Abstract:
Initial high sulfur levels of a hydrocarbon feedstock are reduced to desired low levels without the need for integration of substantial new equipment or hardware with existing hydroprocessing reactors. Ionic liquids are utilized as organic sulfur extraction agents and are added to and mixed with the hydrocarbon feedstock containing organosulfur compounds in, or upstream of, an existing cold separator vessel. The ionic liquid and hydrocarbon mixture is maintained in contact under conditions which promote the formation of ionic sulfur-containing derivatives that are soluble in the ionic liquid to be formed, thereby enabling extractive removal and separation of the organosulfur compounds from the feedstock.

Description:
RELATED APPLICATIONS 
       [0001]    This application is related to and claims priority from United Stated Provisional Patent Application Ser. No. 61/318,274 filed on Mar. 26, 2010, which is incorporated by reference herein in its entirety. 
     
    
     BACKGROUND OF THE INVENTION 
       [0002]    1. Field of the Invention 
         [0003]    This invention relates to a system and process for desulfurizing hydrocarbon fractions, and in particular to a system and process that integrates ionic liquid extractive desulfurization with a hydroprocessing reactor. 
         [0004]    2. Description of Related Art 
         [0005]    The discharge into the atmosphere of sulfur compounds during processing and end-use of the petroleum products derived from sour crude oil pose safety and environmental problems. The discharge into the atmosphere of sulfur compounds during processing and end-use of the petroleum products derived from sour crude oil pose safety and environmental problems. Sulfur-containing compounds in hydrocarbon mixtures can include organosulfur compounds such as mercaptans, thiophenes, benzothiophenes, dibenzothiophenes, which can include substituted alkyl, aryl or alkaryl groups. 
         [0006]    The stringent sulfur specifications applicable to transportation and other fuel products have impacted the refining industry and refiners will have to continue to make investments necessary to greatly reduce the sulfur content in gas oils to 10 parts per million by weight (ppmw). In industrialized countries of the United States, Japan and many countries of Europe, transportation fuel producers have already made investments and are producing environmentally clean transportation fuels. For instance, in 2007 the United States Environmental Protection Agency required sulfur content of highway diesel fuel to be reduced 97%, from 500 ppmw (low sulfur diesel) to 15 ppmw (ultra-low sulfur diesel). The European Union has enacted even more stringent standards, requiring diesel and gasoline fuels sold in 2009 to contain less than 10 ppmw of sulfur. The developing countries are following in the direction of the industrialized nations and moving forward with regulations that will require more refineries to produce low sulfur transportation fuels. 
         [0007]    In order to keep pace with recent trends toward higher production of low sulfur fuels, refiners must choose among the processes or crude oils that provide the flexibility to ensure that future specifications are met with minimum investment by utilizing existing units and capacity. Conventional technologies such as hydrocracking and two-stage hydrotreating offer solutions to refiners for the production of clean transportation fuels. These technologies are available and can be applied as new production facilities are constructed. However, many existing hydroprocessing facilities, such as low pressure hydrotreaters, which represent substantial prior investment, were constructed before these more stringent sulfur requirements were enacted. It is very difficult to upgrade existing hydroprocessing systems because of the comparably more sever operational requirements (i.e., temperature and pressure) for clean fuel production. Available retrofitting options for refiners include increasing the hydrogen partial pressure by increasing the recycle gas quality, applying more active catalyst compositions, installing improved reactor components to enhance liquid-solid contact, increasing reactor volume and increasing the feedstock quality. 
         [0008]    Hydrotreating and hydrocracking systems consist of two main sections: reaction and separation, the configuration of which can vary according to the particular application. In general, in systems that use either a hot separator, commonly referred to as a “hot scheme,” or in systems that use a cold separator, commonly referred to as a “cold scheme,” the effluent from a catalytic reactor is passed to a heat exchanger in which its temperature is reduced by transferring heat to the reactor feedstock. After compression, gases are recycled to the catalytic reactor and bottoms are introduced to a low pressure, low temperature separator for further separation. 
