OLIGOMERISATION This invention relates to a novel catalyst composition comprising ionic liquids and the use thereof in a process such as eg the oligomerisation (including dimerisation) of olefins to linear products in a heterogeneous catalytic process.

The dimerization and oligomerisation of olefins in the presence of homogeneous, Group VIII transition metal catalysts has been studied extensively. With higher olefins (>C2), the products obtained generally consist of mixtures of predominantly branched isomers. For example, gasoline blending components are produced by dimerization and codimerization of propylene and butenes. Bogdanivic et al (Ind Eng. Chem., 62 (12), 1970, pp. 34) have shown that for the catalyst system 7t- allyl-nickel halide/AICl3, the addition of bulky phosphanes gives rise to highly branched products.

Very few catalysts are known which catalyse the dimerisation and oligomerisation of higher olefins to linear products. The dimerisation and oligomerisation of C3-Cs- olefins to linear products is especially and highly desirable for the production of C6-Cl8 plasticisers and detergent range olefins.

The major outlet for C4-dimers is e.g. the conversion thereof, after hydroformylation and hydrogenation, to plasticiser alcohols. Such plasticiser- alcohols made from linear dimers have higher thermal stabilities due to their relatively higher boiling points. Moreover, such linear dimers are preferred for use in the production of detergent-alkylates due to ease of their biological degradability.

Hitherto, the best known catalyst system for the homogeneous, linear dimerization of higher (>C2) olefins is that described by Keim et al. (J. Mol.

Cat 6 1979, pp. 79) in which a square planar Ni-O,O '-chelating systems with

an easily replaceable group such as cyclo-octadienyl, methallyl-, allyl etc. such as e.g: which is Ni-cyclooctadienyl hexafluoroacetyl acetonate, is used. Table 1 shows the catalytic results of Keim et al when using (I) as a homogeneous catalyst in the dimerization of different olefins: Table 1 jolefin i Activityl 1/h Selectivity (%) to Linearity (%) of dimers dimers ethylene 8200 20 100 propene 800 60 75 1-butene 500 85 75 1-hexene 300 90 60 1 octene 50 100 82 1 octene 50 100 82 Although these results are very interesting especially for the dimerization of 1-butene, the high costs of the hexafluoroacetylacetonate-ligand used, the relatively low activity of the catalyst and the amount of catalyst lost due to the homogenous nature of the process has rendered the process commercially unattractive.

To overcome these problems much work has been directed towards the use of heterogeneous catalysis. S. Gruppe (Dissertation RWTHAachen, 1988) tried to anchor the NiO-catalyst (I) on a polymer backbone; A. Mehlhorn (Dissertation RWTHAachen, 1991) investigated the introduction of the above mentioned NiO- catalyst (I) into zeolites. These strategies, however, resulted in considerable loss of catalyst due to leaching and hence resulted in much lower catalyst activity.

Ionic liquids are primarily mixtures of salts which melt below room temperature. Such salt mixtures include aluminium halides in combination with one or more of imidazolium halides, pyridinium halides and phosphonium halides, the latter being preferably substituted eg by alkyl groups. Examples of the substituted

derivatives of the latter include one or more of l-methyl-3-butyl imidazolium halide, 1-butyl pyridinium halide and tetrabutyl phosphonium halides. Ionic liquids have been known as a solvent/activator for dimerization catalysts (eg nickel- phosphine catalysts). Conventional ionic liquid catalysts comprise about 67% aluminium trichloride. However, these catalysts give rise to highly branched dimers (eg C6 hydrocarbons) which are used as high RON/MON octane additives.

Ionic liquids are described as LewisAcid catalysts for Friedel-Crafts reactions in prior published WO 95/21806 and olefin oligomerisation catalysts in prior published WO 95/21871 . These ionic liquids consist of a mixture where the mole ratio of AIX3/RX (in which X represents an alkyl group, a halide or a combination thereof and R is an alkyl group) is usually > 1.5. When such ionic liquids are used for the oligomerisation of isobutene, a product having an average molecular weight of M = 1000 is obtained. In general, these acidic ionic liquids rapidly catalyse unselective oligomerisation of higher olefins to form highly viscous and highly branched oligomers with the product having a broad molecular weight distribution (ie a high dispersity index). The use of such acidic ionic liquids without modification can lead to the formation of very low dimer selectivities (usually < 5 %). At room temperature and above, even with a Ni-catalyst, the main products are usually highly viscous cationic oligomers.

Chauvin et al. describe in a series of publications (J. Chem. Soc., ('hem.

Commun., 1990, pp. 1715; Ind. Eng Chem. Res, 34, 1995, pp. 1149; and. Cat., 165 1997, pp. 275) the preferred formation of dimers by the oligomerisation of higher olefins using slightly acidic ionic liquid of the type RX/AIX3/AIRC12 and a Ni-catalyst. However, at very low temperatures (usually -15°C), they describe the formation of dimers from propene and butenes which are highly branched. Only at very low temperatures [usually -15 "C) or by addition of aluminiumalkyl halides such as AlEtCl2 (ie ethyl aluminium dichloride) are improved dimer selectivities possible.

