Halogen-free ionic liquids in naphtha desulfurization and their recovery

Abstract

Ionic liquids of the general formula C.sup.+A.sup.− where C.sup.+ represents an organic cation, specifically, but not limited to the imidazolium, pyridinium, isoquinolinium, ammonium types, which have aliphatic and aromatic substituents, while A.sup.− represents a carboxylate, aromatic and aliphatic anion. The ionic liquids are synthesized under conventional heating or microwave irradiation This invention is also related to the application of ionic liquids to remove sulfur compounds of naphthas through a liquid-liquid extraction and the recovery and reuse of ionic liquids by the application of heat, reduced pressure and washing with solvents.

Claims

1. An ionic liquid containing a heterocyclic cation and a carboxylate anion and having the formula C.sup.+A.sup.− wherein C.sup.+ is an isoquinolinium cation, and A.sup.− is a carboxylate anion having the formula ##STR00017## where R.sub.4 is selected from the group consisting of cycloalkyl, alkenyl, and benzylic.

2. The ionic liquid of claim 1, wherein said heterocyclic cation is an isoquinolinium cation having at least one substituent selected from the group consisting of benzylic, cycloalkyl, and alkenyl having 1 to 10 carbon atoms.

3. The ionic liquid of claim 1, wherein said isoquinolinium cation has the formula ##STR00018## where R is selected from the group consisting of alkyl, cycloalkyl, alkenyl, benzylic, and functionalized alkyl having 1 to 10 carbon atoms.

Description

DETAILED DESCRIPTION OF THE INVENTION

(1) The present invention is related to the synthesis and application of ionic liquids that have kind of carboxylate anions and are halogen-free and remove efficiently sulfur compounds contaminants from naphtha.

(2) The process of extraction and removal of sulfur compounds from a sulfur containing liquid is composed of the strong agitation of the two phases (ionic liquids and naphtha) followed by a process of separation of phases, where the sulfur compounds pass to phase comprising the ionic liquid and as a result total sulfur content is considerably reduced in the naphtha, this occurs due to the higher affinity of sulfur compounds into the ionic liquid compared with naphtha.

(3) Ionic liquids used in the present invention have general formula C.sup.+ A.sup.− where C.sup.+ is an organic cation such as imidazolium, pyridinium, isoquinolinium and ammonium, and A.sup.− is an anion-type organic carboxylate, including aromatic and aliphatic substituents as shown in Table 1.

(4) TABLE-US-00001 TABLE 1 Overall structure of cations and anions constituting the ionic liquids of this invention C.sup.+ (Cations) A.sup.− (Anions) where: R, R.sub.1, R.sub.2 y R.sub.3 are independently radicals represented by alkyl group, cycloalkyl group, alkenyl group, benzylic group and alkyl functionalized group, preferably these groups have from 1 to 10 carbon atoms; R.sub.4 comprises alkyl group, cycloalkyl group, alkenyl group, benzylic group and alkyl functionalized group, preferably these groups have from 1 to 18 carbon atoms.

(5) In one aspect of the invention, a process for the desulfurization of an organic liquid includes the steps of contacting the organic liquid with the ionic liquid having the formula C.sup.+ A.sup.−, where C.sup.+ and A.sup.− are as defined above. The desulfurization is carried out by a liquid-liquid extraction where the sulfur compounds are recovered in the ionic liquid. The ionic liquid is immiscible with the organic liquid which results in a phase separation. The organic liquid can be, for example, naphtha, as defined above, gasoline, diesel fuel, kerosene, heating oil and other petroleum based liquids.

EXAMPLES

Synthesis of Ionic Liquids of this Invention

(6) Synthesis of halogen-free ionic liquids of this invention was conducted in the following two stages using the methods described in the literature (Saravanabubu M, Wiencek J M, Ren R X, Linhardt R J. Carbohydr. Polymer 63 268-271 (2006); Brindaban C R and Subas B. Org. Lett. 7 3049-3052 (2005).

(7) First Step. Ionic liquid was synthesized by reaction of alkyl, alkenyl, benzyl or alkyl-functionalized chlorides and bromides, with organic nitrogen compounds such as imidazole, pyridine, isoquinoline and tertiary amines.

(8) Second step. An anion exchange performed by the reaction of the respective ionic liquid with a silver carboxylate, resulting in a silver halide which precipitates and is separated from the reaction by filtration

(9) Both steps were prepared using both conventional heating and microwave oven; the last heating method produces ionic liquids with higher yields (5 to 9%) and in shorter times (95 to 99%) than the first one.

