Estimation of dissociation rate constant of CO2 hydrate in water flow

Dissociation processes of CO2 hydrate under water flow conditions were investigated by experimental measurements and numerical calculation. Dissociation experiments were carried out with a CO2 hydrate ball (diameter 10 mm) mounted in a flow cell, and the overall dissociation rate of CO2 hydrate without bubble formation was measured under various conditions of temperature, pressure, and water flow rate. A linear phenomenological rate equation in the form of the product of the dissociation rate constant and the molar Gibbs free energy difference, between the hydrate phase and the ambient aqueous phase, was derived by considering the Gibbs free energy difference as the driving force for the dissociation. The molar Gibbs free energy difference was expressed by the logarithm of the ratio of the concentration of CO2 dissolved in water at the hydrate surface to the solubility of CO2 in the aqueous solution in equilibrium with the hydrate. The dissociation rate constant was determined from the experimental results of the overall dissociation rate combined with the numerical simulation results of the concentration profile of CO2 constructed by the computational fluid dynamics (CFD) method. The obtained dissociation rate constant at the same pressure was found to be dependent on the temperature with the apparent activation energy of 97.51 kJ/mol. A general form with product of the dissociation rate constant times driving force is proposed to calculate the dissociation rate of CO2 hydrate in the water. (c) 2014 Society of Chemical Industry and John Wiley & Sons, Ltd