GB2378701A

GB2378701A - Process for the preparation of alkylene glycols

Info

Publication number: GB2378701A
Application number: GB0215432A
Authority: GB
Inventors: Jong Feike De; With Jan De
Original assignee: Shell Internationale Research Maatschappij BV
Current assignee: Shell Internationale Research Maatschappij BV
Priority date: 2001-07-04
Filing date: 2002-07-03
Publication date: 2003-02-19
Also published as: GB0215432D0

Abstract

The invention provides a process for preparing an alkylene glycol by reacting an alkylene oxide with water in a reaction medium comprising an ionic-liquid phase and in the presence of a catalyst composition which comprises an organic cation and an anion other than a halide anion. The cation is preferably a phosphonium or ammonium ion and most preferably a 1-alkyl pyridinium or a 1,3 dialkyl imidazolium ion. Its counter-ion is preferably bicarbonate or molybdate. The ionic liquid is preferably bmin.PF<SB>6</SB> or omin.PF<SB>6</SB> but may have a tetrafluoroborate counter-ion.

Description

Process for the preparation of alkylene glycols The present invention relates to a process for the preparation of alkylene glycols and a catalyst composition.

Background of the Invention Alkylene glycols, in particular monoalkylene glycols, are of established commercial interest. For example, monoalkylene glycols are used in anti-freeze compositions, as solvents, and as base materials in the production of polyethylene terephthalates which are used in the production of plastic bottles etc.

The production of alkylene glycols by hydrolysis of alkylene oxides is well known, the reaction generally being performed by liquid phase hydration with a large excess amount of water, e. g. of 20 to 25 moles of water per mole of alkylene oxide. A large excess of water is employed in order to maximise the yield of monoalkylene glycol from the reactions. Various catalyst compositions have been proposed to improve the rate and/or the selectivity of the reaction. However, the advantages of employing such a catalyst system must be offset against the requirement of an additional processing step (s) to separate the alkylene glycol products from the catalyst.

Further, the accumulation of salts during the reaction hinders both recycling of the catalyst and purification of the products.

Attempts have been made to overcome this problem by providing a catalyst on a solid support such as an anion exchange resin. For example, WO 95/20559 describes a process wherein an alkylene oxide is reacted with water in the presence of a catalyst composition comprising a

solid material having one or more electropositive sites, which are coordinated with one or more anions other than metallate and halogen anions. The attraction of such a system is that by fixing the catalyst to the solid support the products can be recovered readily. However, anion exchange resins have only a limited tolerance to heat. As described in WO 97/19043 this leads to a deterioration in monoalkylene glycol selectivity.

Further, anion exchange resins are known to be susceptible to swelling. This is problematic as the most efficient way in which to perform the reaction is by packing a reactor with resin wherein such swelling cannot readily be accommodated.

An alternative approach to overcoming the problems associated with the use of catalysts in homogeneous reaction systems is to perform the reaction in a biphasic reaction medium. For example, US 4579982 describes a process wherein alkylene oxides are hydrolysed in a reaction medium containing an aqueous phase, a waterimmiscible liquid phase, and a selectivity enhancing, dissociatable metalate anion-containing material, wherein the concentration of the metalate anion-containing material is greater in the water-immiscible phase than it is in the aqueous phase. Whilst the metalate anioncontaining material may itself form the water-immiscible phase, the water-immiscible phase generally comprises a liquid organic solvent, for example alkyl, cycloalkyl and aromatic-containing solvents, especially halogenated alkyl, cycloalkyls and aromatics, such as cyclopentane, cyclohexane, methylcyclohexane, cycloheptane, benzene, toluene, xylene, naphthene, dichloromethane, and 1, 1, 2- trichloroethane. Whilst processes such as that described in US 4579982 may allow for the facile separation of alkylene glycol product from catalyst, they have yet to be commercially exploited due to the additional cost of

the water-immiscible organic solvent and environmental concerns about the toxicity of such solvents and their contribution to volatile organic emissions.

Therefore, there remains a need for a catalyst system which may be used to improve the rate or selectivity of alkylene oxide hydrolysis and which has the potential for the desired products to be easily separated and the catalyst recycled conveniently.

Ionic-liquids are liquids which are composed of cations and anions only. They have relatively low melting points making them liquid at ambient temperature (20 OC) or at temperatures commonly applied to organic reactions such as the conversion of alkylene oxides to alkylene glycols (e. g. 20 to 200 C). They have a high thermal stability, often in excess of 300 C ; and being salts their vapour pressure is extremely low and they do not contribute to volatile organic emissions. Further, ionicliquids may have a low solubility in aliphatic solvents and water.

Summary of the Invention A catalytic system comprising an ionic-liquid phase has been developed which may be used to promote the hydrolysis of alkylene oxides to alkylene glycols.

Surprisingly, both the rate of conversion and selectivity to monoalkylene glycol of this novel system compare favourably with conventional homogeneous, aqueous phase, catalytic systems. Further, a catalyst composition developed for use in this novel catalytic system has proven to be a highly effective catalyst for the hydrolysis of alkylene oxides even in the absence of any added ionic-liquid.