However, the addition of such aluminiumalkyl halides leads even at very low temperatures to the formation of highly branched dimers (usually < 10 % n-octenes for the dimerisation of 1-butene). This may be due to the tendency of AlEtCl2 to transfer ethyl groups to the nickel thereby destroying the Ni-X,Y-chelating system, which is known to promote high linearity in the dimer. Another problem is that AlEtCl2 is known to have strong isomerisation activity (Chauvin et al, Angew.

Chew., 107, 1995, pp. 2941) and converts the 1-butene rapidly into the

thermodynamically equilibrium distribution of butenes (around 4 % 1-butene at room-temperature).

A further alternative for the heterogenisation of NiO-catalyst (I) is to carry out the process in a two phase system. However, all of the common polar solvents such as eg water, butanediol etc used hitherto deactivate the catalyst system almost completely.

It has now been found that use of a modified ionic liquid as a solvent for the above described chelated complex of nickel such as eg Ni-cyclooctadienyl hexafluoroacetyl acetonate catalyst (I), a di(acetyl acetonate) of nickel or an analogue of either wherein the chelating ligand is a benzoyl trifluoroacetonato group ie n-4-cycloocten-1-yl)(benzoyl-trifluoroacetonato)nickel or a di(acetyl acetonato) group such as in eg nickel di(acetylacetonate) [hereafter Ni(acac)2] produces highly linear dimeric and oligomeric products.

Accordingly, the present invention is a buffered ionic liquid comprising: <BR> <BR> <BR> A. a compound of the formula RnMX3 n or of the formula RmM2X6 m wherein M is a metal selected from aluminium, gallium, boron and iron (III), R is a C,-C6 alkyl radical, X is a halogen atom or an alkoxy group in which the alkyl group of said alkoxy group having 1-4 carbon atoms, n is 0, 1 or 2, and m is 1, 2 or 3 B. an organic halide salt; and optionally, C. an organic base characterised in that the relative mole-fractions of A, B and C in the ionic liquid is within the ranges 0.50-0.67 : 0.33-0.50 : 0.0-0.20.

In the ionic liquids of the present invention, the metal component M of compound A is aluminium, gallium, boron or iron (III) and is preferably aluminium. Where M is aluminium, compound A may be an aluminium halide or an alkyl aluminium halide such as an alkyl aluminium di chloride or dialuminium triethyl trichloride and is preferably ethyl aluminium dichloride. Where X is an alkoxy group compound A may be for instance dialkyl aluminium alkoxide, especially diethyl aluminium ethoxide ie (C2H5)2M(OC2H5).

The organic halide salt (B) in the ionic liquid is suitably: i. a hydrocarbyl substituted ammonium halide such as eg a mono-, di- or tri-alkyl ammonium halide represented by the generic formula R4NRlR2R3CI wherein each of R1, R2, R3 and R4 may be H or a C1-C8 alkyl groups, or

ii. a hydrocarbyl substituted imidazolium halide or iii. a hydrocarbyl substituted pyridinium halide.

Especially preferred are the l-alkyl-3-alkyl-imidazolium halides, the l-alkyl pyridinium halides and the alkylene pyridinium dihalides. Specific examples of these compounds include the following: l-methyl-3-ethyl imidazolium chloride, 1- ethyl-3-butyl imidazolium chloride, l-methyl-3-butyl imidazolium chloride, 1- methyl-3-butyl imidazolium bromide, l-methyl-3-propyl imidazolium chloride, ethyl pyridinium chloride, ethyl pyridinium bromide, ethylene pyridinium dibromide, ethylene pyridinium dichloride, 4-methyl pyridinium chloride, butyl pyridinium chloride and benzyl pyridinium bromide. Of these l-methyl-3-ethyl imidazolium chloride and l-methyl-3-butyl imidazolium chloride are preferred.

The organic base (C) is an optional ingredient. The catalyst will perform adequately even in the absence of a base in the sense that it will still produce a higher proportion of the linear dimers/oligomers if used in conjunction with an ionic liquid solvent than when using toluene as the solvent. The base (C), when used, is suitably such that it has a relatively high solubilty in the ionic liquid.

Examples of bases that may be used include inter alia any cyclic, heterocyclic or aliphatic, aromatic or non aromatic bases which have these properties. The bases used are preferably the pyrroles, pyridines, quinolines and their derivatives, especially their hydrocarbyl substituted or halo-substituted derivatives wherein the hydrocarbyl substituents may be alkyl, aryl, alkaryl, aralkyl or cycloalkyl groups and the halo substituents are eg chloro, bromo of fluoro derivatives, especially the difluoro derivatives such as eg 2,6-difluoro-pyridine.

The buffered ionic liquid comprises (A), (B) and (C) in mole fraction within the ranges of 0,50-0.67 : 0.33-0.50: 0.0-0.20 respectively, suitably in the ranges from 0.50-0.57: 0.45-0.50 : 0.001-0.05 respectively. A typical buffered ionic liquid preferably comprises (A), (B) and (C) in the mole-fraction ratio of 0.53 : 0.47 : 0.04 respectively.

Ionic liquids of the present invention can be used as a solvent/activator for catalysts, especially for catalysts such as the nickel compound (I) used in hydrocarbon conversion reactions such as eg dimerisation or oligomerisation.

