Experimental study and modelling of cyclopentane hydrates in the presence of salt

Son Ho-Van (1, 2, 3) , Jérôme Douzet (1, 2, 3) , Baptiste Bouillot (1, 2, 3) , Jean-Michel Herri (1, 2, 3)

1 PEG-ENSMSE - Département Procédés pour l'Environnement et Géoressources
2 SPIN-ENSMSE - Centre Sciences des Processus Industriels et Naturels
3 LGF-ENSMSE - Laboratoire Georges Friedel

this study aims to investigate cyclopentane hydrate formation and dissociation processes. Two salts were considered, NaCl, and KCl, with a wide range of concentrations: NaCl (0 – 23% wt), KCl (0 – 20% wt) and an equi-mass mixture of NaCl-KCl (0 – 22% wt). Two procedures were applied to determine the equilibrium temperatures. One is at quick dissociation rate; another is at slow dissociation rate. The aim of the quick procedure is to provide an initial estimate of the equilibrium temperature. The slow procedure is then used to obtain more accurate data. Temperature and salt concentration were measured respectively using Pt100 probes, ionic chromatography, and a drying oven. The time-temperature figures during formation and dissociation are generated. A thermodynamic model is then proposed to predict the equilibrium temperatures. A small increase in the temperature of the solution inside the reactor was observed during the hydrate formation process. This can be explained by a typical exothermic property of the crystallization process. In contrast, the temperature remained nearly constant during the hydrate dissociation in the quick dissociation procedure. This behavior is obviously due to the endothermic nature of the dissociation process. As soon as no hydrates were observed, the temperature rose suddenly, providing valuable evidence to determine the equilibrium temperatures. The equilibrium temperatures dropped significantly with an increase in salt concentration, whatever the kinds of salt. In addition, the equilibrium temperatures of cyclopentane hydrate in the presence of NaCl were always lower than those in the presence of KCl and a mixture of KCl and NaCl at the same concentration. This indicates that NaCl has a greater impact on the equilibrium temperature of cyclopentane hydrate at the same quantity. A temperature shift between the equilibrium temperatures following the quick and the slow dissociation was also observed. It is clear that the quick procedure tends to miss the right temperature, and results are slightly higher. In comparison with the literature, the slow procedure in pure water provides the same value reported by Masahiro and Zylyftari. In the presence of NaCl at 5%, 10%, 20%, 23% wt, the results are close to Kishimoto and Zylyftari, obtained either by slow dissociation or micro Differential Scanning Calorimetry (μ-DSC).The results also reveal that the proposed thermodynamic model provided the data which are in good agreement with the experimental data. The absolute deviations between the predicted and experimental data are less than 0.7°C in all kinds of salts.

Mots clés: Cyclopentane Hydrates; Crystallization; Thermodynamic equilibrium; Water activity; Electrolytes

Domaines: Génie des procédés

Son Ho-Van, Jérôme Douzet, Baptiste Bouillot, Jean-Michel Herri. Experimental study and modelling of cyclopentane hydrates in the presence of salt. 16^ème Congrès de la Société Française de Génie des Procédés (SFGP 2017 ^NANCY), SFGP (Société Française de Génie des Procédés); EFCE ( European Federation of Chemical Engineering); LRGP (Laboratoire Réactions et Génie des Procédés); CNRS (Centre National de la Recherche Scientifique; Université de Lorraine, Jul 2017, Nancy, France. ⟨hal-01666734⟩