US20130118955A1

US20130118955A1 - Desulfurization of hydrocarbons by ionic liquids and preparation of ionic liquids

Info

Publication number: US20130118955A1
Application number: US13/733,173
Authority: US
Inventors: Natalya Victorovna Likhanova; Rafael Martinez Palou; Jorge Froylan Palomeque Santiago
Original assignee: Instituto Mexicano del Petroleo
Current assignee: Instituto Mexicano del Petroleo
Priority date: 2008-05-26
Filing date: 2013-01-03
Publication date: 2013-05-16
Also published as: US8821716B2; MX2008006731A; DE102009022284A1; US20090288992A1

Abstract

The present invention relates to an improved desulfurization process using an ionic liquid compound of general formula C⁺A⁻, where C⁺ represents an organic cation such as alkyl-pyridinium, di-alkyl imidazolium and tri-alkyl imidazolium; and A⁻ is an anion of halides of iron (III), such as, for example, FeCl₄ ⁻. The desulfurization process is also improved when producing the ionic liquid compound by heating the reactants using microwave energy. The ionic liquids can be used to desulfurize hydrocarbon mixtures by a liquid-liquid extraction.

Description

CROSS-REFERENCE TO RELATED PATENT APPLICATIONS

This application is a divisional application of Ser. No. 12/471,846, filed May 26, 2009, which claims priority to Mexican Patent Application No. MX/a/2008/006731, filed on May 26, 2008, in the Mexican Patent Office, the disclosure of which is hereby incorporated by reference in its entirety.

FIELD OF THE INVENTION

This invention provides a process for the synthesis of ionic liquids which can be used for the efficient removal of sulfur compounds from hydrocarbon mixtures. The ionic liquids related are insoluble in hydrocarbons but are able to dissolve aliphatic and aromatic sulfur compounds. Thus, the ionic liquids can be used for removal of sulfur compounds by a liquid-liquid extraction process at room temperature and pressure. The invention is also directed to a process for extracting sulfur from a hydrocarbon liquid by contacting the hydrocarbon with the ionic liquid.
More preferably, this invention is related to the synthesis of ionic liquids with general formula C⁺A⁻, where C⁺ is an organic cation preferably but not exclusively alkyl pyridinium, dialkylimidazolium, and trialkylimidazolium, the anion A⁻ is preferably halogen ferrate (III), particularly Cl*FeCl₃ ⁻ and Br*FeCl₃. The invention is also directed to the process for the extraction of sulfur-containing compounds, such as sulfur compound that are present in gasoline and Diesel as contaminant obtained in petroleum refining processes by contacting with the ionic liquids.

