FR2626572A1 - Process for alkylating aliphatic hydrocarbons - Google Patents

Abstract

Process for alkylating isoparaffins via olefins by means of mixtures of aluminium halides and/or boron halides with quaternary ammonium halides, mixtures which are liquid at low temperature.

Description

The object of the present invention is a process for the production of paraffinic hydrocarbons by the reaction of addition of olefins to isoalkanes in the presence of catalysts.
Friedel-Crafts modified.

 A large number of acid catalysts are known, liquid or solid, capable of carrying out the alkylation of isoparaffins such as isobutane or isopentane, by olefins such as propylene, isobutene, butenes-1 or - 2. The catalysts most often used in industrial practice are hydrofluoric acid, alone or in admixture with Lewis acids such as boron trifluoride, and concentrated sulfuric acid, alone or in admixture with organic acids. The use of aluminosilicates such as zeolites has also been recommended. When it is desired to alkylate an isoparaffin with ethylene, aluminum halides such as aluminum chloride and bromide are generally used.

 Although fairly widespread due to the increasing use of "alkylates" in automobile gasoline databases with a high octane number, these processes suffer from drawbacks which limit their extension: hydrofluoric acid to because of its corrosive power, its volatility and its toxicity, forced to take particularly expensive precautions; sulfuric acid, which is not very active, requires large reaction volumes and costly reconcentration installations. As for zeolites, their comparatively low acidity requires operating at high temperature.

Finally the aluminum chloride, solid under the alkylation conditions, is used in the form of "alkylation oils" which are cationic oligomers of olefins which lose their activity over time and which must be periodically eliminate.

 It has now been found, and this constitutes the object of the present invention, that the liquid complexes which aluminum and / or boron halides make with certain quaternary ammonium halides, complexes which are not substantially miscible with paraffins, can advantageously be used to catalyze the alkylation of isoparaffins such as isobutane or isopentane with olefins such as ethylene, propylene, isobutene, butenes -1 or 2.

Some of these ionic media, liquid at the usual alkylation temperatures, that is to say below 100 "C, for example at temperatures between -30 and + 50" C, and which are commonly called "molten salts" , were described in an article by
CH Hussey in "Advances in Molten Salt Chemistry" vol .5 p.185,
Elsevier New-York 1983.

 The aluminum or boron halides more particularly usable according to the invention are trifluorides, trichlorides and / or tri bromides. They can be used pure, for example AlCl3, AlBr3, BC13 or BBr3, or in a mixture, for example AlCl3 with AlBr3, A1C13 with BC13 or AlBr3 with BBr3, in variable proportions ranging from 99% of one of the halides up to 99% of each other.

dans lesquelles R1, R2, R3, R4 ou R5 identiques ou différents, .représentent des restes hydrocarbyles, par exemple alkyl, cycloalkyl, aryl, aralkyl ou alkaryl, R5 pouvant être également l'hydrogène, ou des restes hydrocarbyles substitués comprenant par exemple d'autres atomes comme l'azote. Des radicaux tels que R6 peuvent unir deux molécules telles que ci-dessus comme, par exemple, R1R2N+=
CR3-R6-CR3 = R2 (X )2,R6 pouvant être un reste alkylène ou encore phénylène.Les cycles III et IV sont constitués de 4 à 10 atomes, de préférence de 5 et 6 atomes qui peuvent comprendre, outre l'azote de l'ammonium quaternaire, des atomes de carbone ou éventuellement d'autres atomes d'azote.Quaternary, acyclic or part of a ring ammonium salts correspond to the following general formulas
R1R2R3R4N X
R1R2N + = CR3R4 X (Il)

in which R1, R2, R3, R4 or R5, which are identical or different, represent hydrocarbyl residues, for example alkyl, cycloalkyl, aryl, aralkyl or alkaryl, R5 possibly also being hydrogen, or substituted hydrocarbyl residues comprising for example d 'other atoms like nitrogen. Radicals such as R6 can unite two molecules such as above such as, for example, R1R2N + =
CR3-R6-CR3 = R2 (X) 2, R6 can be an alkylene or phenylene residue. The cycles III and IV are made up of 4 to 10 atoms, preferably 5 and 6 atoms which can comprise, in addition to nitrogen quaternary ammonium, carbon atoms or possibly other nitrogen atoms.

