Semi-batch reactive crystallisation of mono-ammonium phosphate: An experimental study

NH4H2PO4, mono-ammonium phosphate (MAP) and (NH4)2HPO4, di-ammonium phosphate (DAP) have become leading phosphate fertiliser products worldwide. Ammonium phosphates are produced by reactions of ammonia and phosphoric acid resulting in the formation of the mono-basic, di-basic, or tri-basic salts. Inefficiencies in the MAP/DAP production process are due to the lack of a fundamental understanding of the crystallisation–reaction mechanisms. A semi-batch reactive crystalliser equipped with a cooling jacket, a dual feed system and a turbine type agitator has been used in this study. Effects of N/P ratio, seed crystals, feeding system, feed flow rate, initial supersaturation, feeding time and mixing intensity to the real-time supersaturation, crystal yield, crystal shape (aspect ratio) and final crystal size distribution (CSD) were studied in order to understand the kinetics. This study aims to provide new insights into the MAP/DAP reaction–crystallisation mechanisms.