Abstract:
Fuel compositions comprising primarily a mono- or di-butyl succinate as an oxygenation additive are described. The fuels can be diesel fuels which generate carbon based particulates in diesel engines. The result is reduced emissions of particulates from the diesel engines.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    Not Applicable. 
       STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT 
       [0002]    Not Applicable. 
       BACKGROUND OF THE INVENTION 
       [0003]    (1) Field of the Invention 
         [0004]    The present invention relates to fuel compositions containing mono- or di-butyl succinate ester as a primary additive to oxygenate the fuel and reduce particulate emissions. In particular, the present invention relates to diesel fuel compositions. 
         [0005]    (2) Description of Related Art 
         [0006]    Diesel fuels are a significant contribution to pollution. This is shown by U.S. News &amp; World Report for Nov. 4, 2002, page 63. The problem then is to reduce the particulates from diesel fuels. 
         [0007]    In a number of studies the correlation between properties of diesel fuels and emission has been investigated. Most of current additive candidates are ethers, esters or alcohols, but even glycols, carbonates and acetates have been considered. In 1995 Kazushi Tsurutani et al (SAE Paper 952349) examined 11 different oxygenates demonstrated that oxygenates considerably reduce the amount of particles (PM), measured in g/k Wh, but that the effect on NOX was nonexistent or very small. The observed effect was more related to the total oxygen content in the fuel after the additive was combined with the fuel, rather than the structure of the molecule. Noboru Miyamoto et al (SAE Paper 962115 (1996)) showed that the reduction of smoke and particle emissions were proportional (linear) to the oxygen concentration in the fuel despite the additive. A general conclusion would be that all oxygenates reduce smoke and particle emission without influencing NOX, a certain reduction of total carbon (THC) and CO was also seen. 
         [0008]    Matthew Stoner and Thomas Litzinger (SAE Paper 1999-01-1475 (1999)) conducted a test to see how structure and boiling point of maleated glycol ethers affects the emissions. They suspected a connection between molecular structure and the amount of the reduced particle amount. They found that both kinds of oxygenate reduce emission of NOX and soot, but the maleates seems more effective. The maleates also reduced emissions of NOX because a delay of SOC(Start of Combustion). No connection between boiling point and effects on the emission could be detected. In a later study it was shown again that the molecule structure has an influence on the reduction of soot emissions. It was also confirmed that the ignition delay increased slightly and hence the NOX emission was reduced. 
         [0009]    Methanol and ethanol are excellent gasoline additives, but are not miscible with diesel fuel and emulsifiers and ignition improvers need to be added which increase the cost. Methanol is also both more toxic and corrosive than ethanol. Rapeseed methylesters (biodiesel) are of significant interest because they are non-toxic and with small engine modifications they can be used in existing diesel motors. 
         [0010]    A number of alternative fuels that are advocated today have disadvantages because they are expensive. DME (dimethyl ether) has for example good emission properties, works well in a converted diesel motor and is easy to ignite and is a gas non-miscible with diesel fuel. 
         [0011]    Natural gas can on a long-term perspective be a cost effective alternative to diesel, but natural gas is a fossil fuel and therefore not a renewable resource based alternative. 
         [0012]    Relevant patents are U.S. Pat. No. 5,268,008 to Kanne; U.S. Pat. No. 5,752,989 to Henly et al; U.S. Pat. No. 6,458,173 B1 to Lin and U.S. Pat. No. 6,468,319 B1 to Yeh et al. The trend of the patent art is towards high molecular weight additives having a molecular weight greater than or equal to 200, presumably to obtain the necessary solubility and reduced volatility in diesel or other fuels. There is a need for a less expensive additive for internal combustion engines which is readily available and which in particular can be produced from “green” or natural source precursor compounds. To summarize, it can be concluded that there still is a need to find the optimal additive for internal combustion engine fuels. 
         [0013]    There is a general need for replacements of motor fuels in ground transportation. Diesel powered cars and trucks have a significant fuel economy advantage, as much as 40%, over similarly sized gas powered vehicles. In general, diesel fuel has a range of emission problems that include NOx, SOx, and particulate emissions (PM). One approach to solving the emissions problem is to add oxygenated additives to diesel fuel to provide for more full combustions. 
