PROCESS FOR DIMERIZING ALPHA-OLEFINS

Abstract: Process for preparing α-olefins CH₂=C(R)CH₂CH₂R, R being C 1-30 -alkyl, cycloalkyl or cycloalkenyl, by dimerizing α-olefins CH₂=C(R)H, at -60 to +280 °C, with a catalyst comprising a) a metallocene (cyclopentadienyl)₂MY₂, M being Zr or Hf and Y being H, halogen, C 1-5 -alkyl or C 6-20 -aryl, and b) an alumoxane, using an atom ratio Al to M from 1 to 100.

Description: The invention relates to a process for the preparation of alpha-olefins having the general formula I wherein R represents an alkyl, cycloalkyl or cycloalkenyl group having in the range of from 1 to 30 carbon atoms by dimerization of an alpha-olefin having the general formula II wherein R has the same meaning as in the general formula I. Products of the general formula I are useful as intermediates in preparing, for example, specialty detergents or lubricant additives. Metallocene/alumoxane catalysts are known in the art for producing polymers from alpha-olefins. Kaminsky, in Chemical and Engineer News, July 4, 1983, pp 29-30 and in Makromol Chem., Rapid Commun. 4, 417-421 (1983) discloses zirconium and titanium metallo­ cenes in combination with alumoxanes as catalysts for the polymeri­ zation of olefins. U.S. patent specification 4,404,344 deals with the use of zirconium metallocenes in combination with alumoxanes as catalysts for the polymerization of ethylene and propylene or copolymerization of ethylene with other alpha-olefins, respecti­ vely, with which a controlled molecular weight distribution is obtained. This known process is carried out using an atom ratio aluminium to zirconium between 10:1 and 10⁸:1; in the sole example on polymerization of propylene this atom ratio was 1.5×10⁸:1. European patent specification No. 128,045 deals with the use of at least two metallocenes in combination with alumoxane for polymerization of ethylene to products with a broad molecular weight distribution. Metallocenes disclosed are titanocenes, zircono­ cenes, hafnocenes and vanadocenes. A process of the type described in the beginning has now been found which surprisingly yields dimers with a very high selectivi­ ty, little or no polymers being formed. The "selectivity to a certain compound" is defined herein as 100 a:b in which "a" is the amount of starting alpha-olefin of the general formula II that has been converted into that certain compound and "b" is the total amount of starting compound of the general formula II that has been converted. Accordingly, the invention provides a process for the prepara­ tion of alpha-olefins having the general formula I wherein R represents an alkyl, cycloalkyl or cycloalkenyl group having in the range of from 1 to 30 carbon atoms by dimerization of an alpha-olefin having the general formula II wherein R has the same meaning as in the general formula I, which process comprises contacting an alpha-olefin having the general formula II at a temperature in the range of from -60 °C to 280 °C with a catalyst comprising:- a) a metallocene having the general formula III (cyclopentadienyl)₂MY₂ (III) wherein M represents a zirconium or hafnium atom and each Y individually represents a hydrogen atom, a halogen atom, an alkyl group having in the range of from 1 to 5 carbon atoms or an aryl group having in the range of from 6 to 20 carbon atoms, and b) an alumoxane, the catalyst having an atom ratio of aluminium to M in the range of from 1 to 100. In general, R can not be too bulky or dimerization rates are inhibited. The group R is too bulky if the carbon atom with the free valence is a quaternary carbon atom. It is a routine matter to test a particular olefin with the catalysts used in the instant invention. Mixtures of alpha-olefins can be used as starting materials, resulting in various cross dimerization products. Examples of starting olefins that have been utilized in the instant process are propylene, 1-butene, 1-hexene, 1-octene, 1-eicosene and 4-vinyl-1-cyclohexane. 3,3-Dimethyl-1-butene (neohexene) was found to be unreactive alone but would cross dimerize with 1-octene. Styrene, internal olefins and di-olefins were substantially unreactive in the instant process. Di-olefins, particularly conjugated di-olefins adversely affect the dimerization process. The aluminoxanes (or alumoxanes) are well known in the art and are polymeric aluminium compounds which can be represented by the general formula (R-Al-O) n which is a cyclic compound and R(R-Al-O) n AlR₂, which is a linear compound. In the general formula, R represents an alkyl group having in the range of from 1 to 5 carbon atoms such as, for example, methyl, ethyl, propyl, butyl and pentyl and n is an integer from 1 to about 20. Most preferably, R