Erik Högfeldt

On the properties of solid and liquid ion exchangers—VII: A simple model for the formation of mixed micelles applied to salts of dinonylnaphtalene sulfonic acid

In previous papers in this series it was found[1,2] that ion exchange and water sorption data for dinonylnaphtalene sulfonic acid (HD) in various solvents could be fitted by the expression Y=y1X+y2(1-X)+y′2X(1-X) Y is the property studied and yi the same property related to three kinds of micelles, those corresponding to the pure salts (y1 and y2) and mixed micelles containing both ions (y′3). X is the equivalent fraction of metal ion in the organic phase the H+Me2+ exchange being studied. In the present paper it is shown that if it assumed that the distribution of ions over the three kinds of micelles is random the quantities in eqn (1) can be given a simple physical interpretation.

Ten years experience of a simple three-parameter model to fit ion exchange data

Abstract The application of the Hogfeldt three-parameter model to ion exchange data is reviewed. The few cases where it does not work are also mentioned. The model is simple and straightforward to use, and it compares favorably with more elaborate methods for treating weak-acid and complex-forming resins.

Influence of counterion concentration on the ion-exchange equilibria of crosslinked weak-acid polyelectrolyte gels

Abstract The sensitive response of weak-acid ion exchangers to counterion concentrations in the aqueous phase has been attributed to a Donnan potential term. By correcting for this term a constant p K ina has, in a number of cases, been resolved for the repeating unit at each point of their titration with base. It has been suggested that this approach leads to the resolution of the intrinsic p K ina of the weak-acid functionality repeated in these ion exchangers. In other cases, however, this approach has not led to a constant p K ina. An error in the Donnan term introduced by macroporosity of these exchangers has been suggested as the source of this incongruity. A method based on the premise that the Donnan term is uniquely responsible for the variability of the uncorrected p K ina has been outlined and shown to give a satisfactory result.

Influence of counterion concentration on equilibria and conformational properties of linear weak-acid polyelectrolytes

Abstract Since linear, weak-acid polyelectrolytes respond to neutral salt just like their crosslinked analogs, their equilibria have been presumed to be as amenable to analysis with the Gibbs-Donnan approach as the gels. To examine this possibility this approach has been used to estimate solvent uptake by carboxymethyldextran and poly(acrylic acid) in the course of their neutralization with standard base. These estimates have been compared with estimates obtained for the same parameter by using the ion-condensation model of Manning.

On the properties of solid and liquid ion exchangers—IV: Thermodynamic and IR-investigation of the hydration of dinonylnaphthalene sulfonic acid in heptane

Abstract Water sorption, heat effects and IR spectra have been studied as a function of water activity for dinonylnaphthalene sulfonic acid (HDNNS) dissolved in heptane. The water sorption data have been interpreted in terms of a set of simple equilibria HDNNS + n H , 2 O ⇌ HDNNS ( H 2 O ) n with the equilibrium constants and species given in Table 1. The heat data have been fitted with the same species and the ΔH°-values given in Table 2 together with the entropy values obtained from a combination of heat and free energy data. The large negative entropy values indicate strong ordering effects in the HDNNS-micelles. The infrared data also indicate that in the HDNNS-aggregates the water is more structurized than in resinous cation exchangers of the polystyrene sulfonic acid kind. They also give some information about the first steps of the hydration process beginning with a break up of the HDNNS-aggregates followed by the formation of hydronium sulfonate. Upon the addition of further water molecules this highly symmetric structure is destroyed.

On the properties of solid and liquid ion exchangers–VI Application of a simple model to some ion exchange reactions on dinonylnaphtalene sulfonic acid in different solvents and for different cations with heptane as solvent

Abstract A simple model assuming three kinds of micelles has been applied to the K + H + exchange on dimonylnaphtalene sulfonic acid (HDNNS) in the solvents: chloroform, carbon tetrachloride, nitrobenzene and isooctanol, to the Ca 2+ H + exchange in heptane, nitrobenzene and isooctanol. In heptane the following exchanges were also studied: Ag + H + , Cu 2+ H + , Ni 2+ , Fe 3+ H + and Al 3+ H + . Also the water uptake was studied for Ca 2+ H + and K + H + in nitrobenzene as solvent. The three parameters, found to fit each system are collected in Table 2. At present no simple rationalization of these constants seems possible.

