Study On The Crystal Habit Control And Green Crystallization Process Of Nitroguanidine

Nitroguanidine is commonly used in fields such as energetic materials and organic synthesis,and has a large market demand.At present,industrial products of nitroguanidine are mainly needle-shaped,and there are problems in poor flowability and low bulk-density,which leads to difficulties in production and processing operations and poor product performance.Therefore,the precise regulation of the crystal habit of the nitroguanidine crystal product is of great significance for its post-crystallization process and particle properties.At the same time,due to the serious environmental problems in most of the recrystallization processes of high-quality nitroguanidine,the systematical research on the crystal habit control of nitroguanidine in aqueous solution was carried out to develop a green crystallization process of nitroguanidine.It's a disadvantage in industrial production that the needle-shaped nitroguanidine crystals prepared from aqueous solution possess poor flowability and low bulk-density.To eliminate the inferiority in product quality,firstly,several suitable additives were screened out and nitroguanidine crystals with diverse habits were successfully prepared,such as the needle,rod,sheet and block.Secondly,online monitoring technology was used to identify the inhibitory effects of the additives on the nucleation and growth of nitroguanidine,and then combining crystal habit prediction with crystal face analysis,the effects of additives on the crystal habits of nitroguanidine,was explained from a molecular perspective,that the inhibitory effects on different crystal surfaces were diverse because of the different groups exposed.Subsequently,the block nitroguanidine product was optimized by controlling temperature and stirring speeding.From the perspective of powder properties and thermal stability,the effects of different crystal shapes on the properties of nitroguanidine products were analyzed,and the bulk-density was successfully increased from 0.28 g/cm~3 of the needle-shaped crystals to 0.95 g/cm~3of the block crystals.Finally,the crystallization process of high bulk-density nitroguanidine product in aqueous solution with a small amount of the soluble additive was developed,which solved the problems of too large amount of additives used and the difficulty on the dissolution process in the previous investigations.In order to further improve the flowability of the nitroguanidine products prepared from aqueous solution,firstly,the micron-sized nitroguanidine spherulites were prepared in aqueous solution by rationally selecting additives,and the environmental problems existing in the current crystallization processes of nitroguanidine spherulites resulting from using toxic organic solvents were avoided in this study.Secondly,the effects of additives,agitation and temperature on the crystallization of nitroguanidine spherulites were investigated from the aspects of chemical factors and process factors,and the formation mechanism of nitroguanidine spherulites through noncrystallographic branching was analyzed.Subsequently,comparing all the nitroguanidine crystals with different habits prepared in this study,the angle of repose of the products is reduced from 82 ~o of the needle crystals to 36 ~o of the spherulites,while the activation energy of the thermal decomposition process of the spherical nitroguanidine crystals is 66%higher than the needle crystals,which fully demonstrates the spherulites possess the best flowability and thermal stability.Finally,the green crystallization process of compacted nitroguanidine spherulites was realized in this study,and the flowability and thermal stability of the product was greatly enhanced.