WO2000040673A1

WO2000040673A1 - Industrial process and catalysts

Info

Publication number: WO2000040673A1
Application number: PCT/GB1999/004316
Authority: WO
Inventors: Kevin John Green; Philip Nicholas Barnes; Nicholas David James Lever; Kenneth Alan Grant
Original assignee: The Secretary Of State For Defence
Priority date: 1999-01-06
Filing date: 1999-12-21
Publication date: 2000-07-13
Also published as: AU1873700A; GB9900109D0

Abstract

A process for cracking a hydrocarbon compound comprises contacting said hydrocarbon compound with an ionic liquid comprising a salt which comprises an imidazolium or pyridinium ion and aluminium ions under conditions at which cracking can occur. Adjustment of the components of the ionic liquids can be used in order to modify the products obtained. The use of ionic liquids in such processes is also claimed.

Description

Industrial Process and Catalysts

The present invention relates to catalytic processes for effecting chemical reactions, in particular the cracking of hydrocarbons, and catalysts for use in the process.

Reactions of hydrocarbons in salts which are molten at room temperature are known. These reactions however, tend to be bond-forming reactions, such as Friedel- Crafts reactions and acylations. For example, US Patent No. 3,846,503 describes how a mix of the solid copper chloride and aluminium chloride powders was used to isomerise cyclooctane. A similar effect was observed with n-pentane and n-heptane, where skeletal isomerisation was found to occur.

The isomerisation of n-pentane and n-heptane with aluminium chloride and copper sulphate is described in J. Catalysis, 64 (1980) 13-17. The reaction proceeded at room temperature and was attributed to the interaction of the intimately mixed solid powders. The reaction was found to be dependent on surface area, but not the total amount, of the copper sulphate. This was attributed to the catalytically active species being located on the powder surface.

Molten salts, or ionic liquids, are fused materials, consisting of one or more compounds. An example in the prior art is a mixture of KCI and LiCI used as an electrolyte in thermal batteries. It is a solid at room temperature, with a melting point of ca 350 °C. Other ionic liquids have been suggested for use as battery electrolytes.

Imidazolium compounds have also been used as catalysts in certain circumstances. WO 95/21871 (Seddon et al, 1995) describes how dialkyl substituted imidazolium halide can be used to polymerise olefins and the alkylation of paraffins, isoparaffins or aromatics with olefins. In addition to the imidazolium compound, the catalytic liquid contained additional aluminium chloride.

WO 95/21806 (Seddon et al.) describes the use of ionic liquids to catalyse the alkylation of aromatics. These ionic liquids are liquid at room temperature and below, and the catalytic process was performed between - 30 °C to + 50 °C in a batch process.

The reaction rate was found to be dependent on the surface area, but not the total amount of copper sulphate. This was attributed to the catalytically active species being located on the powder surface.

According to a first aspect of the present invention there is provided a process for cracking a hydrocarbon compound, said process comprising contacting said hydrocarbon compound with an ionic liquid comprising a salt which comprises an imidazolium or pyridinium ion and aluminium ions, under conditions at which cracking can occur.

According to a second aspect of the present invention there is provided a process for hydrogenation of a hydrocarbon compound, said process comprising contacting said hydrocarbon compound with an ionic liquid comprising a salt which comprises an imidazolium or pyridinium ion and aluminium ions, under conditions at which hydrogenation can occur.

The expression "ionic liquid" as used herein refers to a salt which is in liquid form. Suitably the salt is liquid at least at the temperatures and pressures used in the reaction. Preferably, the ionic liquid is in a liquid state at room temperature and pressure.

The term "cracking" relates to a process in which hydrocarbon molecules are transformed either into smaller hydrocarbon units, or to hydrogen and unsaturated hydrocarbons. Contact between the reactants such as the hydrocarbon compound and the ionic liquid is suitably effected by bubbling the reactants through the ionic liquid. A stream of reactant, either alone, or if necessary in the presence of a carrier gas is introduced into the lower region of a reaction vessel containing the ionic liquid.

Products can then be vented from an upper region of the reaction vessel, either continuously or in a batch-processing manner.

