Adsorption Characteristics of Refrigerants for Thermochemical Energy Storage in Metal-Organic Frameworks

TL;DR

This study investigates how low-GWP refrigerants R125 and R170 adsorb in various nanoporous materials, analyzing their suitability for thermochemical energy storage through molecular simulations validated against experiments.

Contribution

It provides a comprehensive analysis of refrigerant adsorption behaviors in different MOFs, emphasizing the importance of material properties and operating conditions for energy storage applications.

Findings

MIL-101 shows the best agreement with experimental data for R125.

R125 exhibits higher storage densities and affinity than R170.

Adsorption behavior is highly dependent on material defects and operational parameters.

Abstract

The adsorption of fluorocarbons has gained significant importance as its use as refrigerants in energy storage applications. In this context, the adsorption behavior of two low global warming potential refrigerants, R125 fluorocarbon and its hydrocarbon analog, R170, within four nanoporous materials, namely MIL-101, Cu-BTC, ZIF-8, and UiO-66 has been investigated. By analyzing the validity of our models against experimental observations, we ensure the reliability of our molecular simulations. Our analysis encompasses a range of crucial parameters, including adsorption isotherms, enthalpy of adsorption, and energy storage densities, all under varying operating conditions.We find remarkable agreement between computed and observed adsorption isotherms for R125 within MIL-101. However, to obtain similar success for the rest of the adsorbents, we need to take into account a few considerations, such as the presence of inaccessible cages in Cu-BTC, the flexibility of ZIF-8, or the defects in UiO-66. Transitioning to energy storage properties, we investigated various scenarios, including processes with varying adsorption and desorption conditions. Our findings underscore the dominance of MIL-101 in terms of storage densities, with R125 exhibiting superior affinity over R170. Complex mechanisms governed by changes in pressure, temperature, and desorption behavior make for complicated patterns, demanding a case-specific approach. In summary, this study navigates the complex landscape of refrigerant adsorption in diverse nanoporous materials. It highlights the significance of operating conditions, model selection, and refrigerant and adsorbent choices for energy storage applications.