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through this barrier. The presence or absence of diffusional restrictions due to the barrier depends on the activity test conditions. Diffusional limitations occur when reaction rates of the model compounds are relatively faster than their rates of diffusion and might well be important under processing conditions with large-sized molecules.
Acknowledgment This work was supported by the US Department of Energy at Sandia National Laboratories under Contract DE-AC04-76DP00789and at the University of Utah and the University of New Mexico by subcontract to Sandia. Registry No. Mo, 7439-98-7; C, 7440-44-0; Fe, 7439-89-6; Ti, 7440-32-6; Ni, 7440-02-0; P, 7723-14-0; thiophene, 110-02-1; 1hexene, 592-41-6; isooctene, 107-39-1; dibenzothiophene, 132-65-0; naphthalene, 91-20-3; dibenzofuran, 132-64-9; indole, 120-72-9.
Literature Cited Bhinde, M. V.; Shih, S.; Zwadski, R.; Katzer, J. R.; Kwart, H. In Proceedings of the Third International Conference on the Chemistry and Uses of Molybdenum; Barry, H. F., Mitchell, P. C. H., Eds.; Climax Molybdenum Co.: Ann Arbor, MI, 1979; p 184. Cable, T. L.; Massoth, F. E.; Thomas, M. G. Fuel Proc. Technol. 1981,4 , 265. Cable, T. L.; Massoth, F. E.; Thomas, M. G. Fuel Proc. Technol. 1985,10,105. Furimsky, E. Erdoel Kohle, Erdgas, Petrochem. 1979, 32(8), 383. Kovach, S.M.; Castle, L. J.; Bennett, J. V.; Schrodt, J. T. Ind. Eng. Chem. Prod. Res. Deu. 1978,I7(1), 62. Liu, Y.; Massoth, F. E.; Shabtai, S. Bull. SOC.Chim. Belg. 1984,93, 627. Massoth, F. E.; Cowley, S. W. Ind. Eng. Chem. Fundam. 1976,15(3), 218. Massoth, F. E.; MuraliDhar, G. In Proceedings of the Fourth International Conference on the Chemistry and Uses of Molybdenum; Barry, H. F., Mitchell, P. C. H., Eds.; Climax Molybdenum Co.: Ann Arbor, MI, 1982; p 343. Neuworth, M. B.; Moroni, E. C. Fuel Proc. Technol. 1984,8 , 231. Ocampo, A.; Schrodt, J. T.; Kovach, S. M. Ind. Eng. Chem. Prod. Res. Deu. 1978,17(1), 56. Potts, J. D.; Chillingworth, R. S.; Hastings, K. E.; Unger, H. Coal Proc. Technol. 1980a,6, 11. Potts, J. D.; Hastings, K. E.; Chillingworth, R. S.; Unger, H. Proc. Inter. SOC. Energy Conuers. Eng. Conf. 1980b, I5(3), 1832. Potts, J. D.; Chillingworth, R. S. Report 4804-8, 1980; Cities Service Co., Tulsa, OK.
Prasher, B. D.; Gabriel, G. A.; Ma, Y. H. Ind. Eng. Chem. Process Des. Deu. 1978, 17, 266. Qader, Q. MS Thesis, University of Utah, Salt Lake City, 1986. Satterfield, C. N.; Sherwood, T. K. The Role of Diffusion in Catalysis; Addison-Wesley: Reading, MA, 1963; p 65. Stephens, H. P.; Stohl, F. V. Proc. Am. Chem. SOC.,Diu. Fuel Chem. 1984,29(6), 79. Stiegel, G. J.; Shah, Y. T.; Krishnamurthy, S.; Panvelker, S. V. In Reaction Engineering in Direct Coal Liquefaction; Shah, Y. T., Ed.; Addison-Wesley: Reading, MA, 1981; Chapter 6. Stiegel, G. J.; Tischer, R. E.; Polinski, L. M. Ind. Eng. Chem. Prod. Res. Deu. 1983,22(3), 411. Stiegel, G. J.; Tischer, R. E.; Cillo, D. L; Narain, N. K. Ind. Eng. Chem. Prod. Res. Dev. 1985, 24(3), 206. Stohl, F. V.; Stephens, H. P. Proceedings of the 10th Annual EPRI Contractors' Conference on Clean Liquid and Solid Fuels, Palo Alto, CA, April 23-25, 1985. Tamm, P. W.; Harnsberger, H. F.; Bridge, A. G. Znd. Eng. Chem. Process Des. Dev. 1981,20(2), 262. Thakur, D. S.; Thomas, M. G. Appl. Catal. 1983,6 , 283. Thakur, D. S.; Thomas, M. G. Ind. Eng. Chem. Prod. Res. Deu. 1984, 23(3), 349. Wukasch, J. E.; Rase, H. F. Ind. Eng. Chem. Prod. Res. Deu. 1982, 21 (4),558. Zmierczak, W.; MuraliDhar, G.; Massoth, F. E. J . Catal. 1982, 77, 432.