Carrier gases, where used, may comprise inert gases, such as nitrogen, argon etc., or other more reactive gases such as hydrogen or carbon dioxide, provided that these do not adversely impact on the reaction or the stability of the system. Hydrocarbons, which can be cracked in this way, include alkanes, cycloaikanes, alkenes and alkynes, any of which may be straight or branched chain, as well as aromatic hydrocarbons. They may contain chains for example of from 4-50 carbon atoms, for example from 6-20 carbon atoms, which may have pendant groups such as smaller hydrocarbon groups, thus forming branched chains. The hydrocarbons may comprise a single compound or may be a hydrocarbon mixture, such as diesel, A CAT, gasoline or refinery raffinates with a complex mix of hydrocarbons. Hydrocarbon molecules may possess a wide range of structures, and these are classed according to IUPAC rules.

The degree of cracking will depend upon the nature of the particular hydrocarbon or hydrocarbon mixture being processed, the reaction conditions employed etc. It may be desirable, particularly for fuel cell applications if the hydrocarbons are transformed to hydrogen and carbon oxides such as carbon dioxide and carbon monoxide. If necessary, the reaction products can be recycled through the reaction chamber and/or further reaction chambers in order to effect further cracking to these products. Some additional chemicals may need to be added to obtain the desired products. For instance air or steam are often added to aid hydrogen production, through partial oxidation of hydrocarbons, or by steam reforming. Catalytic cracking is the thermal decomposition of petroleum or hydrocarbons in the presence of a catalyst. Catalysts such as zeolites often carry out these processes. The catalysts is employed as a bead or pellet and may be used in a fixed, moving or floating bed, each technique having its advantages and disadvantages. In industrial terms reforming converts low octane gasolines into high octane gasolines, and is usually performed in the presence of hydrogen. Isomerisation can also be used to increase octane number while converting or removing benzene. Aluminium chloride has been used as a non-regenerable to isomerize hexane, at temperatures less than 370°C. Hydrogenation is also an important industrial process, and is used in many aspects of the chemical industry from the production of polyunsaturated fatty acids to chemical synthesis of specialist compounds, fine chemical and materials. These processes are often performed with expensive noble metal catalysts containing metal such as platinum and rhodium. Alternative methods of hydrogenation include hydrogenation using organo-metallic catalysts, but these usually include platinum of ruthenium as the metallic component, eg Wilkinson's catalyst.

The ionic liquids used in the invention are suitably prepared by mixing an imidazolium or pyridinium salt with an aluminium salt.

Suitably the imidazolium or pyridinium salts are alkyl or dialkyl salts, for example C_1-20alkyl or C_1-20dialkyl salts.

The counter ion present in the salt will affect the melting temperature of the ionic liquid. Suitable counter ions include tetrafluoroborate, trifluoromethane sulphonate, carbonate, sulphate, halide sulphite, hexafluorophosphate, perchlorate nitrate and imide . Preferably the counter ion is a halide, such as chloride. Therefore, particular examples of salts which can be used in the production of the ionic liquids will be alkyl or dialkyl halide salts such as alkyl or dialkyl imidazolium or pyridinium chlorides.

The precise nature of the alkyl groups in these salts affects the solvating properties of the salt. In the reaction of the invention, it is preferable that the reactants and/or products of the reaction do not dissolve to any significant extent in the ionic liquid. These can be selected so as to suit best the particular reaction conditions being employed. For example, when the reaction is effected in a continuous flow method, where hydrocarbon is continuously flowed through the ionic liquid and the products vented in a continuous stream, the residence time in contact with the ionic liquid is short and therefore, solvation effects are not so significant. In batch reactors however, where the hydrocarbon or the products may remain in contact with the ionic liquid for some time, the selection of a salt with particularly low solvating properties may be desirable.

Particular examples of imidazolium and pyridinium salts for use in the ionic liquids include:

3-ethyl-1 — methyl imidazolium chloride

1 — methyl — 3 — ethyl imidazolium chloride

1-ethyl-3-butyl imidazolium chloride

1-methyl-3-butyl imidazolium chloride 1-methyl-3-propyl imidazolium chloride

1-methyl-3-hexyl imidazolium chloride

1-methyl-3-octyl imidazolium chloride

1-methyl-3-decyl imidazolium chloride ethyl pyridinium bromide ethyl pyridinium chloride ethylene pyridinium dichloride butyl pyridinium chloride Suitable aluminium salts for use in the production of the ionic liquid are aluminium halides such as aluminium chloride. In ionic liquids the chemistry is determined by the equilibrium in the solution:

