Conceptual process design and economic analysis of a process based on liquid-liquid extraction for the recovery of glycols from aqueous streams

The recovery of monoethylene glycol (MEG) and 1,2-propylene glycol (PG) from aqueous streams via liquid–liquid extraction (LLE) using a tailor-made ionic liquid [TOA MNaph] is evaluated as an alternative technology to conventional triple effect evaporation of water. In this paper, the conceptual process designs for the purification of aqueous MEG from petrochemical feedstock and the recovery of PG from fermentation broths using both separation technologies are presented. The results show that LLE technology offers high energy savings, around 94% for MEG production (from petrochemical feedstock) and 54% for the PG (from fermentation broth) process compared to triple effect distillation. The economic evaluation shows that at current crude oil prices (€70–95/barrel), LLE for MEG production is not a suitable option. This holds particularly for the biological production of MEG. In the case of PG, even though the capital investment is much higher for the solvent extraction technology, the extraction process is beneficial in terms of total annual costs for the recovery of PG (plant capacity < 100 kton/year and glycol feed concentrations < 10 wt %), which is strongly dependent on the glycol distribution coefficient and selectivity of PG.