FR2687935A1 - Catalyst for paraffin alkylation - Google Patents

Abstract

Catalyst containing silica and a mixture including at least sulphuric acid and sulphur trioxide, and its use in catalytic alkylation of isobutane and/or isopentane in the presence of at least one olefin containing from 3 to 6 carbon atoms per molecule.

Description

 The present invention relates to a catalyst containing silica and at least one mixture comprising at least sulfuric acid and sulfuric anhydride, and its use in catalytic alkylation of isobutane and / or isopentane by means of at least one olefin, which makes it possible to obtain at least one product selected from the group consisting of dimethylbutanes, trimethylpentanes, trimethylhexanes and trimethylheptanes.

 It is known that, in order to supply internal combustion engines and spark ignition engines, and in particular engines with a high compression ratio, it is particularly advantageous to have fuels with high octane numbers, that is to say essentially consisting of by highly branched paraffinic hydrocarbons. The alkylation of isoparaffins (isobutane and / or isopentane) with at least one olefin containing from 3 to 6 carbon atoms per molecule makes it possible to obtain such products. This reaction requires the use of highly acidic catalysts, in particular to reduce parasitic reactions such as olefin hydride abstraction and polymerization reactions, which provide poorly branched low-indexed hydrocarbons. octane and unsaturated hydrocarbons, cracking reactions and disproportionation reactions.

 Existing processes for the production of hydrocarbons by alkylation of isobutane by olefins use either sulfuric acid or hydrofluoric acid as the catalyst. In these processes the acid catalyst constitutes a liquid phase which is contacted with the liquid isobutane-olefin mixture to form an emulsion. These processes are expensive and pose significant problems with respect to the safety of people and the environment. In order to remedy these problems, different catalytic systems of sulfuric and hydrofluoric acid in the liquid phase have been sought.

To catalyze the isoparaffin alkylation reactions by olefins, it has been proposed to develop acid catalysts from many acidic solids of different natures. Among the families of acid catalysts include molecular sieves (see for example
US-A-3,236,762, US-A-3,251,902, US-A-3,644,565, US-A-4,377,721,
US-A-4,384,161 and US-A-4,300.01 5), the macroreticular resins optionally associated with BF3 (see for example US-A-3 855 342,
US-A-3,855,343, US-A-3,862,258 and US-A-3,879,489), perfluorinated resins of NAFION type (see for example US-A-4,056,578 and US-A-4,038,213). ), Lewis and / or Bronsted acids deposited on various inorganic supports (see for example US-A-3,975,299, US-A-3,852,371 and US-A-3,979,476), chlorinated aluminas (see for example US-A-3,240,840, US-A-3,523,142,
US-A-3,607,859, US-A-3,523,142, US-A-4,066,716, US-A-4,083,800 and
US-A-4,066,716), graphites intercalated with Lewis acids and / or
Bronsted (see for example US-A-4.083.885, US-A-4.116.880,
US-A-4,128,596 and US-A-3,976,714) and anions deposited on oxide supports such as ZrO 2 / SO 4 (see, for example, J-01288329, J-011245854, J-01245953, J-61242641 and J-01245953). 61,242,641). These solids lead to the production of branched isoparaffins but suffer from several major defects, among which we can mention the use of isobutane / olefin molar ratios often very high to limit the importance of side reactions and the low stability over time. catalytic activity (inhibition of the catalyst by deposition of unsaturated oligomers); these catalysts must then be frequently regenerated. In addition, the low acidity of certain acidic solids, such as molecular sieves for example, requires the use of high reaction temperatures, which is detrimental to the production of trace hydrocarbons. high octane.

 In the present invention, a novel catalyst has been found which makes it possible to obtain high branching and high octane paraffinic compounds by alkylation of isobutane and / or isopentane by at least one olefin comprising 3 to 6 carbon atoms per molecule. This new catalyst is advantageously used in a process where the olefin and / or a mixture of olefins is introduced into the reactor in the liquid phase and in mixture with the isoparaffin and / or a mixture of isoparaffins. The catalyst may be used in fixed bed, moving bed or fluid bed, or in suspension in the liquid phase of the reagents subjected to efficient stirring.

 The catalyst of the present invention contains silica and a mixture comprising at least sulfuric acid and sulfuric anhydride, the silica being impregnated partially or totally with said mixture. We have discovered that, surprisingly, it is possible to obtain an excellent paraffin alkylation catalyst by impregnating silica with a mixture comprising at least sulfuric acid and sulfuric anhydride.

 Many sources of silica can be used. The specific surface area of said silica is between 0.01 and 1500 m 2 / g, preferably between 0.01 and 150 m 2 / g and even more preferably between 0.01 and 50 m 2 / g. The total pore volume of the silica is in the following ranges: from 0.005 to 1.5 cm 3 / g and preferably from 0.005 to 1 cm 3 / g.

