Ind. Eng. Chem. Res. 2008, 47, 9351–9360
9351
Characterization of Solid Deposits Formed from Jet Fuel Degradation under Pyrolytic Conditions: Metal Sulfides Ramya Venkataraman† and Semih Eser* The PennsylVania State UniVersity, UniVersity Park, PennsylVania 16802
Reaction of the organic sulfur compounds in Jet A with Fe- and Ni-based alloy substrates under pyrolytic conditions formed significant amounts of metal sulfides. Pyrrhotite (Fe(1-x)S) and heazlewoodite (Ni3S2) were formed on SS316 and Inconel 600 surfaces, respectively, in the short duration experiments. After extended periods of thermal stressing, an additional crystal phase, pentlandite (Fe,Ni)9S8, was also observed on both surfaces. The lack of FeS2 (pyrite) formation over extended periods of stressing indicates that the amount of sulfur reacting with the substrates decreased with the increasing thermal stressing time. A focused ion beam (FIB)/SEM analysis showed that the metal sulfide formation can extend up to 2 µm depth from the surface in 2 h of thermal stressing. The formation of metal sulfides on alloy surfaces degrades the alloy surfaces and affects solid carbon deposition from jet fuel. Introduction Studies in the past have clearly shown that the organosulfur compounds present in hydrocarbon fuels react with metal substrates to form metal sulfides.1-3 Surface reconstruction upon addition of sulfur compounds to Fe-Ni surfaces has also been reported in several earlier studies.4 These surface changes play a significant role in solid deposit formation from hydrocarbon degradation, including a dramatic increase in the amount of carbon formed in some cases,5 and clearly suppressed deposit formation in others.5-8 Corrosion of metal surfaces due to sulfide formation is expected to be as problematic as solid carbon deposition from fuel degradation especially under the high temperature-high pressure conditions in future advanced aircraft. Two important metals used in the construction of jet engine components are Fe, Ni, and their alloys. This study characterizes the nature of metal sulfides formed on an ironbased alloy, SS316, and a nickel-based alloy, Inconel 600, from the thermal stressing of a jet fuel sample under pyrolytic conditions for varying reaction times. This was done in an attempt to understand the nature of metal-sulfur interactions under conditions of flight operation in advanced aircraft. Experimental Section An iron-based alloy, SS316, and Ni-based alloy, Inconel 600, were used in this study. Individual coupons measuring 13 cm × 0.3 cm × 0.025 cm were placed in a 1/4 in. (OD), 20 cm long, glass-lined, stainless steel tube reactor inserted in a vertical block heater. The fuel used in the study was commercial aviation Jet A with a sulfur content of 0.1 wt %. The sulfur content of this fuel is higher than usually encountered, but it lies within the sulfur level specifications for commercial aviation fuel (10 wt %). Two different morphologies of the same crystal (pyrrhotite on the SS316 surface and heazlewoodite on the Inconel 600 surface) suggested localized changes in the environment of the substrates, which resulted in preferential growth of specific crystallographic planes in some cases. A focused ion beam (FIB)/SEM analysis showed that the metal sulfide formation can extend up to 2 µm depth from the surface. After extended periods of thermal stressing, sulfides of the minor components, Ni in SS316 and Fe in Inconel
