WO2018178300A1

WO2018178300A1 - Extraction of carbon dioxide from gas

Info

Publication number: WO2018178300A1
Application number: PCT/EP2018/058218
Authority: WO
Original assignee: Ecole Polytechnique Federale De Lausanne (Epfl)
Priority date: 2017-03-31
Filing date: 2018-03-29
Publication date: 2018-10-04
Also published as: EP3600610A1

Abstract

The present invention relates to a method for removing carbon dioxide from gases. Further, the invention relates to a method for preparing organic cyclic carbonates by reacting the carbon dioxide contained in a gas at ambient pressure with an epoxide in the presence of an ionic liquid.

Description

Extraction of carbon dioxide from gas

Background of the invention The concentration of carbon dioxide in the atmosphere is at an all-time high, as a direct consequence of human activity, leading to anthropogenic climate change. Reducing dependence on fossil fuels in is key to reducing carbon dioxide emissions, and carbon dioxide sequestration and utilization have also emerged as approaches that can also significantly lower the carbon dioxide levels in the atmosphere. In this respect, several strategies have been proposed, which mainly involved capture and storage, either underground or undersea. Recently, several capture techniques have been employed on large scale which mainly rely on the affinity of carbon dioxide for basic compounds like hydroxides or polyamines. Carbon engineering (http://carbonengineering.com/our-technology/) describes a technique to extract carbon dioxide from air and the subsequent provision of a stream of a pressurized and purified carbon dioxide. Said technique relies on the capture of carbon dioxide from the air via a base, namely potassium hydroxide (KOH).US 2014/0102297 Al relates to a technique for removing carbon dioxide from gas streams containing several gases, such as exhaust gases produced by internal combustion engines. For the selective removal of carbon dioxide, the technique relies on a specific membrane, a facilitated transport membrane and a subsequent steam sweeping technology to facilitate removal of the carbon dioxide taken up by the membrane. The carbon dioxide obtained by this technique can further be stored in its purified form with the corresponding storage means. The obtained carbon dioxide is generally stored in its pressurized form and thus still increases the instrumental effort and the costs of the above techniques. In parallel, carbon dioxide was proposed as a building block for the synthesis of valuable chemical compounds such as cyclic carbonates (l,3-dioxolan-2-ones). Cyclic carbonates are compounds of particular interest due to their use in different technical fields for example as electrolytes in lithium batteries, as solvents or as starting material for polycarbonates used as plastic for example in bottles and containers. Jiajian Peng and Youquan Deng, New J. Chem., 2001 , 25, pp. 639-64, describe processes in which ethylene carbonate (l,3-dioxolan-2-one) and propylene carbonate (4-methyl-l ,3- dioxolan-2-one) are obtained by a reaction from ethylene oxide or propylene oxide with carbon dioxide. However, this reaction relies on pure, pressurized carbon dioxide, which use requires specific equipment like an autoclave, pressure-resistant glassware and of course a high-pressure cylinder as source for carbon dioxide.

JP 5 851350 B2 relates to a method for refining carbon dioxide, according to which a carbon dioxide absorption step to generate a cyclic carbonate compound by reacting an intramolecular dehydrohalogenated compound of a compound having a hydroxyl group and a halogen group in an intramolecular basic skeleton with carbon dioxide and a carbon dioxide regeneration step to generate carbon dioxide by decomposing the cyclic carbonate compound at a higher temperature than the decomposition temperature of a cyclic carbonate structure in the cyclic carbonate compound and at a lower temperature than the decomposition temperature of the basic skeleton are performed in order.

WO 2016/203408 Al relates to a method of making a polymer, more particularly a polycarbonate, comprising contacting one or more cyclic monomers and carbon dioxide in the presence of one or more of a Lewis acid catalyst, an initiator, and an ionic liquid; and agitating, sufficient to copolymerize the one or more cyclic monomers and carbon dioxide to create a polycarbonate. The reaction is substantially carried out in an autoclave with carbon dioxide at 10 atmospheres and in the presence of an organic solvent.

Thus, there is a need for a method for removing carbon dioxide from a gas which can be applied in a simple and effective manner. It was an object of the present invention to provide a method for removing carbon dioxide from a gas which is compatible with gases containing small amounts of carbon dioxide as well as with gases containing higher amounts of carbon dioxide such as flue or waste gas. Further, said method should provide a direct transformation of carbon dioxide from the gas to prevent the further treatment of pressurizing the obtained carbon dioxide. The method should provide a substantially complete removal of the carbon dioxide from a gas such as ambient air to provide a carbon dioxide-free gas which is of particular interest for environmental reasons as well as for chemical reasons when conducting reactions with ambient air to prevent possible side reactions with the carbon dioxide generally contained therein.

