Long-term impact of air pollutants on thermochemical heat storage materials

Heating of buildings is a highly energy-demanding task. Therefore, improving energy management is crucial for more environmentally friendly development of future constructions, and the use of thermochemical heat storage technologies in solid materials is one of the most promising solutions. Nevertheless, certain drawbacks such as the impact of air pollutants on the long term durability of thermochemical heat storage materials (ageing up to 30 years) need to be studied to implement installations. In certain thermochemical heat storage systems, air passes through porous materials to carry water and heat, and the air's pollutants can interact with the solid material, thus decreasing its storage capacity. In the present work, adsorption tests were performed (under dynamic conditions) on zeolite-base materials, using different model molecules (i.e. toluene, styrene and hexaldehyde) representative of air pollutants. Strong competition between the adsorption of pollutants and water on the storage material was demonstrated. Water molecules were able to displace the molecules of pollutants, previously adsorbed on the material surface, thus delaying the saturation of the material and extending its life. Nevertheless, a lowering of the water adsorption and heat storage capacity was measured for a high number of cycles. The cycled materials have been thoroughly characterised in their physicochemical properties to identify the modifications of the materials (i.e., dealumination) and correlate them with the heat storage capacity. The impact of pollutants was demonstrated to be stronger on the pure zeolite, while the salt present on the MgSO4/13x composite seems to protect the material surface from the pollutant effect.