(10) The syntheses of the present invention are illustrated by the preparation of eight ionic liquids named LI 1, LI 2, LI 3, LI 4, LI 5, LI 6, LI 7 y LI 8 respectively, but it does not mean some restriction. The preparation procedure is exemplified by the synthesis of 1-hexyl-3-methyl-imidazolium acetate (LI-1), using two different methods, conventional and microwave heating.

Example 1

Synthesis of 1-hexyl-3-methyl-imidazolium Acetate (LI-1)

Method 1 Conventional Heating

(11) First step: An oven-dried, 100-mL, three-necked, round bottomed flask equipped with a magnetic stirring bar, thermometer and a reflux condenser is charged with 20 mmol 1-methyl-imidazole and 60 mmol of 1-bromohexane, the resulting solution was heated at 80° C. for 24 hr. At the end of this time, two phases were produced, the upper phase was decanted and the lower phase, which contained the ionic liquid, was washed with ethyl acetate (3×20-mL). The solvent was eliminated at reduced pressure.

(12) Second step (Anion interchange): An oven-dried, 100-mL, three-necked, round bottomed flask equipped with a magnetic stirring bar, thermometer and a reflux condenser, were dissolved 10 mmol of 1-hexyl-3-methyl-imidazolium bromide obtained in first step, in 50-mL of acetonitrile. Silver acetate (10 mmol) was slowly added to the solution. The mixture was refluxed for 10 hr, and then the precipitated was filtered off, the ionic liquid was dried under vacuum conditions and it was obtained a yellow liquid.

Synthesis of 1-hexyl-3-methyl-imidazolium Acetate (LI-1)

Method 2: Microwave Heating

(13) First step: An oven-dried, 100-mL, one-necked, round bottomed flask equipped with a magnetic stirring bar, and a reflux condenser is charged with 20 mmol of 1-methyl-imidazole and 60 mmol of 1-bromohexane, the resulting solution was exposed to microwave irradiation in a CEM Discover Labmate microwave oven (100 watts power) and heated at 80° C. for 10 min. At the end of this time, two phases were produced, the upper phase was decanted and the lower phase, which contained the IL, was washed with ethyl acetate (3×20-mL). The solvent was eliminated at reduced pressure.

(14) Second step (Anion interchange): An oven-dried, 100-mL, one-necked, round bottomed flask equipped with a magnetic stirring bar, and a reflux condenser, were dissolved 10 mmol of 1-hexyl-3-methyl-imidazolium bromide obtained in first step, in 50-mL of acetonitrile. Silver acetate (10 mmol) was slowly added to the solution. The mixture was heated in a CEM Discover Labmate microwave oven (75 watts power) for 12 min; silver bromide was filtered off, the ionic liquid was dried under vacuum conditions and it was obtained a yellow liquid.

Examples 2 to 8

(15) The ionic liquids of this invention were synthesized using two different heating methods, the first one (conventional heating) and the second one (microwave heating). The interchange anion step was done using silver carboxylate (acetate, benzoate, butanoate and stearate). The ionic liquids of this invention were characterized by spectroscopic .sup.1H and .sup.13C Nuclear Magnetic Resonance data, the chemical shifts are reported in ppm in d.sub.6-DMSO and CDCl.sub.3 with tetramethylsilane as an internal Standard.

(16) The spectroscopic data and yields of the ionic liquids synthesized in this invention are summarized as follows:

