title: Temperature effects in supercritical fluid chromatography: a trade-off between viscous heating and decompression cooling.
abstract: The study of radial and axial temperature profiles always has been an area interest both in liquid chromatography (LC) and supercritical fluid chromatography (SFC). Whereas in LC always an increase in temperature is observed due to the dominance of viscous heating, in SFC, especially for low modifier content, a decrease in temperature is found due to the much larger decompression cooling. However, for higher modifier content and higher operating pressure, the temperature effects become a trade-off between viscous heating and decompression cooling, since in SFC the latter is a strong function of operating pressure and mobile phase composition. At a temperature of 40°C and for neat CO2, the effect of decompression cooling and viscous heating cancel each other out at a pressure 450bar. This pressure decreases almost linearly with volume fraction of methanol to 150bar at 25vol%. As a result, both cooling and heating effects can be observed when operating at high back pressure, large column pressure drops or high modifier content. For example at a back pressure of 150bar and a column pressure drop of 270bar decompression cooling is observed throughout the column. However at 300bar back pressure and the same pressure drop, the mobile phase heats up in the first part of the column due to viscous heating and then cools in the second part due to decompression cooling. When coupling columns (2.1mm×150mm, 1.8μm fully porous particles) at very high operating pressure (e.g. 750bar for 8vol%), the situation is even more complex. E.g. at a back pressure of 150bar and using 8vol% methanol, viscous heating is only observed in the first column whereas only decompression cooling in the second. Further increasing the inlet pressure up to 1050bar resulted in no excessive temperature differences along the column. This implies that the inlet pressure of SFC instrumentation could be expanded above 600bar without additional band broadening caused by excessive radial temperature differences.
authors.affiliation: Vrije Universiteit Brussel, Department of Chemical Engineering (CHIS-IR), Pleinlaan 2, 1050 Brussels, Belgium.
authors.forename: Ruben
authors.initials: R
authors.lastname: De Pauw
authors.affiliation: Agilent Technologies Europe, Hewlett-Packard-Strasse 8, 76337 Waldbronn, Germany.
authors.forename: Konstantin
authors.initials: K
authors.lastname: Choikhet
authors.affiliation: Vrije Universiteit Brussel, Department of Chemical Engineering (CHIS-IR), Pleinlaan 2, 1050 Brussels, Belgium.
authors.forename: Gert
authors.initials: G
authors.lastname: Desmet
authors.affiliation: Vrije Universiteit Brussel, Department of Chemical Engineering (CHIS-IR), Pleinlaan 2, 1050 Brussels, Belgium. Electronic address: kbroeckh@vub.ac.be.
authors.forename: Ken
authors.initials: K
authors.lastname: Broeckhoven
mesh_terms: D025924:Chromatography, Supercritical Fluid / Q000379:methods*; D006361:Heating; D000432:Methanol; D016062:Porosity; D011312:Pressure; D012997:Solvents; D013696:Temperature
chemical_list: D012997:Solvents; D000432:Methanol
keywords: Coupled columns; Decompression cooling; Pressure; Supercritical fluid chromatography; Temperature; Viscous heating