         [0009]    There are many hydrotreating units installed worldwide producing transportation fuels containing 500-3000 ppmw sulfur. These units were designed for, and are being operated at, relatively mild conditions, e.g., low hydrogen partial pressures of 30 kilograms per square centimeter for straight run gas oils boiling in the range of 180 C.° to 370° C. 
         [0010]    However, with the stringent environmental sulfur specifications in transportation fuels mentioned above, the allowable sulfur level is being lowered to a maximum of 10 ppmw. This level of sulfur in the end product conventionally requires construction of new hydrotreating units capable of withstanding high temperature and/or pressure conditions, substantial retrofitting of existing facilities (e.g., by integrating new reactors, integrating gas purification systems, reengineering the internal configuration and components of reactors, and the like), and/or deployment of more active catalyst compositions. 
         [0011]    Hydrocarbon mixtures can also contain nitrogen-containing compounds which often inhibit the desulfurization reactions. In a deep desulfurization process, it is therefore advantageous to also eliminate nitrogen-containing compounds. Nitrogen-containing compounds include organonitrogen compounds such as pyridines, amines, pyrroles, anilines, quinoline, and acridine, which can include substituted alkyl, aryl or alkaryl groups. 
         [0012]    The development of non-catalytic processes to carry out the final desulfurization of petroleum distillate feedstocks has been widely studied. Prior art systems describe purification processes based on oxidation of sulfur-containing compounds, e.g., as disclosed in U.S. Pat. Nos. 5,910,440, 5,824,207, 5,753,102, 3,341,448 and 2,749,284; based on adsorption, e.g., as disclosed in U.S. Pat. Nos. 5,730,860, 3,767,563, 4,830,733; or based on the use of feedstock transfer complexes, e.g., as disclosed in PCT Patent Publication Number WO 98/56875. 
         [0013]    A process for desulfurization of light gasoline was investigated based on precipitation of S-alkylsulfonium salts produced by the reaction of sulfur-containing compounds with alkylating agents, as reported by Y. Shiraishi et al., “A Novel Desulfurization Process for Fuel Oils Based on the Formation and Subsequent Precipitation of S-Alkylsulfonium Salts,”  Ind . &amp;  Eng. Chem. Res ., vol. 40, no. 22 (2001), pp. 4919-4924). While this process does not use either catalyst or hydrogen and reportedly can be operated under moderate conditions, insoluble ionic compounds are formed that must be separated, after anion metathetic exchange, by filtration. 
         [0014]    Ionic liquids can also be suitable for desulfurizing hydrocarbon fractions by extraction. Removal rates as high as 40 W % at room temperature have been reported by X. Jiang et al., “Imidazolium-based alkylphosphate ionic liquids—A potential solvent for extractive desulfurization of fuel,”  Fuel , vol. 87, no. 1 (2008), pp. 79-84, and J. Wang et al., “Desulfurization of gasoline by extraction with n-alkyl-pyridinium-based ionic liquids,”  J. Fuel Chem. and Tech ., vol. 35, no. 3 (2007), pp. 293-296. The processes described in the Jiang et al. and Wang et al. references use gasoline as the feedstock to demonstrate extractive desulfurization. 
         [0015]    Non-aqueous ionic liquids of the general formula Q + A − , initially developed by electrochemists, are useful as solvents and catalysts for organic, catalytic or enzymatic reactions, as solvents for liquid-liquid separations or for the synthesis of new materials. H. Olivier-Bourbigou et al., “Ionic liquids: perspectives for organic and catalytic reactions.”  Journal of Molecular Catalysis A: Chemical  (2002), 182-183, 419-437. Because of their completely ionic and polar nature, these media prove to be very good solvents for ionic or polar compounds. Ionic liquids are also suitable solvents for carrying out alkylation of sulfur-containing or nitrogen-containing derivatives of sulfonium and ammonium compounds, respectively. In the Olivier-Bourbigou et al. reference, ionic liquids are used as acid catalysts for alkylation reactions. 
         [0016]    U.S. Pat. No. 6,274,026 describes the use of ionic liquids to remove sulfur using an electrochemical process. Sulfur is removed from a stream containing hydrocarbon and polymerizable sulfur compounds by combining the hydrocarbon feed with a ionic liquid and electrochemically oxidizing the polymerizable sulfur compounds. A first fraction comprising sulfur oligomers, ionic liquid, and entrained hydrocarbon, and a second fraction comprising desulfurized hydrocarbon feed, are recovered. However, the process described in U.S. Pat. No. 6,274,026 cannot be readily integrated with existing hydrotreating facilities. 
