Supercritical Pyrolysis of Toluene

• Main Author: Nguyen, Khue Dang
• Other Authors: Benton, Michael
• Format: Others
• Language: en
• Published: LSU 2011
• Subjects: Chemical Engineering
• Online Access: http://etd.lsu.edu/docs/available/etd-11072011-200036/

The development of future high-speed aircrafts will required the jet fuel to act as the primary engine coolant to absorb excess heat produced by the engine components. To aid in removing the excess heat and reducing the aircrafts weight, future jet fuels used for high-speed aircrafts will act as both coolant and fuel; however, by exposing the fuels to temperatures and pressures above their critical point, they undergo pyrolysis to form larger and/or more abundant polycyclic aromatic hydrocarbons (PAH) and eventually carbonaceous solid deposits in the pre-combustion environment. The formation of solid deposits in the pre-combustion environment results in clogging of the fuel line, reduced engine performance, and meticulous engine maintenance, so it is important to understand the mechanisms leading to the formation of carbonaceous solid deposits from thermally stressed hydrocarbons. Using a flow reactor, an investigation was conducted to understand the reaction mechanisms leading to the formation of PAH, which are known to be precursors to solid deposits. The reactant toluene, selected to be a representative of the aromatic components of real-world jet fuels, was pyrolyzed in a flow reactor under supercritical conditions, with temperature conditions between 550 and 685 C and pressure conditions between 50 and 100 atm. Identification and quantification of the gas- and liquid-phase samples are conducted using gas chromatography (GC) with flame ionization detection and high-pressure liquid chromatography (HPLC) with diode-array ultraviolet-visible (UV) detection the liquid-phase GC and HPLC are in series with mass spectrometry (MS). Identification using gas-phase GC, liquid-phase GC, and HPLC revealed the formation of 60 hydrocarbon (aliphatic and aromatic) products, of which three unsubstituted PAH products have never before been identified as products of toluene pyrolysis. Furthermore, temperature and pressure dependent yields of the identified hydrocarbon products are presented. The formation of gaseous products as well as aromatic products in the supercritical toluene pyrolysis environment is the result of decomposition of toluene, recombination of unstable molecule fragments, dehydrogenation of aromatic products, and/or successive addition of aromatic molecules to low-ring-number aromatic products. At high thermally stressed conditions the formation of increasingly high molecular PAH becomes insoluble in the fuel and forms a distinct solid phase, carbonaceous solid deposits.