In an industrial setting the separation of gas bubbles from the liquid phase can be a slow and costly process. It is therefore desirable to study the separation process in order to understand the mechanisms involved and thereby optimise the separation process. In alkaline hydrogen PtX plants the separation of hydrogen from the lye requires tanks, which are costly, due to the large nickel content in the tank material, and also due to the large size of the tanks that is required for fast gas separation. A dynamic two-phase model is presented using the mimetic discretisation method. The gas-liquid flow is modelled by a Naiver-Stokes system of equations in an Eulerian representation. The motion of gas is modelled by a separate continuity equation.