represents a methyl group. Generally, in the preparation of alumino­ xanes from, for example, trimethylaluminium and water, a mixture of the linear and cyclic compounds are obtained. The aluminoxanes can be prepared in various ways. Preferably, they are prepared by contacting water with a solution of a trialkyl­ aluminium, such as, for example, trimethylaluminium, in a suitable organic solvent such as benzene or an aliphatic hydrocarbon. The solvents that can be used are well-known and include the saturated aliphatic compounds such as butane, pentane, hexane, heptane, octane, isooctane and purified kerosenes; cycloaliphatics such as cyclobutane, cyclopentane, cyclohexane, cycloheptane, methylcycloheptane and the dimethylcyclopentanes; alkenes, such as propylene, butene and 1-octene; aromatic solvents such as benzene, toluene and the xylenes. The major requirements in the selection of a solvent are that it be liquid at reaction temperatures, that it does not react with water or the aluminoxanes or interfere with the desired dimerization reaction. The solvent must be oxygen-free. Hydroxy, ether, carboxyl, keto, and the like groups adversely affect aluminoxane production. A particularly suitable solvent is the olefin to be dimerized. For example, the alkylaluminium is treated with water in the form of a moist solvent or the alkyl­ aluminium such as trimethylaluminium can be desirably contacted with a hydrated salt such as hydrated copper sulphate or aluminium sulphate. The aluminoxane can be prepared in the presence of a hydrated copper sulphate. This method comprises treating a dilute solution of trimethylaluminium in, for example, toluene, with copper sul­ phate represented by the formula CuSO₄.5H₂O. The ratio of copper sulphate to trimethylaluminium is desirably about 1 mol of copper sulphate for 5 mol of trimethylaluminium. The reaction is evidenced by the evolution of methane. In general, the molar ratio of alkylaluminium to water will be about 1:1 although variations of this ratio can occur without adversely affecting the aluminoxane product; i.e., the Al/water molar ratio can vary between 0.66:1 to about 2:1, preferably between about 0.75:1 to about 1.25:1. A continuous method for producing aluminoxanes is given in U.S. patent specification 3,300,458, incorporated herein by reference. Another suitable method involves the use of hydrated aluminium salts as given in U.S. patent specification 4,544,762, incorporated herein by referen­ ce. Another suitable method is to use water which has been ultra­ sonically dispersed in a solvent as described in U.S. patent application Serial No. 896,689, filed on even date, incorporated by reference herein or water which has been dispersed using high speed shearing as described in U.S. patent application Serial No. 896,701, filed on even date, incorporated by reference herein. Preferably each Y in the general formula III individually re­ presents a hydrogen or chlorine atom or a methyl group. It is understood that the two Ys may be the same or different. Bis­ (cyclopentadienyl)zirconium dichloride is the preferred metallocene. For the purposes of this invention, included with the definition of the above cyclopentadienyl moiety is the lower alkyl(C₁-C₅)-­ substituted, preferably the methyl-substituted cyclopentadienyl moiety. Other metallocenes such as those containing titanium, vanadium and niobium have been found not to work adequately in the instant process. In general terms, the catalyst is prepared by adding the aluminoxane dissolved in an organic solvent, preferably the solvent utilized to prepare the aluminoxane, to a well-stirred suspension of the metallocene in an organic solvent, which can be inert with respect to the catalyst system or, preferably can be the olefin which comprises the feed. When the stirred solution to which the aluminoxane has been added becomes homogeneous, the catalyst has been formed, and if the feed olefin has been used as solvent, the dimerization reaction commences. Critical to the production of dimers rather than polymers is the selection of the particular metallocene and the particular atom ratio of Al to Zr in the catalyst. The atom ratio of Al to Zr ranges from 1:1 to 100:1 preferably from 1:1 to 50:1. The atom ratio of Al to Zr in the catalyst effects the selectivity and conversion in opposite ways. As the Al/Zr atom ratio increases, the conversion and rate of reaction increases, but the selectivity to the dimer falls off. Also, as the number of carbon atoms per molecule of the alpha-olefin of the general formula II is increased, the Al/Zr atom ratio also must increase to provide equivalent results. Thus, a given Al/Zr atom ratio may be optimum for a given