Effect of addition of different antisolvents on the crystallization of aqueous ammonium dihydrogen phosphate solutions

The effect of addition of three different antisolvents (namely: methanol, ethanol and acetone) on the metastable zone width (MSZW) for the crystallization of ammonium dihydrogen phosphate (ADP) from their aqueous solutions saturated at 30°C is studied by in situ measurements of solution temperature T as a function of feeding time t of the antisolvents at preselected rate R A . It is found that the value of MSZW, as determined by the value of the maximum antisolvent content Δ x max , for a given R A decreases with decreasing dielectric constant ε a of the antisolvent. The experimental Δ x max ( R A ) data for different antisolvents are analyzed by using two dependences: lnΔ x max ) = Φ + (1/ m )ln R A ) and (Δ x max ) −2 = F (1− Z ln R A ), with constants Φ, m , Z and F , predicted by self‐consistent Nývlt‐like approach and an approach based on the classical three‐dimensional nucleation theory, respectively. Analysis of the Δ x max ( R A ) data revealed that: (1) the empirical constants Φ and m increase linearly with ε a −1 of the antisolvents, and (2) Φ = −ln F /2 and m = −2/ Z . The observations are discussed from consideration of solute−solvent and solute−antisolvent interactions. The results show that the parameter FZ for different antisolvents provides information of solute−solvent interfacial energy γ and diffusion processes.