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1. (WO1998050153) $i(IN)-$i(SITU) FORMATION OF IONIC LIQUID CATALYST FOR AN IONIC LIQUID-CATALYZED CHEMICAL REACTION
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IN-SITU FORMATION OF IONIC LIQUID CATALYST FOR AN IONIC LIQUID-CATALYZED CHEMICAL REACTION

BACKGROUND OF THE INVENTION

In its broadest embodiment, the present invention relates to the in-situ formation of an ionic liquid catalyst for use in an ionic liquid-catalyzed chemical reaction. In its broadest articulation the present invention relies upon the separate addition of the reagents needed to form an ionic liquid into the reactor intended to be used to form the ionic liquid-catalyzed chemical reaction so that the ionic liquid catalyst is formed in-situ in that reactor. The instant process, for example, relies upon the presence of at least one reagent needed to form the ionic liquid catalyst (for example, a metal halide, which may not itself be a catalyst itself for the desired reaction) in the reactor in which the ionic liquid-catalyzed chemical reaction is to take place along with at least one of the reagents for the desired chemical reaction. Thereafter, either before the initiation of the reaction or during that reaction, the other reagent or reagents needed to form the ionic liquid are added. As an example, the other reagent can be a base which, when combined with the metal halide will form the desired ionic liquid catalyst. While this invention is broadly applicable to a variety of ionic liquid-catalyzed chemical reactions including, for example, the alkylation of a benzene or phenol reagent, the oligomerization of an olefin, or the alkylation of a paraffin, it will be described hereinafter, for purposes of illustration, in terms of its use in alkylation reactions, with the emphasis being on the addition of a base reagent to a metal halide reagent to form the ionic liquid in-situ. A reverse order of addition of the reagents needed to form the ionic liquid is also contemplated in accordance with the present invention.
This invention relates, in the most preferred alkylation reaction, to the catalytic alkylation of an aromatic molecule with a suitable alkylating reagent (e.g., a C2 to C20, such as a C4 to C14 olefin or a halogenated alkane of similar chain length) using, as the catalyst, a composition which is liquid at low temperatures and which is formed in situ as previously described. The term "linear alkylbenzene formation" as used herein is intended to cover the process by which higher alkyl moieties are placed on benzene compounds, with the term "alkyl" being intended to cover the conventional paraffinic alkane substituents, "higher" being intended to mean C4 or longer, preferably C8 or longer, and the "benzene" including both unsubstituted as well as substituted (e.g., lower alkyl-substituted) benzene compounds. As is well known in the art, this process is practiced by the catalytic reaction of an unsubstituted or lower alkyl-substituted benzene compound with a higher alkene or a halo-substituted higher alkane, such as a chloro-substituted higher alkane. In commercial practice, the alkylating agent is one or more a long chain alkene or halogenated alkane, such as dodecylchloride or dodecene. Recent patents which illustrate an alkylation reaction of this type include U.S. Patent Nos. 5,196,574 to J.A. Kocal and 5,386,072 to P. Cozzi et al. The Cozzi patent, which describes the use of aluminum trichloride as a preferred alkylation catalyst, is a particular example of a prior art alkylation process to which the present invention in an improvement. A recent publication discussing the LAB reaction, in general terms, is contained in INFORM, Vol. 8, No. 1 (Jan. 1997), pp. 19-24.
A class of ionic liquids which is of special interest to the present in situ process, as the desired product thereof, is the class of fused salt compositions which are molten at low temperature. Such compositions are mixtures of components which are liquid at temperatures below the individual melting points of the components. The mixtures can form molten compositions simultaneously upon contacting the components together, or after heating and subsequent cooling. Examples of conventional low temperature ionic liquids or molten fused salts, which are capable of being made by the present invention, are the chloroaluminate salts discussed by J. S. Wilkes, et al., J. Inorg. Chem., Vol. 21 , 1263-1264, 1982. Alkyl imidazolium or pyridinium salts, for example, can also be formed from aluminum trichloride (AICI3) forming the fused chloroaluminate salts. Also, chlorogallate salts made from gallium trichloride and methylethyl-imidazolium chloride are discussed in Wicelinski et al., "Low Temperature Chlorogallate Molten Salt Systems," J. Electrochemical Soc, Vol. 134, 262-263, 1987. The use of the fused salts of 1-alkylpyridinium chloride and aluminum trichloride as electrolytes are discussed in U.S. Pat. No. 4,122,245. Other patents which discuss the use of fused salts from aluminum trichloride and alkylimidazolium halides as electrolytes are U.S. Pat. Nos. 4,463,071 and 4,463,072 and British Patent No. 2,150,740. All of these species can be the ultimate product formed by the instant in situ process.
U.S. Patent No. 4,764,440 to S.D. Jones describes ionic liquids which comprise a mixture of a metal halide, such as aluminum trichloride, and what is termed a "hydrocarbyl-saturated onium salt", such as trimethylphenylammonium chloride. In such ionic liquids, the onium salt component, if based on the presence of a nitrogen atom, is fully saturated with four substituent groups. These can also be selected as the ultimate in situ products herein.
U.S. Patent No. 5,104,840 to Y. Chauvin et al. describes ionic liquids which comprise at least one alkylaluminum dihalide and at least one quaternary ammonium halide and/or at least one quaternary ammonium phosphonium halide; and their uses as solvents in catalytic reactions. The in situ process of this invention can be used to make these species.
PCT International Patent Publication No. WO 95/21872 describes ternary ionic liquids which can comprise a metal halide, such as aluminum trichloride, an imidazolium or pyridinium halide, and a hydrocarbyl substituted quaternary ammonium halide or a hydrocarbyl substituted phosphonium halide. See page 4, lines 18-24 for the description of the hydrocarbyl substituted quaternary ammonium halide. These might also be selected as products to be made by this invention.