Where the ionic liquids are used in conjunction with a catalytic species such as eg the nickel compound (I) described above, the modification of the conventional ionic liquids by use of buffers minimises the tendency of the ionic liquid to promote any undesirable side-reactions thereby adversely affecting the selectivity towards

the desired linear dimer.

The modified ionic liquid has to satisfy the following criteria: a. it has to be substantially free of any coordinating species such as e.g Cl (present e.g in basic chloroaluminate-based ionic liquids) which are capable of occupying the active sites in the catalyst; b. it should have a slightly latent Lewis-acidity in the melt to allow activation of the catalyst and the substrate is extremely favourable for the reaction.

c. at the same time the presence of any excess of free chloroaluminate-dimer should be avoided to minimise cationic side-reactions through a Lewis Acid-base reaction with the olefin.

d. it is easier to prepare and uses only relatively inexpensive material thereby improving the economics of the process.

For this reason a used chloroaluminate-based ionic liquids has to be slightly acidic in nature but buffered to a certain amount of latent acidity which would enable it to avoid side reactions initiated by the ionic liquid itself without deactivation and destruction of (I): A number of reactions are described in the literature to buffer Lewis-Acid ionic liquids effectively to neutral ionic liquids with latent acidity (see D. King et al, J.Am. Chem Soc., 118, 1996, pp. 11933): Al2Cl7 + MCI + MAICI4 + AICI4- (1) wherein M = Li, Na or K Additionally, an alternative way to buffer the Lewis acidity of common acidic Lewis-acid ionic liquids to latent acidity is as follows: The slightly acidic ionic liquids (having molar ratio of AICI3 in the binary melt of usually of 53-55 %) by the addition thereto of a weak, system adapted, non-coordinating base. The base reacts with any species in the melt which are capable of initiating any undesirable side reactions of the type shown below: wherein B represents the base.

The choice of the base may enable variations in the selectivity of the catalyst to the desired products. A slightly acidic chloroaluminate system buffered down with 2,6-difluorpyridines shows eg a stronger selectivity to the trimerisation product

during the oligomerisation of 1-butene. The use of 2,6-difluoro-pyridine, for instance favours the formation of linear trimers from the mono-olefin. Thus, the choice of base may direct the reaction towards trimer formation in preference to dimers. Similarly, where the catalyst is a Ni(acac)2, it is advantageous to use such a catalyst together with an activator such as eg ethyl aluminium dicholoride ("EADC") in order to improve the selectivity of the catalyst for a particular owner.

In this case, the total amount of EADC and component A present in the formulation is slightly higher than when used in the absence of an activator. The additional amount of EADC used suitably corresponds to the stoichiometric amount corresponding to the Ni(acac)2 used. It is to be noted that if too much EADC is used, there is a risk of forming the higher, relatively less desirable, oligomers. It is not necessary to pre-form a Ni(acac)2-EADC system prior to use thereof as a catalyst in the ionic liquid. Thus, when using a Ni(acac)2 catalyst system, this may be prepared in several ways. For instance, the Ni(acac)2 may be dissolved first in an ionic liquid comprising eg 55% AlCI3, followed by addition of the buffering base, if used, and finally adding a stoichiometric amount of EADC based on the Ni(acac)2 used to this mixture. The resultant product can be used directly as a catalyst for the oligomerisation reaction. Alternatively, the EADC may first be added to the ionic liquid and then to this mixture Ni(acac)2 can be added to form the catalyst.

The buffering procedure enables activation of the NiO-catalyst (I) or the Ni(acac)2 catalyst, or, an analogue of either in such modified ionic liquid solvents so as to maintain the selectivity thereof to the linear products, while suppressing substantially any undesirable cationic oligomerisation even at relatively high temperatures (eg up to 800C).

The activity of the catalyst in two-phase reactions can in some instances be adversely affected by the viscosity of the phase, especially in respect of mixing and transfer phenomena in the system. In such cases, the adverse effect can be mitigated by addition of small amounts (eg < 20 vol % of the ionic liquid phase) of polar cosolvents such as CH2C12, CHC13, fluorobenzene etc. to improve dramatically the physical properties of the ionic liquid. Such an expedient can increase the turn-over frequency of catalytic reaction up to four times without adversely affecting the desired selectivities. Only very small amounts (eg < 2 %) of the cosolvents are likely be lost in the organic layer comprising the feedstock and dimerised products.

Thus, according to a further embodiment, the present invention relates to a hydrocarbon conversion catalyst wherein said catalyst is used as a solution thereof in or activated by a buffered ionic liquid according to the present invention as hereinbefore described.

The hydrocarbon conversion catalyst is suitably a co-ordination complex of nickel and is preferably (rl4-cycloocten-l -yl)-(benzoyl-trifluoroacetonato) nickel or nickel di(acetyl acetonate) or an analogue of either.

The hydrocarbon conversion catalyst according to the present invention is suitably used for the dimerisation or oligomerisation of unsaturated hydrocarbons, suitably olefins having from 2-20 carbon atoms, preferably olefins having 2-10 carbon atoms.

Thus, according to yet another embodiment, the present invention is a hydrocarbon converion process comprising the dimerisation or oligomerisation of unsaturated hydrocarbons characterised in that said process is carried out in the presence of a catalyst which is dissolved in or activated by a buffered ionic liquid of the present invention as hereinabove described.

