The present invention relates to a method for the oligomerization of olefins and olefin mixtures by using a boron trifluoride cocatalyst complex.

The oligomerization and polymerization of various olefins constitute commonly known technology. These reactions may occur thermally without a catalyst; as radical reactions over, for example, peroxide catalysts or coordination polymerization catalysts; by an anionic mechanism over basic catalysts; by a cationic mechanism over Friedel-Crafts catalysts; and by polymerization by using molecular sieves, for example zeolites.

An anionic mechanism is used mainly for olefin dimerization reactions, for example, for the dimerization of propylene to 4-methyl-l-pentene. Coordination polymerization is used mainly for the preparation of various plastics, such as polyethylene, polypropylene, and poly-1-butene, in which it is desirable to determine in advance precisely the structure of the formed product. A cationic mechanism and polymerization by using molecular sieves produce in the polymerization of olefins only light oligomers or viscous liquids, so-called liquid polymers.

The catalysts used in the cationic mechanism have been Lewis acids such as BF ₃ , A1C1 ₃ , AlBr ₃ , TiCl ₄ , SnCl ₄ , etc. It is known that Lewis-acid catalysts cannot alone initiate a polymerization reaction; they require a proton donor, i.e. a cocatalyst. Examples of such cocatalysts are water, alcohols, carboxylic acids, inorganic acids, certain alkyl halides, and halogens. The oligomerization can be carried out in bulk, i.e. without an auxiliary solvent, or in the presence of an inert solvent. Examples of such inert solvents are alkanes such as hexane and heptane, and cycloalkanes such as cyclohexane and cycloheptane.

BF-catalyzed oligomerization has been known at least since 1873, when Butlerov and Gorianov reported that isobutene and propylene became oligomerized by a BF ₃ treatment at room temperature (Kennedy, J., Cationic polymerization of olefins, J. Wiley & Sons, New York, 1975, p. 8).

Oligomerization occurs in the presence of an active catalyst complex. Such a catalyst

complex can be prepared through a reaction between BF ₃ and a cocatalyst, separate from the oligomerization reactor or in situ in the reactor. Water, short-chain alcohols, and or¬ ganic acids are commonly mentioned as the cocatalysts used. A 1-butanol cocatalyst has commonly been used together with BF ₃ when the object has been to produce fractions suitable for use as lubricants or their additives. For the above uses, the monomer has commonly been some long-chain alpha-olefm or internal olefin, or their mixture. In particular, 1-decene has been used as the monomer.

The combination of BF ₃ , 1-butanol and 1-decene has been used by, for example, Cupples et al. (US 4 282 392), Shubkin (US 4 910 355), Dileo (EP 352 723), and Akatsu (EP 364 889). Other cocatalysts used with BF ₃ and decene include water (Bronstert, EP 271 034), alcohol alcoxylate (Theriot, EP 467 345), alcohol mixtures (Pratt, US 4 587 3- 68), an alcohol ester mixture (Brennan, US 3 997 621), and a mixture of butanol and ethyl glycol or of butanol, ethyl glycol and methylethyl ketone (Morgansson and Vayda, US 4 409 415, US 4 436 947, EP 77 113).

Watts et al. (US 4 413 156), Darden et al. (US 4 420 646), Hammond et al. (US 4 420 647, EP 136 377), and Larltin et al. (US 4 434 308) used as the initial materials C ₈ - C _lg internal olefins or mixtures of C ₈ -C, ₈ internal olefins and alpha-olefins. The oligomeri- zation of this fraction with a BF ₃ -l-butanol catalyst yielded as products fractions suitable for use for the preparation of additives for lubricants.

Nipe et al. (US 4 225 739) also used a BF ₃ - 1-butanol catalyst for copolymerization in which the short-chain olefin was propylene and the long-chain olefin was a mixture of C ₁₅ - C ₁₈ olefins.

