Ind. Eng. Chem. Res. 1988,27, 362-363
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COMMUNICATIONS Source of Jet Fuel Thermal Oxidation Tester Deposits from an Oxidized JP-8 Fuel The object of this research was to determine what components of an oxidized fuel are most responsible for deposits on hot engine parts. A 5-deg boiling range cut of a JP-8 fuel was oxidized with air a t 100 "C and then fractionally distilled a t 25- and 5-Torr pressure into (essentially) recovered fuel, a high boiling fraction (containing monomeric oxidation products), and a residue (containing bifunctional and polymeric materials). Restoration of polymeric oxidation products to the original or recovered fuels greatly increased deposit formation in the jet fuel thermal oxidation tester (JFTOT), ASTM D 3241, but restoration of monomeric oxidation products had little effect. An explanation is proposed. 1. Introduction The jet fuel thermal oxidation test (JFTOT), ASTM D 3241, is one of the best measures of the tendency of middle distillates to give deposits on hot engine parts. For control of these deposits, the fractions of an oxidized fuel that cause most of these deposits should be known. In the work described here, a narrow-boiling fraction of JP-8 fuel was oxidized with air at about 100 "C and then cut by fractional distillation into the main fraction (mostly unoxidized fuel), the monomeric oxidation products of higher boiling point (mostly hydroperoxides, alcohols, and ketones), and the undistillable residue. The best data on primary oxidation products of alkanes come from the papers by Jensen and co-workers (Jensen et al., 1979; Korcek et al., 1987) on the oxidation of n-hexadecane in a flow microreactor at 160 "C with a few minutes average residence time and 119 Torr of oxygen: 48.5 mol % hydroperoxides, 38% alcohols, 0.5% ketones, 8% diols (after reduction), 0.3% cyclic ethers, and also 4.5% cleavage products (Jensen et al., 1981),mostly acids and ketones. Longer oxidations give more alcohols, ketones, and cleavage products from decompositions of hydroperoxides. Formation of bifunctional products is favored by higher oxygen pressures and formation of cyclic ethers by lower oxygen pressures. At 120 "C, the C16products were 73.5% monofunctional, 25.2% difunctional, and 1.3% trifunctional (Jensen et al., 1979). Thus, the undistillable residue from oxidation of our JP-8 fuel may contain bifunctional products amounting to perhaps one-third of the amount of monofunctional oxidation products.
Table I. Oxidation of JP-8 boiling range a t 760 mmHg = 137-188 "C boiling range a t 25 mmHg = 50-86 "C 11950 g of JP-8 cut into 4125 g of fraction 77 (boiling range a t 25 mmHg = 67-72 "C) 2 L of fraction 77 (1545 g) oxidized in air with 0.01 M t-BuZO2 for 19 days a t -100 O C to give 1495 g of product 84A (D 25 0.7718) moles of ROOH" product 84A distilled a t 25 torr yielded 1359 g of 84C, boiling range 58-80 "C, mostly 0.119 recovered fuel with some cleaved oxidation products 123 g of 84D, distillation residue 0.006 2 g of HzO 0.085 11-g loss by decomposition during distillation 0.028 (24%) 121 g of 84D distilled in 3 lots a t 5 Torr yielded 60 g of 87A, boiling range 50-80 "C, mostly
