Equilibrium Constants of Pyridinecarboxylic Acid Sorption from Aqueous Solutions by Dowex 50 Cation Exchangers

The sorption of 2-pyridinecarboxylic, 3-pyridinecarboxylic, and 4-pyridinecarboxylic acids by polystyrene sulfonic acid type cation exchange resin Dowex 50W-X8 and Dowex 50W-X4 from aqueous solutions was studied. Based on the analysis of the FT-IR spectra of acids, sulfates of their protonated forms, and an acid-saturated cation exchange resin, it was shown that pyridinecarboxylic acid is in the protonated form in the cation exchange phase. The equilibrium constants of sorption proceeding with participation of pyridinecarboxylic acid, sulfonic cation exchange resin, and proton were calculated according to experimental data on the equilibrium distribution of acids in the aqueous solution–cation exchange resin system. The values of the equilibrium constant of the cation exchange of the sulfonic ion-exchange resin proton by the pyridinecarboxylic acid cation from solution lie in the range 3.2–4.4. The equilibrium constants of sorption of 2-pyridinecarboxylic acid molecules are 25 dm 3 mol –1 , they increase to 195–220 dm 3 mol –1 for 4-pyridinecarboxylic acid, and reach 320–330 dm 3 mol –1 for 3-pyridinecarboxylic acid. Changing the amount of the cross-linking agent (from 4 to 8% divinylbenzene) in the polystyrene sulfonic acid type cation exchange resin does not significantly affect its sorption activity toward pyridinecarboxylic acids.