FR2829131A1 - PROCESS FOR THE DIMERIZATION OF ISOBUTENE - Google Patents

Abstract

A process for the dimerization of isobutene, pure or as a mixture with other hydrocarbons, uses as catalyst and as solvent a composition comprising at least one Bronsted acid, denoted HB, dissolved in an ionic liquid medium comprising at least one organic cation. Q + and an A- anion, this composition being such that when A and B are identical, the molar ratio of Bronsted acid to the ionic liquid is less than 1/1.

Description

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The present invention relates to the dimerization of isobutene, pure or as a mixture with other hydrocarbons.

It has been described and claimed in the French patent application filed on August 31, 2001 under the national registration number 01/11 398 that the addition of at least one Brnsted acid, noted HB, in a nonaqueous liquid medium to ionic character (medium of molten salt type) comprising at least one organic cation Q + and one anion A - and in which, when A and B are identical, the molar ratio of Brnsted acid to the ionic liquid is less than 1 / 1, leads to liquid compositions which can be used as catalysts and solvents for acid catalysis reactions.

In this patent application, it was mentioned that the catalytic composition described could be used more particularly in the alkylation of aromatic hydrocarbons, but also in the oligomerization of olefins, the dimerization of isobutene, the alkylation of olefins. isobutan by olefins, isomerization of n-paraffins to iso-paraffins and isomerization of n-olefins to iso-olefins.

The object of the present invention is to describe more precisely and to illustrate the process for the dimerization of isobutene (pure or as a mixture with other hydrocarbons) using the catalytic composition whose definition is recalled above.

It is known that isobutene dimers (trimethyl-2, 4,4-pentene-1 and-2) are interesting intermediates for the manufacture of various products having a commercial interest. By way of examples, mention may be made of higher alcohols, aldehydes and acids.

Trimethyl-2, 2,4-pentane can be obtained by hydrogenation of trimethylpentenes and constitutes a sought-after additive for the reformulation of gasolines absence of sulfur, aromatics and olefin, and low volatility add to an index of. high octane: Engine Octane Number (RON) = Research Octane Number (RON) = 100].

Thus, the selective dimerization of isobutene, followed by hydrogenation of the products obtained to trimethyl-2, 2,4-pentane having a high octane number, constitutes an interesting route which makes it possible i) to replace MTBE (Methyl -Tert-Butyl-Ether: RON = 118; MON = 100), currently banned in California for environmental reasons, and

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ii) to use isobutene, obtained from C4 cuts from catalytic cracking (FCC) or steam cracking processes, raw material for the manufacture of MTBE.

The dimerization (oligomerization) of isobutene is an exothermic reaction catalyzed by acids. Different acids have been described in the literature such as sulfuric acid, or its derivatives, chlorinated or fluorinated aluminas, zeolites, silica-aluminas, etc. However, the most typically used in industry are acid. phosphoric acid (generally supported or “solid phosphoric acid” SAP) and ion exchange resins (“ion exchange resins” 1ER, SP-Isoether process licensed by Snamprogetti or the InAlk process proposed by UOP).

The main difficulty associated with these processes is obtaining good selectivity for dimers. In fact, the exothermicity of the reaction is often difficult to control and leads to the formation of oligomers (essentially C12 olefins and C16 olefins) obtained by parallel reactions from isobutene. These oligomers have too high boiling points, and are outside, or at the limit, specifications required for reformulated gasolines. Furthermore, these oligomers help deactivate the catalysts.

Various studies in the literature describe certain solutions for minimizing the formation of these oligomers.

In the case of ion exchange resins (Amberlyst-15 or-35 type), the use of a diluent (or solvent) is often recommended. The selectivity for dimers depends on the choice of this solvent. The most effective additives are alcohols (US-A-5,877,372; US-A-4,100,220), which lead to the co-production of ethers, or ethers (in US-A-4,447,668, MTBE, ETBE, etc.). We can cite the work of Snamprogetti (M. Marchionna and al. Catal. Today, 65 (2001) 397-403, GB 2 325 237) who studied the influence of the addition of MTBE or MeOH in the lens. to reuse existing MTBE units. Interesting selectivities for trimethylpentenes can thus be achieved, but at isobutene conversions often less than 85%.

