Solubility Of Caprolactam And Effects Of Impurities On Its Crystallization

This paper is to study the crystallization process for the purification of thecaprolactam produced with toluene, combining the productive practice. Through thedetermination of the solubility of caprolactam in different organic solvents wepreliminary screening the crystallization solvent, we also determined the affect of theimpurities of caprolactam on the PM value and290nm absorbance, caprolactammixed with different impurities were purified by crystallization, optimized theconditions to improve the PM value,290nm absorbance and the crystal sizedistribution.The solubility of caprolactam in methyl tert-butyl ether, isopropyl ether,1-propanol,2-propanol, and n-butanol was measured at the temperature range from278.15to313.15K under atmospheric pressure. The experimental data werecorrelated by the modified Apelblat equation, NRTL1model and UNIQUAC modelwhich fit well with the experimental data.The impurity which has the biggest impact on the PM value and290nmabsorbance of caprolactam is2,6-diaminopyridine, followed by cyclohexanone oximeand N-methyl-4-piperidone, again for cyclohexanol, cyclohexylamine and1,4-cyclohexanedione, however, N-methylcaprolactam and cyclohexanecarboxylicacid have no impact on the PM value and290nm absorbance of caprolactam. Besides,the existence of the impurities will not change the morphology of caprolactam.When use methyl tert-butyl ether as the crystallization solvent it can get betterrefining results, the best condition is: the volume of the solvent is2.5times of thecaprolactam, crystallization temperature is5℃, cooling rate is0.5℃/min,crystallization time is1h. The optimal rotating rate is180rpm for the crystallizationprocess, the main size of the product is about1mm, and the morphology ofcaprolactam crystal is square-flake crystal.