         [0017]    U.S. Pat. No. 7,198,712 describes a process for desulfurization and denitrification of hydrocarbon fractions. The hydrocarbon mixture is brought into contact with a non-aqueous ionic liquid of the general formula Q + A − , in which Q +  is a ammonium, phosphonium or sulfonium cation, that contains at least one alkylating agent of the formula Rx. − , making it possible to form ionic sulfur-containing derivatives and nitrogen-containing derivatives that have a preferred solubility in the ionic liquid. The ionic liquid is separated by decanting it from the resulting hydrocarbon mixture that is low in sulfur and nitrogen. However, such a system is described as a grass root desulfurization system, and there is no suggestion as to how such a process can be integrated in existing hydroprocessing systems. 
         [0018]    As used herein, the term “hydroprocessing” includes hydrocracking, hydrotreating and hydrodesulfurization. 
         [0019]    As is apparent from the above-described disclosures, ionic liquids have been proposed for use in certain types of desulfurization and/or denitrification. However, the prior art disclosures have various drawbacks. A main application of ionic liquids is to promote alkylation reactions. Other disclosures teach systems that require construction or substantial modification to existing refinery plants. Therefore, it is an object of the present invention to increase the level of desulfurization or both desulfurization and denitrification in hydroprocessing systems using ionic liquids without the drawbacks associated with prior art systems and methods. 
         [0020]    It is another object of the present invention to provide a system and process to reduce the sulfur level, or both the sulfur and nitrogen level, of catalytic reactor effluents using existing equipment downstream of the catalytic reactor in hydroprocessing systems. 
       SUMMARY OF THE INVENTION 
       [0021]    The above objects and further advantages are provided by the system and process of the present invention for reducing the sulfur content of a hydrocarbon oil feedstock in which ionic liquid is mixed with a catalytic reactor effluent to thereby promote extractive removal of sulfur compounds. 
         [0022]    According to one embodiment of the present invention, a hydrocarbon oil feedstock containing organosulfur and organonitrogen compounds is introduced to a catalytic reactor along with hydrogen gas. The catalytic reactor effluent is passed to a high pressure separator in which a hydrogen stream is separated and a mixed high pressure separator effluent is produced. The mixed high pressure separator effluent including hydrogen sulfide, ammonia, and a hydroprocessed hydrocarbon mixture is contacted with water to prevent precipitate formation, and an ionic liquid, preferably a non-aqueous ionic liquid. The mixture of the high pressure separator effluent, water and ionic liquid is passed to a low pressure separator, in which water is separated, hydrogen sulfide and ammonia is purged, and from which the remaining hydrocarbon mixture is conveyed to a fractionator. In the low pressure separator and, in certain embodiments, in the piping between the low pressure separator and the location in which the ionic liquid is introduced, the ionic liquid and the hydroprocessed hydrocarbon mixture are retained in contact for a time sufficient for extractive removal of organosulfur and organonotro compounds to occur. Accordingly, ionic sulfur-containing derivatives, i.e., derived from the organosulfur compounds in the hydroprocessed hydrocarbon mixture, and ionic sulfur-containing derivatives, i.e., derived from the organonitrogen compounds in the hydroprocessed hydrocarbon mixture, that are soluble in the ionic liquid are formed and are contained in the hydrocarbon mixture. The low pressure separator effluent is passed to a fractionator in which ionic sulfur-containing derivatives and ionic nitrogen-containing derivatives are removed and from which the final desulfurized hydrocarbon mixture is recovered. 
         [0023]    According to another embodiment of the present invention, a hydrocarbon oil feedstock containing organosulfur compounds is introduced to a catalytic reactor with hydrogen gas. The catalytic reactor effluent is passed to a high pressure separator in which a hydrogen stream is separated and a mixed high pressure separator effluent is produced. The mixed high pressure separator effluent including hydrogen sulfide and a hydroprocessed hydrocarbon mixture is contacted with water to prevent precipitate formation, and an ionic liquid, preferably a non-aqueous ionic liquid. The mixture of the high pressure separator effluent, water and ionic liquid is passed to a low pressure separator, in which water is separated, hydrogen sulfide is purged, and from which the remaining hydrocarbon oil is conveyed to a fractionator. In the low pressure separator and, in certain embodiments, in the piping between the low pressure separator and the location in which the ionic liquid is introduced, the ionic liquid and the hydroprocessed hydrocarbon mixture are retained in contact for a time sufficient for extractive removal of organosulfur compounds to occur. Accordingly, ionic sulfur-containing derivatives, i.e., derived from the organosulfur compounds in the hydrocarbon feed, that are soluble in the ionic liquid are formed and are contained in the hydrocarbon mixture. The low pressure separator effluent is passed to a fractionator in which ionic sulfur-containing derivatives are removed and from which the final desulfurized hydrocarbon mixture is recovered. 
