Determination of asphaltene structural parameters by Raman spectroscopy

Abstract

AbstractThe objective of this study is to determine the aromatic sheet diameter (La) and the number of aromatic sheets per stack (n) for asphaltene molecules from Raman spectra by investigating and optimizing empirical equations proposed in the literature for both crystalline and amorphous carbon materials. The results clearly indicated that the best empirical equation for determining the aromatic sheet diameter for asphaltene was the equation proposed by Tuinstra and Koenig, but only when the graphitization indicator ID/IG would have been determined from the peak integrated ratio, rather than from the peak intensity ratio. The best results of La were obtained when the Raman spectra were deconvoluted and fitted with three peaks using Gaussian function. The number of aromatic sheets per stack for asphaltene was also determined by examining various empirical equations proposed for crystalline carbon materials. The results indicated that these equations could be applied on asphaltene if the first‐order region of Raman spectrum were to be fitted with two peaks, representing the G and D bands. Fitting the spectra with more peaks could result in splitting the G band into two bands (i.e., G and D2 bands), which would shift the G‐band position to a wavenumber below 1581.6 cm−1, and, subsequently, prevent the utilization of these empirical equations.