Estimation of Deprotonation Coefficients for Chelating Ion Exchange Resins. Comparison of Different Thermodynamic Model

Abstract

The deprotonation of quinolic resin P-127 and iminodiacetic resin Amberlite IRC-718 has been studied. The process of salt transfer into the resin phase is considered to be an important contributor to the deprotonation process. Estimation of the salt transfer was based on the principle of equal activity of the salt in both phases at equilibrium. Two assumptions were made: sorbed alkali metal ions are not associated with functional groups, while all hydrogen ions are associated with functional groups. The associated hydrogen ions and functional groups do not contribute to the internal ionic strength value. Two thermodynamic models, describing the deprotonation of ion-exchange resin, were used and compared: the Gibbs-Donnan-based model of Bukata and Marinsky and the model proposed by Erik Högfeldt. Thermodynamic characteristics of the resins' deprotonation are obtained using two different thermodynamic approaches. Högfeldt's three-parameter model provides a better agreement with experimental data. The fitting of the data to Marinsky's method can be improved by taking into account the influence of the resins' macroporosity; however, this requires an additional empirical parameter to describe the resin.

Gibbs–Donnan and specific-ion interaction theory descriptions of the effect of ionic strength on proton dissociation of alginic acid

“…In contrast to the SIT model, the Gibbs-Donnan approach can also be used for the simultaneous description of the dependence of pK Ã on I and a, provided that the variation of pK Ã ðaÞ is properly accounted for [43,47].…”

Ion Exchange and Protonation Equilibria of an Amphoteric Ion-exchange Resin in the Presence of Simple Salt

“…The influence of simple salts on the ion exchange and protonation equilibria of an amphoteric ion-exchange resin, which has strong base and weak acid moieties in a single functional group fixed onto the styrene-DVB matrix, has been investigated. Concentrations of ionic species in the amphoteric ion-exchange resin in equilibrium with various sodium salt solutions were estimated by 23 Na NMR spectroscopy. For the NaClO4 system, the ratio of sodium ion concentration in the resin phase to that in the equilibrium solution was greater than 1 and increased with a decrease in the salt concentration.…”

“…According to the conventional analysis, [22][23][24] the Donnan distribution term, log([Na + ]/[Na + ]), can be assumed to be zero at zero protonation degree, which means that the proton concentrations are the same between the resin phase and the equilibrium solution. If this assumption was valid in the present systems, the logarithm of the intrinsic acid dissociation constant of the functional group, log KH, could be evaluated by the extrapolation of the log Kapp values to the zero protonation degree.…”

“…We should evaluate the intrinsic acid dissociation constant of the functional group according to Eq. (8) using the Donnan distribution terms estimated by the 23 Na NMR method. The estimated log KH values for the NaClO4 system were 2.5 (I = 0.1), 2.8 (I = 0.5) and 2.9 (I = 1.0).…”

“…We have already shown that NMR spectroscopy provides unique methods for probing the adsorbed species and for elucidating the solution environment inside the resin phase. [9][10][11][12][13] In the present study, the concentrations of ionic species in the amphoteric ion-exchange resin in equilibrium with various sodium salt solutions were estimated by 23 Na NMR spectroscopy. On the basis of this information, we elucidated the ion exchange and protonation properties of the amphoteric ion-exchange resin in the NaCl and NaClO4 solutions.…”