An analytical method was developed to quantitatively determine the asphaltene content in petroleum crude oils by Fourier transform infrared spectroscopy (FT-IR). Asphaltenes are a solubility class of compounds found in crude oils. They are black to dark brown solids defined by their insolubility in n-alkane solvents. The structure of asphaltene molecules is polynuclear aromatic rings with alkyl side chains and heteroatoms such as nitrogen, oxygen, and sulfur attached. Asphaltenes are known to cause oil well plugging and irreversible catalyst deactivation in refineries. The asphaltene content of 50 crude oils from a wide array of geochemical conditions was determined by the standard n-pentane insolubles method. FT-IR spectra of the 50 crude oils were collected using an attenuated total reflectance cell. A partial least squares model was generated to predict the amount of asphaltenes from 42 of the crude oils. The model was shown to have an R 2 value of 0.95 and a standard error of estimate of 0.92 wt %. An independent prediction set of eight crude oils was used to test the validity of the model. The prediction set was shown to have an R 2 value of 0.96 and a standard error of prediction of 0.99 wt %. The FT-IR method compares favorably with the current laboratory method in terms of results, is faster, and uses no solvents.

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Nickel(II) complexes of the geochemically significant four regioisomers of tetrahydrobenzoetioporphyrin, NiTHBP-A, -B, -C, and -D, which contain a reduced benzo unit fused onto the Cp atoms of a pyrrole ring, have been synthesized and structurally characterized by resonance Raman (RR) spectroscopy with variable-wavelength excitation. Spectra were obtained from CS2 and CH2Cl2 solution samples at room temperature excited at 406.7, 530.9, and 568.2 nm, in resonance with the porphyrin Soret, Ql, and QO electronic transitions, respectively. For comparison, similar RR spectra were measured for Ni(I1) tetra-p,P-butanoporphyrin (NiTBuP) in which each pyrrole bears a tetrahydrobenzo exocyclic ring. These three excitation wavelengths, which selectively enhanced vibrational modes of different symmetry, the measured Raman band depolarization ratios, and the already available normal coordinates of Ni(I1) octaethylporphyrin (NiOEP) permitted assignment of RR bands to nearly all of the porphyrin in-plane skeletal modes. The frequencies of skeletal modes above 1300 cm-' indicate more planar structures in solution for NiTHBP's and NiTBuP relative to NiOEP and Ni(I1) etioporphyrins. Several unique marker bands are also found for modes of the tetrahydrobenzo exocyclic rings, especially in the 568.2-nm excited spectra. The relative positions of the methyl and ethyl substituents have a marked influenced on the low-(350-550 cm-') and mid-frequency (750-1100 cm-I) vibrational spectra, allowing the four NiTHBP regioisomers to be readily distinguished.

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