VLLE in Hydrocarbon-Water Systems

Hydrocarbon processing often involves water in the streams, and this can resnlt in the coexistence of two liquid phases and a vapor phase. A valid approach in handling such VLLE conditions is to neglect the hydrocarbon solubility in water, and assume the water phase is pure water. This enables the use of a simplified mixed A -value formulation. 

The solubility of water in the liquid hydrocarbon phase is given as X, the mole fraction of water in the water-saturated liquid hydrocarbon phase. With the hydrocarbon phase molar rate designated as L and the water phase as L , the overall mole fraction of water in the mixed liquid phase is calculated as 

This equation is combined with Equation 2.29 to derive the following expression for a  

At equilibrium, Equation 2.25 must be satisfied for the liquid phases. The water phase is assumed pure water, therefore A = 1 and y = 1, and Equation 2.25 for water in the hydrocarbon phase becomes 

Using this expression, the A -valuc of water in the hydrocarbon phase is written as 

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