Charge transfer complexes between tetranitrofluorenone and polyaromatic compounds from gasoil: a combined DFT and experimental study

A new method has been recently developed for the hydrodesulfurization of gasoils based on the formation of charge transfer complexes. This method is highly selective towards the removal of alkyldibenzothiophenes from other aromatic compounds present in gasoils. Total energy calculations based on density-functional theory have been performed to study the complexation phenomenon and clarify its high selectivity. DFT calculations improve the understanding of the process and they are also useful for the design of more efficient acceptor derivatives for the desulfurization process. Five charge transfer complexes between a given acceptor and five representative donor compounds present in gasoils have been studied. Three main criteria have been used to characterize the optimized complexes: their complexation energy, their geometry and their electronic structure. The decomposition of total energy showed that the main contribution to the complexation energy comes from the Pauli repulsion and the electrostatic interactions. Hence the charge transfer complexes are not only ruled by charge transfer but also by electrostatic contributions. However, the selectivity of the complexation phenomenon is controlled by the orbital interactions.