The related applications, however, describe preferred ionic liquids which are intended to be made herein and these applications are incorporated herein by reference for such description.

SUMMARY OF THE INVENTION

As indicated before, the present invention relates to the in-situ formation of an ionic liquid catalyst for use in an ionic liquid-catalyzed reaction (e.g., an aromatic alkylation reaction) by means of the separate addition of the reagents needed to form that ionic liquid into the desired reactor. For example, the present invention can be practiced by the addition to at least one reagent for the formation of the ionic liquid catalyst (e.g., a metal halide) and at least one reagent for the desired reaction, in the desired reaction vessel, of the other reagent or reagents used to form the ionic liquid (e.g., at least one base) which other reagent(s) is or are capable, upon combination with the initially added reagent for the ionic liquid, of forming an ionic liquid catalyst, either before the initiation or during the desired ionic liquid catalyzed reaction (e.g., an alkylation reaction).

DESCRIPTION OF THE DRAWING

The Drawing, which forms a part of the instant specification illustrates an embodiment of the present invention within the broadest scope for that invention.

DETAILED DESCRIPTION OF THE INVENTION

The low temperature molten compositions, or ionic liquids, which are used as catalysts in this invention can be referred to as fused salt compositions, or ionic aprotic solvents. By "low temperature molten" is meant that the compositions are in liquid form below about 100°C at standard pressure. Preferably, the molten composition is in liquid form below about 60° C, and more preferably below about 30°C at standard pressure.
The metal halides useful in this invention (and to which the selected base or bases, for example, can be added) are those compounds which can form anions containing polyatomic chloride bridges in the presence of the alkyl-containing amine hydrohalide salt. Preferred metal halides are covalently bonded metal halides. Suitable metals which can be selected for use herein include those from Groups VIII and IB, IIB and MIA of the Periodic Table of the Elements. Especially preferred metals are selected from the group comprising aluminum, gallium, iron, copper, zinc, and indium, with aluminum being most preferred. The corresponding most preferred halide is chloride and therefore, the most preferred metal halide is aluminum trichloride. Other possible choices for metal halides to select include those of copper (e.g., copper monochloride), iron (e.g., ferric trichloride), and zinc (e.g., zinc dichloride). Aluminum trichloride is most preferred because it is readily available and can form the polynuclear ion having the formula AI2CI7M Furthermore, the molten compositions comprising this polynuclear ion are useful as described hereinbefore. Mixtures of more than one of these metal halides can be used.
Granular (+4 -14 mesh) aluminum trichloride can be an especially preferred metal halide to employ. It is easy to handle in air without fuming problems and has good flow properties. Its reaction with trimethylamine hydrochloride, for example, is slower and more uniform than with aluminum trichloride powder, with a temperature exotherm to about 150°C. While the resulting ionic liquid is slightly hazy due to the presence of insoluble impurities from the aluminum trichloride, the insoluble, which settle out upon storage of the liquid, do not have an adverse effect on the catalytic performance of the ionic liquid in regard to the process of the present invention.