The catalyst for dimerisation or oligomerisation is suitably a co-ordination complex of nickel as described above, preferably (-4-cycloocten- 1 -yl)-(benzoyl- trifluoroacetonato) nickel or nickel di(acetyl acetonate), or, an analogue of either.

Example 1: Use of pyrrole as the buffering base A 30 ml glass pressure vessel connected with a manometer and a stop cock was charged with N-methyl-N-butylpyridiniumchloride-AICI3 (4g, 24.3 mmol, 55% mol AICI3). Pyrrole (0.072g, 1.08 mmol) was added to the charge in the vessel and stirred for 1 h. to form a solution of a buffered ionic liquid. The composition of the ionic liquid so formed was 4-methyl-N-butylpyridiniumchloride/AlCl3/pyrrole corresponding to 0.53/0.43/0.04 mole-fractions of each respectively. Ni- hexafluoro-acetylacetonate (0.04g, 0. lOmmol) catalyst was added to the ionic liquid and stirred for 15 min. when all the Ni-catalyst dissolved in the ionic liquid.

The Ni-catalyst loading with respect to the ionic liquid was 14 mg/ml. The vessel was then cooled to -300C and 20 ml of l-butene (equivalent to 12 g, 0.21 mol) was charged to the vessel. The temperature of the vessel was then allowed to rise to 25"C.

The contents of the vessel were stirred with a stirrer at about 500 rpm and a reaction exotherm was observed over the first 5 minutes of the reaction, which was indicated by a pressure increase up to 4 bar. After another ten minutes (total

15 minutes), the stirring and consequently the reaction was stopped and the vessel was cooled down to OOC. The vessel was then opened and the organic layer in the reaction mixture was decanted off. The organic layer was then stirred at room temperature for 2 hours to remove any traces of butenes. A short centrifugation of the organic layer at 2000 turns/min was carried out to separate small drops of the ionic liquid from the organic layer. Measurements of residual Al and Ni in the organic layer after the reaction gave values of<1 ppm for each which provided evidence of efficient catalyst separation via gravity alone following reaction. The organic layer (mass 2g) was then recovered and analysed by GC and the following results (compound/mass%) were obtained: Traces of butenes 0.5 % Z of all C8-oligomers: 86.0 % Z higher oligomers 13.5 % Total 100 % Distribution of the C8-oligomers: En-Octenes 56 % comprising n-octene-l 1.70 % trans-octene-2 23.43 % cis-octene-2 5.20 % trans-octene-3 18.79 % cis-octene-3 2.20 % trans-octene-4 3.94 % cis-octene-4 0.74 % E Methylheptene 42 % z Dimethylhexene 2 % Total: 100 % The above data correspond to the following: Butene conversion: 16.7 % Sel.(C8 product) 86.0 % Sel.(linear C8 product) 56.0 % Turn-over frequency 1/h 1350 Example 2: Use of quinoline as buffering base: A 30 ml glass pressure-vessel connected with a manometer and a stop-cock was charged with N-methyl-N-butylpyridiniumchloride-A1C13 (4g, 24.3 mmol, 55%

mol AICI3). Then quinoline (0. 139g, 1.08 mmol) was added to the charge in the vessel and stirred for 1 h. to form a solution of a buffered ionic liquid. The composition of the ionic liquid so formed was 4-methyl-N- butylpyridiniumchloride/AlCl3/qunoline corresponding to 0.53/0.43/0.04 mole- fractions of each respectively. Ni-hexafluoro-acetylacetonate (0.04g, 0. lOmmol) catalyst was added to the ionic liquid and stirred for 15 min. when all the Ni- catalyst dissolved in the ionic liquid. The Ni-catalyst loading with respect to the buffered ionic liquid was 14 mg/ml. The vessel was then cooled to -300C and 20 ml of 1-butene (equivalent to 12 g, 0.21 mol) were charged to the vessel. The temperature of the vessel was then allowed to rise to 250C.

The contents of the vessel were then stirred with a stirrer at about 500 rpm and a reaction exotherm was observed over the first 5 minutes of the reaction, which was indicated by pressure increase of up to 4 bar. After another ten minutes (total 15 minutes), the stirring and consequently the reaction was stopped and the vessel was cooled down to OOC. The vessel was then opened and the organic layer in the reaction mixture was decanted off. The organic layer was then stirred at room temperature for 2 hours to remove any traces of butenes. A short centrifugation of the organic layer at 2000 turns/min was carried out to separate small drops of the ionic liquid from the organic layer.

