Adsorption of Linear Alcohols in Amorphous Activated Carbons: Implications for Energy Storage Applications

Thermal energy storage using porous materials has become a key technology for improving efficiency and sustainability of heat storage applications to reduce the carbon dioxide emissions. Choosing the adsorbent-fluid working pairs that improve the performance of an energy storage process is a challenge due to the large number of possible combinations. The use of activated carbons for adsorption, purification, and energy applications as an alternative to other porous materials such as zeolites or silica gel is a promising strategy due to its low production cost combined to a good thermochemical energy storage performance. In this work, we have explored the use of activated carbons derived from the pyrolysis of saccharose coke (CS1000a) for thermal energy storage. For this, we have considered the first four n-alcohols (methanol, ethanol, 1-propanol, and 1-butanol) as working fluids because of their large enthalpy of vaporization. We carried out Monte Carlo simulations combined with the thermodynamical model based on the Dubinin-Polanyi theory to evaluate adsorption, interaction energies, microscopic structure, and thermal energy storage density of CS1000a-alcohol pairs. We compared these properties with the performance of other commercial activated carbon, such as BPL. We employed a realistic model containing functional groups in the internal surface and a simplified model without these functional groups. The role of these functional groups and their consequences on the targeted properties is discussed. CS1000a shows excellent performance to store thermal energy and considerably reduces the operational temperatures, making it a good alternative to those on the market.