One preferred class of base intended to be added to the metal halide in situ to form the ionic liquid is an alkyl-containing amine hydrohalide salt. The terminology "alkyl-containing amine hydrohalide salt", as used herein, is intended to cover monoamines, as well as diamines, triamines, other oligoamines and cyclic amines which comprises one or more "alkyl" groups and a hydrohalide anion. The term "alkyl" is intended to cover not only conventional straight and branched alkyl groups of the formula -(CH2)nCH3 where n is from 0 to about 29, preferably 0 to about 17, in particular 0 to 3, but other structures containing heteroatoms (such as oxygen, sulfur, silicon, phosphorus, or nitrogen). Such groups can carry substituents. Representative structures include ethylenediamine, ethylenetriamine, morpholino, and poloxyalkylamine substituents. "Alkyl" includes "cycloalkyl" as well.
The preferred alkyl-containing amine hydrohalide salts useful in the present invention have at least one alkyl substituent and can contain as many as three alkyl substituents. They are distinguishable from quaternary ammonium salts which have all four of their substituent positions occupied by hydrocarbyl groups. The preferred compounds that are contemplated herein have the generic formula R3N.HX, where at least one of the "R" groups is alkyl, preferably alkyl of from one to eight carbon atoms (preferably, lower alkyl of from one to four carbon atoms) and X is halogen, preferably chloride. If each of the three R groups is designated R.,, R2 and R3, respectively, the following possibilities exist in certain embodiments: each of R R3 can be lower alkyl optionally interrupted with nitrogen or oxygen or substituted with aryl; R-, and R2 can form a ring with R3 being as previously described for R^ R2 and R3 can either be hydrogen with R-, being as previously described; or R1 t R2 and R3 can form a bicyclic ring. Most preferably, these groups are methyl or ethyi groups. If desired the di- and trialkyl species can be used. One or two of the R groups can be aryl, but this is not preferred. The alkyl groups, and aryl, if present, can be substituted with other groups, such as a halogen. Phenyl and benzyl are representative examples of possible aryl groups to select. However, such further substitution may undesirably increase the size of the group, and correspondingly increase the viscosity of the melt. Therefore, it is highly desirable that the alkyl groups, and aryl, if present, be comprised of carbon and hydrogen groups, exclusively. Such short chains are preferred because they form the least viscous or the most conductive melts. Mixtures of these alkyl-containing amine hydrohalide salts can be used.
The mole ratio of alkyl-containing amine hydrohalide salt which is to be combined with the metal halide by in situ addition can, in general, range from about 1 :1 to about 1 :2.5. In a highly preferred embodiment, the low temperature molten composition useful as a catalyst in this invention consists essentially of the metal halide and the alkyl-containing amine hydrohalide salt. Specifically, the most preferred low temperature molten composition formed by the instant in situ process is a mixture consisting essentially of a mole ratio of trimethylamine hydrochloride to aluminum trichloride of from about 1 :1.5 to about 1 :2, preferably about 1 :2.
Typically, the metal halide and the alkyl-containing amine hydrohalide salt are solids at low temperature, i.e., below about 100° C. at standard pressure. After mixing the two solids together in accordance with the present in situ process, the mixture can be heated until the mixture becomes a liquid. Alternatively, the heat generated by the addition of the two solids will result in forming a liquid without the need for additional external heating. Upon cooling, the mixture remains a liquid at low temperature, i.e., below about 100°C, preferably below about 60°C, and more preferably below about 30°C.
Another type of base which can be used in the instant in situ process is a guanidinium salt as will be described in further detail. These guanidinium salts comprise the reaction product of a guanidine or substituted guanidine compound that has been reacted with an acid to form the corresponding guanidinium salt of the acid. In general, the unsubstituted or substituted guanidine compounds will have the formula
(R2N)2C=NH
