WO2001040150A1

WO2001040150A1 - Process for the extraction of an aromatic compoung from an aliphatic phase using a non-neutral ionic liavin

Info

Publication number: WO2001040150A1
Application number: PCT/US2000/032500
Authority: WO
Inventors: Lieh-Jiun Shyu; Zongchao Zhang; Qinglin Zhang
Original assignee: Akzo Nobel N.V.
Priority date: 1999-12-01
Filing date: 2000-11-29
Publication date: 2001-06-07

Abstract

Aromatic compounds can be removed from an aliphatic hydrocarbon fluid by contacting the fluid with a non-neutral ionic liquid that comprises a metal halide-derived anion.

Description

PROCESS FOR THE EXTRACTIO_{N O}F AN _AR_OMATIC COMPOUNDS FROM AN ALIPHATIC PH^ASE USING A NON-NEUTRAL IONIC LIQUID

Background of the Invention

Transition metals species (such as V, Ni, Ti or Fe porphyrin) , nitrogen- and sulfur-containing (such as dibenzothiophene) compounds are normally present in crude oils. The concentration level of nitrogen and sulfur in gasoline and diesel fuel has been projected to be reduced to what cannot be achieved with existing technology without a large increase in cost. The current practice of employing a hydrodesulfurization catalyst has been found to be not effective for the desulfurization of dialkyl-substituted dibenzothiophene. The petroleum industry is under increasing pressure to reduce N and S level from fuels. In fluidized catalytic cracking units, heavy crude fractions are cracked using a zeolite catalyst. However, metals, such as V and Ni, in the oil are known to deactivate the catalyst by surface deposition and by causing structural damage. In addition, benzene is a known toxic aromatic component in the treated fuels. Representative prior art approaches are described in the following U.S. Patent Nos.: 5,435,907; 5,449,452; 5,462,651; 5,472,595; 5,529,968; 5,556,824; 5,576,261; 5,651,878; 5,676,822; and 5,837,640.

U.S. Patent Nos. 4,422,634 and 4,440,634 to H.L. Mitchell describe the use of solid salt compositions, rather than ionic liquid compositions, to remove aromatics from aliphatic liquids. U.S. Patent No. 4,359,596 to K.A. Howard et al . discusses the removal of aromatics from petroleum feedstocks using a quaternary cation-containing liquid salt composition comprising an organic anion. This patent deals primarily with quaternary salts. Some of the quaternary salts taught for use by this patent are known to be toxic. Moreover, this patent, at Col. 4, line 8 names tetrachloroaluminate as a possible anion to select in making its liquid salt compositions. As will be described hereinafter, this anion will yield a neutral composition that does not perform the desired extraction process of the present invention, as demonstrated in Comparative Example 5 hereinbelow.

U.S. Patent No. 5,220,106 to D.R. Boate et al . discusses the removal of aromatics from petroleum feedstocks using one class of non-quaternary clathrate salts comprising organic anions . Most of the clathrate salts described in this patent are solids at low temperature, including certain non-quaternary amine tetrachloroaluminates . The aromatic removal by these solids is extraordinarily less effective than the low temperature ionic liquids to be disclosed hereinafter in the present specification as demonstrated in Example 4. Moreover, this patent also, at Col. 4, lines 35- 36 names tetrachloroaluminate as a possible anion to select in making its clathrate salt compositions. As previously mentioned in connection with the Howard et al . patent hereinabove, the tetrachloroaluminate anion yields a neutral composition that does not perform the desired extraction process of the present invention, as demonstrated in Comparative Example 5 hereinbelow. A moisture stable ionic liquid, such as imidazolium hexafluorophosphate, is known to also be a solvent for the extraction of metal ions from aqueous solutions.

An ionic liquid comprising a metal halide and an organic salt, such as imidazolium chloride, pyridinium chloride and alkyl ammonium chloride, is known to be an effective catalyst for benzene alkylation. A preferred catalyst of this type is trimethylamine hydrochloride which is described in U.S. Patent Nos. 5,731,101 and 5,824,832, which are each incorporated herein in their entirety.