Accordingly, the present invention provides a process for preparing an alkylene glycol by reacting an alkylene oxide with water in a reaction medium comprising an ionic-liquid phase and in the presence of a catalyst

composition which comprises an organic cation and an anion other than a halide anion, wherein the organic cation is selected from :i) cations of general formula [ARIR2R3R4) + or [RRACR- R5~R3C=AR1R2) 2+ wherein A is a nitrogen, phosphorous, arsenic or antimony atom ; wherein each of R1 to R4 independently represents a hydrogen atom or a hydrocarbyl group, provided that at least one of Rl to R4 represents a hydrocarbyl group ; and wherein R5 represents an alkylene or phenylene group ; and ii) cations having a heterocyclic ring comprising at least one ring atom A', which at least one ring atom A' is a nitrogen, phosphorous, arsenic or antimony atom.

Detailed description of the Invention In the following detailed description of the present invention, where reference is made to a hydrocarbyl group, unless otherwise stated the hydrocarbyl group is preferably a hydrocarbyl group having from 1 to 30 carbon atoms, more preferably from 1 to 20 carbon atoms, and most preferably from 1 to 10 carbon atoms ; which hydrocarbyl group may be substituted or unsubstituted, straight or branched chain, saturated or unsaturated; preferred such hydrocarbyl groups being alkyl, cycloalkyl, aryl, alkaryl and aralkyl groups. Where the hydrocarbyl group is substituted or optionally substituted, substituents or optional substituents which a hydrocarbyl group may conveniently carry may be independently selected from one or more of halogen atoms, e. g. fluorine or chlorine ; alkoxy, alkenyloxy, aryloxy, hydroxy, alkylthio, arylthio, alkylsuphonyl, alkylsulphinyl, alkoxycarbonyl, dialkylamino and dialkylamido groups ; preferred such substituents being halogen atoms such as fluorine and chlorine and alkoxy, alkylthio and dialkylamido groups.

The catalyst composition to be employed in the process of the present invention comprises an organic cation and an anion other than a halide anion.

The anion of the catalyst composition of the present invention may be conveniently selected from the group consisting of bicarbonate (hydrogen carbonate) anions, carbonate anions, bisulphite (hydrogen sulphite) anions, carboxylic acid derivatives such as formate and citrate anions, and metal late anions such as molybdate and vanadate anions. Anions which have been found to give particularly good results, and are preferred anions of the catalyst composition of the present invention, are bicarbonate anions, carbonate anions and formate anions.

Most preferably, the catalyst composition of the present invention comprises bicarbonate and/or carbonate anions, as by using catalyst compositions comprising bicarbonate and/or carbonate anions in the process of the present invention particularly good results have been achieved.

The anion of the catalyst composition may not be a halide ion such as a chloride or bromide ion, as the selectivity of the reaction to monoalkylene glycol when using halide anions is unacceptably poor. However, the catalyst composition of the present invention may contain small amounts of halide anion whilst retaining satisfactory selectivity. Such small amounts of halide ion may be present in the catalyst composition if for example it is prepared from the chloride salt of the catalyst cation. Preferably the amount of halide anion catalyst present in the catalyst composition is below 10% wt, more preferably below 5% wt, most preferably below 2% wt.

The organic cation of the catalyst composition may be an organic cation having a general formula [ARIR2R3R4]+ or [R1R2A=CR3~R5~R3C=ARIR2] 2+/wherein A is

a nitrogen, phosphorous, arsenic or antimony atom and wherein each of Rl to R4 independently represents a hydrogen atom or a hydrocarbyl group, provided that at least one of Rl to R4 represents a hydrocarbyl group, and wherein R5 represents an alkylene or a phenylene group.

When the organic cation of the catalyst composition is of general formula [AR1R2R3R4]+ or [R1R2A=CR3-R5- RC=AR-R] 2+, A is preferably a nitrogen or a phosphorous atom, most preferably a nitrogen atom. R5 is preferably an alkylene group, more preferably a methylene (-CH2-) or an ethylene (-CH2CH2-) group.

Examples of organic cations of general formula [ARIR2R3R4]+ or [RIR2A=CR3~R5~R3C=ARIR2]2+ which may conveniently be used in the catalyst compositions of the present invention include ammonium cations derived from amines selected from trialkyl amines, triaryl amines, alkyl diaryl amines, and aryl dialkyl amines; ammonium cations derived from aliphatic amines such a triethyl amines, trimethyl amines and triphenyl amines being preferred.

The organic cation of the catalyst composition is preferably a cation having a heterocyclic ring comprising at least one ring atom A', which at least one ring atom A'is a nitrogen, phosphorous, arsenic or antimony atom.

The at least one ring atom A'is preferably a nitrogen or a phosphorous atom.

A heterocyclic ring is a cyclic ring containing more than one kind of atom. An organic cation according to the present invention having a heterocyclic ring may be monocyclic (i. e. containing a single heterocyclic ring) or it may be polycyclic (i. e. containing two or more rings, at least one of which is heterocyclic).

