Neutrals, asphaltene aromatic

Oil and Asphaltene Aromatic Neutrals. Tables III and IV summarize the compositional data for the CnH2n+z and CnH2n+zO compounds present in the oil and asphaltene neutrals. In addition, LV/EI/MS analysis using direct... 

The weight percents of the individual homologs in each specific-Z series (carbon-number distributions) were calculated from LV/EI/MS molecular-ion intensities assuming constant mole sensitivities for each specific-Z series. An invalid factor was inadvertently used in the previous conversion of the LV/EI/MS carbon-number distributions for the asphaltene neutral fraction to carbon-number distributions based on the total liquid. Consequently, the entries in the LV/EI/MS carbon-number distributions for Z(H), Z(O), and Z(S) asphaltene neutral aromatic compounds in References 35 and 47, the total weight percentages of these specific-Z series in References 35, 47, and 48, and the sums of these latter weight percentages reported in all these references should be multiplied by 0.892. 

The agreement between the two analyses regarding the percentage saturates in the asphaltene neutrals is satisfactory as follows. The Oklahoma State University (OSU) value of 3.9% was obtained from silica gel chromatography of the pentane-soluble (88.2%) asphaltene neutrals and, hence, represents a lower limit for the percentage saturates in the asphaltene neutrals. The value of 5.2% results from a proprietary Exxon saturate/aromatic hydrocarbon EI/MS technique developed for low-boiling coal liquids. 

The IR spectra of the oil and asphaltene neutrals (35) exhibited no significant absorptions in the region 3200-3600 cm-1 except for H20 bands at 3620-3695 cm-1 in the matrix-isolation spectrum of the oil neutrals. Weak absorptions near 1700 cm-1 are indicative of minor amounts of ketones/ aldehydes in both neutral fractions. The absorptions at 2860, 2950, and 3050 cm-1 are ascribable to aliphatic and aromatic CH stretching. The band at 1600 cm-1 is characteristic of aromatic ring C=C. Thus, the oxygen-containing compounds in both neutral fractions are principally composed of ethers. 

The IR data, as discussed above, and the molecular formulas for the first homologs in at least the less-negative Z(O) series in Table IV, indicate that furans dominate the oxygen-containing compounds in both the oil and asphaltene neutral fractions. Furthermore, comparison of the Z(H) and Z(O) values in Tables III and IV, respectively, suggests that the furans are phenomenologically derived from the aromatic hydrocarbons by replacement of ring CH2 by O. 

The carbon-number distributions (35) for the CnH2n+zO compounds in the oil neutrals are relatively short and exhibit maxima near the center of each Z(O) series. In contrast, the carbon-number distributions for the asphaltene-neutral Z(O) compounds are characterized by the occurrence of maximums in the beginning of each distribution. The origin of the differences in these Z(O) distributions is not clear. Furthermore, the former result contrasts with the result obtained for the oil aromatic hydrocarbons and the latter parallels the distribution of weight percents in each Z(H) series for the asphaltene neutrals. It is tempting to ascribe the difference in the distribution of weight percents of the various Z(O) compound types in the oil and asphaltene neutrals to the chemistry associated with the COED process. However, the fact that considerable overlap exists in the neutral-aromatic Z(O) compounds between the oils and asphaltenes precludes this conclusion because the results could reflect phenomena associated with solvent extraction. 

Separation Procedure. The petroleum asphaltenes were separated into five fractions acids, bases, neutral nitrogen compounds, saturate hydrocarbons, and aromatic hydrocarbons. Acids were isolated using anion-exchange resin, bases with cation-exchange resin, and neutral nitrogen compounds by complexation with ferric chloride adsorbed on Attapulgus clay. The remaining hydrocarbon fraction is separated on silica gel to produce saturate and aromatic hydrocarbon fractions. 

SiLLCA Gel Chromatotraphy. The acid-, base-, and neutral-nitro-gen-free asphaltene (.126 g) was dissolved in n-pentane (10 mL) and placed on a silica gel column (30 g) that had been wet-packed with n-pentane. The column was eluted with n-pentane (500 mL) to remove the saturate hydrocarbons. Aromatic hydrocarbons were eluted from the column using 85% n-pentane-15% benzene (250 mL) and 60% benzene-40% methanol (250 mL). UV analyses of the saturate fraction indicated that trace amounts of aromatic hydrocarbons were present. The amount of saturates in the aromatic fraction, if any, is unknown. 

The neutral nitrogen fraction is 1% of the total asphaltene, and the saturate hydrocarbon and aromatic hydrocarbon fractions are 3% and 2%, respectively. The recovery of material after the separation amounted to 99% of the total asphaltene. 

Because the asphalt system is not a true solution, it can be fractionated into saturates, aromatics, resins, and asphaltenes by the solvent fraction method, SARA method, or TLC method. The polarity of these four fractions is increased in the order of saturates, aromatics, resins, asphaltenes. In crude oil, asphaltene micelles are present as discrete or dispersed particles in the oily phase. Although the asphaltenes themselves are insoluble in gas-oil (saturates and aromatics), they can exist as fine or coarse dispersions, depending on the resin content. The resins are part of the oily medium but have a polarity higher than gas-oil. This property enables the molecules to be easily adsorbed onto the asphaltene micelles and to act as a peptizing agent of the colloid stabilizer by charge neutralization. 

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