During the impregnation of said silica, the mixture comprising at least sulfuric acid and sulfuric anhydride occupies a fraction of the total pore volume of the silica of between 5% and 100%, and preferably between 60% and 90% . The catalyst thus obtained is characterized by a specific surface area of between 0.01 and 500 m 2 / g, preferably between 0.01 and 150 m 2 / g and even more preferably between 0.01 and 40 m 2 / g.

 The mixture comprising at least sulfuric acid and sulfuric anhydride employed in the present invention is commonly referred to as "oleum". The weight content of sulfuric anhydride in the oleum used in the context of the present invention is in the following ranges: from 0.01 to 60% and preferably from 1 to 30%.

 According to a preferred embodiment of the embodiment of the invention, it is advantageous to add to the oleum used in the present invention, an additive to enhance the acidity of the catalyst and thus improve the catalytic performance. The preferred additive is boric acid (H3BO3), the weight content of boric acid in the mixture comprising sulfuric acid and sulfuric anhydride is advantageously between 0.01 and 50% and even more preferably between 0.01 and 10%.

 The silica used in the present invention may contain impurities such as, for example, oxides, alkalis, alkaline earths, aluminum or boron compounds or any other impurity known to those skilled in the art, the total amount of these impurities being less than 5% by weight relative to the silica.

 The process for preparing the catalyst according to the invention comprises two stages. In a first step, the silica is calcined at a temperature greater than 50 ° C., preferably greater than 80 ° C. and even more preferably between 200 and 6000 ° C., for example equal to about 500 ° C. The duration of this calcination step is usually between 10 minutes and 50 hours The calcination can be carried out in the presence of air or air / nitrogen mixture, with a flow rate of between 0.001 and 10 l / h / g The second stage consists in the impregnation of the product calcined by the mixture comprising at least sulfuric acid and sulfuric anhydride To carry out this step, it is possible to use all the techniques well known to those skilled in the art.Conserved at a temperature below the melting temperature of the mixture comprising at least less sulfuric acid and sulfuric anhydride and protected from moisture, the catalyst according to the present invention thus contains silica impregnated by the mixture in the solid state e comprising at least sulfuric acid and sulfuric anhydride.

 According to the preferred embodiment of the embodiment according to the invention, the silica is calcined and then impregnated with the mixture consisting of sulfuric acid, sulfuric anhydride and boric acid.

 The catalyst according to the present invention can be used pure or diluted with various materials having little catalytic activity in the reaction considered, for example, silica, alumina, magnesia or various clays, such as, for example, bentonite or montmorillonite. or kaolin.

 The isoparaffin (s) -olefin mixture (s) may be introduced into the reactor at a space velocity per hour, expressed by weight of introduced olefin per unit weight of catalyst per hour, between 0.001 and 10 h -1 and preferably between 0.002 and 2 h -1. Said mixture can also be produced inside the reactor. In all cases, the mixture thus formed is in the reactor under conditions of pressure and temperature such that the hydrocarbon mixture remains liquid on the catalyst and the constituents of the catalyst remain in the solid state.

 The reaction temperature is between -50 and 150 ° C., but the catalytic performances are improved when the reaction temperature is less than 0 ° C., preferably less than -5 ° C. and even more preferably less than -10 ° C. The reactor pressure must be sufficient to maintain the hydrocarbons in the liquid state in the reactor.

 In order to limit the side reactions, it is possible to use an excess of isoparaffin with respect to the olefin. For example, in the case of the alkylation of isobutane with butene, isobutane may be introduced pure in the feedstock or in the form of a mixture of butanes containing, for example, at least 40% of isobutane. In addition, pure butene or a mixture of isomeric butenes can be introduced. In all cases, the molar ratio of isobutane / butenes in the feed is between 1 and 100, preferably between 3 and 50 and often preferably between 5 and 10.

 When the nature of the catalyst and the working conditions (in particular the temperature) of the catalyst are judiciously chosen, the catalyst according to the invention allows the production of paraffin alkylation products by olefins which are of interest as fuels for the engines and gasoline constituents and which comprise, for example, at least 60% (in moles) of paraffins having 8 carbon atoms per molecule and less than 1% (in moles) of unsaturated compounds, the paraffins having 8 carbon atoms per molecule being composed of 70 to 98% (in moles) of trimethylpentanes.

 Another advantage of the catalyst according to the present invention is the possibility of alkylating, at low temperature, isobutane with olefin mixtures comprising from 3 to 6 carbon atoms per molecule, where the proportion of olefins having at least 5 carbon atoms per molecule is very important (at least 10% by weight, preferably at least 40% by weight).

 The following examples illustrate the invention without, however, limiting its scope.

Example 1 (according to the invention)
Preparation of Catalyst A
14 g of macroporous silica with a specific surface area equal to 27 m 2 / g and a pore volume of 1 cm 3 / g are activated by calcination in air for 4 hours at 500 ° C. The solid thus activated is stored under argon. then proceeded to a dry impregnation of 10 g of the calcined solid with 7 cm 3 of the mixture consisting of 80% by weight of sulfuric acid (99.99%) and 20% by weight of sulfuric anhydride.The catalyst thus obtained, catalyst A contains 13.5 g of oleum and 10 g of silica and is stored under an argon atmosphere at -18 ° C.

