Effect of THF on equilibrium pressure and dissociation enthalpy of CO ₂ hydrates applied to secondary refrigeration

The present work investigates the formation conditions and the latent heat of dissociation of hydrates formed from tetrahydrofuran (THF)-CO ₂-water mixtures. The conditions investigated are 3.8-15 wt% for THF concentration and 0.2-3.5 MPa for the CO₂ partial pressure range, conditions that are adapted to the use of the corresponding hydrate slurries as secondary refrigerants. Both differential thermal analysis (DTA) and differential scanning calorimetry (DSC) methods were used for the experimental determinations. Experimental values were compared with modeling, combining the van der Waals and Platteeuw approach with the Redlich-Kwong equation of state associated to a modified Huron-Vidai (MHV2) mixing rule. At fixed temperature, adding THF to the systems results in a drastic reduction of Co₂ equilibrium pressure. For instance, at 280 K, a 78.9% decrease of CO ₂ pressure is experimentally observed if the solution contains 3.8 wt% of THF. Furthermore, a dissociation enthalpy of (CO₂: + THF) hydrates roughly two times higher that that of CO₂ hydrates was calculated from measured and predicted data of hydrate formation.