2AICI - => AI₂CI₇ ^"+ Cr

In acidic melts the equilibrium lies to the right i.e. AI₂CI ^". whereas in basic melts, the equilibrium shifts to the left. In all the salt mixtures the organic cation is independent of this equilibrium. In basic melts AICLf and Cl^" predominate and in acidic melt AICI ^" and AI₂CI ^" are the dominate species. A buffered neutral melt only contains the organic cation and AICI₄ ^". Neutrality may be achieved by adding a metal chloride to a sparingly acidic melt. When the melt is added to an acidic melt the following reaction occurs:

MCIn + pAI₂CI₇ ^" = MCI_n._p ^p+ + 2pAICI ^". Where MCI_n is a metal chloride. The buffering of a melt may be altered by changing the oxidation sate of the metal or by choosing another metal. The addition of metal chloride addition is a chloride displacement reaction, and adding excess metal chloride (in relation to the available chloride) produces a neutral melt. Initial experiments have used an ionic liquid, which is prepared by mixing aluminium chloride and an imidazolium salt such as 3-ethyl-1 -methyl imidazolium chloride (EMIC). The exact mole ratio of organic chloride to metal chloride can be varied to create a Lewis acidic melt or a Lewis basic melt or a Lewis neutral melt. In an acidic melt there is an excess of aluminium chloride, in a basic melt an excess of the imidazolium chloride. In a neutral melt the mole ratio is unity. Thus ratio of the aluminium salt: imidazolium or pyridinium salt used in the production of the ionic liquid is suitably in the range of from 1:9 to 9:1, preferably from 1:3 to 3:1 and often at about 1:1 depending upon the acidity or basicity required.

The acidity or basicity may have an effect on the reaction products obtained, particularly in hydrocarbon cracking reactions.

In a preferred embodiment, a third component comprising a metal salt such as a transition metal salt is added to the ionic liquid. Particular transition metal salts include copper and cobalt salts. The counter-ion may be any of those listed above in relation to the imidazolium or pyridinium salts, but are preferably halides such as chlorides.

The nature of the third component may change the reaction products, in particular in hydrocarbon cracking, and can therefore be used to produce products of the required nature, for example having a preponderance of a desired molecular weight. The metal salt of the third component forms an integral part of the ionic liquid.

The amount of third component added to the ionic liquid is relatively small. For example, the third component will make up from 0.05 to 5% w/w of the total ionic liquid.

In addition to or as an alternative to the third component mentioned above, other catalysts may be dissolved or suspended in the molten salt. These additional catalysts may enhance the degree of cracking or modify the product ratio, depending upon their nature. Examples of other catalysts which may be used in this way include metal sols, where the metal is for example, nickel, platinum, tungsten, rhodium or other noble metals or alloys of these, or homogeneous catalysts such as Wilkinson's catalyst RhCI(PPh₃)_3l or similar. Some of the metals such as nickel will dissolve in the ionic liquid. This will be true also for the homogenous catalysts such as Wilkinson's catalyst. Others, such as platinum and tungsten, will remain suspended. Wilkinson's catalyst catalyses hydrogenation of unsaturated hydrocarbons at ambient pressure. Other homogeneous catalysts have different effects. Combined with the hydrocarbon cracking properties of the molten salts, the additional catalyst may enhance the selectivity of the cracking reaction. This may be particularly useful when the reaction is performed under a reactive atmosphere such as hydrogen or carbon monoxide.

The selection of suitable further catalysts will depend upon the nature of the reaction being undertaken, as well as the conditions used and the precise nature of the ionic liquid. They will be determinable in any particular case, by routine testing methods well known in the art.

An initial test can be to simply add the two liquids in a reaction vessel and monitor the change of composition. Gas chromatography is a well-known method of hydrocarbon component analysis. However, the hydrocarbon and the ionic liquid, the reactants, are often immiscible and the contact area between the two therefore limits the reaction rate. To speed up the reaction rate the experiment can be performed at an elevated temperature. A better experiment would be to use a continuous reactor in which the gases are introduced as a flowing gas stream into the catalytic liquid. In this flow system there is a relatively short (<1s) contact time between the feed stock and the catalyst mixture. Suitable temperatures may be from 100 °C -160 °C. Batch processes or processes with a flow design modified to provide longer contact times could be effected at lower temperatures, for example from 0 °C to 100 °C.

The feed: catalyst mole ratios can be varied to give vastly different reaction efficiencies (defined as total amount of products divided by total amount of feed). In general, the feed: catalyst ratio will be in the range of from 1 :1000 and 1000:1 w/w. The process can be carried out at a range of pressures, for example from 1 to

30 bar, conveniently at atmospheric pressure.