600, were formed on the surfaces. Correspondingly, reaction of pyrrhotite and heazlewoodite on both surfaces led to the formation of Pentlandite ((Fe,Ni)9S8) in the long duration experiments. The formation of carbon-coated metal sulfides on the surfaces during thermal stressing appears to affect the diffusion of metal and sulfur species from the bulk to the surface with increasing thermal stressing times. The oxidation of the top layers of metal sulfides on the substrate foils led to the formation of a protective oxide layer, which prevented the subsequent oxidation of any sulfide species in the bulk. Acknowledgment We would like to thank Dr. Trevor Clark and Josh Maier of The Materials Research Institute at Penn State University for their help with the SAED patterns and FIB/SEM of samples. The funding for this work was provided by Roll-Royce plc, Derby and Rolls-Royce Corp., Indianapolis. Literature Cited (1) Kim, M. S.; Rodriguez, N. M.; Baker, R. T. K. The Interplay Between Sulfur Adsorption and Carbon Deposition on Cobalt Catalysts. J. Catal. 1993, 143, 449. (2) Reyniers, M.; Froment, G. F. Influence of Metal-Surface and Sulfur Addition on Coke Deposition in the Thermal-Cracking of Hydrocarbons. Ind. Eng. Chem. Res. 1995, 34, 773–785. (3) Raymundo-Pinero, E.; Altin, O.; Eser, S. Effects of Sulfur Compounds on Solid Deposition on Metal Surfaces from Thermal Decomposition of n-Dodecane. 224th ACS National Meeting, Boston, MA, August 1822, 2002. (4) Rodriguez, N. M.; Kim, M. S.; Fortin, F; Mochida, I.; Baker, R. T. K. Carbon Deposition on Iron-Nickel Alloy Particles. Appl. Catal., A 1997, 148, 265–282. (5) Tibbetts, G. G.; Bernardo, C. A.; Gorkiewicz, D. W.; Alig, R. L. Role of Sulfur in the Production of Carbon-Fibers in the Vapor-Phase. Carbon 1994, 32, 569–576. (6) Bramley, A.; Haywood, F. W.; Cooper, A. T.; Watts, J. T. The Diffusion of Non-metallic Elements in Iron and Steel. Trans. Faraday Soc. 1935, 31, 0707-0733. (7) Bajus, M.; Vesely, V. Pyrolysis of Hydrocarbons in the Presence of Elemental Sulfur. Collect. Czech. Chem. Commun. 1980, 45, 238–254. (8) Bajus, M.; Baxa, J. Coke Formation During the Pyrolysis of Hydrocarbons in the Presence of Sulfur-Compounds. Collect. Czech. Chem. Commun. 1985, 50, 2903–2909. (9) Altin, O.; Eser, S. Analysis of Solid Deposits from Thermal Stressing of a JP-8 Fuel on Different Tube Surfaces in a Flow Reactor. Ind. Eng. Chem. Res. 2001, 40, 596–603. (10) Crystallographic and Crystallochemical Database for Mineral and their Structural Analogues, 2000; http://database.iem.ac.ru/mincryst/index.php, date accessed: 2/26/07. (11) Zhang, F. Carbon Deposition on Heated Alloy Surfaces from Thermal Decomposition of Jet Fuel. M.S. Thesis, The Pennsylvania State University, 2000. (12) Pareek, V. K.; Ozekcin, A.; Mumford, J. D.; Ramanarayanan, T. A. Transport of Sulfur through Preformed Spinel films on Low Alloy Fe-Cr Steels. J. Mater. Sci. Lett. 1997, 16, 128–130. (13) Predel, B. Dy-Er-Fr-Mo. Phase Equilibria, Crystallographic and Thermodynamic Data of Binary Alloys. In Landolt-Bo¨rnstein - Group IV Physical Chemistry; Madelung, O., Ed.; Springer-Verlag: New York, 1995; Vol. 5e. (14) Predel, B.; Hoch, M. J. R.; Pool, M. Non-Tetrahedrally Bonded Binary Compounds II. Phase Diagrams and Heterogenous Equilibria: A Practical Introduction, 1995. (15) Waldner, P.; Pelton, A. D. Critical Thermodynamic Assessment and Modeling of the Fe-Ni-S System. Metall. Mater. Trans. B 2004, 35, 897–907. (16) Waldner, P.; Sitte, W. Thermodynamic Modeling of High-Temperature Fe-Ni Heazlewoodite. AdV. Eng. Mater. 2006, 8, 11. (17) Cahn, R. W. Material Science and Technology: A ComprehensiVe Treatment; Weinheim: New York, 1991; Vol. 5. (18) Brandt, A. J. Sulfur Effects on the Formation of Solid Deposits from Heated Jet Fuel. M.S. Thesis, The Pennsylvania State University, University Park, PA, 2006.
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ReceiVed for reView June 29, 2008 ReVised manuscript receiVed August 29, 2008 Accepted September 08, 2008 IE801007R
