Mineral oils: processes and products – Refining – Sulfur removal
Reexamination Certificate
2001-05-16
2003-04-08
Dang, Thuan D. (Department: 1764)
Mineral oils: processes and products
Refining
Sulfur removal
C208S219000, C208S222000, C208S244000, C208S25400R, C208S255000, C208S256000, C208S295000, C208S299000
Reexamination Certificate
active
06544409
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a process for the catalytic oxidation of sulfur, nitrogen and unsaturated compounds present in hydrocarbon streams of fossil oils, in the presence of a peracid and pulverized raw iron oxide, the process being carried out at atmospheric pressure and ambient or higher temperature supplied by self-heating. More specifically, the invention relates to a process for the simultaneous removal of sulfur, nitrogen and unsaturated compounds aided by the catalyst action of limonite clays that improve the oxidation potential of a peracid in oil phase, the peracid being either added as such or generated in situ by the combination of a peroxide and organic acid. The inventive process is specially suited to the removal of sulfur, nitrogen and unsaturated compounds from light, medium and heavy distillates obtained from petroleum, liquefied coal, shale oil and tar, with the preferred streams being heavy diesel oil or petroleum gasoils. The products from the oxidizing process are relatively lighter than the original oils, with sulfur compounds in the range of 0.010 weight % to 0.2 weight % and nitrogen compounds in the range of 0.0010 weight % to 0.15 weight %, according to process conditions. The inventive process encompasses still the removal of up to 50 weight % of olefins present in the feed.
BACKGROUND INFORMATION
The peroxide-aided oxidation is a promising path for the refining of fossil oils, and may be directed to several goals, for example to the removal of sulfur and nitrogen compounds present in fossil hydrocarbon streams, mainly those used as fuels for which the international specification as for the sulfur content becomes more and more stringent.
One further application is the withdrawal of said compounds from streams used in processes such as hydrotreatment, where the catalyst may be deactivated by the high contents in nitrogen compounds.
Basically, the peroxide oxidation converts the sulfur and nitrogen impurities into higher polarity compounds, those having a higher affinity for polar solvents relatively immiscible with the hydrocarbons contaminated by the sulfur and nitrogen compounds. This way, the treatment itself comprises an oxidation reaction step followed by a separation step of the oxidized products by polar solvent extraction and/or adsorption and/or distillation.
The oxidation reaction step using peroxides, as well as the separation steps of the oxidized compounds from the hydrocarbons have been the object of various researches.
Thus, EP 0565324A1 teaches a technique exclusively focused on the withdrawal of organic sulfur from petroleum, shale oil or coal with an oxidation reaction step with an oxidizing agent like H
2
O
2
initially at 30° C. and then heated at 50° C. in the presence of an organic acid (for example HCOOH or AcOH) dispensing with catalysts, followed by (a) a solvent extraction step, such as N,N′-dimethylformamide, dimethylsulfoxide, N,N′-dimethylacetamide, N-methylpyrrolidone, acetonitrile, trialkylphosphates, methyl alcohol, nitromethane among others; or by (b) an adsorption step with alumina or silica gel, or (c) a distillation step where the improved separation yields are caused by the increase in boiling point of the sulfur oxidized compounds.
A similar treatment concept is used by D. Chapados et al in “Desulfurization by Selective Oxidation and Extraction of Sulfur-Containing Compounds to Economically Achieve Ultra-Low Proposed Diesel Fuel Sulfur Requirements”, NPRA 2000 Annual Meeting, Mar. 26-28, 2000, San Antonio, Tex., Paper AM-00-25 directed to a refining process also focused on the reduction of the sulfur content in oils, the oxidation step occurring at temperatures below 100° C. and atmospheric pressures, followed by a polar solvent extraction step and by an adsorption step. The authors further suggest the use of a solvent recovery unit and another one for the biological treatment of the concentrate (extracted oxidized products) from the solvent recovery unit, this unit converting said extracted oxidized products into hydrocarbons.
