Compressed liquid density measurements of acetic acid and carbon dioxide mixtures for reactive heat pump applications

High-Temperature Heat Pumps (HTHPs) are pivotal technologies for industrial decarbonization, enabling the recovery of waste heat at temperatures suitable for process steam generation. To overcome the limitations of conventional inert refrigerants, reactive working fluids are gaining attention as a promising alternative. These fluids exploit reversible chemical reactions—specifically dimerization and association equilibria—to enhance the effective thermal capacity and enthalpy change during compression and expansion cycles. In this context, acetic acid represents a benchmark reactive fluid due to its well-known dimerization equilibrium (2𝐶𝐻3𝐶𝑂𝑂𝐻 ⇋ (𝐶𝐻3𝐶𝑂𝑂𝐻)2 ). The addition of small quantities of carbon dioxide (CO2) allows to tailor the saturation pressure of the mixture, lifting it to technically viable levels without suppressing the reactive benefits of the solvent. Accurate thermophysical properties are fundamental for the development of reliable Equations of State (EoS) and the proper design of heat pump devices. However, available experimental data for this reactive system are insufficient for HTHP applications. While recent studies have investigated the phase equilibrium and density of acetic acid + CO2 mixtures, they are largely confined to temperatures below 340 K and CO2-rich mixtures. Data in the high-temperature compressed liquid region, where the reaction kinetics and thermodynamic benefits are most relevant, remain virtually non-existent. This work presents new experimental density measurements of pure acetic acid and binary mixtures with carbon dioxide (CO2 mass fraction < 15%). The data were collected using a vibrating tube densimeter over a temperature range of 300 to 420 K and pressures up to 8 MPa. The experimental results are used to extend the validation of advanced cubic equations of state into the high-temperature domain. These measurements provide essential insight into the volumetric behavior of reactive mixtures, bridging the gap between low-temperature characterization and realworld industrial process conditions.