BACKGROUND OF THE INVENTION

The production of gasoline according with the new European Environmental Standards requires that the refiners to lower the sulfur content in gasoline to values that are lower than 50 ppm since 2005. For example in Germany he content of sulfur in gasoline should be lower than 10 ppm. For the case of USA the content of sulfur is limited to lowest than 80 ppm and with average of 30 ppm. In attention to this claims, PEMEX Refining should be produce gasoline with sulfur content between 15 and 30 ppm for the years 2008-2010.
The classic method used for sulfur removal in Refining Processes is the catalytic Hydrodesulfurization (HDS technology) at high temperature and pressure. This method is very costly process that required drastic operation conditions and it is inefficient to reduce aromatic sulfur compounds especially for Mexican heavy crude oil, so is more reasonable the use of alternative desulfurization process. For increasing the efficiency of HDS process some technology modification are required such as the addition of other catalytic bed, more efficient catalyst, higher temperature and pressures and to reduce LHSV to expense of few processing capacity.
New technologic lines have been develop on in several countries in order to resolve this problem (Zaczepinski, S. Exxon, Diesel Oil Deep Desulfurization (DODD) in Handbook of Petroleum Refining Processes, ed. R. A. Meyer, Mc Graw-Hill, NY, 1996, Ch. 8.7), i.e.: the absorption of sulfur compounds over solid absorbents, like IRVAD® process (U.S. Pat. No. 5,730,860, dated Mar. 24, 1998) from Black & Veatch Pritchard Inc.; the process S-Zorb® from Phillips Petroleum (http://www.eia.doe.gov/oiaf/servicerpt/ulsd/uls.html), the process Haldor Topsoe (EP 1057879, dated Dec. 6, 2000); and the liquid-liquid extraction with volatile organic solvents (Petrostar Refining, 217 National Meeting, American Chemical Society, Anaheim, Calif., Marzo, 1999). An original process is the oxidative desulfurization with different oxidant agents (Unipure Corp., NPRA Meeting No AM-01-10, Marzo 2001; Sulphco Corp, NPRA Meeting No AM-01-55, March 2001; BP Chemicals UK, Journal of Molecular Catalysis A: Chemical (1997) 397-403; UOP LLC, U.S. Pat. No. 6,171,478, dated Jan. 9, 2001; EXXON Research and Engineering Co., U.S. Pat. No. 5,910,440, dated Jun. 8, 1999; U.S. Patent Publication No. 2002/0035306 A1 with publication date of Mar. 21, 2002; U.S. Pat. No. 6,596,914 B2, dated Jul. 22, 2003; U.S. Pat. No. 6,406,616, dated Jun. 18, 2002 and U.S. Pat. No. 6,402,940 B1 dated Jun. 11, 2002; Fuel 82 (2003) 4015; Green Chemistry 5 (2003) 639). Recently the extraction of sulfur-containing compounds using liquid-liquid extraction employing ionic liquids have been welcome by scientific community.
Ionic liquids are known for more than 30 years, but their industrial applications began in the last 10 years (Rogers, R. D.; Seddon, K. R (Eds.), Ionic Liquids: Industrial Applications of Green Chemistry, ACS, Boston, 2002). They are applied as solvents and catalyst in alkylation reactions, polymerization and Diels-Alder cycloaddition. In addition they are employed in electrochemical processes, in supercritical CO₂extraction of aromatic compounds and sulfur compounds in hydrocarbon mixtures. One of the first publications mention the use of ionic liquids for the removal of mercaptans (WO 0234863, dated May 2, 2002). The patented method is based on the use of sodium hydroxide in combination with ionic liquids for the conversion of mercaptans to mercaptures, which were removed using ionic liquids. Peter Wassercheid and coworkers published several papers and patents between 2001 and 2005 about the use of ionic liquids for desulfurization of gasolines (Chem. Comun. (2001) 2494; WO 03037835, with publication date of 2003 May 8; U.S. Publication No. 2005/0010076 A1, published Jan. 13, 2005). In these works the authors employed ionic liquids with C⁺ being 1,3-dialkylimidazolium or tetralkylammonium, and A⁻ being tetrachloroaluminates or methanesulfonates. By means of a process with several extractions (up to 8 extractions), high extraction of sulfur compounds were achieved using model gasolines. However these kinds of compounds are air and moisture sensitive and a polymerization reaction was observed during the extraction process. U.S. Patent Publication No. 2003/0085156 A1 published May 8, 2003 and U.S. Pat. No. 7,001,504, dated Feb. 21, 2006, also mention the use of ionic liquids, where C⁺ is an ammonium o fosfonium and quaternary, A⁻ being tetrachloroaluminates for the extraction of sulfur from model gasoline. In the paper published in Energy & Fuels 18 (2004) 1862, the use of ionic liquids containing Copper chloride (I) anion with the same application, and in the papers Ind Eng. Chem. Res. 43 (2004) 614 and Ind. Eng. Chem. Res. 46 (2007) 5108-5112) several ionic liquids were evaluated for the extraction of sulfur and nitrogen-containing compounds. More recently, some papers (Energy & Fuels 20 (2006) 2083-2087; Green Chemistry 8 (2006) 70-77; Progress in chemistry 19 (2007) 1331-1344; Green Chemistry 10 (2008) 87-92) also report the use of IL for desulfurization processes. U.S. Patent Publication No. 2004/00445874 A1, published Mar. 11, 2004, discloses a procedure for desulfurization and denitrogenation of hydrocarbons fractions using a wide family of ionic liquids and alkylations agents with high efficiency in some cases.