 Among the groups R1, R2, R3, R4 and R5, mention may be made of the radicals, methyl, ethyl, propyl, isopropyl, butyl, secondary butyl, tertiary butyl, amyl, methylene, ethylidene, phenyl or benzyl; R6 may be a methylene, ethylene, propylene or phenylene group.

 In these formulas X represents a halide ion, for example the bromide ion or the chloride ion.

 As examples of ammonium salts which can be used according to the invention, there may be mentioned more particularly the imidazolium and pyridinium salts such as chlorides and bromides of N, N'-dihydrocarbyl imidazolium and N-hydrocarbylpyridinium, in particular methyl chlorides - 3-ethylimidazolium, methyl-1-butyl-3-imidazolium bromide, phenyl-1-isopropyl-3 imidazolium chloride, N-methylpyridinium chloride, N-isopropylpyridinium bromide, N-benzylpyridinium chloride.

 These compounds are used alone or in admixture with metal halides.

 For components of a determined nature, the relative proportions of aluminum and / or boron halides and of quaternary ammonium halides determine both the acidity (or basicity) of the medium and its crystallization point. When the molar fraction of aluminum halide and / or boron is less than 0.5 the mixture is very weakly acid, even basic. If it is higher than this value the medium is all the more acidic as this molar fraction is larger. We therefore have a very wide range of acidity and that we can vary according to the reactivity of 1 ' olefin, which has the advantage of minimizing parasitic oligomerization reactions; thus in the case of ethylene, the least reactive of the olefins, a molar fraction of, for example, between 0.6 and 0.7 will be chosen; for propylene and n-butenes a molar fraction between 0.49 and 0.55 will be preferable.

 These mixtures have their own melting diagrams and most often have two eutectic points, one rich in aluminum and / or boron halide, the other rich in ammonium salt.

 A liquid composition will therefore be chosen at the temperature of the alkylation reaction, and the acidity of which will be optimal for the case considered.

 The alkylation is carried out in the presence of two liquid phases: the "molten salt" on the one hand, and the reagents (also containing the products) on the other hand. Vigorous stirring is necessary to ensure the best possible contact between the catalytic phase and the reactants, so that the diffusion between the phases does not constitute a limitation to the chemical reaction.

 The reaction can be carried out in a closed system (the reactants and the catalyst being completely introduced at the start of the reaction), in a semi-open system (the, or one of the reactants being introduced as the reaction progresses ) or in an open system (the reagents, and possibly of the catalytic phase, are introduced continuously; the products, and possibly part of the catalytic phase being withdrawn continuously). If one operates in a closed or semi-open system, the reaction stirring is finally stopped, the two phases are allowed to separate and the hydrocarbon phase is drawn off from which the components are separated by distillation; a new charge can then be introduced. When operating in an open system, the reaction stage is followed by a decantation stage which makes it possible to separate the two phases, the hydrocarbon phase being withdrawn and separated into its constituents, the catalytic phase being wholly or partly returned to the reaction stage. Both stages can be included in the same container.

 Isoparaffin, such as isobutane or isopentane, and olefin such as ethylene, propylene and / or butenes, are used in proportions such that the alkane / olefin molar ratio is between 2 and 50, and preferably between 3 and 30; the higher this ratio, the higher the selectivity for monoalkylation products. Conversely, a lower ratio will lead to polyalkylation products.

 The individual isoparaffins or a mixture can be treated, as well as the individual olefins or a mixture.

