Ethylene Glycol Purification by Melt Crystallization: Removal of Short-Chain Glycol Impurities

Ethylene glycol (EG), synthesized from coal-based syngas, is frequently contaminated with refractory impurities 1,2-butanediol (BDO) and 1,2-propanediol (PDO), which affect the quality of EG for polyester production. Distillation, one of the existing methods employed, is still difficult for separation and purification due to the close boiling points. Melt crystallization is an effective technology to obtain high-purity organic compounds based on the difference in the melting points of each component in the mixture. Thus, in this work, we have explored the feasibility of the static melt crystallization on the separation of these two binary systems, EG/BDO and EG/PDO, respectively. For this purpose, a jacketed crystallization tube was adopted and the process was divided into three stages: seed generation, crystallization, and sweating. The crystallization parameters were investigated and fractal porous media theory was used to describe the state of the crude crystals. Furthermore, sweating was applied as a finishing treatment. The purity of ethylene glycol was recorded using gas chromatography, and its corresponding UV transmittance spectrum was studied. The results showed that the purity of ethylene glycol could reach ≥99.8% from the two binary systems studied and its UV transmittance at 220 nm was significantly improved by the tertiary separation process. Overall, melt crystallization has been proved as an effective way to solve the difficulty of separating these short-chain glycols.