Measurements of residual Al and Ni in the organic layer after the reaction gave values of <1 ppm for each which provided evidence of efficient catalyst separation via gravity alone following reaction. The organic layer (mass 1.8g) was then recovered and analysed by GC and the following results (compound/mass%) were obtained: Traces of butenes 0.1 % E of all Cs-oligomers: 98.0 % E higher oligomers 1.9 % Total 100 % Distribution of the C8-oligomers: E n-Octenes 64 % comprising n-octene-1 1.96% trans-octene-2 26.79 % cis-octene-2 5.89% trans-octene-3 21.48 % cis-octene-3 2.49 %

trans-octene-4 4.50 % cis-octene-4 0.86 % E Methylheptene 34 % CDimethylhexene 2 % Total: 100 % The above data correspond to the following: Butene conversion: 15.0 % Sel. (C8 product) 98.0 % Sel (linear C8 product) 64.0 % Turn-over frequency 1/h 1240 Example 3: Use of 2*6-Lutidine (26-Dimethylpyridine) as buffering base: A 30 ml glass pressure vessel connected with a manometer and a stop-cock was charged with N-methyl-N-butylpyridiniumchloride-A1C13 (4.0g, 24.3 mmol, 55% mol AlCI3). Then 2,6-lutidine (0.116g, 1.08 mmol) was added to the charge in the vessel and stirred for 1 h. to form a buffered ionic liquid. The composition of the ionic liquid so formed was 4-methyl-N-butylpyridiniumchloride/AlCl3/2,6- lutidine corresponding to 0.53/0.43/0.04 mole-fractions of each respectively. Ni- hexafluoro-acetylacetonate (0.04g, 0. lOmmol) catalyst was added to the ionic liquid and stirred for 15 min. when all the Ni-catalyst dissolved in the ionic liquid.

The Ni-catalyst loading with respect to the ionic liquid was 14 mg/ml. The vessel was then cooled to -300C and 20 ml of l-butene (equivalent to 12 g, 0.21 mol) was charged to the vessel. The temperature of the vessel was then allowed to rise to 25"C.

The contents of the vessel were stirred with a stirrer at about 500 rpm and a reaction exotherm was observed over the first 5 minutes of the reaction, which was indicated by a pressure increase up to 4 bar. After another five minutes (total 10 minutes), the stirring and consequently the reaction was stopped and the vessel was cooled down to OOC. The vessel was then opened and the organic layer in the reaction mixture was decanted off. The organic layer was then stirred at room temperature for 2 hours to remove any traces of butenes. A short centrifugation of the organic layer at 2000 turns/min was carried out to separate small drops of the ionic liquid from the organic layer. Measurements of residual Al and Ni in the organic layer after the reaction gave values of <1 ppm of each which provided evidence of efficient catalyst separation via gravity alone following reaction. The organic layer (mass 2.4g) was then recovered and analysed by GC and the

following results (compound/mass%) were obtained: Traces of butenes 0.5 % E of all Cs-oligomers: 55.0 % E higher oligomers 44.5 % Total 100 % Distribution of the C8-oligomers: E; n-Octenes 68 % comprising n-octene-1 2.08 % trans-octene-2 28.42 % cis-octene-2 6.28 % trans-octene-3 38.08 % cis-octene-3 2.65 % trans-octene-4 4.76 % cis-octene-4 0.89 % E Methylheptene 29 % CDimethylhexene 3 % Total: 100 % The above data correspond to the following: Butene conversion: 20.0 % Sel.(C8 product) 55.0 % Sel.(linear C8 product) 68.0 % Turn-over frequency 1/h 2480 Example 4: Use of N-Methylpvrrole as buffering base A 30 ml glass pressure-vessel connected with a manometer and a stop-cock was charged with N-methyl-N-butylpyridiniumchloride-A1C13 (3.5g, 22.4 mmol, 55% mol Air13) and cooled to -30 OC. Then 20 ml of 1-butene (equivalent to 12 g, 0.21 mol) were added. The catalyst was prepared by dissolving Ni-hexafluoro- acetylacetonate (0.12g, 0.31 mmol) in 2 ml of N-methylprrole. Next, 0.08 mg of this catalyst solution were added rapidly into the vessel at -30 °C to give a yellow organic layer. The vessel temperature was allowed to rise to 25 OC.

The contents of the vessel were then stirred by a stirrer at about 500 rpm and very quickly, during the first 20 seconds, the organic layer became colourless and the ionic liquid changed its colour to a dark orange-brown. At this stage no N- methyl pyrrole could be found in the organic layer so that its composition was 4- methyl-N-butylpyridiniumchloride/A1C13/ N-methyl pyrrole corresponding to

0.53/0.43/0.04 mole fractions of each respectively. The Ni-catalyst loading with respect to ionic liquid was thus 2mg/ml.

The contents ofthe vessel were stirred with a stirrer operating at 500 rpm and a reaction exotherm was observed over the first 5 minutes of the reaction, which was indicated by pressure increase of up to 4 bar. After a further 10 minutes (total 15 minutes) the stirring and consequently the reaction was stopped and the reaction vessel cooled down to OOC. The cooled vessel was then opened and the organic layer from the contents thereof was decanted off. The decanted organic layer was then stirred at room temperature for 2 hours to remove any traces of butenes. A short centrifugation of the organic layer at 2000 turns/min was carried out to separate small drops of the ionic liquid out of the organic layer.