International patent application WO-A-01/51 435 describes a sequence of processes in which isobutene is produced by dehydration of tert-butyl alcohol. Isobutene is preferably dimerized with a resin of the Amberlyst A-15 type &commat; in the presence of tert-butyl alcohol (selectivity promoter) and alkane (butane or isobutane) as diluent. The presence

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of hindered alcohol detracts from the formation of ether but also decreases the reaction rate.

International patent application WO-A-01/46 095 describes a process for manufacturing isooctanes from a C4 cut with a catalyst comprising a beta zeolite which makes it possible to selectively convert isobutene in the presence of butenes (butenes conversion < 10%). However, the C8 selectivities described in the examples do not exceed 60%. Furthermore, the service life of the catalyst is not described.

All the processes described above have limitations such as selectivities for trimethylpentenes which are still too low for high pass conversions of isobutene, which requires, for example, recycling of isobutene and increases the cost of the process. The risks of premature deactivation of the catalyst by fouling by the heavier oligomers or by the impurities contained in the feeds exist and the lifetime of the sulfonic resins is consequently shorter for the production of trimethylpentenes than for the synthesis of MTBE.

Non-aqueous ionic liquids of composition Q + A - have been the subject of several reviews (eg, T. Welton, Chem. Rev. 1999,99, 2071). They find many applications as solvents for catalysis by transition metals or as extraction solvents for carrying out liquid-liquid extractions. Their use as solvents and acid catalysts has above all been described for ionic liquids of the acid organochloroaluminate type, and applied to the alkylation of aromatic hydrocarbons (WO-A-95/21806, WO-A-98/03 454, WO- A-00/41 809, EP-A-693 088, EP-A-576 323) to the alkylation of olefins with isobutan (US-A-5 750 455) or to the production of synthetic lubricants (EP- A-791 643).

The advantage of these liquid catalytic systems is that they are not very miscible with the reaction products, which can thus be separated by decantation. The catalytic phase can then be recycled and reused, the consumption of catalyst is thus reduced. However, these systems still have limitations. For example, these organochloroaluminate ionic media are sensitive to humidity. In the presence of protons, the ionic medium can generate hydrochloric acid by reaction with AICI3 potentially present in the medium, which can lead to the formation of chlorinated organic impurities and contaminate the products.

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acide de Brnsted tel que le rapport de l'acide sur la base est supérieur ou égal à 1/1. Ces milieux sont utilisés pour catalyser l'alkylation du benzène avec le décène-1. International patent application WO-A-00/16902 describes the use of an ionic liquid, not containing Lewis acidity, obtained by reaction of a nitrogen compound (for example an amine or a quaternary ammonium) with a

Brnsted acid such that the ratio of acid to base is greater than or equal to 1/1. These media are used to catalyze the alkylation of benzene with decene-1.

The isobutene dimerization process of the invention is therefore defined in general terms by the use of a composition serving as catalyst and solvent comprising at least one Brnsted acid denoted HB, dissolved in a non-liquid medium. -aqueous with an ionic character (medium of molten salt type) comprising at least one organic cation Q + and one anion A- and in which, when A and B are identical, the molar ratio of the Brnsted acid to the ionic liquid is less than 1/1, preferably 0.001 / 1 to 0.7 / 1.

The use according to the invention of the catalyst-solvents in a process for the dimerization of isobutene has a certain number of advantages. The strength of Brnsted acid, which depends on the one hand on its speed in releasing a proton (dissociation equilibrium) and on the other hand on the strength of solvation of this proton by the surrounding medium, can be adjusted by playing on the nature of the anions A and of the cations Q + constituting the ionic liquid. It is thus possible to adjust the level of acidity of the medium in order to optimize the selectivity of the isobutene dimerization reaction.