Alkylation of isobutane with butene-1 with catalyst A
20 g of catalyst A prepared according to the method described in Example 1 are introduced into a Fischer & Porter type glass reactor of a volume of 360 cm 3 previously purged under an argon flow. The reactor containing the catalyst is then closed and placed under a primary vacuum, and then cooled to -20 C.

 72 cm3 of isobutane are then added to the reactor containing the catalyst with stirring, said reactor being immersed in a cold bath at -20 C. The catalyst + isobutane system is left stirring for a period of 30 minutes in order to homogenize the temperature.

 50 cm3 of a mixture consisting of 24% by volume of butene-1 and 76% by volume of isobutane are added regularly for a total duration of 10 hours, the temperature of the reactor being maintained at -15.degree. duration of the injection.

 After reaction, the hydrocarbon phase is withdrawn from the reactor, isobutane is evaporated slowly. The alkylate is collected and analyzed by vapor phase chromatography; its weight composition is given below (Table 1).

Table 1

<tb> 1 <SEP> | <SEP> 1.5
<tb> C6 <SEP> 1 <SEP> 1,1
<tb> G7 <SEP> 1.9
<tb> C8 <SEP> 90
<tb> Cg <SEP> 1,2
<tb> Cg + <SEP> 4.3
<Tb>
The olefin conversion is 98%. The yield of the alkylation is 200% relative to the olefin transformed. The C8 fraction contains 89% by weight of trimethylpentanes.

Example 2 (according to the invention)
Catalyst B preparation
To prepare catalyst B, 13 g of the same macroporous silica as used for the preparation of catalyst A are used, the calcination conditions are identical. A mixture consisting of oleum and boric acid is prepared: for this, use is made of 7 cm 3 of the same mixture as that used to obtain catalyst A, to which 0.81 g of anhydrous boric acid is added. 14.31 g of a mixture of sulfuric acid (75.47% by weight), sulfuric anhydride (18.86% by weight) and boric acid (5.67% by weight) are then obtained.

 A dry impregnation of 11 g of the calcined silica is then carried out using all of the mixture described above. The catalyst thus obtained, catalyst B, contains 14.31 g of acid phase and 11 g of silica, and is stored under an argon atmosphere at -18 ° C.

Alkylation of isobutane with butene-1 with catalyst B
The catalytic test for the alkylation of isobutane with butene-1 is repeated under the same experimental conditions as those described in Example 1. The results are collated in Table 2 below.

Table 2

<tb> iG5 <SEP> 0.8
<tb> Cl <SEP> 0.5 <SEP>
<tb> C7 <SEP> 1,1
<tb> C8 <SEP> 94.6
<tb> C9 <SEP> 0.9
<tb> Cg + <SEP> 2.1
<Tb>
The yield of the alkylation is 201% relative to the olefin transformed. The fraction Cg contains 92% by weight of trimethylpentanes.

 This table highlights the interest of adding to the sulfuric acid-sulfuric anhydride mixture of boric acid, which is one of the preferred embodiments of the invention.

Claims (9)

A catalyst comprising a silica having a specific surface area of between 0.01 and 1500 m 2 / g and a total pore volume of between 0.005 and 1.5 cm 3 / g and the mixture in the solid state comprising at least sulfuric acid and sulfuric anhydride, the silica having been impregnated with said mixture. 2. Catalyst according to claim 1 such that the silica, before its impregnation, comprises at most 5% of impurities. 3. Catalyst according to one of claims 1 and 2 wherein, during the impregnation, the mixture comprising at least sulfuric acid and sulfuric anhydride occupies between 5% and 100% of the total pore volume of the silica. 4. Catalyst according to one of claims 1 and 3 wherein the weight content of sulfuric anhydride in the mixture comprising sulfuric acid and sulfuric anhydride is between 0.01 and 60%. 5. Catalyst according to one of claims 1 to 4 such that the mixture consists of sulfuric acid, sulfuric anhydride and boric acid, the weight content of boric acid being between 0.01 and 50%. 6. Process for preparing a catalyst according to one of claims 1 to 5 such that the silica is calcined and impregnated with the mixture comprising at least sulfuric acid and sulfuric anhydride. 7. Process for preparing a catalyst according to one of claims 1 to 6 such that the silica is calcined and then impregnated with the mixture consisting of sulfuric acid, sulfuric anhydride and boric acid. 8. Use of the catalyst according to one of claims 1 to 5 or prepared according to one of claims 6 or 7, in a catalytic alkylation process of at least one element selected from the group consisting of isobutane and isopentane by at least one member selected from the group consisting of olefins comprising from 3 to 6 carbon atoms per molecule. 9. Use according to claim 8 wherein the temperature of the reaction is less than 0 C.