Chromatographic Separation of Conventional and Experimental Fuels

This research was performed in order to develop a chromatographic method for the separation and isolation of the various classes of hydrocarbons present in conventional and experimental aircraft fuels. The objective of such a technique is to provide a convenient means of estimating the relative proportions of the hydrocarbon classes, i.e., normal and branched alkanes, alkylbenzenes, alkenes, etc., and to render the initially complex fuels tractable to conventional methods of analysis and characterization. The procedure developed consists of a semi-preparative column chromatographic method, using spherical particulate silica gel column packing and isobutane as the mobile phase. The fuel samples are fractionated by passing them through the column and collecting the eluting fractions at regular intervals. The volatile isobutane carrier is evaporated from the fractions and the residues are analyzed by techniques such as gas chromatography. Because the isobutane vaporizes quantitatively at low temperatures, the fractions are obtained free of interfering solvent. In this respect, the technique is novel and unprecedented. Results of the analyses show that the method provides good separation of aliphatic and aromatic hydrocarbons, and partial resolution of aliphatic and olefinic hydrocarbons. Resolution may be improved substantially by optimizing the column temperature and by using low-boiling mobile phases of varying polarity.