Energy & Fuels 1997, 11, 1311-1312
1311
Removal of Copper from Hydrocarbon Fuels Using Novel Azamacrocycle Polymers Dhanajay B. Puranik,†,‡ Vikram A. David,‡ Robert E. Morris,§ and Eddie L. Chang*,† Code 6930, Naval Research Laboratory, Washington, D.C. 20375-5348, Geo-Centers, Inc., Ft. Washington, Maryland 20744, and Code 6181, Naval Research Laboratory, Washington, D.C. 20375-5348 Received July 28, 1997. Revised Manuscript Received September 11, 1997 Solubilized copper contamination can seriously impair the thermal stability of hydrocarbon fuels.1 Contamination occurs from copper alloys present in refinery rigs or fuel-handling systems.2 The presence of as little as 15-20 parts per billion (ppb) or lower quantities of copper in jet fuel can lead to nozzle clogging and flow reduction.3 Long-term exposure of fuel to copper at ambient temperatures can lead to degradation.4 Efforts to remove the copper contamination by clay filtration were unsuccessful because they also remove beneficial fuel constituents and additives. The current practice of using solubilized chelators is limited by the high-temperature environment in injector nozzles and military jet augmentors.5,6 Thus, there exists a need for new alternative materials to address this problem. The approach we are investigating is to attach copper chelators to a solid substrate. This allows us to select a chelator that is optimal for copper removal without the constraints imposed by a soluble chelant. We have examined the use of novel azamacrocycle polymers to remove the copper from hydrocarbon fuels. The preliminary prerequisites placed on the material were that it possess a high number of chelators, that the material negligibly contaminates the media after metal removal, and that the preparation be practical. Methacrylate polymers were chosen as suitable substrates because they are easy to prepare and manipulate.7,8 The choice of the chelator is dictated by the need for copper specificity and a high formation constant for copper. In a survey of metal chelators possessing a high copper affinity, 1,4,8,11-tetraazacyclotetradecane (cyclam) 1 emerged as the most suitable candidate with potential for near-complete metal extraction.9-12 Derivatives of 1, such as 2 (1-hexadecyl-1,4,8,11tetraazacyclotetradecane), prepared via substitution of †
Code 6930, Naval Research Laboratory. Code 6181, Naval Research Laboratory. Geo-Centers, Inc. (1) Droegemuller, E. A. Fuel Requirements for Supersonic Transport, Sixth World Petroleum Congress, Frankfurt, West Germany, June 1963; Elsevier Publishing Co.: Barking, U.K. (2) Tyler J. C.; Cueller, J. P., Jr.; Moses, C. A. An Alternative Test Procedure to Qualify Fuels for Navy Aircraft: Phase II Continuation. Final Report, Vol. I. Report for NAPC-PE-176C, Southwest Research Institute on contract with Naval Air Propulsion Center; Naval Air Propulsion Center: Trenton, NJ, August 1987. (3) Shertzer, R. H. Report NAPTC-PE-14; Naval Air Propulsion Test Center: Trenton, NJ, January 1973. (4) Kendall, D. R.; Mills, J. S. Ind. Eng. Chem. Prod. Res. Dev. 1986, 25, 360. (5) Morris, R. E.; and Turner, N. H. Fuel Sci. Technol. Int. 1990, 8, 327. (6) Nowack, C. J. Report NAPTC-PE-9; Naval Air Propulsion Test Center: Trenton, NJ, January 1977. (7) Nakano, T.; Okamoto, Y.; Sogah, D. Y.; Zheng, S. Macromolecules 1995, 28, 8705. (8) Kim, Y. S.; Sung, C. S. P. J. Appl. Polym. Sci. 1995, 57, 363. ‡ §
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a ring nitrogen have been reported.13-17 Though such substitutions decrease the formation constant of 1 with copper (for 1, log KCu ) 27 to ca. log KCu ) 1820), the formation constant is still higher than other chelants.9,10,15,17 Accordingly, we have investigated acrylate polymers of 1 for their capability to remove copper from hydrocarbons. We report herein the results of these initial studies. Acrylate monomers 5a-5c with carbon chain lengths of 2, 6, and 8 carbons were prepared and polymerized as shown in Figure 1. In a typical procedure, 1 mmol of the bromo alcohols 3 with methacryloyl chloride yielded yellow, light sensitive oils 4 in 75-80% yields. Reaction of these with an 8-fold excess of cyclam in chloroform produced the acrylate esters 5 in 70-80% yields. Free-radical polymerization to yield polymers 6a-6c was induced by adding AIBN