Patent Application
20060130394
As the fuel and auto industries operate under continuing pressure for higher efficiency and lower emission fuels, the requirement for better ignition efficiency of diesel fuels has increased. The cetane number of a fuel is an indication of the ignition efficiency of the fuel as defined below.
Cetane improvers are known in the art and have been used for many years to improve the ignition quality of fuels. Cetane improvers include alkyl nitrates such as amyl nitrate, hexyl nitrate and mixed octyl nitrates. A commonly used cetane improver is ethyl hexyl nitrate. It is further known that ethyl hexyl nitrate has a destabilizing effect on diesel fuels and the use of a thermal stabilizer with a cetane improver is described in U.S. Pat. No. 6,676,715. The prior art however, does not address the effect on lubricity of fuels containing cetane improvers, and particularly low sulfur and ultra low sulfur fuels in which lubricity is compromised.
The present disclosure addresses certain deficiencies in the prior art by providing diesel fuels containing cetane improvers sufficient to improve the ignition quality of the fuel by at least 2 cetane numbers, and further addresses the lack of lubricity of such fuels. The disclosed fuels also contain surface absorption compounds to provide diesel fuels with high cetane number and improved lubricity.
The following drawings form part of the present specification and are included to further demonstrate certain aspects of the present invention. The invention may be better understood by reference to one or more of these drawings in combination with the detailed description of specific embodiments presented herein.
The present disclosure is directed to diesel fuel compositions containing chemical additives that give the fuel a better ignition performance to meet the demands of more efficient and/or higher performance diesel engines and that provide the proper chemistry to increase the lubricity and thermal stability of the diesel fuel. It is a surprising discovery of the present inventors that treating diesel fuel to improve ignition performance results in a significant detriment to the fuel's lubricity and thermal stability properties. The additives disclosed herein address these unexpected problems by providing chemistries to overcome the detrimental effects of cetane improvers in diesel fuels.
As is well known in the art, cetane number is a measure of fuel ignition quality, or an indication of the time delay from ignition to combustion for a particular diesel fuel. The rating compares the diesel fuel's performance in a standard engine with that of a mixture of cetane and alpha-methyl-naphthalene. The cetane number is the percentage by volume of cetane in the mixture that has the same performance as the fuel being tested. As diesel fuels become more refined and thus contain less sulfur, and as diesel engines evolve, there are requirements for fuels with higher cetane numbers. It is known in the industry that the cetane number of a fuel can be increased by additives such as 2-ethyl hexyl nitrate, tertiary butyl peroxide, diethylene glycol methyl ether, cyclohexanol, or mixtures thereof, for example. As disclosed herein, however, the use of cetane improvers has detrimental effects on other qualities of the fuel, such as the lubricity and thermal stability, for example. It is an aspect of the present disclosure that fuels with improved cetane number must also incorporate additional chemistries to compensate for these effects.
The present disclosure may be described in certain embodiments, therefore, as including a diesel fuel additive composition that includes a base oil, a cetane improver such as those listed above, effective to increase the cetane number of the diesel fuel by at least 2 cetane numbers, and an amount of a surface absorption compound effective to improve the lubricity of a diesel fuel containing the additive to less than 520 microns, to less than 460 microns, or even to less than 400 microns in an HFRR wear test. An HFRR wear test is a measure of a fuel's lubricity using a High Frequency Reciprocating Rig. The HFRR test results in a measure in microns of the wear scar size developed on a steel ball vibrating on a flat plate, lubricated with the test fuel. The preferred ASTM test method for lubricity by the HFRR method is ASTM D 6079.
In certain embodiments, the surface absorption compound may include one or more of alkyl esters, fatty acids, mono acids or alkyl esters of fatty acids, functionalized synthetic polymers or combinations thereof. The surface absorption compounds may be synthetic, petroleum based, or they may be plant based alkyl esters of fatty acids, such as methyl esters or ethyl esters of fatty acids, for example.
The fuel additives disclosed herein may also contain thermal stabilizers, detergents or deposit control chemistries, microbicides, dispersants, de-icers, and marker chemicals. Such diesel additives are known in the art and are included in the disclosed additives in various combinations and proportions dependent on the particular base oils for which the additive is designed. Examples of such ingredients include fuel detergent and dispersants such as Lubrizol® 9531A, Lubrizol® 9570, and low temperature flow improvers such as Lubrizol® 8052J. Preferred thermal stabilizers include organic amines, and organic amines in kerosene solvents. Broad spectrum microbicides suitable for refined oils such as those containing methylene bis(thiocyanate) or 2-(thiocyanomethylthio)benzothiazole may be added for control of microorganisms in the fuel. For cold weather applications a de-icer such as ethylene glycol monobutyl ether may be added and chemical markers may also be added for product identification. Suitable markers include Mortrace® SB marketed by Rohm Haas.
