US3163593A

US3163593A - Desulfurization of heavy oils

Info

Publication number: US3163593A
Application number: US183714A
Authority: US
Inventors: Webster Alfred Bentley; Small Norman James Herbert; Rigby Richard
Original assignee: Shell Oil Co
Current assignee: Shell USA Inc
Priority date: 1961-04-06
Filing date: 1962-03-30
Publication date: 1964-12-29
Anticipated expiration: 1981-12-29
Also published as: DE1470636A1; GB976707A; NL276740A; FR1325139A

Description

. 3,163,593 DESULFUREZATIGN F EEAVY CHIS Alfred Bentley Webster, Wallasey, Norman James Herbert Small, Christleton, near Chester, and Richard Rigby,

Wirral, England, assignors to heli Oil Company, New

York, N .Y., a corporation of Delaware No Drawing. Filed Mar. 30, 1962, Ser. No. 183,714 Claims priority, application Great Britain, Apr. 6, 1961,

12,373/61 7 Claims. (Cl. EM -2 .0)

This invention is concerned with improvements in or relating to the desulfurization of hydrocarbon oils and more particularly to the desulfurization of heavy hydrocarbon oils.

It has been known to treat hydrocarbon fractions with oxidants of various kinds followed by removal of the oxidation products by acid washing, solvent extraction,

fractional distillation, extractive distillation, or a combination of such methods such that desulfurization is accomplished by loss of the hydrocarbon portions of the sulfur bearing molecules and result in low yields of treated product.

The'present invention provides a new and improved process for reducing the sulfur content of heavy hydrocarbon oils without the concomitant loss of valuable hydrocarbon' oils. In accordance with the present invention, a heavy. petroleum oil is treated with an oxidant to form compounds containing'both oxygen and sulfur and then oil containing these compounds is subjected to a thermal treatment to rupture the sulfur-carbon bond, volatile sulfur compounds and a heavy hydrocarbon oil of low sulfur content are thereby produced with little loss of product. Y 1 The present invention is therefore particularly advantageous when applied to the treatment of hydrocarbon oils in which many of the molecules contain a sulfur atom. A further advantage of the present invention is that it can be applied to sulfur containing heavy hydrocarbon oils for which catalytic hydrodesulfurization processes (as may be'employed for the desulfurization of lighter hydrocarbon oils, for example gasolines, kerosenes, light fuel oils, lubricating oils, transformer oils) are either too costly or are unsuited to the particular sulfur compounds contained in the heavy hydrocarbon oil;

It is believed that the sulfur-carbon bonds of the sulfur containing molecules are weakened by the formation of oxidation products thereof and are ruptured by thermal treatment at temperatures insuflicient to degrade the hydrocarbons present in the oil. I

Preferably, the oxidative treatment should be suiiicient to form sulfones without further oxidationto sulfonic acid derivatives. The presence of such acid derivatives may be disadvantageous during the thermal after treatment due to sulfuric acid formation and resultant sludge and coke formation.

By heavy hydrocarbon oil, it is meant a hydrocarbon A United States Patent 0 ddhhs Patented Eco. 29,, 1964 hydrogen peroxide with formic or acetic acids. Other suitable oxidizing agents are organic hydroperoxides, in-

organic peracids and salts thereof, aqueous hypochlorite solutions, nitrogen peroxide or air.

' Particularly suitable oxidizing agents however are mixtures of hydrogen peroxide and lower alkyl mono carboxylic acids having from 1 to 2 carbon atoms, preferably formic acid, since such mixtures appear to be selective for sulfone formation and the thermal treatment of oils thus oxidized enables the total sulfur content of the heavy oils to be reduced significantly. It has beenffound that particularly satisfactory proportions of reactants to use in the oxidizing step are those where the molar ratio of acid to peroxide is less than 4:1 and greater than 1:10, preferably from about 1:1 to about 1:5. At the higher ratios of acid to peroxide, the by-product formation during the thermal after-treatment tends to increase, whereas at the lower ratios the degree of desulfurization achieved is less satisfactory. It is preferred that the molar ratio of peroxide employed to the sulfur present be greater than 1, and further it has been found that no significant increase in desulfurization is achieved using a molar ratio greater than 8. For economic reasons it is desirable to use as oil of which at least 50% by volume boils above 250;?C.

The present invention is particularly applicable to sulfurcontaining hydrocarbon oils of which at least 90% by volume boils above 300" C. Examples of hydrocarbon oils to which the present invention may be usefully ap-.

plied are cracked gas oils, residual fuel'oils, topped or reduced crudes, ciriidejetroleunifrom which the lighter "fractions are absent, vacuum residues, residues from cracking processes, oils frorntar sands and oil shale." The invention is especially applicable to such of these and other like materials as cannotbe deeply flashed without extensive carry overof sulfur containing compounds.

Exemplary ofoxidizing agents that have been found suitable for use in the present invention are the organic pe'racids, e.g., performic or peracetic acid or mixtures of little peroxide as is commensurate with effective desulfurization.