Larkin et al. (US 4 395 578, US 4 417 082, and US 4 434 309) used for copolymerization 1-butene or propylene as the short-chain olefin and from one to three C ₆ -C _lg alkenes of different lengths as the long-chain olefin. The catalyst system consisted of BF ₃ and 1- butanol and possibly a transition-metal cation.

Pasky (US 4 451 684) used for co-oligomerization propylene oligomers having an average carbon chain length of 12-18 and C ₅ -C ₆ olefins, the catalyst complex comprising BF ₃ and

butanol.

Nelson and Zuech (US 4 484 014) used a two-step method in which the first step was a coordination catalyzed reaction for the oligomerization of ethylene with TEA (triethyl aluminum) into C ₆ -C ₁₆ olefins. The reaction occurs at a higher temperature than does normal oligomerization of ethylene. For this reason the C ₆ -C ₁₆ fraction contained branched olefins 10 - 55 %, whereas under normal conditions nearly 100 % straight-chain alpha- olefins would have been produced with TEA. In the second step, the produced mixture of ethylene oligomers was further oligomerized in a batch reaction into a lubricant fraction by using a BF ₃ -propanol catalyst. In this, the catalyst complex formed in situ through a reaction between BF ₃ and propanol.

Schick and Gemmil (US 4 182 922) used propylene or a mixture of ethylene and propyle¬ ne as the monomer feed in the first step. This mixture was oligomerized with a catalyst of VOCl ₃ and ethyl aluminum chloride. The produced oligomer mixture was further co- oligomerized with a longer-chain olefin or a mixture of propylene and a longer-chain olefin by using a BF ₃ -propanol complex formed in situ. The longer-chain olefin used was butene, hexene or decene. The longer-chain olefin or the mixture of propylene and a longer-chain olefin was fed into the second step in a Vi-batch manner. The viscosity index of the reaction products was dependent on the longer-chain olefin used. When butene was used, the viscosity index of the end product was 113 and, when decene was used, it was 133.

Hsia Chen and Tabak (US 4 568 786) used as the feed in the first step a mixture of propylene and butene, which was oligomerized with an HZSM-5-zeolite catalyst. From the formed product there was separated a C ₉ -C _lg fraction, which was oligomerized in the second step with a zeolite or BF ₃ catalyst. In a BF ₃ -catalyzed batch reaction, butanol was used as a cocatalyst, and the complex was formed separate from the oligomerization reactor.

Heckelsberg et al. (US 4 319 064, US 4 386 229) used as the 1st step a disproportionation reaction of 1-octene and/or 1-decene to produce a mixture of C ₈ -Cι ₈ internal olefins. This mixture or a part of it was oligomerized in the 2nd step with a BF ₃ -propanol or BF ₃ -

phosphoric acid catalyst complex formed in situ.

The catalysts used for the oligomerization of the Raffinate I stream flow, which contains n-butenes and inert butanes in addition to the principal component i-butene, depend in part on the desired product distribution. Torck et al. (GB 1 312 950) used as a di- and trimerization catalyst, for example, a BF ₃ -HF complex in a tetramethylene sulfonic solution. Chen et al. (US 4 849 572) used water and/or methanol as a cocatalyst, in which case the product, poly-i-butene, had M„ = 520-1500 g/mol. Samson (EP 145 235) used a BF ₃ -ethanol complex for the oligomerization of Raffinate I.

For the oligomerization of the Raffinate II stream, which contains 1- and 2-butenes and inert butanes as the principal components, Halaska et al. (EP 337 737) used BF ₃ or alkyl aluminum chlorides having a general formula of R2A1C1 or RA1C1 ₂ , where R is a C,-C ₈ alkyl. As cocatalysts they used HF, HC1, or compounds which contained a reactive chlorine or fluorine atom bound to a tertiary, benzylic or allylic carbon atom. These catalyst systems are the same as the catalysts used in the patent of Loveless et al. (US 4 041 098) for the oligomerization of C ₃ -C ₁₄ olefins, preferably C ₈ -C, ₀ olefins.

