Antisolvent crystallization of aqueous ammonium dihydrogen phosphate solutions by addition of methanol

Experimental results of antisolvent crystallization of ammonium dihydrogen phosphate from their aqueous solutions saturated at 30 °C by addition of methanol at preselected feeding rate RA, studied by in situ measurements of laser beam intensity I transmitted through solutions and their temperature T as functions of feeding time t for methanol at rate RA, are described and discussed. It was found that (1) measurement of temperature of solutions during antisolvent feeding is more informative and is more reliable than transmitted laser beam intensity measurements, (2) there are two regions of methanol feeding durations involving endothermic reactions and one region involving exothermic reactions, (3) the data of metastable zone width determined from the values of maximum antisolvent content Δxmax calculated from methanol feeding duration are reliable when the temperature difference ΔT=Ts−Tw, where Ts and Tw are temperatures of solution and water, respectively, for theoretical analysis, (4) rates ΔT/Δt of linear changes in temperatures of solution and water with methanol feeding time t increases with feeding rate RA, and (5) the maximum changes ΔTmax in the temperature of solution and water are related to antisolvent content Δx associated with their appearance. It is argued that feeding of antisolvent methanol to saturated solutions or water leads to chemical reactions with evolution of heat.