olefin feed, but not for a different olefin feed. The dimerization reaction is carried out in a conventional fashion. It may be carried out continuously in a stirred tank reactor wherein olefin and catalyst are added continuously to a stirred tank and reactant, product and catalyst are removed from the stirred tank with the product separated and the catalyst and used reactant recycled back to the stirred tank. Alternatively, the reaction may be carried out in a batch reactor, wherein the catalyst, or the catalyst precursors, and reactant olefin are charged to an autoclave, and after being reacted for an appropriate time, product is separated from the reaction mixture by conventio­ nal means, such as distillation. The dimerization is preferably carried out at a temperature in the range of 0 °C to 150 °C. Pressures are not critical and can range from about 1 to about 506 bar or higher. The following Examples further illustrate the invention. Example 1 A typical catalyst was prepared in a dry box by adding 4.6 g of a solution of 25% by weight of trimethylaluminium (16 mmol) in toluene to a magnetically stirred bottle containing 1.0 g copper sulphate pentahydrate (containing 16 mmol water) in 20 ml toluene. After 15 min the gas evolution slowed and slow stirring was star­ ted. At 1.5 h the material was heated to 60 °C and cooled. The liquid was withdrawn and added to a 100 ml autoclave containing 0.29 g (1 mmol) bis(cyclopentadienyl)zirconium dichloride (Cp₂ZrCl₂). Propylene (25 g, 0.6 mol) was charged to the autoclave, and the vessel heated at 40-46 °C for 3 h. The pressure rose to a maximum of 13.8 bar and dropped to a final pressure of 3.8 bar. The reaction product was removed and analyzed. Conversion of the propylene was greater than 95%. The selectivities to C₆-olefins and to C₉-olefins were 95.8 and 4.2%, respectively. NMR analysis of the C₆-hydrocarbons showed the following composition: It can be seen that the C₆-hydrocarbons had a very high content of 2-methyl-1-pentene, being an olefin of the general formula I. Example 2 A catalyst was prepared as described in example 1 except that the quantities were cut in half. The catalyst was added to 1-octene (200 ml, 1.23 mol) in a 500 ml round bottomed flask fitted with a magnetic stirrer, a thermometer and a nitrogen purged stopcock for sample withdrawal. The flask was heated to about 33-40 °C. After 24 h the conversion of 1-octene was 94.8%, with a selectivity to dimer of 92.6% and to trimer of 3.0%. NMR showed the C₁₆ consisted of more than 96% by weight of 2-hexyl-1-decene. Examples 3-7 and Comparative Experiments A-C Catalysts were prepared similar to Example 1 with varying Al:Zr ratios. These catalysts were prepared from methylaluminoxane (from trimethylaluminium) and bis(cyclopentadienyl)zirconium dichloride and were used to dimerize propylene. The dimerization was carried out in a 100 ml autoclave, using 21-23 g propylene, a reaction temperature of 20-33 °C and autogenous pressure. A reaction time of 1 h was used. The results presented in Table I hereinafter show that only at an atom ratio Al to Zr below 100 a high selectivity to dimers (C₆) is obtained. Examples 8 and 9 and Comparative Experiment D These experiments show the effects of the atom ratio Al:Zr on the dimerization of propylene. Example 3 was repeated with a run time of 2 h instead of 1 h using toluene (20 ml), propylene (25-27 g), (cyclopentadiene)₂ ZrCl₂ and methylaluminoxane, a temperature of 35-47 °C and autogenous pressure. The isomer composition of the dimers was determined. The results observed after a reaction time of 2h and presented in Table II show that only at an atom ratio Al to Zr below 100 a high selectivity to dimers is obtained. Examples 10-13 Catalysts were prepared similar to Example 1 with varying Al:Zr atom ratios. The catalysts were prepared from methylaluminoxane (from trimethylaluminium) and bis(cyclopentadienyl)zirconium dichloride and were used to dimerize 1-octene. The results are shown in Table III. Examples 14-17 Catalysts were prepared similar to Example 1, from methylaluminoxane (from 4 mmol of trimethylaluminium and 5 mmol of water) and bis(cyclopentadienyl)zirconium dichloride (various amounts) and were used to dimerize 1-hexene (400 mmol). Toluene (30 ml) was used as a solvent and the temperature was 40 °C. The results are presented in Table IV. Examples 18-20 and Comparative Experiment E These experiments illustrate the differences in reactivities as the number of carbon atoms per molecule of the feed increases. The catalysts were prepared from methylaluminoxane (from trimethyl­ aluminium) and bis(cyclopentadienyl)zirconium dichloride and had an atom ratio Al to Zr of 16:1. The feeds were