Utilization of FBRM and PVM to analyze the effects of different additives on the crystallization of ammonium dihydrogen phosphate

•On-line analysis of ammonium dihydrogen phosphate crystallization using the FBRM and PVM technologies.•Observing the effect of stirring speed, feeding rate and supersaturation level on the CLD of ammonium dihydrogen phosphate.•Monitoring the influence of KNO3 and a new chelating agent on ammonium dihydrogen phosphate crystallization process.•Determination of nucleation and crystal growth rates of ammonium dihydrogen phosphate crystals. The purpose of this study is to determine the effect of feeding rate, supersaturation level, stirring speed and the additives such as potassium nitrate (KNO3) and a new chelating agent (NCA) on the chord length distribution (CLD) as well as the crystal form of ammonium dihydrogen phosphate (MAP). The MAP crystals’ growth is investigated by using the FBRM G400 and the PVM V19 probes respectively in an MSMPR (Mixed Suspension Mixed Product Removal) crystallizer. Herein, the FBRM ensures an on-line determination of the CLD, which is expressed as the cumulative undersize square-weight percentage distribution of MAP crystals. CLD is statistically proportional to crystal size distribution. The PVM ensures the real-time monitoring of crystal morphology. In addition, an optical microscope is used to characterize the shapes of the crystals obtained in the MSMPR crystallizer. The chemical structures of the crystals are characterized by Fourier transform infrared (FT-IR) analysis. The population density of the nuclei, the nucleation rate, and the growth rate of the MAP crystals are also calculated. Industrial problems encountered in the production of MAP crystals, such as filtration and small crystal size, are eliminated especially in the presence of KNO3 and 1% NCA, which is proved by FBRM, PVM and number density theory application.