Suitably the process is effected in an inert atmosphere, for example under nitrogen or in the presence of reactive gases, e.g. hydrogen, carbon monoxide. Oxygen may also be present provided either, that water is not produced as a result in the reaction, or that water is produced, but does not have an adverse effect on the stability of the ionic liquid.

The invention will now be particularly described by way of Example:

Initial screening of the catalysts can be performed in a batch process using a stirred reaction vessel. This simple arrangement is not an ideal catalytic reactor, but gives some indication of overall performance. The reactor consisted of a sealed flask in which the liquid was stirred by a magnetic flea. The liquids under test were added under an inert atmosphere. In a typical experiment hexane (20ml) was added to the melt (2ml), the reactor sealed and removed from the inert atmosphere. The vessel was then warmed (in the screening experiments a temperature of 40°C was chosen arbitrarily) to a set temperature and then the experiment began. Monitoring of the reaction was achieved by gas chromatography. Both the liquid and the gas phases could be monitored using this technique. Since the molten salt and the organic liquid were immiscible, one being a polar ionic liquid, the other a non-polar organic aliquots of the organic liquid could be removed and tested. The reaction takes place at the interface between the two liquids, so removing portions of the organic layer should not effect the reaction rate since the ionic liquid was always covered. Several molten salts were tested for reactions with organic liquids, and hexane cracking primarily being of interest.

Example 1 - Basic melt This melt was prepared by adding aluminium chloride and 1-ethyl-3-methyl- imidazolium chloride together (molar ratio: 2:1) to give what is known in the field as a 'basic melt', which was a slightly viscous liquid at room temperature. The term basic refers to its chemical nature. This melt (2ml) was added to hexane (20ml) under argon, according to the procedure described above. Table 1 below compares the components of the liquid phase after 90 minutes of continuous reaction at 40°C. Example 2 - Neutral melt This melt was prepared by adding aluminium chloride and 1-ethyl-3-methyl- imidazolium chloride together (molar ratio: 1:1) to give what is known as a 'neutral melt', which was neutralised by the addition of lithium chloride. The melt was a slightly viscous liquid at room temperature. The term basic refers to its chemical nature. This melt (2ml) was added to hexane (20ml) under argon, according to the procedure described above. Table 1 below compares the components of the liquid phase after 90 minutes of continuous reaction at 40°C.

Example 3 - Acidic melt This melt was prepared by adding aluminium chloride and 1-ethyl-3-methyl- imidazolium chloride together (molar ratio: 1 :2) to give an 'acidic melt', which was a slightly viscous liquid at room temperature . The term basic refers to its chemical nature. This melt (2ml) was added to hexane (20ml) under argon, according to the procedure described above. The table below compares the components of the liquid phase after approximately 90 minutes of continuous reaction at 40°C.

Neutral and basic melts have different proportions of chloroaluminate species, and therefore their Lewis acidity and related reactivity may be expected to be different from each other and acidic melts.

Table 1 : Results of batch reaction of hexane with different melts

Example 4 - Acidic melt saturated with copper chloride

This melt was prepared by adding copper chloride(anhydrous) to the acidic melt described above. Copper chloride is sparingly soluble in this melt and so a saturated solution was prepared by adding powdered copper chloride. The copper coloured, clear supernatant liquid was used for catalytic testing. This melt (2ml) was added to hexane (20ml) under argon, according to the procedure described above. Table 2 compares the components of the liquid phase after approximately 90minutes of continuous reaction at 40°C.

Example 5 - Acidic melt doped with hexachloroplatinic acid This melt was prepared by adding hexachloroplatinic acid to the acidic melt described above. This platinum salt is sparingly soluble in this melt and so a saturated solution was prepared by adding this powdered salt and stirring for 48 hours. Excess platinic acid was then allowed to settle. The reddish/brown coloured, clear supernatant liquid was used for catalytic testing. This melt (2ml) was added to hexane (20ml) under argon, according to the procedure described above. Table 2 compares the components of the liquid phase after approximately 90minutes of continuous reaction at 40°C.

Example 6 - Acidic melt doped with cobalt chloride This melt was prepared by adding cobalt chloride(anhydrous) to the acidic melt described above. Cobalt chloride is soluble in this melt and so a solution (0.1 mol) was prepared by adding powdered cobalt chloride. The resultant deep blue coloured liquid was used for catalytic testing. This melt (2ml) was added to hexane (20ml) under argon, according to the procedure described above. Table 2 compares the components of the liquid phase after approximately 90minutes of continuous reaction at 40°C.

