834 Volume 55, Number 7, 2001 APPLIED SPECTROSCOPY 0003-7028 / 01 / 5507-0834$2.00 / 0 q 2001 Society for Applied Spectroscopy Geographical Origin Classication of Petroleum Crudes from Near-Infrared Spectra of Bitumens M. BLANCO,* S. MASPOCH, I. VILLARROYA, X. PERALTA, J. M. GONZA ´ LEZ, and J. TORRES Departament de Quõ ´mica, Unitat de Quõ ´mica Analõ ´tica, Facultat de Cie `ncies, Universitat Auto `noma de Barcelona, E-08193 Bellaterra, Barcelona, Spain (M.B., S.M., I.V.); and Asfaltos Espan ˜oles S.A., Autovia de Salou s/n, Apdo 175, E-43080 Tarragona, Spain (X.P., J.M.G., J.T.) Petroleum crudes of different geographical origin exhibit differenc- es in chemical composition that arise from formation and ripening processes in the crude. Such differences are transmitted to the frac- tions obtained in the processing of petroleum. The use of unsuper- vised classication/sorting methods such as principal component analysis (PCA) or cluster analysis to near-infrared (NIR) spectra for bitumens obtained from petroleum crudes of diverse origin has revealed that composition differences among bitumens are clearly reected in the spectra, which allows them to be distinguished in terms of origin. Accordingly, in this work we developed classica- tion methods based on soft independent modeling of class analogy (SIMCA) and articial neural networks (ANNs). While the latter were found to accurately predict the origin of the crudes, SIMCA methodology failed in this respect. Index Headings: Geographical origin classication; Bitumen; Near- infrared spectroscopy. INTRODUCTION Petroleum was formed millions of years ago from or- ganic sediments that built up in the bottom of the sea. The reducing environment, combined with bacterial ac- tion and the increased temperature and pressure, caused conversions in organic matter that lasted thousands of years. Because of its uid nature, petroleum moved from its sites of formation to those of accumulation, where it continued to ripen (and its composition to change). 1 All these processes yielded petroleum crude; however, each petroleum well has a geological history of its own, so crudes of different geographical origin exhibit a differ- ential chemical composition that is reected in the frac- tions separated during its processing. Bitumen is the residue obtained in the vacuum distil- lation of the crude oil, and it is formed basically by a complex mixture of high-molecular-weight hydrocarbons together with heteroatoms. The distillation process makes the residue poor in volatile compounds, preserving the heaviest ones. Due to its composition and the interactions among its components, bitumen is a black, high-viscous material that behaves as a non-Newtonian uid to am- bient temperature. Bitumens can be assumed to be a mixture of four com- pound families, viz., saturated hydrocarbons, aromatic hydrocarbons, resins, and asphaltenes. The proportions of these components and their mutual interactions dictate the physical properties of each bitumen and, therefore, its nal use as road pavements, waterproof surfaces, pipeline Received 25 September 2000; accepted 2 March 2001. * Author to whom correspondence should be sent. coatings, joint llers, etc. The most important properties habitually determined in bitumens are those which dene their reological behavior (viz., penetration, viscosity, soft- ening point, breaking point, ductility, etc.). However, the relationship between the composition and physical prop- erties of a bitumen is not always a simple one; in fact, bitumens of different composition can exhibit identical or very similar properties. This was demonstrated by Cor- bett in 1969 2 in analyzing four bitumens of different or- igin that exhibited a similar penetration at 25 8C and also a similar softening point. From the chemical character- ization of the fractions obtained, he concluded that the proportion of the four compound families (asphaltenes, saturated hydrocarbons, aromatics, and resins), their av- erage molecular size, and the degree of aromaticity and naphthenicity vary with the origin of the bitumen. Compositional differences due to the geographical or- igin make bitumens from certain sources more suitable for given applications. Some bitumens with a high het- eroatom content in their structure are optimal as road pavements. Other kinds of bitumens, after a blowing pro- cess with hot air, are especially suitable to produce wa- terproof products. Light bitumens, which have a low as- phaltene content, cannot be used directly, but they are especially able to be mixed with other bitumens or ad- ditives (such as rubbers or polymers) to modify their properties. Differences in chemical composition among petroleum crudes of different origin have led some authors to test various identication methods for petroleum products. The procedure invariably involves recording a multipa- rameter signal that is subsequently processed chemo- metrically. Thus, Kvalheim et al. characterized petroleum crudes from various wells in the Northern Sea by means of 13 C-NMR spectra, using principal component analysis (PCA) and soft independent modeling of class analogy (SIMCA) as chemometric techniques. 3 Some aviation fu- els have been discriminated by using articial neural net- works (ANNs) to process their chromatographic data. 4,5 Also, uorescence spectra have enabled the identication of various types of petroleum and fuels 6,7 and the com- pilation of libraries with a view to identifying petroleum hydrocarbons in sea water. 8 However, no application of these procedures to the classication of bitumens appears to have been reported to date. Near-infrared (NIR) spectroscopy has advantages over the previous analytical techniques in that it requires no sample pretreatment and it allows the expeditious deri- vation of information for classication purposes. The