Further, it was an object of the present invention to provide a method for preparing a cyclic carbonate which can for example be carried out with the carbon dioxide available in the ambient air. Moreover, a method for preparing a cyclic carbonate should be provided that does not require the use of pure and pressurized carbon dioxide and the high instrumental complexity involved therewith. In particular, prior sequestration or purification techniques should be avoided.

In particular, a method should be provided that removes carbon dioxide from a gas and simultaneously enables the preparation of cyclic carbonates at ambient pressure.

According to the present invention, the above objectives are achieved by the specific methods as described herein for the removing carbon dioxide from a gas and the specific method for preparing a cyclic carbonate.

Summary

The present invention has unexpectedly solved the above objectives by the provision of a new method for removing carbon dioxide from a gas by contacting the gas with a liquid mixture comprising epoxide and ionic liquid. In addition, a method could be provided for preparing a cyclic carbonate by contacting a gas containing carbon dioxide provided at ambient pressure with a liquid mixture comprising epoxide and ionic liquid and allowing the carbon dioxide contained in the gas to react with the epoxide to give the cyclic carbonate.

Thus, the subject of the present invention is a method for removing carbon dioxide from a gas comprising the steps of

(i) providing a gas comprising carbon dioxide at ambient pressure,

(ii) contacting the gas with a liquid mixture comprising epoxide and ionic liquid, (iii) allowing the carbon dioxide to react with the epoxide.

Gases or gas streams containing carbon dioxide are widely known. For example, the atmosphere of the earth can be regarded as the mixture of gases surrounding our planet and is commonly known as air. The carbon dioxide content is reported to be about 0.04% by volume. Further, carbon dioxide is obtained for example during the combustion of organic material. Examples for further gases containing carbon dioxide are waste gas from internal combustion machines, waste gas from energy plants, industrial waste gases such as flue gas or gases from fermentation processes. The latter named gases are reported to contain significantly higher carbon dioxide contents. Internal combustion machines for oil are reported to have carbon dioxide contents of more than 15% by volume.

Step (i) of the present invention is the provision of a gas comprising carbon dioxide at ambient pressure.

In step (i) any gas comprising carbon dioxide can be used. For example, the atmosphere of the earth can be regarded as the mixture of gases surrounding our planet and commonly known as air. Air is reported to contain a certain content of carbon dioxide. Further examples are gases comprising carbon dioxide which can for example be obtained by the combustion or fermentation of organic material. Examples for such gases containing carbon dioxide are waste gas from internal combustion machines, waste gas from energy plants, industrial waste gases such as flue gas or gases from fermentation processes. These gases are reported to contain significantly higher carbon dioxide contents than the air.

In step (i) the gas comprising carbon dioxide is provided at ambient pressure. Ambient pressure can also be referred to as surrounding pressure. For example in case the surrounding pressure is caused by the weight of air it is referred as atmospheric pressure. Further, the atmospheric pressure varies with altitude, for example the atmospheric pressure of air at sea level is 101325 Pa (1 atmosphere), while the atmospheric pressure of air at an altitude of 5486.4 meters (18Ό00 feet) is 50663 Pa (1/2 atmosphere). In addition, the atmospheric pressure varies with weather conditions, such as high pressure and low pressure areas.

In view of the above, the ambient pressure depends on different conditions. In this application, providing a gas comprising carbon dioxide at ambient pressure excludes providing the gas under pressurized conditions. Pressurized conditions are conditions under which a gas is compressed to a smaller volume, thereby increasing its density. Examples are pressurized gases in high pressure containers.

Gases like air can further comprise water in vaporous form, which can be referred to as air moisture or humidity. One measurement of humidity is the relative humidity, which depends on the temperature. The relative humidity measures the current absolute humidity relative to the maximum humidity for a specific temperature. The relative humidity φ is expressed in per cent and calculated by the following equation:

with

/being current absolute humidity; and fmax being maximum humidity at that temperature.

The relative humidity can for example be determined by a hygrometer such as a hair hygrometer.

A very common value for relative humidity of ambient air at 20°C, for example in Germany, is about 50%.