(17) TABLE-US-00002 Yields and spectroscopic data of ionic liquids (1 to 8) Ionic Liquid 1 (LI-1) Method 1 Yield 82% Method 2 Yield 90% 1-hexyl-3-methyl-imidazolium acetate .sup.1H NMR (DMSO-d.sub.6) δ 0.82 (t, J = 6.9 Hz, 3H), 1.22 (m, 6H), 1.75 (sx, J = 5.6 Hz, 2H), 1.80 (s, 3H), 3.87 (s, 3H), 4.18 (t, J = 7.1 Hz, 2H), 7.78 (dd, J.sub.1 = 1.6 Hz, J.sub.2 = 1.9 Hz, 1H), 7.87 (dd, J.sub.1 = 1.6 Hz, J.sub.2 = 1.9 Hz, 1H), 9.39 (s, 1H) ppm. .sup.13C NMR (DMSO-d.sub.6) δ 14.3, 22.4, 22.9, 25.7, 29.9, 31.1, 36.3, 49.3 122.8, 124.1, 137.2, 173.5 ppm. Ionic Liquid 2 (LI-2) Method 1 Yield 85% Method 2 Yield 91% 1-octyl-3-methyl-imidazolium acetate .sup.1H NMR DMSO-d.sub.6) δ 0.82 (t, J = 6.9 Hz, 3H), 1.24 (m, 10H), 1.82 (sx, J = 6.8 Hz, 2H), 2.04 (s, 3H), 3.85 (s, 3H), 4.15 (t, J = 7.0 Hz, 2H), 7.42 (dd, J.sub.1 = 5.5, 1.1 Hz, 2H), 8.69 (s, 1H) ppm. RMN .sup.13C (75.4 MHz, DMSO-d.sub.6) δ 13.6, 22.2, 22.7, 25.5, 28.3, 28.4, 29.4, 31.2, 35.9, 49.8, 122.4, 122.7, 137.0, 175.0 ppm. Ionic Liquid 3 (LI-3) Method 1 Yield 85% Method 2 Yield 90% 1,2-dimethyl-3-octyl-imidazolium acetate .sup.1H NMR(CDCl.sub.3) δ 0.87 (t, J = 6.6 Hz, 3H), 1.26 (m, 10H), 1.81 (sx, J = 7.0 Hz, 2H), 2.04 (s, 3H), 2.78 (s, 3H), 3.99 (s, 3H), 4.18 (t, J = 7.4 Hz, 2H), 7.45 (d, J = 2.0 Hz, 1H), 7.67 (d, J = 2.0 Hz, 1H) ppm. RMN .sup.13C (75.4 MHz, CDCl.sub.3) δ 10.3, 13.6, 21.4, 22.2, 25.9, 28.6 (2C), 29.5, 31.3, 35.6, 48.6, 120.9, 122.7, 143.4, 175.2 ppm. Ionic Liquid 4 (LI-4) Method 1 Yield 89% Method 2 Yield 95% 1-benzyl-3-methyl-imidazolium acetate .sup.1H RMN (CDCl.sub.3) δ 1.98 (s, 3H), 4.02 (s, 3H), 5.52 (s, 2H), 7.33-7.51 (m, 7H), 10.43 (s, 1H) ppm. RMN .sup.13C (75.4 MHz, CDCl.sub.3) δ 22.6, 36.5, 53.2, 121.8, 123.7, 128.8 (2C), 129.4 (3C), 133.4, 138.2, 175.6 ppm. Ionic Liquid 5 (LI-5) 0 Method 1 Yield 89% Method 2 Yield 95% 1,2-dimethyl-3-butyl-imidazolium benzoate .sup.1H RMN (CDCl.sub.3) δ 0.82 (t, J = 7.2 Hz, 3H), 1.20 (sx, J = 7.6 Hz, 2H), 1.55 (qi, J = 7.4 Hz, 2H), 2.47 (s, 3H), 3.71 (s, 3H), 3.87 (t, J = 7.4 Hz, 2H), 7.22-7.32 (m, 5H), 7.97 (dd, J.sub.1 = 8.2, 1.6 Hz, 2H) ppm. RMN .sup.13C (75.4 MHz, CDCl.sub.3) δ 9.6, 13.4, 19.5, 31.6, 35.3, 48.3, 121.0, 123.1, 127.6, 129.5, 130.1, 137.3, 143.3, 171.1 ppm. Ionic Liquid 6 (LI-6) Method 1 Yield 83% Method 2 Yield 91% Butyl-isoquinolinium butanoate .sup.1H RMN (CDCl.sub.3) δ 0.82 (t, J = 7.5 Hz, 3H), 0.95 (t, J = 7.2 Hz, 3H), 1.30 (m, J = 7.6 Hz, 6H), 1.7 (m, J = 7.2 Hz, 2H), 2.1 (t J = 6.0 Hz, 2H), 2.3 (t, J = 7.2 Hz, 2H), 5.0 (t, J = 6.0 Hz, 2H), 7.5-7.86 (m, 5H), 8.5 (s, 1H), 9.15 (s, 1H) ppm. RMN .sup.13C (75.4 MHz, CDCl.sub.3) δ 13.8, 14.1, 18.6, 22.3, 25.9, 28.8, 31.1, 36.1, 61.9, 120.4, 126.4, 127.15, 128.63, 130.2, 135.7, 142.9, 152.4, 173.8 ppm Ionic Liquid 7 (LI-7) Method 1 Yield 78% Method 2 Yield 89% Dimethyl-diethyl-ammonium stearate .sup.1H RMN (CDCl.sub.3) δ 0.9 (s, 3H), 1.39 (t, J = 7.26 Hz, 6H), 1.5 (m, 28H), 1.6 (m, 2H), 2.28 (m, 2H), 2.92 (s, 6H), 3.34 (c, J = 7.14 Hz, 4H), ppm. RMN .sup.13C (75.4 MHz, CDCl.sub.3) δ 7.8, 14.1, 22.7, 25.0, 29.3, 29.7, 32.0, 34.1, 49.16, 60.1, 174.8 ppm Ionic Liquid 8 (LI-8) Method 1 Yield 83% Method 2 Yield 91% Butyl-pyridinium butanoate .sup.1H RMN (CDCl.sub.3) δ 0.86(t, J = 7.5 Hz, 3H), 0.95 (t, J = 7.2 Hz, 3H), 1.24 (m, J = 7.6 Hz, 6H), 1.7 m, J = 7.2 Hz, 2H), 2.15 (t J = 6.0 Hz, 2H), 2.4 (t, J = 7.2 Hz, 2H), 5.2 (t, J = 6.0 Hz, 2H), 8.23 (t, J = 6.0 Hz, 2H), 8.61 (t, J = 6.0 Hz, 1H), 9.62 (d, J = 6.0 Hz, 2H) ppm. RMN .sup.13C (75.4 MHz, CDCl.sub.3) δ 13.5, 13.8, 18.9, 21.3, 25.5, 28.8, 31.2, 36.1, 63.8, 128.5, 145.2, 177.6 ppm

