A New Model for the Simulation of Ion Exchange Equilibria

A perfectly mixed batch reactor was used for the determination of the intraparticle diffusivities of Na + and K + on commercial Amberlite IR-120 resin in different solvents: water and solvents composed of different percentages of water and methanol, water and ethanol, and water and 2-propanol. A theoretical model was developed to describe the response of the system that includes the resistance to mass transfer inside the particle and the effect of the electric field (NernstPlanck approximation). Equilibria were described using a homogeneous model based on the mass action law in which nonideal behavior for both the solution and the solid phase was taken into account. Simulations were performed to analyze the effect of the model parameters on the response curves. The values of intraparticle diffusivities of Na + and K + were obtained by nonlinear regression. Both the regression and the parameters were highly meaningful from the statistical point of view. A simple dimensionless relationship that relates diffusivity (through the Schmidt number) to different physical properties of solvents (namely, viscosity, dipolar moment, and density) and resin swelling was found.

Section: Introductionmentioning

confidence: 99%

Determination of Intraparticle Diffusivities of Na⁺/K⁺ in Water and Water/Alcohol Mixed Solvents on a Strong Acid Cation Exchanger

Rodríguez

Lucas

Leal

et al. 2002

“…In this work we present an equilibrium model which can be applied to all amino acids and accounts for variable selectivities. This is based on, besides the dissociation equilibria in the aqueous phase, a recently developed model for ion exchange equilibria (Melis et al, 1995). This model accounts for the heterogeneous nature of the ion exchanger, as the Myers and Byington (1986) model, while it describes the exchange equilibrium of every single site through the law of mass action.…”

Section: Introductionmentioning

confidence: 99%

Ion-Exchange Equilibria of Amino Acids on a Strong Acid Resin

Melis

Markoš

Cao

et al. 1996

Self Cite

The exchange equilibria of several amino acids, with particular emphasis on those displaying two basic groups, on a strong-acid cation exchange resin (Amberlite IR120) are investigated. The behavior of the experimental data is described through a mathematical model which takes into account the dissociation equilibria of amino acids in aqueous solution, the electroneutrality condition, and an ion-exchange isotherm recently proposed in the literature. In the latter, by assuming ideal behavior for both the solution and the solid phase, the exchange process is treated on the basis of the mass action law, while the existence of a distribution of two types of functional groups with different energies is assumed in order to describe the resin heterogeneity. The developed model is then used in order to satisfactorily correlate binary uptake data and to predict with good accuracy the uptake of amino acids in multicomponent systems.

“…Equation does not provide a selectivity of the resin toward different counterions, as usually found in ion-exchange models . As anticipated, in fact, in IEC applications, the main counterion in solution is the same as that exposed by the resin and no ion-exchange occurs; therefore, no such a selectivity is required.…”

Section: Model Equationsmentioning

confidence: 89%

Ion Exclusion Chromatography: Model Development and Experimental Evaluation

Lodi

Storti

Pellegrini

et al. 2017

Self Cite

Ion exclusion chromatography (IEC) is a separation technique used both at analytical scale for the simultaneous determination of ionic species and at preparative scale for the separation of strong electrolytes from weak electrolytes and nonelectrolytes. In this work, a column model for IEC is developed and evaluated by comparison with experimental data. The model explicitly takes into account the Donnan equilibria responsible for the exclusion of electrolytes from the resin pores. At the high electrolytes concentrations typical of preparative scale separations, resin shrinking becomes an important factor, affecting the variation of inter-and intraparticle void fractions. The effect of the electrolytes concentration on resin shrinking has been experimentally studied, and the volumes variation was included in the model equations. At the analytical scale, the proposed model is able to predict the effect of electrolytes concentration on the extent of exclusion from the resin pores and the influence of the degree of dissociation of weak electrolytes on their retention time. At preparative conditions, discrepancies between the experimental data and simulations results are observed for divalent salts. Since such discrepancies arise at the largest concentrations, they have been imputed to the main model assumption of ideal thermodynamics.