Summary of the Invention

The present invention relates to the use of a non- neutral ionic liquid that comprises a metal halide-derived anion for the extraction of aromatic compounds that may also contain heteroatoms such as sulfur, nitrogen, and metals from an aliphatic hydrocarbon fluid, such as a lubricant oil or a petroleum oil.

Description of Preferred Embodiments

The present invention relates to the use of non-neutral ionic liquids that comprise a metal halide-derived anion (either a moisture stable or moisture sensitive ionic liquid, or mixture thereof) to extract aromatic compounds, for example those containing N, S, and metals, from such oil and fuel sources. The ionic liquid phase is immisible with the saturated lubricant oil or crude oil. By using the present invention, the oil or fuel can be effectively cleaned using this ionic liquid treatment. As used herein, the term "non-neutral" is to be construed on the basis of the definition of Lewis acid and Lewis base. The Figure gives a plot of such acidity or basicity as a function of the anion fraction as a function of aluminum trichloride in an ionic liquid comprising a nitrogen atom-containing cation and such an anion. At equimolar proportions, which is the case for the tetrachloroaluminate species, where the mole fraction equals 0.5, the resulting composition is neither acidic nor basic. It is neutral in the sense that that term is used herein.

The metal halides useful in the ionic liquid component used in the process of this invention (and to which the selected organic base or bases, for example, are added) are those compounds which can form anions containing polyatomic chloride bridges in the presence of the alkyl-containing a ine hydrohalide salt. Preferred metal halides are covalently bonded metal halides. Suitable metals that can be selected for use herein include those from Groups VIII and IB, IIB and IIIA of the Periodic Table of the Elements. Especially preferred metals are selected from the group comprising aluminum, gallium, iron, copper, zinc, and indium, with aluminum being most preferred. The corresponding most preferred halide is chloride and therefore, the most preferred metal halide is aluminum trichloride. Other possible choices for metal halides to select include those of copper (e.g., copper monochloride) , iron (e.g., ferric trichloride), and zinc (e.g., zinc dichloride) . Aluminum trichloride is most preferred because it is readily available and can form the polynuclear ion having the formula A1₂C1₇ ^" . Furthermore, the molten compositions comprising this polynuclear ion are useful as described hereinbefore. Mixtures of more than one of these metal halides can be used. Granular aluminum trichloride (+4 -14 mesh or having a particle size between 1.41 mm and 4.76 mm) can be an especially preferred metal halide to employ. It is easy to handle in air without fuming problems and has good flow properties. Its reaction with trimethylamine hydrochloride, for example, is slower and more uniform than with aluminum trichloride powder, with a temperature exotherm to about 150°C. While the resulting ionic liquid is slightly hazy due to the presence of insoluble impurities from the aluminum trichloride, the insoluble, which settle out upon storage of the liquid, do not have an adverse effect on the performance of the ionic liquid in regard to the process of the present invention .

One preferred class of organic base intended to be added to the metal halide to form the ionic liquid component that is used in the process of the present invention is an alkyl-containing amine hydrohalide salt. The terminology "alkyl-containing amine hydrohalide salt", as used herein, is intended to cover monoamines, as well as diamines, triamines, other oligoamines and cyclic amines which comprises one or more "alkyl" groups and a hydrohalide anion. The term "alkyl" is intended to cover not only conventional straight and branched alkyl groups of the formula - (CH₂)_nCH₃ where n is from 0 to about 18, preferably 0 to about 8, in particular 0 to 3 , but other structures containing heteroatoms (such as oxygen, sulfur, silicon, phosphorus, or nitrogen) . Such groups can carry substituents . Representative structures include ethylenediamine, ethylenetriamine, morpholino, and poloxyalkylamine substituents. "Alkyl" includes "cycloalkyl" as well.

