Distribution of Higher n-Alkanes in Partially Frozen Middle Distillate Fuels

摘要

In conjunction with continuing studies on the effect of composition on the freezing points of middle distillate fuels, attention was directed to partially frozen fuels. The crystals and residual liquid from partially frozen JP-5 and DFM fuel samples derived from both petroleum and shale were separated from each other and collected by means of the NRL liquid-solid separator apparatus (LSS) at several temperatures below the freezing points of the original samples. The original fuel samples, the solid material (precipitate), and liquid (filtrate) were characterized by gas chromatography (GC). The filtrate data were straightforward. As expected, Van't Hoff plot of the n-alkanes concentrations (log concentrations vs reciprocal absolute temperature) formed straight lines, and their slopes demonstrated the importance of the higher n-alkanes in fuel crystallization at cold temperatures. The precipitate data presented some problems of interpretation since it was observed that the waxy crystal precipitate matrix entrapped significant amounts of liquid (filtrate). The data on solid which were obtained by these methods demonstrated that the higher n-alkanes play the key role in fuel crystallization at low temperatures, concentrating as much as tenfold in the crystallized solids compared to the liquid. Also, it was clearly shown that the n-alkanes form the major part, up to least 95% by weight in some fuels, of the solid crystals formed.