(513e) Phase Separation Behavior of Aqueous Mixed Organic Acid Solutions through Selective Extraction Using Non-Ionic Surfactants

Aqueous two-phase systems (ATPS) have become an attractive separation technology due to its unique features such as simplicity of the process, easy scale-up, low cost of materials used, and high constituent recovery and selectivity. One of the growing applications of ATPS is the recovery of organic acids from aqueous streams. Organic acids are highly demanded building blocks for a range of other chemicals in industry, thus are produced in considerable volumes. Among these organic acids, butyric acid is one of the most sought-after platform chemical because of its potential for various industrial applications. It is typically co-produced with acetic acid in Clostridia fermentations. However, the synthesis of acetic acid reduces the butyric acid yield and increases the separation costs of butyric acid. Hence, in this study, four commercially available non-ionic surfactants (Ecosurf EH-3, Triton X-45, Nonidet RK-18 and Makon NF-12) were tested for selective extraction of butyric acid from aqueous acid solutions prepared by mixing Modified Savin’s fermentation medium with varying concentrations of butyric acid and acetic acid. The surfactant concentration was fixed at 40% w/w and the settling time was set constant at 5 hr for all experimental runs. Results show that the highest selectivity of 9.35 for butyric acid was obtained from a mixture of 20% w/w butyric with 5% w/w acetic acid by using Ecosurf EH-3. This corresponds to the highest recovery of 72.59% and distribution coefficient of 3.18. With reference to the highest recovery of 94.27% from aqueous pure butyric acid solution using the same surfactant, a significant 23-37% decrease on the butyric acid recovery and 20-57% increase on the acetic acid recovery were observed with increasing acetic acid concentration ratio with butyric from 0.25 to 4. Similar trend was obtained from using Triton X-45 with the second highest selectivity of 6.23 achieved from the same concentration of butyric (20% w/w) with acetic acid (5% w/w). These results may be attributed to shorter hydrophobic alkyl chain length that Ecosurf EH-3 (C2) and Triton X-45 (C8) have as compared to Makon NF-12 (C10-C12) and Nonidet RK-18 (C12-C13). Surfactants with longer alkyl chain tend to reduce the ability of their polar groups to accommodate more water and polar molecules and disrupt the electrostatic attraction and repulsion balance of surfactant molecules, hence leads to poorer separation of the acids. In addition to that, it was easiest to collect the surfactant-rich phase (i.e., the layer concentrated with more butyric acid molecules) from aqueous solutions with Ecosurf EH-3 as they were less viscous as compared to other samples containing other tested non-ionic surfactants. With these results, Ecosurf EH-3 is recommended as the most suitable extractant in recovering butyric acid from mixed acid solutions because of its high selectivity towards butyric acid.