A New Test Method for Determination of Wax Content in Crude Oils, Residues and Bitumens

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.

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.

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Authors

Xiaohu Lu, Björn Kalman and Per Redelius

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