A NEW FORMATION KINETICS STUDY METHOD OF TBPB AND CO2 HYDRATES BASED ON DTA

摘要

Clathrate hydrates are crystalline compounds which can be used as phase change material (PCM) for thermal energy storage. Moreover hydrate slurries could be a good solution for industrial issues of cold distribution at various temperature levels. In fact, hydrates formed from tetra-n-butylphosphonium bromide (TBPB) + water mixtures have equilibrium conditions required for air-conditioning applications, with melting temperature at 281 K at atmospheric pressure. Moreover, their flowing conditions are also suitable. Hydrates are also able to trap molecules of carbon dioxide resulting in mixed hydrates when combined with TBPB salt. The present work investigates kinetics studies of CO_2 hydrates and TBPB hydrates for various conditions of salt concentrations (15 %wt, 25 %wt and 37 %wt) and for a range of subcooling temperature between 3 and 8 K. A calorimetric method is used to determine the rate of hydrate formation thanks to a Differential Thermal Analysis (DTA). In a first time, the calorimetry method has been validated by evaluating the kinetic formation rate of CO_2 hydrates then it was applied to TBPB hydrates. The results showed that the kinetic formation rate is faster when the driving force increases for each initial salt concentration. Finally, two empirical kinetics models have been tested for describing the experimental result, Avrami-Erofeev and Nakamura, and a better agreement is observed with Nakamura model.