Propylene glycol and ethylene glycol recovery from aqueous solution via reactive distillation

Propylene glycol (PG) and ethylene glycol (EG) are recovered from aqueous solution via reaction with acetaldehyde to form acetals in a reactive distillation column. The reaction takes place over Amberlyst 15 cationic exchange resin catalyst, held in structured packing in the column reactive zone. Gycol solution is fed to the column at the top of the reactive zone and acetaldehyde is fed at the bottom of the reactive zone. The acetals produced, 2,4-dimethyl-1,3-dioxolane from PG and 2-methyl-1,3-dioxolane from EG, form minimum-boiling azeotropes with water and exit the top of the column along with excess acetaldehyde; residual water exits the column as the bottoms stream. In a 0.05 m OD ×6.0 m pilot-scale column, steady-state PG conversions of over 90% are obtained. Hydrolysis of both acetals is rapid and allows complete recovery of high purity PG and EG and recycle of acetaldehyde. Simulation of PG acetalization using a kinetic rate-based model in AspenPlus process simulation software gives good agreement with experimental data using an HETP of 0.6 m . The proposed recovery scheme has application for PG and EG recovery from pure polyol solutions and from mixed polyol streams such as those generated in carbohydrate hydrogenolysis.