In a preferred embodiment the gas comprising carbon dioxide provided in step (i) is substantially free of water. In this application a gas being substantially free of water can be referred to as having a relative humidity of less than 5%, preferably less than 2%, more preferably less than 0.5%. In a particularly preferred embodiment the relative humidity of the gas comprising carbon dioxide is 0%, i.e. the gas does not contain water. Gases having a relative humidity of less than 5% can be regarded as dry gases. Drying of a gas can be conducted by contacting the gas with a desiccant. A desiccant is a substance able to bind water, for example either by physically absorbing water or reacting with water. Drying can preferably be conducted by directing gas over or through a desiccant, such as a molecular sieve, bentonite, silica gel and or by reacting the water with a desiccant, such as concentrated sulfuric acid, for example by blubbing it through said acid.

In step (ii) of the present method the gas from step (i) is contacted with the liquid mixture comprising epoxide and ionic liquid. Bringing the gas from step (i) in contact with the liquid mixture comprising epoxide and ionic liquid is meant as conducting any method for contacting the gas from step (i) with at least the surface of the liquid mixture comprising epoxide and ionic liquid. Thus, contacting the gas from step (i) with a liquid mixture comprising epoxide and ionic liquid can for example be conducted by bubbling the gas through the liquid mixture, sucking the gas into the liquid mixture, vortex the liquid mixture to contact the gas. In step (ii) the liquid mixture comprises epoxide and ionic liquid. An epoxide is a cyclic compound which is characterized by a ring in which an oxygen atom is bonded via two single bonds to two carbon atoms which are bonded by a single bond to each other. An epoxide can be represented by the following chemical formula

Epoxide, wherein R¹, R², R³ and R⁴ are independently hydrogen or an organic residue. The three- membered ring of the epoxide is strained and thus epoxides are considered to be more reactive than other ethers. Further, epoxide also comprises compounds containing more than one ring in which an oxygen atom is bonded via two single bonds to two carbon atoms (epoxy group). The term "organic residue" generally refers to a residue known in organic chemistry. Preferably, the skeleton of the organic residue contains predominately carbon atoms, nitrogen atoms and/or oxygen.

In a preferred embodiment of the invention the atom of the residues R¹, R², R³ and R⁴, which is covalently bonded to one of the carbon atoms of the three-membered ring, is hydrogen or a carbon atom. It is preferred that at least one of R¹, R², R³ and R⁴ is hydrogen.

In a preferred embodiment of the invention R¹, R², R³ and R⁴ can be an aromatic residue or an aliphatic residue.

An aromatic residue includes at least one ring system predominately containing carbon, nitrogen, sulphur or oxygen atoms, wherein said ring system comprises, according to the Hiickel-Rule, a number of 4n+2 (n=0, 1 , 2,...) delocalized electrons in conjugated double bonds, free electron-pairs or unoccupied p-orbitals.

In a preferred embodiment of the invention an aromatic residue refers to a residue with an aromatic skeletal structure, wherein the ring atoms of the aromatic skeletal structure are carbon atoms. In an alternatively preferred embodiment the aromatic residue can be substituted with one or more substituents.

Substituents can preferably be selected independently from one or more of the following substituents: alkyl groups with 1 to 4 carbon atoms, halogen, nitro, nitrile, carboxylic group, carboxylic esters and carboxylic amide, methoxy and ethoxy.

Examples for aromatic residues are phenyl, o-tolyl and p-tolyl. In a more preferred embodiment R¹, R², R³ and R⁴ is an aliphatic residue. An aliphatic residue is a non-aromatic hydrocarbon compound which can comprise, apart from carbons and hydrogen atoms, for example also oxygen, sulphur and nitrogen atoms. The aliphatic residue might be substituted or unsubstituted. The same as described above with regard to the aromatic residue can be applied to the substituents, wherein the aliphatic residue can be further substituted with an unsubstituted or substituted aromatic residue.

Examples of epoxide are for example oxirane, methyloxirane, ethyloxirane, oxiran-2- ylmethanol, 2-vinyloxirane, 2-allyloxirane, 2-(chloromethyl)oxirane, 2-phenyloxirane, 2-benzlyloxirane 2,2'-(4,4'-(propane-2,2-diyl)bis(4,l-phenylene))bis(oxy)bis- (methylene)dioxirane.

In a preferred embodiment of the invention the epoxide has a boiling point of 40°C to 350°C, more preferably of 42°C to 320°C, in particular of 45°C to 300°C. Preferably, the temperature is determined at 1013 mbar. In this application a "boing point of 40° to 350°C" also encompasses those epoxides that undergo decomposition in said temperature range. Further, the boiling point is not related to a single temperature but can also refer to a temperature interval, for example when a mixture of epoxide is used. It is preferred that in step ii) of the present method the epoxide is selected from a compound according to one of Formulae E(I)-E(XIII)

E(XIII), and mixtures thereof.

