13C and 1H NMR measurements to investigate the kinetics and the mechanism of acetic acid (CH3CO2H) ionization as a model for organic acid dissociation dynamics for polymeric membrane water filtration

The formation of ionic charge carriers and their transport in acetic acid (CH3COOH): water mixtures have been investigated by 13C and 1H NMR. The obtained dissociation constant from the NMR measurements is close to pKa = 4.70 in a highly diluted system which is in full agreement with literature values. The maximum molar concentration of ions (H3O+ and CH3COO−) is found at a water mole fraction around 0.5 to 0.6. Remarkably, minima in the molecular diffusion coefficients and ionic mobility are observed at this concentration. Ionic concentrations, ionic strength and the pH curve were obtained for any water content based on the 13C and 1H NMR as well as pH measurements and the numerical calculations. The data is relevant for the understanding and optimization of the properties of polymeric nanofiltration membranes for organic ion removal. They provide interesting insight into the water dependence of the viscoelastic and kinematic properties, the charge formation mechanism and the dissociation limit, especially for highly diluted systems simulating the case of ionic pollutants.