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.