Sulfone removal process

CROSS-REFERENCE TO RELATED APPLICATIONS

[0001] Not Applicable

STATEMENT RE: FEDERALLY SPONSORED RESEARCH/DEVELOPMENT

[0002] Not Applicable

BACKGROUND OF THE INVENTION

[0003] The present invention is directed to methods for generating and facilitating the removal of oxidized sulfur species, and in particular sulfones, from liquid fossil fuels.

[0004] In this respect, sulfur is a common impurity found on most crude oil, and is known to contribute to air pollution, most notably by contributing to the formation of acid rain, and is considered a health hazard.. Such sulfur containing species are further known to cause corrosion in pipeline, pumping and refining equipment, and can further substantially decrease the life span catalysts used in refining and combustion of fossil fuels.

[0005] Due to its detrimental effects, legislation has been enacted to reduce sulfur content in refined petroleum products. Exemplary of such newly enacted standards include requirements set by the Environmental Protection Agency, pursuant to the Clean Air Act of 1964, that set an upper limit of 15 parts per million by weight (ppmw) of the sulfur content in ultra low sulfur diesel (ULSD) by Jun. 1, 2006. Similar requirements have been enacted in Europe and other industrialized countries, such as Japan.

[0006] The process most widely utilized for removing sulfur present in crude oil fractions is hydrodesulfurization, which involves subjecting fossil fuels to high temperatures and pressure in the presence of hydrogen and an inorganic catalyst. Through such process, the organic sulfur is converted to hydrogen sulfide, which is further processed to yield elemental sulfur. Such process is deemed generally cost-effective to the extent the crude oil subjected to such process does not contain a heavy sulfur content or if the refined petroleum product meets existing sulfur levels, such as the current diesel sulfur content of 500 ppmw or less.

[0007] To the extent hydrodesulfurization is utilized to reduce diesel sulfur content to substantially lower levels, namely, 15 ppmw or less, such process becomes substantially less effective it dramatically increases operating costs. In this regard, to hydro treat oil to attain such lower levels requires the use of substantially higher temperatures, higher pressures, and catalyst volume then is typically utilized. Indeed, even by utilizing such advanced hydrodesulfurization processes, substantially difficulties still arise in removing sulfur below 20 ppmw, as well as removing more difficult to remove sulfur compounds, such as aromatic, cyclic and condensed multicyclic sulfur compounds.

[0008] An alternative approach to hydrodesulfurization is oxidative desulfurization. Essentially, such process involves oxidizing any sulfur species that may be present, typically through the use of an oxidizing agent, such as a hydroperoxide or peracid, to thus convert the sulfur compounds to sulfones. To facilitate such oxidative reaction, ultrasound may be applied as per the teachings of U.S. Pat. No. 6,402,939, issued to Yen et al., entitled “Oxidative Desulfurization of Fossil Fuels With Ultrasound”; and U.S. Pat. No. 6,500,219, issued to Gunnerman, entitled “Continuous Process for Oxidative Desulfurization of Fossil Fuels With Ultrasound and Products Thereof”, the teachings of each are expressly incorporated herein by reference.

[0009] Advantageously, oxidative desulfurization can be performed under mild temperatures and pressures, and further typically does not require hydrogen. Additionally advantageous is the fact that oxidative desulfurization requires much less in terms of capital expenditures to implement. In this respect, oxidative desulfurization can be selectively deployed to treat only a single fraction of refined petroleum, such as diesel, and can be readily integrated as a finishing process into existing refinery facilities. Perhaps most advantageous is the fact that oxidative desulfurization can substantially eliminate all sulfur species present in a given amount of crude oil such that ultra-low sulfur levels can be attained, and in particular the lower standards being set forth in various legislative requirements regarding sulfur content levels.

[0010] Despite the various benefits associated with the use of oxidative desulfurization, however, the utilization of such process to remove sulfur continues to be problematic in several respects. Of most concern is the ability to effectuate the removal of the sulfones from the fuel, which is typically achieved either through solvent extraction or absorption, based upon the differential polarity of the sulfones. With respect to absorbents, silica gel, activated alumina, polymeric resins, and zeolites can be utilized to effectuate solid-liquid extraction. With respect to solvent extraction, solvents such as dimethyl formaldehyde, N-methylpyrrolidone, or acetonitrile can be utilized. Alternatively, organic solvents that are either immiscible or marginally immiscible with the fossil fuel can be utilized.

[0011] Such removal techniques, however, substantially complicate the sulfur removal process, and add considerably to the time and expense associated with oxidative desulfurization. As a result of the expense and complications associated with the sulfone removal step associated with oxidative desulfurization, oxidative desulfurization typically is only feasible for small to medium refinery operations.

[0012] As such, there is a substantial need in the art for a process for effectuating the removal of sulfur from refined crude oil that is substantially effective in removing virtually all of the sulfur species present in the fossil fuel that is further extremely cost effective and can be readily integrated into conventional oil refining processes. There is an additional need for such a process that can be utilized in either large scale or small scale refinery operations that is further effective to achieve sulfur removal requirements to be implemented regarding the sulfur content of refined petroleum products, and in particular diesel fuel and gasoline.

