Abstract:
Fuel additive compositions for enhancing the lubricity of hydrocarbon fuels in which the natural lubricity has been diminished due to treatment of the fuel to reduce sulfur and aromatic components for improved emissions are disclosed. Preferably, the fuel additive compositions include (1) a polyalkenylsuccinimide having a high molecular weight; (2) a low aromatic paraffinic base oil; and (3) a low aromatic petroleum distillate to impart improved lubricity to hydrocarbon fuels.

Description:
BACKGROUND 
       [0001]    1. Field of the Invention 
         [0002]    The present invention relates to additive compositions for enhancing the lubricity of hydrocarbon fuels in which the natural lubricity has been diminished due to treatment of the fuel to reduce sulfur and aromatic components for improved emissions. 
         [0003]    2. Description of the Art 
         [0004]    Hydrocarbon distillates and residuals used as fuel can typically contain up to 5,000 ppm sulfur. The sulfur oxidizes during the combustion process to form SO 2  and SO 3  which, in addition to be emitted as acid gas, can also form sulfates. The sulfates then become part of the diesel engines particulate emissions. Therefore, reducing sulfur can reduce particulate emissions. Sulfur reductions in fuel have been mandated in many parts of the world including the U.S. and in the European Union. The result will be sulfur levels phased down to less than 15 ppm with eventual reductions to less than 5 ppm. 
         [0005]    In many fuel systems, particularly diesel fuel systems, the fuel itself provides lubrication for the fuel pump and injectors. A fuel with poor lubricity can result in unacceptable wear and premature failure of these parts. With reductions in sulfur levels, fuel lubricity is becoming a bigger concern. Refining techniques and processes to reduce sulfur and aromatics in the fuel for improved emissions also reduces the natural lubricity of the fuel. This lubricity problem has been made even worse by proposed requirements to limit the maximum distillation point of diesel fuel. 
         [0006]    Many refiners and fuel formulators are using lubricity improver additives to impart acceptable lubricating properties back to the fuel. Various injector and injector pump tests and several laboratory tests have been developed to measure the lubricity of diesel fuels. ASTM D 6079 High Frequency Reciprocating Rig (“HFRR”) test is the most widely used and accepted. 
         [0007]    The addition of minor proportions of long chain fatty acids to liquid hydrocarbon fuels to increase lubricity is well known. These types of compositions are described in U.S. Pat. Nos. 4,002,437 (to Broeckx, et al.) and 4,185,594 (to Perilstein). Long chain fatty acids, however, can react with other components in many modern fuel and lubricant additive packages resulting in loss of effectiveness and formation of undesirable gels and sludges. There is a need, therefore, for lubricity additives that have a reduced affinity to interact with the other fuel and lubricant additives. 
         [0008]    Esters of long chain fatty acids have also been disclosed as fuel lubricity additives. The acid group of these molecules has been blocked by the esterification reaction and, thus, is not available for interaction with the other fuel and lubricant additives. However, the lubricity imparting function of the fatty acid has been reduced. 
         [0009]    Amides of long chain fatty acids disclosed as fuel lubricity additives have the advantage of reduced affinity to react with other fuel and lubricant additives but, like the esterification reaction described above, amination can also result in loss or reduction of the lubricity function of the fatty acid. Esters and amides of fatty acids are disclosed in U.S. Pat. Nos. 3,273,981 (to Furey) 4,204,481 (to Malec), 4,729,769 (to Schlicht, et al.). Alkoxyamides are disclosed in U.S. Pat. No. 4,427,562 (to Horodysky, et al.). 
         [0010]    Other prior compounds include reaction products of an amine, an aldehyde and mercaptan further reacted with a boron compound are described in U.S. Pat. No. 4,486,321 (to Horodysky, et. al.). However, sulfur containing additives are undesirable since they can increase amount of SO x  emissions and are thus not consistent with efforts to reduce the sulfur content of hydrocarbon fuels. 