         [0014]    There are several compounds that have been utilized in attempts to reduce emissions from fuel combustion, such as disclosed in U.S. Application Nos. 2002/0023384, 2004/0088909, 2002/053334, 2005/144835, 2006/167146, 2006/205615, 2004/128905 and 2004/128905, as well as U.S. Pat. Nos. 4,482,356, 5,268,008, 5,916,825, 6,113,661, 6,468,319, and 6,733,550, the disclosure of each of which is incorporated herein by reference in its entirety. 
         [0015]    However, there remains a need to develop methods and compositions to reduce emissions from fuel combustion. 
       OBJECTS 
       [0016]    It is therefore an object of the present invention to provide novel internal combustion engine fuel compositions incorporating a low molecular weight additive which is miscible with the fuel. Further, it is an object of the present invention to provide compositions which are easily prepared, are economical and can be prepared from natural source precursor compounds. These and other objects will become increasingly apparent by reference to the following description and the drawings. 
       SUMMARY OF THE INVENTION 
       [0017]    The invention is directed to compositions and methods for reducing emissions resulting from combustion of fuel, such as diesel fuel. In some aspects of the invention, mono- and di-butyl esters of succinic acid, including but not limited to, butyl succinate, dibutyl succinate, butyl-ethylsuccinate, butyl-methylsuccinate, can be used for diesel fuel oxygenates and extenders. In other aspects a butyl succinate, is of the general formula butyl-x-succinate, where, x is a straight chain hydrocarbon molecule having 1-5 carbons, 4-10 carbons, 8-15 carbons, 12-20 carbons. In some embodiments, the succinate ester (e.g. dibutyl succinate) can completely replace the diesel fuel in a diesel engine. In all cases these same additives could be added to biodiesel. 
         [0018]    In some aspects of the invention, the entire range of butyl succinate esters could be made from renewable resources as fermentation processes exist for ethanol, butanol, and succinic acid. Therefore, one aspect of the invention provides a complete biobased solution to emission and liquid fuel problems. 
         [0019]    In other aspects of the invention, butyl succinates (e.g., dibutyl succinate) are produced in micro-organisms, such as bacteria or yeast. 
         [0020]    The present invention relates to a method of reducing emissions from an internal combustion engine by combusting a fuel composition containing a butyl succinate. 
         [0021]    The present invention further relates to a fuel composition comprising butyl succinates which function as oxygenates, extenders, and replacers. 
         [0022]    The present invention still further relates to a composition comprising fuel and a butyl succinate. In further embodiments, said fuel is diesel fuel. In further still embodiments, said butyl succinate is about 1-5% w/w relative to said fuel. In still further embodiments, said butyl succinate has a formula C 4 H 9 O 2 CCH 2 CH 2 CO 2 C 4 H 9 . In further still embodiments, said butyl succinate is dibutyl succinate. 
         [0023]    The present invention still further relates to a composition which comprises: a liquid hydrocarbon fuel; and between 0.1 and 30 percent by weight of mono- or di-butyl succinate ester as a primary organic oxygenation source for the fuel. In still further embodiments, the fuel is diesel fuel. In further still embodiments, the dibutyl succinate is 5 to 10 percent by weight of the fuel. In still further embodiments, the fuel is substantially free of contaminants which cause pollution. 
         [0024]    The present invention still further relates to a method for increasing combustion of a fuel to water and carbon dioxide, and reducing particulates from the combustion, which comprises: providing a composition which comprises a liquid hydrocarbon as the fuel and between 0.1 and 30 percent by weight of dibutyl succinate ester as a primary organic oxygenation source to run the engine so as to increase the combustion and reduce the particulates from the combustion. In further embodiments, the fuel is diesel fuel. In still further embodiments, the diesel fuel is 5 to 10 percent by weight of the fuel. In still further embodiments, the fuel is substantially free of contaminants which cause pollution. In further still embodiments, the dibutyl succinate is the sole organic oxygenation source for the fuel. In still further embodiments, the dibutyl succinate is the sole organic oxygenation source for the fuel. In further still embodiments, the composition comprises a secondary oxygenation source. 
         [0025]    The term “primary” is intended to mean more than 50% and preferably more than 80% of the oxygenation source for the fuel is mono- or di-butyl succinate. 
         [0026]    All publications and patent applications mentioned in this specification are herein incorporated by reference to the same extent as if each individual publication or patent application was specifically and individually indicated to be incorporated by reference. 
