Aromatic from Kuwait crude

Figure 4a. 13C NMR of aromatic fractions from Kuwait crude oil...

Crude oil contains about 0.01% metals and up to 5% sulfur present in large aromatic structures. These levels are highly dependent on the origin of the crude. For example, California crude is relatively low in sulfur but higher in metals than crude from Kuwait. Any process to remove them must be economical with little destruction of the hydrocarbons and minimum consumption of H2. The catalyst is Co, Mo/A1203 with particles a few mm in diameter. Although sulfur is usually a poison for catalytic reactions it is used here in a positive function to control selectivity. It is presulfided to decrease activity towards excessive consumption of H2 that leads to unwanted saturation of aromatic molecules. 

This concept of optimum aromaticity and the role of sulfur compounds as inhibitors were further established by a study by Bum and Greig (British Petroleum) of the oxidation of solvent extracted base stocks.18 They chose samples from a North African (Sahara) and three Middle East (Iran, Abu Dhabi, and Kuwait) crudes. The aromatic + heterocyclic (A + II) and paraffin + naphthene (P + N) components were separated by alumina chromatography from each base stock (Table 5.9 includes their composition and sulfur contents) and recombined in several ratios and the resistance of the blends to oxidation measured by the oxygen uptake method. 

Figure 4a shows the 13C spectra of the total aromatics and di- + triaromatics subfractions of Kuwait crude oils. Figure 4b shows the 13C spectra of the monoaromatics and di- + triaromatics from South Louisiana crude. These have been recorded with a commercially available CFT-20 Varian Associates 13C NMR spectrometer. CDC13 solutions of each fraction have been utilized along with tetramethylsilane (TMS) for calibration purposes. The numbers under the individual peaks indicate the chemical shifts of nonaromatic carbons in the range of 14.11 ppm to about 37.16 ppm. 

Table IV gives some of the parameters that have been derived from the manipulation of the integrated intensities of the various chemically shifted signals of the aromatic fractions and subfractions of Kuwait and South Louisiana crudes. Profiles that emerge from these baseline studies are the following ...

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