The chemical name of the compound according to Formula E(I) is 2,2' -bioxirane.

The chemical name of the compound according to Formula E(II) is 2-(chloro- methyl)oxirane (also known as epichlorohydrin). The chemical name of the compound according to Formula E(III) is 2-(allyloxy- methyl)oxirane (also known as allyl glycidyl ether).

The chemical name of the compound according to Formula E(IV) is 1 ,4-di(oxiran-2- yl)butane.

The chemical name of the compound according to Formula E(V) is 1 ,4-bis(oxiran-2- yl)methoxy)butane. The chemical name of the compound according to Formula E(VI) is bis(oxiran-2- ylmethyl) cyclohexane-1 ,2-dicarboxylate.

The chemical name of the compound according to Formula E(VII) is 2-phenyloxirane. The chemical name of the compound according to Formula E(VIII) is 3-(benzyloxy)oxirane (also known as phenyl glycidy ether).

The chemical name of the compound according to Formula E(IX) is ethyl 3-methyl-3- phenyloxirane-2-carboxylate.

The chemical name of the compound according to Formula E(X) is l,3-bis(oxiran-2- ylmethoxy)benzene.

The chemical name of the compound according to Formula E(XI) is bis(4-(oxiran-2- ylmethoxy)phenyl)methane.

The chemical name of the compound according to Formula E(XII) is 2,2'-(4,4'-(propane- 2,2-diyl)bis(4,l-phenylene))bis(oxy)bis(methylene)dioxirane (also known as bisphenol A diglycidyl ether). The chemical name of the compound according to Formula E(XIII) is tris(4-(oxiran-2- ylmethoxy)phenyl)methane.

An ionic liquid is a compound considered to be a salt of the structure C⁺X^" containing an organic cation and an anion. Further, in this application the ionic liquid can be regraded as a substance having a melting point of -20 to 120°C, more preferably of 0°C to 110°C, in particular of 20°C to 100°C measured at 1013 mbar.

The organic cation C⁺ can preferably be a monovalent organic cation ion. Examples of organic cations are imidazolium, imidazolidinium, pyridinium, pyrrolidinium, piperidinium, ammonium and phosphonium. Preferred are imidazolium, ammonium, phosphonium, pyrrolidinium.

In a preferred embodiment of the invention in step (ii) the ionic liquid is a compound represented by one of Formulae IL(I), IL(II), IL(III) or IL(IV)

wherein R⁵, R⁶, R⁷, R⁷, R⁸, R⁹, R¹⁰, R¹¹, R¹², R¹³, R¹⁴, R¹⁵ and R¹⁶ are independently organic residue, and

wherein X^" is an anion.

As far as the organic residue(s) R⁵ to R¹⁶ are concerned, substantially the same applies described above.

The anion X^" can be any inorganic or organic anion. It is preferred that X^" can preferably be a monovalent anion.

In a preferred embodiment of the present invention X^" can be a nucleophilic anion. Examples of nucleophilic anions are halogens, such as chloride, bromide, iodide, and carboxylates, such as acetate, triflate mesitylate. Preferred are chloride and bromide.

In a preferred embodiment of the present invention X^" can be a non-nucleophilic anion. Examples of non-nucleophilic anions are borates, such as tetrafluoroborate, or phosphates, such as hexafluorophosphate.

The compound according to Formula IL(I) can be referred to as 1,3-substituted imidazolium salts. Examples for compounds according to Formula IL(I) are 3-butyl-l-methylmidazolium chloride or bromide, l-butyl-3-methyl-imidazolium chloride or bromide, 3-ethyl-l- methylmidazolium chloride or bromide, l-ethyl-3-methyl-imidazolium chloride or bromide, 3-butyl-l-(2-cyanoethyl)-imidazolium chloride or bromide, l-butyl-3-(2-cyanoethyl)- imidazolium chloride or bromide, l-methyl-3-(4-vinylbenzyl)-imidazolium chloride or bromide, 3-methyl-l-(4-vinylbenzyl)-imidazolium chloride or bromide and 1,1'-(1,4- phenylenebis(methylene))bis(3-(4-vinylbenzyl)-imidazolium) chloride or bromide. Especially preferred is l-butyl-3-methyl-imidazolium chloride.

The compound according to Formula IL(II) can be referred to as an ammonium salt. In a preferred embodiment R⁷, R⁸, R⁹ and R¹⁰ can be independently an alkyl with 1 to 12 carbon atoms, preferably with 1 to 9 carbon atoms, in particular with 1 to 6 carbon atoms.

