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

Abstract

Ethylene glycol (EG), synthesized from coal-based syngas, is frequently contaminated with refractory impurities 1,2butanediol (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.

Recent advances in melt crystallization, towards process intensification and technique development

“…Quench cooling nucleation refers to the rapid decrease of temperature, causing large supersaturation and promoting the formation of the crystal nucleus. Dong et al 6 applied the quench cooling technique to induce tiny crystals to appear in random locations, and then the temperature quickly increased to the set temperature. At the same time, an external disturbance was introduced so that the as-grown crystal grains were broken and uniformly dispersed to become a solid–liquid coexisting crystal slurry.…”

“…The layer melt crystallization possesses a fast crystal growth rate that can be used to produce high-purity substances, but it is generally multi-stage batch operations and easily causes high energy consumption. 6 The suspension melt crystallization device has a large solid–liquid interface, which is beneficial to heat and mass transfer, but the separation performance is a considerable issue. 77 Besides, single melt crystallization sometimes cannot achieve the separation target.…”

“…Therefore, Ulrich et al supposed that melt crystallization can be considered as a green technology. 1 Considering these advantages, melt crystallization is widely applied in manufacture and industry, including wastewater treatment, 4,5 ultrapure chemical production, 6,7 ionic liquid purification, 3 nuclear engineering, 8–10 and the food industry. 11 To achieve the desired separation efficiency and product purification, two key steps in melt crystallization: crystallization and sweating, have gained much attention.…”

Purification of 2-Pyrrolidone by Falling Film Melt Crystallization

“…13−18 In recent years, melt crystallization technology has been attracting much attention and is widely applied in separation and purification of isomers, heat-sensitive materials, and mixtures exhibiting azeotropes because of its advantages including low energy consumption, no requirement for a solvent, no damage to heat-sensitive materials with a low melting point, and safe operation. 19−24 Various substances, including milk fat, 25 p-xylene, 26 phosphoric acid, 27 dodecanedioic acid, 28 p-cresol, 29 caprolactam, 30 ethylene glycol, 31 chlorobromobenzene, 32 and N-vinylpyrrolidone, 33 were successfully purified by melt crystallization.…”

“…Melt crystallization is an environmentally friendly purification technology in which separation and purification are achieved according to the melting point difference between the main component and the impurities in the liquid mixture. , The principle of melt crystallization technology is to obtain crude crystals by gradually reducing the temperature below the crystallization temperature at a certain cooling rate, and subsequently, the sweating process is necessary to purify the crude crystals because of some impurities entrapped between crystals. − In recent years, melt crystallization technology has been attracting much attention and is widely applied in separation and purification of isomers, heat-sensitive materials, and mixtures exhibiting azeotropes because of its advantages including low energy consumption, no requirement for a solvent, no damage to heat-sensitive materials with a low melting point, and safe operation. − Various substances, including milk fat, p -xylene, phosphoric acid, dodecanedioic acid, p -cresol, caprolactam, ethylene glycol, chlorobromobenzene, and N -vinylpyrrolidone, were successfully purified by melt crystallization.…”