(597c) Reactive Extraction of Lactic Acid with Trioctylamine/Octanol/n-Undecane

The pulp and paper industry serves as backbone in the biorefinery. Black liquor from pulping contains, besides lignin which is mainly used for heat production, different carboxylic and hydroxycarboxylic acids in considerable amount.These acids are not recovered at present [1]. Especially formic acid, acetic acid and lactic acid are of interest, as they may serve as platform chemicals in the future.Isolation of lactic acid from industrial process streams is a promising way to cover the increasing demand of lactic acid. Due to its use as monomer for the poly lactic acid production lactic acid receives priority attention in the present work. The conventional lactic acid production and isolation from fermentation broths requiresa high amount of chemicals, andthe process generatesa high amount of unwanted, low value by-products.

Liquid-liquid extraction is a promising alternative separation technology to state of the art isolation of lactic acid [2]. The present work provides the basis for selective separation of lactic acid by using reactive liquid/liquid extraction. Phase equilibrium measurements were performed in dependence on the composition of the solvent phase starting with physical extraction with n-Undecane and Octanol, followed by reactive extraction with mixtures of Trioctylamine/Octanol/Undecane. Trioctylamine (TOA) is well known for its ability to extract carboxylic acids [3]. The modifier Octanol affects the distribution characteristic and, together with the diluent n-Undecane, it affects the physical properties of the solvent to avoid third phase formation at higher acid concentration. The optimized solvent phase containing 40w% TOA/40w% Octanol/20w% Undecane provides highly efficient extraction of lactic acid.The influence of the pH-value on distribution and hence on separation was considered. Back extraction was performed with NaHCO₃.

As mentioned, black liquor does contain several carboxylic acids. Isolation of lactic acid with amines must consider co-extraction of carboxylic acids. The effect of acetic acid and formic acid on yield and selectivity of lactic acid extraction was therefore investigated too.

The results underline the high potential of reactive liquid/liquid extraction for the recovery of carboxylic and hydroxycarboxylic acids from black liquor.

[1] E. Sjoestroem, “The behavior of wood polysaccharides during alkaline pulping processes,” Tappi, vol. 60, no. 9, pp. 151–154, 1977.

[2] S. Basetty and B. R. V V, “Equilibrium Studies on Reactive Extraction of Lactic Acid using Tri- butyl amine in Chloroform,” vol. 38, pp. 99–104, 2012.

[3] C. I. Sci, C. Engimeer, N. York, A. Review, F. Mechanics, A. Reviews, P. Alto, F. Mech, M. N. York, A. Sci, P. Press, N. York, A. Sci, and T. R. The, “Amine Extraction of Hydroxycarboxylic Acids . 1 . Extraction of Citric,” pp. 1554–1562, 1992.