     
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         [0027]      FIG. 1  depicts the chemical structure of dibutyl succinate. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0028]    While preferred embodiments of the present invention have been shown and described herein, it will be obvious to those skilled in the art that such embodiments are provided by way of example only. Numerous variations, changes, and substitutions will now occur to those skilled in the art without departing from the invention. It should be understood that various alternatives to the embodiments of the invention described herein may be employed in practicing the invention. It is intended that the following claims define the scope of the invention and that methods and structures within the scope of these claims and their equivalents be covered thereby. 
         [0029]    In some aspects of the invention, microorganisms are modified to produce butyl succinate, dibutyl succinate, butyl-ethylsuccinate, butyl-methylsuccinate, which are added to fuels for combustion in engines, generators or home heating apparatus (e.g., lamps). Therefore, in some embodiments, a butyl succinate is of the formula butyl-x-succinate, where x is a straight chain hydrocarbon, having 1-5, 4-10, 8-12, or 10-15 carbons. 
         [0030]    In one embodiment of the invention, a fuel composition comprise an additive having the formula ROOC(CH 2 ) 2 COOR 1 , where both R and R r  are butyl. In other embodiments, where R or R 1  is butyl, then the corresponding R or R 1 , respectively is a straight chain hydrocarbon having 1,2,3,4,5,6,7,8,9,10,11,12,13,14,15,16,17,18,19 or 20 carbons. 
         [0031]    In other aspects of the invention, butyl succinate, dibutyl succinate, butyl-ethylsuccinate, butyl-methylsuccinate or a combination thereof are added to fuel compositions, to reduce emissions. In various embodiments, a fuel composition comprises a base fuel and at least about 1,2,3,4,5,6,7,8,9,10,11,12,13,14,15,16,17,18,19,20, 25 or 30% by weight (w/w) one or more butyl succinate or dibutyl succinate compositions disclosed herein. 
         [0032]    Fuel that can be blended with compositions disclosed herein includes but is not limited to light oil, heavy oil or kerosene, which are utilized a fuel for a diesel engine of automotive vehicles, electric power generating apparatuses and marine vehicles. 
         [0033]    In some aspects of the invention, butyl succinates are produced in micro-organisms such as species of yeast or bacteria. Butyl succinates are derived from succinic acid (e.g., Butanedioic Acid) which is a dicarboxylic acid of four carbon atoms. It occurs naturally in plant and animal tissues. It plays a significant role in intermediary metabolism (Krebs cycle) in the body. Succinic acid is a colourless crystalline solid with a melting point of 185-187 C; soluble in water; slightly dissolved in ethanol, ether, acetone and glycerine; not dissolved in benzene, carbon sulfide, carbon tetrachloride and oil ether. The common method of synthesis of succinic acid is the catalytic hydrogenation of maleic acid or its anhydride. Carboxylic acid can yield acyl halides, anhydrides, esters, amides, and nitriles for the application of drug, agriculture, and food products, and other industrial uses. 
         [0034]    In some embodiments, a yeast is genetically modified to produce a butyl succinate or combination of butyl succinates (e.g., butyl and di-butyl succinate). In other embodiments, a bacterium is genetically modified to produce a butyl succinate or combination of butyl succinates (e.g., butyl and di-butyl succinate). 
         [0035]    Specifically, U.S. Pat. Nos. 6,468,319 B1, to Yeh et al., and U.S. Pat. No. 5,752,989 to Henly et al., which are incorporated by reference contains a detailed description of the various oxygenation secondary additives which can be used with diethyl succinate as well as a discussion of the art of testing oxygenates. The other patents discussed previously are also incorporated by reference showing secondary oxygenation additives. 
       EXAMPLE 1 
       [0036]    Dibutyl succinate (DBS) is tested as an additive in diesel fuel. DBS fulfils properties that are required for an additive: renewable, non-toxic, inexpensive and miscible with diesel fuel. Engine tests are performed to show the reduction in particulates as a function of rpm and percentage DBS. 
         [0037]    There are numerous published sources of diesel fuel compositions. One is shown at lubrizol.com/ReadyReference. The present invention can reduce particulates in any of the diesel fuels sold worldwide in the same manner as Example 1. 
         [0038]    It is intended that the foregoing description be only illustrative of the present invention and that the present invention be limited only by the hereinafter appended claims.