         [0024]    In the system and process of the present invention, the sulfur content is reduced to low levels without the need for integration of substantial new equipment to existing hydroprocessing facilities. Ionic liquids are added to the hydrocarbon mixtures as organic sulfur extraction agents in or upstream of an existing cold separator vessel. 
         [0025]    Hydrocarbon feedstocks suitable for desulfurization by the system and method of the present invention can include hydrocarbon fractions boiling in the range of about 36° C. to about 520° C., preferably about 36° C. to about 370° C. The organosulfur compounds that can advantageously be removed include mercaptans, thiophenes, benzothiophenes, dibenzothiophenes, which can include substituted alkyl, aryl or alkaryl groups. The organonitrogen compounds that can advantageously be removed include pyridines, amines, pyrroles, anilines, quinoline, and acridine, which can include substituted alkyl, aryl or alkaryl groups. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0026]    The invention will be described in further detail below and with reference to the attached drawings in which the same or similar elements are referred to by the same number, and where: 
           [0027]      FIG. 1  is a schematic diagram of a hydroprocessing system showing the region where the system and process of present invention is included; and 
           [0028]      FIG. 2  is a schematic of an embodiment of the system and process of present invention for reducing sulfur- and nitrogen-containing compounds using ionic liquid extractive removal in the low pressure separator. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0029]    Referring to  FIG. 1 , a typical hydrotreating system  100  is shown which includes a processing section  110  within which the ionic liquid extractive desulfurization process of the present invention is integrated. A feedstock  10  is introduced to one or more feedstock surge vessels  12 . A make-up hydrogen stream  14  is compressed in compressor  16  and mixed with the feedstock  18  from the surge vessel  12 , and the temperature of the mixture is raised in heat exchanger  20  which circulates high temperature reactor effluents as the exchanging fluid. The partially heated feedstock-hydrogen mixture  21  is further heated to a suitable reaction temperature in a furnace  22  and the heated feedstock mixture  23  is introduced to the hydrotreating reactor  24  in which it is contacted with additional recycle hydrogen over a catalyst composition or mixture. In the hydrotreating reactor  24 , sulfur compounds including certain organosulfur compounds, and nitrogen compounds including certain organonitrogen compounds, are converted to gaseous components such as H 2 S and NH 3 . Effluents  25  from the hydrotreating reactor  24  include H 2 S and NH 3  and a hydrocarbon mixture of reduced sulfur and nitrogen content. 
         [0030]    The reactor effluents  25  are cooled in the exchanger  20  and passed to a high pressure separator  26 . The high pressure separator  26  can be a high pressure cold separator or a high pressure hot separator, depending upon whether the hydrotreating system employs a cold scheme or a hot scheme. A portion of the gaseous components H 2 S, NH 3 , C 1 -C 4  and some heavier components such as C 5 -C 6  are discharged from the separator  26  and sent for further processing (not shown). The separator tops  48  are treated to remove H 2 S in an amine unit  28 , and the H 2 S-free hydrogen rich gas stream  29  is passed to the recycle compressor  30  for use as a recycle gas stream  31  in the hydrotreating reactor  24 . 
         [0031]    The separator bottoms  50 , which are mostly liquid, exit the high pressure separator  26  at a temperature of about 225° C. to about 275° C. and are washed by process water introduced at inlet  46  downstream of the high pressure separator  26  to prevent formation of salts with H 2 S and NH 3 . The mixture of high pressure separator bottoms  50  and process water is typically cooled, for example using an air cooler  34 , such as a fin fan cooler, and a water cooler  36 , to a temperature of about 35° C. to about 60° C., preferably about 40° C. to about 50° C. The cooled bottoms from the high pressure separator are then introduced to a low pressure cold separator  32 . Any remaining gases, including H 2 S, NH 3  and light hydrocarbons, which can include C 1 -C 4  hydrocarbons, are purged via line  38  from the low pressure cold separator  32  and sent for further processing, such as flare processing, fuel gas processing, or hydrogen recovery (not shown). Water  40  is separated in the low pressure cold separator and the hydrocarbon fraction  42  is then sent to the fractionator  44 . 
