(84b) Organophosphorus Solvents for Lactic Acid Extraction From Dilute Aqueous Solution

Separation of lactic acid from dilute aqueous solution is complex.  It still accounts for a major part in lactic acid production costs. Due to high polarity and the hydrophilic character of lactic acid, it is poorly extracted with conventional organic extractants. On the contrary, reactive extraction based on reversible adduct formation is a promising, sustainable alternative. Phosphorus-bonded oxygen-bearing extractants provide good partition of carboxylic acids due to their high Lewis basicity. Temperature dependence of the liquid-liquid partition equilibrium allows extraction at room temperature and re-extraction by stripping with water at elevated temperature.

Efficiency and selectivity of various organophosphorus compounds such as tri-n-butylphosphate, tri-n-octylphosphine oxide and Cyanex 923 were investigated. Shellsol T was used as a non reactive, unpolar diluent. The liquid phosphine oxide Cyanex 923 proved best with respect to both lactic acid partition and hydrodynamic properties.

Liquid-liquid phase equilibria were investigated and modeled based on the law of mass action. Experimental data and model data showed good agreement. The effect of water co-extraction and lactic acid selectivity from multi acid solution was considered too.