Alkyl groups with 1 to 6 carbon atoms can comprise all linear and branched alkyl groups like methyl, ethyl, propyl, isopropyl, butyl, isobutyl and tert.-butyl, pentyl, 2-pentyl, 3- pentyl, hexyl, 2-hexyl and 3-hexyl.

Preferred are methyl, ethyl, butyl, pentyl and hexyl. In a preferred embodiment butyl is particularly preferred. An example for a compound according to Formula IL(II) is tetrabutylammonium chloride or bromide.

The compound according to Formula IL(III) can be referred to as a pyrrolidinium salt. In a preferred embodiment substantially the same applies to R¹¹ and R¹² as to residues R⁷, R⁸, R⁹ and R¹⁰as described above, namely R¹¹ and R¹² can be independently an alkyl with 1 to 12 carbon atoms, preferably with 1 to 9 carbon atoms, in particular with 1 to 6 carbon atoms.

An example for a compound according to Formula IL(III) is 1 -butyl- 1 -methyl pyrrolidinium chloride or bromide.

The compound according to Formula IL(IV) can be referred to as a phosphonium salt. In a preferred embodiment R¹³, R¹⁴, R¹⁵ and R¹⁶ can be each an aromatic group. As far as the aromatic group is concerned, substantially the same applies as described above. An example for a compound according to Formula IL(IV) is tetraphenyl phosphonium chloride or bromide.

In a preferred embodiment ionic liquid refers to a compound as described above. In an alternatively preferred embodiment ionic liquid refers to a mixture of compounds as described above. In a further alternative embodiment ionic liquid also comprises poly ionic liquid of the compounds as described above.

A mixture comprising epoxide and ionic liquid is present in a liquid form when at least one component of epoxide and ionic liquid is present in liquid form and when, if necessary, that component is able to dissolve the second component. In case both components epoxide and ionic liquid are present in solid form, the mixture is heated to an elevated temperature above the melting point of at least one of the components such that the mixture becomes a liquid. In a preferred embodiment step (ii) is carried out at elevated temperature. An elevated temperature is regarded as temperature being above 23 °C (corresponding to room temperature). An elevated temperature can for example be obtained by the supply of energy, such as heating. In a preferred embodiment step (ii) is carried out at a temperature of 40°C to 150°C, preferably 45°C to 130°C, more preferably 50°C to 110°C, in particular 60°C to 100°C.

In a preferred embodiment, step (ii) is carried out in the absence of a solvent; i.e. the mixture comprising epoxide and ionic liquid does not need to be dissolved in any solvent to be in a liquid state. Otherwise expressed, in step (ii) one of epoxide and ionic liquid is in a liquid state and dissolves the other or both of epoxide and ionic liquid are in a liquid state.

In alternatively preferred embodiment in step (ii) a first solvent is present. The first solvent is preferably present to dissolve at least one of the components epoxide and ionic liquid. The first solvent can preferably be selected from dimethyl sulfoxide (DMSO), dimethylformamide (DMF), dimethylacetamide (DMA) and acetonitrile. Preferably, step (ii) can be carried out in a first solvent at a temperature of 50°C to 110°C with l-butyl-3-methylimidazolium chloride as ionic liquid. More preferred step (ii) can be carried out at a temperature of 50°C to 110°C with l-butyl-3-methylimidazolium chloride as ionic liquid in the absence of a solvent.

Step (ii) can preferably be regarded as a step in which the carbon dioxide is captured in a liquid mixture comprising epoxide and ionic liquid.

It is preferred that in step (ii) of the method according to the present invention epoxide and ionic liquid can be present in a molar ratio of 50: 1 to 1 : 1 , preferably 40: 1 to 2: 1 , in particular 25: 1 to 3: 1. It turned out that with the above molar ratios a favourable dissolution and thus an advantageous contacting of carbon dioxide with the mixture comprising epoxide and ionic liquid can be achieved.

In a preferred embodiment, step (ii) is carried out in the absence of a Lewis acid.

In a more preferred embodiment in step (ii) the gas is contacted with a liquid mixture consisting of epoxide and ionic liquid.

In an alternative more preferred embodiment in step (ii) the gas is contacted with a liquid mixture consisting of epoxide, ionic liquid and first solvent.

Step (ii) can preferably be carried out under mechanical movement, such as stirring.

In step (iii) the carbon dioxide is allowed to react with the epoxide. While the other constituents of a gas, such nitrogen in ambient air, do not react under the above conditions, carbon dioxide can react with an epoxide in the presence of an ionic liquid, wherein the ionic liquid is not consumed in said reaction. Thus, the ionic liquid can be regarded as a catalyst for said reaction. By reacting with the epoxide the carbon dioxide is bound as a solid or liquid product, which preferably remains in the liquid mixture as described above. Consequently, remaining gas can be regarded as purified gas from which carbon has been removed, preferably completely.

