Deep desulfurization of hydrocarbon fuels

PATENT
Deep desulfurization of hydrocarbon fuels
PATENT number: 8158843
Issue date: Apr 17, 2012
Application number: 10/365,574
Inventors: Chunshan Song, Xiaoliang Ma, Michael J. Sprague, Velu Subramani
Original Assignee: The Penn State Research Foundation
Abstract
The invention relates to processes for reducing the sulfur content in hydrocarbon fuels such as gasoline, diesel fuel and jet fuel. The invention provides a method and materials for producing ultra low sulfur content transportation fuels for motor vehicles as well as for applications such as fuel cells. The materials and method of the invention may be used at ambient or elevated temperatures and at ambient or elevated pressures without the need for hydrogen.

FEDERALLY FUNDED RESEARCH

The subject matter of this patent application was funded under U.S. department of Energy Contract No. DE-FG26OONT40821.

FIELD OF THE INVENTION

The invention relates to deep desulfurization of hydrocarbon fuels. More particularly, the invention relates to desulfurization of hydrocarbon fuels for use in internal combustion engines as well as for use in applications such as fuel cells for use in transportation, residential and portable applications and also for stationary power plants.

BACKGROUND OF THE INVENTION

Deep desulfurization of transportation fuels is receiving greater attention due to increasingly stringent regulations and fuel specifications for environmental protection purposes. Recently, the U.S. Environmental Protection Agency issued regulations that require refineries to reduce the sulfur content of gasoline from a current average of 300 parts per million by weight (ppmw) to 30 ppmw by 2006, and the sulfur content of highway diesel fuel from a current limit of 500 ppmw to 15 ppmw by 2006.
 
Deep desulfurization of hydrocarbon fuels to produce ultra-low-sulfur fuel also is motivated by emission-control technologies which are sensitive to sulfur, as well as the need for ultra-low-sulfur fuel foruse in fuel cells. Because sulfur is a strong poison to reforming as well as fuel cell catalysts, the sulfur content in liquid hydrocarbon fuels needs to be reduced to an ultra low level, preferably to less than about 10 ppmw for solid oxide fuel cells and to less than about 1 ppmw for polymer electrolyte membrane fuel cells.
 
Liquid hydrocarbon fuels usually contain sulfur compounds as well as aromatic hydrocarbons at concentrations of about 5-30 Wt %. It is well known that naphtha from FCC accounts for over 90% of the sulfur and olefins in gasoline. Sulfur can be removed from FCC by the catalytic hydrodesulfurization (HDS) process. This process, however, requires high consumption of hydrogen and significantly reduces fuel octane number due to olefin saturation. Because gasoline contains olefins which have high-octane value, selective removal of sulfur without loss of olefins is highly desirable.
 
Although it may be possible to reduce the sulfur content in gasoline to below 30 ppmw by the HDS process, the HDS process is very inconvenient for production of ultra low sulfur content gasoline, particularly for fuel cell applications. This is due in part to the need to use severe operating conditions, including high hydrogen consumption and consequent octane loss. The HDS process also is not suitable for reducing sulfur content in diesel fuel to below 15 ppmw because the remaining sulfur compounds such as 4,6-dimethyldibenzothiophene (4,6-DMDBT) and trimethyl dibenzothiophene (TMDBT) are refractory and very diflicult to remove.
 
A need therefore exists for new methods and materials for deep desulfurization of liquid hydrocarbon fuels to meet environmental concerns as well as to produce ultra-low sulfur fuels for fuel cell applications.
SUMMARY OF THE INVENTION

The present invention relates to adsorbent materials and processes for reducing the sulfur content in hydrocarbon fuels and liquid hydrocarbon feedstocks such as naptha, gasoline, diesel fuel, jet fuel, and kerosene as well as middle distillate fuels such as #2 fuel oil. Gasolines which may be treated include but are not limited to those which have about 10 ppm S to about 350 ppm S. Diesel fuels which may be treated include but are not limited to those which have about 10 ppm S to about 500 ppm S. Jet fules which may be treated include but are not limited to those which have up to about 3000 ppm S. The invention provides materials and a method for producing ultra low sulfur content transportation fuels for motor vehicles as well as for applications such as fuel cells. The materials and method of the invention may be used at ambient or elevated temperatures and at ambient pres sure without the need for hydro gen.
 