According to the cited reference by Chapados et al., the reaction phase consists of an oxidation where a polarized —O—OH moiety of a peracid intermediate formed from the reaction of hydrogen peroxide and an organic acid performs an electrophilic oxidation of the sulfur compounds, basically sulfides such as benzothiophenes and dibenzothiophenes and their alkyl-related compounds so as to produce sulfoxides and sulfones.
U.S. Pat. No. 3,847,800 teaches that the oxidation of the nitrogen compounds, such as the quinolines and their alkyl-related compounds so as to produce N-oxides (or nitrones) can be promoted as well when reacting these compounds with a nitrogen oxide.
The mechanisms for the oxidation of sulfur containing compounds with a peracid derived from a peroxide/organic acid couple are shown in
FIG. 1
attached, with dibenzothiophene taken as model compound.
According to U.S. Pat. No. 2,804,473, the oxidation of amines with an organic peracid leads to N-oxides, therefore a reaction pathway analogous to that of sulfur-containing compound is expected for the oxidation of nitrogen-containing compounds with a peracid derived from the peroxide/organic acid couple, as shown in
FIG. 2
attached, with quinoline taken as model compound. In addition, the same U.S. patent teaches a process for the production of lower aliphatic peracids. According to this publication, peracids are useful in a variety of reactions, such as oxidation of unsaturated compounds to the corresponding alkylene oxide derivatives or epoxy compounds.
As illustrated in
FIG. 3
attached, it is also well-known that hydrogen peroxide naturally decomposes into unstable intermediates that yield O
2
and H
2
O, such process being accelerated by the action of light, heat and mainly by the pH of the medium.
U.S. Pat. No. 5,917,049 teaches a process for preparing dicarboxylic acids containing at least one nitrogen atom where the corresponding heterocyclic compound of fused benzene ring bearing at least one nitrogen atom is oxidized in the presence of hydrogen peroxide, a Bronsted acid and an iron compound. The preferred iron compound is iron nitrate and nitric acid is used as the Bronsted acid. The reaction occurs in an aqueous medium.
Besides, U.S. Pat. No. 4,311,680 teaches a process for removal of sulfur containing compounds such as H
2
S, mercaptans and disulfides from gas streams exclusively such as natural gas by flowing the said gas stream through a Fe
2
O
3
fixed bed in presence of an aqueous solution of hydrogen peroxide.
On the other hand, several publications report the use of the Fenton's reagent exclusively directed for the withdrawal of pollutants from aqueous municipal and industrial effluents. See the article by C. Walling, “Fenton's Reagent Revisited”, Accts. Chem. Res., Vol. 8, p. 125-131 (1975), U.S. Pat. No. 6,126,838 and U.S. Pat. No. 6,140,294 among others.
Fenton's reagent, known since 1894, is traditionally a mixture of H
2
O
2
and ferrous ions exclusively in an aqueous medium, so as to generate the hydroxyl radical OH. as illustrated in
FIG. 4
attached. The hydroxyl radical is one of the most reactive species known. Its Relative Oxidation Power (ROP) ROP=2.06 (relative to Cl
2
whose ROP=1.0), is higher than that for example of singlet oxygen (ROP=1.78)>H
2
O
2
(ROP=1.31)>HOO. (ROP=1.25)>permanganate (ROP=1.24), this making it able to react with countless compounds.
However, side reactions consume or compete with the hydroxyl radical due to the presence of Fe
3+
or due to the natural dissociation of the hydrogen peroxide, as illustrated in
FIG. 5
attached.
Such side reactions may be minimized by reducing the pH in the medium, since the protic acidity reverts the dissociation equilibrium of the H
2
O
2
into H
+
and OOH
−
(as per
FIG. 3
attached), so as to prevent the transformation of the generated OOH— into HOO. which will lead more H
2
O
2
to H
2
O and O
2
in spite of
Dang Thuan D.
Petroleo Brasileiro S.A. - Petrobras
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