The preferred alkyl-containing amine hydrohalide salts useful in the present invention have at least one alkyl substituent and can contain as many as three alkyl substituents. The preferred compounds that are contemplated herein have the generic formula R₃N.HX, where at least one of the "R" groups is alkyl, preferably alkyl of from one to eight carbon atoms (preferably, lower alkyl of from one to four carbon atoms) and X is halogen, preferably chloride. If each of the three R groups is designated R₁ R₂ and R₃, respectively, the following possibilities exist in certain embodiments: each of R_;L-R₃ can be lower alkyl optionally interrupted with nitrogen or oxygen or substituted with aryl; R_x and R₂ can form a ring with R₃ being as previously described for R-; R₂ and R₃ can either be hydrogen with R_x being as previously described; or R₁ R₂ and R₃ can form a bicyclic ring. Most preferably, these groups are methyl or ethyl groups. If desired the di- and trialkyl species can be used. One or two of the R groups can be aryl, but this is not preferred. The alkyl groups, and aryl, if present, can be substituted with other groups, such as a halogen. Phenyl and benzyl are representative examples of possible aryl groups to select. However, such further substitution may undesirably increase the size of the group, and correspondingly increase the viscosity of the melt. Therefore, it is highly desirable that the alkyl groups, and aryl, if present, be comprised of carbon and hydrogen groups, exclusively. Such short chains are preferred because they form the least viscous or the most conductive melts. Mixtures of these alkyl-containing amine hydrohalide salts can be used.

The mole ratio of alkyl-containing amine hydrohalide salt which is to be combined with the metal halide is preferably, in general, range from above about 1:1 to about 1:2.5 so as to yield an acidic melt. In a highly preferred embodiment, the low temperature molten composition in the process of this invention consists essentially of the metal halide and the alkyl-containing amine hydrohalide salt.

Specifically, the most preferred, acidic, low temperature molten composition is a mixture consisting essentially of a mole ratio of trimethylamine hydrochloride to aluminum trichloride of from about 1:1.5 to about 1:2, preferably about 1:2.

Typically, the metal halide and the alkyl-containing amine hydrohalide salt are solids at low temperature, i.e., below about 100° C. at standard pressure. After mixing the two solids together, the mixture can be heated until the mixture becomes a liquid. Alternatively, the heat generated by the addition of the two solids will result in forming a liquid without the need for additional external heating. Upon cooling, the mixture remains a liquid at low temperature, i.e., below about 70°C, preferably below about 50°C, and more preferably below about 30°C.

The following Table illustrates typical melting points for a number of ionic liquid compositions and can be used in the selection of one or more for use with the present invention:

Table 1

The advantages of using the type of low temperature ionic liquid described for use herein include having an easy-to-pump liquid employed in the reaction vessel and an extraction performance that does not depend upon the dissolution rate of a solid in the extracting liquid phase. The extraction capability is much greater using an ionic liquid rather than a composition that is a solid phase material (as demonstrated in Example 4 and 5) .

The minimum amount of ionic liquid that is preferably used to remove the aromatic compound component from the aliphatic fluid will be substantially equivalent to the stoichiometric amount of the target aromatic compound or compounds that are present in the fluid. The use of an excess of the ionic liquids is within the contemplation of the present invention since any excess ionic liquids can be recycled and reused. It is within the contemplation for the ionic liquid used herein to be supported, for example, by a metal oxide support, including those of silica, alumina or a zeolite, carbon, graphite, fibers, or porous polymers. A representative microporous polymeric support that can be used is described in U.S. Patent No. 4,519,909 to A.J. Castro (which is incorporated herein by reference in its entirety) . This particular microporous polymer is commercially available under the ACCUREL. This invention is further illustrated by the Examples that follow.

Example 1

Dodecane (10 gm) and 0.05 gm of dibenzothiophene were weighed into a glass bottle. The resulting clear solution was then analyzed by GC and was shown to contain 4758 ppm of dibenzothiophene. Then, 5.1 gm of an ionic liquid comprising trimethylamine hydrochloride (TMAC) /Al₂Cl₇ ionic liquid into the glass bottle containing the dodecane and dibenzothiophene-containing solution. The solution was stirred for one half hour at room temperature, and a sample of the clear solution above the ionic liquid layer was withdrawn and was analyzed by GC. The analysis showed that the dibenzothiophene level in the clear solution had decreased 93% to 344 ppm. Example 2

Dodecane (10 gm) and 0.05 gm of naphthalene were weighed into a glass bottle. The resulting clear solution was then analyzed by GC and was shown to contain 4713 ppm of naphthalene. Then, 5.4 gm of an ionic liquid comprising trimethylamine hydrochloride (TMAC) /A1₂C1₇ ionic liquid into the glass bottle containing the dodecane and naphthalene- containing solution. The solution was stirred for one half hour at room temperature, and a sample of the clear solution above the ionic liquid layer was withdrawn and was analyzed by GC. The analysis showed that the naphthalene level in the clear solution had decreased 70% to 1496 ppm.

