Catalytic composition, for alkylation of aromatic hydrocarbons, comprises Bronsted acid(s) dissolved in non-aqueous liquid medium with ionic nature

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 Bronsted acid, noted HB, in a nonaqueous liquid medium to ionic character (medium of “molten salt” type) comprising at least one organic cation Q⁺ and an anion A^- and wherein when A and B are the same, the molar ratio of Bronsted acid to ionic liquid is less than 1/1, results in 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. isobutane 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 d '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 allows

i) to replace MTBE (Methyl-Tert-Butyl-Ether: RON = 118; MON = 100), currently banned in California for environmental reasons, and ii) to use isobutene, obtained from C4 cuts of the Catalytic cracking (FCC) or steam cracking, raw material for the manufacture of MTBE.

The dimerization (oligomerization) of isobutene is an exothermic reaction catalyzed by acids. Various 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 phosphoric acid (generally supported or solid phosphoric acid SAP) and ion exchange resins (ion exchange resins 1ER, SP-lsoether process licensed by Snamprogetti or the InAlk process offered 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, of the 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, ΙΈΤΒΕ, 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 order to reuse existing units of MTBE. 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 ferf-butyl alcohol. Isobutene is preferably dimerized with an Amberlyst A-15® type resin in the presence of tert-butyl alcohol (selectivity promoter) and alkane (butane or isobutane) as diluent. The presence 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 to 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-A98 / 03 454, WO-A- 00/41 809, EP-A-693 088, EP-A-576 323) to the alkylation of olefins with isobutane (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 poorly 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 AICb potentially present in the medium, which can lead to the formation of chlorinated organic impurities and contaminate the products.

International patent application WO-A-OO / 16 902 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 Bronsted 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 a general manner by the use of a composition serving as catalyst and solvent comprising at least one Bronsted acid denoted HB, dissolved in a non-liquid medium. -aqueous with an ionic nature (medium of “molten salt” type) comprising at least one organic cation Q⁺ and an anion A^- and wherein when A and B are the same, the molar ratio of Bronsted acid to 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 Bronsted acid, which depends on the one hand on its speed in releasing a proton (dissociation equilibrium) and on the other hand on the solvation force of this proton by the surrounding environment, can be adjusted by playing on the nature of the anions Aand Q cations⁺ 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 Bronsted acid. They can be separated by settling and the catalytic phase can be recycled.

The medium of the “molten salt” type in which the Bronsted HB acid is dissolved has the general formula Q⁺AT^- in which Q⁺ represents a quaternary ammonium and / or a quaternary phosphonium and / or a trialkylsufonium and A represents any anion known to be non-coordinating capable of forming a liquid salt at low temperature, that is to say below 150 ° C

The anions A considered in the invention will preferably be chosen from the anions of tetrafluoroborates, tetraalkylborates, hexafluorophosphates, hexafluoroantimonates, alkylsulfonates and arylsulfonates (for example methylsulfonate or tosylate), perfluoroalkylsulfonate, eg fluorosulfonfluoromethyl sulfates, phosphates, perfluoroacetates (for example trifluoroacetate), perfluoroalkylsulfonamides (for example bis-trifluoromethanesulfonyl amide (N (CF3SC> 2) 2), fluorosulfonamides, perfluoroalkylsulfomethides (for example tristrifluoromethanesulfonyl methylide (C (CF₃SC> 2) 3 ') and carboranes.

The quaternary ammonium and / or phosphonium considered preferably correspond to the general formulas NR ^ RSR⁴* and PR^IR²R³R⁴⁺, or the general formulas R¹r2n = CR3r4 + _et r1r2p = cr3r4 + _où R¹, R², R³ and R⁴, identical or different, represent hydrogen with the exception of the NH4 cation⁺ and preferably a single substituent may represent hydrogen, or hydrocarbyl residues 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 atoms of carbon. 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:

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

The quaternary ammonium or phosphonium can also consist of a cation corresponding to one of the general formulas:

r1r2 + n = CR3-r5.r3c = N⁺r1r2 and r1 r2 + p = cr3-r5_r3c = P⁺r1 r2 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 R¹, 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; R ^ 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 , trimethylphenylammonium, tetrabutylphosphonium and methylethylpyrrolidinium.

The trialkylsufonium considered in the invention have the general formula SR'R²R³⁺ where R¹, R² and R³ 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.

