Pressure gradient in SFC

For calculation of the pressure drop the relation after Darcy can be used, in which the constant Iir is fitted to experimentally determined pressure drops. 

The viscosity p and the superficial velocity w are dependent on pressure and density, respectively. Therefore, a new density has to be calculated for each pressure by means of an equation of state, e.g. for CO2 by the equation of Span and Wagner [60]  

For calculation of the viscosity an approach of Chung can be used, the influence of pressure is taken into account by the method of Reichenberg [61]. The viscosity of a gas at low pressure and a temperature T Tc can be calculated after Chung by  

Starting from the viscosity at low pressure, the influence of pressure can be calculated after Reichenberg by  

Via the continuity equation, velocity and density are linked to each other  

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The density and therefore the solvating power of supercritical fluids varies according to the pressures to which they are submitted. As a consequence, a pressure gradient in SFC is equivalent to an elution gradient in HPLC, or a temperature gradient in GC. 

I 9 Modeling of Simulated Moving-bed Chromatography 9.4.2.6 Modeling of Pressure Gradient in SFC... 

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