Example 3

This Example illustrates a multiple step treatment in accordance with the present invention.

Dodecane (10 gm) and 0.05 gm of dibenzothiophene were weighed into a glass bottle. The clear solution was then analyzed by GC that showed that there was 4772 ppm of dibenzothiophene in the background sample. Then, 3 gm of trimethylamine hydrochloride (TMAC) /A1₂C1₇ ionic liquid was added into the glass bottle holding the sample containing the dodecane and dibenzothiophene. The resulting sample was stirred for one half hour at room temperature, and a sample of the clear solution above the ionic liquid layer was than withdrawn and was analyzed by GC. Analysis showed that the dibenzothiophene level in the clear solution had decreased 88% to 573 ppm. Then, 6.09 g of the dodecane clear liquid above ionic liquid layer was placed into another glass bottle, and 3.25g of the same ionic liquid was added to it. This sample was then stirred for one half-hour. A sample was withdrawn and analyzed by GC. The analytical results showed that the dibenzothiophene had been completely removed by the second treatment with ionic liquid.

Example 4

Decane (10 gm) and 0.05 gm of dibenzothiophene were weighed into a glass bottle. The resulting clear solution was then analyzed by GC and was shown to contain 5211 ppm of dibenzothiophene. Then, 3 gm of an ionic liquid comprising trimethylamine hydrochloride (TMAC) /A1₂C1₇ ionic liquid was placed into the glass bottle containing the dodecane and dibenzothiophene-containing solution. The solution was stirred for one half hour at room temperature, and a sample of the clear solution above the ionic liquid layer was withdrawn and was analyzed by GC. The analysis showed that the dibenzothiophene level in the clear solution had decreased 89% to 564 ppm.

Example 5 (Comparative Example)

This Comparative Example illustrates that the selection of tetrachloroaluminate as an anion, which produced a neutral composition in regard to either Lewis acidity or basicity does not remove aromatics from an aliphatic liquid.

Decane (10 gm) and 0.05 gm of dibenzothiophene were weighed into a glass bottle. The resulting clear solution was then analyzed by GC and was shown to contain 6049 ppm of dibenzothiophene. Then, 3 gm of an ionic "liquid" comprising trimethylamine hydrochloride (TMAC)/A1C1₄ ionic "liquid" was placed into the glass bottle containing the dodecane and dibenzothiophene-containing solution. The trimethylamine hydrochloride (TMAC) /A1C1₄ ionic "liquid" was made from one mole of trimethylamine hydrochloride and one mole of A1C1₃. It is a solid at room temperature.

The solution containing the solid phase ionic "liquid" was stirred for one half hour at room temperature, and a sample of the clear solution above the ionic "liquid" layer was withdrawn and was analyzed by GC. The analysis showed that the dibenzothiophene content in the clear solution had remained at the same level. The solid phase ionic "liquid" did not show any extraction capability. The clear decane solution containing the solid phase ionic "liquid" was then heated to 90°C with stirring for one half hour. The dibenzothiophene level in the clear solution was analyzed by GC again. It showed that the dibenzothiophene level had remained the same after treatment at 90°C. The solid phase ionic "liquid" did not show any extraction capability even when the system had been heated to 90°C. Example 6

Preparation of TMAC-A1C1₃ Ionic Liquids

A. A1C1₃/TMAC = 2:1

Two moles of aluminum trichloride (266.7 g) were added slowly to one mole of stirred trimethylamine hydrochloride salt (95.57 g) , both from Aldrich, in a glove box under dry nitrogen. The reaction was exothermic. A light brown liquid was formed with a very small amount of solids. This liquid was stirred for five hours, and the liquid had a density of 1.4-1.5 g/mL at room temperature. The product was stable as a liquid at room temperature under a dry atmosphere.

