Thermodynamic and kinetic study of fluorinated gas hydrates for water purification

Abstract

This study investigated and compared the thermodynamic stability, kinetic behaviour, and effectiveness of a water purification process using pentafluoroethane (HFC125a) and 1,1,1,2-tetrafluoroethane (HFC134a) as guest molecules. The hydrate phase equilibria of each fluorinated gas (F-gas) in pure water and NaCl solution were predicted using the Hu-Lee-Sum correlation, which agreed well with the experimental results from our previous studies. Under the same subcooling temperature of 3 K (at 0.3 MPa), the rate of hydrate growth with HFC134a was faster than that of HFC125a in the absence or presence of NaCl. In situ Raman spectroscopy confirmed that the HFC134a and HFC125a molecules occupy only a large cage of structure II hydrate. The Raman shifts of C H and C C bands in all phases (gas, liquid, and hydrate phases) of HFC125a shifted to higher wavelengths than those of HFC134a due to the increase in the number of fluorine atoms. The change in the salinity was studied to evaluate the effectiveness of an F-gas hydrate-based water purification process. In addition, the desalination efficiency of the HFC134a and HFC125a hydrates was compared by separating hydrate crystals from the slurries. The results showed that the desalination efficiency (or total dissolved solids removal efficiency) of HFC134a hydrate was higher than that of HFC125a hydrate. This study proves the importance of the water purification process using hydrates.

Exploring the Potential of HFC-125a Hydrate for Innovative Fire Suppression: A Gas Hydrate Technology Approach

“…Detailed descriptions of the working process are explained in our previous works. 15,18,19 The water-to-hydrate conversion of the final hydrate pellets was determined by comparing pellet weights before and after dissociation. After extracting the pellets from the reactor vessel, their weight was measured, and upon complete decomposition under atmospheric pressure, the dissociated water was sonicated (30 s) to ensure complete dispersion of dissolved gas.…”

Simulated and experimental thermodynamic investigations for the selection of suitable hydrate formers for water treatment

“…These studies were conducted to evaluate the potential of gas hydrates for water purification, which are reported in several publications. [2,10,11] They focused on the performance of the hydrate-based water treatment process. However, the criteria for the selection of guest molecules for pilot plants before starting the design process have not been adequately studied.…”

“…[20] Recently, the thermodynamic properties of the pentafluoroethane (HFC-125a) hydrates were compared with those of the HFC-134a hydrates. [10] In this study, two guest molecules (CO2 and HFC-134a) were experimentally and theoretically investigated to select suitable guests for hydratebased water treatment. CO2 was investigated because it is one of the most common guest gases.…”

“…[ 20 ] Recently, the thermodynamic properties of the pentafluoroethane (HFC‐125a) hydrates were compared with those of the HFC‐134a hydrates. [ 10 ]…”

Preface to the special issue section honouring Professor P. Raj Bishnoi

“…Paul et al [ 14 ] report gas‐uptake kinetics, water recovery, and separation efficiency of a desalination process that is based on CO 2 and N 2 clathrate hydrate formation. Truong‐Lam et al [ 15 ] describe the thermodynamic stability, kinetic behaviour, and effectiveness of a water desalination/purification process that is based on the use of tetra‐ or penta‐fluoroethane gas hydrates. Maruyama and Ohmura [ 16 ] explore the design implications of their thermodynamic and crystal growth results for a hydrate‐based isotopic water separation process.…”