Table 2: Reaction of hexane with different doped acidic melts

Doping the acidic melt with three different metal chlorides results in three different product distributions. The metal ion must therefore be having an effect on the reaction pathway and outcome. It is therefore possible to alter the outcome of a reaction in other ways apart from the acid-base ratio, which is an advantage over the simple undoped melts. This benefit could lead to a number of applications either where one major product is required or where a number of products is required.

To further examine the range of compounds and possible reactions of this melt, and to explore possible benefits, the copper chloride doped acidic melt was tested with cyclohexane and cyclohexene.

Example 7 - Catalytic reaction of cyclohexane and molten salt that contains copper chloride

This melt was prepared by adding copper chloride (anhydrous) to the acidic melt described above. Copper chloride is sparingly soluble in this melt and so a saturated solution was prepared by adding powdered copper chloride. The copper coloured, clear supernatant liquid was used for catalytic testing. This melt (2ml) was added to cyclohexane (20ml) under argon, according to the procedure described above. Table 3 compares the components of the liquid phase after approximately 90minutes of continuous reaction at 40°C. Example 8 - Catalytic Reaction of cyclohexene and molten salt that contains copper chloride

This melt was prepared by adding copper chloride (anhydrous) to the acidic melt described above. Copper coloured, clear supernatant liquid was used for catalytic testing. This melt (2ml) was added to cyclohexene (20ml) under argon, according to the procedure described above. The melt was partially soluble in cyclohexene, this meant that with the experimental restriction in the laboratory Table 3 compares the components of the vapour phase after approximately 90 minutes of continuous reaction at 40°C.

Table 3: Reaction of cyclohexane and cyclohexene with copper chloride doped acid molten salt The results for the cyclohexane reaction indicate that there is a reaction to form either hexane. Cyclohexene reacts in a different way to previous examples in that the cyclohexene is reduced to cyclohexane. This reaction also has a very high reaction rate, presumably as a result of the partial solution of the melt in the organic liquid, which is a benefit. This reaction expands the uses of the melt. Other uses for this reaction outside the heavy petroleum industry, and may include the facile hydrogenation of organic species at relatively low reaction temperatures. In addiiton the reaction proceeds without the use of an expensive supported noble metal catalyst or reagent, or equally expensive organo-metallic catalyst. These examples demonstrate that there is a reaction occurring, and this simple procedure may be used as a screening process to enable catalyst outcomes to be predicted. As mentioned previously a better experiment, where greater reaction rates could be expected would be to flow the reactants through the catalysts to increase the surface area. Example 9

A basic (defined in terms of its aluminium chloride to EMIC ratio) ionic liquid was prepared by adding aluminium chloride (18.13 g, 0.136 mol) to EMIC (39.58g, 0.27mol) slowly over a period of several hours via a powder funnel. The final product was a clear, viscous, slightly yellow ionic liquid. The ionic liquid was transferred to a reaction vessel (1) as shown in Figure 1 , and the reaction rig was then completed by insertion of a hydrocarbon delivery tube (2). The reaction chamber was heated to the desired temperature of 140°C, under a flow of nitrogen through the tube (2). At this temperature the gas was switched to the nitrogen/hexane feed whereupon the reaction proceeded until the feed was changed back to pure nitrogen. Product was vented out through a tube (4) and analysed by gas chromatography. The distribution of major products as determined by GC analysis is given in Table 4. Additional small amounts of unknown organics were also detected.

Table 4

Example 10

An acidic melt (again defined in terms of this AIC^EMIC mole ratio) was prepared by slowly adding aluminium chloride (52.0 g, 0.4 mol) to EMIC (29.0 g, 0.2 mol) over a period of several hours. The reaction was performed as given in Example 9 and the reaction products as determined by GC analysis are given in Table 4.

Table 5

Clearly the acidity or basicity of the melt has a significant impact on the product distribution. In addition reactions that were previously very slow or undetectable in the batch process reactor are now apparent using the flow through reactor. Example 11

An aliquot of the acidic melt described previously (Example 10) was taken and copper chloride added. The final product was a copper coloured, clear liquid. The reaction was carried out as previously (Example 9) and the products as determined by GC analysis are given in Table 6.

