In this step, we want to separate the organic constituents of the rock powder. The method of extraction exploits the different solubilities of bitumen and kerogen in organic solvents. An example of separating two substances using their different solubilities would be in separating a sand/salt mixture. To separate these two components, you would add water to the mixture, swirl and wait a few moments, and the salt can now be poured off, as it is dissolved in the water. Similarly, we treat the rock sample with organic solvents (we use a 9:1 mixture of methanol:DCM) to extract the bitumen, which is soluble, from the kerogen, which is insoluble in this mixture.
There are several methods that may be used for extraction, including Soxhlet extraction and sonication. The fastest and most efficient method is in our lab, using a machine called the Accelerated Solvent Extractor (or ASE). By cycling several times, and using high pressures and temperatures (the solvent boils at a higher temperature at higher pressures, and thus we can get maximum solubility), we get the fastest and most effective extraction.
After the extraction, we now have 2 fractions: the stuff that remained with the solid, and the stuff that dissolved in the organic solvent. By definition,
- Kerogen is organic matter that is insoluble in organic solvents and acids
- Bitumen is organic matter that is soluble in organic solvents and acids. Above is a picture of the extracted bitumen.
The bulk of sediment is an inorganic matrix. The remaining part, the total organic carbon (TOC) content, of sediment may vary between .5 and 2.5 weight %.
We might perform an isotopic analysis on the kerogen, to get a bulk carbon isotopic composition, and further, analyze the kerogen using pyrolysis. With the bitumen (shown above), we continue to separate using silica column fractionation.