Extended Simulated Distillation by Capillary Supercritical Fluid Chromatography

Abstract : Simulated distillation (simdist) based on separation using gas chromatography (GC) is widely spread in the petroleum industry for evaluation of fossil fuels as well as petroleum feeds and cuts produced by refining and conversion processes. Through a calibration curve relating the boiling point of normal paraffins to their elution temperature or retention time, simdist provides the hydrocarbon distribution of the sample (in weight percent) versus the boiling range of the fraction. The operating conditions used for simdist are tuned to be in agreement with preparative distillation that gives the True Boiling Point (TBP) curve. However, this technique is not compatible to heavy ends (FBP higher than 700°C) due to the limitation of volatility of the products and the lack of resistance of high molecular-weight hydrocarbons to cracking reactions. The interest of supercritical-fluid chromatography (SFC) is that high temperatures are not needed to elute heavy ends and that the mechanism for extending the upper limit of simdist depends only on sample solubility into the supercritical mobile phase. This paper presents recent advances in Simdist using SFC of heavy fractions. Compared to GC, SFC extends the range of this application up to nC126 hydrocarbons and makes possible to calibrate up to nC200. Thus, SFC could be the tool of choice for better determination of conversion in heavy petroleum-fraction processing.