         [0011]    Additionally, coupling reaction products of polyalkylene amines with heterocyclic compounds are described in U.S. Pat. Nos. 5,538,520 and 5,552,069 (both to Avery, et al.). Although the resulting compounds are claimed to provide fuel lubricity, they can contain sulfur moieties which can increase sulfur emissions on combustion of the fuel. 
         [0012]    With respect to other prior compounds, U.S. Pat. No. 6,296,677 (to Ribeaud, et al.) describes the reaction of various oils with active hydrogen compounds and carboxylic acids. These compounds are claimed to reduce wear in the fuel system of diesel engines operating on fuels with reduced sulfur and aromatic content. U.S. Pat. No. 6,793,696 (to Krull, et al.) discloses low sulfur diesel fuel oil compositions containing salts of fatty acids with short chain oil soluble amines. U.S. Pat. No. 6,835,217 (to DeRossa, et al.) discloses fuel compositions comprising a major amount of hydrocarbon fuel containing at least one alcohol and substantially free from MTBE, and a friction modifying amount of a friction reducing agent prepared by the reaction of at least one natural or synthetic oil with at least one alkanolamine. U.S. Pat. No. 6,872,230 (to Cross, et al.) discloses reaction products of alkylated polyamines with various ureas or isocyanates and derivatives thereof. U.S. Pat. Nos. 6,866,690 (to Aradi, et al.), 6,896,708 (to Conner, et al.) and 6,923,838 (to Maubert) disclose other amides and esters of carboxylic acids and transesterification and transamidation products of natural or synthetic oils. MacMillian, et al. in U.S. Pat. No. 6,156,082 describes a process to improve fuel lubricity and reduce corrosion by the use of glycol esters of polyalkenylsuccinic anhydrides. None of these prior compounds provide both significant reduction of sulfur emissions and significant enhancement of lubricity. 
         [0013]    Another group of compounds used in lubricating oils are polyalkenylsuccinimides. Polyalkenylsuccinimides are well known and are used extensively as dispersants in lubricating oils. These dispersants function by surfactant action to hold polar dirt and sludge compounds into the oil matrix so they can be removed by filtration. Generally, the polyalkenylsuccinimide dispersants have a relatively high molecular weight hydrocarbon tail to provide oil solubility. The molecular weight is generally in the range from about 1,000 to 2,000 daltons. 
         [0014]    Examples of the use of polyalkenylsuccinimides as dispersants of this type in lubricating oil compositions, and methods of preparations are disclosed in the following U.S. Pat. Nos.; 3,873,460 (to Coon, et al.), 3,897,456 (to Brewster), 4,234,435 (to Meinhardt, et al.), 4,472,588 (to Keasey), 4,713,189 (to Nalesnik, et al.), 4,857,217 (to Guiterrez), 5,334,321 (to Harrison), 5,792,730 (to Guiterrez), 5,821,205 (to Harrison), 6,548,458 (to Loper), 6,770,605 (to Stachew) and 6,933,351 (to Michaued), each of which is hereby incorporated by reference. 
         [0015]    Although high molecular weight polyalkenylsuccinimides are disclosed as dispersants in oil lubricants, these compounds, to the inventor&#39;s knowledge, are not used in fuels. The reason is that polyalkenylsuccinimides of the type described above, although very good dispersants, are relatively poor detergents. As a result, when used in lubricating oils, other additives, usually containing divalent metals, are combined with the polyalkenylsuccinimides to impart detergency to the lubricating oil. Therefore, high molecular weight polyalkenylsuccinimides have not been desired for use in fuels because it is not desirable to add divalent metals to fuels. 
         [0016]    Another class of compounds commonly known as polyalkyleneamines function very well as fuel detergents and are effective at cleaning intake valve deposits (“IVD”) without contributing to combustion chamber deposits (“CCD”). Thus, polyalkyleneamines generally are utilized as fuel additives. 
         [0017]    Although high molecular weight polyalkenylsuccinimides are not utilized as fuel additives, low molecular weight polyalkenylsuccinimides and derivatives, i.e., having molecular weights lower than 1,000 daltons but usually 350-750 daltons are used in fuel as stabilizers because the higher nitrogen content prevents fuel degradation during storage. These low molecular weight polyalkenylsuccinimides do not provide any lubricity enhancement of fuels. Accordingly, prior to the development of the present invention, there has been no lubricity enhancing fuel additive or process for forming lubricity enhancing fuel additives that: provide reduction in sulfur emissions; provide increased lubricity of fuels, and in particular, diesel fuels; and include a high molecular weight polyalkenylsuccinimide. Therefore, the art has sought lubricity enhancing fuel additives and processes for forming lubricity enhancing fuel additives that: provide reduction in sulfur emissions; provide increased lubricity of fuels, and in particular, diesel fuels; and include a high molecular weight polyalkenylsuccinimide. 
