Pressure, temperature and density drops along supercritical fluid chromatography columns in different thermal environments. III. Mixtures of carbon dioxide and methanol as the mobile phase

• Isenthalpic expansion of the mobile phase occurs in SFC columns.
• The temperature drop can be computed from the Joule–Thomson coefficient.
• The measured pressure and temperature drops agree with calculated values.
• Combined Joule–Thomson and kinematic viscosity plots are useful design tools.

The pressure, temperature and density drops along SFC columns eluted with a CO2/methanol mobile phase were measured and compared with theoretical values. For columns packed with 3- and 5-μm particles the pressure and temperature drops were measured using a mobile phase of 95% CO2 and 5% methanol at a flow rate of 5 mL/min, at temperatures from 20 to 100 °C, and outlet pressures from 80 to 300 bar. The density drop was calculated based on the temperature and pressure at the column inlet and outlet. The columns were suspended in a circulating air bath, either bare or covered with foam insulation. The experimental measurements were compared to theoretical results obtained by numerical simulation. For the convective air condition at outlet pressures above 100 bar the average difference between the experimental and calculated temperature drops and pressure drops were 0.1 °C and 0.7% for the bare 3-μm column, respectively, and were 0.6 °C and 4.1% for the insulated column. The observed temperature drops for the insulated columns are consistent with those predicted by the Joule–Thomson coefficients for isenthalpic expansion. The dependence of the temperature and the pressure drops on the Joule–Thomson coefficient and kinematic viscosity are described for carbon dioxide mobile phases containing up to 20% methanol.