Measurements of residual Al and Ni in the organic layer after reaction gave values of <1 ppm for each which provided evidence of efficient catalyst separation via gravity alone following reaction. The organic layer (mass 1.8g) was then recovered and analysed by GC and the following results (compound/mass %) were obtained: Traces of butenes: 0.2 % E of all Cs-oligomers: 98.0 % E higher oligomers: 1.8 % Total 100 % Distribution of the C8-oligomers: X n-Octenes 56 % n-octene-l 1.70 % trans-octene-2 23.43 % cis-octene-2 5.20 % trans-octene-3 18.79 % cis-octene-3 2.20 % trans-octene-4 3.94 % cis-octene-4 0.74 % E Methylheptene 42 % z Dimethylhexene 2 % Total: 100 % The above data correspond to the following: Butene conversion: 15 % Sel. (C8 product) 98 % Sel (linear C8 product) 55 %

Turnover frequency 1/h 9920 Example 5: Use of (h-4-Cvcloocten- 1 -yl)(benzovl-trifluoroacetonato nickel as catalyst: A 30 ml glass pressure-vessel connected with a manometer and a stop-cock was charged with N-methyl-N-butylpyridiniumchloride-A1C13 (4g, 24.3 mmol, 55% mol AICI3). Then pyrrole (0.072g, 1.08 mmol) was added to the charge in the vessel and stirred for 1 h. to form a solution of a buffered ionic liquid. The composition of the ionic liquid so formed was 4-methyl-N-butylpyridiniumchloride/ AlCl3/pyrrole corresponding to 0.53/0.43/0.04 mole-fractions respectively. 0.04g (0.1 mmol) of(h-4-cycloocten-1-yl)-(benzoyl-trifluoroacetonato) nickel was added to the ionic liquid and stirred for 5 min. when all the Ni-catalyst dissolved in the ionic liquid. The Ni-catalyst loading with respect to ionic liquid was thus 14 mg/ml.

The vessel was then cooled to -30 OC and 20 ml of 1-butene (equivalent to 12 g, 0.21 mol) were charged to the vessel. The temperature of the vessel was allowed to rise to 250C.

The contents of the vessel were then stirred by a stirrer operating at about 500 rpm and a reaction exotherm was observed over the first 5 minutes of the reaction, which was indicated by pressure increase up to 4 bar. After a further 10 minutes (total 15 minutes), the stirrer and consequently the reaction was stopped and the vessel was cooled down to OOC. The vessel was opened and the organic layer of the contents thereof was decanted off. The organic layer was then stirred at room temperature for 2 hours to remove any traces of butenes. A short centrifugation of the organic layer at 2000 turns/min was carried out to separate small drops of the ionic liquid out of the organic layer. Measurements of residual Al and Ni in the organic layer after reaction gave values of <1 ppm for each which provided evidence of efficient catalyst separation via gravity alone following reaction. The organic layer (mass 0.65g) was then recovered and analysed by GC and the following results (compound/mass%) were obtained: Traces of butenes: 0.1 % E of all Cs-oligomers: 55.0 % E higher oligomers: 44.9 Total 100 % Distribution of the C8-oligomers: E; n-Octenes 66 %

n-octene-1 1.98 % trans-octene-2 27.59 % cis-octene-2 6.08 % trans-octene-3 22.16 % cis-octene-3 2.57 % trans-octene-4 4.62 % cis-octene-4 0.87 % z Methylheptene 31% CDimethylhexene 3 % Total: 100 % The above data correspond to the following: Butene conversion: 5.4 % Sel. (C8 product) 55 % Sel (linear C8 product) 66 % Turnover frequency 1/h 450 Example 6: Influence of methvlene chloride A 30 ml glass pressure vessel connected with a manometer and a stop-cock was charged with N-methyl-N-butylpyridiniumchloride-A1C13 (5g, 31.3 mmol, 55% mol AlCI3). Then pyrrole (0.072g, 1.08 mmol) were added to the charge in the vessel and stirred for 1 h. to form a buffered ionic liquid. The composition of the ionic liquid so formed was 4-Methyl-N-butylpyridiniumchloride/ AlCl3/pyrrole equal to 0.53/0.43/0.04 mole fractions of each respectively. 0.04g (0.lmmol) of(h- 4-cycloocten- 1 -yl)-(benzoyl-trifluoroacetonato) nickel were added to the ionic liquid and stirred for 5 min. when all the Ni-catalyst dissolved in the ionic liquid.

The Ni-catalyst loading with respect to the buffered ionic liquid was thus 14 mg/ml. At this stage 1 ml of methylene chloride was added to the buffered ionic liquid and the resulting solution stirred for another 3 min. The vessel was then cooled to -30°C and 20 ml of 1-butene (equivalent to 12 g, 0.21 mol) were charged to the vessel. The temperature of the vessel was allowed to rise to 250C.

The reaction mixture in the vessel was stirred by a stirrer operated at about 500 rpm and a reaction exotherm was observed over the first 5 minutes of the reaction, which was indicated by pressure increase of up to 4 bar. After a further 10 minutes (total 15 minutes), the stirring and consequently the reaction was stopped and the vessel was cooled down to OOC. The vessel was opened and the organic layer was decanted off. The organic layer was then stirred at room