More preferably, the organic cation of the catalyst composition has a heterocyclic ring comprising at least one ring atom A', which at least one ring atom A'is a nitrogen atom. The organic cation carries at least one positive charge and it is preferred that when the organic cation of the catalyst composition has a heterocyclic ring comprising at least one ring atom A', that the at least one ring atom A'carries the positive charge.

When the organic cation of the catalyst composition has a heterocyclic ring, the at least one ring atom A' may be optionally substituted. The at least one ring atom A'may carry a wide range of substituents. Examples of substituents that the at least one ring atom A'may conveniently carry include optionally substituted hydrocarbyl groups.

Preferably, the at least one ring atom A'of the catalyst composition carries at least one substituent which is a hydrocarbyl group having from 1 to 8 carbon atoms. Particularly preferred substituents that the at least one ring atom A'may carry are n-alkyl groups having from 1 to 8 carbon atoms, e. g. methyl, ethyl, propyl, butyl, pentyl, hexyl, heptyl and octyl groups.

When the organic cation of the catalyst composition comprises a heterocyclic ring, the heterocyclic ring may be substituted at atoms other than the at least one ring atom A'. For example, carbon atoms in the heterocyclic ring may conveniently be substituted with hydrocarbyl groups. For example, when the organic cation is a 1,3dialkyl imadazolium cation the 2 position of the heterocyclic ring may be conveniently substituted with an n-alkyl group having from 1 to 10 carbon atoms, more preferably 1 to 6 carbon atoms, most preferably a methyl or an ethyl group.

Examples of organic cations having a heterocyclic ring comprising at least one ring atom A'which may

conveniently be used in the catalyst compositions of the present invention include ammonium cations derived from heterocyclic amines, such as N-alkyl pyrroles, N-alkyl pyridines, N, N'-dialkyl imidazoles and N, N'-dialkyl pyrazoles; N-alkyl pyridines and N, N'-dialkyl imidazoles being preferred.

Preferably, the organic cation of the catalyst

composition of the present invention is a is a l-alkyl pyridinium or a 1, 3-dialkyl imidazolium cation, most preferably a 1,3-dialkyl imidazolium cation. Organic cations which may advantageously be employed in the catalyst composition of the present invention include 1butyl-3-methyl imidazolium, l-ethyl-3-methyl imidazolium, l-octyl-3-methyl imidazolium and 1-butyl-pyridinium cations.

The process of the present invention comprises reacting an alkylene oxide with water in a reaction medium comprising an ionic-liquid phase. An ionic-liquid to be employed in the ionic-liquid phase may be any compound consisting of ions only and which is substantially insoluble in water. Therefore, the reaction medium is heterogeneous comprising at least an aqueous phase and an ionic-liquid phase. More preferably, the process of the present invention comprises reacting an alkylene oxide with water in a bi-phasic reaction medium comprising an ionic-liquid phase and an aqueous phase.

Preferred ionic-liquids are those having a very low solubility in water as the lower the water solubility of the ionic-liquid the greater the phase separation between the ionic-liquid phase and the aqueous phase.

Accordingly, preferred ionic-liquids are liquids having a water content on saturation at 22 OC of less than 20% w/w, more preferably less than 15% w/w, even more

preferably less than 10% w/w and most preferably less than 5% w/w.

The ionic-liquids employed in the ionic-liquid phase of the present invention comprise an organic cation and an anion. The ionic-liquids are liquid at the reaction temperature to be used for the conversion of an alkylene oxide into an alkylene glycol, preferably having a

melting point below 100 C, more preferably below 20 C, even more preferably below 10 C, and most preferably below 0 C ; and they are thermally stable, preferably being stable up to a temperature of at least 150 C, more preferably at least 200 C, most preferably at least 250 C.

The anion of the ionic-liquid is preferably a fluorine-containing anion. Examples of fluorinecontaining anions which the ionic-liquid may advantageously comprise include hexafluorophosphate,

tetrafluorborate, triflate (CFgSO'), methide ( (CFSOsC)-), 2-bis (trifluoro-methanesulfonyl) imide ( (CFSO) N)'), and anions of general formula CFSO' wherein X is an integer of 1 or greater (e. g. nonaflate CFCFO'). Fluorine-containing anions are preferred as ionic-liquids comprising such anions have a low solubility in water.

The organic cation of the ionic-liquid employed in the ionic-liquid phase may be any cation which when combined with the anion of the ionic-liquid gives an ionic-liquid which is substantially insoluble in water. Conveniently, the organic cation of the ionic-liquid may be selected from the same organic cations described herein before with regard to the organic cation of the catalyst composition of the invention, with organic cations preferred as organic cations of the catalyst

composition being similarly preferred as organic cations of the ionic-liquid.

