Taylor dispersion is used to measure ternary mutual diffusion in aqueous citric acid(1) + calcium citrate(2) solutions at 25 deg.C. Main diffusion coefficients D11 and D22 reach values 25% to 60% larger than the respective binary diffusion coefficients of aqueous citric acid and calcium citrate. Of additional interest, cross-coefficient D12 is large and negative, indicating that each mole of diffusing calcium citrate counter-transports up to two moles of citric acid. Nernst-Planck (NP) equations are used to relate the fluxes of the citric acid and calcium citrate components to the fluxes of the solution species: molecular citric acid (H3Cit) and its dissociation products (H+, H2Cit-, HCit2- and Cit3- ions), Ca2+ ions, and calcium complexes produced by ion association (CaCit-, CaHCit, CaH2Cit+). The NP analysis identifies key roles in the coupled diffusion of citric acid and calcium citrate played by ion association and by ion migration in the electric field generated by hydrogen-ion concentration gradients.
Compounds
#
Formula
Name
1
C6H8O7
citric acid
2
C12H10Ca3O14
calcium citrate
3
H2O
water
Datasets
The table above is generated from the ThermoML associated json file (link above).
POMD and RXND refer to PureOrMixture and Reaction Datasets. The compound numbers are included in properties, variables, and phases, if specificied;
the numbers refer to the table of compounds on the left.