Supported liquid membrane permeation for selective lactic acid recovery

1. Introduction
Lactic acid is handled as a future bulk chemical due the use for poly lactic acid production. State of the art production for lactic acid is fermentation followed by precipitation and hydrolysis. Much attention has been drawn to the optimization of the fermentation as well as the downstream processing, however the best solutions has not been found yet [1]. Besides the state of the art production lactic acid is present in aqueous effluent from the pulping industry [2]. Following the biorefinery approach, valuables from the black liquor in pulping process may lead to a biorefinery including the carboxylic acids formic acid and acetic acid as well as lactic acid as valuables. This approach is applied in textile fiber production since long, but is new for the cellulose production. The present paper develops the basics for the selective recovery of formic acid, acetic acid and lactic acid from black liquor using supported liquid membrane permeation device.

2. Experimental
Main advantage of liquid membrane permeation is the simultaneous extraction and back-extraction, leading to a continuous phase contact of three phases, further called three phase contact. Basis for application of liquid membrane permeation is the phase equilibrium. The phase equilibria measurements were carried out in temperature controlled separation funnels. Experiments in the three phase contact were carried out in lab equipment which was developed behind the background of heavy metal recovery [3]. For phase equilibria measurement the influence of the temperature (25°C - 45°C), the pH-value (1-4) and the composition of the liquid membrane (TOA/octanol/undecane) were varied.

3. Results and Discussion
While the temperature influence can be neglected in the used system, the influence of pH-value is given. However the influence of the membrane composition is clearly seen. With a composition of the membrane phase of 30w%TOA/30w%ocatnol/40w%undecane a distribution coefficient of 4.7 was obtained in the phase equilibria measurement. When transferring the results to the three phase contact, just little mass transfer is observed. In figure 1 the membrane composition 30w%TOA/30w%ocatnol/40w%undecane and the membrane composition 60w%TOA/ 40w%undecane are compared in three phase contact. , whereas with the mixture 60w%TOA/40w%undecane mass transfer was increased. The distribution coefficient for the phase equilibria measurement in that case is 1.2.
With a membrane composition of 60w%TOA/40w%undecane selective separation of the three acids is not possible in one step. However by adapting the membrane composition selective separation shall be possible. The optimization of the membrane composition is part of ongoing research activities.