Distillates of most crude oils contain n-alkanes in relatively high amounts. The concentration of n-alkanes a&cts important properties of the distillate fuels, such as engine knocking, freezing point, pour point and viscosity. Two common approaches for isolating n-alkanes from other hydrocarbons are urea adduction and adsorption in molecular sieves. The latter method is used in the PNA (paraffins, naphthenes, aromatics) analysis, but can be used only for naphtha with boiling points below 21OV. Since the urea adduction method is highly time-consuming and also of questionable analytical value, there is a need for fast methods which can be applied to all kinds of petroleum samples.
The most likely method of choice today would appear to be some kind of high-performance liquid chromatography (HPLC), such as the work of Alfredsson2v3 which separated paraffins from naphthenes in gasoline range petroleum on an experimental polystyrenedivinylbenzene support (40 A). However, this separation can not be achieved with higher boiling fractions. Rearing in mind the complexity and wide size range of a crude oil, separation of different groups of saturates can realistically be obtained only in limited cuts or fractions. Since reversed-phase materials are known to separate n-alkanes on the basis of chain length4e5, we decided to examine the possibility of using reversed-phase columns for separation of saturated hydrocarbons of high-boiling (above 350Β°C) fractions of crude North Sea oil.