When the procedures and materials of the invention are employed to desulfurize hydrocarbon fuel, sulfur compounds or sulfur in the fuel are removed by selective absorption onto an adsorbent material to yield a desulferized fuel. When applied to gasoline, sulfur compounds are removed from the gasoline with little or no loss of aromatics, olefinic hydrocarbons or open chain and cyclic paraflinic hydrocarbons. After the sulfur compounds are adsorbed onto the adsorbent, the spent adsorbent can be regenerated by, such as, polar solvents or by hydrogen. For example, hydrogen can be used to regenerate activated Ni adsorbents, mixed metal oxides derived from layered double hydroxides, and Ni supported on Silicaalumina.
 
Adsorbents of the invention include transition metal chlorides supported on a support material, activated nickel, metal ion exchanged zeolites and metal impregnated zeolites, mixed metal oxides derived from hydrotalcites (HTs) also known layered double hydroxides (LDHs), Ni supported on silica-alumina, sulfided transition metals on a support, and transition metal phosphides on a support.
 
The process entails removing sulphur compounds from hydrocarbon fuels or hydrocarbon feedstocks by contacting the fuel with an adsorbent material such as transition metal chlorides, activated Ni adsorbent, metal ion exchanged zeolite, metal ion impregnated zeolite, NiAl-LDHcal, NiZnAlLDHcal, Ni supported on silica-alumina, regenerated Ni on silica-alumina, sulfided CoiMo/alumina, and regenerated sulfided metal/ aluminum such as sulphided CoiMo/alumina in a temperature range of about 10° C. to about 340° C. The hydrocarbon fuels include gasoline, model gasoline, diesel fuel, model diesel fuel, jet fuel, model jet fuel and kerosene.
 
The transition metal chloride adsorbent includes a transition metal chloride on a support material, preferably a porous support material. The support material has about 1% to about 75% loading of the transition metal containing compounds. The transition metal compound is represented by A2BCl4 or by XZCl4 where AIK, Na, and H, B:a transition metal, X:a transition metal and Z is a noble metal. X preferably is any of Mn, Ni, Co, Fe, Ce and Ru, B preferably is any of Pd, Ni, Cu, Co, Al, and Zn, and Z preferably is Pd or Pt. The support material is any of MCM-41 type mesoporous alumino silicate molecular sieve, silica gel, alumina, activated carbon, and zeolites, preferably MCM-41 type mesoporous alumino silicate molecular sieve. In a preferred aspect, the adsorbent includes MCM-41 type mesoporous alumino silicate molecular sieve bearing K2PdCl4 and silica gel support material bearing H2PdCl4. In another preferred aspect, the fuel is gasoline having about 210 ppmw sulfur and the adsorbent material is activated Ni and the temperature is about 200° C.
 
Another aspect of the invention relates to a process for removing sulphur compounds from a hydrocarbon fuel. The process entails passing a fuel feedstock over a first absorbent bed from a plurality of adsorbent beds to adsorb the sulfur compounds onto the adsorbent bed and to generate desulferized fuel. The fuel feedstock then can be redirected to another of the adsorbent beds to continue to generate desulphurized fuel while regenerating the first adsorbent bed. Regenerating may be done by using a solvent to elute adsorbed sulfur compounds from the first absorbent bed to generate an eluate of sulphur compounds and solvent. The eluate then is treated to remove the solvent and to yield a concentrated sulphur fraction. The concentrated sulphur fraction is treated with hydrogen to generated a hydrodesulfurized product that may be blended with the desulferized fuel. The process may be used with fules such as gasoline, diesel fuel, kerosene and jet fuel. Adsorbents which may be employed include transition metal chlorides, activated Ni adsorbent, metal ion exchanged zeolite, metal ion impregnated zeolite, NiAl-LDHcal, NiZnAl-LDHcal, Ni supported on silica-alumina, regenerated Ni on silica-alumina, sulfided metal/alumina such as sulphided CoiMo/ alumina, and regenerated metal/ alumina such as regenerated sulfided CoiMo/alumina.
 
Adsorbents such as transition metal chlorides on a support porous material, metal ion exchanged zeolites, metal impregnated zeolites, and sulfided transition metals on a support can be treated with a solvent to regenerate the adsorbent by eluting adsorbed sulfur compounds. The spent solvent that contains the eluted sulfur compounds is evaporated to obtain a concentrated sulfur fraction, which then may be hydrodesulfurized with hydrogen. The resulting hydrodesulfurized product then may be blended with the desulferized fuel.
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