Pure 1-butene was oligomerized by Audisio and Priola (Makromolekulare Chemie, vol. 191, 1990, pp. 725-730) by using a separately prepared catalyst complex which was made up of BF ₃ and water or phosphoric acid.

Carboxylic acid cocatalysts are little known in the oligomerization of short-chain olefins. Sheng and Arnold (US 4 263 465) used as a cocatalyst a carboxylic acid having at maximum five carbon atoms. Their process was a two-step process. The first step comprised the oligomerization of 1-butene into a fraction having a number-average carbon chain length of 8-18, preferably 10-16 carbon atoms. In the second step, the product fraction of the first step is co-oligomerized with C ₈ -C, ₈ alpha-olefin. In each step there was used in the batch reaction a catalyst complex which had been prepared by a reaction between BF ₃ and a cocatalyst, separate from the oligomerization reactor.

Carboxylic acids, among them those containing five carbon atoms, have also been used for the oligomerization of longer-chain olefins. For example, in patent GB 1 378 449, n-

and i- valeric acid, methylbutanoic acid, or mixtures of these were used for catalyzing the oligomerization of C ₆ -C ₁₂ olefins, preferably 1-decene, together with BF ₃ . In this patent the catalyst complex was formed separate from the oligomerization reactor. Furthermore, two different flows were fed into the reactor, in a Vi-batch manner. These flows consisted of a BF ₃ -cocatalyst complex and a monomer saturated with BF ₃ .

The present invention relates to a method for the oligomerization of olefins and olefin mixtures in a one-step process by using a boron trifluoride cocatalyst complex. In this invention, the oligomerization of olefins or olefin mixtures is carried out in a one-step process by using as the catalyst a boron trifluoride cocatalyst complex in which the cocatalyst is water, a C ₂ -C, ₀ monoalcohol, or a C ₂ -C ₈ monocarboxylic acid, preferably pentanol or valeric acid. The invention is characterized by the characteristics presented below in the patent claims.

By the process according to the present invention it is possible to oligomerize olefins and olefin mixtures. The olefin mixture is preferably the so-called Raffinate II stream, in which the principal components are 1- and 2-butenes and butanes, or a mixture of a longer-chain, C ₆ -C ₂₀ olefin and Raffinate II. A method for the oligomerization of such mixtures is not previously known in the literature. In addition, it is also possible by the method to oligomerize long-chain olefins alone, as shown in the examples.

When olefin mixtures are oligomerized by the method according to the invention, the products formed are co-oligomers and not, for example, mixtures of oligomers of butene and oligomers of longer-chain olefin (homo-oligomers). In the reaction the olefins may randomly link with a hydrocarbon chain, and this can be demonstrated with the appended mass spectrometric analyses (the experiments corresponding to the chromatograms presented are Examples 63-66). The analyses were performed by direct inlet mass spectrometry by using as the apparatus a VG Trio-2-quadrupole mass spectrometer (VG Masslab, Manchester, U.K.). Analysis conditions: mass range 200-1000 g/mol, scanning time 3 s, electron energy 70 eV, ionization current 200 μA, ion source temperature 200 °C. The temperature program used for the sample evaporation was: 50 °C (2 min) + 50 °C/min 400 °C.

Olefin oligomers are technically important intermediates which can be used for the preparation of highly various end products.

Oligomers prepared according to the present invention contain in the polymer chain an olefinic double bond having increased reactivity. The properties of the oligomers include resistance to oxidation under the effect of heat, a low pour point, low volatility, and a good temperature-viscosity dependence. The above properties are important, especially if the oligomers are used for the production of lubricants and their additives. On the other hand, the method according to the invention can also be used for producing oligomers having a low viscosity index. These oligomers and their derivatives are used in the main for applications other than lubricants and their additives.

