In situ Raman spectroscopy for the evaluation of solubility in supercritical carbon dioxide mixtures

Solubility phenomena in supercritical carbon dioxide (SC-CO2) mixtures have been studied in situ using Raman spectroscopy. A Raman spectroscopy instrumentation has been linked to a high-pressure optical cell. The set-up was tested in the system SC-CO2/alkyl ketene dimer (AKD) under pressures up to 300 bars and temperatures up to 80 °C. As a proof of concept, the possibility to study solubility of AKD in SC-CO2 as well as solubility of SC-CO2 in AKD by studying the Raman signal of SC-CO2 has been presented. Statistically tested results show how these competitive phenomena depend on the density region of the SC-CO2. Raman spectra of AKD in the system AKD/SC-CO2 have also been acquired, demonstrating the prospect of quantitative analysis for solubility studies in SC-CO2. Furthermore, this versatile set-up provides information about thermal expansion of the vessel and evidences the need for corrected equations in this commonly used region of pressures and temperatures.