminium fumarate impregnation. Salt deposition improves the surface affinity of the solids for water, resulting in a more energetic process and thus higher values of the total heat released [77]. Expressed in kg mol -1 H O, AF-Ca 2 shows the same heat storage capacity as AF-Ca 3 , although it contains a lower amount of CaCl 2 .…”

Solid‐State MAS NMR Study of Hydrated/Dehydrated Phosphorus‐modified ZSM‐5 Zeolite

“…By comparing MAS NMR spectra of the hydrated and the dehydrated zeolites, we could get a valuable information of the chemical structure of the zeolite. [7][8][9][10] Here, two types of P-ZSM-5 zeolites were used for investigating the change of chemical structure of ZSM-5 in the hydration/dehydration process. One is the P-ZSM-5 washed with hot water and the other is the P-ZSM-5 treated with steam.…”

“…In this paper we conducted solid‐state MAS NMR measurements of the hydrated/dehydrated P‐ZSM‐5 zeolite and analyzed the MAS NMR spectra to get the information of the chemical structure of the zeolites. By comparing MAS NMR spectra of the hydrated and the dehydrated zeolites, we could get a valuable information of the chemical structure of the zeolite …”