Growth kinetics—the Englezos-Bishnoi model

The role of hydrate intrinsic kinetics has been more recently suggested to play a smaller role in hydrate growth in real systems than heat and mass transfer effects. In view of this, the discussion on the kinetics models is only briefly presented here. For a more thorough treatment, the reader is referred to the original references (Englezos et al., 1987a,b Malegaonkar et al., 1997). 

Englezos et al. (1987a,b) generated a kinetic model for methane, ethane, and their mixtures to match hydrate growth data at times less than 200 min in a high pressure stirred reactor. Englezos assumed that hydrate formation is composed of three steps (1) transport of gas from the vapor phase to the liquid bulk, (2) diffusion of gas from the liquid bulk through the boundary layer (laminar diffusion layer) around hydrate particles, and (3) an adsorption reaction whereby gas molecules are incorporated into the structured water framework at the hydrate interface. 

Modifications to the model by Englezos et al. were later made to remove some minor inconsistencies and to account for the high solubility of carbon dioxide in water (Malegaonkar, et al., 1997). The last two steps are concepts with initial basic equations discussed in Section 3.2.1. Similarly to Equation 3.17, Englezos modeled steps (2) and (3) using Equation 3.18, where at steady state the rates of the two steps are assumed equal. Therefore, the rate of growth per particle is given by  

K = hydrate formation growth rate constant, representing a combined rate constant for diffusion (mass transfer) and adsorption (reaction) processes 

However, as with any model, it is well to recognize the limitations before attempting usage. Below are some inherent restrictions in the Englezos-Bishnoi-Malegoankar model  

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