Thus, the organic cation of the ionic-liquid is preferably an organic cation having a heterocyclic ring comprising at least one ring atom A", which at least one ring atom All is a nitrogen, phosphorous, arsenic or antimony atom, preferably a nitrogen or phosphorous atom, most preferably a nitrogen atom. Whilst the at least one ring atom A", may carry a wide range of substituents, it is preferred that the at least one ring atom At'carries at least one substituent which is a hydrocarbyl group.

Preferably, the at least one ring atom A"of the ionic-liquid cation carries at least one substituent which is a hydrocarbyl group having from 1 to 8 carbon atoms. Particularly preferred substituents that the at least one ring atom A"of the ionic-liquid cation may carry are n-alkyl groups e. g. methyl, ethyl, propyl, butyl, pentyl, hexyl, heptyl and octyl groups.

Examples of organic cations having a heterocyclic ring comprising at least one ring atom A"which may conveniently be used in the ionic-liquid include organic cations derived from heterocyclic amines, such as N-alkyl pyrroles, N-alkyl pyridines, N, N'-dialkyl imidazoles and N, N'-dialkyl pyrazoles; N-alkyl pyridines and N, N'dialkyl imidazoles being particularly preferred.

More preferably, the organic cation of the ionic liquid is a l-alkyl pyridinium or a 1, 3-dialkyl imidazolium cation. Ionic-liquids containing these cations are preferred as they are stable in the reaction conditions and may have low solubility in water. Most preferably, the organic cation of the ionic-liquid is a 1, 3-dialkyl imidazolium cation.

The ionic-liquid preferably comprises a l-alkyl pyridinum or a l, 3-dialkyl imidazolium cation and a fluorine-containing anion. Examples of ionic-liquids

which may advantageously be employed in the ionic-liquid phase of the present invention include, l-octyl-3-methyl

imidazolium hexafluorophosphate, 1-butyl-3-methyl imidazolium hexafluorophosphate, l-butyl pyridinium hexafluorophosphate and 1-butyl pyridinium tetrafluoroborate.

The ionic-liquids of the present invention may be prepared by any convenient method. For example, ionicliquids carrying alkyl substituents may be prepared by alkylating a nitrogen, phosphorous, arsenic or antimony containing compound with an alkyl halide, or alkyl tosylate, to produce a salt. The salt is then converted to the ionic-liquid by anion exchange, either by treatment with an acid e. g. tetrafluoroboric or hexafluorophosphoric acid; or by mixing with an anion exchange resin loaded with the desired anion, e. g. triflate, imide or methide anions. Alternatively, the ionic-liquid may be prepared by mixing a chloride or bromide salt of the ionic-liquid cation with an alkali metal salt or ammonium salt of the ionic-liquid anion.

Ionic-liquids having cations carrying substituents other than alkyl groups may be prepared by analogous methods.

Conveniently, the organic cation of the ionic-liquid will be of a type similar to the organic cation of the catalyst composition. For example, where the organic cation of the ionic-liquid is an N-alkyl pyridinium cation it is preferred that the organic cation of the ionic-liquid be an N-alkyl pyridinium cation; and when the organic cation of the ionic-liquid is an N, N'-dialkyl imidazolium cation it is preferred that the organic cation of the ionic-liquid be a N, N'-dialkyl imidazolium cation. Conveniently, the cation of the catalyst composition and the cation of the ionic-liquid may be the same.

Ionic-liquids of the type utilised in the process of the present invention are either known and commercially available from a variety of sources, or are easily preparable by, or analogously to, published techniques.

The commercial sources of such ionic-liquids include Solvent Innovation (Aachen), Sachem (Austin, Texas), and Fluka. Synthesis of such ionic-liquids may be carried out by, or analogous to, the methods described by Suarez et al., Polyhedron 15 (1996) 1217, or Bonhote et al., Inorg. Chem. 35 (1996) 1168.

The use of a heterogeneous reaction medium comprising an ionic-liquid phase, as provided by the present invention, allows alkylene oxides to be converted to alkylene glycols at both a good rate of conversion and with a high selectivity to monoalkylene glycol, giving results approaching or superior to those obtained using conventional catalysts such as sodium bicarbonate in homogeneous, aqueous phase, reaction systems. A preferred feature of the process is that less salts accumulate during the reaction than in other catalytic systems, facilitating the purification of the alkylene glycol product from the aqueous phase. A still further preferred feature is that as the process is bi-phasic, comprising an ionic-liquid phase and an aqueous phase, there is the potential for the products and the catalyst to be easily separated by the development of a catalyst which resides predominantly in the ionic-liquid phase.

The catalyst compositions developed for use in combination with an ionic-liquid phase in accordance with the present invention have also been found to act as efficient catalysts for the conversion of alkylene oxides into alkylene glycols in the absence of an added ionicliquid in the reaction medium.

Accordingly, a further embodiment of the present invention provides a process for preparing an alkylene

glycol which comprises reacting an alkylene oxide with water in the presence of a catalyst composition which comprises an organic cation and an anion other than a halide anion, wherein the organic cation has a heterocyclic ring comprising at least one ring atom A', which at least one ring atom A'is a nitrogen, phosphorous, arsenic or antimony atom. In this further embodiment the reaction medium preferably comprises no added ionic-liquid. Organic cations having a heterocyclic ring atom A'whch were described herein before as being preferred organic cations for a catalyst composition to be employed when the reaction medium comprises an ionic-liquid phase are similarly preferred as organic cations to be employed in the catalyst composition of this further embodiment.

