Mineral oils: processes and products – Refining – Sulfur removal
Reexamination Certificate
2002-01-10
2003-10-28
Griffin, Walter D. (Department: 1764)
Mineral oils: processes and products
Refining
Sulfur removal
C208S240000, C208S237000, C208S238000, C208S219000, C208S222000, C208S223000, C208S196000, C435S282000, C435S262000, C435S281000
Reexamination Certificate
active
06638419
ABSTRACT:
The invention relates to a method for obtaining oil products that can possibly be used either for the formulation of fuel for internal combustion engines with compression ignition (of the diesel type) or as a fuel, as well as the oil product of the gas oil type and the sub-products obtained by this method.
The gas oils currently found on the market in France in the form of fuels for diesel type engines, are products of the refining that contain sulfur in a quantity equal at most to 0.05% by weight (500 ppm, or parts per million); however, stricter and stricter standards of sulfur content are being considered, namely by the European Union for the year 2000 (<350 ppm) and for 2005 (≦50 ppm).
These gas oils are usually obtained following a treatment called hydrodesulfurization from very diverse hydrocarbon charges that can result from the direct distillation of a crude oil, from viscosity breaking, from hydroconversion or from catalytic cracking. Among the sulfur compounds contained in these charges, we find in order of increasing difficulty of elimination: thio alcohols, sulfides and disulfides, then thiophenes, and within this group, namely the family of dibenzenethiophenes (DBT) and their alkyl derivatives, which are known for being the compounds most resistant to desulfurization.
The catalytic hydrodesulfurization method consumes large quantities of hydrogen and must be operated at higher and higher temperatures and pressures or at a lower hourly space speed of the charge, and with more performing catalysts when we wish to eliminate said last quantities of sulfur contained in said organosulfur compounds; yet this makes the installations more and more costly and the method less interesting from an economic point of view.
This is why various alternatives have been proposed to try and correct these disadvantages.
This is namely the case of the method for obtaining a gas oil fraction from a hydrocarbon charge with a high sulfur content, described in the patent EP-0 621 334, which combines at least one liquid/liquid extraction step per solvent making it possible to extract at least in part the polyaromatic compounds that are contained in said charge and one or several hydrodesulfurization steps, more or less advanced. The major disadvantages of such a method are on the one hand that it combines one low pressure unit and one or several high pressure units and, on the other hand, that the extract obtained with a high concentration of sulfur or polyaromatic compound it is not easy to upgrade.
Another path that has been explored for some time, consists in using a method of desulfurization of hydrocarbon charges through the culture of specific microorganisms such as bacteria (or biocatalytic desulfurization), that produce enzymes that catalyze the degradation of the resistant compounds such as dibenzenethiophenes; however the difficulty of selecting said microorganisms came from their specific action by cutting the C—C links of the organosulfur compounds, which generated a loss of quality of said charges and in particular of their calorific power; however genetically modified microorganisms, acting by oxidation cutting of the C-S links of the dibenzenethiophenes, were described namely in the patents U.S. Pat. No. 5,002,888, U.S. Pat. No. 5,104,801 and U.S. Pat. No. 5,132,219; the bio-desulfurization reaction passes through the following successive intermediary products: DBTsulfoxides, DBTsulfones; HPBSulfinates (hydroxyphenyl-benzenesulfinate), HPBSulfonates and the 2-hydroxybiphenyl and non organic sulfate final products.
In using specific genetically modified microorganisms as biocatalysts, we can stop the reaction at the stage of the intermediary products such as the hydroxyphenyl-benzenesulfinates or their derivatives, which are soluble in water and can thus be extracted from the hydrocarbon charges. However, the implementation of such a method requires the formation of an oil/water and biocatalyst emulsion, in a reactor whose ratio by volume can be 25/75%, and produces as a disadvantage the use of treatment capacities with high volumes.
U.S. Pat. No. 5,232,854 describes an advanced desulfurization method of a hydrocarbon charge, consisting of a traditional hydrodesulfurization step followed by a biocatalytic desulfurization step by incubation of the charge in the presence of oxygen with microorganisms such as those described in the above-mentioned patents and a step for separating the hydrocarbon effluent with a sulfur content of ≦500 ppm from the residues in the form of non organic sulfurs. However, such a method does not make it possible to reduce the sulfur content of the charges treated at rates that are clearly less than 500 ppm, for example approximately 50 ppm.
This is why the object of this invention is thus to improve the advanced desulfurization of hydrocarbon charges with a high sulfur content, without implementing high temperature and pressure conditions, while upgrading the sub-products obtained.
Surprisingly, the Applicant has established that it is particularly wise to couple the extraction and oxidizing desulfurization steps that take place under low temperature and pressure conditions, close to room temperature and atmospheric pressure, and without consuming hydrogen, therefore very interesting from an economic point of view, and namely to concentrate the more resistant organosulfur compounds using an extraction method, then to treat the extracts obtained using a method of desulfurization by oxidation, so as to separate the hydrocarbon effluents obtained with a low sulfur content from the oxidized organosulfur compounds and recuperate said sub-products; the latter can then be upgraded, after treatment, namely as detergents.
With this end in view, the object of the invention is a method for obtaining oil products of the gas oil type with improved quality, from a gas oil fraction that contains organosulfur compounds of the dibenzenethiophene type and/or their derivatives, with initial and final boiling points usually ranging between 170 and 480° C., characterized by the fact that it comprises at lest two steps, one a) a liquid/liquid extraction step wherein the gas oil fraction is put in contact with a solvent, so as to obtain a gas oil type raffinate with a low content of sulfur and aromatic compounds and an extract rich in solvent and a high content in sulfur an aromatic compounds and the other b) oxidation of the extract sulfur compounds, so as to obtain, after the separation, a heavy gas oil type hydrocarbon effluent with low sulfur content, and a residue comprising oxidized organosulfur compounds.
According to a first preferred mode of execution, the two steps are carried out at pressures that are less than or equal to 1 MPa, and at temperatures ranging between room temperature and 100° C.
In particular, the solvent used in step a) is chosen from among the group consisting of methanol, acetonitrile, monomethyl formamide, dimethyl formamide, dimethyl acetamide, N-methyl-pyrrolidone, dimethyl sulfoxide and furfural.
According to a second preferred mode of execution, step b) consists of a biodesulfurization in which the extract is treated in a reactor, possibly cleared of the solvent, preferably at atmospheric pressure, in the presence of a biocatalyst in an aqueous phase, comprising an appropriate strain of microorganisms that produce enzymes capable of oxidizing the organosulfur compounds.
In particular, step b), when it is a biodesulfurization, is followed by a first step c) of separation of the oily phase that contains the hydrocarbon effluent and of the aqueous phase, where the latter contains the biocatalyst and the residue comprised of compounds of the organosulfinate type, in particular, benzenesulfinates and/or their derivatives; where the latter are formed by the opening of the thiophenic cycles by oxidation.
Preferably, the separation of the residue and the biocatalyst is done in during a second step d) of separation, that consists either of an extraction by a polar solvent or over ion exchanging resins, or of a filtration or of an adsorption
Da Silva Pedro
Le Gall Raphaël
Arnold Jr. James
Griffin Walter D.
Sughrue & Mion, PLLC
Total Raffinage Distribution , S.A.
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