B: A1C1₃/TMAC = 1.5:1

The same procedure described in part A of this Example was followed, except that only 1.5 mole aluminum trichloride (200 g) was used. A light brown liquid was formed. The product was stable as liquid at room temperature under a dry atmosphere. No undissolved solids were formed.

Example 7

The ionic liquid (A1C1₃/TMAC = 2:1) prepared in Example 6, Part A was weighed into a glass bottle and then the selected model compound was added dropwise to the ionic liquid at room temperature. Control the speed of addition of model compounds so the temperature of the mixture can be kept below 30°C. The resulting mixture in the bottle was shaken for a few minutes to obtain a biphasic separation. The organic phase was then separated from ionic phase. The absorption capacity for each model compound was given in table 1:

Table 1: Adsorption capacity of A1C1₃/TMAC=2 : 1 for model compound

Upon addition of thiophene or 2-methylthiophene into the ionic liquid, the color of the mixture changed immediately to brown and then to dark brown with formation of a solid phase. The ionic liquid interacts with (CH₃) ₂CHCH₂SH mildly and led to formation of a solid phase and a colorless organic phase.

Addition of 1-hexene into the ionic liquid resulted in the formation reddish brown solution initially. Further addition of 1-hexene led to a light brown organic phase and an ionic liquid phase.

The mixing of aromatics with the ionic liquid resulted in formation of yellow brown or dark brow solution as an organic phase. The saturated hydrocarbons did not interact with the ionic liquid. Upon mixing, a clear two-phase solution was formed.

Example 8

Follow the same procedure as described in Example II except that the ionic liquid made according to Example I B was used. The absorption capacity for each model compound was given in table 2 :

Table 2 shows the adsorption capacity of AlCl₃/TMAC=l .5 : 1 for the selected model compound:

No interaction occurred between 2 -methylpentane and the ionic liquid. Mixing of aromatics with the ionic liquid resulted in a slight color change to light yellow. Addition of 1-hexene into the ionic liquid resulted in formation of brown solution initially and a light brown organic phase.

Addition of thiophene or 2 -methylthiophene into the ionic liquid resulted in formation of a brown organic phase and a brown solid phase . Mixing of (CH₃ ) ₂CHCH₂SH with the ionic liquid led to formation of a solid phase and a colorless organic phase .

Comparison of the absorption capacity of the tested TMAC/AICI₃ ionic liquids

# = ionic liquids became solid after interaction with the selected model compound.

Examples 9 - 15

Table 1 lists the sulfur content of gasoline and diesel samples received for the testing in Examples

9-15.

*numbers in brackets were given by supplier

Example 9: Treatment of High-S Level Naphtha

In this Example, 5.95 g of an ionic liquid formed by mixing aluminum trichloride and trimethylaluminum chloride, "TMAC" (A1C1₃/TMAC = 1.5:1) was mixed with 37.36 g of high S- level naphtha in a Pyrex flask under vigorous agitation at room temperature. The ionic liquid became light brown in one hour and was partially solidified. After separation from the ionic liquid, the liquid naphtha was analyzed by X- ray fluorescence. The total sulfur concentration was reduced by 54.9% (from 820 ppm to 370 ppm) .

Example 10: Treatment of High-S Level Naphtha

The same procedures were followed in this Example were described in Example 9 except that 3.71 g of the ionic liquid (A1C1₃/TMAC = 1.5) was mixed with 43.3 g of high-S level naphtha. X-ray fluorescence analysis of the treated sample indicated a 42.7% total sulfur reduction (from 820 ppm to 470 ppm) . Example 11: Treatment of Low-S Level Naphtha

In this Example, the same procedures were followed as described in Example 9 except that 2.8 g of the ionic liquid (A1C1₃/TMAC = 1.5) was mixed with 46.51 g of low-S level naphtha. X-ray fluorescence analysis of the treated sample indicated a 40.9% total sulfur reduction (from 220 ppm to 130 ppm) .

