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Energy & Fuels 1996, 10, 812-815
High-Temperature Stabilizers for Jet Fuels and Similar Hydrocarbon Mixtures. 2. Kinetic Studies Emily M. Yoon, Leena Selvaraj, Semih Eser, and Michael M. Coleman* Department of Materials Science and Engineering, The Pennsylvania State University, University Park, Pennsylvania 16802 Received November 16, 1995. Revised Manuscript Received January 16, 1996X
While 1,2,3,4-tetrahydroquinoline and benzyl alcohol are fine high-temperature (>400 °C) thermal stabilizers that efficiently inhibit the thermal degradation of dodecane, jet fuels, and similar hydrocarbon mixtures, kinetic studies reveal that the rate of dodecane degradation in the mixtures is a very strong function of temperature above 400 °C. In fact, we conclude that it will be extremely difficult to adequately stabilize hydrocarbon fuels using hydrogen donors at temperature much above 500 °C.
Introduction In the preceding paper1 we presented the results of a number of screening experiments designed to seek hydrogen donor molecules that function as high-temperature stabilizers (i.e., >400 °C) in mixtures with the model compound dodecane (Dod), jet fuels, and similar hydrocarbons. The most important conclusion of this work was that in the temperature range between 400 and 450 °C, 1,2,3,4-tetrahydroquinoline (THQ) was by far the best thermal stabilizer that we have discovered to date and significantly more effective than benzyl alcohol (BzOH), our previous benchmark.2,3 Two obvious questions that now come to mind are, What is the optimum concentration of THQ required to thermally stabilize jet fuels and similar hydrocarbon mixtures for a particular time and temperature? and What is the influence of temperature on the degradation rate for jet fuel mixtures containing hydrogen donors of fixed initial concentration? This naturally leads to another important question: At what temperature is THQ no longer an effective thermal stabilizer for jet fuel? There is clearly a temperature above which the rate of hydrocarbon bond cleavage completely overwhelms the rate of hydrogen transfer from a potential hydrogen donor (which may itself be also subject to bond cleavage at this temperature) and degradation of the jet fuel will proceed rapidly to the formation of carbonaceous solids. In order to address these questions we need to study the degradation kinetics of hydrocarbon mixtures in the presence of hydrogen donors, which is the major topic of this paper. Experimental Section Dodecane (Dod), benzyl alcohol (BzOH), and 1,2,3,4-tetrahydroquinoline (THQ) were purchased from Aldrich Chemical Co. * To whom correspondence should be addressed. X Abstract published in Advance ACS Abstracts, March 15, 1996. (1) Yoon, E. M.; Selvaraj, L.; Song, C.; Stallman, J. B.; Coleman, M. M. Energy Fuels 1996, 10, 806. (2) Coleman, M. M.; Selvaraj, L.; Sobkowiak, M. and Yoon, E. Energy Fuels 1992, 6, 535. (3) Selvaraj, L.; Sobkowiak, M.; Song, C.; Stallman, J. B.; Coleman, M. M. Energy Fuels 1994, 8, 839.
0887-0624/96/2510-0812$12.00/0
and used without further purification. Details of the thermal stressing experiments performed on pure Dod and the mixtures containing BzOH or THQ at different temperatures in the range from 400 to 500 °C, together with the analysis of the products, are given in the preceding paper.1
Results and Discussion As mentioned in the preceding paper,1 Dod is considered a good representative model compound for jet fuel and we will again restrict ourselves here to results obtained from the thermal stressing of Dod mixtures. Before we discuss the main body of the work it is informative to consider the results obtained from a preliminary study performed to determine the optimum concentration of THQ necessary to stabilize the model compound Dod for 6 h at 425 °C under N2. Thermal stressing experiments were performed on Dod samples containing varying initial amounts of THQ from 1 to 10 mol %. [This is perhaps a good place to emphasize that we believe for THQ, or any similar hydrogen donor, to be effective thermal stabilizers for jet fuels it will need to be present as a significant component (≈1-10%), in other words, in a hydrocarbon “blend” or mixture. This is to distinguish it semantically from an “additive”, a word commonly reserved to describe minor amounts (