 The ratio of the volume of the catalytic phase to the volume of the hydrocarbon phase can vary within very wide limits ranging from 100: 1 to 1: 100, preferably from 20: 1 to 1: 20. In each case, the ratio leading, for a given overall volume, to optimum results.

 We choose a fairly low reaction temperature, between -30 C and + 50au, preferably between -10 "C and +30 OC a high temperature promotes the reaction rate but also the secondary reactions of oligomerization of olefins and polyalkylation conversely, a low temperature increases selectivity at the expense of speed.

 A pressure is imposed such that at least the major part of at least one of the reactants forms a liquid phase, but the pressure is not limited to the high values.

 The following examples illustrate the invention without limiting its scope.

EXAMPLE # 1
A catalyst consisting of 2.23 g of aluminum trichloride and 2.57 g of methyl-1-butyl-3-imidazolium chloride (molar fraction of aluminum chloride 0.53) was prepared according to known methods. . Was introduced into a stainless steel reactor covered with a Teflon film, provided with a double jacket and a mechanical stirrer, 4 ml of this catalyst and 30 g of isobutane; the stirring was started 1,500 rpm and the reactor was pressurized to 0.43 MPa with propylene while maintaining the temperature at 15 "C. After 30 minutes of reaction, the two phases were allowed to separate , and from the hydrocarbon phase, 8 g of isoheptanes were isolated, consisting mainly of 2,3-dimethyl and 2,4-dimethyl pentanes, 0.8 g of isohexanes (mainly 2,3-dimethyl butane) and 0, 8 g of isooctanes (mainly 2,2,4-trimethyl pentane).

 The same reaction was repeated three times with no apparent loss of activity.

EXAMPLE 2
In a reactor-settler whose useful reaction volume is 50 ml, 18 g of a catalyst consisting of methyl-1-butyl-3-imidazolium chloride and aluminum chloride (molar fraction 0.66) were placed. A mixture of isobutane (89% by weight) and ethylene (11.0% by weight) is then introduced continuously, at a flow rate of 30 ml / hour and at a pressure of 1.6 MPa. The temperature is maintained at 16 ° C. and effective agitation is ensured.

The weight composition of the effluent is as follows
methylene 2.2%
isobutane 81.5%
12.6% isohexanes (including 11.5% 2,3-dimethyl butane)
isoheptanes 1.1%
isooctanes 1.9%
higher 0.7%
The ethylene conversion is 80%

Claims (6)

 quaternary ammonium.  aluminum and / or boron halide with at least one halide  catalyst consists of a liquid mixture of at least one  aluminum or boron halide, characterized in that the  olefin in the presence of a catalyst containing at least one  CLAIMS 1. Process for the alkylation of at least one isoparaffin with at least one 2. The method of claim 1 wherein the halide  aluminum or boron is aluminum fluoride, chloride  aluminum, aluminum bromide, boron fluoride,  boron chloride and / or boron bromide. 3. Method according to claim 1 wherein the halide  of quaternary ammonium meets one of the general formulas  R1R2R3R4N + X (I) R1R2N + = CR3R4 X (Il)

 in which R1R2R3R4 and R5 represent hydrocarbon residues, R5 can also be hydrogen, and X a halide ion. 4. Method according to one of claims 1 to 3 wherein  the quaternary ammonium halide is a chloride or a bromide  of N, N 'dialkyl imidazolium or a chloride or bromide of  N-alkylpyridinium. 5. Method according to 1 one of claims 1 to 4 wherein the  catalyst consists of the interaction product of chloride  aluminum with methyl-3-butyl chloride imidazolium or  aluminum chloride or boron trichloride with chloride  N-methyl pyridinium. 6. Method according to one of claims 1 to 5 wherein  isobutane is added to ethylene, propylene,  n-butenes, or their mixtures in the presence of said catalysts,  between, -30 "C and +50 OC and at a pressure sufficient for the  most of at least one of the reactants is in the liquid phase.