(309e) Isolation of Lactic Acid by Reactive Extraction with Organophosphorous Compounds

Lactic acid is an important commodity chemical with a wide range of different applications. Synthesis of lactic acid either through fermentation of carbohydrates or through chemical synthesis is state of the art. However, separation from dilute aqueous solution is complex and accounts for the major part of production costs. The current method, precipitation as calcium lactate, is expensive and contradicts intentions of sustainability.

Reactive extraction based on reversible adduct formation could be a promising alternative for the separation of carboxylic acids from aqueous solutions. Due to Lewis-acid-base interaction phosphorus-bonded oxygen-containing extractants efficiently extract carboxylic acids from aqueous solution.

Aim of this project was the investigation of the extraction of lactic acid extraction with tributylphosphate, trioctylphosphine oxide and Cyanex 923 which is a mixture of four trialkylphosphine oxides. Shellsol T was used as diluent. The effect of the type and concentration of the extractant, initial lactic acid concentration and temperature on the liquid-liquid equilibrium were determined.

Distribution coefficients, handling and solubility of Cyanex 923 in water recommend it as extractant of choice. The mole balance indicates unimolecular ratio of lactic acid and extractant. At elevated temperature the acid can easily be stripped from the extractant Cyanex 923 with water.

In order to determine the selectivity of the extractant, separation of formic acid and glycolic acid, byproducts of the synthesis of lactic acid, was investigated.

The whole process was validated with broths from electrochemical synthesis of lactic acid based on aqueous glycerol feed. Residual glycerol does not have a negative impact on the process performance.