BRIEF SUMMARY OF THE INVENTION

[0013] The present invention specifically addresses and alleviates the above-identified deficiencies in the art. Specifically, the present invention provides the process for facilitating the removal of sulfur-containing species from crude oil and/or any fractions derived therefrom by subjecting the same to a first oxidative process whereby a majority, if not substantially all the sulfur-containing species present in such crude oil or fraction are converted to sulfones. To accomplish that end, any of a variety of conventional processes known in the art to effectuate oxidative desulfurization may be utilized. In this respect, conventional chemical processing utilizing oxidizing agents, such as peracids, to sufficiently convert the sulfur species to sulfones may be utilized. Alternatively, or in addition to the use of oxidizing agents, ultrasound may be deployed to effectuate oxidation of substantially all of the sulfur containing species to sulfones.

[0014] Once a substantial portion of the sulfur containing species have been converted to sulfones, the resultant fossil fuel is subjected to conventional hydrodesulfurization. In this respect, the sulfone-containing fossil fuel is fed directly to a conventional hydrotreater and thus subjected to conventional hydrodesulfurization processing, namely, elevated temperature, elevated pressure, and hydrogen gas in the presence of catalysts, such that a cobalt-molybdenum (Co/Mo) or nickel-molybdenum (Ni/Mo) catalyst, such that all the sulfur present in the sulfones are converted to hydrogen sulfide and thereafter removed through conventional processes. In this respect, the gaseous hydrogen sulfide may converted to elemental sulfur via the Claus process.

[0015] Substantially all of the sulfur species are removed from the fossil fuel as a result of process. Advantageously, the hydrodesulfurization need not be performed at substantially elevated, temperatures, pressures, or otherwise use a greater volume of catalysts, as is typically required to remove sulfur to 15 ppmw or less. Additionally, the processes of the present invention are operative to substantially eliminate those sulfur compounds, such as aromatic, cyclic and condensed multicyclic sulfur compounds, that are less responsive to the hydrodesulfurization process alone. Furthermore, the process of the present invention eliminates those drawbacks associated with conventional oxidative desulfurization processing requiring the removal of sulfones produced thereby through solvent extraction or absorption.

BRIEF DESCRIPTION OF THE DRAWINGS

[0016] These as well as other features of the present invention will become more apparent upon reference to the drawings.

[0017]
FIG. 1 is a flow chart illustrating the steps utilized in the sulfone removal process of the present invention.

DETAILED DESCRIPTION OF THE INVENTION

[0018] The detailed description set forth below is intended as a description of the presently preferred embodiment of the invention, and is not intended to represent the only form in which the present invention may be constructed or utilized. The description sets forth the functions and sequences of steps for constructing and operating the invention. It is to be understood, however, that the same or equivalent functions and sequences may be accomplished by different embodiments and that they are also intended to be encompassed within the scope of the invention.

[0019] In this regard, the present invention is directed to methods for effectuating the removal of sulfur-containing compounds from a liquid fossil fuel. At the outset, it should be recognized that the term “liquid fossil fuel” is used herein to denote any carbonaceous liquid that is derived from petroleum, coal, or any other naturally occurring material that is used for energy generation for any kind of use, including industrial uses, commercial uses, governmental uses, and consumer uses. In this respect, it should be understood that liquid fossil fuels expressly include automotive fuels, such as gasoline, diesel fuels, jet fuel, rocket fuel, as well as petroleum residuum based fuel oils including bunker fuels and residual fuels. It should be further understood that such term includes any fraction derived from petroleum, namely, those fractions derived through conventional refining processes, and in particular fractional distillation. In this respect, such fractions expressly include but are not limited to gas, naphtha, gasoline, kerosene, gas oil or diesel, lubricating oil, heavy gas or fuel oil, and residual, plus any and all products derived therefrom through further processing, such as through cracking, unification and alteration.

[0020] With respect to the processes for effectuating the removal of sulfur from fossil fuels, there is depicted in FIG. I a flow chart diagram illustrating the steps necessary for practicing the same. Such process comprises the initial step of providing a fossil fuel 20 which, as discussed above, should be interpreted broadly. Along these lines, it is contemplated that for most practical applications, the fossil fuel provided in step 20 will comprise various fractions of the refined petroleum, and that diesel fuel will be particularly well suited for the practice of the present invention given the soon-to-be implemented requirements that mandate that diesel sulfur content be substantially minimized to levels of 15 ppmw or less.