The alkylene oxides, used as starting materials in the process of the present invention, have their conventional definition, i. e. they are compounds having a vicinal oxide (epoxy) group in their molecules.

Preferred alkylene oxides are alkylene oxides of the general formula

wherein each of R6 to R9 independently represents a hydrogen atom or an optionally substituted alkyl group having from 1 to 6 carbon atoms. Any alkyl group, represented by R6, R7, R8 and/or R9, preferably has from 1 to 3 carbon atoms. Optional substituents on the alkyl groups are inactive moieties such as hydroxy groups.

Preferably, R6, R7, and R8 represent hydrogen atoms and R9 represents a non-substituted alkyl group having from 1

to 3 carbon atoms and, more preferably, R6, R7, RB and R9 all represent hydrogen atoms.

Examples of alkylene oxides which may conveniently be employed include ethylene oxide, propylene oxide, 1,2epoxybutane, 2,3-epoxybutane and glycidol. The alkylene oxide is preferably ethylene oxide or propylene oxide, most preferably ethylene oxide; ethylene glycol and propylene glycol being alkylene glycols of particular commercial importance.

The process of the present invention is preferably performed without using excessive amounts of water. In the process according to the present invention, the amount of water is preferably in the range of from 1 to 15 moles per mole of alkylene oxide, more preferably in the range from 1 to 6. In the process of the invention high selectivities with respect to the monoalkylene glycol are often achieved when only 4 to 6 moles of water per mole of alkylene oxide are supplied.

The process of the invention may be carried out in batch operation or, in particular for large scale embodiments, the process can be operated continuously.

In order to obtain improved rates of conversion, the process of the present invention may be performed under elevated temperature and/or pressure conditions.

Preferred reaction temperatures are in the range of

from 50 to 200 C, more preferably in the range of from 70 to 150 C. When the reaction is performed under pressure, the pressure is conveniently in the range of from 200 to 3000, more conveniently 200 to 2000 kPa. For batch operations of the process, the selected reaction pressure is advantageously obtained by pressurizing with an inert gas, such as nitrogen. If desired, mixtures of gases may be used, for example a mixture of carbon

dioxide and nitrogen is in certain instances advantageous.

When the reaction medium comprises an ionic-liquid, the volume/volume ratio of water to ionic-liquid present in the reaction medium is preferably in the range of from 10: 1 to 1: 2, more preferably 6: 1 to 1: 1.

The present invention further provides a catalyst composition which comprises an organic cation and an anion other than a halide anion, wherein the organic cation has a heterocyclic ring comprising at least one ring atom A', which at least one ring atom A'is a nitrogen, phosphorous, arsenic or antimony atom; preferred catalyst compositions as described herein before with respect to the process of the present invention being similarly preferred as the catalyst composition provided by the present invention.

The catalyst compositions of the present invention may be prepared by any convenient method. For example, the catalyst composition may be prepared by mixing a chloride salt of the organic cation of the catalyst composition with a anion exchange resin loaded with bicarbonate anions. Chloride salts of the organic cation of the catalyst composition, for example 1-butyl-3methylimidazolium chloride, are obtainable from Solvent Innovation, Aachem, or may be prepared by the methods, or by analogous methods, to those described hereinbefore for the synthesis of the ionic-liquids.

The invention will be further understood from the following illustrative examples.

Catalyst compositions in accordance with the present invention were prepared as follows. In the preparations that follow, all reactions were carried out at ambient temperature (20 OC), unless otherwise stated. Reagents and solvents were obtained from commercial suppliers and used without further purification.

l-Butyl-3-methylimidazolium chloride (bmim. Cl), 1butyl-3-methylimidazolium hexafluorophosphate (bmim. Pop6), and 1-octyl-3-methylimidazolium chloride (omim. Cl), were obtained from Solvent Innovation, Aachen.

l-Octyl-3-methylimidazolium hexafluorophosphate (omim. PF6) was prepared by adding an aqueous solution of omim. Cl (23.1 g) in water (50 ml) to a stirred aqueous solution (100 mL) of NaPF6 (16.8 g) (ex. Aldrich) at 70 OC over a period of from 5 to 10 minutes. Following addition the reaction mixture was stirred for another 10 minutes and then cooled to room temperature. The mixture was transferred to a separatory funnel and the (lower) ionic liquid layer separated and subsequently washed 3 times with water (100 ml each). The resultant omim. PF6 was dried in vacuo at 70 OC to yield 25. 5 g of product.

