Comment from editor :

It seems that there are basic mistakes in the modeling approach, both in the balance equations and in the boundary conditions. According to Figure 1, there is a longitudinal (axial) flux of liquid through the absorption unity (this is also confirmed by the use of equation 7 - Ergun equation - to calculate the pressure drop along the direction of the flow).  However, the balance equations (3) and (4) does not include the term corresponding to the axial flux of mass. All transport in the axial direction is represented by the diffusion/dispersion term, which is wrong. Regarding the boundary conditions adopted, they are also strange. For the problems in which flow and dispersion/mixing/diffusion occurs in the axial directions, the appropriate boundary conditions are the so-called Danckwertz boundary conditions. The authors imposed as boundary conditions (section 2.3) that T(0,t)=Tinlet and T(L,t)=Toutlet. Although this is possible, this choice makes the model less useful, because the exit condition must be known a priori to set the boundary conditions at z=L. It is more useful id the exit conditions are calculated (predicted) by the model, instead of the need to be known a priori. In general the usefulness of a model is to predict the exit conditions.