Similar to step (ii), step (iii) can preferably be carried out under mechanical movement such as stirring.

Step (ii) and step (iii) can preferably be carried out simultaneously.

Further, the present invention relates to a method for preparing a cyclic carbonate comprising the steps of

(i) providing a gas comprising carbon dioxide at ambient pressure,

(ii) contacting the gas with a liquid mixture comprising epoxide and ionic liquid,

(iii) allowing the carbon dioxide to react with the epoxide to give a cyclic carbonate,

(iv) separating the cyclic carbonate.

A cyclic carbonate which is also referred to l ,3-dioxolan-2-one is a five-membered cyclic compound which can be represented by the following formula

wherein R¹ , R² , R³ and R⁴ are independently hydrogen or an organic residue.

As far as the organic residues R¹ , R² , R³ and R⁴ are concerned, the same applies as to organic residues R¹, R², R³ and R⁴ described above. Further steps (i) and (ii) of the method for preparing a cyclic carbonate correspond to steps (i) and (ii) as described above.

Further, step (iii) the method for preparing a cyclic carbonate substantially corresponds to step (iii) as described above.

In step (iii) carbon dioxide is allowed to react with the epoxide to give a cyclic carbonate. Thus, the cyclic carbonate can preferably be prepared via the following route:

wherein R¹, R², R³ and R⁴ independently can be hydrogen or an organic residue as described above. As also described above, the ionic liquid can be regarded as a catalyst for said reaction. The ionic liquid is reported to activate the epoxide followed by the reaction with the carbon dioxide and the recovery of the ionic liquid and the formation of the cyclic carbonate. Further, step (iii) is conducted under the conditions and with the compound as described above.

In step (iv) the cyclic carbonate formed in step (iii) is separated. In case that step (iii) is carried out at elevated temperature, step (iv) can preferably include cooling the reaction mixture for example to a temperature of 0° to 23°C. Cooling can be carried out with cooling devices as known in art, such as ice bath and/or cooling coil. In case that step (ii) was carried out in the presence of a first solvent, step (iv) can preferably include the removal of the first solvent for example by distilling off the first solvent from the reaction mixture of step (iii). Distilling off the first solvent can preferably be carried out at elevated temperature and/or under reduced pressure.

Separation of the cyclic carbonate from the reaction mixture can be carried out by all methods known in the art and regarded as suitable to separate different compounds, such as for example extraction, filtration chromatography, distillation and crystallization.

In a preferred embodiment step (iv) comprises dissolving the cyclic carbonate in a second solvent and separating the solution from the ionic liquid. It is preferred that the second solvent is selected from ethyl acetate, pentane, hexane and diethylether. In step (iv) the cyclic carbonate can preferably be dissolved, preferably completely dissolved, in the second solvent. Further, in step (iv) the solution of the second solvent containing the dissolved cyclic carbonate can preferably be separated from the ionic liquid by filtration. After filtration, the second solvent can preferably be removed, preferably completely removed from the solution containing the cyclic carbonate at elevated temperature and/or reduced pressure. The obtained cyclic carbonate can preferably be further purified, preferably by crystallization or distillation. In a preferred embodiment of the method for preparing a cyclic carbonate the cyclic carbonate is selected from a compound according to one of Formulae C(I) -C(XIII)

Thus, it turned out that the method of the invention for preparing a cyclic carbonate provides a method which enables the provision of hardly accessible and valuable cyclic carbonates without the need of an extensive instrumental effort and complex equipment.

Further, the present invention relates to the use of a liquid mixture comprising epoxide and ionic liquid in the absence of a solvent for removing CO₂ from a gas and/or for preparing a cyclic carbonate under ambient pressure.

The invention will now be illustrated with reference to the following examples. Experimental part:

General:

Reagents and solvents:

l-hydroxyethyl-3-methylimidazolium chloride ([HEMIm]Cl) was synthesised by reacting 2- chloroethanol with 1-methylimidazole. All further chemicals were purchased from commercial sources and used as received. l-Butyl-3-methylimidazolium chloride, Bisphenol A diglycidyl ether, styrene oxide, allyl glycidyl ether and phenyl glycidyl ether were purchased from Sigma-Aldrich. Epichlorohydrin and CDCl₃ were purchased from Acros. Instrumentation:

The gas chromatography (GC-MS) was recorded on a Gas Chromato graph Agilent 7890B equipped with an Agilent 7000C MS triple quad detector and a capillary column from Agilent (1 x d x f: 30 m x 0.25 mm x 0.25 μπι) using N2 as carrier gas. GC of gas samples were analysed on a Gas Chromatograph 7890A from Agilent equipped with a CP-CarboPlot P7 GC column from Agilent (27.5 m x 0.53 mm x 25 μm). ¹Η and ¹³C NMR spectra were recorded on a Bruker 400 MHz instrument.