where R is hydrogen in the case of the unsubstituted compounds and is independently selected from alkyl (e.g., lower alkyl, such as methyl, ethyl, propyl, isopropyl, butyl, isobutyl, and t-butyl) and/or aryl (e.g., phenyl). The guanidine molecule, HN=C(NH2)2, is a strong base, pKa = 13.65, making it the strongest organic base after the quaternary ammonium hydroxides (see P. Smith, "The Chemistry of Open-Chain Organic Nitrogen Compounds", Volume I, W.A. Benjamin, Inc. New York (1965), pp. 277-279). Alkyl guanidines are also strongly basic and form very stable salts. In salt formation, the proton is added to the dicoordinated nitrogen, forming a trigonally symmetrical cation, in which all three nitrogen atoms are seen to be equivalent. The cation with HCI, for example, can be represented as [C-(NH2)3]+CIM The cation can be represented as an immonium ion with a double bond to any of the three nitrogens or as a carbonium ion. When such a salt, with a melting point of 181°C, is mixed with a metal halide salt, such as aluminum chloride with a melting point of 190°C, for example, in a molar ratio of 1 :2, respectively, an exothermic reaction takes place, resulting in the formation of a product that is a liquid about 70°C. The chloride ion present in the guanidine HCI will react with aluminum trichloride, for example, to form the AICI4" anion. The result is an ionic liquid.
A representative, nonlimiting flow diagram of use of the process in the alkylation of benzene (an LAB process) is given in the Drawing. Line 11 shows the introduction of the paraffin reagent for the chemical reaction into dehydration vessel 12 with a paraffin/olefin feedstock for the reaction passing through line 13 into reactor 14. The other reagent for the reaction (benzene) is introduced into the reactor 14 by line 22. The LAB product is eventually withdrawn through line 15 into separator 16 where the ionic liquid 18 is separated and recycled through line 19 into reactor 14 and benzene reagent is also separated and recycled through line 17 into reactor 14. The LAB product is collected via line 25.
The in-situ preparation of the ionic liquid is practiced by the separate introduction of the reagents needed to form it into the reactor. In the case of an ionic liquid comprising a metal halide and a base, a number of possibilities exist for addition to these reagents separately through feed lines (or through recycle line 19 with the previously formed ionic liquid product). For example, appropriate amounts of each reagent to form either the original ionic liquid (or needed make up ionic liquid) can be added by lines 20-24 so that they combine in reactor 14.
The use of in-situ addition according to this invention has a number of advantages. It uses existing equipment needed for the actual reaction and avoids the need for a separate ionic liquid makeup reactor. The individual reagents are separately added through any of the respective inlet lines 13 or 22 for the reagents and/or the recycle lines 17 or 19. Since the process of forming the ionic liquid may be highly exothermic, the in-situ preparation affords a desired dilution effect on that reaction. Also, corrosion problems that could take place if a separate reactor and/or feed lines is or are for the ionic liquid formation and transport might be alleviated by having the ionic liquid, when formed, largely present with other substances which dilute it (except possibly for recycle line 19 in the Drawing.

The following Example is given to further illustrate one embodiment of the present invention.

EXAMPLE 1

This Example demonstrates the in-situ preparation of an ionic liquid catalyst by adding trimethylamine hydrochloride and aluminum trichloride separately during the alkylation of benzene with an olefin reagent.
Initially, 18.7 g of benzene and 5.1 g of 1-dodecene were weighed into a 3-neck flask. The mixture was kept at 25°C under nitrogen atmosphere. A sample was taken and was analyzed by GC. It showed that no reaction had occurred at this point. However, immediately after the addition of 1.2 g of aluminum trichloride, 0.42 g of trimethylamine hydrochloride was then also added to the benzene/dodecene mixture. A brown ionic liquid was formed, and the desired alkylation reaction took place instantaneously. The resulting product was analyzed by GC, and it showed that over 99% of the dodecene had been converted to dodecyl benzenes.