Ind. Eng. Chem. Res. 1988, 27, 1971-1977 C.E. Symposium, Montreux, Switzerland, April 8-11, 1979. Hautman, D. J.; Santoro, R. J.; Dryer, F. L.; Glassman, I. "An Overall and Detailed Kinetic Study of the Pyrolysis of Propane". Znt. J. Chem. Kinet. 1981,13,149-172. Herriott, G. E.; Eckert, R. E.; Albright, L. F. "Kinetics of Propane Pyrolysis". AZChEJ. 1972,18,84-89. Hoffman, T.; Hofmann, T. Einfuhrung in die Optimierung; Verlag Chemie Gmbh: Erlangen, 1970. Ill&, V. "The Pyrolysis of Gaseous Hydrocarbons, 111. Kinetics and Mechanism of the Thermal Decomposition of Propane". Acta Chin. Acad. Sci. Hung. 1971,67,41-60. Isbarn, G.; Ederer, H. J.; Ebert, K. H. Springer Series in Chemical Physics; Springer Verlag: Berlin, 1981. Kunugi, T.; Soma, K.; Sakai, T. "Thermal Reaction of Propylene: Mechanism". Znd. Eng. Chem. Fundam. 1970,9,319. Leathard, D. A.; Purnell, J. H. "Paraffin Pyrolysis". Ann. Rev. Phys. Chem. 1970,21,177. Lifshitz, A.; Frenklach, M. "Mechanism of the High Temperature Decomposition of Propane". J. Phys. Chem. 1975,79,686-692. Lin, M. C.; Back, M. H. "The Thermal Decomposition of Ethane. Part I. Initiation and Termination Steps". Can. J. Chem. 1966a, 44,505. Lin, M. C.; Back, M. H. "The Thermal Decomposition of Ethane. Part 11. The Unimolecular Decomposition of the Ethane Molecule and the Ethyl Radical". Can. J. Chem. 1966b,44,2357. Lin, M. C.; Back, M. H. "The Thermal Decomposition of Ethane. Part 111. Secondary Reactions". Can. J. Chem. 1966c,44,2369. Moens, J. "A Rigorous Kinetic Model for the Simulation of the Thermal Cracking of Light Hydrocarbons and Their Mixtures". Ph.D. Dissertation, Ghent State University, Belgium, 1982. Murata, M.; Takeda, N.; Saito, S. "Simulation of Pyrolysis of Paraffinic Hydrocarbon Binary Mixtures". J . Chem. Eng. Jpn. 1974, 7,286. NBS "Tables of Experimental Rate Constants for Chemical Reactions Occurring in Combustion (1971-1977)". Interim Report 81-2254,1981. Pacey, P. D.; Purnell, J. H. "Propylene from Paraffin Pyrolysis". Znd. Eng. Chem. Fundam. 1972a,11, 233.
1971
Pacey, P. D.; Purnell, J. H. "Arrhenius Parameters of the Reaction CH3. + C2Hs---CHI + CzH{''. J. Chem. SOC.,Faraday Trans. 1 1972b,68,1462. Powell, M. J. D. "An Efficient Method for Finding the Minimum of a Function of Several Variables without Calculating Derivatives". Comput. J . 1964,7, 155-166. Rice, F. 0."The Thermal Decomposition of Organic Compounds 1931, from the Standpoint of Free Radicals". J . Am. Chem. SOC. 53, 1959. Rice, F. 0.; Kossiakoff, A. "Thermal Cracking of Hydrocarbons, Resonance Stabilization and Isomerization of Free Radicals". J . Am. Chem. SOC.1943,65,590. Sagert, N. H.; Laidler, K. J. "Kinetics and Mechanism of the Pyrolysis of n-Butene". Can. J. Chem. 1963,41,838. Sankaran, N. "Thermal Cracking of Cyclohexane and Methylcyclopentane". Ph.D. Dissertation, Ghent State University, Belgium, 1982. Scharfe, M.; Ederer, H. J.; Stabel, U.; Ebert, K. H. "Modeling of n-Hexane Pyrolysis: Experimental Investigation in a Flow Reactor at Normal Pressure". Ger. Chem. Eng. 1985, 8, 119-129. Semenov, N. N. Some Problems in Chemical Kinetics and Reactiuity, Vol I; Princeton University Press: Princeton, NJ, 1958. Sundaram, K. M.; Froment, G. F. "Modeling of Thermal Cracking Kinetics. 3. Radical Mechanisms for the Pyrolysis of Simple Paraffins, Olefins and Their Mixtures". Ind. Eng. Chem. Fundam. 1978,17,174-182. Tsang, W. "Thermal Decomposition of 3,4-Dimethylpentene-2,3,3Trimethylpentane, 3,3-Dimethylpentane, and Isobutylbenzene in a Single Pulse Shock Tube". Znt. J . Chem. Kinet. 1969, 1, 245-278. Volkan, A. G.; April, G. C. "Survey of Propane Pyrolysis Literature". Ind. Eng. Chem. Process Des. Deu. 1977,16,4269-436. Willems, P. A.; Froment, G. F. "Kinetic Modeling of the Thermal Cracking of Hydrocarbons. 1. Calculation of Frequency Factors". Znd. Eng. Chem. Res. 1988,preceding paper in this issue. Received for review December 8, 1987 Accepted July 7, 1988