Examples: Example 1: Transformation of styreneoxide (SO; 2-phenyloxirane) into styrenecarbonate (SC; 4-phenyl-l,3-dioxolan-2-one)

Examples 1.1 - 1.8

A 10 mL two-neck flask was charged with ionic liquid and styrene oxide (100 mg; 0.83 mmol). The flask was connected to a Schlenk line via an adaptor and equipped with a C02-filled balloon. After three vacuum-C0₂ cycles, the mixture was brought to the corresponding temperature in a pre-heated oil bath. After reaction for the appropriate time, the mixture was allowed to cool to room temperature, and CDCI3 (1 mL) was added to the mixture. The yield of the reaction product was determined by NMR spectroscopy using Dl = 3 sec.

Example 1.9

Example 1.9 was carried out under the same conditions as Examples 1.1-1.8 in the presence of DMSO (1 ml) as solvent. Reference Example 1 (Ref. 1)

Styrene oxide (100 mg; 0.83 mmol) was reacted with carbon dioxide at 10 atm in an autoclave in the presence of ionic liquid under the following conditions with the corresponding yield.

Table 1 :

[BMIm]Cl corresponds to l-butyl-3-methylimidazolium chloride. [HEMIm]Cl corresponds to l-hydroxyethyl-3-methylimidazolium chloride.

Since in every example styrene carbonate is formed, the conditions are suited to extract carbon dioxide form the ambient gas. Further, as can be seen from Examples 1.1 to 1.9 there is no need of pressurized carbon dioxide to prepare a cyclic carbonate. Indeed, several of the present examples show a better yield than the one obtained with pressurized dioxide (Ref. 1). Example 2: Transformation of different epoxides into the corresponding carbonates

A 10 mL two-neck flask was charged with l-butly-3-methylimidazolium chloride (25 mol ) and the appropriate epoxide (0.83 mmol). The flask was connected to a Schlenk line via an adaptor and equipped with a CO₂-filled balloon. After three vacuum-CO₂ cycles, the mixture was brought to 100°C in a pre-heated oil bath. After reaction for 24 h, the mixture was allowed to cool to room temperature, and CDCl₃ (1 mL) was added to the mixture. The yield of the reaction product was determined by NMR spectroscopy using Dl = 3 sec.

From examples 2.1 to 2.6 it can be seen that different epoxides were converted into the corresponding carbonates. In particular, 2,2'-(4,4'-(propane-2,2-diyl)bis(,l- phenylene))bis(oxy)bis(methylene)dioxirane (also known as Bisphenol A diglycidyl ether) was converted into the corresponding carbonate in good yield. Moreover, the resulting carbonate is a key product of polycarbonates, which are an important class of plastics used as packing material.

Example 3: Transformation of epoxides with different carbon dioxide sources

A 10 mL two-neck flask was charged with ionic liquid (25 or 100 mol ) and the appropriate epoxide (0.83 mmol). The flask was connected to a Schlenk line via an adaptor and equipped with a gas or dry ice was added. After three gas cycles or directly, when dry ice was added, the mixture was brought to the selected temperature. After reaction, the mixture was brought to room temperature, and CDCl₃ (1 mL) was added to the mixture. The yield of the reaction product was determined by NMR spectroscopy using Dl = 3 sec.

Table 3:

PO corresponds to propylene oxide.

SO corresponds to styrene oxide.

[BMIm]Cl corresponds to l-butyl-3-methylimidazolium chloride. From Example 3.1 to 3.6 it can be seen that cyclic carbonate can be obtained by the present method using the different temperatures and sources of carbon dioxide. The reaction can be carried out by adding a stoichiometric amount of dry ice as well as in the presence of a gas containing small amounts of carbon dioxide such as breath.

