Crude Oil Dissolved in Water

Fuel oil has a complex and poorly studied molecular structure. Due to depleting of light oil reserves, hydrocracking of fuel oil is becoming more important for gasoline production. Hydrocrackers are expensive and special catalysts have to be used. Knowing the precise composition of crude oil would be important to make refining as efficient as possible. However, the extreme complexity of crude oil makes it impossible to separate it into individual compounds and determine their structure by NMR or X-ray spectroscopy.

Isotope exchange combined with high-resolution mass spectrometry (MS) can be used. ¹⁶O/¹⁸O exchange allows enumeration of =O groups and speciation of furans. H/D exchange allows enumeration of –OH groups, –NH groups, aromatic hydrogens, α-hydrogens, etc. Water is the most readily available and the cleanest source of isotopes. However, oil is insoluble in water under normal conditions. Therefore, harsh conditions, such as concentrated acids or bases, are required which can considerably modify the sample’s composition.

Yury Kostyukevich and Eugene Nikolaev, Skolkovo Institute of Science and Technology, Russian Federation, and colleagues, have developed a cheap and simple approach to analyze the composition of crude oil using H/D and ¹⁶O/¹⁸O exchange. They used high temperature and pressure to dissolve oil in water. The sample was heated to 360 °C in heavy water at a pressure above 300 atm for one hour. This incubation in near-critical water was monitored by high-resolution Fourier transform mass spectrometry (FTMS). The team determined the number of exchanges for each molecule simultaneously. They determined the number of ¹⁶O/¹⁸O exchanges in 276 species and the number of H/D exchanges in 150 species.

The method avoids environmentally hazardous solvents. According to the researchers, the findings might help better understand the composition of crude oil and will contribute to the development of new catalysts for more efficient oil refining. In addition, the method may be used to study other complex nonpolar compounds at the molecular level.