Supercritical n Alkane Adsorption Data On 5A Zeolite Using the Gaussian Adsorption Isotherm Model

Monday, October 17, 2011: 1:20 PM
205 B (Minneapolis Convention Center)
Kevin F. Loughlin, Chemical Engineering, American University of Sharjah, Sharjah, United Arab Emirates and Dana Abouelnasr, Department of Chemical Engineering, American University of Shatjah, Sharjah, United Arab Emirates

Supercritical adsorption data available in the literature for C1 to nC12  n alkanes on 5A zeolite is correlated using the Gaussian Adsorption model.  This isotherm model has three parameters: qmax, the saturation loading; the 50% adsorbate loading pressure P50; and the standard deviation σ. The latter two parameters are deduced from a log plot of the isotherm pressure P versus the inverse Gaussian cumulative frequency distribution plot Φ-1(q). The slope of this plot is σ and the y-intercept is log P50.  The temperature dependency of P50 is deduced from a plot of log P50 versus 1/T: this is actually the isosteric heat of adsorption plot at 50 % loading with slope proportional to the heat of adsorption at 50 % loading (4.5 g/100g Z).

 The model is tested using 63 supercritical n alkane isotherms from the literature on 5A zeolite. The 63 isotherms from 18 different studies are fitted with the model using a qmax of 9 g/100g Z applicable to n alkane / 5A isotherms in the supercritical temperature range. The mean standard deviation σ is observed to be 0.960 with a standard deviation of 0.127. All 63 isotherms reduce to one characteristic curve when θ is plotted against (P/P50)1/ϭ.

The isosteres of P50 indicate heats of adsorption (-ΔH50) that are equal to or greater than literature values at zero loading (-ΔH0); the difference between the two is negligible  for low carbon numbers rising to over 10 kcal/mole at higher carbon numbers (nC10). This is expected as the heat of adsorption is calculated at 50% loading.  

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