Fundamental Research On Seperation Process Of Nitrobenzaldehyde Isomers Via Solvent Crystallization

Nitrobenzaldehyde contains three isomers,o-nitrobenzaldehyde,m-nitrobenzaldehyde and p-nitrobenzaldehyde.They are all important chemical intermediates and widely used in medicine,dyes and other industries.The demand is very large in domestic and foreign market.At present,the m-nitrobenzaldehyde is mainly produced by nitration of benzaldehyde in the industry,and a small amount of o-nitrobenzaldehyde and p-nitrobenzaldehyde are produced at the same time where large amount of the m-nitrobenzaldehyde is obtained.Based on a wide range of uses and good market prospects,the separation of nitrobenzaldehyde isomers has become a hot research topic now.Nitrobenzaldehyde isomers can be separated by an adsorption-desorption process,distillation process,extraction process and chemical conversion process.However they all have shortcomings.Solvent crystallization as a low energy separation method can effectively compensate for the shortcomings of existing separation methods.The existing separation method and solvent crystallization separation combined,can achieve green safe separation.In this paper,the solid-liquid equilibrium of different systems was studied by low-energy and high-efficiency crystallization separation method.At the same time,the separation process of o-nitrobenzaldehyde-p-nitrobenzaldehyde and m-nitrobenzaldehyde-p-nitrobenzaldehyde was discussed.In this paper,the solubility data of o,m,p-nitrobenzaldehyde in ethanol,isopropanol,n-propanol,n-butanol,acetone,ethyl acetate,N,N-dimethylformamide(DMF),cyclohexane and toluene were measured by using isothermal dissolution method.The solubility data were correlated by Apelblat model,?h model,Wilson model and NRTL model.The results showed that the four models could be well correlated with the nitrobenzaldehyde solubility data,and Apelblat model provided better results than the other three models.In addition,the solubility data of o-,m-,p-nitrobenzaldehyde in mixed solvent(DMF+ethanol),(DMF+n-propanol)and(DMF+n-butanol)were determined.The Jouyban-Acree model,van't Hoff-Acree model and Apelblat-Acree model were used to correlate the experimental data.The calculated values were in good agreement with the experimental values,and the Jouyban-Acree model gave best correlation results.Furthermore,the preferential solvation parameters of nitrobenzaldehyde isomers in these three mixed solvents were obtained.When the content of DMF is 0?0.44 in DMF + ethanol and DMF + n-butanol system and the content of DMF is 0?0.5 in DMF +n-propanol system,the value of ?x1,3 is negative,The solute is solvated by ethanol,n-propanol or n-butanol.While when the content of DMF is 0.44?1 in DMF + ethanol and DMF + n-butanol system,and when the content of DMF is 0.5?1,0 in DMF + ?n-propanol system,the value of?x1,3 is positive,The solute is solvated by DMF.Based on the solubility data of the nitrobenzaldehyde in pure solvents and the mixed solvent,ethyl acetate and n-butanol were selected as the solvent for the separation of o-nitrobenzaldehyde-p-nitrobenzaldehyde and m-nitrobenzaldehyde-p-nitrobenzaldehyde mixtures.The solubility for ternary system of o-nitrophthalimide-p-nitrophthalimide-ethyl acetate at three temperatures of 278.15 K,288.15 K,298.15 K and m-nitrophthalimide-p-nitrophthalimide-n-butanol at three temperatures of 278.15 K,288.15 K and 293.15 K were measured by Schreinemaker's method,and the corresponding ternary phase diagrams were constructed.The solubility of ternary system was correlated by NRTL model and Wilson model,and the Wilson correlation results were better than NRTL model.Based on the phase diagram of the ternary system,the crystallization separation process of o-nitrobenzaldehyde-p-nitrobenzaldehyde mixtures was discussed.The amount of solvent added and the product yield were calculated from the ratio of raw materials.The solubility for ternary system of m-nitrophthalimide-p-nitrophthalimide-ethyl acetate and m-nitrobenzaldehyde-p-nitrobenzaldehyde-n-butanol at three temperatures of 278.15 K,288.15 K and 298.15 K were measured by Schreinemaker's method.The mutual solubilities were determined and the corresponding phase diagrams were constructed.The NRTL model and the Wilson model were also used to correlate the experimental data.From the calculation results,NRTL model provided better correlation results than Wilson model for o-nitrobenzaldehyde-p-nitrobenzaldehyde-ethyl acetate system,and Wilson model gave better results than NRTL model for o-nitrobenzaldehyde-p-nitrobenzaldehyde-n-butanol system.Based on the phase diagram of ternary system,the crystallization separation process of m-nitrobenzaldehyde-p-nitrobenzaldehyde was designed.The amount of solvent added and the product yield were calculated from the ratio of raw materials.The results provided the basis for the separation of nitrobenzaldehyde isomers in industrial scale.