         [0032]      FIG. 2  illustrates the processing section  110  including the extractive desulfurization system and process of the present invention. The desulfurized and denitrified hydrocarbon stream  50  from the high pressure cold separator is mixed with process water  46  and ionic liquids  54 , e.g., by injection. The combined streams, identifies as stream  52 ′, is introduced into a low pressure cold separator vessel  32 . The ionic liquid and hydrocarbons are provided with sufficient residence time in the vessel  32 , and optionally also in the piping, e.g., about 15 minutes to about 30 minutes, to promote the requisite mixing and contact. In addition, the ionic liquid and hydrocarbons are maintained at a temperature sufficient for the extractive desulfurization, and optionally removal of other heteroatom compounds such as organonitrogen compounds, to occur, e.g., about 225° C. to about 275° C. A combined stream  40  of wastewater and ionic liquid is decanted from the remainder of the liquids in the low pressure separator  32  and passed to a phase separation vessel  80  in which an ionic liquids stream  84  and a water stream  92  are phase separated. The ionic liquids stream  84  from the phase separation vessel  80  is passed to a distillation vessel  90  in which an ionic liquids stream  94  is regenerated by vacuum distillation and recycled  64 , e.g., mixed with stream  54 , or discharged from the system via a stream  66 . A distilled diesel fraction stream  92 , which is sulfur-rich, is sent to a cracking unit or fuel oil pool for sulfur reduction (not shown). Any miscible water in the ionic liquids is also distilled and can be recovered with the stream  92 . 
         [0033]    The hydrocarbon stream  58  containing ionic liquid is passed to a fractionator  44 . Light fractions  60  boiling in the range of the feedstock or lower, e.g., about 36° C. to about 370° C., are collected from the top of fractionator  44  and can be used as transportation fuel. The fractionator bottoms  62 , containing mostly ionic liquid, can be recycled via line  64 , e.g., mixed with stream  54 , or discharged from the system via stream  67 . Since the ionic liquids have high boiling temperatures, they are readily separated from the hydrocarbon mixture by distillation. 
         [0034]    The ionic liquid introduced via stream  54  can be any suitable ionic liquid that is effective for removing the organosulfur compounds and, if desired, organonitrogen compounds. Ionic liquids generally having very high boiling points, e.g., greater than about 425° C., are particularly suitable for use in the process of the present invention. The ratio of ionic liquid to feedstock, e.g., stream  50 , is generally about 1:4 to about 1:25, and preferably about 1:6 to about 1:20. 
         [0035]    In general, suitable ionic liquids for use in the process of the present invention are non-aqueous ionic liquids of the general formula Q + A − . These media are also very good solvents for extractive sulfur removal and, in particular, they are excellent solvents for carrying out the removal of sulfur-containing or nitrogen-containing derivatives of sulfonium and ammonium ions, respectively. Ionic liquids are also suitable for eliminating sulfur-containing compounds and, with certain known types of ionic liquids, nitrogen-containing compounds from a mixture of hydrocarbons. These ionic liquids include those described, by way of example, in H. Olivier-Bourbigou et al., “Ionic liquids: perspectives for organic and catalytic reactions.”  Journal of Molecular Catalysis A: Chemical  (2002), 182-183, 419-437. 
         [0036]    In the case of a non-aqueous ionic liquid of the general formula of Q + A − , the A −  anions can be selected from the group consisting of halide anions, nitrate, sulfate, phosphate, acetate, haloacetates, tetrafluoroborate, tetrachloroborate, hexafluorophosphate, hexafluoroantimonate, fluorosulfonate, alkyl sulfonates, perfluoroalkyl sulfonates, bis(perfluoroalkylsulfonyl) amides, tris-trifluoromethanesulfononyl methylide of the formula C(CF 3 SO 2 ) 3   − , unsubstituted arenesulfonates, arenesulfonates substituted by halogen or haloalkyl groups, tetraphenylborate anions and tetraphenylborate anions having substituted aromatic cores. 
         [0037]    The corresponding Q +  cations can be any suitable ammonium, phosphonium or sulfonium cation. 
         [0038]    The quaternary ammonium and/or phosphonium Q +  cations can be of the general formulas: 
         [0000]      NR 1 R 2 R 3 R 4   +  and PR 1 R 2 R 3 R 4   + ,
 