       SUMMARY OF THE INVENTION 
       [0018]    A lubricity enhancing fuel additive is needed that removes one or more of the negative characteristics associated with current fuel lubricity technologies. The lubricity enhancing fuel additives disclosed herein advantageously resist the process of readily hydrolyzing or degrading to species that can interact with the other additives, used in either the fuel or engine lubricant, and furthermore advantageously resist contributing to undesirable emissions or generation of undesirable emissions and therefore should advantageously be low in sulfur and low in aromatic content and not contain heavy metals. 
         [0019]    Surprisingly, it has now been found that lubricity enhancing fuel additives comprising a polyalkenylsuccinimide of higher molecular weights improve the lubricity of fuels. Such polyalkenylsucinimides are not typically used in fuel. Preferably, a low aromatic paraffinic base oil and a low aromatic petroleum distillate are included with the polyalkenylsuccinimide of the lubricity enhancing fuel additives to improve lubricity of hydrocarbon fuels. 
         [0020]    The polyalkenylsuccinimide component preferably is a mixture of a mono-polyalkenylsuccinimide and a di-polyalkenylsuccinimide. 
         [0021]    The composition of the current invention can be added to fuels of poor lubricity, such as middle distillate fuels that have been treated to reduce sulfur and aromatics including, gasoline, diesel fuel, kerosene, fuel oils and heavy fuel oils. 
         [0022]    This new invention also comprises methods of increasing fuel lubricity by treatment of the fuel with the lubricity enhancing fuel additives disclosed herein. 
         [0023]    The fuel may contain, in addition to the lubricity enhancing fuel additives disclosed herein, other additives commonly added as minor constituents to the fuel such as cold flow improvers, antifoam additives, cetane improvers, combustion improvers and the like. These other components can be added individually or as part of a complete multifunctional package. 
         [0024]    In accordance with the disclosure herein, one or more of the foregoing advantages can be achieved through a lubricity enhancing fuel additive comprising a polyalkenylsuccinimide having a molecular weight greater than 2,000 daltons wherein the lubricity enhancing fuel additive increases the lubricity of a hydrocarbon fuel by at least 10 percent using the High Frequency Rotating Rig test described in ASTM D 6079. 
         [0025]    A further feature of the lubricity enhancing fuel additive is that the polyalkenylsuccinimide can comprise a mono-polyalkenylsuccinimide. Another feature of the lubricity enhancing fuel additive is that the polyalkenylsuccinimide can comprise a di-polyalkenylsuccinimide. An additional feature of the lubricity enhancing fuel additive is that the polyalkenylsuccinimide can comprise a mono-polyalkenylsuccinimide and a di-polyalkenylsuccinimide. Still another feature of the lubricity enhancing fuel additive is that the mono-polyalkenylsuccinimide and the di-polyalkenylsuccinimide can be present in a ratio of 3 to 1. A further feature of the lubricity enhancing fuel additive is that the mono-polyalkenylsuccinimide and the di-polyalkenylsuccinimide can be present in a ratio of 1 to 3. Another feature of the lubricity enhancing fuel additive is that the mono-polyalkenylsuccinimide and the di-polyalkenylsuccinimide can be present in a ratio of 1 to 1. An additional feature of the lubricity enhancing fuel additive is that the lubricity enhancing fuel additive can further comprise a low aromatic paraffinic base oil having a molecular weight in the range from 250 to 650 daltons and preferably in the range from 350 to 450 daltons. Further, aromatic portion of the paraffinic base oil is preferably less than 5% and more preferably less than 1%. Still another feature of the lubricity enhancing fuel additive is that the weight proportion