Owing to the reactive double bond the oligomers can be used as intermediates in the production of various chemical compounds. In the preparation of chemicals, oligomers are used for the preparation of, for example, alkyl benzenes, alkyl phenols, and alkyl succinic acid anhydride. From alkyl benzenes and alkyl phenols, surface active agents are prepared by sulfonation. In additives of lubricants, oligomers can be used, for example, in the preparation of sulfonates, phenates, thiophosphonates, and ash-free dispersing agents, alkenyl succinimides. In these compounds the molecular mass of the hydrocarbon fraction is approx. 350-1200 g/mol, in alkenyl succinimide as high as 2500 g/mol. Other uses include the use as a lubricant in two-stroke spark-ignition engines, as the processing oil in the rolling and drawing of metallurgic materials, in the leather and rubber industries, and in making various surfaces hydrophobic. By the hydrogenation of oligomers it is possible to obtain high-quality transformer oils, electrical insulation and cable oils, and non-toxic cosmetic oils and white oils.

To illustrate the present invention, the oligomerization of olefins and olefin mixtures by a one-step method is further described in a number of examples, which do not, however, limit the scope of the invention in any way.

Unless otherwise mentioned, the oligomerization reactions of olefins and olefin mixtures were performed in a steel reactor the volume of which was 300 ml and which was cooled internally by means of a cooling coil and was heated, when necessary, externally in an

electric mantle. The reactor was equipped with a stirrer. The temperature of the reaction mixture was monitored by means of a thermocouple. The temperature of the reaction mixture was maintained at the set value with a precision of ± 1 °C. The reagents used and their amounts are mentioned in the examples.

The reactor was first charged with a solvent, if necessary, and with the cocatalyst mentioned in the examples. Liquid monomer was fed into the reactor in the desired amount. After the adding of the monomer, the reactor was pressurized by means of BF ₃ gas, whereupon the catalyst complex formed in situ and the reaction started immediately. The monomer or the monomer mixture and the catalyst were fed into the liquid phase of the reactor. The reactor pressure was maintained constant by means of BF ₃ gas. The pressure was sufficient to keep the monomers in the liquid phase. The reaction parameters used were as follows: pressure 0-10 bar, expressed as overpressure; reaction temperature 10-70 °C; and reaction time 1-120 minutes or 1-8 hours. The reaction was halted by adding into the reactor an excess of either an NaOH solution or water. The product fraction was washed with an NaOH solution and was neutralized with water after the wash. The product distribution was analyzed by the GC method.

The examples illustrate the various possibilities of the process for producing oligomer fractions with different monomers and catalyst systems. The reference examples are Examples 1-15. The present invention is illustrated by Examples 16-66. It should be borne in mind that by the process being disclosed it is possible to produce highly different product distributions, so the examples only suggest the possibilities offered by the process.

Reference examples, in which the monomer is 1-butene (Examples 1-15).

Examples 1 and 2.

The cocatalyst used was n-valeric acid at 5.1 mmol per one mole of 1-butene. The reactor pressure was 4.0 bar and temperature 20 °C. In Example 1 the reaction time was 9 min¬ utes and in Example 2 it was 49 minutes. After the said reaction times, the reactions were halted by means of an NaOH solution. The hydrocarbon phases were analyzed, the results being as follows.

The number-average molecular masses of the product distributions according to the examples were 268 g/mol and 383 g/mol. From the product of Example 2, the C ₁₆ hydrocarbons and fractions lighter than this were separated by vacuum distillation. The viscosity index determined on this unhydrogenated product was 81, the kinematic viscosity being KV100 = 4.3 cSt.

Example 3.

The cocatalyst used was n-valeric acid at 13.4 mmol per one mole of 1-butene. The reactor pressure was 2.5 bar and temperature 20 °C. In Example 3 the reaction time was 49 minutes. After the said reaction time, the reaction was halted by means of an NaOH solution. The hydrocarbon phase was analyzed, the result being as follows:

The number-average molecular mass of the product distribution according to the example was 202 g/mol.

