Phase equilibrium and dissociation enthalpies of CO2/cyclopentane hydrates in presence of salts for water treatment and CO2 capture: New experimental data and modeling

The applications of clathrate hydrates on carbon dioxide capture and desalination is an attractive and growing subject within the hydrate community. While many promoters exists to overcome the numerous issues of hydrate-based technologies (mostly how to mild the operating conditions and improve the kinetics), there is a need to find a guest that could be recovered easily. That is why cyclopentane (CP), an organic molecule not miscible into water that can form hydrates under atmospheric pressure at 7 degrees C, has been studied widely in the literature. However, its behavior in forming mixed hydrates with CO2 in presence of salts is still not well understood. This work is an effort to investigate the thermodynamics of mixed CO2/CP hydrates to fulfill the gap in this field from a thermodynamic point of view. In this effort, new equilibrium dat a of mixed CO2/CP hydrates in the presence of salts (NaCl-KCl, MgCl2, CaCl2 which are among the main factors of hard water) have been obtained under different concentrations and pressures. Final dissociation points and as well as intermediate metastable points were obtained. Furthermore, thermodynamic consistency tests have been performed on our data and literature data to discuss their reliability. This test is important to question the idea of thermodynamic equilibrium since we suspect from a previous work the formation of several hydrate structures. Finally, three modeling approaches were considered: van der Waals and Platteeuw (vdW-P) approach, Hu-Lee-Sum (HLS) correlation, and ice melting point method derived from HLS proposition. Results showed a greater inhibition effect of cation Ca2+ compared to Mg2+ and that vdW-P method can predict equilibrium temperature within 0.2 degrees C uncertainty. (C) 2022 Elsevier B.V. All rights reserved.

Automated summary

This study investigates the thermodynamics of mixed CO2/CP hydrates and discusses the equilibrium data obtained under different concentrations and pressures, as well as the thermodynamic consistency tests conducted on the data. Results show a greater inhibition effect of cation Ca2+ on mixed hydrates.