temperature for 2 hours to remove any traces of butenes. A short centrifugation of the organic layer at 2000 turns/min was carried out to separate small drops of the ionic liquid out of the organic layer. Measurements of residual Al and Ni in the organic layer after reaction gave values of<1 ppm for each which provided evidence of efficient catalyst separation via gravity alone. The organic layer (2.4g) was then analysed by GC and the following results (compound/mass%) were obtained: Traces of butenes: 0.1 % Methylenchloride 0.05 % E of all C8-oligomers: 52.0 % E higher oligomers: 47.85 % Total 100 % Distribution of the Cg-oligomers: E n-Octenes 64 % n-octene-l 1.96 % trans-octene-2 26.79 % cis-octene-2 5.89 % trans-octene-3 21.48 % cis-octene-3 2.49 % trans-octene-4 4.50 % cis-octene-4 0.86 % CMethylheptene 33 % # Dimethylhexene 3 % Total: 100 % The above data correspond to the following: Butene conversion: 20 % Sel. (C8 product) 98 % Sel (linear C8 product) 64 % Turnover frequency 1/h 1680 Example 7: Use of Pyrrole as the buffering base at 60°C A 30 ml glass pressure-vessel connected with a manometer and a stop-cock was charged with N-methyl-N-butylpyridiniumchloride-A1C13 (4 g, 24.3 mmol, 5% mol AlCI3). Then pyrrole (0.072 g, 1.08 mmol) was added to charge in the vessel and stirred for 1 h to form a solution of a buffered ionic liquid. The composition of the ionic liquid so formed was 4-methyl-N-butylpyridiniumchloride/AlCl3/pyrrole

corresponding to 0.53/0.43/0.04 mole-fractions of each respectively. 0.04g (0.10 mmol) Ni-hexafluoroacetyl-acetonate were added to the ionic liquid and stirred for 15 min. when all the Ni-catalyst dissolved in the ionic liquid. The Ni-catalyst loading with respect to the ionic liquid was thus 14 mg/ml. The vessel was then cooled to -30°C and 20 ml of 1-butene (equiv to 12 g, 0.21 mol) were condensed in. The vessel was heated to 60"C.

The contents of the vessel were stirred with a stirrer operating at 500 rpm and a reaction exotherm was observed over the first 5 mins of the reaction, which was indicated by a pressure increase of up to 8 bar. After a further 10 minutes (total 15 minutes), the stirring and consequently the reaction was stopped and the vessel was cooled down to 0°C. The vessel was then opened and the organic layer in the reaction mixture was decanted off. The organic layer was then stirred at room temperature for 2 hours to remove any traces of butenes. A short centrifugation of the organic layer at 2000 turns/min was carried out to separate small drops of the ionic liquid out of the organic layer. Measurements of residual Al and Ni in the organic layer after reaction gave values of<l ppm for each which provided evidence of efficient catalyst separation via gravity alone following reaction. The organic layer (mass 2.1 g) was then recovered and analysed by GC and the following results (compound/mass%) were obtained: Traces of butenes 0.5 % S of all C8-oligomers: 86.0 % S higher oligomers 13.5 % Total 100 % Distribution of the C8-oliomers: S n-Octenes 56 % n-octene- 1 trans-octene-2 cis-octene-2 trans-octene-3 ci s-octene-3 trans-octene-4 cis-octene-4 S Methylheptene 42 % CDimethylhexene 2 %

Total: 100 % The above data correspdnd to the following: Butene conversion: 17.5 % Sel. (C8 product) 86.0 % Sel. (linear C8 product) 56.0 % Turnover frequency 1/h 1450 Example 8: (n-4-Cycloocten-1-yl!(benzovl-trifluoroacetonato!nickel at 600C A 30 ml glass pressure-vessel connected with a manometer and a stop-cock was charged with N-methyl-N-butylpyridiniumchloride-A1C13 (4 g, 24.3 mmol, 55% mol AIC13). Then pyrrole (0.072 g, 1.08 mmol) was added to the charge in the vessel and stirred for 1 h. to form a buffered ionic liquid. The composition of the ionic liquid was 4-methyl-N-butylpyridiniumchloride/AlCl3/pyrrole corresponding to 0.53/0.43/0.04 mole-fractions of each respectively. 0.04g (0.lmmol) of(rl-4- cycloocten- 1 -yl)-(benzoyl-trifluoroacetonato) nickel was added to the ionic liquid and stirred for 5 minutes when all the Ni-catalyst dissolved in the ionic liquid. The Ni-catalyst loading with respect to the ionic liquid was thus 14 mg/ml. The vessel was then cooled to -300C and 20 ml of 1-butene (equiv to 12 g, 0.21 mol) were condensed in. The vessel was heated to 600C.

The contents of the vessel were stirred with a stirrer operating at 500 rpm and a reaction exotherm was observed over the first 5 mins of the reaction, which was indicated by a pressure increase of up to 8 bar. After a further 10 minutes (total 15 minutes), the stirring and consequently the reaction was stopped and the vessel cooled down to OOC. The vessel was then opened and the organic layer in the reaction mixture was decanted off. The organic layer was then stirred at room temperature for 2 hours to remove any traces of butenes. A short centrifugation of the organic layer at 2000 turns/min was carried out to separate small drops of the ionic liquid out of the organic layer. Measurements of residual Al and Ni in the organic layer after reaction gave values of<l ppm for each which provided evidence of efficient catalyst separation via gravity alone following reaction. The organic layer (mass 0.7 g) was then recovered and analysed by GC and the following results (compound/mass%) were obtained: Traces of butenes: 0.1 % E of all Cg-oligomers: 55.0 % S higher oligomers: 44.9 Total 100 %

Distribution of the Cs-oligomers: S n-Octenes 66 % n-octene- 1 trans-octene-2 cis-octene-2 trans-octene-3 cis-octene-3 trans-octene-4 cis-octene-4 CMethylheptene 31% x Dimethylhexene 3 % Total: 100 % The above data correspond to the following Butene conversion: 5.8 % Sel. (C8 product) 55 % Sel. (linear C8 product) 66 % Turnover frequency 1/h 500 Comparative Test 1: 1-Butene as catalyst solvent (not according to the invention) A 30 ml glass pressure-vessel connected with a manometer and a stop-cock was charged with Ni-hexafluoroacetylacetonate (0.04g (0.10 mmol). The vessel was then cooled to -300C and 20 ml of 1-butene (equiv to 12 g, 0.21 mol) were condensed in. The temperature of the vessel was allowed to rise to 250C.