         [0039]    or of the general formulas: 
         [0000]      R 1 R 2 N═CR 3 R 4   +  and R 1 R 2 P═CR 3 R 4   + 
 
         [0000]    in which R 1 , R 2 , R 3  and R 4 , are the same or different, can each be represented by hydrogen, with the exception of the NH 4   +  cation for NR 1 R 2 R 3 R 4 . It is preferable that a single substituent represents hydrogen, or hydrocarbonyl radicals that have 1 to 30 carbon atoms, for example, alkyl, alkenyl, cycloalkyl or aromatic groups, aryl or aralkyl groups, optionally substituted, comprising 1 to 30 carbon atoms. 
         [0040]    The ammonium and/or phosphonium cations can also be derived from nitrogen-containing and/or phosphorus-containing heterocyclic compounds that comprise 1, 2 or 3 nitrogen and/or phosphorus atoms, with cyclic compounds containing 4 to 10 atoms, preferably 5 to 6 atoms. General structural formula for the nitrogen-containing heterocyclic compounds include: 
         [0000]    
       
                 
         
             
             
         
       
     
         [0000]    in which R 1 , R 2 , R 3 , R 4  and R 5  are the same or different and represent hydrogen or hydrocarbonyl radicals that have 1 to 30 carbon atoms, for example, alkyl, alkenyl, cycloalkyl or aromatic groups, aryl or aralkyl groups, optionally substituted, comprising 1 to 30 carbon atoms. Examples of phosphorus-containing heterocyclic compounds include PF 6 , ethyltriphenylphosphorane or tributyl(ethyl)phosphorane: 
         [0000]    
       
                 
         
             
             
         
       
     
         [0041]    The quaternary ammonium or phosphonium cations can also correspond to one of the following general formulas: 
         [0000]      R 1 R 2   + N═CR 3 —R 5 —R 3 C═N + R 1 R 2  and
 
