Online Chemical Analysis of Flowing n-Hexane and n-Dodecane on Quartz and Stainless-Steel Surfaces in a Pyrolysis Reactor by Optical Spectroscopy and Molecular Beam Mass Spectrometry

Date of Award

5-9-2026

Degree Name

M.S. in Chemical Engineering

Department

Department of Chemical and Materials Engineering

Advisor/Chair

Andrew DeBlase

Abstract

The pyrolysis of hydrocarbons at high temperatures and pressures is key to the development of advanced thermal management systems and aviation fuel decomposition. A novel experimental technique based on a glass tube reactor (GTR) can be used to probe the pyrolysis of neat hydrocarbon fuel surrogates at supercritical conditions. The GTR combines optical absorption spectroscopy to sensitively measure the onset and rate of deposition with simultaneous chemical speciation by online quadrupole mass spectrometry. Two hydrocarbon surrogates were chosen and used to study amorphous coking on quartz tubes: n-hexane and n-dodecane. For n-hexane and n-dodecane four chemical regimes are revealed with increasing temperature: (1) negligible chemistry, (2) cracking with little-or-no deposition, (3) cracking with deposition, and (4) rapid, severe deposition. These regimes are consistent between both fluids with only minor shifts in the onset temperature of cracking. The deposition of n-hexane on stainless steel was studied using reflection spectroscopy with a stainless-steel insert within the GTR. The addition of a metal insert allowed filamentous deposition. Furthermore, the deposition appeared before the onset of thermal cracking and created a new series of regimes: (1) negligible chemistry, (2) deposition with little-or-no cracking, (3) cracking with deposition, and (4) rapid, severe deposition. SEM images of the surface deposit confirm filamentous coking. The GTR was modelled using computational fluid dynamics. The calculated reaction times can be used in chemical kinetics models to describe the pyrolysis of n-hexane on quartz. The fluid phase decomposition of n-hexane, evident by MS, is consistent with an overall first-order process with an activation energy of 217.7 ± 2.4 kJ·mol–1. Furthermore, several plausible two-step models were derived for n-hexane decomposition in the quartz reactor without the metal insert by constructing Arrhenius plots from the GTR optical absorbance data. This work provides a proof-of-concept that the GTR can be used to both evaluate the thermal stability of supercritical hydrocarbon model compounds and validate purported chemical models for decomposition and deposition.

Keywords

Chemical Engineering, Chemistry

Comments

OCLC No. 1591830115

Rights Statement

Copyright 2026, author.

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