石油与环境生物技术杂志

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Chemical Characterization of Gilsonite Bitumen

Nader Nciri, Suil Song, Namho Kim and Namjun Cho*

This research provides new insights into the chemical composition of the Gilsonite in order to ascertain its properties which can assist in the refining and processing paths of the natural resource. Gilsonite, naturally occurring asphaltite bitumen, consists of a complex mixture of organic compounds. It was collected in the Uinta Basin near the town of Bonanza, Utah. The aim of this work is to obtain a more complete picture of molecular structure of Gilsonite, very important in fuel processing industry, matching and interpreting the results from different techniques. The Gilsonite was characterized by elemental analysis (EA) to determine the concentrations of C, H, N, S, and O, by Fourier transform infrared spectroscopy (FTIR) for comparative analysis of the chemical structures, by Nuclear magnetic resonance spectroscopy of hydrogen (1H NMR) to ascertain the aliphatic and aromatic hydrogen fractions, and by Thin layer chromatography-flame ionization detection (Iatroscan TLC-FID) to quantify saturated and aromatic hydrocarbons, and resin/asphaltene fractions. The results were evaluated in combination with the available geological data and with some bitumens to evaluate, chemically, possible mechanisms of Gilsonite formation. Low hydrogen to carbon atomic ratio (1.44), low sulfur (0.27 wt.%) and high nitrogen (3.25 wt.%) contents were the main characteristics of the Gilsonite from Uinta Basin. FTIR revealed the presence of alkane, aromatic rings, phenyl rings, alcohols, carbonyl groups, organic sulfoxides, and sulfate salts, confirming the fact that Gilsonite is composed of high molecular weight polycyclic constituents comprising of nitrogen, sulfur and oxygen heteroatoms. Likewise, FTIR proved that Gilsonite includes fingerprint of clay minerals. Iatroscan data showed interestingly that Gilsonite contains considerable amount of asphaltenes (79.7 wt.%) and nil amount of aromatics (0 wt.%). While, the yields of saturates and resins account only for 1.6 wt.% and 18.7 wt.%, respectively. Furthermore, SARA method estimated that Gilsonite is extremely instable (Colloidal instability index, CII = 4.34). Proton NMR measurements indicated that the aliphatic hydrogen portion is approximately 95.38% and the aromatic hydrogen fraction is about 4.62%.