         [0000]      R 1 R 2   + P═CR 3 -R 5 —R 3 C═P + R 1 R 2  
 
         [0000]    in which R 1 , R 2  and R 3 , are the same or different, and represent hydrogen or hydrocarbonyl radicals that have 1 to 30 carbon atoms and R 5  represents an alkylene radical or a phenylene radical. Among the groups R 1 , R 2  and R 3 ,&#39; the radicals methyl, ethyl, propyl, isopropyl, butyl, sec-butyl, tert-butyl, amyl, phenyl or benzyl are particularly suitable; R 5  can be a methylene, ethylene, propylene or phenylene group. 
         [0042]    The sulfonium cations have as a general formula: 
         [0000]      SR 1 R 2 R 3   + , 
         [0000]    where R 1 , R 2  and R 3 , each represents a hydrocarbonyl radical that has 1 to 12 carbon atoms, for example, a saturated or unsaturated aliphatic group, or a cycloalkyl or aromatic group, aryl, alkaryl or aralkyl group, comprising 1 to 12 carbon atoms. 
         [0043]    Ionic liquids particularly suitable for use in the process of the present invention include N-butyl-pyridinium hexafluorophosphate, N-ethyl-pyridinium tetrafluoroborate, pyridinium fluorosulfonate, butyl-3-methyl-1-imidazolium tetrafluoroborate, butyl-3-methyl-1-imidazolium bis-trifluoromethane-sulfonyl amide, triethylsulfonium bis-trifluoromethane-sulfonyl amide, butyl-3-methyl-1-imidazolium hexafluoro-antimonate, butyl-3-methyl-1-imidazolium hexafluorophosphate, butyl-3-methyl-1-imidazolium trifluoroacetate, butyl-3-methyl-1-imidazolium trifluoromethylsulfonate, butyl-3-methyl-1-imidazolium bis(trifluoromethylsulfonyl)-amide, trimethyl-phenylammonium hexafluorophosphate, and tetrabutylphosphonium tetrafluoroborate. 
         [0044]    In the process of the present invention, the ionic liquid that dissolves the sulfur-containing derivatives and the nitrogen-containing derivatives, can be regenerated. For instance, ionic liquids can be regenerated by vacuum distillation, as they have high boiling points and most ionic liquids have almost zero vapor pressure. This is advantageous for regenerating the ionic liquids when the solute has a relatively low boiling point, such as diesel. 
       EXAMPLES 
     Example 1 
       [0045]    Experiments were conducted using diesel oil containing 8251 ppmw of sulfur. Four types of ionic liquids were used in the experiments namely, 3-methyl-N-butylpyridinium methylsulfate (C 11 H 19 NO 4 S), 1,3-dimethylimidazolium methylsulfate (C 6 H 12 N 2 O 4 S), p-anisaldehyde (4-methoxybenzaldehyde), and proplyene carbonate. The ionic liquid-to-diesel ratio was maintained at 1:20 for all the tests. Samples of 50 cc were mixed for 10 minutes by shaking and then the diesel oils were analyzed for sulfur content. Table 3 lists the remaining sulfur content of the diesel and percentage of sulfur removal. 
         [0000]    
       
         
               
               
               
             
               
               
               
             
           
               
                 TABLE 3 
               
               
                   
               
               
                 Ionic Liquid 
                 Sulfur, ppm 
                 % Removed 
               
               
                   
               
             
             
               
                   
               
             
          
           
               
                 3-methyl-N-butylpyridinium methylsulfate 
                 6840 
                 17.10 
               
               
                 1,3-dimethylimidazolium methylsulfate 
                 8142 
                 1.32 
               
               
                 p-anisaldehyde 
                 3805 
                 53.89 
               
               
                 proplyene carbonate 
                 7269 
                 11.90 
               
               
                   
               
             
          
         
       
     
       Example 2 
       [0046]    Following the process flow diagram of  FIG. 2 , a stream  50  of hydrotreated diesel from Arab light crude oil, the properties of which are given in Table 4, was mixed with water, stream  46 , at a 20:1 diesel:water volume ratio and with essentially pure ionic liquid, stream  54 , introduced at a 5:1 diesel:ionic liquid ratio. The ionic liquid was 1-ethyl-3-methyl imadazolium trifloro sulfonate (C 8 H 16 N 2 O 4 S), CAS Number: 342573-75-5, molecular weight: 236.29, a colorless liquid, having the following formula: 
         [0000]    
       
                 
         
             
             
         
       
