Semibatch Reaction Crystallization for Scaled-Up Production of High-Quality CL-20/HMX Cocrystal: Efficient Because of Solid Dosing

CL-20/HMX cocrystal is one of the most promising energetic cocrystals, but scaled-up production was prevented by the large inherent solubility difference of 2,4,6,8,10,12-hexanitro-2,4,6,8,10,12-hexaazaisowurtzitane (CL-20) and 1,3,5,7-tetranitro-1,3,5,7-tetrazoctane (HMX) and, therefore, unacceptable CL-20 efficiency. Reaction cocrystallization (aka. reaction crystallization or slurry technique) has been extensively used as an efficient, straightforward cocrystallization screening method, but only few attempts at utilizing this method for scaled-up cocrystal production have been undertaken and none have realized its full potential. By utilizing solid dosing and process analytical technology, semibatch reaction cocrystallization (SBRC) provided the first scale-up of high-quality CL-20/HMX cocrystal with a particle diameter D(4,3) of 163 mm and a batch size of 100 g. The CL-20 recovery is 63%, which is over two times better than the theoretical recovery rate of the next best method (evaporation crystallization), and the crystal quality is comparable to crystals obtained from controlled antisolvent crystallization. It is shown that SBRC is a valuable crystallization technique for efficient scale-up of cocrystal systems whose coformers exhibit significantly different solubilities.