Antisolvent crystallization of aqueous ammonium dihydrogen phosphate solutions by addition of acetone at different rates

Abstract

Results of an investigation of in situ measurements of laser‐beam intensity Is and Im transmitted through aqueous ammonium dihydrogen phosphate (ADP) solutions saturated at 30 °C and water, respectively, and temperature Ts of solution and Tm of water during feeding of antisolvent acetone at different rates RA, using an indigenously designed experimental setup, are presented and discussed. It was found that: (1) for the measurement of MSZW, defined as the maximum volume fraction of acetone content Δxmax in the solution, obtained from temperature measurements are more reliable than transmitted laser‐beam intensity measurements for solutions, (2) two minima ΔTmin1 and ΔTmin2 associated with endothermic reactions, separated by a maximum ΔTmax due to exothermic reactions appear in the plots of temperature difference ΔT = Ts−Tm against acetone feeding time t, and (3) in the ΔT(t) plots there are time intervals Δt of constant rates RT of increase in ΔT of aqueous ADP solutions, and these values of RT increase linearly with acetone feeding time rate RA. The experimental data on the observed dependence of MSZW on antisolvent feeding rate RA, the appearance of minima ΔTmin1 and ΔTmin2 and maximum ΔTmax and their dependence on RA, and the relationship between RT and RA are discussed from consideration of processes of nucleation and growth of crystallites.