to the monomer in the minimum amount of toluene or THF and heating the solution. The number average molecular weights (Mn) of the polymers were 7.2 × 104, 5.4 × 104, and 8.0 × 104 for 6a-6c, respectively. Following preparation, the polymers 6a-6c were tested for their metal removal capability. Solutions of dodecane and JP-5 were prepared with 20 ppm of dissolved copper as copper ethyl acetoacetate. In a typical experiment, approximately 1.0 g of the polymer and 5.0 g dodecane, or JP-5, containing the dissolved copper were stirred overnight. The chelator-to-copper ratio was biased in favor of the chelator in order to test the general principle of this approach. Although metalchelating polymers for the removal of metals from water (9) Loh, S. E.; Gan, L. M.; Chew, C. H. Pure Appl. Chem. 1995, A32, 1681. (10) Bianchi, A.; Micheloni, M.; Paoletti, P. Coord. Chem. Rev. 1991, 110, 17. (11) Lauffer, R. B. Chem. Rev. 1987, 87, 901. (12) Yamada, K.; Koide, Y.; Yamanokuchi, H.; Ohmura, H.; Shosenji, H. Bull. Chem. Soc. Jpn. 1989, 62, 2867. (13) Cabbiness, D. K.; Magerum, D. W. J. Am. Chem. Soc. 1969, 91, 6541. (14) Helps, I. M.; Parker, D.; Morphy, J. R.; Chapman, J. Tetrahedron 1989, 45, 219. (15) Puranik, D. B.; Singh, A. N.; Chang, E. L. J. Coord. Chem. 1996, 39, 321. (16) Sillen, L. G.; Martell, A. E. Stability Constants of Metal-Ion Complexes. Special Publication No. 17; The Chemical Society: Burlington House, WI, 1964. (17) De Santis, G.; Dicasa, M.; Mariani, M.; Seghi, B.; Fabbrizi, L. J. Am. Chem. Soc. 1989, 111, 2422.
© 1997 American Chemical Society
1312 Energy & Fuels, Vol. 11, No. 6, 1997
Communications
Figure 1. Reaction scheme for the synthesis of polymerizable monomers 5a-5c and their subsequent free-radical polymerization to form 6a-6c. Table 1. Results from the AA-ICP (graphite furnace) Analysis of Residual Copper in Dodecane and JP-5 after Treatment with Polymers 6A-6ca dodecane
compound
copper concn before treatment (ppm)
copper concn after treatment (ppm)
6a 6b 6c 1 2
20 20 20 20 20
0.002 0.003 0.002 0.052 0.319
a
JP-5 copper concn before treatment (ppm)
copper concn after treatment (ppm)
20 20 20
0.002 0.003 0.002
Error ) (0.006 ppm.
are well-known, the suitability of these polymers for metal removal from nonaqueous media is not obvious. Therefore, the efficiency of such polymers for metal removal from nonaqueous media must be examined on a case-by-case basis. With our polymers, the green tint imparted to the dodecane and JP-5 by the copper salt rapidly disappeared upon addition of the polymer. The polymers, being insoluble in dodecane, were easily filtered after treatment. The same filtered polymer samples used for treating copper-containing dodecane were subsequently reused to treat the copper-doped JP-5 jet fuel. Similar to dodecane, the polymers were again easily filtered from the JP-5 after treatment. Measurement of the residual copper in the dodecane and JP-5 was performed with an atomic absorption spectrometer equipped with
an ICP-graphite furnace. The results showed negligible amounts of copper left in either dodecane or JP-5. Table 1 shows the residual copper concentration after treatment of 20 ppm copper in dodecane and JP-5 jet fuel with the polymers 6a-6c. It is seen from Table 1 that the cyclam-functionalized polymers were quite effective in removing copper from the media. The advantage of preparing and using such polymers over mere addition of metal chelants 1 and 2 can be seen in the higher residual copper concentrations for 1 and 2 due, likely, to contamination of the media by the metal-chelator complex. Such potential contamination of the fuel by soluble chelators18 is considerably reduced, if not eliminated, by polymerizing the chelators. Polymers containing appropriate metal chelants could provide a practical and economical means for removing dissolved metals present in parts per million (ppm) levels in organic media such as dodecane or jet fuels. Further work on turnover ratio and defining the effectiveness of other chelants with other metals is currently in progress. Acknowledgment. We acknowledge support for this project from ONR and Naval Air Propulsion Center and Dr. Mei-Hsia Huang at NAWC in Trenton for the copper analysis. EF970128A (18) Morris, R. E.; Hazlett, R. N.; McIlvaine, C. L. Ind. Eng. Chem. Res. 1988, 27, 8.
