Detection, Identification, and Quantification of Nonpolar High Molecular Weight Contaminants in Jet and Diesel Fuels by Liquid Chromatography

Abstract

A straightforward analytical methodology has been developed for the identification and characterization of nonpolar high molecular weight contaminants, such as lubricant oils and greases, in jet and diesel fuels. Such contaminants typically contain a distribution of compounds with carbon numbers in the range C25–C40, or 350–600 Da, which are sufficiently larger than fuel constituents to be effectively detected via liquid chromatography. The methodology is based on high performance liquid chromatography, utilizing a xylenes–cyclohexane mobile phase gradient to separate these contaminants from fuels by means of dual porous graphite stationary phase columns and evaporative light scattering detection. The limits of detection for n-pentacosane, n-triacontane, n-pentatriacontane, and n-tetracontane were determined to be approximately 0.1 ppm, with an upper limit of 10% by volume. The newly developed methodology improves upon a previously developed methodology by both enhancing the resolution of high molecular weight contaminants from diesel fuels and eliminating the need for a chlorinated solvent while still minimizing gradient artifacts in the baseline. Uninformative variable elimination–partial least squares modeling was used to construct a comprehensive modeling framework trained with data collected from fuels with known contaminants, to characterize detected contaminants in at least a semiquantitative fashion. The overall methodology was successfully tested for use with various grades of jet and diesel fuel samples.

Recent Advances in Separation-Based Techniques for Synthetic Polymer Characterization

“…A general trend of research in this field has been in the separations of polymers, waxes and as part of multitechnique analysis of fractionated components from complex polymers. The enhanced resolution for stereoisomers and small molecules on porous graphitic carbon packed columns has been utilized to analyze polypropylene stereoisomers, oxidized waxes, tacticity in poly-1-octenes and high molecular weight fractions in Jet and diesel fuels . Standard HTLC routines have been adapted to analyze poly­(ethylene-co-propylene) elastomers, carboxylic acid–functionalized PE, poly­(ethylene-co–vinyl acetate) copolymers, heterogeneity in chain walking PE and to investigate changes in the microstructure of heterophasic poly­(ethylene-co-propylene)­s with increasing ethylene content, before and after visbreaking .…”

“…The enhanced resolution for stereoisomers and small molecules on porous graphitic carbon packed columns has been utilized to analyze polypropylene stereoisomers, 125 oxidized waxes, 95 tacticity in poly-1-octenes 93 and high molecular weight fractions in Jet and diesel fuels. 106 Standard HTLC routines have been adapted to analyze poly(ethylene-co-propylene) elastomers, 96 carboxylic acid−functionalized PE, 105 poly(ethylene-co−vinyl acetate) copolymers, 104 heterogeneity in chain walking PE 29 and to investigate changes in the microstructure of heterophasic poly(ethylene-co-propylene)s with increasing ethylene content, before and after visbreaking. 108 In furthering work toward understanding the separation mechanism in HTLC, experimental separations of poly(ethylene-co-octene) copolymers were compared with theoretical predictions.…”