On-column Separation Of Wax And Asphaltenes In Petroleum fluids

摘要

The utility of a novel method based on the new on-column precipitation and redissolution technique is explored. This method, called waxphaltene determinator (WAD), is strictly solubility-based and allows for the detection of waxes and asphaltenes in minutes. The principle of the method is to first precipitate waxes and asphaltenes together on a ground polytetrafluoroethylene (PTFE)-packed column using methyl ethyl ketone at -20 ℃ and then redissolve the precipitate with solvents of increasing polarity at different temperatures. Waxes precipitated under these conditions are composed mainly of n-alkanes, with carbon numbers greater than C_(20), and heptane-soluble alkanes that are slightly to moderately branched. The method is first verified with model compounds, including n-alkanes and commercial waxes, and then applied to waxy crude oils and deposits. The method is compared to differential scanning calorimetry (DSC), and a linear correlation is found between the wax content by WAD and DSC. Asphaltene amounts by WAD also compare well to the gravimetric data.