The results of a number of screening experiments are reported that were designed to seek hydrogen donor molecules that function as high-temperature stabilizers (i.e., >400 °C) in jet fuels and similar hydrocarbon mixtures. 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.

The purpose of this study was to examine the feasibility of using 13C NMR spectroscopy to analyze urinary metabolites produced following coadministration of two structurally similar carbon-13-labeled compounds to rodents. Acrylonitrile (AN) and acrylamide (AM) are used in the chemical industry to manufacture plastics and polymers. These compounds are known to produce carcinogenic, reproductive, or neurotoxic effects in laboratory animals. The potential for human exposure to AN and AM occurs in manufacturing facilities and environmentally. Male F344 rats and B6C3F1 mice were coadministered po [1,2,3-13C]AN (16-17 mg/kg) and [1,2,3-13C]AM (21-22 mg/kg) after 0 or 4 days of administration of unlabeled AN or AM. Urine was collected for 24 h following administration of the 13C-labeled compounds and analyzed by 13C NMR spectroscopy. Rats and mice excreted metabolites derived from glutathione (GSH) conjugation with AM or AN or derived from GSH conjugation with the epoxides cyanoethylene oxide (CEO) or glycidamide (GA). GA and its hydrolysis product were also detected in the urine of rats and mice. For mice, an increased urinary excretion of total AN- and total AM-derived metabolites (p < 0.05) on repeated coadministration suggested a possible increase in metabolism via oxidation. In addition, mice had an increased (p < 0.05) percentage of dose excreted as metabolites derived from GSH conjugation with AM, AN, CEO, or GA after five exposures as compared with one exposure that may be related to a significant increase in the synthesis of GSH or an increase in glutathione transferase activity. The only significant (p < 0.05) increase between one and five exposures for the rat was in the percentage of metabolites produced following conversion of AM to GA. The use of 13C NMR spectroscopy has provided a powerful methodology for elucidation of the metabolism of two 13C-labeled chemicals administered simultaneously.

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.

In addition to the complex chemistry of cracking and reforming reactions that occur when jet fuels are subjected to thermal stresses at temperatures above 400 °C, carbonaceous solids and deposits are formed and these present serious problems. The principal reaction pathways that lead to the formation of carbonaceous solids at these temperatures have been studied using FTIR spectroscopy.Using these results as a guide we have successfully identified a number of additives, most notably benzyl alcohol and 1,4-benzenedimethanol, that retard the formation of carbonaceous solids in Jet A-l fuel at 425 °C.

We have previously demonstrated that additives such as benzyl alcohol and the like successfully retard the formation of carbonaceous materials in jet fuels at temperatures in excess of 400 "C. An understanding of the underlying mechanisms is important and could point the way to the design of superior additives. Here we report the results of thermal stressing studies performed on a model system consisting of dodecane/benzyl alcohol mixtures. Dodecane has been the subject of many prior studies and is a good representative model compound for jet fuel. Furthermore, deuterated compounds of both dodecane and benzyl alcohol are available and results obtained using these compounds were found to be particularly useful in rationalizing why benzyl alcohol acts as a thermal stabilizer in hydrocarbon mixtures at such high temperatures.