Amounts of residual bmim. Cl and omim. Cl in the catalysts were measured by combustion microcoulometric analysis. bmim. HC03 1-Butyl-3-meth. ylimidazolium bicarbonate (bmim. HC03) A commercially available chloride loaded anion exchange resin was stirred with an excess of saturated sodium bicarbonate solution for 1 hour. The solution was then filtered and the filtrate washed with water until its pH was neutral. The resin was air-dried using a vacuum pump to yield a bicarbonate loaded anion exchange resin (IER. HC03), having a water content of 50 to 60 % wt, and approximately 1.2 eq/Kg of bicarbonate anions.

A solution of l-butyl-3-methylimidazolium chloride (bmim. Cl) (2. 0g) in water (10 ml) was added to a slurry of the IER. HC03 (25g) prepared above in water (90 ml) and the resulting mixture stirred for 15 minutes and then filtered. The filtrate was collected and added to a fresh

batch of IER. HCO3 (25g) in water (90 ml). This procedure was repeated five times, after which the filtrate was recovered and dried in vacuo at a temperature of 70 C. Before the filtrate was fully dried, the external heating was removed and the remaining water removed at ambient temperature to yield bmim. HC03 as a yellow viscous oil.

The residual quantity of bmim. Cl was approximately 8% wt. bmim. HC03 (no detectable bmim. Cl) A column of bicarbonate loaded anion exchange resin (IER. HC03) (300ml) was prepared by eluting at least a 10 fold excess of sodium bicarbonate solution through a chloride loaded anion exchange resin, and washing with water. The column was charged with an aqueous solution of l-butyl-3-methylimidazolium chloride (bmim. Cl) (lOg) and eluted with water. After being eluted through the column, the water was removed by evaporation at a temperature of 70 C. Before the filtrate was fully dried, the external heating was removed and the remaining water removed at ambient temperature to yield bmim. HC03 as a yellow viscous oil. The bmim. HC03 contained no detectable bmim. Cl. omim. HCO- 1-Octyl-3-methylimidazolium bicarbonate (omim. HC03) l-Octyl-3-methylimidazolium bicarbonate (omin. HC03), was prepared in an analogous manner to that described above for bmim. HCO3, except that the column of bicarbonate loaded exchange resin was charged with an aqueous solution of 1-octyl-3-methylimidazolium chloride (omim. Cl) (15g). The resultant omim. HC03 contained no detectable bmim. Cl.

(bmim) 2. Mo04- l-Butyl-3-methylimidazolium molybdate ( (bmim) 2. Mo04)

1-Butyl-3-methylimidazolium molybdate ( (bmim) . MoO, was prepared in an analogous method to that described above for bmim. HCOg, except that an aqueous solution of 1-butyl-3-methylimidazolium chloride (bmim. Cl) (1. 25g) was eluted through a column filled with molybdate loaded anion exchange resin (IER. Mo04). The resultant (bmim) 2. MoO4 contained no detectable bmim. Cl. The molybdate loaded anion exchange resin (IER. MoO4) was prepared by eluting an aqueous sodium molybdate solution through a column of chloride loaded anion exchange resin, and then washing with water. bmim. HC02

I-But I-Butyl-3-methylimidazolium formate (bmim. HC02) 1-Butyl-3-methylimidazolium formate (bmim. Hic02 was prepared in an analogous method to that described above for bmim. HC03, except that the an aqueous solution of 1butyl-3-methylimidazolium chloride (bmim. Cl) (lOg) was eluted through a column filled with formate loaded anion exchange resin (IER. Ho2). The resultant bmim. HC02 contained 0-9 wt % bmim. Cl. The formate loaded anion exchange resin (IER. HC02) was prepared by eluting a molar solution of formic acid through a column of bicarbonate loaded anion exchange resin, and then washing with water.

Example 1: Ethylene oxide hydration in the presence of bmim. HC03 and an added ionic-liquid (bmim. PF6).

A titanium headed sapphire high pressure NMR tube was loaded with 1-butyl-3-methylimidazolium hexafluorophosphate (bmim. PF6) ionic-liquid (0.5 ml) and a solution of bmim. HC03 (1. 5 mmol), which contained approximately 8% wt of bmim. Cl, dissolved in a 20: 80 v: v mixture of 20/H20 (3 ml). The NMR tube was cooled in an

ice bath and ethylene oxide (1. 5 ml) was introduced (condensed) into the tube. The water/ethylene oxide molar ratio was 5.5/1.

The NMR tube was sealed and brought into a NMR probe. After heating to 80 C, the 13C-NMR spectra were recorded every 30 minutes and the conversion of ethylene oxide to ethylene glycol was calculated from the decrease of the signal at 42 ppm and the increase of the signals at 63 ppm (mono-ethylene glycol [MEG]) and 61 ppm (diand tri-ethylene glycol [DEG and TEG]). The 13C-NMR spectra were measured on a Varian Inova 400 MHz instrument.

From this data a conversion vs time plot was made and an apparent rate constant calculated for the reaction. For the purposes of calculating the rate constant the reaction was taken to have a pseudo first order rate constant. The apparent rate constant and selectivity of the reaction to MEG is shown in Table 1.

The conversion of ethylene oxide after 4 hours was 96 %.

Example 2: Ethylene oxide hydration in the presence of bmim. HCO3.

