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

Abstract

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 RA. It is found that the value of MSZW, as determined by the value of the maximum antisolvent content Δxmax, for a given RA decreases with decreasing dielectric constant εa of the antisolvent. The experimental Δxmax(RA) data for different antisolvents are analyzed by using two dependences: lnΔxmax) = Φ + (1/m)lnRA) and (Δxmax)−2 = F(1−ZlnRA), 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 Δxmax(RA) data revealed that: (1) the empirical constants Φ and m increase linearly with εa−1 of the antisolvents, and (2) Φ = −lnF/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.