of the low aromatic paraffinic base oil can be in the range from 50 to 90 weight percent of the lubricity enhancing fuel additive. A further feature of the lubricity enhancing fuel additive is that the weight proportion of the low aromatic paraffinic base oil can be in the range from 60 to 80 weight percent of the lubricity enhancing fuel additive. Another feature of the lubricity enhancing fuel additive is that the lubricity enhancing fuel additive can further comprise a low aromatic petroleum distillate having a molecular weight in the range from 250 to 650 daltons and preferably in the range from 350 to 450 daltons. Further, aromatic portion of the petroleum distillate is preferably less than 5% and more preferably less than 1%. An additional feature of the lubricity enhancing fuel additive is that the weight proportion of the low aromatic petroleum distillate can be in the range from 5 to 50 weight percent of the lubricity enhancing fuel additive. Still another feature of the lubricity enhancing fuel additive is that the weight proportion of the low aromatic petroleum distillate can be in the range from 15 to 40 weight percent of the lubricity enhancing fuel additive. A further feature of the lubricity enhancing fuel additive is that the weight proportion of the low aromatic petroleum distillate can be in the range from 20 to 25 weight percent of the lubricity enhancing fuel additive. 
         [0026]    In another aspect, one or more of the foregoing advantages can also be achieved through a process for forming a lubricity enhancing fuel additive. The process can comprise the steps of: forming a first polyalkenylsuccinimide having a molecular weight greater than 2,000 daltons and combining at room temperature the first polyalkenylsuccinimide with a low aromatic paraffinic base oil and a low aromatic petroleum distillate to form the lubricity enhancing fuel additive, wherein the low aromatic paraffinic base oil is present in the lubricity enhancing fuel additive in a range from 50 to 90 weight percent and the low aromatic petroleum distillate is present in the lubricity enhancing fuel additive in a range from 5 to 50 weight percent, wherein the lubricity of the fuel is increased at least 10 percent using the High Frequency Rotating Rig test described in ASTM D 6079. 
         [0027]    A further feature of the process for forming an lubricity enhancing fuel additive is that a second polyalkenylsuccinimide can be combined with the first polyalkenylsuccinimide, the low aromatic paraffinic base oil, and the low aromatic petroleum distillate to form the lubricity enhancing fuel additive. Another feature of the process for forming an lubricity enhancing fuel additive is that the first polyalkenylsuccinimide and the second polyalkenylsuccinimide can be combined in a ratio of 3 to 1. An additional feature of the process for forming an lubricity enhancing fuel additive is that the first polyalkenylsuccinimide and the second polyalkenylsuccinimide can be combined in a ratio of 1 to 3. Still another feature of the process for forming an lubricity enhancing fuel additive is that the first polyalkenylsuccinimide and the second polyalkenylsuccinimide can be combined in a ratio of 1 to 1. A further feature of the process for forming an lubricity enhancing fuel additive is that the first polyalkenylsuccinimide can comprise a mono-polyalkenylsuccinimide and the second polyalkenylsuccinimide can comprise a di-polyalkenylsuccinimide. 
         [0028]    In a particularly preferred embodiment, the lubricity enhancing fuel additive contains only a polyalkenylsuccinimide, a low aromatic paraffinic base oil, and a low aromatic petroleum distillate. In still another preferred embodiment, the lubricity enhancing fuel additive includes a polyalkenylsuccinimide, a low aromatic paraffinic base oil, and a low aromatic petroleum distillate, a dispersant, a solvent, and other non-functional elements from the formation of the polyalkenylsuccinimide. In either of the foregoing embodiments, the polyalkenylsuccinimide can include one or both of mono-polyalkenylsuccinimide or di-polyalkenylsuccinimide. 
         [0029]    As mentioned above, the lubricity enhancing fuel additives and processes for forming lubricity enhancing fuel additives have the advantages of: providing reduction in sulfur emissions; providing an increase in the lubricity of fuels, and in particular, diesel fuels; and including a high molecular weight polyalkenylsuccinimide. 
     
