Chemistry: molecular biology and microbiology – Process of utilizing an enzyme or micro-organism to destroy... – Petroleum oil or shale oil treating
Reexamination Certificate
2000-06-19
2002-01-08
Lilling, Herbert J. (Department: 1651)
Chemistry: molecular biology and microbiology
Process of utilizing an enzyme or micro-organism to destroy...
Petroleum oil or shale oil treating
C435S262000
Reexamination Certificate
active
06337204
ABSTRACT:
This invention relates to five pure strains of
Rhodococcus erythropolis
CNCM I-2204
, Rhodococcus erythropolis
CNCM I-2205
, Rhodococcus erythropolis
CNCM I-2207
, Rhodococcus erythropolis
CNCM I-2208, and
Rhodococcus rhodnii
CNCM I-2206 that can selectively eliminate organic sulfur from sulfur-containing organic molecules present in certain fossil fuels, and their use in processes for desulfurizing these fuels, in particular petroleum and some of its fractions and their derivatives.
In addition to carbon, fossil fuels such as coal and petroleum contain other elements, such as, for example, sulfur and nitrogen. Thus, crude oil contains sulfur, mainly in organic form, in more or less high concentrations, in general between 0.025% and 5%. This sulfur still remains in a more or less high ratio in the petroleum fractions obtained by distillation (for example up to 10% in certain heavy fractions), and subsequently also in the various petroleum products. In crude oil, sulfur is present mainly in the form of organic sulfur (sulfides, thiols, thiophene, benzothiophene, dibenzothiophene and their substituted derivatives). In several crude oils such as Texas crude, about 70% of the organic sulfur is present in the form of dibenzothiophene (DBT) or alkylated derivatives of DBT.
Combustion of the sulfur present in the fuels causes formation of sulfur dioxides that give rise to acid rain and that are considered to be among the worst air pollutants. In order to limit these noxious emissions, legislation has set standards for sulfur content in petroleum fuels. Moreover, these standards are becoming increasingly strict. For example, the nations of the European Union decided to set the upper limit of gasoil sulfur content at 350 ppm in the year 2000 and it will probably be around 50 ppm in the year 2005. The current specifications for gasoil have been 500 ppm since October 1996, and the preceding specification was 0.2%.
Such specifications dictate accelerated desulfurization of petroleum products by high-performing and economical processes.
Conventional desulfurization processes used in the refining industry implement physico-chemical hydrodesulfurization techniques which allow the reduction of the C—S bonds in hydrogen sulfide (H
2
S). This reaction is catalyzed by metallic catalysts and takes place in the presence of hydrogen at a high temperature. The deep desulfurization processes required by the new standards call for working at higher temperatures and at increasingly higher partial hydrogen pressures, and lengthening the dwell time in the reactors. All these factors considerably increase the cost of the desulfurization process. In addition, to attain very low sulfur contents, it is becoming necessary to remove the most refractory sulfur compounds in hydrodesulfurization. To use the example of gasoil, the most refractory compounds are often represented by DBT and its derivatives. It is therefore necessary to increase the hydrogen pressure, the temperature and the dwell time to attain low sulfur contents, thereby considerably increasing operating costs. Moreover, hydrodesulfurization operating conditions can sometimes be so strict that a possible degradation of hydrocarbons other than said sulfur-containing compounds results. Finally, in certain cases, the high concentration of heavy metals in the petroleum may limit the use of hydrodesulfurization catalysts which are sensitive to the presence of the latter. Since the heavy metal concentration and sulfur concentration often increase in a parallel manner during refining, this problem may also limit the implementation of hydrodesulfurization processes.
This is why the development of processes for desulfurization of petroleum or at the very least of some petroleum compounds other than chemical hydrodesulfurization has been studied for several years. This is particularly the case of biological processes that are still called biodesulfurization (BDS) processes.
Several methods of microbiological desulfurization have been described in the literature. Thus, certain sulfate-reducing anaerobic microorganisms are able to degrade DBT with production of H
2
S. These are slow processes that require reducing elements that may be supplied electrochemically as described in U.S. Pat. No. 4,954,229 or in the form of molecular hydrogen.
