Extended Langmuir equation for correlating multilayer adsorption equilibrium data

The Langmuir adsorption isotherm equation is extended to include a third parameter. The extended Langmuir model is then compared with the Aranovich–Donohue (A–D) and the n-layers BET models in their ability to fit experimental data. The extended Langmuir model shows the smallest deviation of all the three-parameter models discussed, and has a smaller deviation than certain of four-parameter models. Unlike the models that have a singularity when pressure equal to saturation vapor pressure, the extended Langmuir model performs well in numerical calculation as well as its ability to fit experimental data.