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Bitumen containing natural waxes and their effect on asphalt performance has been debated for many years. The objective of this paper is to develop a simple method for determining waxes in bitumens and in crude oils.
Bitumen containing natural waxes and their effect on asphalt performance has been debated for many years. In determination of wax content, two European standard methods, EN 12606-1 (Method by distillation) and 12606-2 (Method by extraction), are currently used. The methods in general are very time-consuming and the waxes measured may differ from those actually present in the bitumen. The objective of this paper is to develop a simple method for determining waxes in bitumens and in crude oils. The method is based on thin layer chromatography with flame ionization detection (TLC-FID).
In the test, a small amount of sample solution is spotted on a quartz rod coated with a thin layer of sintered silica. After the separation of saturates with n-heptane at room temperature, the rod is placed upside down in another chamber containing methyl-ethyl ketone (MEK) at a low temperature, typically -20°C. The second development separates waxes that are insoluble in the cold MEK from other saturated compounds. The waxes are then quantified by FID. The method is verified using various model compounds, as well as commercial waxes. It has been satisfactorily applied to study a variety of crude oils and bitumens.
Results showed that the new method for determining waxes is simple and quick, and has reasonable repeatability. A round robin test with three laboratory participants shows that there is a need to improve reproducibility of the test method. In addition, it is presumed that, by changing MEK temperature in the development chamber, waxes may be further characterized by TLC-FID.
Xiaohu Lu, Björn Kalman, Per Redelius
The 4th Eurasphalt & Eurobitume Congress, Copenhagen, 21-23 May 2008