The Study On Crystallization Processes Of 2,2',4,4',6,6'-hexanitrostilbene

Hexanylstilbene(HNS)is an excellent heat-resistant explosive,which is broadly applied in aerospace and deep well oil production.Except ultrafine products,HNS crystals are almost needle like and in the form of thin strip obtained by solution crystallization,which are of great length-diameter ratio,low bulk density and mobility.Therefore,it hardly meet the needs of modern weapon system.And its applications or development as insensitive explosive have been hindered.As a result,the research on crystallization processes and the crystal technology about granulated HNS are of great significance both in theory and practice.In this study,the single crystal of HNS was produced in concentrated nitric acid,and its cell parameters were determined by X-ray diffraction.The vacuum habit and the important crystal faces in morphology of HNS were predicted by BFDH and Attachment Energy model embedded in molecular modeling software.The layer structures of seven solvents such as DMF and five additives such as OP-10,and the layers structure of HNS crystal face were constructed.The interaction energies between all the solvent layer,the additive layer and the crystal layer were calculated by molecular dynamics.The crystal habits of HNS in all above solvents and additives were predicted by the Modified Attachment Energy model.The non-bond interaction on {100} of HNS crystal was analyzed by PBC method.The results show that the key to control the crystal morphology of HNS is to locate the solvents and additives which can enlarge the normal non-bond force on {100} and restrain the growth of tip surface.The best organic solvent for HNS crystallization is N-methyl-pyrrolidone/chlorobenzene(NMP/PhCl)mixed solvent followed by DMF or N,N-dimethyl-formamide /acetonitrile(DMF/ACN)mixed solvent.The efficient additives are the polyoxyethylene surfactants such as Span 80 and OP-10.The solubilities of HNS in nitric acid and seven organic solvents were investigated by laser dynamic method.The solubility equations of HNS were obtained by correlation the empirical equation of Apelblat,CNIBS/RK.Surface tension and surface entropy factor were calculated in above solvents.The dissolved enthalpy,dissolution entropy and Gibbs energy change value of HNS in these solvents were estimated by the Van't Hoff equation.The crystallization metastable zone of HNS in five pure organic solvents such as DMF was studied.The results show that the solubilities of HNS in eight solvents are all increased with the temperature.The solvent with the largest solubility for HNS was 98% nitric acid,and the second was N-methyl-pyrrolidone.The smaller the solubility,the bigger the surface tension and surface entropy factor was.Crystal growth of HNS in the above-mentioned solvents are of spiral growth mode in the range of 25~115?.The kinetics of batch cooling crystallization of HNS in DMF and NMP/PhCl were studied.The process data such as crystallization solution concentrations,suspension densities and stirring intensities were determined and calculated at the sampling moment.The nucleation and growth rate equations are obtained by solved population balance equation.The results show that the Pre-exponential factor of growth rate and the activation energy of nucleation rate are similar in the DMF and NMP/PhCl.In DMF the activation energy of growth is larger than it in the NMP/PhCl.The effect of supersaturation on nucleation rate and in DMF is less than it in NMP/PhCl.Aiming at the crystal morphology and bulk density,the cooling and solvent-out crystallization technology of HNS was studied.Three better solvent systems and best additive,i.e.J3 were determined.The influences on the target of initial temperature of crystallization,cooling rate,rate of addition of anti-solvent,addition amount of additive,and ultrasonic were investigated.The results show that in nitric acid,hexagonal flat of HNS crystals were prepared by cooling crystallization,the granulated particles obtained by solvent-out crystallization and the combine method.The biggest crystal bulk density is 0.87g/cm3,the crystallization technology parameters are nitric acid concentration 90%,starting temperature 80?,cooling rate 0.3?/min,stirring rate 250 r/min,and water addition rate 0.1mL/min.In DMF,the long strip HNS crystals would occur by cooling crystallization,but fusiform-like blocky crystal can be prepared by employing0.75% J3 additives,the biggest crystal bulk density is 0.68g/cm3,the crystallization technology parameters arestarting temperature115?,cooling rate 0.3?/min and stirring rate 300 r/min.Like the status in DMF,long strip of HNS was obtained in cooling crystallization in NMP/PhCl,but the smooth fusiform blocky crystals with a bulk density of 0.77g/cm3 can be prepared by employing 0.75% J3 additives.The optimum crystallization process conditions are starting temperature 125?,cooling rate 0.3?/min and stirring rate 300 r/min.The crystallization craft of HNS by cyclic utilization of nitric acid is proposed which is practical for industrial amplification.The saturated solution of HNS in 95% nitric acid at the room temperature as the starting solution,on which the crude HNS was added at the ratio of 7g/100 m L and then was heated to 80?,maintained under constant temperature for 1h,then naturally cooled to room temperature,the crystals were filtered out,followed by wash and drying;3 portion filtrate and 1portion fresh 98% nitric acid were employed and HNS was added into it by the above-mentioned ratio.Cycle operation was operated.The crystal production is with the bulk density of 0.74g/cm3.In the present study,the HNS crystallization processes were researched systematically and comprehensively.The key technology for transforming HNS from needle like to granulated was developed.The best crystallization technology parameters for three solvents was determined.A crystallization scheme which is suitable for commercial cycle utilize of nitro acid was proposed.This experimental achievement is of great value for improving the behavior of HNS crystal and extending the application both in military and civilian fields.