Example 4.

The cocatalyst used was n-valeric acid at 13.0 mmol per one mole of 1-butene. The reactor pressure was 4.0 bar and temperature 20 °C. The reaction time was 6 hours. After the said reaction time, the reaction was halted by means of an NaOH solution. The hydrocarbon phase was analyzed, the result being as follows:

The number-average molecular mass of the product distribution according to Example 4 was 386 g/mol.

Examples 5 and 6.

The cocatalyst used was n-valeric acid at 4.9 mmol per one mole of 1-butene. The reactor pressure was 10 bar and temperature 40 °C. In Example 5 the reaction time was 4 min¬ utes and in Example 6 it was 121 minutes. After the said reaction times the reactions were halted by means of an NaOH solution. The hydrocarbon phases were analyzed, the results being as follows:

The number-average molecular masses of the product distributions according to the examples were 275 g/mol and 371 g/mol. The viscosity index determined on this unhydrogenated product was 82, the kinematic viscosity being KV100 = 7.0 cSt.

Examples 7 and 8.

The cocatalyst used was n-valeric acid at 5.0 mmol per one mole of 1-butene. The reactor pressure was 10 bar and temperature 70 °C. In Example 7 the reaction time was 9 min¬ utes and in Example 8 it was 121 minutes. After the said reaction times the reactions were halted by means of an NaOH solution. The hydrocarbon phases were analyzed, the results being as follows:

The number-average molecular masses of the product distributions according to the examples were 219 g/mol and 286 g/mol. From the product of Example 8, the C, ₆ fraction and fractions lighter than this were separated by vacuum distillation. The viscosity index determined on this unhydrogenated product was 58, the kinematic viscosity being KVIOO = 2.8 cSt.

Examples 9-15.

1 -Butene can also be oligomerized with organic acid catalysts other than n-valeric acid, for example, with alcohols and water, as shown by Examples 9-15. The reactor pressure used was 4.0 bar and temperature 20 °C, the reaction time being 36 minutes. The cocatalysts used were acetic acid (Example 9), n-octanoic acid (10), ethanol (11), 1- pentanol (12), 1-octanol (13), and water (14). The reference example (15) is a reaction performed with n-valeric acid under the same conditions. Cocatalyst was used at a ratio of 14.5-15.9 mmol of cocatalyst per one mole of 1-butene. The results are shown in the following table, where n^ stands for mmol of cocatalyst per one mole of butene.

The invention is illustrated in the following examples 16-62, in which the monomers shown in the table below were used.

Example Monomer

16-29 Raffinate II, i.e. a mixture of butene and butane 30-50 Raffinate II + alpha-olefin 51-62 long-chain alpha-olefin

Example 16.

The cocatalyst used was n-valeric acid at 32 mmol per one mole of the butene mixture. The reactor pressure was 4.0 bar and temperature 20 °C. In Example 16 the reaction time was 75 minutes. After the said reaction time the reaction was halted by means of an NaOH solution. The hydrocarbon phase was analyzed, the result being as follows:

Examples 17 and 18.

The cocatalyst used was n-valeric acid at 52 mmol per one mole of the butene mixture. In Example 17 the reactor pressure was 5.7 bar and temperature 30 °C. In Example 18 the reactor pressure was 4.5 bar and temperature 10 °C. The reaction time was 120 minutes in both examples. After the said reaction times the reactions were halted by means of an NaOH solution. The hydrocarbon phases were analyzed, the results being as follows:

From the products of Examples 17 and 18, the C, _{6 ft} - _clion and fractions lighter than thi were separated by vacuum distillation. Kinematic viscosities (KV100, cSt) were measured and viscosity indices (VI,-)were determined for these unhydrogenated products. For the product of Example 17, KV100 = 3.3 cSt and VI = 21. For the product of Example 18, V100 = 4.0 cSt and VI = 12.

Examples 19 and 20.

