Several kinetic models have been proposed for gas hydrate formation but they use empirical parameters which are sensitive to experimental conditions and are equipment specific. They cannot provide a molecular level understanding of the reaction mechanism or cannot detect the maximum rate of hydration in surfactant solutions that was reported in the previous literature [1,2]. To overcome these deficits, a new kinetic model is introduced based on molecular collisions. In this theory, the reaction rate is a function of gas-water collisions and the total energy of the system. MD simulations are used to calculate the total energy of all the molecules. This new model can be used to determine the rate constant for other gas hydrates also as none of the parameters are experiment sensitive and equipment specific. The mechanistic model developed has only one adjustable parameter, which would determine the ratio to lead reaction from the total number of collision. The difference between the collision numbers of the dissolved gas and the three phase equilibrium water-gas-hydrate collisions is used as the driving force for hydrate formation. The proposed model is found to fit the data obtained experimentally within 10% error. The model reveals that the formation rate is a strong function of difference in the collision number at system pressure and the three-phase equilibrium pressure at a given temperature. The rate constant is a weak function on temperature.

Reference:

1.Kalogerakis, N., Jamaluddin, A. K. M., Dholabhai, P.D., and Bishnoi, P.R., “Effect on Surfactant on Hydrate Formation Kinetics”, SPE 22188, Proceedings of the SPE International Symposium on Oilfield Chemistry, 1993, March 2-5, New Orleans, 375-383.

2.Karaaslan, U. and Parlaktuna, M., “Surfactants as Hydrate Promoters?”, Energy & Fuels, 2000, 14, 1103-1107.