Residual fuel oil additive

This application claims the benefit of Provisional Application No. 60/753,318, filed Dec. 21, 2005, the entire disclosure of which is incorporated by reference.

The invention pertains to fuel additives for carbonaceous fuels having high asphaltene content such as residual fuel oil and coal. Benefits from the use of such fuel additives may include one or more of reduced particulate matter emissions, reduced nitrogen oxide emissions, and improved combustion efficiency.

Carbonaceous fuels with high asphaltene content such as residual fuel oil and coal tend to liberate large amounts of energy on combustion, and therefore, find utility in applications where a low cost, high energy fuel is desired. However, such high-asphaltene carbonaceous fuels generally burn with less efficiency than other hydrocarbon fuels, and may often contain quantities of undesirable compounds that limit combustion and result in elevated levels of pollutants.

Residual fuel oils (also referred to as “resid” or “resid fuel”) are generally the low grade products that remains after the distillation of lighter petroleum products which may include gasoline, jet fuel, diesel fuel, No. 4 fuel oil, and No. 5 light or heavy fuel oil. Examples of residual fuel oils include No. 6 fuel oil and Bunker C fuel oil.

The compounds referred to as “asphaltenes” generally include polynuclear aromatics and/or polycyclic materials. While certain parts of the world such as North America tend to have specifications which limit the amount of asphaltenes in fuels such as residual fuel oils, such fuels still have relatively high levels of asphaltenes compared to other, lighter hydrocarbon fuels. For example, in the United States, specifications limit the asphaltene content of residual fuel oil to less than about 8 wt. %. However, in other parts of the world, asphaltene specifications tend to be either non-existent, or significantly higher than those in North America. Therefore, residual fuel oils in other parts of the world may have asphaltene contents of 10 wt. % or higher. As a fairly heavy carbonaceous fuel, coal also tends to have high concentrations of ring structures which may include anthracene and phenanthrene which for purposes of this specification are to be included as “asphaltenes.” It should be noted that as coal becomes “older,” more of such rings form and become interconnected such that coal can also be considered a high-asphaltene carbonaceous fuel. For purposes of this specification, the term “high-asphaltene carbonaceous fuel” is intended to broadly encompass carbonaceous fuels which have asphaltene content of at least 4 wt %.

Examples of the pollutants that can result from the combustion of high-asphaltene carbonaceous fuels include ozone, particulate matter (PM), carbon monoxide, nitrogen oxides (NO_x), sulfur dioxide, polynuclear aromatic compounds, and soluble organic fractions. In the United States, numerous state and national agencies have or are adopting ambient air quality standards which may require reduced emissions from the combustion of high-asphaltene carbonaceous fuels. Among the users of resid oils are power plants and ocean-going ships. In Southern California, for example, emissions from ships entering the port of Los Angeles are considered to be a major cause of regional air pollution.

Considerable effort has been expended by petroleum refiners to formulate fuels that reduce emissions. The most common approach to formulating compliant fuels involves adjusting refinery processes so as to produce a fuel meeting the specifications set forth by appropriate government agencies. However, such an approach is difficult for residual fuels, and the drawbacks to such an approach include high costs in reconfiguring refinery processes, and possible negative effects on the quantity or quality of other refinery products.

Embodiments of the present invention include systems, methods, and compositions which may provide improved combustion characteristics of high-asphaltene carbonaceous fuels. Examples of the combustion characteristics which may be improved by embodiments of the invention include one or both of increased combustion efficiency, and reduced pollutant discharge. Examples of the pollutants which may be reduced include one or more of ozone, particulate matter (PM), carbon monoxide, nitrogen oxides (NO_x), sulfur dioxide, polynuclear aromatic compounds, and soluble organic fractions.

In some embodiments, a fuel additive is provided comprising a plant extract. In this specification, the term “plant extract” is intended to broadly encompass extracts of all types of plants, excluding the roots and bark, and even includes plants such as algae. Suitable plant extracts are extracts from green and other colored plants as such plants tend to have high concentrations of desirable extracts. However, even white and light colored plants include such extracts, though at lower concentrations. Particularly suitable extracts are from green and other dark leafy plants such as those from the Leguminosae family which includes fescue, alfeque, and alfalfa.

