Using a Fused Silica Capillary Cell and In Situ Raman Spectroscopy To Develop a Setup for Measurement of the Volume Expansion of Carbon Dioxide + n-Hexane

To investigate the volume expansion of a carbon dioxide (CO2) + n-hexane mixture at different temperatures and pressures, we developed a measurement setup using an optically transparent fused silica capillary cell (FSCC) combined with Raman spectra. The results showed that the method is feasible, the water seal is effective in its ability to avoid vaporization of n-hexane, and Raman spectra can help ensure the system equilibrium. The volume expansion factor of the CO2 + n-hexane mixture increased with increasing pressure from 1 to 10 MPa and decreased with increasing temperature from 30 to 80 °C. It was found that the trend of the expansion factor of the CO2 + n-hexane mixture was steeper at a higher temperature. When the temperature was 30 °C, the volume expansion factor increased from 2.15 to 13.61 as the pressure increased from 5.0 to 6.5 MPa. Meanwhile, the volume expansion factor increased from 2.36 to 19.40 as the pressure increased from 8.0 to 9.2 MPa at 60 °C. In addition, we obtained a significant and positive relationship between the volume expansion factor and the Raman peak height ratio of CO2 and n-hexane using a quadratic equation.