Ethylene oxide was converted into ethylene glycol using bmim. HC03 in an analogous manner to that described in Example 1, with the exception that no 1-butyl-3methylimidazolium hexafluorophosphate (bmim. PF6) ionicliquid was included in the reaction mixture.

The apparent rate constant and selectivity of the reaction to MEG is shown in Table 1. The conversion of ethylene oxide after 3 hours was 95 %.

Example 3: Ethylene oxide hydration in the presence of bmim. HC03 and an added ionic-liquid (bmim. PF6) Ethylene oxide was converted to ethylene glycol in an analogous manner to that described in Example 1, with the

exception that the bmim. HC03 contained no detectable bmim. Cl.

The apparent rate constant and selectivity of the reaction to MEG is shown in Table 1. The conversion of ethylene oxide after 5 hours was 83%.

Example 4: Ethylene oxide hydration in the presence of bmim. HC03 Ethylene oxide was converted to ethylene glycol in an analogous manner to that described in Example 3, except that no 1-butyl-3-methylimidazolium hexafluorophosphate (bmim. PF6) ionic liquid was included in the reaction mixture.

The apparent rate constant and selectivity of the reaction to MEG is shown in Table 1. The conversion of ethylene oxide after 5 hours was 92 %.

Comparative Example A: Ethylene oxide hydration without added catalyst or ionic-liquid.

In a comparative example, ethylene oxide was converted into ethylene glycol in an analogous manner to that described in Example 1, with the exception that no catalyst composition was employed and no ionic-liquid was included in the reaction mixture.

The apparent rate constant and selectivity of the reaction to MEG is shown in Table 1. The conversion of ethylene oxide after 23 hours was 87 %.

Comparative Example B: Ethylene oxide hydration in the presence of NaHC03.

In a comparative example, ethylene oxide was converted into ethylene glycol in an analogous manner to that described in Example 1, with the exception that sodium bicarbonate (1.5 mmol) was employed as the catalyst in place of bmim. HC03 and no 1-butyl-3methylimidazolium hexafluorophosphate (bmim. PF6) ionicliquid was included in the reaction mixture.

The apparent rate constant and selectivity of the reaction to MEG is shown in Table 1. The conversion of ethylene oxide after 6 hours was 81 %.

Comparative Example C: Ethylene oxide hydration in the presence of an ionic-liquid (bmim. PF6) and without added catalyst.

In a comparative example, ethylene oxide was converted into ethylene glycol in an analogous manner to that described in Example 1, with the exception that no catalyst was employed.

The apparent rate constant and selectivity of the reaction to MEG is shown in Table 1. The conversion of ethylene oxide after 5.5 hours was 15 %.

Comparative Example D: Ethylene oxide hydration in the presence of NaHC03 and an ionic-liquid (bmim. Pi6).

In a comparative example, ethylene oxide was converted into ethylene glycol in an analogous manner to that described in Example 1, with the exception that sodium bicarbonate (1.5 mmol) was employed as the catalyst in place of bmim. HCOg.

The apparent rate constant and selectivity of the reaction to MEG is shown in Table 1. The conversion of ethylene oxide after 6 hours was 66 %.

Comparative Example E: Ethylene oxide hydration in the presence of bmim. Cl and an ionic-liquid (bmim PF6).

In a comparative example, ethylene oxide was converted into ethylene glycol in an analogous manner to that described in Example 1, with the exception that bmim. Cl (1.5 mmol) was employed as the catalyst in place of bmim. HC03.

The apparent rate constant and selectivity of the reaction to MEG is shown in Table 1. Two rate constants are given, a rate constant for first two hours of reaction (tao to t=2) and a rate constant for the second

two hours of reaction (t=2 to t=4). Two rate constants are given as the reaction rate accelerated significantly after two hours. The conversion of ethylene oxide after 4 hours was 95%, but the selectivity to the desired monoethylene glycol was extremely poor.

Example 5: Ethylene oxide hydration in the presence of omim. HC03 and an added ionic-liquid (omim. PF6) Ethylene oxide was converted to ethylene glycol in an analogous manner to that described in Example 1, except that an omim. HC03 catalyst was used in place of bmim. HCO3, and that the ionic liquid was 1-octyl-3- methylimidazolium hexafluorophosphate (omim. Pi6). The omim. HC03 contained no detectable bmim. Cl.

The apparent rate constant and selectivity of the reaction to MEG is shown in Table 1. The conversion of ethylene oxide after 5 hours was 96 %.

Example 6: Ethylene oxide hydration in the presence of (bmim) 2. Mo04 and an added ionic-liquid (bmim. PF6) Ethylene oxide was converted to ethylene glycol in an analogous manner to that described in Example 1, except that a (bmim) 2. Mo04 catalyst was used in place of bmim. HCO3. The (bmim) 2. Mo04 contained no detectable bmim. Cl.

The apparent rate constant and selectivity of the reaction to MEG is shown in Table 1. The conversion of ethylene oxide after 5 hours was 84 %.

