Experimental and quantum chemical investigation into the nature of jet fuel deposition on surfaces

Chemical analysis of undissolved deposits formed on a simulated jet fuel burner feed arm suggest a higher concentration of oxidized polar fuel species at the wall-deposit interface. To investigate the nature of their adsorption, the adsorption energies of various jet fuel species classes were calculated using plane-wave DFT methods on two oxide surfaces Fe₂O₃ -(0001) and Cr₂O₃ -(0001), which were chosen to represent a stainless steel surface. A mixed termination approach was chosen to encapsulate the heterogeneous nature of stainless steel surfaces. On metal-terminated Fe₂O₃ and Cr₂O₃ surfaces, the order of the absolute adsorption energies was RSO₃H > RSO₂H > RCOOH > RSH > ROH > RCOH > RH. Dissociative chemisorption was observed for all the acid species, with sulfur acids having a higher absolute adsorption energy on Cr₂O₃ but carboxylic acids having a higher adsorption energy on Fe₂O₃. On oxygen-terminated Fe₂O₃, the order of the absolute adsorption energies was RSO₂H > RSR > RSO₃H > RSH > ROH > RCOH > RCOOH > RH. On the other hand, for oxygen-terminated Cr₂O₃, the order of the absolute adsorption energies were RSO₂H > RSR > RSH > RSO₃H > RCOH > ROH > RCOOH > RH. In contrast to the metal terminated surface, acids do not chemisorb on the oxygen terminated surfaces. Instead, the sulfur acids are found to form surface hydroxyl species from the dissociation of the acidic -OH group. The reactivity of the surfaces followed the general pattern: metal terminated-Fe₂O₃ > metal-terminated Cr₂O₃, oxygen-terminated Fe₂O₃ ≈ Cr₂O₃. Overall, a combination of experimental and quantum chemical techniques confirmed the theory that sulfur acids are the initial species to deposit on stainless steel.