Supercritical carbon dioxide extraction of petroleum on kieselguhr

Abstract

Carbon dioxide-based supercritical fluid extraction (CO2 SFE) has been an excellent alternative to solvent extraction in many industries. In this study, a heavy crude oil was adsorbed to kieselguhr and performed for comparison of different extraction processes. The oil extract by dichloromethane Soxhlet extraction was used as a benchmark. Another batch of the sample was subjected to sequential short-time and longer-time CO2 SFE, and subsequent dichloromethane Soxhlet extraction, yielding three distinct extracts. All of these four extracts were then fractionated by a standard saturates/aromatics/resin/asphaltene (SARA) method. Each SARA fraction was then analyzed by high temperature gas chromatography simulated distillation (SIMDIS), gas chromatography–mass spectrometry (GC–MS) and Fourier-transform ion cyclotron resonance mass spectrometry (FT-ICR MS). It was found that CO2 SFE selectively extracts relatively low molecular weight compounds with low degrees of molecular condensation. The remaining un-extracted components are mainly in polar resin and asphaltene fractions, containing the chemical species with large carbon numbers and high degrees of molecular condensation. Most of these components are in low volatility with boiling points higher than 500°C, beyond the upper temperature limit of common GC columns. CO2 SFE can serve as an environmental-friendly alternative to Soxhlet solvent extraction if the goal of the analysis is to determine petroleum biomarker or compositional analysis by GC–MS. In addition, CO2 SFE for extracts only volatile compounds of small molecular weight has an advantage of leaving most non-volatile components that would be detrimental to the GC systems.