* To whom correspondence should be addressed. Present address: Harshaw-Filtrol, 23800 Mercantile Road, Beachwood, OH 44122.
Frances V. Stohl' Sandia National Laboratories Organization 6254 Albuquerque, N e w Mexico 87185 Qusro A. Qader, F. E. Massoth Department of Fuels Engineering University of U t a h Salt Lake City, U t a h 84112 Deepak S. Thakurf Department of Chemical Engineering University of N e w Mexico Albuquerque, N e w Mexico 87131 Received f o r review November 4, 1985 Accepted December 9, 1986
Thermolysis of Higher Molecular Weight Straight-Chain Alkanes (c9-C22) Experimental results are reported from a study on the vapor-phase thermolysis of several straight-chain alkanes and their mixtures, including C9,CI2, CI3, CI6, and C22,under atmospheric pressure and temperatures from 623 to 893 K. Thermolysis of unbranched alkanes yields series of 1-alkenes as major products. The 1-alkene selectivity strongly depends upon pressure-the lower the pressure, the higher the selectivity. Straight-chain-alkane thermolysis, under whatever pressure, follows a free-radical mechanism which produces alkenes with double bonds in the a-position via @-scissionof C-C bonds. Low pressure favors the radical decomposition over hydrogen abstraction. Thermolyses of hydrocarbons are fundamental reactions occurring in industrial processes such as thermal cracking, visbreaking, and coking. Studies on hydrocarbon cracking have been involved mainly with light reactants, and only recently have there been recorded investigations on the cracking behavior of a few high-molecular-weight hydrocarbons (Rebick, 1983; Mushrush and Hazlett, 1984; Van Camp et al., 1984; Blouri et al., 1981, 1985; Zhou and Crynes, 1986). This article reports the experimental results of a study on the vapor-phase thermolysis of several straight-chain alkanes and their mixtures, including nonane, dodecane, 0888-5885/87/2626-0846$01.50/0
tridecane, hexadecane, and docosane, under atmospheric pressure and temperatures from 623 to 893 K. A brief discussion of the reaction kinetics and mechanism is presented.
Experimental Section The thermolysis experiments were conducted in an unpacked, downflow reactor of 304 stainless steel (304 S.S.), 81-mm inside diameter and 305" length, with a central sheath of the same material for an adjustable chromelalumel thermocouple to measure the reactor temperature. The reactor tube was placed in an electrically heated 0 1987 American Chemical Society
Ind. Eng. Chem. Res., Vol. 26, No. 4, 1987 847
WET TEST METER
TO GC.
Y
ASCARITE
Figure 1. Experimental flow system.
copper block, and the required temperature profile was maintained by three discrete temperature controllers. The reactants were fed without any carrier by an infusion/ withdrawal pump, preheated and fully vaporized in a tube (304 S.S.), 12.7-mm diameter and 300-mm length. The preheat temperature profile was essentially linear, and the axial temperature variation in the reactor section was within f 2 K. The reactor effluent was immediately cooled and condensed through a series of air and ice traps. The flow scheme of the reactor system is shown in Figure 1. The system was thoroughly purged with nitrogen before and after each run. Steady temperature and flow conditions were achieved usually 10-20 min after the feed pump had started, and then gas metering and liquid collection began. The run proceeded for 30 min more when three successive gas samples were taken. The analytical results of these gas samples had to be in reasonable agreement for the run to be considered satisfactory. Product gas samples were analyzed by two chromatographs: HP 5880A equipped with a level four terminal and H P 5890 with a 3392A integrator. Liquid sample analysis was performed on the latter only. Thermal conductivity detectors were used for both chromatographs. The former was fitted with a stainless steel column, 2-m length and 3.2-mm diameter, packed with Porapak Q. The conditions were helium flow rate of 60 cm3/min, injector temperature of 473 K, detector temperature of 523 K, and column temperature of 393 K. The H P 5890 was equipped with a fused silica capillary column, 60-m length and 0.32-mm diameter, with DB-1 Durabond liquid phase. Its operating conditions were as follows: hydrogen flow of 45 cm/s, injector temperature of 523 K, detector temperature of 573 K, and column temperature programmed for 308 K (for 300 s) to 543 K at a rate of 5 deg/60 s. The alkanes used for this study were nonane (Phillips, 99 TO),dodecane (Fisher Scientific, purified grade), tridecane (Aldrich), hexadecane (Alfa Products, 9970), and docosane (OSU extracted with NaHC03). Mixtures were composed of (1)C12+ CI6,94 + 6 wt %, and (2) C9 + C12 C13 + C16 + C22, 25 + 26 + 1 2 + 31 + 6 wt 70. For the thermolysis runs, material balances were in the range 96.5-98.9 wt %. All sample analyses were duplicated, and the standard deviation was less than 1% ;except for those components of very low concentration (