Example 7: Ethylene oxide hydration in the presence of bmim. HC02 and an added ionic-liquid (bmim. PF6) Ethylene oxide was converted to ethylene glycol in an analogous manner to that described in Example 1, except that a bmim. HC02 catalyst was used in place of bmim. HCO3.

The bmim. HC02 had a bmim. Cl content of 0.9 wt %.

The apparent rate constant and selectivity of the reaction to MEG is shown in Table 1. The conversion of ethylene oxide after 5 hours was 42 %.

TABLE 1

Example Catalyst Ionic-liquid Rate Constanta Selectivity b K (h)-1 (%) 1 bmim.HCO3f bmin.PF6 0.82 88 2 bmim.HCO3f NONE 1.04 88 3 bmim.HCO3g bmim.PF6 0.34 92 4 bmim. HC03 9 NONE 0. 51 91 Comp. A NONE NONE 0.03 64 Comp. B NaHC03 NONE 0.25 89 Comp. C NONE bmin. PF6 0. 03 90 Comp. D NaHC03 bmin. PF6 0. 16 91 Comp. E bmim. Cl bmim. PF6 0. 27 : 1. 35e 19 5 omim. HC03 omim. PF6 0.64 89 6 (bmim) 2. Mo04 bmim. PF6 0.35 92 7 bmim. HC02 bmim. PF6 0.11 84 a) pseudo first order rate constant b) selectivity is 100 x MEG/ (l MEG + 2 DEG + 3 TEG) c) conversion is 100 x (EOt=0 - EOt)/EOt=0 e) rate constant (t=O to t=2) : (t=2 to t=4) f) contains approximately 8% wt bmim. Cl g) contains no detectable bmim. Cl

From Examples 1 and 3 it can be seen that with the process of the present invention it is possible to convert an alkylene oxide to an alkylene glycol in a reaction medium comprising an ionic-liquid phase at a fast rate of reaction and with a good selectivity to mono-ethylene glycol; the reaction of Examples 1 and 3 having a far superior reaction rate to that obtained using sodium bicarbonate as the catalyst (comparative example D) or with no added catalyst (comparative example C). Whilst the reaction rate of Example 3 (no detectable bmim. Cl) was lower than that of Example 1, it had a higher selectivity. When a catalyst having solely a halide anion was employed (comparative example E), the selectivity to mono-ethylene glycol was very poor.

Further, from Examples 2 and 4 it can be seen that the catalysts of the present invention also give excellent performance in the absence of an added ionicliquid, displaying both a faster reaction rate and a better selectivity than that obtained using sodium bicarbonate as the catalyst (comparative example B), or with no catalyst at all (comparative example A).

Examples 5 to 7 demonstrate the utility of the present invention using a range of anion types, and cations/ionic-liquids.

Claims

CLAIMS 1. Process for preparing an alkylene glycol by reacting an alkylene oxide with water in a reaction medium comprising an ionic-liquid phase and in the presence of a catalyst composition which comprises an organic cation and an anion other than a halide anion, wherein the

organic cation is selected from i) cations of general formula [ARIR2R3R4]+ or [RRA=CR-R-RC=ARR] wherein A is a nitrogen, phosphorous, arsenic or antimony atom ; wherein each of Rl to R4 independently represents a hydrogen atom or a hydrocarbyl group, provided that at least one of Rl to R4 represents a hydrocarbyl group ; and wherein R5 represents an alkylene group or a phenylene group ; and ii) cations having a heterocyclic ring comprising at least one ring atom A', which at least one ring atom A'is a nitrogen, phosphorous, arsenic or antimony atom.
2. Process according to claim 1 wherein the organic cation of the catalyst composition has a heterocyclic ring comprising at least one ring atom A', which at least one ring atom A'is a nitrogen atom.
3. Process according to claim 1 or claim 2, wherein the at least one ring atom A'carries at least one substituent which is a hydrocarbyl group having from 1 to 20 carbon atoms.
4. Process according to any one of claims 1 to 3, wherein the organic cation of the catalyst composition is a l-alkyl pyridinium or a 1, 3-dialkyl imidazolium cation.

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5. Process according to any one of claims 1 to 4, wherein the organic cation of the catalyst composition is a l, 3-dialkyl imidazolium cation.
6. Process according to any one of claims 1 to 5, wherein the ionic-liquid phase comprises an ionic-liquid comprising a l-alkyl pyridinium or a l, 3-dialkyl imidazolium cation and a fluorine-containing anion.
7. Process according to any one of claims 1 to 6, wherein the anion of the catalyst composition is a bicarbonate and/or a carbonate anion.
8. Process for preparing an alkylene glycol by reacting an alkylene oxide with water in the presence of a catalyst composition which comprises an organic cation and an anion other than a halide anion, wherein the organic cation is selected from cations having a heterocyclic ring comprising at least one ring atom A', which at least one ring atom A'is a nitrogen, phosphorous, arsenic or antimony atom.
9. Process according to any one of claims 1 to 8 wherein the alkylene oxide is ethylene oxide.