The cocatalyst used was n-valeric acid at 10 mmol per one mole of the butene mixture. In Example 19 the reactor pressure was 4.7 bar and temperature 10 °C. In Example 20 the reactor pressure was 5.1 bar and temperature 30 °C. The reaction time in both examples was 30 minutes. After the said reaction times the reactions were halted by means of an NaOH solution. The hydrocarbon phases were analyzed, the results being as follows:

Examples 21 and 22.

In Example 21, the cocatalyst used was n-valeric acid at 51 mmol per one mole of the butene mixture. The reactor pressure was 3.1 bar and temperature 10 °C. In Example 22, the cocatalyst used was n-valeric acid at 53.5 mmol per one mole of the butene mixture. The reactor pressure was 3.8 bar and temperature 30 °C. The reaction time in both ex- amples was 30 minutes. After the said reaction times the reactions were halted by means of an NaOH solution. The hydrocarbon phases were analyzed, the results being as

follows:

Examples 23-29.

The monomer was Raffinate II, i.e. a mixture of butene and butane. Raffinate II can also be oligomerized with organic acid catalysts other than n-valeric acid, for example, with alcohols and water, as shown by Examples 23-29. The reactor pressure was 6-7 bar and temperature 20 °C, the reaction time being 120 minutes. The cocatalysts used were acetic acid (Example 23), n-octanoic acid (Example 24), ethanol (Example 25), 1 -pentanol (Example 26), 1-octanol (Example 27), and water (Example 28). The reference example (29) was a reaction performed under the same conditions by using n-valeric acid. Cocatalyst was used at a ratio of 2.8-3.7 mmol of cocatalyst per one mole of the butane mixture.

Examples 30-35.

The table shows the alpha-olefin used as the comonomer, the cocatalyst used, and the product distributions as yields. Into the reactor there were fed 100 grams of Raffinate II and 20-21 grams of the alpha-olefin mentioned in the examples. The reaction conditions used were: temperature 40 °C; pressure 7-8 bar; and reaction time 120 minutes. The

cocatalyst used was n-valeric acid (C ₅ acid) or 1-pentanol (C ₅ alcohol); the amounts are mentioned in the examples (kk, g). The product properties were determined on products from which the C ₁₆ fraction and fractions lighter than this had been removed by vacuum distillation. Kinematic viscosity (KVlOO, cSt), viscosity index (VI,-) and pour point (PP, °C) were determined on these unhydrogenated products.

Example 36.

60 g of dodecene and 66 g of Raffinate II were fed into the reactor. The cocatalyst used was 2.2 grams of 1-pentanol. The reaction conditions were: reaction time 120 minutes; temperature 30 °C; and pressure 6 bar. After the said reaction time, the reaction was halted by means of an NaOH solution. The hydrocarbon phase was analyzed, the result being as follows:

C ₈ -C _I6 13.4 %; C ₂₀ -C ₂₈ 43.6 %; C ₃₂₊ 5.3 %; KVlOO 119; VI 119; and PP -51 °C.

Kinematic viscosity (KVlOO, cSt), viscosity index (VI,-) and pour point (PP, °C) were determined on the unhydrogenated product from which the C, ₆ fraction and fractions lighter than this had been removed by vacuum distillation.

Examples 37-50.

The examples show the monomer feed compositions, the reaction times, and the product distributions. Raffinate II and alpha-olefin were fed into the reactor in the amounts mentioned in the examples. The reaction conditions were: temperature 30 °C and pressure 4-8 bar, i.e. sufficient to maintain Raffinate II in liquid state in each experiment. The cocatalyst used was n-valeric acid in an amount of 2.85 grams. After the said reaction times, the reactions were halted by means of an NaOH solution. The hydrocarbon phases were analyzed, the results are shown in the tables.