As previously mentioned it is desirable that the oxida-.

'tion of the sulfur-containing compounds present in the oils being treated should proceed no further than sulfone formation. The conditions to achieve this end are readily known to those skilled in the art. For any given oxidant, the oxidation conditions may be varied to determine those which result in optimum sulfone formation, the presence of which may be detected by infrared analysis.

Although not essential, it is often desirable before treat- I ing a highly viscous heavy hydrocarbon oil to dissolve the oil in a low-boiling organic solvent, e.g., benzeneor carbon tetrachloride; the reduction in viscosity thereby achieved enables a more thorough oxidation to take place and the overall degree of desulfurization to be improved.

These solvents are well known in the art and'need not be enumerated here.

The thermal after-treatment may be carried out in any manner Well-known in the art, the temperature being so chosen as to minimize the degree of thermal degradation ofthe hydrocarbons present in the oil and being suificient to rupture the sulfur-carbon bonds of the sulfur-containing molecules, which bonds, as mentioned above, have been weakened by the oxidation reaction. Generally temperatures in excess of 350 C. are sumcient for this purpose,

i.e., about 350 C. to about 450 C. and temperaturesof about 400 C. are particularly suitable. The thermal treatment may take place in the rials such as dolomite or lime.

The sequence of treating steps may be repeated with advantage and thereby the sulfur content of the heavy oil reduced still further. v

I The present invention will be more readily understood by reference to the following examples? EXAMPLEI the solvent and excess reagents were removed by distillapresence of alkaline mate sneases achieved using a molar ratio of acid/ peroxide/ sulfur of 8:8:1, and employing a temperature of 350 C. or 400 C. in the thermal after-treatment. The thermal treatment at 300 (3., although effective to a certain extent did not result in satisfactory sulfur removal.

EXAMPLE H In this example the same reagent ratios and conditions as in Example I were employed, but 200 grams of the Kuwait Long Residue were used and 113 grams of the oxidized product thermally treated at 400 C. This treatment produced 90% yield of a residual oil having a sulfur content of 1.9% by weight and only 0.3% by weight of coke was formed.

EXAMPLE III 100 grams of the same heavy oil as used in the above examples was dissolved in benzene and stirred for 6 hours in the presence of 176 milliliters of 29% w./v. hydrogen peroxide and 76 grams of 90% w. formic acid. After removing excess reagents and solvent, samples of the oxidized oil were heated at 350 C. and 400 C. respectively forv 1 /2 hours, and yielded residual oils with sulfur contents of 2.74% by weight and 1.71%. by weight respectively. The product from the thermal treatment at 350 C..was reoxidized using the same amount of hydrogen peroxide as in the first oxidation and a formic acid/ peroxide molar ratio of 2.0. After solvent removal, the product was heated for 1 /2 hours at 350 C. to yield a residual oil having a sulfur content of 1.79% by weight, and this oil was heated further for 1 /2 hours at 400 C. to yield a residual oil having a sulfur content of 1.45% by weight.

EXAMPLE IV In a series of experiments using a hydrogen peroxide/ formic acid mixture as the oxidant, carried out to illustrate the effect of varying peroxide/sulfur molar ratio, samples of the same feedstock as was used in the previous examples were treated for 6 hours at 50 C. in the presence of benzene with formic acid and hydrogen peroxide at an acid/ peroxide molar ratio of 1 and with varying peroxide/sulfur mole ratios. The products were thermally treated at 400 C. for 1 /2 hours and the results obtained are set out in Table I.

These results indicate that with a formic acid/ hydrogen peroxide oxidant system, the molar ratio vof peroxide to sulfur should be greater than 1 and no beneficial effect is to be obtained using a mole ratio greater than 8.

EXAMPLE V A series of experiments was carried out using the same feedstock as in the previous examples, using a formic acid/ hydrogen peroxide oxidant system, in order to determine the effect on dcsulfurization by varying the mole ratio of formic acid to peroxide used in the oxidation step. All

a the runs were carried out using a peroxide/sulfur mole ratio of 4 and oxidation was performed by treating the Oil with the oxidant for 6 hours at C. in the presence of benzene. The results obtained are set out below in Table II.

Table II Thermal eragrilng at 400 C. or 1 iour Mole ratio, 2 S i HCO err mods Percent residual Percent Percent r i 1 m1 011 coke distillate 2 2. 3 18. O 70. 3 i 2. 66 4. 6 13. 8 70. 3 2. 52 3. 8 2. 3 76. 7 2. 25 3. 8 13. 7 74. O 2. 26 2. 5 14. 3 70. 8 2. 20 O. 4 2. 5 88. 0 1. 98 Nil 5. 4. 86. 3 3. 84

At higher mole ratios of acid to peroxide the by-product formation during the thermal treatment tends to increase, while at the ratios less than 1:5 the degree of desulfurization is unsatisfactory.