Furthermore, the products formed (C8 olefins) are poorly miscible with ionic liquids containing Brnsted acid. They can be separated by settling and the catalytic phase can be recycled.

trifluorométhylsulfonate), le fluorosulfonate, les sulfates, les phosphates, les The medium of molten salt type in which the Brnsted HB acid is dissolved has the general formula Q + A - in which Q + represents a quaternary ammonium and / or a quaternary phosphonium and / or a trialkylsufonium and A - represents any anion known as being non-coordinating capable of forming a liquid salt at low temperature, that is to say below 150 oc
The anions A-considered in the invention will preferably be chosen from anions tetrafluoroborates, tetraalkylborates, hexafluorophosphates, hexafluoroantimonates, alkylsulfonates and arylsulfonate (for example methylsulfonate or tosylate), perfluoroalkylsulfonates (for example

trifluoromethylsulfonate), fluorosulfonate, sulfates, phosphates,

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perfluoroacetates (eg trifluoroacetate), perfluoroalkylsulfonamides (eg bis-trifluoromethanesulfonyl amide (N (CF3S02) 2-), fluorosulfonamides, perfluoroalkylsulfomethides (eg tristrifluoromethanesulfonyl methylide (CF3SO2) (3-3Sulfonyl) ) and carborans.

dans lesquelles les cycles sont constitués de 4 à 10 atomes, de préférence 5 à 6 atomes, RI et R2 étant définis comme précédemment. The quaternary ammonium and / or phosphonium considered preferably correspond to the general formulas NRIR2R3R4 + and PRIR2R3R4 +, or to the general formulas R1 R2N = CR3R4 + and R1 R2p = CR3R4 + where RI, R2, R3 and R4, which are identical or different, represent hydrogen in the 'With the exception of the NH4 + cation and preferably a single substituent may represent hydrogen, or hydrocarbyl radicals having from 1 to 12 carbon atoms, for example alkyl groups, saturated or unsaturated, cycloalkyl or aromatic, aryl or aralkyl, comprising from 1 to 12 carbon atoms. Ammonium and / or phosphonium can also be derived from nitrogenous or phosphorus heterocycles comprising 1,2 or 3 nitrogen and / or phosphorus atoms, of general formulas:

in which the rings consist of 4 to 10 atoms, preferably 5 to 6 atoms, R1 and R2 being defined as above.

dans laquelle R1, R2 et R3, identiques ou différents sont définis comme précédemment et R5 représente un reste alkylène ou phénylène. The quaternary ammonium or phosphonium can also consist of a cation corresponding to one of the general formulas:

in which R1, R2 and R3, which are identical or different, are defined as above and R5 represents an alkylene or phenylene residue.

Among the groups RI, R2, R3 and R4, there will be mentioned the methyl, ethyl, propyl, isopropyl, butyl, secondary butyl, tertiary butyl, amyl, methylene, ethylidene, phenyl or benzyl radicals; R5 may be a methylene, ethylene, propylene or phenylene group.

The ammonium and / or phosphonium cation is preferably chosen from the group formed by N-butylpyridinium, N-ethylpyridinium, 3-butyl-1-methyl imidazolium, diethylpyrazolium, 3-ethyl-1-methyl imidazolium, pyridinium , the

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trimethylphenylammonium, tetrabutylphosphonium and methylethylpyrrolidinium.

