Ind. Eng. Chem. Prod. Res. Dev. 1985, 2 4 ,
68
F = Fisher's function
K i= adsorption equilibrium constant for component i, atm-' k = kinetic constant kads = kinetic constant of the oxygen adsorption k,, = kinetic constant of the reoxidation of the catalyst k , = kinetic constant of the reduction of the catalyst pi = partial pressure of component i, atm rr = initial rate of formation of product i , mol of i formed/h g of cat.) W / F = contact time, g of cat./mol C4= h-' xT = total conversion and mol C,= transformed, h-' Subscripts a = acetone h = hydrocarbon (for isobutene) i = reactant or product i m = methacrolein 0 = oxygen w = water Registry No. CH2=C(CH3)CH0,78-85-3; CH3COCH3,6764-1; isobutene, 115-11-7;molybdenum oxide, 11098-99-0;uranium oxide,
11113-93-2.
Literature Cited Bielinski, A.; Haber, J. Catal. Rev.-Sci. Eng. 1979, 19, 1. Bond, G. C. "Catalysis by Metals"; Academic Press: New York, (1962), p 128. Cartlidge, J.; McGrath, L.: Wilson, S. H. Trans. Inst. Chem. Eng. 1977, 5 5 , 164. Cortds Corberin, V.; Corma, A.; Kremenld, G. Ind. Eng Chem Prod. Res. Dev. 1884, 23, 546. Cullis, C. F.; Hucknall, D. J. I n "Catalysis"; Bond, G. C.; Webb, G., Ed.; Specialist Periodical Reports; The Chemical Soclety: London, 1982: Vol. 5, Chapter 7. Exner, 0. Collect. Czech. Chem. Commun. 1988, 31, 3222.
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Fisher, T. "Statistical Methods for Chemists"; Wiley: New York, 1955. Gerai, S. V.; Rozhkova. E. V.; Gorokhovatskii, Ya. B. J . Catal. 1973, 28. 241. Gupta, R. B.; Viswanathan, B., Sastri, M. V. C. J . Catal. 1972. 26, 212. Hinshelwood, C. N. "The Kinetics of Chemical Change": Oxford University Press: New York, 1940; p 207. Hucknall, D. L. "Selectlve Oxidation of Hydrocarbons"; Academic Press: London, 1974. Juusola. J. A.; Mann, R. F.; Downie, J. J . Catal. 1970, 7 7 , 106. Kobayashi, M., Futaya, R. J . Catal. 1979, 56, 73. KremeniE, G.; Fierro, J. L. G.; Cortds Corberin, V. Actas ' 8 Simp. Iberoam. de CaGlisis, 1982; Vol. 1, p 346. Krenzke, L. D.; Keulks, G. W. J . Catal. 1980, 6 4 , 295. Kubokawa, Y.; Ono, T. Bull. Chem. Soc. Jpn. 1978, 57(12), 3435. Mann, R. S.; KO, D. W. J . Catal. 1973, 30,276. Mann. R. S.; Yao, K. C.; Dosi, M. K. J . Appl. Chem. Biotechnol. 1972, 22. 915. Mars, P.; van Krevelen, D. W. Chem. Eng., Sci. Suppl. 1954, 3 , 41. Muller, A.; Julllet, F.; Telchner, J. Bull. SOC. Chim. F r . 1976, 9 - 7 0 , 1356. Portefaix, J. L.; Figueras, F.; Forissler, M. J . Catal. W80, 6 3 , 307. Ray, S. K.; Chanda, M. Ind. Eng. Chem. Prod. Res. Dev. 1978, 75,234. Sahzar, E. Ph.D. Thesis, Univ. de Bilbao, Spain 1983. Schuhl, Y.; Delobel, R.; Baussart, H. C . R . Acad. Sci. Paris. Ser. C 1980, 290, 5. Sheltad, K. A.: Downie, J.; Graydon, W. F. Can. J . Chem. Eng. 1960, 38, 102. Tasc6n, J. M. D.; Cortds Corberin, V.; KremeniE, G.; Gonzilez Tejuca, L. 1984; to be published. Van der Wiele, K.; Van der Berg, P. J. "Comprehensive Chemical Kinetics", Bramsford, C. H., Tipper, C. F. H., Ed.; Elsevier: Amsterdam, 1978: Vol. 20, Chapter 2. Vinogradova. 0. M.; Vytnov. G. F.; Margoiis, L. Ya. Kinef. Katal. 1977, 18, 1595. Weller, S. W. AIChE J . 1958, 2,59. Weller, S.W. Adv. Chem. Ser. 1975, No. 148, 26. Zhiznevskii, V. M.; Kabubowskaya, L. F.; Tolopko, D. K . Zh. Fiz. Khim. 1978. 52. 1058.
Received for review March 8, 1984 Accepted November 16, 1984
Effect of Nitrogen Compounds on Cracking Catalysts Chla-Mln Fu and Arnold M. Schaffer' Phllllps Petroleum Company, Phillips Research Center, Bartlesviiie, Oklahoma 74004
The present study was undertaken to determine how catalytic cracking is affected by the presence of various nitrogen compounds. The effects on conversion and selectivity of about 30 different nitrogen compounds were determined. There is good agreement between the molecule's gas-phase proton affinity and its poisoning effect on cracking catalysts. Moreover, proton affinity accounts for the strong dependence of poisoning on the nitrogen compound's molecular structure including such factors as the type of nitrogen heterocyclic, size of the molecule, and presence of alkyl substituents. For example, conversions for 0.5 wt % nitrogen added to a gas oil from pyridine, pyrrole, quinoline, indole, acridine, and carbazole are 5 1.4, 54.1, 39.2, 49.6, 34.7, and 51.7 vol % , respectively. Results have also been obtained demonstrating that conversion and selectivity are also sensitive to the nitrogen concentration, the cracking temperature, the type of feed, and the properties of the cracking catalyst.
