Identification of impurities affecting commercial ethylene glycol UV transmittance

As a raw material for making polyesters, ethylene glycol has a special specification of UV transmittance. At present, ethylene glycol produced by some plants still has low UV transmittance rendering it unsuitable for use in polyester production. In this paper, a method was developed for the identification of the impurities that cause commercial ethylene glycol to have low UV transmittance, using solid-phase extraction (SPE) and some analytical techniques such as high-performance liquid chromatography, gas chromatography–mass spectrometry and gas chromatography–Fourier transform infrared spectroscopy. The major UV-absorbing impurities were identified as some alkyl homologues of 2-hydroxycyclopent-2-en-1-one, including 2-hydroxy-3,5-dimethylcyclopent-2-en-1-one, 2-hydroxy-3-methylcyclopent-2-en-1-one, 2-hydroxy-3,4-dimethylcyclopent-2-en-1-one, 2-hydroxy-3-ethyl-4-methylcyclopent-2-en-1-one and 2-hydroxy-3-ethylcyclopent-2-en-1-one. Their concentrations were estimated to be less than 2 μg ml−1. It is believed that with the above results, ethylene glycol-producing plants might make process improvements to remove these impurities more effectively and more easily.