The trialkylsufonium considered in the invention have the general formula SRIR2R3 + where R1, R2 and R3, which are identical or different, represent hydrocarbyl residues having from 1 to 12 carbon atoms, for example alkyl or alkenyl, cycloalkyl or aromatic, aryl or aralkyl groups. , comprising from 1 to 12 carbon atoms.

méthyl-1 imidazolium, le trifluorométhylsulfonate de butyl-3 méthyl-1 imidazolium, le fluorosulfonate de pyridinium, l'hexafluorophosphate de triméthylphénylammonium, le bis-trifluorométhylsulfonylamidure de butyl-3 méthyl-1 imidazolium, le bis-trifluorométhylsulfonylamidure de triéthylsufonium, le bis-trifluorométhyl-

sulfonylamidure de tributylhexylammonium, le trifluoroacétate de butyl-3 méthyl-1 imidazolium et le bis-trifluorométhylsulfonylamidure de butyl-3 di-méthyl-1, 2 imidazolium. As examples of the salts which can be used, mention may be made of N-butylpyridinium hexafluorophosphate, N-ethyl pyridinium tetrafluoroborate, butyl-3-methyl-1 imidazolium hexafluorophosphate, butyl-3 hexafluorophosphate.

1-methylimidazolium, 3-butyl-1-methyl-1-imidazolium trifluoromethylsulfonate, pyridinium fluorosulfonate, trimethylphenylammonium hexafluorophosphate, 3-butyl-1-methylfluoromethylsulfonylamidide, bis-3-methylfluoromethylsulfonylamidide, bis-3-methylfluoromethyl-1-bisulfomethyl-triulfomethyl tri-sulfomethyl tri-sulfomethyl-1-triazo-sulfonate trifluoromethyl-

tributylhexylammonium sulfonylamide, 3-butyl-1-methyl-imidazolium trifluoroacetate and bis-trifluoromethylsulfonylamide-3-butyl-1,2-methyl-1, 2 imidazolium.

These salts can be used alone or as a mixture. They have a function of catalysts and solvents.

Brnsted acids are defined as being acidic organic compounds capable of donating at least one proton. These Brnsted acids have the general formula HB, in which B represents an anion.

The anions B are preferably chosen from the anions of tetrafluoroborates, tetraalkylborates, hexafluorophosphates, hexafluoroantimonates, alkylsulphonates and arylsulphonates (for example methylsulphonate or tosylate), perfluoroalkylsulphonates (for example trifluonofluoromethylsulphonate, fluoromethylsulphonates, for example trifluonofluoromethylsulphonates, fluoromethylsulphonates, for example. sulfates, phosphates, perfluoroacetates (for example trifluoroacetate), perfluoroalkylsulfonamides (for example bis-trifluoromethanesulfonyl amide (N (CF3S02), fluorosulfonamides, perfluoroalkylsulfomethides (for example trifluoroalkylsulfomethides (CF3fluorO2) methylide ) 3-) and carboranes.

Brnsted acids can be used alone or as a mixture.

Preferably, in the formula of the Brnsted acids used, B represents an anion of the same chemical nature as the anion A-present in the

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ionic liquid. In this case, the molar ratio of Bronsted acid to ionic liquid is less than 1/1, preferably 0.01 / 1 to 0.7/1.

The catalytic composition used in the process of the invention can also comprise at least one Lewis acid. The Lewis acids considered are those which are soluble in ionic liquids. By way of examples, mention may be made of scandium tris-trifluoromethylsufonate, ytterbium tristrifluoromethylsufonate, scandium tris (bis-trifluoromethanesulfonylamide), aluminum trichloride, zirconium tretrachloride, titanium trichloride, triphenylamide, boron trifluoride and antimony pentafluoride.

If a Lewis acid is used, the concentration of this Lewis acid in the ionic liquid is not critical. It is advantageously from 1 to 500 mmoles of Lewis acid compound per liter of ionic liquid, preferably from 2 to 200 mmoles per liter, and more preferably from 2 to 100, or even from 2 to 50 per liter.

The compounds entering into the catalytic composition used in the process of the invention can be mixed in any order. Mixing can be done by simple contact followed by stirring until a homogeneous liquid is formed. This mixing can be done outside the reactor used for the catalytic application or in this reactor.