As examples of the salts which can be used, there may be mentioned N-butylpyridinium hexafluorophosphate, N-ethyl pyridinium tetrafluoroborate, butyl-3-methyl-1 imidazolium hexafluorophosphate, butyl-3-methyl-1 hexafluorophosphate. imidazolium, 3-butyl-1-methyl-imidazolium trifluoromethylsulphonate, pyridinium fluorosulphonate, trimethylphenylammonium hexafluorophosphate, 3-butyl-1-methyl-1-imidazolium bis-trifluoromethylsulphonylamide, triethylsufonium bis-trifluoromethylsulfonylamide, tributylhexylammonium bis-trifluoromethylsulfonylamide, 3-butyl-1-methyl-imidazolium trifluoroacetate and butyl-3-methyl-1-imidazolium bis-trifluoromethylsulfonyl amideazole 3-butyl-3-di-methylolium-1,2-1,2-imidazole.

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

Bronsted acids are defined as being acidic organic compounds capable of donating at least one proton. These Bronsted 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 trifluoroalkylsulphonates, phosphates, sulfonates, phosphates, sulfonates, etc.) , perfluoroacetates (for example trifluoroacetate), perfluoroalkylsulfonamides (for example bistrifluoromethanesulfonyl amide (N (CF₃SC&gt; 2) 2), fluorosulfonamides, perfluoroalkylsulfomethides (for example tris-trifluoromethanesulfonyl methylide (C (CF₃SO₂)₃') and carborans.

Bronsted acids can be used alone or in a mixture.

Preferably, in the formula of the Bronsted acids used, B represents an anion of the same chemical nature as the anion A^- present in the 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. Mention may be made, by way of examples, 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 the dehydrogenation of isobutane, the 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, isobutane 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.

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 phase separation.

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.

Example 1: Preparation of the BMI - CF3SO catalytic system₃/ HN (CF₃SO2) 2

8.50 g (6 mL) of trifloromethylsulfonate (triflate CF₃SO₃') 1-butyl-3-methyl imidazolium (ΒΜΓ CF₃SO₃) containing 25 ppm of water - prepared from butyl-1 -imidazole and methyl triflate - with 0.23 g (0.82 mmol) of bis-triflylamidide HN (CF₃SO2) 2 · 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 dried beforehand during the study and drawn under vacuum, the whole of the 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., the stirring 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 on MgSCU It is composed of 83% trimethyl-2,4,4-pentenes, 16% trimers (C12).

Example 3: Preparation of the BMI - CF3SO3 / CF3SO3H catalytic system

8.50 g (6 mL) of trifloromethylsulfonate (triflate CF₃SO₃') 1-butyl-3-methylimidazolium (BMI⁺CF₃SO₃·) 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. Then, 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 ° C 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 trimethyl2,4,4-pentenes, of 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 feed consisting of 95% isobutene and 5% n-butane are added. The operation is carried out as in Example 4. After reaction for 12 minutes, the conversion of isobutene is 36% and the selectivity for dimers is 88%.

Example 6: Reuse of the system from Example 5

All of the supernatant organic phase of Example 5 is withdrawn. 30 ml of a feed consisting of 95% isobutene and 5% n-butane are added. The procedure is 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 feed consisting of 95% isobutene and 5% n-butane are added. The procedure is 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 feed 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 is prepared. 8.50 g (6 ml) of this mixture is injected into a tube of the Fisher-Porter type. A liquid feed (30 mL) is then introduced containing 3.3% of n-butane, 48.2% of butene-1 and 48.5% of isobutene. 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.

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% 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% 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 a BMI - N composition (CF₃SO₂) 2 / HN (CF₃SO2) 2

6 mL of an ionic liquid bis-trifluoromethylsulfonylamide of butyl-1 -methyl-3-imidazolium (BMI-NTf₂) by reaction of an equivalent of the lithium salt (LiNTf₂) with butyl-1-methyl-3-imidazolium chloride in water as described in the literature. To this salt, 1 mg (0.004 mmol) of HNTf acid was added₂. A liquid was obtained at room temperature which contained 0.01% by weight of acid.

Example 15: Dimerization of isobutene using the BMI - N catalytic system (CF₃SO₂)₂/ HN (CF₃SO₂)₂

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).