Aromatic content is a key characteristic of hydrocarbon oils and can affect a variety of properties of the oil including its boiling range, viscosity, stability, and compatibility of the oil with polymers.
Existing methods for estimating aromatic contents use physical measurements, such as refractive index, density, and number average molecular weight (see Test Method D 3238
The aromatic hydrogen and aromatic carbon contents determined by this test method can be used to evaluate changes in aromatic contents of hydrocarbon oils due to changes in processing conditions and to develop processing models in which the aromatic content of the hydrocarbon oil is a key processing indicator.
TABLE 1 Sample and Instrument Conditions for Continuous Wave (CW) Measurements of 1 H NMR Spectra
| Solvent | Chloroform-d |
| Sample concentration | Up to 50 % v/v for distillable oils |
| Sample temperature | Instrument ambient |
| Internal lock | None |
| Sample spinning rate | As recommended by manufacturer, typically 20 Hz |
| r-f Power level | As recommended by instrument manufacturer |
| Signal to noise level | A minimum of 5:1 for the maximum height of the smaller integrated absorption band |
| Chemical shift reference | Preferably tetramethylsilane (0.0 ppm) at no greater than 1 vol % concentration |
| Integration | Integrate over the range − 0.5 to 5.0 ppm for the aliphatic band and 5.0 to 10.0 ppm for the aromatic band |
1.1 This test method covers the determination of the aromatic hydrogen content (Procedures A and B) and aromatic carbon content (Procedure C) of hydrocarbon oils using high-resolution nuclear magnetic resonance (NMR) spectrometers. Applicable samples include kerosenes, gas oils, mineral oils, lubricating oils, coal liquids, and other distillates that are completely soluble in chloroform at ambient temperature. For pulse Fourier transform (FT) spectrometers, the detection limit is typically 0.1 mol % aromatic hydrogen atoms and 0.5 mol % aromatic carbon atoms. For continuous wave (CW) spectrometers, which are suitable for measuring aromatic hydrogen contents only, the detection limit is considerably higher and typically 0.5 mol % aromatic hydrogen atoms.
1.2 The reported units are mole percent aromatic hydrogen atoms and mole percent aromatic carbon atoms.
1.3 This test method is not applicable to samples containing more than 1 mass % olefinic or phenolic compounds.
1.4 This test method does not cover the determination of the percentage mass of aromatic compounds in oils since NMR signals from both saturated hydrocarbons and aliphatic substituents on aromatic ring compounds appear in the same chemical shift region. For the determination of mass or volume percent aromatics in hydr......
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