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0030]    Fuels may be treated with the composition of the current invention at weight proportions of 1 to 10,000 ppm, preferably between 5 and 5,000 ppm and most preferably between 800 and 1,600 ppm to impart improved lubricity characteristics to the fuel. 
         [0031]    The mono-polyalkenylsuccinimide can be represented by the general structure (I): 
         [0000]    
       
                 
         
             
             
         
       
     
         [0032]    where R is a polyisobutenyl group and may be from 150 to 3,000 molecular weight, preferably from 500 to 1,200 molecular weight and most preferably from 800 to 1,200 molecular weight; y can be an integer from 0 to 10 and preferably from 2-10 and most preferably from 2-5. 
         [0033]    The di-polyalkenylsuccinimide can be represented by the general structure (II): 
         [0000]    
       
                 
         
             
             
         
       
     
         [0034]    where R is a polyisobutenyl group and may be from 300 to 3,000 molecular weight, preferably from 1,200 to 2,800 molecular weight and most preferably from 2,200 to 2,800 molecular weight; y can be an integer from 0 to 10 and preferably from 2-10 and most preferably from 2-5. 
         [0035]    The weight ratio of polyalkenylsuccinimide of structure I to structure II can range from 99:1 to 1:99, preferably from 75:25 to 25:75 and most preferably 50:50. 
         [0036]    The weight proportion of the low aromatic paraffinic base oil can range from 50 to 90%, preferably from 50 to 85%, and most preferably from 60 to 80%. 
         [0037]    The weight proportion of the low aromatic petroleum distillate can range from 5 to 50%, preferably from 15 to 40% and most preferably from 20 to 25%. 
         [0038]    The weight proportion the polyalkenylsuccinimide of Structure I and Structure II combined can range from 1 to 10%, preferably from 2 to 8% and most preferably from 4 to 8%. 
         [0039]    In addition to the composition specified above, the total base number (“TBN”), as measured by ASTM D 2896, is a specification and is preferably at least 1 mg KOH/gram and most preferably greater than 3 mg KOH/gram. 
         [0040]    The low aromatic paraffinic base oil can be an API Group II, III or IV base oil or white oil or mixtures thereof. The aromatic content can be less than 5 ppm, preferably less than 2 ppm and most preferably less than 1 ppm. The paraffinic content can be greater than 80%, more preferably greater than 85% and most preferably greater than 90%. The sulfur content may be less than 300 ppm, preferably less than 200 ppm and most preferably less than 100 ppm. 
         [0041]    The low aromatic light petroleum distillate may have a boiling point of less than 300° C., preferably less 250° C. and most preferably less than 225° C. and a flash point greater than 50° C., preferably greater than 55° C. and most preferably greater than 60° C. The aromatic content may be less 5 ppm, preferably less than 2 ppm and most preferably less than 1 ppm. The sulfur content may be less 5 ppm, preferably less than 2 ppm and most preferably less than 1 ppm. 
       Preparation of Compounds 
     Example I 
     Mono-Polyalkenylsuccinimide (I) 
       [0042]    A reaction mixture containing 98 grams (1.0 mole) of maleic anhydride and 950 grams (1.0 mole) of TPC 595 (highly reactive polyisobutylene of 950 molecular weight, available from Texas Petrochemicals) was heated at 240° C. for 6 to 8 hours. The mixture was then vacuum stripped to remove un-reacted maleic anhydride and cooled to less than 80° C. This intermediate polyalkylenesuccinic anhydride (“PIBSA”) was light yellow in color, free of char with a saponification number of 118 and a residual maleic anhydride content of less 0.1%. The PIBSA was mixed with 100 milliliters of toluene. While maintaining the pot temperature at 70-80° C., 146 grams (1.0 mole) of triethylenepentamine (“TEPA”) was added over a one-hour period and then allowed to digest for an additional hour. The reaction mixture was heated to 110° C. and the water of reaction was removed by azeotropic distillation with toluene. The distillation was continued until the theoretical amount of water and all of the toluene was removed. A vacuum was applied to remove any un-reacted TEPA. The resulting polyalkenylsuccinimide (“PIBSI”) product had a nitrogen content of 4.7% and was diluted to 2% nitrogen with 100 N base oil and cooled to room temperature. 