EXAMPLE VI In this example, a sample of the same Kuwait Long Residue as used in the previous examples was subjected to oxidation with a formic acid/ hydrogen peroxide oxidant system using a molar ratio of acid/peroxide/sulfur of 8:4:1 for 6 hours at 50 C. in the presence of benzene. 13.2 grams ofthe product was thermally treated in the presence of 2.7 grams of lime for 1 /2 hours at 400 C. A sample of the oxidation product was also cracked under the same conditions except there was no lime present. The following table illustrates the beneficial effect obtained when the thermal after-treatment iscarried out in the presence of lime.

In this examples a sample of reduced crude is subjected to oxidation with an acetic acid/hydrogen peroxide oxidant system using a molar ratio of acid/peroxide/sulfur of 8:4:1 at 50 C. to form sulfones without further oxidation to sulfonic acid derivatives. The oil is separated from the oxidant system and is thermally treated for 1 /2 hours at 400 C. The resultant heavy petroleum oil has a lower sulfur content than the feed to the process.

We claim as our invention:

1. A process for reducing the sulfur content of a sulfurcontaining heavy hydrocarbon oil, at least 50% by volume of said oil boils above 250 C., which comprises treating the oil with an oxidant to form compounds containing both oxygen and sulfur, said oxygen and sulfur being chemically combined, heating the treated oil containing said compounds at a temperature from about 350 C. to about 450 C. under conditions to rupture the sulfurcarbon bond yielding volatile sulfur compounds, and recovering a heavy hydrocarbon oil of reduced sulfur content.

2. A process for reducing the sulfur content of a sulfurcontaining heavy hydrocarbon oil, at least 50% by volume of said oil boils above 300 C., which comprises treating the oil with a peroxide-containing oxidant, the mol ratio of peroxide to the sulfur present being from about 1 :1 to about 8:1 to form sulfones without further oxidation to sulfonic acid derivatives, heating the treated oil containing sulfones at a temperature from about 350 C. to about 450 C. under conditions to rupture the sulfur-carbon bond yielding volatile sulfur compounds, and recovering a heavy hydrocarbon oil of reduced sulfur content.

3. A process for reducing the sulfur content of a sulfur-containing heavy hydrocarbon oil, at least 90% of said oil boils above 300 C., which comprises treating the oil with a peroxide-containing oxidant consisting essentially of hydrogen peroxide and a lower alkyl monocarboxylic acid having from 1 to 2 carbon atoms, the mol ratio of 10 peroxide to the sulfur present being from about 1:1 to about 8:8 and the mol ratio of acid to peroxide being from about 1: 10 to about 4:1 to form sulfones without further oxidation to sulfonic acid derivatives, heating the treated oil containing sulfones of from about 350 C. to about 1 6 containing heavy hydrocarbon oil is dissolved in a low boiling organic solvent before treatment.

7. A process for reducing the sulfur content of a sulfur-containing heavy hydrocarbon oil, at least 90% by volume of the oil boils above 300 C., which comprises treating the oil with a peroxide-containing oxidant consisting essentially of hydrogen peroxide and formic acid, the mol ratio of peroxide to the sulfur present being from about 1:1 to about 8:1 and the mol ratio of acid to peroxide being from about 1:1 to about 1:5, to form sulfones without further oxidation to sulfonic acid derivatives, heating the treated oil containing sulfones at about 400" C. to rupture the sulfur-carbon bond yielding volatile sulfur compounds, and recovering a heavy hydrocarbon oil of reduced sulfur content.

References Cited in the file of this patent UNITED STATES PATENTS 20 1,972,102 Malisofi Sept. 4, 1934 2,414,963 McConnell Jan. 28, 1947 2,749,284 Noble June 4, 1956 Disclaimer 3,163,593.Alf1"ed Bentley Webstew, Wallasey, N owmem James H erbert Small,

Christleton, near Chester, and Riehaml Rigby, ix-ml, England. DE- SULFURIZATION OF HEAVY OILS. Patent'clated Dec. 29,1964:. Disclaimer filed Dec. 20, 1965, by the assignee, Shell Oil Company.

Hereby enters this disclaimer to claims 1 and 2 of said patent. [Ofielal Gazette May 5, 1966.1

Claims

1. A PROCESS FOR REDUCING THE SULFUR CONTENT OF A SULFURCONTAINING HEAVY HYDROCARBON OIL, AT LEAST 50% BY VOLUME OF SAID OIL BOILS ABOVE 250*C., WHICH COMPRISES TREATING THE OIL WITH AN OXIDANT TO FORM COMPOUNDS CONTAINING BOTH OXYGEN AND SULFUR, SAID OXYGEN AND SULFUR BEING CHEMICALLY COMBINED, HEATING THE TREATED OIL CONTAINING SAID COMPOUNDS AT A TEMPERATURE FROM ABOUT 350* C. TO ABOUT 450*C. UNDER CONDITIONS TO RUPTURE THE SULFURCARBON AND YIELDING VOLATILE SULFUR COMPOUNDS, AND RECOVERING A HEAVY HYDROCARBON OIL OF REDUCED SULFUR CONTENT.