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Deconvolving the absorbance of methyl and methylene groups in the FT-IR 3000-2800 cm-1 band of petroleum fractions

Zervakis Michalis, Livanos Georgios, Pasadakis Nikos

Πλήρης Εγγραφή

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Περίληψη

A new algorithm is proposed to deconvolve the infrared spectrum of complex hydrocarbon mixtures in the 3000-2800 cm-1 region. The algorithm enables the accurate estimation of the contribution of methyl and methylene groups in petroleum samples, which is highly characteristic for their composition. The algorithm is developed based on the analysis of FT-IR spectra of seventy oil fractions, practically covering the whole range of a petroleum refinery intermediate and final products. The experimentally derived spectra are deconvolved by fitting three Lorentzian and one asymmetric Gaussian distributions, corresponding to methyl and methylene asymmetric and symmetric stretching vibrations. Molar absorptivities for these peaks are estimated from the FT-IR spectra of pure n-alkanes and alkyl-aromatics. The curve fitting procedure is implemented in Sequential Quadratic Programming (SQP) utilizing linear and non-linear constraints to incorporate chemical information, including the absorbance band positions and their molar absorptivity values. The developed methodology manages to reconstruct efficiently the FT-IR spectra of petroleum fractions, as indicated by the Mean Square Error (MSE) metric.

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