(Solid–)Liquid–Liquid Equilibria in the Ternary Acetonitrile + n -Heptane + Palmitic Acid System between 298 and 313 K

Abstract

High-value, low-volume solutes are characteristic of bioprocessing waste residues and are typically the focus of separation process design; the equilibria of the waxy bulk components are often overlooked despite their ubiquity. In this work, a low-volume method for measuring (solid–)liquid–liquid equilibrium data is validated and applied to generate new data for the ternary system acetonitrile + n-heptane + palmitic acid between 298 and 313 K. Results show the fatty acid reports overwhelmingly to the alkane phase, highlighting acetonitrile’s potential as a selective solvent for polar solutes in waxy residues. Temperature had a small effect on palmitic acid’s distribution between phases but a significant effect on the liquid operating region, with solubility decreasing rapidly at lower temperatures. The data were modeled predictively with the new modified UNIFAC 2.0 model and correlated with NRTL. Modified UNIFAC 2.0 failed to quantitatively capture the experimental equilibria, while NRTL showed excellent agreement across all temperatures despite parameters being fitted only to independent sub-binary data, and ternary data at a single temperature. These results reassert the importance of quantifying all equilibria present in a system for effective separation process design and establish a low-volume methodology for generating such data in future work on similar systems.