The dimerization process according to the invention applies to pure isobutene or as a mixture with other hydrocarbons.

The origins of isobutene are diverse. However, the most common are dehydrogenation of isobutane, dehydration of tert-butyl alcohol. The isobutene can also come from a C4 cut of FCC (“Fluid Catalytic Cracking”) or from steam cracking.

In the latter case, isobutene can be used as a mixture with n-butenes, isobutan and butane. The process according to the invention then has the additional advantage of making it possible to selectively convert isobutene without having to separate it from the other constituents of the cut. Another advantage of the process according to the invention is that isobutenebutene co-dimerization can be limited.

The volume ratio between the reactants and the liquid salt can be between 0.1 / 1 and 1000/1, preferably between 1/1 and 100/1. It will be chosen so as to obtain the best selectivities.

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The reaction can be carried out in a closed system, in a semi-open system or continuously with one or more reaction stages. On leaving the reactor, the organic phase containing the reaction products is separated.

In the dimerization process of the invention, it is possible to add to the catalytic composition an organic solvent such as an aliphatic hydrocarbon which is not or partially miscible with the ionic liquid, which allows better separation of the phases.

The dimerization reaction can be carried out in the presence of an alcohol or an ether.

The temperature at which the dimerization reaction is carried out ranges for example from -50 C to 200 C; it is advantageously less than 100 C.

The dimerization reaction can be carried out using a reactive distillation technique.

The products obtained by the present invention can be subsequently transformed according to various reactions, such as hydrogenation, hydroformylation, oxidation, etherification, epoxidation or hydration.

The following examples illustrate the invention without limiting its scope.

(6 mL) de trif ! orométhy) su ! fonate (triftate CFgSOs') de butyl-1 méthyl-3 imidazolium (BMI+ CF3SO3-) contenant 25 ppm d'eau-préparé à partir de butyl-1-imidazole et de triflate de méthyle-avec 0,23 g (0,82 mmoles) d'acide bis-triflylamidure HN (CF3S02) 2. Le mélange est agité quelques minutes et conduit à une solution limpide contenant 2,7 % en poids d'acide. Example 1: Preparation of the catalytic system SMI - CF3S03 / HN (CF3S02) 2
Was mixed at room temperature, under an inert atmosphere, 8.50 g

(6 mL) of trif! oromethy) su! 1-butyl-3-methylimidazolium fonate (CFgSOs' triftate (BMI + CF3SO3-) containing 25 ppm of water-prepared from butyl-1-imidazole and methyl triflate -with 0.23 g (0.82 mmoles) of bis-triflylamidide HN (CF3S02) 2 acid. The mixture is stirred for a few minutes and results in a clear solution containing 2.7% by weight of acid.

Example 2: Dimerization of isobutene using the catalytic composition of Example 1
In a Fisher-Porter tube with a volume of 50 mL, fitted with a magnetic bar and previously dried under study and drawn under vacuum, the entire mixture prepared in Example 1 is introduced under an argon atmosphere. 30 mL of a liquid feed containing 95% isobutene and 5% n-butane are introduced at room temperature. Stirring is then started (zero reaction time). The reaction starts. After 52 minutes of reaction at 25 C,

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the agitation is stopped. The gas phase is completely recovered and analyzed by CPV (25 C isothermal PONA column). 85% of the starting isobutene has been converted. The supernatant organic phase is separated from the ionic liquid phase and analyzed by CPV (with heptane as external standard) after treatment with sodium hydroxide (10N) to remove any traces of acid and drying over MgSO4.

It is composed of 83% of trimethyl-2, 4, 4-pentenes, 16% of trimers (C12).

