Modeling Growth Kinetics of Methane Hydrate in Stirred Tank Batch Reactors

Hydrate formationcould be looked upon as multicomponent and multiphasereaction which is heavily dependent on mass transfer and heat transferlimitations even under favorable thermodynamic conditions. Gas uptakemeasurement is one of the easiest ways to understand the kineticsof hydrate growth. In a typical gas uptake measurement, one couldeasily observe three phases of hydrate formation: in phase-I, hydrateforming gas dissolves in the liquid phase which leads to hydrate nucleation;in phase-II, fast hydrate growth is observed; and in phase-III, hydrategrows slowly for relatively longer time periods. In a batch reactor,a slow down in hydrate growth rate as seen in phase-III is eitherdue to a drop in the pressure of the reactor during hydrate growthand/or reduced mass transfer due to hydrate accumulation at the interface.In this work, a model is developed to predict phase-II events. Themodel proposed is based on an earlier model available in the literaturewhich captured the intrinsic kinetics of gas hydrate growth for asemibatch reactor. Model discussed in the current study works forbatch and semibatch reactor, it captures the kinetics for differentstirrer speeds, water to gas ratios and different thermodynamic conditions.Experimental validation was done in a batch reactor at 274 K and 6MPa with methane as the hydrate forming gas. A batch reactor withtwo different stirrer arrangements, different water-to-gas ratios,and different stirrer speeds were considered, and the mass transferlimitations for both the reactor configurations were studied. Further,a comparison study with the existing model and the modified model(current study) showed that the current model can be extended to otherreactor types.