Coke Deposition Inhibition for Endothermic Hydrocarbon Fuels in a Reforming Catalyst-Coated Reactor

Coke formation is an obstacle in using hydrocarbons as the coolant in hypersonic flight vehicles. In this paper, effective inhibition of coke deposition was realized by the addition of wall catalytic steam reforming, and the corresponding mechanism was revealed. The anticoking tests were evaluated during the thermal cracking and catalytic steam reforming processes of an endothermic hydrocarbon fuel under 3.0 MPa and outlet temperature from 600 to 680 degrees C. The amount and properties of coke deposited in the thermal cracking with and without steam reforming were investigated on the basis of their temperature-programmed oxidation profiles and scanning electron microscopy. The results show that the mass percentages of filamentous and amorphous cokes deposited during thermal cracking without steam reforming are 20.32 and 79.68%, respectively. The amount of coke deposited in a bare reactor is nearly twice that deposited in a reforming catalyst-coated reactor, and the coke formation rate in the former case is 8 times that in the latter case. The absence of filamentous deposits during catalytic steam reforming is ascribed to the catalyst layer on the inner surface, which prevents contact between the hydrocarbon fuel and active metal sites. Filamentous coke formation is therefore totally inhibited. Moreover, catalytic steam reforming also inhibits amorphous coke deposition. Analyses of the gaseous products and residual liquids from thermal cracking of jet fuel show that the monocyclic and polycyclic aromatic hydrocarbon contents decrease significantly under catalytic steam reforming. The large amount of hydrogen generated from the wall catalytic steam reforming reaction suppresses dehydrogenation, Diels-Alder, and condensation reactions; therefore, coke deposition decreases.