Heat-Flow Measurements for n-Hexane Reactions on H-ZSM-5 and H(Zn)-ZSM-5: Implications for Endothermic Reforming in Hypersonic Aircraft

Abstract

The heat flows associated with conversion of nhexane on H-ZSM-5 and H(Zn)-ZSM-5 were measured for reaction at 60 bar and both 673 and 773 K for application to endothermic reforming for hypersonic flight. The heat flows were determined by measuring the power required to maintain a constant reactor temperature upon introduction of flowing nhexane. The acid-catalyzed reactions over H-ZSM-5 were found to be only mildly endothermic (<10 kJ/mol) at low conversions and exothermic at all conversions above 50%. The reactions on H(Zn)-ZSM-5 were significantly more endothermic (40−50 kJ/mol) for conversions of <70%; however, the reactions also became exothermic at very high conversions. Measurements of the product distributions showed that the reaction endothermicity for H(Zn)-ZSM-5 at lower conversions was likely due to the formation of significant amounts of benzene, toluene, and xylene, but that these were converted to higher-molecular-weight products at high conversions. Implications of these results for preparing improved endothermic-reforming catalysts is discussed.

Distinguishing Condensed-Phase Cracking Products with the Same Mass-To-Charge Ratio Using a Triple Quadrupole Mass Spectrometer in Product Scan Mode

“…Although these authors pointed out the possibility that aromatic species larger than benzene, toluene, or naphthalene are likely formed by the catalyst under high conversion/high pressure conditions, they were not able to identify these species using their gas chromatography technique because of their higher molecular weight (C7+). As research continues that involves the synthetic modification of zeolite catalysts (e.g., H(Zn)-ZSM-5) 17 or novel fuel catalyst combinations (e.g., dehydrogenation of alkylamines over ZrO 2 ) 29 to optimize endothermicity, it will be important to elucidate the chemical structures of the products so that the reaction endothermicity can be better understood via calculation of the reaction enthalpies (i.e., Hess' Law). Based on the results of the current study, it is likely that such products include alkyl chainsubstituted benzenes.…”

“…The H-ZSM-5 catalyst was obtained from Prof. Raymond Gorte at the University of Pennsylvania or purchased from Zeolyst (ZSM-5: CBV 5524G) and calcined following the previously reported procedure. 17 2.2. Instrumentation.…”

“…Our current work addresses issue (2) and follows from a previous study, 7 which addressed issue (1) by applying the triple quadrupole instrument to analyze the catalytic cracking products of n-hexane and n-dodecane over a zeolite catalyst (H-ZSM-5). This catalyst has been used previously by Gorte and coworkers 17 to promote endothermic cracking chemistry at temperatures lower than the threshold for coke formation.…”

In Situ Diagnostic of Supercritical Fuel Surrogates: Probing Heterogeneous Catalysis by Collision-Induced Dissociation in a Molecular Beam Tandem Mass Spectrometer

“…long). The H-ZSM-5 catalyst, which can be purchased from Zeolyst, 10 was obtained from Prof. Raymond Gorte at the University of Pennsylvania.…”

“…We chose this zeolite catalyst because it has been previously well characterized and has been suggested as a candidate catalyst for high-speed flight applications. For example, Gorte and co-workers 10 measured the heat flows for the conversion of n-hexane on H-ZSM-5. Therefore, cracking of alkyl fuel surrogates on H-ZSM-5 is a suitable model system to test the capabilities of our new instrument.…”