(279d) A Group Contribution Method for the Prediction of the Mid Infrared (MIR) Absorption Spectra of Species Involved in Fluid Catalytic Cracking (FCC)

Authors: 
Lopez-Zamora, S. M., Universidad Nacional de Colombia
Molina, A., Universidad Nacional de Colombia – Sede Medellín, Facultad de Minas, Bioprocesos y Flujos reactivos
de Lasa, H., Western University
A methodology, based on a group contribution method, for the prediction of the cross section of hydrocarbons in the MIR region (3200−2800 cm−1), is proposed. Among the process technologies in a refinery, FCC is one of the most important and profitable. Its installed capacity worldwide is 14 million barrels/day [1] as reported in [2,3]. The FCC feedstock is basically composed of large hydrocarbons (C30−40+) that are converted into a diverse number of smaller molecules. The study of the variation of the concentration of each molecule in the FCC reaction is considered almost impossible. A rapid characterization of the global reaction that takes place in FCC is of great practical interest given the relatively short residence time (< 5 s) of this process. The MIR region between 3200 cm−1 and 2800 cm−1 includes the C − H stretching bands characteristic of hydrocarbons. A relation of the absorption cross section (σ) and the integrated absorption band intensity (Ψ) with the number of C − H bonds over the range 3200-2800 cm−1 has been previously reported [4–8]. This behavior has been studied in the case of alkanes by Sharpe et al. [9]. However, as far as we know, no similar correlation has been attempted in the case of olefins, aromatics and naphthenes.

We propose a group contribution method that predicts the MIR spectra of hydrocarbons.. The quantitative spectral database available by Pacific Northwest National Laboratory (PNNL) [10] was used as source library for spectra of 65 hydrocarbons. The contribution method uses structural information of individual chemical species (e.g. functional groups) and associated parameters to calculate the absorption cross section at a given wavenumber as a function of the sum of group parameters. This methodology does not require prior experiments nor the knowledge of physical or chemical properties of the substance, only the chemical structure of the molecule for the prediction of the spectra of hydrocarbons in the MIR region (3200 − 2800cm−1). We applied the proposed method to predict the MIR spectra of 21 different gasoline samples previously measured by Klingbeil et al. [5]. A good correlation coefficient between experimental and predicted spectra was obtained (R2 > 0.9). The method was also successfully employed for the prediction of the concentration of the aromatic and iso-paraffinic fractions of premium gasolines with relative absolute errors of the order of 10% and has a potential application in the understanding of the coupling between chemistry and hydrodynamics in FCC reactors.

Acknowledgements

The authors would like to acknowledge the financial support from the Colombian Science Foundation (COLCIENCIAS) and the Colombian state oil company (ECOPETROL S.A.) under contract No. 0423 2013 and the Emerging Leaders in the Americas Program (ELAP) Canadian Exchange Program.

References

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