Example 3: Preparation of the BM) -CFaSOs / CFsSOsH catalytic system
Was mixed at room temperature, under an inert atmosphere, 8.50 g (6 mL) of trifloromethylsulfonate (triflate CFgSOs ') of butyl-3-methyl-3 imidazolium (BtvttCFsSOg') containing 25 ppm of water-prepared from butyl -1-imidazole and methyl triflate -with 0.12 g (0.8 mmol) of triflic acid (CF3SO3H). The mixture is stirred for a few minutes and results in a clear solution containing 1.4% by weight of acid.

Example 4: Dimerization of isobutene using the catalytic composition of Example 3
In a Fisher-Porter tube with a volume of 50 mL, fitted with a magnetic bar and previously dried during the study and drawn under vacuum, the entire mixture prepared in Example 3 is introduced under an argon atmosphere. 30 ml of a liquid feed containing 95% isobutene and 5% butane are introduced at room temperature. Stirring is then started (zero reaction time). The reaction starts. After 95 minutes of reaction at 25 ° C., the stirring is stopped. The gas phase is completely recovered and analyzed by CPV (25 OC isothermal PONA column). 79% of the starting isobutene has been converted. The supernatant organic phase is separated from the ionic liquid phase and analyzed as in Example 2. It is composed of 86% of trimethyl-2,4, 4-pentenes, 14% of trimers (C12).

Example 5: Reuse of the system from Example 4
All of the supernatant organic phase of Example 4 is withdrawn. 30 ml of a charge consisting of 95% isobutene and 5% n-butane are added. The procedure is as in Example 4. After reaction for 12 minutes, the conversion of isobutene is 36% and the selectivity for dimers is 88%.

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Example 6: Reuse of the system of Example 5
All of the supernatant organic phase of Example 5 is withdrawn. 30 ml of a charge consisting of 95% isobutene and 5% n-butane are added. The operation is carried out as in Example 4. After reaction for 45 minutes, the conversion of isobutene is 67% and the selectivity for dimers is 89%.

Example 7: Reuse of the system from Example 6
All of the supernatant organic phase of Example 6 is withdrawn. 30 ml of a charge consisting of 95% isobutene and 5% n-butane are added. The operation is carried out as in Example 4. After reaction for 95 minutes, the conversion of isobutene is 70% and the selectivity for dimers is 88%.

Example 8: Reuse of the system from Example 7
All of the supernatant organic phase of Example 7 is withdrawn. 30 mL of a feed consisting of 95% isobutene and 5% n-butane are added to the mixture. The operation is carried out as in Example 4. After reaction for 95 minutes, the conversion of isobutene is 67% and the selectivity for dimers is 89%.

Example 9: Reuse of the system from Example 8
All of the supernatant organic phase of Example 8 is withdrawn. 30 ml of a charge consisting of 95% isobutene and 5% n-butane are added. The operation is carried out as in Example 4. After reaction for 95 minutes, the conversion of isobutene is 68% and the selectivity for dimers is 88%.

Example 10 Dimerization of an isobutene-butene-1 mixture
A mixture identical to that described in Example 3.8 is prepared, 50 g (6 ml) of this mixture is injected into a tube of the Fisher-Porter type. A liquid feed (30 mL) containing 3.3% of n-butane, 48.2% of butene-1 and 48.5% of isobutene is then introduced. The procedure is as in Example 4. After reaction for 150 minutes, the analysis of the gas phase is carried out by vapor phase chromatography (VPC). The conversion of isobutene is 86% and the conversion of butene-1 to co-dimers is 5.1%. 0.7% of butene-1 is isomerized to butenes-2. The liquid phase is separated and analyzed.

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It consists of 82% dimers, 17% trimers and 1% tetramers.

Example 11: Reuse of the salt of Example 10
All of the supernatant organic phase of Example 10 is withdrawn. 30 mL of a charge identical to that used in Example 10 are added. After reaction for 150 minutes, the conversion of isobutene is 86% and the conversion of butene-1 to co-dimers is 2.9. %. 0.7% of butene-1 is isomerized to butenes-2. The liquid phase is separated and analyzed.