[0021] The fossil fuel provided in step 20 is then subjected to an oxidative reaction such that at least the majority, if not substantially all of the sulfur-containing compounds present in the liquid fossil fuel are converted to sulfones. In this regard, sulfones are generally represented by the formula: R—S(O)2—R and can be produced via the oxidation of sulfides and sulfoxides via a variety of reactions well-known to those skilled in the art. In this respect, sulfur-containing compounds present in the liquid fossil fuels may be oxidized via reactions with oxidizing agents, such as hydroperoxides and peracids. Exemplary of those types of processes operative to effectuate the conversion of the sulfur-containing compounds to sulfones include those oxidative desulfurization processes developed by the Lyondell Chemical Company which utilizes t-butylhydroperoxide as an oxidizing agent to convert sulfur-containing species present in a liquid fossil fuel, and in particular diesel, to sulfones using mild temperatures and pressures. Other known oxidative desulfurization processes include those processes disclosed in U.S. Pat. No. 6,402,939, issued to Yen et al., entitled “Oxidative Desulfurization of Fossil Fuels With Ultrasound”; and U.S. Pat. No. 6,500,219, issued to Gunnerman, entitled “Continuous Process for Oxidative Desulfurization of Fossil Fuels With Ultrasound and Products Thereof”, the teachings of which are incorporated herein by reference, that deploy ultrasound in combination with hydroperoxide such that a substantial portion of the sulfur-containing compounds present in the liquid fossil fuel are converted to sulfones.

[0022] As will be appreciated by those skilled in the art, the oxidative process will be effective to oxidize those sulfur-containing compounds that are typically less responsive or otherwise nonreactive to hydrodesulfurization processing. In this respect, such oxidative reactions, such as those utilized in oxidative desulfurization, are substantially effective in oxidizing aromatic sulfur compounds, cyclic sulfur compounds, and condensed multicyclic sulfur compounds, such as thiophene, benzothiophene, dibenzothiophene, and other condensed-ring thiophenes, which are typically resistant to hydrogenation via to hydrodesulfurization.

[0023] Once the sulfur-containing compounds have been sufficiently oxidized to convert the majority, if not substantially all, of such compositions to sulfones, such sulfone/fossil fuel mixture is subjected to conventional hydrodesulfurization. In this respect, such sulfone/liquid fossil fuel mixture is fed directly to a conventional hydrotreater to thus subject the sulfone/fossil fuel mixture to elevated temperature, elevated pressure, and hydrogen in the presence of a catalyst. In this regard, such hydrodesulfurization in step 40 can be conducted per conventional practices, such as those necessary to effectuate a sulfur content of approximately 500 ppmw, and need not utilize substantially elevated temperatures, elevated pressure, and/or increased catalyst volume, as is necessary to attain lower sulfur content levels utilizing the hydrodesulfurization process by itself.

[0024] Once subjected to the hydrodesulfurization process, most, if not substantially all of the sulfones present in the liquid fossil fuel are converted to hydrogen sulfide gas via conventional hydrotreater processing. As is well-known to those skilled in the art, hydrogen sulfide gas is readily removed as part of the hydrodesulfurization process and can ultimately be converted to elemental sulfur. In this respect, the vast majority of refineries currently operating are provided with hydrotreater units that are operative to effectuate the hydrodesulfurization process, and hence isolate the hydrogen sulfide gas byproduct produced thereby. As such, the continuous implementation of hydrodesulfurization using conventional hydrotreaters will not result in increased capital expenditures necessary to practice the processes of the present invention

[0025] Advantageously, however, by virtue of the fact that a substantial portion, if not all of the sulfur-containing compounds are oxidized to sulfones prior to being subjected to hydrodesulfurization, the hydrodesulfurization process is operative to convert virtually all of the sulfones readily into hydrogen sulfide gas. As discussed above, hydrodesulfurization by itself is typically inoperative to remove a wide variety of sulfur-containing compounds unless the same pre-exist in oxidized state as attained by prior oxidative process. At the same time, the processes of the present invention eliminate the need to remove sulfones via conventional oxidative desulfurization practices, namely, solvent extraction or adsorption. In this regard, by deploying hydrodesulfurization, as opposed to such conventional sulfone removal practices, refineries need not integrate such sulfone removal processes as part of their refining process, particularly at the expense of hydrodesulfurization.

[0026] Additional modifications and improvements of the present invention may also be apparent to those of ordinary skill in the art. Along these lines, it is contemplated that the combination of an oxidative reaction followed by hydrodesulfurization (or any other reaction for that matter which subjects the liquid fossil fuel to increased temperature, increased pressure and hydrogen in the presence of a catalyst) may further be operative to effectuate the removal of other undesirable non-sulfur-containing compounds. For example, it is contemplated that those processes known or later developed in the art effectuating the oxidation of nitrogen-containing compounds may first be deployed followed by hydrodesulfurization such that the oxidized nitrogen-containing compounds become converted to ammonia. In this respect, it is contemplated that the removal of nitrogen will closely mimic the processes described herein for effectuating the removal of sulfur. Thus, the particular combination of parts and steps described and illustrated herein is intended to represent only certain embodiments of the present invention, and is not intended to serve as limitations of alternative devices and methods within the spirit and scope of the invention.

Sulfone removal process

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