The product properties mentioned in the examples, i.e. kinematic viscosity (KVlOO, cSt), viscosity index (VI,-) and pour point (PP, °C), were determined on an unhydrogenated product from which the C ₁₆ fraction and fractions lighter than this had been removed by vacuum distillation. In Examples 37-41 the alpha-olefin was 1-octene (59 g) and the feed was Raffinate II (68 g).

Examples 42-46.

In the examples the feed materials were 1-dodecene (60 g) and Raffinate II (42 g).

Examples 47-50.

The alpha-olefin was 1-hexadecene (71 g) and the feed was Raffinate II (38 g).

Examples 51-62.

Into the reactor was fed 100 g of alpha-olefin. The reaction conditions used were a temperature of 30 °C and a pressure of 3.0-3.2 bar, and the cocatalyst was n-valeric acid in an amount of 2.9-3.0 g. After the said reaction times the reactions were halted by

means of an NaOH solution. The hydrocarbon phases were analyzed, the results being as follows (fractions: mono = monomer; di-tetra = di-, tri-, and tetramers; penta+ = pentamers and fractions higher than this). In Examples 51-54 the alpha-olefin is 1-octene, in Examples 55-58 it is i-dodecene, and in Examples 59-62 it is 1-hexadecene.

The results are shown in the following table.

Examples 63-66.

In Example 63 the reaction conditions were: reaction temperature 30 °C; pressure 3 bar expressed as BF ₃ overpressure; and reaction time 4 hours. Raffinate II was fed in as the monomer in an amount of 100 g and n-valeric acid as the cocatalyst in an amount of 2.86 g. The obtained product was analyzed mass spectrometrically.

The product in Example 64 was a product prepared according to Example 58, which was analyzed mass spectrometrically.

The product in Example 65 was a product prepared according to Example 46, which was

analyzed mass spectrometrically.

The product in Example 66 had been prepared by mixing in mass proportions 50:50 the products of Example 63 and Example 58. This mixture was analyzed mass spectrometri- cally.

The appended mass spectrometric analyses depict the analyses of four different experi¬ ments graphically, showing the absolute intensities of corresponding peaks of whole molecules (the molecular mass of which corresponds to the molecular mass of the alkene having a certain carbon number) with different molecular mass values. The peaks corresponding to fragmented products have been omitted from these alkene graphs; the be¬ havior of these peaks with different values of molecular mass, however, corresponds to the peaks of whole molecules. The following observations can be made from the graphs:

- In the alkene graph of butene oligomers (Fig. 1: Raffinate II oligomers), the dominating alkene peaks are observable at carbon numbers 16, 20, 24, 28, 32, etc., i.e. at carbon numbers corresponding multiples, oligomers, of the carbon number of butene. The absolute intensities of the alkene peaks corresponding to butene oligomers decrease as the carbon number increases steadily.

Respectively, the alkene peaks dominating in the alkene graph of dodecene oligo¬ mers (Fig. 2: Dodecene oligomers) are at carbon numbers 24, 36, 48, etc., i.e. at carbon numbers corresponding to multiples, oligomers, of the carbon number of dodecene. The absolute intensities of the alkene peaks corresponding to dodecene oligomers decrease as the carbon number increases steadily.

The alkene peaks dominating in the alkene graph of products produced in the co- oligomerization between butenes and dodecene (Fig. 3: C12-Raff II co-oligomers) are at carbon numbers 16, 20, 24, 28, 36, etc. The absolute intensities of the alkene peaks decrease as the carbon number increases steadily.

The alkene peaks dominating in the alkene graph of a blend of butene oligomers and dodecene oligomers (Fig. 4: C12-Raff I oligomer blend) are at carbon numbers

16, 24, 36 and 48. The peak at carbon number 16 is due to butene oligomers, but at carbon numbers 24, 36 and 48 the peaks are mainly due to dodecene oligomers. These graphs show clearly that olefin mixtures oligomerized by the method accor¬ ding to the invention do not produce mixtures of homo-oligomers but produce co- oligomers during the reaction when olefins may link randomly to the carbon chain.