THERMODYNAMICS OF PERVAPORATION PROCESS IN REACTING SYSTEMS
Advancing the chemical engineering fundamentals
Thermodynamics (T2-1P)
Keywords: thermodynamics, membrane, pervaporation, reacting systems, nonequilibrium processes
Pervaporation is one of the main membrane separation processes with a great advantages for the industrial application. The most widely utilized mode of operation is a vacuum pervaporation when the pressure gradient in membrane system exists. Because of it the pervaporation system should be considered as nonequilibrium system; accordingly the capacity of the use of classical thermodynamic methods (equilibrium approach) is rather limited. In the case of reacting systems the complexity of the analysis of pervaporation process increase. Nevertheless thermodynamic methods combined with kinetic approach and nonequilibrium theory give good opportunities for the analysis of such complex systems. In presented paper some aspects of thermodynamic theory of pervaporation and its application to reacting systems are considered.
Nonequilibrium approach for the thermodynamic analysis of membrane process including pervaporation is well-known. Kedem (1986) was one of the first who introduce some elements of nonequilibrium thermodynamics in the theory of pervaporation. First of all the theory was applied for the description of the coupling between fluxes. Unfortunately the further development of the thermodynamic theory of pervaporation was not so intensive and only few works of last decade were based on nonequilibrium thermodynamic approach.
Our consideration of pervaporation in reacting systems is based on the combined thermodynamic and kinetic method with the use of nonequilibrium theory. For the small fluxes (usual for the pervaporation) and the fast reaction the feed solution can be considered as a system in a chemically equilibrium state. Accordingly the residue curve map of reactive pervaporation process (similar to simple distillation of reactive mixtures) may be presented with the use of transformed concentration variables (Zharov, 1970, Barbosa and Doherty, 1987). For the fluxes we apply classical phenomenological equations (linear phenomenological laws). These equations are also used for the prediction of permeate compositions and the modeling of the process. In the case of low reaction rate additional parameters similar to Damköhler number can be taken into account.
The pervaporation process significantly depends on the nature of membranes and compounds of feed solutions. For example the sorption (the initial stage of pervaporation) can be considered as an equilibrium process if the rate of diffusion throw membrane is low. In this case the data on equilibrium sorption were applied for the analysis of membrane mass transfer. Some example will be given on the base of our experimental data.
The brief review of the data on reactive pervaporation and the analysis of further opportunity of application and advantages of the thermodynamic approach for the study of pervaporation process in reacting systems will be presented.
Presented Monday 17, 13:30 to 15:00, in session Thermodynamics (T2-1P).