There are microorganisms that can aerobically oxidize DBT. In the majority of cases, such systems degrade DBT by using the so-called Kodama metabolic method (Kodama et al., Agr. Biol. Chem., 34, 1320, (1970)). In this case, there is no actual desulfurization, since oxidation is accomplished on one of the aromatic cores of DBT without the final product losing its sulfur atom. Likewise, there are microorganisms that can aerobically mineralize DBT (Kropp and Fedorak, Canad. J. Microbiol., 44, 605 (1998)). The use of these microorganisms for desulfurization purposes is not considered, because a significant loss of calorific power of the fuel thus treated would result therefrom.
The discovery of the strain Rhodococcus sp. IGTS8 (ATCC No. 53968) described in U.S. Pat. No. 5104801 allowed biodesulfurization to be considered as a conceivable proces that can be economically advantageous. This strain can aerobically remove sulfur from dibenzothiophene by specific oxidation of sulfur using the so-called 4S metabolic method (sulfoxide, sulfone, sulfinate, sulfite or sulfate). The final product resulting from desulfurization of DBT is 2-hydroxybiphenyl, and the sulfur is released in the form of sulfite (Oldfield et al., Microbiology, 143, 2961 (1997)). This new metabolic method was the subject of numerous studies. The DBT desulfurization phenotype is conferred by a dsz operon located on a plasmid. This operon codes for three enzymes, Dsz A, B and C, which are responsible for the oxidation reactions of DBT in hydroxybiphenyl (Li et al., J. Bacteriol., 178, 6409 (1996)). This operon was cloned and sequenced, and the metabolic method was described (Piddington et al., Appl. Environm. Microbiol., 61, 468 (1995)). A fourth enzyme, DszD, which acts to transport electrons, is also involved in this metabolism (Xi et al., Biochem. Biophys. Res. Commun., 230, 73 (1997)). These different enzymes have been purified and characterized (Gray et al., Nature Biotechnol., 14, 1705 (1996)). Genetic analysis revealed the existence of a promoter and activity regulation mechanisms. Thus, the expression of genes in the 4S method is suppressed by sulfur that is easily available such as sulfate, cysteine or methionine. Many patents have been filed on the use of the IGTS8 strain.
Since the isolation of the IGTS8 strain was described, several other groups of researchers reported the isolation of other strains able to use the 4S method by enrichment on a minimum mineral medium containing only DBT as a sulfur source. It is thus possible to cite Rhodococcus sp. SY1 (Omori et al., Biosci. Biotechnol. Bioeng., 59, 1195 (1995)) first described as being a Corynebacterium (Omori et al., Appl. Environm. Microbiol., 58, 911 (1992)),
Rhodococcus erythropolis
D-1 (Izumi et al., Appl. Environm. Microbiol., 60, 223 (1994)),
Rhodococcus erythropolis
H-2 (Ohshiro et al., FEMS Microbiol. Lett., 142, 65 (1996)), Rhodococcus UM3 and UM9 (Purdy et al., Curr. Microbiol., 27, 219 (1993)),
Rhodococcus erythropolis
(Wang and Krawiec, Arch. Microbiol., 161, 266 (1994)), Mycobacterium sp. strain G3 (Nekodzuka et al., Biocatal. Biotrans., 15, 17 (1997)), Paenibacillus sp. strain A11-1 and A11-2 (Konishi et al., Appl. Environm. Microbiol., 63, 3164 (1997)) which have the particular characteristic of being thermophilic,
Arthrobacter paraffineus
ECRD-1 (Lee et al., Appl. Environm. Microbiol., 61, 4362 (1995)) which was reclassified as actually being a Rhodococcus (Denis-Larose et al., Appl. Environm. Microbiol., 63, 2915 (1997)) and which was isolated on 4,6-diethyl dibenzothiophene, Arthrobacter sp. (E.P. 795603) which has the particular characteristic of acting on petroleum products without the addition of surfactants, Gordona CYSKI (Rhee et al., Appl. Environm. Microbiol., 64,
Abbad-Andaloussi Samir
Monot Frederic
Warzywoda Michel
Institut Francais du Pe'trole
Lilling Herbert J.
Millen White Zelano & Branigan P.C.
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