NMR and Chemometric Characterization of Vacuum Residues and Vacuum Gas Oils from Crude Oils of Different Origin

摘要

NMR spectroscopy in combination with statistical methods was used to study vacuum residuesand vacuum gas oils from 32 crude oils of different origin. Two chemometric metodes were applied. Firstly,principal component analysis on complete spectra was used to perform classification of samples andclear distinction between vacuum residues and vacuum light and heavy gas oils were obtained. To quantitativelypredict the composition of asphaltenes, principal component regression models using areas of resonancesignals spaned by 11 frequency bins of the 1H NMR spectra were build. The first 5 principal componentsaccounted for more than 94 % of variations in the input data set and coefficient of determinationfor correlation between measured and predicted values was R2 = 0.7421. Although this value is not significant,it shows the underlying linear dependence in the data. Pseudo two-dimensional DOSY NMR experimentswere used to assess the composition and structural properties of asphaltenes in a selected crude oiland its vacuum residue on the basis of their different hydrodynamic behavior and translational diffusioncoefficients. DOSY spectra showed the presence of several asphaltene aggregates differingin size and interactions they formed. The obtained results have shown that NMR techniques in combinationwith chemometrics are very useful to analyze vacuum residues and vacuum gas oils. Furthermore, weexpect that our ongoing investigation of asphaltenes from crude oils of different origin will elucidate inmore details composition, structure and properties of these complex molecular systems.