Separation of propionic acid by diethyl carbonate or diethyl malonate or diethyl fumarate and the synergistic effect of phosphorus compounds and amines

The recovery of propionic acid from aqueous solutions such as fermentation broth and wastewater is an important problem where liquid extraction is the favorite process. Liquid–liquid equilibrium (LLE) data were investigated for mixtures of water + propionic acid + diethyl carbonate or diethyl malonate or diethyl fumarate at 298.15 K. The solubility curves and the tie-line end compositions of liquid phases at equilibrium were determined experimentally, and the tie-line results compared with the data correlated by means of UNIQUAC model. The phase diagrams for the ternary mixtures including both the experimental and correlated tie-lines are presented. The reliability of the experimental tie-lines was confirmed by using Othmer–Tobias correlation. The distribution coefficients and the separation factors for the immiscibility region are calculated. In order to boost the distribution of propionic acid between aqueous and organic phases, the distribution was investigated by using organic solutions composed of amine {tributylamine (TBA)} and phosphorus containing compounds {trioctylphosphine oxide (TOPO) or tributyl phosphate (TBP)} dissolved in diethyl carbonate, diethyl malonate and diethyl fumarate, in the concentration range of about 0.06–1.00 mol/l. It was observed that the used solvents may serve individually as adequate agents to extract propionic acid from its dilute aqueous solution; however, the extraction performance can be improved by using phosphorus containing compounds or amines, mostly by using tributylamine dissolved in diethylmalonate.