Reaction in ion-exchangers: characterization of the ethylenediamine protonation equilibrium in a sulfonic membrane devoted to carbon dioxide facilitated transport

A method of characterization of the protonation equilibrium of ethylenediamine (EDA) in a cation-exchange membrane is propounded. This method involves an intermediate reaction of the membrane (initially in the mixed EDAH⁺EDAH₂²⁺ form) with gaseous carbon dioxide then the elution and the titration of the carbamic acid formed. This method is more precise and is preferred to the conversion of the sorbed EDAH⁺ and EDAH₂²⁺ into EDA by sodium hydroxide followed by an acidic titration. The selected method allows to calculate accurately the apparent equilibrium constant K^∗ of the protonation of EDA in the membrane and is very useful to characterize the carrier (EDAH⁺) content of membranes conditioned to achieve facilitated transport of carbon dioxide. The data obtained will be used in an improved analysis of this transport process.