Introduction The decreased availability of sweet light crudes has caused significant changes in refinery operation (Murphy et al., 1979; Green and Broderick, 1981). For example, fluid catalytic crackers (FCC's) must process feedstocks that are heavier, more aromatic, and higher in metals, sulfur, and nitrogen. There have been several recent studies reviewing the effects of feedstock changes on FCC operation (Tolen, 1981;Ritter et al., 1981;Magee et al., 1979);however, these reports do not deal specifically with the effects of nitrogen compounds. This is somewhat surprising since it has long been recognized that basic nitrogen compounds can poison acid cracking catalysts (Mills et al., 1950; Voge et al., 1951; Viland, 1957). Furthermore, as indicated by Table I, nitrogen poisoning will become even more important if heavy oil, shale oil, tar sands liquids, and direct coal liquids 0196-432118511224-0068$01.50/0
Table I. Nitrogen Content of Various Feedstocks N content. feedstock
wt %
E a s t Texas gas o i l A r a b l i g h t 650 O F + West Texas topped crude N o r t h Slope 650 O F + direct coal liquids Gulf o f Suez 650 O F + t a r sands l i q u i d s off-shore California Monagas 650 O F + San Joaquin 650 O F + (California) Paraho shale o i l
0.07 0.10 0.18 0.21
0.3 0.37 0.4 0.9 0.91 1.02 2.1
become available as refinery feedstocks (Hochman, 1982; deRosset et al., 1979). The present study was thus undertaken to determine how the crackability of a typical 0 1985 American Chemical
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FCC feed over a modern zeolitic cracking catalyst is affected by the presence of various nitrogen compounds. Although there have been a number of studies on nitrogen poisoning of acidic catalysts, none of them used realistic FCC feeds or zeolitic cracking catalysts. For example, to study nitrogen poisoning, Mills et al. (1950) cracked cumene over silica-alumina while Voge et al. (1951) cracked decalin over silica-zirconia-alumina in the presence of various compounds. More typical of the work in this area is that of Jacobs and co-workers (Jacobs et al., 1974; Jacobs and Heylen, 1974) in which selective adsorption of such nitrogen compounds as pyridine and 2,6-dimethylpyridine was used to obtain information about the acid site distribution and number of active sites for cumene cracking on a hydrogen Y zeolite. There has also been some work on trying to predict how the total nitrogen concentration in the FCC feed will affect the performance of a cracking catalyst (Jacob et al., 1976; Schwab and Baron, 1981); however, these kinetic models did not take into account differences in the poisoning characteristics of the individual nitrogen compounds. As Sie (1980) has pointed out, it is generally a serious oversimplification to ignore these differences. As suggested above, the extent of nitrogen poisoning depends on the specific nitrogen compounds in the catalytic cracker feed. Recently, there has been a great deal of progress made in characterizing not only the type of nitrogen compound but even the individual compounds themselves (Raith and Lanik, 1982; Schmitter et al., 1982; Shue and Yen, 1981; Holmes and Thompson, 1981). Most of the basic nitrogen compounds are present as alkylpyridines or alkylquinolines while nonbasic nitrogen compounds are generally pyrroles or carboxamides (Raith and Lanik, 1982; Holmes and Thompson, 1981). The type of nitrogen compounds in the catalytic cracker feed will also depend on processing conditions, particularly if the feed is hydrotreated before it is cracked (Culberson and Rolniak, 1981). Depending on such factors as reaction severity and catalyst type, hydrotreatment can dramatically alter the nitrogen type distribution (Rollman, 1971; Katzer and Silvasubramanian, 1979). For example, hydrotreating can convert pyridinic and pyrrolic compounds to such nitrogen types as alkylanilines, alkylpyridines, hydroindoles, and pyrrolidines (Holmes and Thompson, 1981). This report will summarize the results of a study on the effects of various nitrogen compounds on a steam-aged fresh FCC catalyst and two metals-contaminated equilibrium FCC catalysts. Most studies were made in a bench-scale fluidized reactor with a gas oil feed. A large variety of nitrogen compounds, each of which was tested separately, was studied including amines, heterocyclics (including mono-, di-, and triaromatics), plus alkylated and hydrogenated heterocyclics. The report then discusses the relationship between the properties of the nitrogen compounds (basicity being most important) and their effect on cracking. Finally, results on varying catalyst, feedstock, concentration of nitrogen compound, and cracking temperature are discussed.
Experimental Section 1. Measurement of Catalytic Activity. As a measure of catalyst activity, the cracking of a gas oil or a hydrotreated vacuum resid with and without the addition of a nitrogen compound was studied. The activity tests were conducted in a micro-confined fluid bed unit (MCBU) containing about 35 g of cracking catalyst. Details about this system have been described elsewhere (McKay and Bertus, 1979). Basically, it is a batch system operated in the fluidized mode. Nitrogen was used as the fluidizing
69
Table 11. Selected Properties of Fresh Steam-Aged F-950M Catalyst, a West Texas Refinery Equilibrium Catalyst, and an East Texas Refinery Equilibrium Catalyst West Texasb East Texas' fresh catsn eauil cat. eauil cat. surface area, m2/g 67 85 94 pore volume, cm3/g 0.44 0.34 0.35 metals, ppm Ni
