Crystal Morphology Manipulate Of HMX Based On Membrane Crystallization Technology

To date,the simultaneous achievement of crystal characteristics control and environmentally benign is challenging the formulation processing of energetic materials（EMs）manufacturing.The crystallization methods（evaporation,antisolvent and cooling,etc.）of the conventional explosive are difficult to accurately control the uniformity of supersaturation and the low solvent recovery rate.With the advantages of precisely regulating supersaturation and relatively low energy input,membrane crystallization（MCr）technology provides a potential solution for the“green”development of EMs by coupling membrane separation technology and crystallization process.Firstly,aiming at the above problems,this paper designs an organic solvent nanofiltration（OSN）membrane crystallization apparatus based on pressure-driven and cross-flow filtration and is used to study on the crystal morphology manipulate of 1,3,5,7-tetranitro-1,3,5,7-tetrazacyclooctane（HMX）.Combing with the properties of HMX and nanofiltration membrane,DM200 series nanofiltration membrane and acetonitrile（ACN）solvent system were selected.The solubility and metastable zone width of HMX in ACN are experimentally measured.The results show that with the increase of temperature,the solubility increases gradually,while the metastable zone width gradually narrows.Secondly,the effects of key process parameters（temperature and pressure）on the crystal morphology and particle size were discussed,and the properties of HMX crystals recrystallized by MCr and evaporation crystallization（ECr）were characterized and compared.The long-term operation stability of nanofiltration membrane was further investigated,and the solvent recovered by permeation was recrystallized again.The long-term operational stability of the nanofiltration membrane was further investigated,and the solvent recovered by permeation was used to re-crystallized.The results show that compared with ECr,MCr has the advantages of strengthening supersaturation manipulation and preparing high-quality crystals.After repeated use,the nanofiltration membrane showed good permeation selectivity stability,indicating that this technology can realize the efficient recovery and utilization of the solvent.Finally,the above MCr process was optimized,and a membrane-cooling coupled crystallization（MCr-CCr）with complete solvent recovery is demonstrated for the preparation of 1,3,5,7-tetranitro-1,3,5,7-tetraazacyclooctane（HMX）crystals with high sphericity and controlled sizes.The permeate flow rate,cooling rate and feed flow rate are found to be the key process parameters in MCr-CCr that determine the supersaturation,seeds number and population density,which collectively dictate the morphology and sizes of the crystalline products.The L₉（3⁴）orthogonal experiment indicates that the influential order of the aforementioned three parameters varies with the evaluation indicators（means size and coefficient of variation）.Combing the growth kinetics parameters that was estimated by the population balance equation（PBE）under the optimal conditions with the in-process sampling morphology analysis,the formation mechanism of spherical HMX was revealed by the agglomeration-dissolution mechanism.The agglomeration period is the key to improve the crystal size,and the shaping period（dissolution and abrasion）can significantly improve the sphericity.This novel MCr process can prepare spherical HMX with high purity（>99.5%）and high bulk density(1.17 g·cm^-3),which provides an efficient,green and sustainable new crystallization route for EMs.