On the phase behavior of the quaternary system acrylic acid-water-ethanol-CO2 by in situ infrared spectrometry

• Acrylic acid (AA) is stocked and transferred from a liquid aqueous medium to scCO2.
• Ethanol added to the biphasic ternary mixture limits the transfer of the monomer.
• FTIR and ATR-IR allow obtaining complete phase diagram and partition coefficients.
• Drops of AA in water are like monomer reservoirs, feeding polymerization in scCO2.

The phase equilibrium of acrylic acid (AA)/carbon dioxide (CO2) as well as mixtures containing water, AA, CO2 and/or ethanol (EtOH) has been investigated. An in-situ infrared analysis method combining FTIR and ATR-IR spectrometry techniques has been used to obtain concentrations of each component in both phases, i.e. CO2-rich and water-rich ones, as a function of pressure and temperature. Measurements have been performed at 65 and 75 °C for pressures ranging between 0.1 and 20 MPa. The solubilities of AA, water and EtOH in the CO2-rich phase and the concentrations of AA, EtOH and CO2 in the water-rich phase have been obtained. From these measurements, a complete phase diagram of the binary AA-CO2 system as well as the partition coefficient of each component in the quaternary system have been established. It has been demonstrated that AA is in equilibrium between the water- and the CO2-rich phases and that EtOH limits this transfer. Nevertheless, aqueous droplets of AA in CO2 at high pressure can be used as monomer reservoirs releasing the monomer in the CO2-rich phase.

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