Crude Buyer rejecting oil 1

[nonAPI]

I'm having a problem with crude oil being rejected by the refinery's buyer. The oil is around a 44 gravity @ 180 degrees. It is a high paraffin content oil.
The problem is that during the grind out what appears to be asphaltenes (at least to me) is settling out above the water and below the oil. There are some solids settling to the bottom of the water. The crude is poured off and then the asphaltenes(?) are cut using xylene. It is spun again and no more water or solids come out but the asphaltenes(?) still collect above the water and do not stay in solution in the xylene. The oil buyer says that it is not asphaltenes(?) but is possibly an emulsion of paraffin and water and consequently rejects the oil.
The asphaltenes(?) will not melt or burn using a flame. Am I dealing with asphaltenes or some other problem? Shouldn't asphaltenes be soluble in xylene and stay that way during the grind out?
Any suggestions or knowledge would be appreciated.

Cliff

 

[jmw]

Can i suggest the Fuel Handbook (McGraw and Hill) as a source?
Asphaltenes, Maltenes etc are normally bound up with the resins. I have come across problems associated with asphaltenes in crude oil before. This is also a problem with heavy fuel oil blending. Where the heavier crudes which are diluted with distillate fuel prior to being put into the pipeline to reduce the viscosity asphaltene drop out occurs. The problem is that the resins are soluble in the distilate which then causes the asphaltenes to drop out. In the Canadian oilfields this caused a problem decause of the effect of asphaltenes on the viscometers, asphaltene coating meant they had to be removed and cleaned every couple of weeks (until PTFE coating was used which prevented the asphaltene coating). However, the important point is that this asphaltene drop out was only a problem in one blending line. In 4 identical lines doing the same job on the same crude there was no problem. The difference? the problem viscometer was too close to the blend point where the dropout was most pronounced. One thought is that after the initial drop out, and further down the pipeline, a true blend was created and no further precipitation occured. Or maybe the asphaltenes were picked up again by the resins. Once we had a solution, we did not look further at the mechanisms involved. It is possible that what you are seeing is the resins being disolved and causing precipitation of the asphaltenes. Asphaltenes are always found in crudes, heavy fuel oils, residual oil etc. The problem may be not how to disolve them out of the crude but how to get them associated with the resins once more.
Possibly, with a high parafinic crude the effect of xylene is the same as where crude (or heavy fuel oil) is cut with an incompatible distillate. Maybe their is an alternative to the xylene? (I'm sorry, i don't ask this because i have any special knowledge, i'm just curious)
You might find the article at

http://www.bre.com/technicalpapers/technicalpaper.asp?articlenumber=33

provides useful information on incompatible blends. (Compatibility and stability are not the same thing).
Hopefully someone with the right experience can provide some answers for you. I shall be interested to see the comments myself.