An approach for determination of asphaltene crystallite by X-ray diffraction analysis: A case of study

Asphaltenes were precipitated from atmospheric residue and divided into two fractions. One of them was left as such and the second one was submitted to washing under reflux. Characterization of both fractions was carried out through elemental analysis and X-ray diffraction. Diffractograms were analyzed in order to obtain crystallite parameters by smoothing processes previous to deconvolution and then local maxima of a polynomial function were detected. Major peaks were found at around 20°, 25°, and 41° corresponding to γ, (002) and (10) bands. Bragg and Scherrer equations were used to determine the aromatic interlayer and aliphatic distances, as well as thickness and diameter of aromatic sheets. The full-width at half-maximum (FWHM) of the main peaks was firstly estimated using the corrector formula, and therefore the corrector procedure was applied to improve the initial guesses of FWHM. Differences in crystallite parameters between both analyzed samples were observed when using this mathematical approach.