Mineral oils: processes and products – Refining – Sulfur removal
Reexamination Certificate
2000-09-01
2004-04-27
Griffin, Walter D. (Department: 1764)
Mineral oils: processes and products
Refining
Sulfur removal
C208S244000, C208S089000, C208S143000, C208S20800M, C208S209000
Reexamination Certificate
active
06726836
ABSTRACT:
TECHNICAL FIELD
The present invention relates to a method for desulfurizing gasoline, diesel fuel or like hydrocarbon fuel streams so as to render the fuel more suitable for use in a mobile vehicular fuel cell power plant assembly. More particularly, the desulfurizing method of this invention is operable to remove organic sulfur compounds found in gasoline to levels which will not poison the catalysts in the fuel processing section of the fuel cell power plant assembly. The method of this invention involves the use of a nickel reactant bed which has an extended useful life cycle due to the addition of hydrogen to the fuel stream in appropriate amounts.
BACKGROUND OF THE INVENTION
Gasoline, diesel fuel, and similar hydrocarbon fuels have not been useful as a process fuel source suitable for conversion to a hydrogen rich stream for small mobile fuel cell power plants due to the existence of relatively high levels of naturally-occurring complex organic sulfur compounds. Hydrogen generation in the presence of sulfur results in a poisoning effect on all of the catalysts used in the hydrogen generation system in a fuel cell power plant. Conventional fuel processing systems used with stationary fuel cell power plants include a thermal steam reformer, such as that described in U.S. Pat. No. 5,516,344. In such a fuel processing system, sulfur is removed by conventional hydrodesulfurization techniques which typically rely on a certain level of recycle as a source of hydrogen for the process. The recycle hydrogen combines with the organic sulfur compounds to form hydrogen sulfide within a catalytic bed. The hydrogen sulfide is then removed using a zinc oxide bed to form zinc sulfide. The general hydrodesulfurization process is disclosed in detail in U.S. Pat. No. 5,292,428. While this system is effective for use in large stationary applications, it does not readily lend itself to mobile transportation applications because of system size, cost and complexity. Not only is the hydrodesulfurization process more complicated because it is a two step process, but to be effective in desulfurizing heavier fuels containing thiophenic sulfur compounds, it must operate at elevated pressures, usually greater than about 150 psig.
Other fuel processing systems, such as a conventional autothermal reformer, which use a higher operating temperature than conventional thermal steam reformers, can produce a hydrogen-rich gas in the presence of the foresaid complex organic sulfur compounds without prior desulfurization. When using an autothermal reformer to process raw fuels which contain complex organic sulfur compounds, the result is a loss of autothermal reformer catalyst effectiveness and the requirement of reformer temperatures that are 200° F.-500° F. higher than are required with a fuel having less than 0.05 ppm sulfur. Additionally, a decrease in useful catalyst life of the remainder of the fuel processing system occurs with the higher sulfur content fuels. The organic sulfur compounds are converted to hydrogen sulfide as part of the reforming process. The hydrogen sulfide can then be removed using a solid absorbent scrubber, such as an iron or zinc oxide bed to form iron or zinc sulfide. The aforesaid solid scrubber systems are limited, due to thermodynamic considerations, as to their ability to lower sulfur concentrations to non-catalyst degrading levels in the fuel processing components which are located downstream of the reformer, such as in the shift converter, or the like.
Alternatively, the hydrogen sulfide can be removed from the gas stream by passing the gas stream through a liquid scrubber, such as sodium hydroxide, potassium hydroxide, or amines. Liquid scrubbers are large and heavy, and are therefore useful principally only in stationary fuel cell power plants. From the aforesaid, it is apparent that current methods for dealing with the presence of complex organic sulfur compounds in a raw fuel stream for use in a fuel cell power plant require increasing fuel processing system complexity, volume and weight, and are therefore not suitable for use in mobile transportation systems.
An article published in connection with the 21
st Annual Power Sources Conference
proceedings of May 16-18, 1967, pages 21-26, entitled “Sulfur Removal for Hydrocarbon-Air Systems”, and authored by H. J. Setzer et al, relates to the use of fuel cell power plants for a wide variety of military applications. The article describes the use of high nickel content hydrogenation nickel reactant to remove sulfur from a military fuel called JP-4, which is a jet engine fuel, and is similar to kerosene, so as to render the fuel useful as a hydrogen source for a fuel cell power plant. The systems described in the article operate at relatively high temperatures in the range of 600° F. to 700° F. The article also indicates that the system tested was unable to desulfurize the raw fuel alone, without the addition of water or hydrogen, due to reactor carbon plugging. The carbon plugging occurred because the tendency for carbon formation greatly increases in the temperature range between about 550° F. and about 750° F. A system operating in the 600° F. to 700° F. range would be very susceptible to carbon plugging, as was found to be the case in the system described in the article. The addition of either hydrogen or steam reduces the carbon formation tendency by supporting the formation of gaseous carbon compounds thereby limiting carbon deposits which cause the plugging problem.
Commonly owned co-pending U.S. patent application Ser. No. 09/470,483, filed Dec. 22, 1999 describes a system and method for desulfurizing gasoline and/or diesel fuel by passing the fuel through a nickel reactant bed wherein a major portion of the sulfur in the fuel is converted to nickel sulfide. The fuel stream contains an oxygenate such as ethanol, methanol or MTBE which acts to extend the useful like of the nickel reactant bed by suppressing carbon formation on the reactant bed. The use of such oxygenates has been found to increase the capacity of the nickel reactant bed to convert sulfur in organic sulfur compounds in the fuel to nickel sulfide by about five hundred percent. The operating conditions of the system and method described in the above-noted patent application are suitable for use in mobile applications of fuel cell power plants, such as those usable in powering vehicles. One problem incurred by using MTBE is that the MTBE itself decomposes to an unsaturated hydrocarbon so it adds to the total potential carbon deposited onto the nickel. Carbon formation tends to poison the reactant by blocking pores and active sites of the nickel reactant.
It would be highly desirable from an environmental standpoint to be able to power electrically driven vehicles, such as an automobile, for example, by means of fuel cell-generated electricity; and to be able to use a fuel such as gasoline, diesel fuel, naphtha, lighter hydrocarbon fuels such as butane, propane, natural gas, or like fuel stocks, as the fuel consumed by the vehicular fuel cell power plant in the production of electricity. In order to provide such a vehicular power source, the amount of sulfur in the processed fuel gas would have to be reduced to and maintained at less than about 0.05 parts per million.
The desulfurized processed fuel stream can be used to power a fuel cell power plant in a mobile environment or as a fuel for an internal combustion engine. The fuel being processed can be gasoline or diesel fuel, or some other fuel which contains relatively high levels of organic sulfur compounds such as thiophenes, mercaptans, sulfides, disulfides, and the like. The fuel stream is passed through a nickel desulfurizer bed wherein essentially all of the sulfur in the organic sulfur compounds reacts with the nickel reactant and is converted to nickel sulfide leaving a desulfurized hydrocarbon fuel stream which continues through the remainder of the fuel processing system. Previously filed U.S. patent applications Ser. No. 09/104,254, filed Jun. 24, 1998; and Ser. No. 09/221,429, filed Dec. 28,
Cocolicchio Brian A.
Lesieur Roger R.
Vincitore Antonio M.
Arnold Jr. James
Griffin Walter D.
Jones William W.
UTC Fuel Cells LLC
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