It consists of 82% dimers, 17% trimers and 1% tetramers.

Example 12: Reuse of the salt of Example 11
All of the supernatant organic phase of Example 11 is withdrawn. 30 mL of a charge identical to that used in Example 10 are added. After reaction for 150 minutes, the conversion of isobutene is 84% and the conversion of butene-1 to co-dimers is 0.7. %. 0.6% of butene-1 is isomerized to butenes-2. The liquid phase is separated and analyzed.

It consists of 85% dimers, 14% trimers and less than 1% tetramers.

Example 13: Reuse of the salt of Example 12
All of the supernatant organic phase of Example 12 is withdrawn. 30 mL of a charge identical to that used in Example 10 are added. After reaction for 150 minutes, the conversion of isobutene is 85% and the conversion of butene-1 to co-dimers is 0.7. %. 0.7% of butene-1 is isomerized to butenes-2. The liquid phase is separated and analyzed. It consists of 86% dimers, 13% trimers and less than 0.5% tetramers.

Example 14: Preparation of an SMI - N (CF3S02) 2 composition! HN (CF3S02) 2
6 mL of an ionic liquid bis-trifluoromethylsulfonylamide butyl-1-methyl-3-imidazolium (BMI-NTf2) was prepared by reacting one equivalent of the lithium salt (LiNTf2) with butyl-1-methyl chloride. -3-imidazolium in water as described in the literature. To this salt, we added 1 mg (0.004 mmol)

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of HNTf2 acid. A liquid was obtained at room temperature which contained 0.01% by weight of acid.

Example 15: Dimerization of isobutene using the BMI-N (CF3SO2) 2 / HN (CF3S02) 2 catalytic system
To the mixture prepared in Example 14 is added 30 mL of a liquid feed containing 95% isobutene and 5% butane (as in Example 2).

Stirring is then started (zero reaction time). The reaction starts. After 95 minutes of reaction at 25 ° C., the stirring is stopped. The gas phase is completely recovered and analyzed by vapor phase chromatography (CPV: isothermal PONA column 25 C). 76% of the starting isobutene has been converted. The supernatant organic phase is separated. It is composed of 77% of trimethyl-2, 4,4-pentenes and of 20% of trimers (C12).

Claims (13)

tetraalkylborates, hexafluorophosphate, hexafluoroantimonate, alkylsulfonates, perfluoroalkylsulfonates, fluorosulfonate, sulfates, phosphates, perfluoroacetates, perf) uoroa! ky! su) fonamides, ftuorosutfonamides, perftuoroaikytsuifomethides and carboranes.

CLAIMS 1. Process for the dimerization of isobutene, characterized in that it involves a catalytic composition comprising at least one Bronsted acid, denoted HB, dissolved in a non-aqueous liquid medium with ionic character of general formula Q + A -, in which Q + represents an organic cation and A- represents an anion and for which, when A and B are identical, the molar ratio of Bronsted acid to the ionic liquid is less than 1/1 2. Method according to claim 1 characterized in that, in the general formula Q + A-, the anion A- is chosen from tetrafluoroborate anions, 3. Method according to claim 1 or 2, characterized in that, in the general formula Q + A-, Q + represents a quaternary ammonium and / or a quaternary phosphonium and / or a trialkylsulfonium and A- represents any anion known to be non-. coordinating and capable of forming a liquid salt at low temperature, i.e. below 150 C. 4. Method according to claim 3 characterized in that the ammonium cation and / or quaternary phosphonium is chosen from: - quaternary ammonium and / or phosphonium cations corresponding to one of the general formulas NR1 R2R3R4 + and PR1 R2R3R4 +, or to the one of the general formulas R1 R2N = CR3R4 + and R1 R2p = CR3R4 + where R1, R2, R3 and R4, identical or different, represent hydrogen with the exception, for NR1R2R3R4 +, of the NH4 + cation, a single substituent representing the atom d 'hydrogen, or hydrocarbyl residues having from 1 to 12 carbon atoms, - quaternary ammonium and / or phosphonium cations derived from nitrogenous or phosphorus heterocycles containing 1,2 or 3 nitrogen and / or phosphorus atoms, of formulas general: <Desc / Clms Page number 14> R1 R2 + N = CR3 ~ R5 ~ R3C = N + R1 R2 R 1 R2 + p = CR3 ~ R5 ~ R3C = P + R 1 R2 in which R1, R2 and R3, identical or different, are defined as above and R5 represents an alkylene or phenylene residue. in which the rings consist of 4 to 10 atoms, preferably 5 to 6 atoms, R1 and R2 being defined as above; - quaternary ammonium and / or phosphonium cations corresponding to one of the general formulas:

5. Method according to claim 4 characterized in that the ammonium cation and / or quaternary phosphonium is chosen from the group formed by N-butylpyridinium, N-ethylpyridinium, butyl-3-methyl-1 imidazolium, diethylpyrazolium, l ' 3-ethyl-1-methyl imidazolium, pyridinium, trimethylphenylammonium, tetrabutylphosphonium and methylethylpyrrolidinium. 6. Method according to claim 3, characterized in that the trialkylsulfonium cation corresponds to the general formula SR1 R2R3 +, in which R1, R2 and R3, which are identical or different, represent hydrocarbyl residues having from 1 to 12 carbon atoms. 7. Method according to one of claims 1 to 6 characterized in that the ionic liquid is chosen from N-butylpyridinium hexafluorophosphate, N-ethyl pyridinium tetrafluoroborate, butyl-3-methyl-1 imidazolium hexafluoroantimonate, 3-butyl-1-methyl-imidazolium hexafluorophosphate, 3-butyl-1-methyl-imidazolium trifluoromethylsulfonate, pyridinium fluorosulfonate, trimethylphenylammonium hexafluorophosphate, 1-bis-trifluoromethylsulfonylazolium-1-butyl-1-bis-trifluoromethylsulfonyl-azolamidide triethylsulfonium trifluoromethyl sulfonylamide, tributylhexylammonium bis-trifluoromethylsulfonylamide, 3-butyl-1-methyl-imidazolium trifluoroacetate and

butyl-3-di-methyl-1,2-imidazolium bis-trifluoromethylsulfonylamide. <Desc / Clms Page number 15> 8. Method according to one of claims 1 to 7 characterized in that the anion B of Brnsted's acid is chosen from tetrafluoroborate, tetraalkylborates, hexafluorophosphate, hexafluoroantimonate, alkylsulfonates, perfluoroalkylsulfonates, fluorosulfonate, sulfates, phosphates, perfluoroacetates anions , perfluoroalkylsulfonamides, fluorosulfonamides, perfluoroalkylsulfomethides and carboranes. 9. Method according to one of claims 1 to 8 characterized in that, in the formula of Brnsted acid, B represents an anion of the same chemical nature as the anion A- present in the ionic liquid and the molar ratio of Brnsted acid on the ionic liquid is less than 1/1. 10. The method of claim 9 characterized in that the molar ratio of Brnsted acid to the ionic liquid is from 0.01 / 1 to 0.7 / 1. 11. Method according to one of claims 1 to 10 characterized in that it further comprises at least one Lewis acid soluble in the ionic liquid. 12. The method of claim 11 characterized in that said Lewis acid is chosen from scandium tris-trifluoromethylsulfonate, ytterbium tristrifluoromethylsulfonate, scandium tris (bis-trifluoromethanesulfonylamide), aluminum trichloride, zirconium tretrachloride , titanium trichloride, triphenylboron, boron trifluoride and antimony pentafluoride. 13. Method according to one of claims 11 and 12 characterized in that the concentration of said Lewis acid in the ionic liquid is 1 to 500 mmoles of Lewis acid compound per liter of ionic liquid.