Detailed FTIR spectroscopy characterization of crude oil extracted asphaltenes: Curve resolve of overlapping bands

Abstract

In recent years, characterization of asphaltenes as an appropriate way to deal with their related problems in the oil industry has been received considerable attention. The Fourier-transform infrared (FTIR) analysis, since its appearance in the 1880s, become one of the most applicable techniques to gain the valuable information about characteristics and functional groups of different samples especially petroleum related materials (e.g. asphaltenes). Despite these advantages, this technique suffers from a severe drawback especially in analyzing complex compounds such as asphaltenes. This problem is defined as overlapping related to the functional groups with the near occurrence bands which can hinder thorough qualitative and quantitative analyzing. A considerable number of studies were dedicated to FTIR analysis of asphaltenes, but the curve resolving of petroleum asphaltenes spectra has not yet been extensively studied. In this paper, four asphaltenes extracted from crude oils were analyzed by FTIR and then these spectra were completely resolved. The results, for the first time, provide a deep insight into the functional groups present in asphaltenes and their attaching substitutions. The comprehensive investigation of bands shifting and the relationship of their band area with elemental results reveal that carboxylic acids are linked to both saturate (band at about 1743 cm−1) and aromatic compounds (band at about 1698 cm−1); however, esters and alcohols (e.g., secondary and tertiary alcohols) are attached to saturated compounds in the studied asphaltenes (band at 1743 cm−1 for saturated esters and bands at 1347, 1160 and 1110 cm−1 for saturated alcohols). Ketones occur as diaryl and mixed (1616 and 1685 cm−1 bands), but ethers appear as alkyl/aryl (1018 cm−1). The sulfoxide (1033 cm−1), secondary amides (bands at 3239, 1649, 1575 and 1310 cm−1), polyaromatic (with different substitutions at region below 900 cm−1), phenols (3430 and 1229 cm−1) and aliphatic compounds (such as methyl, methylene, and methine in the 1460 and 1375 cm−1 bands and in the 3850-3000 cm−1 region) are also present in the studied asphaltenes.