Chemistry: molecular biology and microbiology – Process of utilizing an enzyme or micro-organism to destroy... – Destruction of hazardous or toxic waste
Statutory Invention Registration
1999-05-07
2001-08-07
Jordan, Charles T. (Department: 3641)
Chemistry: molecular biology and microbiology
Process of utilizing an enzyme or micro-organism to destroy...
Destruction of hazardous or toxic waste
C435S182000, C435S822000
Statutory Invention Registration
active
H0001986
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a method for removing organic sulfur from a liquid composition containing sulfur-containing organic compounds. This method can be employed in the production of transportation fuels and, in particular, gasoline and diesel fuels produced by the fluidized catalytic cracking of a feedstock.
The auto industry has long been faced with the problems associated with sulfur in fuels and, in particular, transportation fuels. These problems have largely crystallized around three areas, first, the degradation or poisoning of catalyst employed in emission control systems. Second, the problems associated with sulfur monitoring, i.e., false sensor readings relating to catalyst performance. To this end, recent amendments to the Clean Air Act will require the automotive industry to equip future vehicles with onboard diagnostic devices that can measure the effectiveness of catalyst emission controls for 100,000 miles. The diagnostic devices will measure oxygen storage capacity to determine catalyst efficiency. The sulfur in gasoline can interfere with this oxygen storage measurement causing the sensor to show an erroneous decrease in catalyst efficiency. In order to prevent these erroneous readings, the sulfur content of gasoline should be no more than 50 ppm.
Third, sulfur dioxide emissions are a precursor to the formation of sulfate aerosols which are believed to play a substantial role in the total amount of ambient “fine particulate” matter. Moreover, recent epidemiological studies cited through the EPA suggest that sulfate aerosols are at least a contributory constituent of 2.5-micron particulate matter. Thus, the need to reduce sulfur emissions is also tied -at least in part-to ongoing efforts to reduce the emission of 2.5-micron particulate matter.
In modern refineries, fuels are produced from a number of streams. A primary source of sulfur-containing organic compounds in the gasoline pool is FCCU gasoline, i.e., gasoline produced in a fluidized catalytic cracking unit. The primary source of sulfur in FCCU fuels is thiophenic sulfur comprised of dibenzothiophene, benzothiophene, and thiophene and their various derivatives.
In order to produce a low sulfur FCCU fuel, the art has focused on either (i) hydrotreating the FCCU feed or (ii) treating the FCCU product for sulfur removal. Neither of these techniques, however, have been entirely effective.
The hydroprocessing of FCCU feed has been in commercial practice for over thirty years. In this regard, FCCU fuels have a high octane number due -at least in part-to the olefin content of the lighter, lower-boiling fraction. The hydrotreatment of FCCU fuels for sulfur removal can, however, result in a significant loss of efficiency. For example in gasolines, R+M
2
octane losses of 3-10 numbers or more can result depending on the severity of the hydrotreatment.
Moreover, hydrotreatment to a sulfur level of, e.g., 50 ppm, can be cost prohibitive. In particular, the costs of decreasing sulfur content from 500 ppm to 200 ppm by desulfurizing heavy FCCU fuels can be on the order of about one cent per gallon. However, the next increment of decrease in sulfur, e.g., from 200 ppm to 50 ppm, can be on the order of four cents a gallon. This cost is only further increased in those instances where processing, e.g., isomerization, is needed to offset fuel efficiency loss during hydrotreatments.
Separately, microorganisms have been employed in processes for removing organic sulfur from certain thiophenic compounds.
The biological pathways employed are either “carbon-destructive” which results in the overall degradation of the compound or “sulfur-specific” which results in the selective attack on the sulfur atom. A preferred sulfur specific process involves four enzymatic steps of “sulfoxide-sulfane-sulfonate-sulfate” and is hence termed the “4S pathway”. The 4S pathway is illustrated in FIG. 1
a
-
1
d.
Attention in this regard is directed towards the article entitled “Desulfurization of Coal: The Microbial Solution”, Trends Biotechnol., 7,97-101, April 1989, by J.J. Kilbane, that discusses the 4S pathway in detail. Attention is also directed towards U.S. Pat. Nos. 5,496,720; 5,510,265; and 5,529,930, which are all incorporated by reference in their entirety for all purposes.
For example, non-commercial techniques for the desulfurization of diesel fuel have employed biocatalysts such as
Rhodococcus erythropilis,
which catalysts produce enzymes capable of selectively oxidizing sulfur found in heterocyclic sulfur-containing organic compounds, such as dibenzothiophene (DBT), to sulfone. The sulfur is then “clipped” from the molecules to produce an oxygenated, sulfur-free derivative of biphenyl and inorganic sulfate.
Although biocatalytic oxidation by way of the 4S pathway is capable of removing sulfur in diesel fuels, it has been severely limited both in terms of its applicability and its effectiveness. In particular, biodesulfurization as it exists in the art is currently focused on the desulfurization of diesel fuels not gasolines. Moreover, biodesulfurization has suffered from the same cost and octane problems that can be associated with traditional hydroprocessing. In light of these problems, it has not found commercial success.
Accordingly, the need still exists for a method of removing sulfur-containing compounds from feed streams for fuels and, in particular, FCCU fuels.
SUMMARY OF THE INVENTION
The present invention is based at least in part on the surprising discovery that biocatalytic oxidation by way of the 4S pathway which is halted prior to the last of the four enzymatic steps, is capable of providing an activated sulfur-containing compound that can be subsequently treated to remove the sulfur. Moreover, this process can effectively remove sulfur at a reduced cost and without the disadvantages, e.g., fuel performance loss, associated with traditional catalytic or biodesulfurization techniques.
To this end, one aspect of the invention relates to a process for removing sulfur which includes oxidizing a heterocyclic sulfur-containing compound so as to introduce an oxygen atom to the sulfur heteroatom ring structure. The process further includes the subsequent removal of the sulfur therefrom.
In one embodiment, the method according to the invention comprises:
(a) providing a liquid composition containing an aliphatic and/or heterocyclic sulfur-containing organic compound;
(b) activating the heterocyclic sulfur-containing organic compound by oxidizing either the organic sulfur or carbon atom adjacent to the sulfur;
(c) treating the activated compound so as to remove sulfur therefrom.
The method according to the present invention preferably employs an active biocatalyst in connection with step (b) but not in connection with step (c).
The biocatalyst can be whole cell living microorganisms, lyophilized cells, cell parts or enzymes. The biocatalyst can be immobilized and operate in aqueous or non-aqueous mediums. The source of the biocatalyst can be any bacteria or microorganism with the capability to oxidize sulfur to the sulfoxide, sulfone, or sulfonic acid.
In a preferred embodiment, the activation step (b) involves the use of a biocatalyst suitable for providing the enzymatic 4S pathway. However, the biocatalytic oxidation is halted prior to the enzymatic 4S step in that pathway. Moreover, step (c) preferably involves fluidized catalytic cracking.
REFERENCES:
patent: 5874294 (1999-02-01), Valentine
Atlas Ronald M.
Boron David J.
Deever William R.
Johnson Axel R.
McFarland Beverly Lynn
Alston & Bird LLP
Baker Aileen J.
Jordan Charles T.
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