SUMMARY OF THE INVENTION

The present invention is directed to the use of ionic liquids containing halogens of Fe (III) as an anion for these purposes, where these compounds presented very high efficiency for extracting sulfur-containing compounds from gasoline, turbosin, diesel and other petroleum fractions. Another important and novel aspect of the invention is the use of microwave irradiation for synthesizing the ionic liquids suitable for use as extracting agents (symmetric and non-symmetric compounds) with a corresponding shorter time and higher yields in the synthesis of these ionic liquids compared to the conventional methods of synthesis.
The invention is also directed to a process for extracting sulfur and sulfur compounds from a sulfur-containing hydrocarbon liquid by contacting the hydrocarbon liquid with an ionic liquid of the invention for sufficient time to extract the sulfur and sulfur-containing compounds, and thereafter recovering the hydrocarbon liquid.
The ionic liquids of the invention comprise a heterocyclic cation and an iron (III) halide. The heterocyclic cation is an imidazolium compound having at least one C₁-C₁₀alkyl group or alkoxy group where the alkyl group and alkoxy group can be linear, branched, substituted or unsubstituted. The heterocyclic cation can be symmetrical or asymmetrical.

DETAILED DESCRIPTION OF THE INVENTION

This invention relates to the field of the synthesis of new ionic liquids and their application for the desulfurization of hydrocarbon fractions by means a liquid-liquid extraction (ionic liquid-hydrocarbon fraction) method. This removal of sulfur compounds is carried out due to the higher affinity among sulfur-containing compounds and the ionic liquid media with respect to the very low polarity of the hydrocarbon media. By means a vigorous stirring between the low immiscible phases following by phase separation step, the sulfur content in the hydrocarbon phase is considerably reduced.

The Ionic Liquids

The ionic liquids employed in this invention present the general formula C⁺A⁻, where C⁺ is an organic cation, and A⁻ is the anion. The cation can be, for example, an alkylpyridinium, alkylimidazolium, dialkylimidazolium, hydroxy-alkyl alkyl imidazolium and 1,2,3-trialkylimidazolium, A⁻ is FeCl₄ ⁻ or a derivative thereof.
The ionic liquids of this invention were derived from cations produced from imidazol and pyridine derivatives. The imidazol and pyridine cations can have the following formula:
Imidazolium:
wherein the imidazole nucleus may be substituted with at least one group selected from a linear or branched C₁-C₁₀alkyl, a linear or branched C₁-C₁₀alkoxy group and functionalized alkyl groups having one heteroatom selected from N, O and S or halogen atoms.
R₁, R₂, and R₃are independently selected from a group consisting of hydrogen; linear or branched, saturated or unsaturated, aliphatic or alicyclic alkyl groups having from 1 to 10 carbon atoms; a linear or branched alkoxy group or functionalized alkyl groups, having one heteroatom selected from N, O and S or halogen atoms.
The alkyl and alkoxy groups have 1 to 10 carbon atoms, and preferably 2 to 8 carbon atoms. In one embodiment, R₁is a hydrogen or a methyl group. The R₁and R₂groups can be the same to define a symmetrical ionic liquid or different to define an asymmetrical ionic liquid. In another embodiment, R₁is methyl, R₂is a hydrogen or methyl, and R₃is a C₂-C₈alkyl. The R₃alkyl group can be a methyl, ethyl, propyl or butyl group. In one preferred embodiment, R₃is a butyl group. The alkyl group can be substituted with a functional group such as a hydroxy group. In one embodiment, R₃is a 2-hydroxyethyl group. In another embodiment, R₁is methyl, R₂is a hydrogen atom or methyl, and R₃is a C₂-C₈alkyl which can be substituted or unsubstituted.
Pyridinium:
wherein the pyridine nucleus may be substituted with at least one group selected from a linear or branched C₁-C₁₀alkyl.
R₁, and R₂are independently selected from group consisting of hydrogen; linear or branched, saturated or unsaturated, aliphatic or alicyclic alkyl groups having from 1 to 10 carbon atoms.
In one embodiment, R₁is a hydrogen atom or a alkyl group and R₂is a linear or branched alkyl group. R₁and R₂can be a linear or branched alkyl group having 1 to 10 carbon atoms, and preferably 2 to 8 carbon atoms. In one embodiment, R₁is a hydrogen and R₂is an actyl group. In both cases the anion is of the FeCl₄ ⁻ type.