The use of the hammett acidity function, H0, for estimating the hydrogen ion concentration in acids

A method is described where the hydrogen ion concentration in acid solutions is evaluated from H0-data. For CF3COOH, good agreement is found between this and the NMR methods below 6 M. For the acids HF,CH2ClCOOH and CHCl2COOH, pK-values in rather good agreement with those in the literature are obtained. Application to HCl and HBr gives the following tentative K-values for these acids: 1·05 < log KHCl < 2·60; 27·15 < log KHBr < 4·65 Only upper and lower limits can be given for K because of the difficulty in making a sound extrapolation to pure water. It has also been found that, because of a large variation of the activity coefficient of the undissociated acid, Raoults law cannot be used for estimating its concentration in aqueous solutions of strong acids.

ON THE PROPERTIES OF SOLID AND LIQUID ION EXCHANGERS X. ION EXCHANGE, WATER UPTAKE AND AGGREGATION OF SALTS OF DINONYLNAPH- THALENE AND DIDODECYLNAPHTHALENE SULFONIC ACIDS

ABSTRACT Ion exchange, water uptake and VPO studies have been performed on the two liquid cation exchangers, dinonylnaphthalene and didodecylnaphthalene sulfonic acids and some of their salts. It is found that didodecylnaphthalene sulfonic acid is slightly less aggregated than dinonylnaphthalene sulfonic acid, its water uptake is also less, but the selectivity is about the same. In heptane the presence of water increases the aggregate size, in benzene this increase is smaller and in chloroform no increase is observed. It is also demonstrated that in the concentration range used, the size of a certain aggregate is practically constant. It has been possible to follow the change in aggregate size during the ion exchange process for the system Al3+ - H+. The fact that the three parameter model applies suggests that the interactions at an exchange site are practically independent of aggregate size.

On the properties of solid and liquid ion exchangers—V: The potassium-hydrogen exchange on dinonylnaphthalene sulfonic acid in heptane in the temperature range 1–80°C

Abstract The potassium-hydrogen exchange on dinonylnaphthalene sulfonic acid dissolved in heptane has been studied in the temperature range 1–80°C using batch techniques and titrimetric analysis. The data can be fitted with a simple model, where it is assumed that the system contains three kinds of micelles, HDNNS-micelles. KDNNS-micelles and a mixed micelle (K. H)DNNS each with a different ion exchange constant. The relation between the experimental value for the equilibrium quotient (κ) and the three parameters κ 1 , κ 2 and κ 3 is log κ= X log κ 1 +{l− X } log κ 2 + X (l− X ) log κ 3 where X is the mole fraction of potassium in the organic phase, i.e. the distribution of micelles is assumed to be statistical. From the curves log κ( 1 T ) x the function ΔH( X ) is obtained at each temperature. These data can be fitted with the same model i.e. δH ° =δH 1 ° X +δH 2 ° (1− X )+δH 3 ° X (1− X ) Together with the free energy data ( ΔG ° = − RT ln κ ) entropies are computed for the three kinds of micelles. It is found that while the two pure micelles have negative entropy changes, the mixed micelle has a positive entropy change, provided the assumptions inherent for the equation above are correct. The mixed micelle concept also explains the water extraction in the system HDNNS-KDNNS in heptane as shown for data at 25°C.

On the extraction of water from sulphuric acid solutions into tri-n-butyl phosphate

Abstract Using dilute solutions of TBP (1–5 per cent) in kerosene and in benzene (1 per cent), a maximum in the amount of water extracted from sulphuric acid solution is obtained at about 5 M H2SO4. This behaviour can be explained by assuming the following main reaction: TBP(org) + 2H+(H2O)4(aq) + SO42−(aq) ⇌ TBP·(H2O)8·H2SO4(org) with an equilibrium constant of ∼10−2 in kerosene. However, other compositions for the hydrated protons cannot be excluded, e.g. H+(H2O)5 and H+(H2O)3. At somewhat higher concentrations of TBP (7·5–10 per cent) in kerosene the main reaction seems to be TBP(org) + H2O(aq) ⇌ TBP·H2O(org) in the range 2·5 M ⩽ [H2SO4]aq ⩽ 6 M, with an equilibrium constant of ∼10−1. For each dilution of TBP in kerosene the amount of acid extracted per mole of TBP tends towards a limit of several moles of H2SO4 per TBP, the number increasing with the dilution of TBP.