# Phase Behaviour of Binary Mixtures Involving Near-Critical and Supercritical Carbon Dioxide—A Review

## TL;DR

This review summarizes phase behavior of CO2 mixtures for industrial applications, highlighting challenges and opportunities in supercritical CO2 technologies.

## Contribution

The paper provides a comprehensive review of experimental methodologies and phase behavior trends in CO2 mixtures, identifying gaps and future research directions.

## Key findings

- Enhanced solubility in CO2 mixtures is observed with increasing pressure and CO2 density.
- Lewis acid–base interactions significantly influence solvation in polar systems.
- Chain-length dependencies are noted in hydrocarbons and alcohols mixed with CO2.

## Abstract

Near-critical and supercritical carbon dioxide (SC-CO2) is extensively utilized in high-pressure separation, extraction, polymer processing, and carbon capture and utilization (CCU) technologies owing to its tunable density, low viscosity, high diffusivity, and environmentally benign nature. Reliable phase equilibrium data are indispensable for process design and optimization, especially in the near-critical region characterized by pronounced non-idealities, high compressibility, and density fluctuations. This review synthesizes experimental phase behaviour studies for binary mixtures of CO2 with diverse components, including hydrocarbons, alcohols, ethers, esters, ketones, water, monomers/polymers, ionic liquids (ILs), and deep eutectic solvents (DESs), compiling extensive vapour–liquid equilibrium (VLE), liquid–liquid equilibrium (LLE), and critical data across industrially relevant pressure (up to 40 MPa) and temperature (up to 400 K) ranges. It critically evaluates analytical (sampling and non-sampling) and synthetic methodologies, addressing challenges in CO2-rich phase handling, depressurization artefacts, and near-critical phenomena, while assessing data consistency against established reliability criteria. Key trends emerge, such as enhanced solubility with increasing pressure and CO2 density, chain-length dependencies in hydrocarbons and alcohols, and Lewis acid–base interactions driving solvation in polar systems. The review highlights gaps in multicomponent data and proposes integrating high-quality experiments with advanced thermodynamic modelling to enhance predictive accuracy. Future directions emphasize high-precision in situ techniques, expanded datasets for complex mixtures, and novel CO2-philic solvents to advance sustainable SC-CO2 applications.