Formation Kinetics of the Mixed Cyclopentane-Carbon Dioxide Hydrates in Aqueous Sodium Chloride Solutions

Hydrate formation from cyclopentane (CP) and carbon dioxide was measured at 281 K by powder X-ray diffraction (PXRD) and macroscopic methods. The effect of initial pressure and CP mass fraction in liquid phase was analyzed. The results showed that hydrate formation was assumed to start with the nucleation of the mixed CP-CO(2)hydrate with small fraction of CO(2)followed by a large continuous CO(2)adsorption. Initial pressure was found to have a positive correlation with the total CO(2)consumptions when the initial pressure was below 2.5 MPa. However, the total CO(2)consumptions dropped by over a half as the initial pressure was 3.0 MPa. PXRD revealed that all the hydrate samples formed at different initial pressures were structure II. The CO(2)consumptions were assumed to be inhibited by the competitive occupation of 5(12)6(4)cages between CP and CO(2)molecules when the initial pressure was above 2.5 MPa. The CO(2)consumptions were also found to be reduced as the CP mass fraction was above 0.25. An excess of CP molecules was not assumed to strengthen the formation of the mixed CP-CO(2)hydrates at the initial stage, but increased the thickness of liquid CP film at aqueous brine and hydrate particles, which increased the diffusion resistance of CO(2)molecules. Therefore, the suitable initial pressure and the CP mass fraction for the mixed CP-CO(2)hydrate formation should be around 2.5 MPa and 0.2, respectively