In a preferred embodiment, the plant extract is combined with an organometallic material. The inclusion of an organometallic compound is especially useful for treating fuels having particularly high asphaltene contents in the range of 8 wt. % or higher. Examples of organometallic materials are hydrocarbon-soluble organometallic compounds that include a metal selected from the first and second row transition metals. One metal of particular interest is iron, and particularly suitable organometallic materials include iron pentacarbonyl, iron naphthenate, ferrocene, and combinations. The fuel additive may optionally include an oil-soluble carrier. Examples of suitable oil-soluble carriers include hydrocarbons such as toluene, aromatic blends, naphthas, gasoline, diesel fuel, jet fuel, and mixtures thereof. In one embodiment, the oil soluble carrier is non-oxygenated.

In certain embodiments, the fuel additive may include other optional ingredients. Such optional ingredients may include one or more of an oxygen carrier, a stability aid, a lubricity aid, an anti-oxidant, and a combustion improver. Meadowfoam oil may be used as a stability aid, an anti-oxidant, and a lubricity aid. Suitable oxygen carriers include carotenoids. Examples of antioxidants include 1,2-dihydroquinolines, and in particular, 2,2,4-trimethyl-6-ethoxy-1,2-dihydroquinoline. Examples of combustion improvers include compounds known as cetane improvers or ignition accelerators. Examples of combustion improvers include alkyl nitrates such as 2-ethylhexyl nitrate.

In another embodiment of the present invention, a method for improving the combustion characteristics of a high-asphaltene carbonaceous fuel comprises adding a fuel additive as described above to a high-asphaltene carbonaceous fuel prior to or during combustion.

In another embodiment of the present invention, an additized high-asphaltene carbonaceous fuel is provided which comprises a high-asphaltene carbonaceous fuel and a fuel additive as described above.

In still another embodiment of the invention, a method for preparing a fuel additive comprises mixing a plant extract with an oil-soluble carrier and one or more of an organometallic material, an oxygen carrier, a stability aid, a lubricity aid, an anti-oxidant, and a combustion improver. In another embodiment of the invention, the fuel additive is prepared in an oxygen-free or reduced-oxygen atmosphere, and optionally may include the step of excluding sources of UV radiation during the preparation. In still another embodiment, non-oxidized oil-soluble carriers and non-oxidized oxygen carriers are used.

The plant extract used in various embodiments of the invention may be obtained by solvent extraction from whole plants using hydrocarbon-soluble solvents. Polar or nonpolar hydrocarbon-soluble solvents may be used for the extraction. The extract resulting from the extraction process is a crude material containing over 300 individual compounds. In one embodiment, the extract has a paste- or mud-like consistency that may be described as a solid or semi-solid, rather than a liquid. Such extracts typically contain chlorophyll A and chlorophyll B with a higher concentration of chlorophyll A over chlorophyll B. The color of such an extract is generally a deep black-green with some degree of fluorescence. Such an extract may be recovered from most plants though green and darker leafy plants tend to have higher concentrations. Extracts from plants from the Leguminosae family are suitable. While such a solid or semi-solid form is generally considered to be preferred for most embodiments, in other embodiments, a liquid or other form may be suitable, and may even be preferred. Furthermore, synthetic materials, for example synthetic carotenoids, chlorophylls, or xanthopylls, may be used instead of or in addition to natural plant extracts.

The foregoing has outlined rather broadly the features and technical advantages of the present invention in order that the detailed description of the invention that follows may be better understood. Additional features and advantages of the invention will be described hereinafter which form the subject of the claims of the invention. It should be appreciated by those skilled in the art that the conception and specific embodiments disclosed may be readily utilized as a basis for modifying or designing other structures for carrying out the same purposes of the present invention. It should also be realized by those skilled in the art that such equivalent constructions do not depart from the spirit and scope of the invention as set forth in the appended claims. The novel features which are believed to be characteristic of the invention, both as to its organization and method of operation, together with further objects and advantages will be better understood from the following description when considered in connection with the accompanying figures. It is to be expressly understood, however, that each of the figures is provided for the purpose of illustration and description only and is not intended as a definition of the limits of the present invention.