Study On Separation Of Amine Compounds By Melt Crystallization

In this paper, in order to get pure p-phenylenediamine and phenazine, meltcrystallization technology was used to separate and purificate the two aminecompounds: p-phenylenediamine isomers and waste of4-aminodiphenylamine whichare difficult to separate.Firstly, the differential scanning calorimetry (DSC) was used to measure thesolid-liquid phase diagram of p-phenylenediamine, which is appeared as the eutecticone according to the experimental results and literature.Based on the above fundamental researches, the melt crystallization process forpurification p-phenylenediamine was systemically investigated. The effects of thecooling rate, the final crystallization temperature, the sweating rate, the final sweatingtemperature of the melt crystallization process on the purity and yield ofp-phenylenediamine were studied. Finally, an optimal melt crystallization technologyfor purification p-phenylenediamine was determined. The purity ofp-phenylenediamine higher than90%which is the product of paradinitrobenzene aftercatalytic hydrogenation was used as the material of this new developed technology andp-phenylenediamine with purity higher99.7%can be obtained without adding anysolvent. And the mother liquid produced by the melt crystallization process can berecycled by the previous process, so this is a green process.The result of separation phenazine mixtures by multistage melt crystallizationshowed that the purity and yield of phenazine was not good.According to the different solubilities of each compound in solvent, solid-liquidextraction method can be used to purify the phenazine mixtures. We firstly improvedthe purity of phenazine to about86%by melt crystallization and then purifiedphenazine by extraction. The optimum extraction conditions of extraction10g rawmaterial were determined by orthogonal experiments and signal factor experiments as follows: the extraction temperature was30℃, the extraction time was25min, thedosage of solvent was30mL. Purity of phenazine could be improved to99.5%underthe optimum conditions. The yield of phenazine relatived to the material with thepurity86%was around89%and the total yield was around75%. The dosage ofsolvent, the cost of production and solvent recovery were greatly reduced under thecombination of extraction and melt crystallization. So this is a good way for separationand purification phenazine.