Synthesis of the Ionic Liquids

For non-symmetrical ionic liquids, the synthesis is made in two steps, based on the alkylation method and metathesis of anion, (refs: Tetrahedron 2003, 59, 2253-2258; New J. Chem. 2002, 26, 1667-1670; J. Org. Chem. 2005, 70, 7882-7891; Green Chem. 2003, 5, 181-186; Inorg. Chem. 2001, 40, 2298-2304; J. Chem. Eng. Data 2006, 51, 691-695). In the first step the following reaction is carried out; and the subsequent reactions, this nomenclature is used:

Nomenclature:

Im=Imidazole
(CH₃)₃SiNHSi(CH₃)₃=Hexamethyldisilazane
Im-Si(Me)₃=N-(Trimethylsilyl)imidazol
(CH₃)₃SiNH₂=Trimethylsilylamine
Cl-Alq=Alkyl chloride
Alq-Im⁺-Alq Cl⁻=Dialkyl imidazolium chloride
Alq-Im⁺-Alq FeCl₄ ⁻=Dialkyl imidazolium tetrachloroferrate
HetCic-N=Heterocycle with nitrogen
HetCic-N⁺-Alq Cl⁻=Alkyl imidazolium chloride
HetCic-N⁺-Alq FeCl₄ ⁻=Alkyl imidazolium tetrachloroferrate

HetCic-N+Cl-Alq-^Δ→HetCic-N⁺-Alq Cl⁻ I)
In the second step the alkyl imidazolium chloride reacted with iron chloride (III), obtaining the ionic liquid with anion FeCl₄ ⁻:
HetCic-N⁺-Alq Cl⁻+Fe Cl₃→HetCic-N⁺-Alq FeCl₄ ⁻ II)
The first step of synthesis takes place heating by microwaves irradiation, with which the times of reaction diminish from the 95 to 98%, to comparison with conventional heating synthesis.
In the case of symmetrical ionic liquids, the synthesis is carried out in three steps, based in the method of activation of secondary nitrogen with the trimethylsilyl group, alkylation and metathesis of anion, (refs.: Polymer 2004, 45, 5031-5045; Chem. Commun. 2001, 1466-1467). In first, the 1-trimethylsilyl derived was synthesized from the nitrogen compound by the following chemical reaction:
Im+(CH₃)₃SiNHSi(CH₃)₃-^Δ→Im-Si(Me)₃+(CH₃)₃SiNH₂ I)
In the second step, both nitrogen atoms were alkylated with a alkyl chloride:
Im-Si(Me)₃+2 Cl-Alq→Alq-Im⁺-Alq Cl⁻ II)
And in the third step, the precursor is reacted with FeCl₃:
Alq-Im⁺-Alq Cl⁻+FeCl₃→Alq-Im⁺-Alq FeCl₄ ⁻ III)
Of the same way that for not-symmetrical the ionic liquids, the symmetrical ones are synthesized with the use of the microwaves like nonconventional source of heating, with which the times of reaction is diminish more than 90%, with comparable yields respect to conventional method.
To continuation some examples are described, and are not intended to limit the scope of the present invention.

EXAMPLE 1

Synthesis of 1-butyl-3-methylimidazolium tetrachloroferrate ([BMIM]FeCl₄)

Step 1: In glass reactor, 1.64 g (20 mmol) of 1-methylimidazole was mixed with 5.55 g (60 mmol) of 1-chlorobutane. After 48 hours of stirring and refluxing with conventional heating, the two-phase mixture was formed. The top layer was decanted off. The residue was washed with ethyl acetate (3×20 ml) and vacuum dried at 90° C. for 5 hours. A viscous colorless liquid was obtained (yield 70%)
Step 2: In glass reactor that is equipped with a magnetic stirring mechanism 0.87 g (5 mmol) of 1-butyl-3-methylimidazolium chloride, obtained from step 1, was introduced and 1.22 g (7.5 mmol) of iron chloride (III) anhydrous was added. The mixture was stirred for 20 minutes at room temperature under an inert atmosphere. A dark red liquid was obtained. The spectroscopic characterizations (¹H and ¹³C NMR) confirm the following chemical structure:

EXAMPLE 2

Synthesis of 1-butyl-2,3-dimethylimidazolium tetrachloroferrate ([BDMIM]FeCl₄)

Step 1: The 1-butyl-2,3-dimethylimidazolium chloride was obtained (yield 86%) in the same manner described in Example 1 (Step 1) with the exception that 1,2-dimethylimidazole was used instead of 1-methylimidazole.
Step 2: In glass reactor that is equipped with a magnetic stirring mechanism 0.94 g (5 mmol) of 1-butyl-2,3-dimethylimidazolium chloride was introduced and 1.22 g (7.5 mmol) of iron chloride (III) anhydrous was added. The mixture was stirred for 20 minutes at room temperature under an inert atmosphere. A dark red liquid was obtained.