The present disclosure may also be described in certain preferred embodiments as a diesel fuel to which a cetane improver has been added to improve the ignition quality of the fuel by at least 2 cetane numbers and which includes surface absorption compounds to achieve a lubricity of less than 500 microns, or less than 460 microns, or even less than 400 microns in an HFRR wear test.
The disclosed fuels may also contain various additives as needed, which have been added sequentially, or in a single additive composition. Such additives to the fuel may include from about 100 to about 6000 ppm cetane improver, in which the cetane improver is 2-ethyl hexyl nitrate, tertiary butyl peroxide, diethylene glycol methyl ether, cyclohexanol, or combinations thereof.
The fuels may additionally include from about 100 to about 6000 ppm 2-ethyl hexyl nitrate, tertiary butyl peroxide, diethylene glycol methyl ether, cyclohexanol, or combinations thereof, and optionally from about 10 to about 500 ppm alkyl esters, mono acids of fatty acids, alkyl esters of fatty acids, functionalized synthetic polymers or combinations thereof, including synthetic alkyl esters, or plant derived alkyl ester. The fuels of the present disclosure may further include from about 10 to about 200 ppm thermal stabilizer, from about 50 to about 500 ppm of a detergent, from about 2 to about 15 ppm microbicide, a chemical marker substance, or a dispersant in any combination.
Certain preferred embodiments of the present disclosure can thus be described as a diesel fuel that includes a base oil and an additive comprising a cetane improver and a surface absorption compound and in which the ignition quality is improved by at least 2 cetane numbers and in which the lubricity is below 500 microns.
Any of the various base oils or diesel fuels may be used as the base oil in the disclosed compositions. For example, the base oil may be a #2 diesel product, a #1 diesel product, or a low sulfur diesel product, a low temperature diesel product, or a diesel product with less than 15 ppm sulfur.
The following examples are included to demonstrate preferred embodiments of the invention. It should be appreciated by those of skill in the art that the techniques disclosed in the examples which follow represent techniques discovered by the inventor to function well in the practice of the invention, and thus can be considered to constitute preferred modes for its practice. However, those of skill in the art should, in light of the present disclosure, appreciate that many changes can be made in the specific embodiments which are disclosed and still obtain a like or similar result without departing from the spirit and scope of the invention.
The present example demonstrates additives altering the chemistry of a diesel fuel that contains cetane improvers such that the fuels have very high lubricity in spite of the detrimental effects of added cetane improvers, and especially in fuels in which the ignition qualities of the fuel have increased by at least 2 cetane numbers.
As shown in Table 1, when a multi-component additive is added to a diesel fuel base oil A, the lubricity is compromised. The numbers in Table 1 are the wear scar in microns resulting from an HFRR test as described above. Additive A is a performance enhancing additive for diesel fuels that increases fuel economy and power when added to #2 diesel, and includes a thermal stabilizer, a cetane improver and other ingredients. The #2 diesel base oil A used in the studies of the present example is a specially formulated diesel fuel that combines an exclusive refining process and additives that provide improved cold weather performance and engine efficiency. As additional cetane improver is added to the fuel, the lubricity decreases significantly (increasing wear scar to 629 microns). These data represent an unexpected side effect that is detrimental to the quality of the fuel when attempts are made to improve the cetane number.
There is, in fact a direct relationship between the amount of cetane improver added to diesel fuel A and the loss of lubricity as shown in Table 2. These data also appear in a graphical representation in
The data in Table 3 demonstrate the ability to counteract the detrimental effects of cetane improvers by altering the surface absorption chemistry of the diesel fuels containing cetane improvers. In Table 3, H4103 is a cetane improver. The mono-acid chemistry improves surface absorption, and includes mono-acids of fatty acids, such as found in the commercial product, LZ539S.
The data in Table 4 indicate an even greater lubricity effect at a lower concentration of additive when using functionalized polymeric surface absorption chemistry such as that found in the commercial product, Octel 9070.
Cetane improvers also affect the thermal stability of a diesel fuel. An aspect of the disclosure is a fuel or fuel additive containing a cetane improver and a surface absorption compound and that also contains a compound to increase thermal stability. In the present example, an organic amine compound was added to the fuel. As shown in the data in
All of the compositions and methods disclosed and claimed herein can be made and executed without undue experimentation in light of the present disclosure. While the compositions and methods of this invention have been described in terms of preferred embodiments, it will be apparent to those of skill in the art that variations may be applied to the compositions and/or methods and in the steps or in the sequence of steps of the methods described herein without departing from the concept, spirit and scope of the invention. More specifically, it will be apparent that certain agents which are both chemically and physiologically related may be substituted for the agents described herein while the same or similar results would be achieved. All such similar substitutes and modifications apparent to those skilled in the art are deemed to be within the spirit, scope and concept of the invention as defined by the appended claims.