Example 12 : Treatment of Low S Level Naphtha

The same procedures as described in Example 9 were followed except that 3.79 g of the ionic liquid (A1C1₃/TMAC = 1.5) was mixed with 45.54 g of low-S level naphtha. X-ray fluorescence analysis of the treated sample indicated a 50% total sulfur reduction (from 220 ppm to 110 ppm) .

Example 13: Treatment of High S Gas-Oil

The same procedures as described in Example 9 were used except that 9.24 g of the ionic liquid (A1C1₃/TMAC = 1.5) was mixed with 47.26 g of high-S level gas-oil. X-ray fluorescence analysis of the treated sample indicated a 33.18 % total sulfur reduction (from 12,122 ppm to 8,100 ppm) .

Example 14: Treatment of High S Gas-Oil

The same procedures described in Example 9 was used in this Example except that 4.24 g of the ionic liquid (AICI₃/TMAC = 1.5) was mixed with 42.53 g of high-S level gas-oil. X-ray fluorescence analysis of the treated sample indicated a 20.81 % total sulfur reduction (from 12,122 ppm to 9, 600 ppm) . Example 15: Treatment of Low S Gas-Oil

The same procedures as described in Example 9 were used except that 5.74 g of the ionic liquid (AlCl₃/TMAC = 1.5) was mixed with 44.07 g of low-S gas-oil. X-ray fluorescence analysis of the treated sample indicated a 28% total sulfur reduction (from 250 ppm to 180 ppm) .

Summary: Treatment Results for Ionic Liquid (A1C1₃/TMAC = 1.5)

Example No. Ionic Untreated Untreated S before S after S Naphtha or

Liquid g Treatment Treatment Removal Gas-oil /IL g ppm ppm % g/g

9 5.95 High S Naphtha 37.36 820 370 54.9 6

10 3.71 High S Naphtha 43.3 820 470 42.7 12

1 1 2.8 Low S Naphtha 46.51 220 130 40.9 17 12 3.79 Low S Naphtha 45.54 220 110 50 12

13 9.24 High S Gas-oil 47.26 12122 8100 33.18 5 652M

14 4.24 High S Gas-oil 42.53 12122 9600 20.81 10 652M

15 5.74 Low S Gas-oil 868 44.07 250 180 28 8 16 4.72 Low S Gas-oil 868 46.35 250 180 28 10

The foregoing Examples have been presented to merely illustrate certain embodiments of the claimed invention and, for that reason, should not be construed in a limiting fashion. The scope of protection sought is set forth in the Claims that follow.

Claims

We Claim :

1. A process for the removal of aromatic compounds from an aliphatic hydrocarbon fluid which comprises contacting the fluid with an effective amount for such removal of a non-neutral ionic liquid that comprises a metal halide-derived anion.

2. The process of Claim 1 wherein the metal halide is a covalently bonded metal halide.

3. The process of Claim 2 wherein the metal of the metal halide is selected from the group comprised of aluminum, gallium, iron, copper, zinc, and indium.

4. The process of Claim 3 wherein the metal halide is aluminum trichloride.

5. The process of Claim 4 wherein the ionic liquid is an alkyl-containing amine hydrohalide salt containing three alkyl groups .

6. The process of Claim 5 wherein the ionic liquid consists essentially of a mole ratio of a chloride of the alkyl-containing amine hydrohalide salt to aluminum trichloride of from above about 1:1 to about 1:2.

7. The process of Claim 1 wherein the ionic liquid is an alkyl-containing amine hydrohalide salt of the formula R₃N.HX, where at least one R group is alkyl.

8. The process of Claim 7 wherein the alkyl-containing amine hydrohalide salt is of the formula R₃N.HX where at least one R group is alkyl and the metal halide contains a metal which is selected from Group VIII, Group IB and Group IIB of the Periodic Table of The Elements.

9. The process of Claim 8 wherein the metal halide is ferric trichloride.

10. The process of Claim 1 wherein the aliphatic fluid containing the aromatic compound is treated by the ionic liquid in multiple steps until the aromatic compounds are substantially removed.

11. The process of Claim 1 wherein the contacting of the aliphatic fluid with the ionic liquid takes place at a temperature that ranges from about room temperature to about 150°C.