Example 9

Extraction of Sulfured Compounds from Naphtha

(18) The procedure for the sulfured compound removal of the naphtha consisted of putting in contact one part of ionic liquid with 10 parts of naphtha (w/w) whose sulfur content has been determined previously. The mixture is shaken vigorously during 10 minutes, the two phases are separated and the sulfur content is determined in the naphtha after the extraction to determine the percentage of total sulfur removal. The determination of the sulfur content was carried out by method ASTM-D 5453-05: Standard Test for Method Determination of Total Sulfur in Light Hydrocarbons, Fuels Motor and Oils by Ultraviolet Fluorescence.

(19) The percentage of sulfur removed after the extraction liquid-liquid is shown in Table 2.

(20) TABLE-US-00003 TABLE 2 Total sulfur removed % of total sulfur Ionic liquid removed of the gasoline LI-1 68 LI-2 72 LI-3 68 LI-4 70 LI-5 67 LI-6 66 LI-7 69 LI-8 68 Total sulfur in the natural gasoline: 210 ppm Note: LI-1 = 1-hexyl-3-methyl-imidazolium acetate LI-2 = 1-Octyl-3-methyl-imidazolium acetate LI-3 = 1,2-dimethyl-3-octyl-midazolium acetate LI-4 = 1-benzyl-3-methyl-imidazolium acetate LI-5 = 1,2-dimethyl-3-butyl-imidazolium benzoate LI-6 = Butyl-isoquinolinium butanoate LI-7 = Dimethyl-diethyl ammonium stearate LI-8 = Butyl-pyridinium butanoate

(21) From the Table No 2 is come off that the greater extraction sulfured compounds to start off of naphtha, was made with 1-octyl-3-methyl-imidazolium acetate (Ionic liquid, LI-2). The tests of recovery and recycling were made with this compound.

(22) ##STR00014##

1-Octyl-3-methyl-imidazolium acetate

Example 10

Recovering and Recycling of the Ionic Liquids

(23) After each extraction the regeneration of the ionic liquids was realized by a procedure which consists of three steps; in the first step the ionic liquid was heated between 60 and 90° C., preferably of 75 to 85° C., in conditions of reduced pressure between 130 and 150 mmHg, preferably from 135 to 145 mmHg, for elimination of volatile compounds, in the second step, the ionic liquid was washed with solvents as ether, hexanes, heptanes, ether of petroleum or using mixtures of them in a proportion v/v between 1 and 15, preferably from 1 to 10; and in the third step the solvent was eliminated under vacuum.

(24) The Table 3 shows the results of the sulfur removal after 3 cycles of regeneration and recycling of the LI-2, using original naphtha in each cycle.

(25) TABLE-US-00004 TABLE 3 Desulfurization of original naphtha using recovered ionic liquid. Extraction Sulfur removal Ionic liquid IL-2 cycle (%) 1 2 3 72 70 67

(26) As listed in Table 3, the ionic liquids can be used several times in removing sulfur compounds, because the performance of sulfur removing is very similar, indicating that they do not lose their physicochemical characteristics during the extraction process and recovery

(27) Quantitative desulfurization of naphtha was accomplished in three consecutives cycles of extraction (over 95%), using the ionic liquids described in this invention, as shown in Table 4.

(28) TABLE-US-00005 TABLE 4 Total sulfur removed using the desulfurated naphtha of previous extraction Extraction Sulfur removal Ionic liquid IL-2 cycle (%) 1 2 3 72 87 96

(29) In Table 4 shown that with increasing the number of extraction cycles, increases the removal of sulfur, reaching values very close to the total extraction (100%).

(30) 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.