A new Gaussian adsorption isotherm model: test data is methane-5A zeolite

摘要

An adsorption isotherm model is deduced based on the Gaussian cumulative frequency distribution principles. This isotherm has three parameters: q_(max) the 50% ad-sorbate loading pressure P_(50), and the standard deviation σ. The isotherm development hinges on establishing P_(50) and σ. These are deduced from a log plot of the isotherm pressure P versus the inverse Gaussian cumulative frequency distribution plot. The slope of this plot is σ and the y-intercept is P_(50), The temperature dependency of P_(50) is deduced from a plot of log P_(50) versus 1/ T: this is actually the isosteric plot at 50% loading with slope equal to the heat of adsorption at 50% loading.The model is tested using the literature methane data for 5A zeolite. Twenty-four isotherms from six different studies are fitted with the model using a q_(max) of 9 g/100 gZ applicable to methane 5 A isotherms in the temperature range of the study, as reported in the literature. The standard deviation σ is observed to be 0.98 ± 0.088. The isostere of P_(50) indicates a heat of adsorption between 4.62-4.97 kcals/mole consistent with literature values. All 24 isotherms reduce to one characteristic curve when 6 is plotted against (P/P_(50))~(1/σ), The θ values approaching zero (<0.05) are shown to be consistent with reported Henry constant data using the heat of adsorption value calculated at 50% loading as is expected for homogeneous adsorption.