THE COUPLING EFFECT OF THE THERMODYNAMIC SWELLING PROCESS IN PERVAPORATION

In order to analyze the coupling effect in thermodynamic swelling proc ess, the relationship between the activity and volume fraction of each component within membrane was defined as alpha(i)(m) = gamma(i)(m) ph i(i)(m). The concept of reference state in thermodynamic swelling proc ess which only considered the interaction between individual component and membrane matrix was also set up. The difference of activity coeff icient of each component within the membrane from reference state refl ected the contribution of coupling effect to thermodynamic swelling pr ocess. For chitosan and H2SO4 crosslinking chitosan membrane the influ ence of coupling effect on selectivity of H2O in thermodynamic swellin g process could be described from distribution coefficients and compet ition distribution coefficients of H2O and EtOH successfully. The inte raction between H2O and the membrane matrix dominated the activity coe fficient of H2O within the membrane, and the coupling effect between H 2O and EtOH within the membrane only had a little influence on the act ivity coefficient of H2O. However, the activity coefficient of EtOH wa s dominated strongly by the coupling effect between H2O and EtOH withi n the membrane. This was attributed to the large amount of H2O present in the membrane. The distribution coefficient of EtOH, k(2)(m) and co mpetition distribution coefficient of membrane k(12)(m) directly deter mined the selectivity of H2O in thermodynamic swelling process and the coupling effect between H2O and EtOH within the membrane had a negati ve influence on the selectivity of H2O within the membrane. (C) 1998 E lsevier Science B.V.