Dimerization of Ethylene to 1-Butene Catalyzed by the Titanium Alkoxide-Trialkylaluminum System S. Muthukumaru Pillai,* Gopal L. Tembe, Marayil Ravindranathan, and Swaminathan Sivaram Research Centre, Indian Petrochemicals Corporation Limited, Baroda 391 346,India
Dimerization of ethylene to 1-butene catalyzed by Ti(OC4H9-n)4-A1R3(R = CH3, C2H6,i-C4H9)was investigated a t 1-12.5 kg/cm2 of ethylene pressure and 25-45 "C in hydrocarbon solvent. The influence of reaction conditions such as Al/Ti ratio, nature of alkylaluminum, nature of alkoxy or aryloxy group around titanium, solvents, pressure, temperature, catalyst concentration, and additives on the rate, conversion of ethylene, and selectivity to 1-butene was studied. The experimental observations conform to a titanium metallacycle as intermediate in selective dimerization of ethylene to 1-butene. Selective dimerization of olefins catalyzed by transition-metal compounds has received considerable attention in the literature (Lefebvre and Chauvin, 1970; Muthukumaru Pillai et al., 1986). Recently, commercial interest in the selective conversion of ethylene to butenes has been revived (Commereuc et al., 1984; Cooper and Banks, 1985). Of the metals studied for dimerization of ethylene, titanium-based compounds have been found to be ideally suited, giving high yields of 1-butene at ambient temperature and pressure (Muthukumaru Pillai et al., 1987; Commereuc et al., 1984; Lequan et al., 1985; Knee, 1962; Ono and Yamada, 1970; Belov et al., 1975; Beach and Kissin, 1984, 1986). However, 1-butene formation is invariably accompanied by formation of higher oligomers of ethylene and polymers. Formation of these byproducts which complicate the efficacy of an industrial process is 0888-5885/88/2627-1971$01.50/0
believed to be a function of catalyst type and reaction conditions. In this paper, we wish to report the results of a systematic study of the role of catalysts and reaction parameters on the kinetics of dimerization of ethylene as well as on conversion and selectivity of the reaction.
Experimental Section Melting points (uncorrected) were determined on a Toshniwal melting point apparatus. Infrared spectra were recorded on a Perkin-Elmer 567 instrument. DSC derivatograms were run on Du Pont 990 derivatograph under nitrogen atmosphere. Gas chromatographic analyses were carried out on a Shimadzu GC-7AG gas chromatograph using a column packed with AgN03 (2%) and Carbowax 20M (15%)on Chromosorb W. GC-MS analyses were 0 1988 American Chemical Society
1972 Ind. Eng. Chem. Res., Vol. 27, No. 11, 1988
/ I
1001
I
/
t 8011 '
-' 7 0 J
60-
B 2 503
1030-
'Ti(OC4Hg-n)4-Al(C4Hg-i)3; Al/Ti (mole/mole)
iL
O
20-
= 8; 35 "C; PcZb
= 12.5 kg/cm2; CI1-C,, cut = 500 mL; 30 min.
S
0
Table I. Composition of the Products of Ethylene Dimerization' fraction olefin composition, w t % c41-butene 84.8 c63-methyl-1-pentene 1-hexene 13.8 2-ethyl-1-butene 2-hexenes C81-octene 2-octenes 0.6 2-ethyl-1-hexene 3,4-dimethyl-l-hexene polymer 0.7
1
2
3
L
5 6 TIME I MIN 1
?
8
9
Ki
11
1 12
Figure 1. Volume of ethylene absorbed versus reaction time. Ti(OC4H@)4 = 2.94 X lo-' mol; A1(CzH& with Al/Ti (mole/mole) = 7.6; heptane = 80 mL; 26 "C; PCzH, = 1 kg/cm2.
?/
6 -
t -1
5 -
E
conducted on HP-5985 instrument with a methylsilicone (cross-linked) coated capillary column connected to electron capture detector (70 eV). CI-MS studies were carried out with isobutane gas at 0.5 Torr as CI reagent, keeping the ionization source a t 200 "C. Materials. Titanium tetraisopropoxide and titanium tetra-n-butoxide (Synthochem, Indore, India) were purified by vacuum distillation. C11-C14 refers to the straight-chain paraffin hydrocarbons having carbon numbers varying from 11 to 14 (composition, wt %, Cll = 8.1, C12= 15.5, C13 = 33.0, C14 = 42.4; nonnormals = 1;sulfur =