     
         [0047]    The diesel, water and ionic liquid were continuously mixed at 1000 RPM in a bench-top laboratory vessel at 60° C. and atmospheric pressure for 20 minutes. The two-phase liquid was mixed thoroughly at the reaction conditions, and separated clearly after the reaction. The total diesel recovery was 99 W %. The oil phase, stream  58 , was sampled and analyzed by total sulfur analyzer using ASTM D5453 method. 
         [0048]    The product diesel contained 430 ppmw of sulfur, resulting in 39.4% desulfurization. The desulfurization of individual sulfur species was also quantitatively monitored using a 2-dimensional GC method. Table 5 summarizes the extent of desulfurization for benzothiophenes, dibenzothiophenes, naphtha benzothiophenes, dibenzothiophenes and tetrahydro-dibenzothiophenes.  FIG. 3  illustrates the amount of benzothiophenes and dibenzothiophenes in the feedstock and product as a function of carbon number of the alkyl groups attached to the core aromatic rings of the sulfur molecule. As is apparent, the sulfur removal was very selective for certain classes of compounds. For example, the desulfurization was as high as 95.5 W % for napthabenzothiophenes. It has been observed that the ionic liquid remained in the bottom of the combined stream  40  of wastewater and ionic liquid as a separate light green color phase. 
         [0000]    
       
         
               
               
               
               
               
             
               
               
               
               
               
             
           
               
                   
                 TABLE 4 
               
               
                   
                   
               
               
                   
                 Property\Feed 
                 Units 
                 Method 
                 Diesel 
               
               
                   
                   
               
             
             
               
                   
               
             
          
           
               
                   
                 Sulfur 
                 ppmw 
                 D-5453 
                 710 
               
               
                   
                 Nitrogen 
                 ppmw 
                   
                 59 
               
               
                   
                 Density 
                 Kg/L 
                 D-4052 
                 0.829 
               
               
                   
                 Distillation 
                   
                 D-86 
               
               
                   
                 IBP 
                 ° C. 
                   
                 186 
               
               
                   
                  5% 
                 ° C. 
                   
                 205 
               
               
                   
                 10% 
                 ° C. 
                   
                 217 
               
               
                   
                 30% 
                 ° C. 
                   
                 253 
               
               
                   
                 50% 
                 ° C. 
                   
                 287 
               
               
                   
                 70% 
                 ° C. 
                   
                 321 
               
               
                   
                 90% 
                 ° C. 
                   
                 362 
               
               
                   
                 95% 
                 ° C. 
                   
                 380 
               
               
                   
                 FBP 
                 ° C. 
                   
                 396 
               
               
                   
                   
               
               
                   
                 IBP—Initial Boiling Point, FBP—Final Boiling Point 
               
             
          
         
       
     
         [0000]    
       
         
               
               
               
               
               
             
           
               
                 TABLE 5 
               
               
                   
               
               
                   
                 Structure 
                 Feedstock 
                 Products 
                 % Conversion 
               
               
                   
               
             
             
               
                 Benzothiophenes 
                 
                   
                             
                     
                         
                         
                     
                   
                 
                 158 
                 100   
                 36.90 
               
               
                   
               
               
                 Naphthobenzothiophenes 
                 
                   
                             
                     
                         
                         
                     
                   
                 
                  6 
                  0.3 
                 95.59 
               
               
                   
               
               
                 NaphthoDibenzothiophenes 
                 
                   
                             
                     
                         
                         
                     
                   
                 
                  27 
                  12   
                 55.56 
               
               
                   
               
               
                 Dibenzothiophenes 
                 
                   
                             
                     
                         
                         
                     
                   
                 
                 504 
                 312   
                 38.13 
               
               
                   
               
               
                 Tetrahydro Dibenzothiophenes 
                 
                   
                             
                     
                         
                         
                     
                   
                 
                  14 
                  5   
                 58.28 
               
               
                 Total 
                   
                 710 
                 430   
                 39.44 
               
               
                   
               
             
          
         
       
     
         [0049]    The method and apparatus of the present invention have been described above and in the attached drawings; however, modifications will be apparent to those of ordinary skill in the art and the scope of protection for the invention is to be defined by the claims that follow.