Example 4: Purification of an air-stream by converting styrene oxide to styrene carbonate

A 25 mL three-neck flask was charged with l-butly-3-methylimidazolium chloride (5-50 mol%) and styrene oxide (25 g, 0.208 mol). The flask was equipped with a septum and a condenser. The air was bubbled through a frit in the system. To remove moisture from the air-flow, the stream was first bubbled through concentrated H2SO4 (97 %), and then silica beads. Every 24 h, one drop of the reaction mixture was removed and analysed by ¹Η-ΝΜΚ spectroscopy using a Dl = 3 sec. for quantification. A gas sample was collected every 24 h and analysed by GC. With several reactions run in series, a near-quantitative uptake of CO₂ can be obtained.

Table 4:

SO corresponds to styrene oxide.

[BMIm]Cl corresponds to l-butyl-3-methylimidazolium chloride Example 5: Quantitative removal of CO₂ from CO₂-containing gas stream by converting styrene oxide to styrene carbonate

Reactions with a stationary liquid phase and a continuous gas flow (semi-batch operation) were carried out in a commercial, stainless steel reactor (150 cm³ Biichi AG, Uster, Switzerland) equipped with 6 wall baffles. A mass-flow controller (Bronkhorst AG, Switzerland) was used to deliver a controlled flow rate of gas to the reactor from the gas cylinders (the pressure was reduced to c.a. 8 bar before reaching the MFC). The reaction temperature was controlled using a heating circulator Colora K4 (Lorch, Germany) connected to the reactor jacket. A 6-blade disk turbine impeller ensured intensive mixing. The stirrer was driven by a magnetic drive and equipped with a speed controller (cyclone 075/cc 075, Biichi AG, Uster, Switzerland). The reactor temperature, pressure and stirring rate were monitored and recorded via a control unit (bpc 6002/bds mc, Biichi AG, Uster, Switzerland).

Prior to the start of each experiment the reactor was charged with the catalyst (3.6 g, 0.02 mol, 5 mol ) and 49.5 g of styrene oxide (0.40 mol) in order to reach of total volume of 50 mL. After flushing the reactor with N2 (3 times) to remove ambient air, the reactor was heated (333-348 K) and equilibrated for 5 min. The introduction of a synthetic, % or pure CO₂ flow though the reactor defined the start of the reaction. A typical reaction was performed with a gas flow of 20 mL/min and a stirring rate of 2000 rpm. Every 30 min during the reaction, 0.1 mL of the reaction mixture was withdrawn using a 1 mL syringe (Codan Medical AG) connected to the sampling valve and one drop of it was analysed by ¹Η NMR spectroscopy.

Claims

1. Method for removing carbon dioxide from a gas comprising the steps of

i) providing a gas comprising carbon dioxide at ambient pressure,

ii) contacting the gas with a liquid mixture comprising epoxide and ionic liquid, wherein step ii) is carried out in the absence of a solvent

iii) allowing the carbon dioxide to react with the epoxide.

2. Method for preparing a cyclic carbonate comprising the steps of

i) providing a gas comprising carbon dioxide at ambient pressure,

iii) allowing the carbon dioxide to react with the epoxide to give a cyclic carbonate,

iv) separating the cyclic carbonate.

3. Method according to claim 1 or 2, wherein in step i) the gas is substantially free of water.

4. Method according to any one of claims 1 to 3, wherein in step ii) the epoxide has a boiling point of 40°C to 350°C.

5. Method according to any one of claims 1 to 4, wherein in step ii) the epoxide is selected from a compound according to one of Formulae E(I)-E(XIII)

and mixtures thereof.

6. Method according to any one of claims 1 to 5, wherein in step ii) the ionic liquid is a compound represented by one of Formulae IL(1), IL(2), IL(3) and IL(4)

wherein R⁵, R⁶, R⁷, R⁷, R⁸, R⁹, R¹⁰, R¹¹, R¹², R¹³, R¹⁴, R¹⁵ and R¹⁶ are independently an organic residue, and

wherein X^" is an anion.

7. Method according to any one of claims 1 to 7, wherein step ii) is carried out a temperature of 40°C to 150°C.

8. Method according to any one of claims 1 to 7, wherein in step ii) epoxide and ionic liquid are present in a molar ratio of 50: 1 to 1: 1.

9. Method according to any one of claims 2 to 8, wherein step iv) comprises dissolving the cyclic carbonate in a second solvent and separating the solution from the ionic liquid.

10. Method according to claim 9, wherein the second solvent is selected from ethyl acetate, hexane, pentane and diethyl ether.

11. Method according to any one of claims 2 to 10, wherein the cyclic carbonate is selected from a compound according to one of Formulae C(I)-C(XIII)

12. Use of a liquid mixture comprising epoxide and ionic liquid in the absence of a solvent for removing CO₂ from a gas and/or for preparing a cyclic carbonate under ambient pressure.