283086 Simple Prediction of Adsorption Henry Constants for Supercritical n Alkanes On 5A Zeolite
Simple Prediction of adsorption Henry Constants for Supercritical n alkanes on 5A zeolite
A simple model is proposed to calculate Henry constants for supercritical n alkanes on 5A zeolite using mid isotherm data. The Gaussian isotherm contains three model parameters, qmax the saturation loading, se the standard deviation and P50 the log mean pressure for the entire isotherm. Since the slope of the Gaussian isotherm approaches zero as the pressure approaches zero, the equation dlnq/dlnp = 1 is used instead for the derivation of the Henry constants. Using this equation, the dimensionless temperature-independent Henry constant may be derived as
where is expressed as KH*P50/qmax. ZH is the Z value for the Gaussian model at the point where dlnq/dlnp = 1, and σe is the standard deviation of the isotherm. For supercritical n alkanes on 5A zeolite, σe is equal to ln 10 and ZH is equal to -1.92. Upon substitution KH* becomes:
The temperature-independence of occurs because the temperature dependence of KH is cancelled by the temperature dependence of P50 the log mean pressure for the entire isotherm. It is important to note that P50 is calculated at the middle of the isotherm. Therefore Henry's constants can be estimated for isotherm data far from the Henry's Law region. Using the equation, , the model is observed to satisfactorily predict the Henry's law data for all supercritical n alkane isotherms on 5A zeolite.
To completely predict Henry's constants for this system, a predictive model is incorporated based on a correlative approach for 63 isotherms for carbon numbers varying from 1 to 10. The calculated values from this approach are also in remarkable agreement with reported experimental values. A summary of the equations needed to predict the properties of supercritical isotherms of n alkanes on 5A zeolite is provided.
KEYWORDS: separations, Henry constants, 5A zeolite, n alkanes, supercritical isotherms
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