propylene, butene, 3-methyl-1-butene and 3,3-dimethyl-1-butene. Toluene (10 ml) was used as a solvent and a reaction temperature of 28-35 °C was used. The results observed after a reaction time of 1.0 h are presented in Table V. They show that 3-methyl-1-butene can be dimerized, the vinyl group thereof being bound to a tertiary carbon atom. 3,3-Di­ methyl-1-butene can not be dimerized, the vinyl group thereof being bound to a quaternary carbon atom and the tertiary butyl group to which this vinyl group is bound being too bulky. Examples 21-23 Catalysts were prepared similar to Example 1 with differing aluminoxane precursors and bis(cyclopentadienyl)zirconium dichlori­ de at a Al:Zr ratio of 16:1. The experiments were carried out in a 100 ml autoclave, using 21-25 g propylene, 16 mmol of R₃Al and 20 mmol of water from CuSO₄.5H₂O, 1.0 mmol of (cyclopentadiene)₂ZrCl₂, a reaction temperature of 35-45 °C and autogenous pressure. The results presented in Table VI show that the highest conversion is obtained with trimethylaluminium. Example 24 Bis(cyclopentadienyl)zirconium dimethyl (0.5 mmol), alumino­ xane (4 mmol) and 1-octene (50 ml) were heated in the stirred round bottomed flask at 40 °C for 1 h. Analysis of the reaction product showed a 19.1% conversion of 1-octene, with a selectivity to octene dimer of 72.2% and to octene trimer of 19.7%. Example 25 Bis(cyclopentadienyl)zirconium hydrogen chloride (1 mmol), aluminoxane (8 mmol) and 1-butene (0.47 mol) were heated in an autoclave at 70 °C for 1 h. Analysis of the reaction product showed a 20% conversion of 1-butene, with a selectivity to dimer of 96% and to trimer of 4%. Example 26 Bis(cyclopentadienyl)zirconium hydrogen chloride (1 mmol), aluminoxane (4 mmol) and 1-octene (50 ml) were heated in an auto­ clave at 40 °C for 1 h. Analysis of the reaction product showed an 8% conversion of the 1-octene, with a selectivity to the dimer of 72% and to the trimer of 1.5%. Examples 27-33 In these experiments various amounts of water were used to prepare the aluminoxane and the results on the dimerization cata­ lysts were measured. The catalysts were prepared as follows: 20 ml of dry toluene were placed in a bottle fitted with a nitrogen purge system and the bottle was placed in an ultrasonic bath (Branson). The ultrasonic was started and the designated amount of water was added through a hypodermic syringe. After a five min period of sonification, 4 mmol of trimethylaluminium (as a 25% by weight solution in toluene) was added. After the reaction was completed (as evidenced by termina­ tion of gas evolution), 50 ml of 1-octene and 0.5 mmol of bis­ (cyclopentadienyl)zirconium dichloride was added and the mixtures were heated to 40 °C. After 30 min samples were removed for analysis. The results specified in Table VIII show that the highest conversions of 1-octene are obtained at an Al:water molar ratio between 0.75:1 and about 1.25:1.

Claims: 1. A process for the preparation of alpha-olefins having the general formula I wherein R represents an alkyl, cycloalkyl or cycloalkenyl group having in the range of from 1 to 30 carbon atoms by dimerization of an alpha-olefin having the general formula II wherein R has the same meaning as in the general formula I, which process comprises contacting an alpha-olefin having the general formula II at a temperature in the range of from -60 °C to 280 °C with a catalyst comprising:- a) a metallocene having the general formula III (cyclopentadienyl)₂MY₂ (III) wherein M represents a zirconium or hafnium atom and each Y individually represents a hydrogen atom, a halogen atom, an alkyl group having in the range of from 1 to 5 carbon atoms or an aryl group having in the range of from 6 to 20 carbon atoms, and b) an alumoxane, the catalyst having an atom ratio of aluminium to M in the range of from 1 to 100. 2. A process as claimed in claim 1 wherein each Y in the general formula III individually represents a hydrogen or chlorine atom or a methyl group. 3. A process as claimed in claim 1 or 2 wherein M in the general formula III represents a zirconium atom. 4. A process as claimed in claim 3 wherein the metallocene of the general formula III is bis(cyclopentadienyl)zirconium dichloride. 5. A process as claimed in any one of the preceding claims wherein the atom ratio of aluminium to M is in the range of from 1 to 50. 6. A process as claimed in any one of the preceding claims which is carried out at a temperature in the range of from 0 °C to 150 °C.

Inventors: SCHOENTHAL, GALEON WAYNE, SLAUGH, LYNN HENRY
Applicants: SHELL INTERNATIONALE RESEARCH MAATSCHAPPIJ B.V.
Application year: 1987
Main classification: C07C2
IPC codes: C07C11, B01J31, C07C2, C07C67, C07B61, C07C1