Crystallization of HMX in acetone-water system

Cyclotetramethylene-tetranitramine (HMX) is prepared by continuous nitrolysis of hexamine using nitric acid and ammonium nitrate in the presence of acetic anhydride and acetic acid. HMX obtained after nitrolysis contains RDX and some nitro compounds as impurities. It is purified by evaporative crystallization technique using acetone as the solvent. In this work a ternary system consisting of HMX as the solute, acetone as solvent and water as anti-solvent was studied in order to obtain solubility data and influence of different parameters viz. percentage recovery of solvent, stirrer speed, cooling rate, and rate of recovery of solvent on the crystal size distribution (CSD) of HMX. The crystal morphology was also studied by using scanning electron microscope (SEM). The CSD of HMX obtained by using acetone-water mixture is compared with the CSD obtained by using acetone as solvent. It has been observed that under similar conditions of crystallization, crystals obtained from acetone-water mixture are smaller than those obtained from acetone. Also, the crystals obtained from acetone-water system are more regular ill shape and have smooth surfaces.