       Example II 
     Di-Polyalkenylsuccinimide (II) 
       [0043]    A lab preparation was conducted as above except 2,300 grams (1.0 moles) of TPC 5230 (highly reactive polyisobutylene of 2,300 molecular weight, available from Texas Petrochemicals) and 98 grams (1.0 mole) of maleic anhydride was reacted at 240° C. for 4 hours and the reaction continued at 260° C. for an additional 4 hours. The PIBSA intermediate was dark yellow in color and had a saponification number of 77 and a residual maleic anhydride content of less than 0.1%. After cooling to 70-80° C., 100 milliliters of toluene was mixed with the PIBSA and 73 grams (0.5 moles) of TEPA was added over a one-hour period. The reaction mixture was digested for an additional hour and then heated to 110° C. and the water of reaction was removed by azeotropic distillation. The distillation was continued until the theoretical amount of water and all of the toluene was removed. A vacuum was applied to remove any un-reacted TEPA. The resulting polyalkenylsuccinimide (“PIBSI”) product which had a nitrogen content of 2.1% was diluted to 1% nitrogen with 100 N base oil and cooled to room temperature. 
       Example III 
     Formulation of Fuel Lubricity Composition 
       [0044]    A composition capable of imparting lubricity to fuels was prepared by mixing 244 grams of Motiva Star 4 base oil, 78 grams of Ashland Solvent 142, 10 grams of mono-polyalkenylsuccinimide from Example I and 10 grams of di-polyalkenylsuccinimide from Example II. The mixture was stirred at room temperature (19-25° C.) until a clear light yellow solution with a nitrogen value of 870 ppm was obtained. The TBN was 3.45. 
       Improvement of Fuel Lubricity 
       [0045]    The High Frequency Rotating Rig (“HFRR”) test described in ASTM D 6079 can measure the lubricity of fuels and fuels treated with lubricity additives. The results are reported as wear on the surface of the oscillating ball measured as mean scar diameter in microns. Lower wear scar diameters are indicative of better fuel lubricity. 
         [0046]    HFRR scar diameters are compared in Table 1 for a reference ultra-low sulfur diesel fuel (“ULSD”) containing 8 ppm Sulfur with the same ULSD dosed with the composition of Example III. 
         [0047]    The fuel lubricity composition of the current invention reduced the wear scar by 18%, clearly demonstrating a substantial improvement in fuel lubricity. 
         [0000]    
       
         
               
             
               
               
             
               
               
             
           
               
                 TABLE 1 
               
             
             
               
                   
               
               
                 High Frequency Reciprocating RIG (“HFRR”) Test at 60° C. With 
               
               
                 Ultra-Low Sulfur Diesel Containing 8 ppm Sulfur 
               
             
          
           
               
                 Example III 
                   
               
               
                 Additive Concentration (mg/kg) 
                 Wear Scar Diameter (microns) 
               
               
                   
               
             
          
           
               
                 0 
                 595 
               
               
                 800 
                 484 
               
               
                 1600 
                 487 
               
               
                   
               
             
          
         
       
     
         [0048]    It is to be understood that the invention is not limited to the exact details of construction, operation, exact materials, or embodiments shown and described, as modifications and equivalents will be apparent to one skilled in the art. Accordingly, the invention is therefore to be limited only by the scope of the appended claims.