EXAMPLE 3

Synthesis of 1,3-dibutylimidazolium tetrachloroferrate ([DBIM]FeCl₄)

This ionic liquid can be obtained by two alternative procedures and using the conventional heating or the microwaves irradiation as the heating source.

Procedure 1

Step 1: The 1,3-dibutylimidazolium chloride was obtained (yield 90%) in the same manner described in Example 1 (Step 1) with the exception that 2.48 g (20 mmol) of 1butylimidazole was used instead of 1-methylimidazole.
Step 2: In a glass reactor equipped with a magnetic stirring mechanism 1.08 g (5 mmol) of 1,3-dibutylimidazolium chloride was introduced and 1.22 g (7.5 mmol) of iron chloride (III) anhydrous was added. The mixture was stirred for 20 minutes at room temperature under an inert atmosphere. A dark red liquid was obtained.

Procedure 2

This procedure consists of three steps.
Step 1 (Synthesis of 1 (trimethylsilyl)-imidazol): In a reactor 1.36 g (20 mmol) of imidazol and 4.85 g (30 mmol) of 1,1,1,3,3,3-hexamethyldisilazanol was mixed under an inert atmosphere. The mixture was refluxing for 12 hrs. The reaction formed N-trimethylsilyl-imidazol which was distilled under reduced pressure to afford a viscous colorless liquid (yield 95%).
Step 2 (Synthesis of 1,3-dibutylimidazolium chloride): In a reactor, to a mixture formed by 1.40 g (10 mmol) of N-trimethylsilyl-imidazol obtained previously and 2.78 g (30 mmol) of 1-chlorobutane was added 30 ml of toluene. After 48 hours of stirring and refluxing, the two-phase mixture was formed. The top layer was decanted off. The residue was washed with ethyl acetate (3×20 ml). Removal of the solvent under reduced pressure afforded a viscous colorless liquid (yield 60%)
Step 3: In a glass reactor that is equipped with a magnetic stirring mechanism 1.08 g (5 mmol) of 1,3-dibutylimidazolium chloride was introduced and 1.22 g (7.5 mmol) of iron chloride (III) anhydrous was added. The mixture was stirred for 20 minutes at room temperature under an inert atmosphere. A dark red liquid was obtained.
The described compound also was synthesized according to the two alternative procedures previously described, but using microwave irradiation (300 W) for 15 minutes of irradiation for step 1 of the first alternative procedure and for 10 minutes and 20 minutes of irradiation for steps 1 and 2 of alternative procedure 2, to obtain the compound in quantitative yields.

EXAMPLE 4

Synthesis of N-octylpyridinium tetrachloroferrate ([OP]FeCl₄)

Step 1: N-octylpyridinium chloride was obtained (yield 68%) in the same manner described in Example 1 (Step 1) with the exception that 1.58 g (20 mmol) of pyridine was used instead of 1-methylimidazole and 8.92 g (60 mmol) of 1-chlorooctane was used instead of 1-chlorobutane
Step 2: In a glass reactor equipped with a magnetic stirring mechanism 1.14 g (5 mmol) N-octylpyridinium chloride, obtained from step 1, was introduced and 1.22 g (7.5 mmol) of iron chloride (III) anhydrous was added. The mixture was stirred for 20 minutes at room temperature under an inert atmosphere. A dark red liquid was obtained. The spectroscopic characterizations (¹H and ¹³C NMR) confirm the following chemical structure:

EXAMPLE 5

Synthesis of 1-(2-hydroxyethyl)-3-methylimidazolium tetrachloroferrate ([HEMIM]FeCl₄)

Step 1: The 1-(2-hydroxyethyl)-3-methylimidazolium chloride was obtained with a 90% yield. In a reactor, to a mixture formed by 11.64 g (20 mmol) of 1-methylimidazole and 3.2 g (40 mmol) 2-chloroethanol was added 30 ml of toluene. After 48 hours of stirring and refluxing, the two-phase mixture was formed. The top layer was decanted off. The residue was washed with ethyl acetate (3×20 ml). Removal of the solvent under reduced pressure afforded a viscous colorless liquid.
Step 2: In a glass reactor equipped with a magnetic stirring mechanism 0.81 g (5 mmol) of 1-(2-hydroxyethyl)-3-methylimidazolium chloride was introduced and 1.22 g (7.5 mmol) of iron chloride (III) anhydrous was added. The mixture was stirred for 20 minutes at room temperature under an inert atmosphere. A dark red liquid was obtained. The spectroscopic characterizations dates (¹H and ¹³C NMR) confirm the following chemical structure:

Tests of Performance of Ionic Liquids for Desulfurization of Hydrocarbons

The ionic liquids of the invention can be used in a process for extracting sulfur and sulfur compounds from a hydrocarbon liquid by contacting the hydrocarbon liquid with the ionic liquid.
The evaluations were performed with a mixture model prepared through the dissolution of benzothiophene and thiophene in equal parts, in a hexane/heptane mixture (1:1), having a total sulfur concentration of 500 ppm. The extraction tests were done by contacting 1 part of ionic liquid with 5 parts of the mixture model (weight/weight, w/w), in such a way that the extraction process was made with a relation weight of ionic liquid to hydrocarbon. The ionic liquid can be contacted with the hydrocarbon liquid at a ratio of about 1:1 to 1:20 (w/w), and preferably a ratio of about 1:1 to 1:10 (w/w). The determination of the sulfur content was determined by x-ray diffraction.
To 5.0 g of a model mixture (that contained 500 ppm of sulfur) 1.0 g of corresponding ionic liquid was added (obtained from examples 1-5); in the reaction mixture two phases were formed, after 30 min of agitation at room temperature. The ionic liquid phase was separated form the model mixture.
In Table 1 are the obtained results.

TABLE 1

Hydrocarbon sulfur removal by extraction with ionic liquids.

	Final sulfur content in	% of total removed
Ionic liquid	hydrocarbon (ppm)	sulfur in hydrocarbon

1*	>10	99
2*	>10	99
3*	14	97
4*	152	70
5*	325	35

*Notes:
1*: 1-butyl-3-methylimidazolium tetrachloroferrate.
2*: 1-butyl-2,3-dimethylimidazolium tetrachloroferrate.
3*: 1,3-dibutylimidazolium tetrachloroferrate.
4*: N-octylpyridinium tetrachloroferrate.
5*: 1-(2-hydroxyethyl)-3-methylimidazolium tetrachloroferrate.

As observed in Table 1, the ionic liquids with the tetrachloroferrate anion can almost quantitatively remove the sulfur content of the sample original model, especially the ionic liquids with imidazolium cation. Thus, the ionic liquids can be used for the deep desulfurization of hydrocarbon mixtures, such as, gasoline, diesel engine fuel, kerosene, jet fuel and light cyclical oil.
While various embodiments have been chosen to illustrate the invention, it will be understood that various changes and modifications can be made without departing from the scope of the invention as recited in the appended claims.

Claims

What is claimed is:

1. An ionic liquid for the desulfurization of hydrocarbons, comprising a heterocyclic cation and an iron (III) halide anion wherein said ionic liquid is capable of removing sulfur and sulfur compounds from a liquid hydrocarbon.

2. The ionic liquid according to claim 1, wherein the ionic liquid is symmetrical or asymmetrical and the heterocyclic cation is imidazolium or a derivative thereof having linear or branched, saturated or unsaturated, aliphatic or alicyclic alkyl groups having from 1 to 10 carbon atoms; linear or branched alkoxy groups or functionalized alkyl groups having one heteroatom selected from the group consisting of N, O and S or halogen atoms.

3. The ionic liquid according to claim 2, wherein the anion is a halide of iron (III) derived from FeCl₃.

4. The ionic liquid according to claim 2, wherein said heterocyclic anion has the formula

R₁, R₂, and R₃are independently selected from group consisting of hydrogen; linear or branched, saturated or unsaturated, aliphatic or alicyclic alkyl groups having from 1 to 10 carbon atoms; linear or branched alkoxy groups or functionalized alkyl groups having one heteroatom selected from N, O and S or halogen atoms and the anion is FeCl₄ ⁻.

5. The ionic liquid according to claim 4, wherein the imidazolium cation is symmetrical when R₁is the same as R₂or asymmetrical where R₁is not the same as R₂.

6. The ionic liquid according to claim 1, wherein said heterocyclic anion has the formula

wherein the pyridine nucleus is substituted with at least one group selected from a linear or branched C₁-C₁₀alkyl.

