Crystallization of RDX by Drowning-Out Combined with Fines Dissolution and Cooling Process

A new process of drowning-out combined with fines dissolution and cooling crystallization (the DFC process) was proposed to recover 1,3,5-trinitro-1,3,5-triazinane (RDX) from RDX/gamma-butyrolactone solution with relatively large crystal size and high yield. In this process, fine crystals induced by drowning-out are dissolved into the solution by heating so that the dissolved solute can contribute to grow seed crystals by cooling. The DFC process is repeated to reach the desired yield. Estimation of the amount of antisolvent for drowning-out is made by a simple mass balance model in which the mass of fine particles produced by drowning-out equals to that dissolved. Considering dissolution of seeds at the fines dissolution stage, an empirical parameter alpha which is smaller than 1 was employed for the estimation of the optimum amount of antisolvent added. alpha = 1 indicates that effect of dissolution of seeds is negligible. In the present work, initial seeds were prepared by rapid injection of 15 g of water into a saturated RDX/gamma-butyrolactone solution of 30 degrees C. Heating temperature for fines dissolution and cooling temperature for further crystal growth were 40 and 20 degrees C, respectively. In those operating conditions with alpha = 0.8, the average crystal size of RDX with the yield of 90% was 67.6 mu m, which was a remarkably improved result when compared with that of 40.4 mu m by drowning-out only.