Question

Which of the following isotherm is applicable to physical adsorption?

(a) Langmuir

(b) BET

(c) Freundlich

(d) Kisluik

I have been asked this question at a job interview.

I'd like to ask this question from Adsorption in section Unit Operations of Bioprocess Engineering

Answer 1

Correct option is (c) Freundlich

To explain I would say: The Freundlich isotherm was the first isotherm model proposed for sorption processes. It can be applied for non ideal sorption on heterogeneous surfaces, as well as, multilayer sorption. A variation in the slope between 0 and 1 is associated with a chemisorption process, which is more heterogeneous as the value gets closer to 0. Due to the lack in fundamental thermodynamic basis, since there is no approach to Henry’s law at vanishing concentrations, this represents a limitation of this isotherm model.