7. The ionic liquid according to claim 6, wherein R₁, and R₂are independently selected from group consisting of hydrogen, linear or branched, saturated or unsaturated, aliphatic or alicyclic alkyl groups having from 1 to 10 carbon atoms.

8. The ionic liquid according to claim 6, wherein R₁is a hydrogen atom and R₂is a C₂to C₁₀alkyl group and the anion is FeCl₄ ⁻.

9. A process for the synthesis of a symmetrical ionic liquid of claim 2, comprising the steps of:

activating a secondary nitrogen with a trimethylsilyl group according to the following reaction step to form a 1-trimethylsilazane and N-trimethylsilylimidazol:

Im+(CH₃)₃SiNHSi(CH₃)₃-^Δ→Im-If(Me)₃+(CH₃)₃SiNH₂ I)

alkylizing the reaction product with an alkyl chloride according to the following reaction step:

Im-If(Me)₃+2 CL-Alq→Alq-Im⁺-Alq CL⁻ II)

and treating the precursor with FeCl₃to produce an dialkylimidazolium tetrachloroferrate according to the following reaction step:

Alq-Im⁺-Alq CL⁻+FeCl₃→Alq-Im⁺-Alq FeCl₄ ⁻ III)

where:

Im=Imidazolium

(CH₃)₃SiNHSi (CH₃)₃=Hexamethylbisilazane

Im-If (Me)₃=N-Trimethylsilylimidazolium

(CH₃)₃SiNH₂=Trimethylsilylamine

CL-Alq=Alkyl chloride

Alq-Im⁺-Alq CL⁻=Dialkyl imidazolium chloride

Alq-Im⁺-Alq FeCl₄ ⁻=Dialkylimidazolium tetrachloroferrate

10. A process for the synthesis of asymmetrical ionic liquids of claim 2, comprising the steps of:

HetCic-N+CL-Alq-^Δ→HetCic-N⁺-Alq CL⁻ I)

and treating the reaction product of step I with FeCl₃to form an alkylimidazolium tetrachloroferrate according to the following reaction:

HetCic-N⁺-Alq CL⁻+Faith CL₃→HetCic-N⁺-Alq FeCl₄ ⁻ II)

where:

HetCic-N=Heterocycle with nitrogen

HetCic-N⁺-Alq CL⁻=Alkyl imidazolium chloride

HetCic-N⁺-Alq FeCl₄ ⁻=Alkyl imidazolium tetrachloroferrate

11. The process of claim 9, wherein the first and second steps comprises irradiating the reaction mixture with microwave energy for 10 min. to 1 hr.

12. The process of claim 10, wherein said first step comprises irradiating the reaction mixture with microwave energy for 10 min. to 1 hour.

13. An ionic liquid composition comprising

a hydrocarbon liquid containing sulfur compounds, and

an ionic liquid in an amount sufficient to remove the sulfur compounds from hydrocarbon liquid, said ionic liquid has a heterocyclic cation and an iron (III) halide anion.

14. The ionic liquid composition according to claim 13, wherein the ionic liquid is symmetrical or asymmetrical and the heterocyclic cation is imidazolium or a derivative thereof having linear or branched, saturated or unsaturated, aliphatic or alicyclic alkyl groups having from 1 to 10 carbon atoms; linear or branched alkoxy groups or functionalized alkyl groups having one heteroatom selected from the group consisting of N, O and S or halogen atoms.

15. The ionic liquid composition according to claim 14, wherein the anion is a halide of iron (III) derived from FeCl₃.

16. The ionic liquid composition according to claim 14, wherein said heterocyclic anion has the formula

17. The ionic liquid composition according to claim 16, wherein the imidazolium cation is symmetrical when R₁is the same as R₂or asymmetrical where R₁is not the same as R₂.

18. The ionic liquid composition according to claim 13, wherein said heterocyclic anion has the formula

19. The ionic liquid composition according to claim 18, wherein R₁, and R₂are independently selected from group consisting of hydrogen, linear or branched, saturated or unsaturated, aliphatic or alicyclic alkyl groups having from 1 to 10 carbon atoms.

20. The ionic liquid composition according to claim 18, wherein R₁is a hydrogen atom and R₂is a C₂to C₁₀alkyl group and the anion is FeCl₄ ⁻.