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A new method for determining wax content in petroleum materials is developed. It is based on thin layer chromatography with flame ionization detection (TLC-FID) and involves two-step development with two solvents.
The principle of the test method is first to separate saturates from other more polar components based on good solubility of saturates in n-heptane and weak strength of interaction with an adsorbent (silica). Waxes are then separated from the saturate fraction using a poor solvent methyl-ethyl ketone (MEK) at such a low temperature (typically −20 °C) that waxes are in solid state. The separated fractions are quantified with FID. The test method is verified using various model compounds including n-alkanes of different molecular weight, isoalkane, as well as commercial waxes. Results indicate that the TLC-FID method detects the waxes mainly composed of n-alkanes ranging from C20 to C40, and large isoalkanes and cycloalkanes which are soluble in n-heptane. The method has been satisfactorily applied to a variety of samples of crude oils, residues, and bitumens. It is simple, quick, and reliable. By changing MEK temperature in the development chamber, waxes may be further characterized.
Xiaohu Lu, Björn Kalman and Per Redelius