Abstract: In order to evaluate the influence of impurity on the quality of caprolactam product, 10 kinds of impurities, such as aromatic amines, ketones, oximes, ethers and caprolactam homologs, were added to purified caprolactam, and the influences on volatile basicity, chromaticity, ultraviolet absorption at 290 nm, alkalinity and acidity, potassium permanganate value was investigated. The results showed that the aromatic amines had a sigenificant effect on all five indexes, and the presence of trace aromatic amines would lead to the unqualified caprolactam products. The in-crease of 2-methoxy cyclohexanone and 2,3-epoxy cyclohexanone would lead to the increase of the volatile basicity, ultraviolet absorption at 290 nm and potassium per-manganate value, leading to a worse product quality. Trace caprolactim methyl ether in caprolactam would cause the unqualified alkalinity caprolactam, and the alkalinity increased by 0.1 mmol/kg for every 25μg/g increase in its mass fraction. Cyclohexanone oxime had a medium effect on the volatile basicity and potassium permanganate value. Cyclohexanone and N-methyl caprolactam had no effect on those indexes of caprolactam.

Key words: caprolactam, volatile basicity, chromaticity, potassium permanganate absorption, absorbance