Modelling of transient diffusion and adsorption or diffusion and reaction processes results in coupled partial differential equations. In most cases of practical interest these equations do not have analytical solutions and tedious numerical methods have to be applied. The substantial simplification of computations achieved by the use of driving force approximations (Eq. (I)) motivated extensive research work towards derivation of such equations. Starting from the paper [4], the methodology based on the intraparticle concentration profile approximation concept became dominating in this area of scientific research. A new method for derivation of the driving force approximations is presented. It is based on the introduction of the functions F(tau) (Eq. (7)) and G(tau) (Eq. (10)). The function G(($) over bar gamma(tau)/eta) is shown in Fig. 1. The analysis based on the theory of diffusion in a semi-infinite medium has been carried out justyfying the independence of the short time limit of the G(($) over bar gamma(tau)/eta) function on the Thiele modulus. The G(tau) function was approximated with a linear function (Eq. (14)) leading to required nonlinear driving force approximation (Eq. (15)). At the short time region this approximation reduces to Eq. (16) which, upon integration, leads to the well-known asymptotically exact relation (13a). At the long time legion Eq. (15) reduces to the linear driving model. A series of numerical tests has been performed and their results are discussed. The aim of these computations was to compare the accuracy of the presented approximation with the results of analogous existing equations [12-14]. These tests were carried out for the cases of negligible (Bi-->infinity) and finite (Bi

Keywords:PARABOLIC PROFILE APPROXIMATION;INTRAPARTICLE DIFFUSION;ADSORPTION