Fixed bed sorption: setting the record straight on the Bohart-Adams and Thomas models

The Bohart-Adams model and the so-called Thomas model are commonly used in the modeling of fixed bed breakthrough curves in environmental sorption and biosorption research. Some authors fit the two equations to the same set of experimental breakthrough data and compare their modeling capabilities, implying that the two expressions are separate and independent models. This article clarifies unambiguously and demonstrates conclusively that the two models are in reality mathematically equivalent to each other and their parameters interchangeable. The salient features of the Bohart-Adams model and the genuine Thomas model are outlined here and their relationship delineated. The main difference between the Bohart-Adams and actual Thomas models lies in the form of the sorption isotherm assumed. The former assumes a rectangular (irreversible) isotherm while the latter assumes a Langmuir (favorable) isotherm. It is shown that, when the sorption isotherm is highly favorable, the actual Thomas model reduces to the Bohart-Adams model.