High-pressure phase behaviour and modelling of the 1‑nonanol + n‑hexadecane + supercritical CO2 system

This work presents measured high-pressure phase transition data for mixtures containing 1‑nonanol + n‑hexadecane (solute + solute) with supercritical CO₂ (solvent) and thermodynamic modelling of the measured data. The data was measured using the static synthetic visual phase method for four (1‑nonanol + n‑hexadecane) mixtures with CO₂ as well as 1‑nonanol + CO₂ at temperatures between 308.2 K and 358.2 K and solute mass fractions ranging from 0.008 to 0.65 g·g^-1. Solute-solute interactions strongly influence the observed phase behaviour, resulting in complex phenomena such as cosolvency effects and temperature inversions. The measured data revealed distinct cosolvency effects and exhibited temperature inversions at 308.2 K and 318.2 K for solvent-free alcohol compositions of 0 g·g^-1, 0.8 g·g^-1 and 1 g·g^-1.

A modified version of the Soave-Redlich-Kwong (SRK) equation of state implemented in Aspen Plus®, RK‑Aspen, was used to correlate experimental pure component and binary data, and to predict the high-pressure phase transition data for the ternary system. Incorporating polar parameters, solute-solvent binary interaction parameters (BIPs), and solute-solute BIPs in the RK-Aspen model provided reasonably accurate descriptions of the measured data in the dew- and bubble point composition ranges at moderate temperatures. However, future work should focus on improving the model's performance at temperatures near the solvent's critical temperature and compositions near the mixture critical region. Additionally, an in-house thermodynamic model can be developed to better describe complex phase behaviour.