Poynting correction factor

The fundamental fact on which the analysis of heterogeneous reactions is based is that when a component is present as a pure liquid or as a pure solid, its activity may be taken as unity, provided the pressure on the system does not differ very much from the chosen standard state pressure. At very high pressures, the effect of pressure on solid or liquid activity may be determined using the Poynting correction factor. 

Here, the exponential term is the Poynting correction factor, which may be negligible at low to moderate pressures. Disregarding the Poynting factor, Eq. (1.218) becomes... 

This equation neglects the Poynting correction factor. (See discussion following... 

The Poynting correction factor being nearly equal to 1... 

The above equation simply states that the fugacity of solid component k at pressure P equals the fugacity of pure k at its vapor pressure multiplied by a Poynting correction factor. 

The exponential term in Equations 3.59 and 3.60 is called the Poynting correction factor. For liquids and solids, the partial molar volume is generally small, and the Poynting correction may be neglected if the pressure does not vary by a large am.ount. 

The Poynting correction factor, It accounts for the effect of pressure on liquid higacity. Since f is evaluated at the vapor pressure of the pure component, i) < is used to account for the difference between the pure component vapor pressure and the mixture pressure. This effect is small and can be neglected at low pressures (11,27), but is important at high pressures. 

The first integral involves the vapor volume, V, and may be evaluated using an equation of state. The second integral, known as the Poynting correction factor, takes into account the effect of pressure on the fugacity in the liquid. The volume in this integral, is the liquid molar volume and may be obtained from experimental data or from hquid density estimation methods (API, 1978 Racket , 1970). 

The reference fugacity for ammonia, which is the soluble component, is evaluated from the saturation fugacity of ammonia and a Poynting correction factor. For the dissolved gases, the reference fugacity is the Henry s constant referred to the saturation pressure of ammonia. For further details of the theory and the necessity of including the Poynting correction factor, see Reid et al. [50]. 

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