The contents of the vessel were stirrered with a stirrer operating at 500 rpm and no reaction exotherm was observed over a reaction time of 15 mins. The stirring and consequently the reaction was stopped and the vessel cooled down to 0°C. The vessel was then opened and the organic layer in the reaction mixture was then stirred at room temperature for 2 hours to remove any traces of butenes. No organic product was obtained.

mass of the organic layer was: Og Comparative Test 2: Toluene as catalyst solvent (not according to the invention) A 30 ml glass pressure-vessel connected with a manometer and a stop-cock was loaded with 4 g toluene. 0.04g (0.10 mmol) Ni-hexafluoroacetylacetonate were added and stirred for 3 min. when all the Ni-catalyst dissolved in toluene. The

vessel was then cooled to -30°C and 20 ml of l-butene (equiv to 12 g, 0.21 mol) were condensed in. The temperature of the vessel was allowed to rise to 250C.

The contents of the vessel were then stirrered with a stirrer operating at 500 rpm and no reaction exotherm was observed over a reaction time of 15 minutes. The stirring and consequently the reaction was stopped and the vessel cooled down to OOC. The vessel was then opened and the organic layer in the reaction mixture was then stirred at room temperature for 2 hours to remove any traces of butenes. The organic layer (4g) was then recovered and analysed by GC and the following results (compound/mass%) were obtained: Traces of butenes 0.45 % Toluene 99.5 % S of all C8-oligomers: 0.05 % Total 100 % Example 9 A stoichiometric ratio of Ni(acac)2 catalyst to EADC activator was dissolved in an ionic liquid (IL) of formula 2-methylbutylpyridinium chloride-aluminium chloride (55 % mol AICI3), the ratio of(catalyst+activator) to IL being 1:150 mol/mol. 1- butene feedstock was added such that the ratio of IL:feed was 150:1400 mol/mol.

This mixture was stirred in a batch autoclave at 230C for 15 mins at 600 rev/min.

N-methylpyrrole was added in some cases to the ionic liquid in order to minimise side reactions of olefin feedstock to higher oligomers. Table 1 below shows the effect of the level of free base addition on catalyst performance where TOF represents turnover frequency, ie moles of product over number of active nickel atom sites: Table 1 wt% N- TOF/ second Selectivity (C8) Linearity (C8) methylpyrrole % 2 320 45 75 3 600 68 48 4 700 98 50 6 900 98 40 Table 1 shows that the Ni(acac)2 catalyst can also produce C8 dimer, without the presence of fluorinated side groups. In addition, the data show that the addition of

free base is beneficial to catalyst performance, in terms of activity, selectivity to dimer and dimer linearity.

The Ni(acac)2 catalyst system is much easier to handle and is much cheaper than the fluorinated catalysts. When used in combination with a free base, it is possible to obtain linear dimer product with equivalent activity, selectivity and linearity as with fluorinated catalyst.

Example 10 A mixture of 4-methylbutylpyridinium chloride-AICI3 ionic liquid (IL) and N- methylpyrrole in the ratio of 96:4 mol/mol was used to solvate Ni(acac)2:ETAC catalyst and rafffinate 2 feedstock (butanes 25.7%, 2-butenes 58.8%, 1-butene 11.3%, iso-butene < 5% w/w) added to the mixture, in the ratio IL/catalyst/feedstock = 1/150/1400 mol/mol. Stirring was maintained at 600 revs/min and temperature of 500C for 60 mins. Table 2 below shows the results Table 2 TOF/hr Selectivity (C8 dimer)% Linearity (C8) % 149 71 11 The data highlight the poor catalyst activity (turnover) and low linearity of dimer product when using raffinate 2 as feedstock instead of 1-butene. This is believed to be due to the difficulty of dimerising 2-butene to linear product, with 2-butene being present at levels of 58.8 % w/w in the raffinate 2 feedstock.

Example 11 By mixing Ni hexafluoroacetylacetonate catalyst, ionic liquid (IL) buffered with 2,6-difluorolutidine (96:4 IL:base mol), and 1-butene feedstock in the ratio catalyst:IL:feed = 1:150:1400 at 600 revs/min at 230C for 15 mins in batch autoclave mode, the catalyst behaviour was modified such that it was now selective to C12 trimer rather than C8 dimer. The results of this experiment are shown in Table 3 below: Table 3 TOF/hr Selectivity Selectivity Linearity (C8) Linearity (C,2) % (C8 dimer)% (C12 trimer) % 730 29 50 72 10