Table 6 The addition of a transition metal salt in the presence of aluminium chloride illustrates the effects of the co-catalysts. In the flow through reactor the benefits of metal salt addition to reaction rate are apparent in that the copper chloride melt exhibits superior cracking characteristics than the plain acidic melt; this is to be expected from the batch process reactor. It may be that the additional non aluminium metal ions are very active sites for catalytic behaviour, or there is an initial reduction step that causes the formation of colloidal particles of metal. The metal species present in the ionic liquid may therefore interact along two reaction pathways, which could explain the differing products obtained.

Claims

1. A process for cracking a hydrocarbon compound, the process comprising contacting the hydrocarbon compound with an ionic liquid comprising a salt which comprises an imidazolium or pyridinium ion and aluminium ions under conditions at which cracking can occur.

2. A process for hydrogenation of a hydrocarbon compound, the process comprising contacting the hydrocarbon compound with an ionic liquid comprising a salt which comprises an imidazolium or pyridinium ion and aluminium ions under conditions at which hydrogenation can occur.

3. A process according to claim 1 or claim 2, wherein reactants are bubbled through the ionic liquid.

4. A process according to claim 3, wherein the reactants are bubbled through in the presence of a carrier gas.

5. A process according to any preceding claim, which is operated as a continuous process.

6. A process according to any one of claims 1 to 4, wherein the process is operated as a batch process.

7. A process according to any preceding claim, wherein the hydrocarbon compound has up to 20 carbon atoms.

8. A process according to any preceding claim, wherein the hydrocarbon compound is a mixture of compounds.

9. A process according to claim 8, wherein the mixture is diesel, AVCAT, gasoline or refinery raffinates.

10. A process according to any preceding claim, wherein the reaction products can be recycled through the reaction chamber and/or further reaction chambers.

11. A process according to any preceding claim, wherein the ionic liquid is prepared by mixing an imidazolium or pyridinium salt with an aluminium salt.

12. A process according to claim 11, wherein the imidazolium or pyridinium salts are alkyl or dialkyl salts, for example Cι_-2o alkyl or Cι_-2o dialkyl salts.

13. A process according to claim 12, wherein each alkyl group has from 1 to 20 carbon atoms.

14. A process according to claim 12 or claim 13, wherein the counter ion present in the imidazolium or pyridinium salt is tetrafluoroborate, trifluoromethane sulphonate, carbonate, sulphate, halide, sulphite, hexafluorophosphate, perchlorate nitrate and imide.

15. A process according to claim 14, where the counter ion is a halide such as chloride.

16. A process according to at least claim 11 , wherein the imidazolium or pyridinium salt is selected from 3-ethyl -1- methyl imidazolium chloride; 1 -methyl - 3 - ethyl imidazolium chloride; 1 -ethyl - 3 - butyl imidazolium chloride; 1-methyl-3-butyl imidazolium chloride; 1- methyl-3-propyl imidazolium chloride; 1-methyl-3-hexyl imidazolium chloride; 1-methyl-3-octyl imidazolium chloride; 1-methyl-3-decyl imidazolium chloride; ethyl pyridinium bromide; ethyl pyridinium chloride; ethylene pyridinium dichloride; and butyl pyridinium chloride

17. A process according to at least claim 11 , wherein said aluminium salt is aluminium chloride.

18. A process according to at least claim 11 , wherein the ratio of the aluminium salt: imidazolium or pyridinium salt is in the range of from 1:9 to 9:1.

19. A process according to any preceding claim, wherein the catalyst mixture contains a third component (iii) which is a metal salt other than an aluminium salt.

20. A process according to claim 19, wherein said metal salt is a transition metal salt.

21. A process according to any preceding claim which is conducted at a temperature of from -30°C to the thermal limit of the ionic liquid.

22. A process according to any preceding claim, wherein the feed: catalyst mole ratio is in the range of from 1 :1000 and 1000:1 w/w.

23. A process according to any preceding claim, which is effected at a pressure of from 1 to 30 bar.

24. A process according to any preceding claim, which is effected in an inert atmosphere.

25. A process according to any preceding claim, wherein a further catalyst is present in the ionic liquid.

26. A process according to claim 25, wherein said further catalyst is Wilkinson's catalyst, a metal sol or a non ionic additive.

27. The use of an ionic liquid comprising imidazolium or pyridinium ions and aluminium ions as a catalyst for hydrocarbon cracking.

28. The use of an ionic liquid comprising imidazolium or pyridinium ions and aluminium ions as a catalyst for hydrogenation of hydrocarbons.

29. The use of an ionic liquid comprising imidazolium or pyridinium ions and aluminium ions as a solvent or support medium for a further catalyst.