Preparation and Anticoking Performance of MOCVD Alumina Coatings for Thermal Cracking of Hydrocarbon Fuels under Supercritical Conditions

Abstract

For advanced thermal management technology of next-generation aircraft, hydrocarbon fuel cooling technology using endothermic cracking reactions is taken as a promising approach to removing heat loading but with a fatal drawback of forming carbonaceous deposits. To develop an effective anticoking technique to resolve this problem, a series of alumina coatings with various thicknesses (318–1280 nm) were prepared in stainless steel 321 tubes (2-mm i.d.) by metal–organic chemical vapor deposition (MOCVD) using aluminum tri-sec-butoxide. X-ray diffraction characterization showed that the prepared MOCVD alumina coatings were essentially amorphous. The anticoking performances of the MOCVD alumina coatings were evaluated using thermal cracking of Chinese RP-3 jet fuel under supercritical conditions (inlet temperature, 575 °C; outlet temperature, 650 °C; pressure, 5 MPa). The results showed that the anticoking performance increased from 37% to 69% as the thickness of the alumina coatings increased from 318 to 1280 nm. Further characterizations of the cokes with temperature-programmed oxidation and scanning electron microscopy indicated that the MOCVD alumina coatings were favorable for depressing metal catalysis cokes over the tube surface, as well as aromatic condensation cokes from bulk cracked fuel.