Process for producing low sulfur and high cetane number petroleum fuel

Abstract

The present invention relates to a process for producing clean petroleum fuel by reducing sulfur content, and raising the Cetane Number to a value above 50, in a process that may be carried out at one atmospheric pressure.

Description

CONTINUITY DATA

This application is a continuation of U.S. patent application Ser. No. 12/454,896, filed on May 26, 2009, which is a continuation of U.S. patent application Ser. No. 11/102,867, filed on Apr, 11, 2005, which is now abandoned.

FIELD OF THE INVENTION

The present invention relates to a process for producing clean petroleum by reducing sulfur content in petroleum, and raising the Cetane Number to a value above 50.

BACKGROUND OF THE INVENTION

Several states as well as certain European nations have increasingly brought about stricter requirements for the sulfur content of petroleum fuel. Aside from reducing corrosion in engines, lower sulfur provides for cleaner air with reduced toxicity to human life. An example of the potential danger from air polluted with sulfur is the formation of acid rain from oxidized forms of sulfur.

Hydrodesulfurization is a catalytic chemical process used worldwide to remove sulfur from refined petroleum products. The process is carried out at elevated temperatures ranging from 300 to 400° C. with elevated pressures ranging from 30 to 130 atmospheres. A catalyst is usually employed and comprises an inert substrate containing cobalt and molybdenum. Prior to exposure to the catalyst, the sulfur rich feed is joined by a stream of hydrogen rich gas. In a typical reaction, ethyl mercaptan is converted to the hydrocarbon ethane plus hydrogen sulfide. Other organic sulfur containing compounds such as sulfides, disulfides, thiophene and thiophene derivatives are also converted to the corresponding hydrocarbon plus hydrogen sulfide, which is subsequently converted into elemental sulfur. Most of the sulfur produced worldwide is by-product sulfur from this refinery process.

Modification of the hydrodesulfurization process had been reported in the literature. For example, U.S. Pat. No. 5,770,047 to Salazar, et al. discloses a process for reducing sulfur content by 30 to 60%. The process requires the introduction of hydrogen gas at high temperatures in the range of 280 to 320° C. with best results achieved at a pressure of 400 psig. A special catalyst of Group III or Group VI metals impregnated within in a high surface area inert support was also required.

U.S. Pat. No. 8,062,322 to Schmidt discloses that desulfurization of sulfur containing fuels by a pyrolysis method conducted at a temperature of between 600° and 900° C. in the presence of a finely divided metal such as iron powder.

U.S. Pat. No. 4,80,885,662 to Mead discloses a process for producing low sulfur petroleum fuel. The process comprises the steps of contacting the fuel with an oxygen containing gas, mixing the fuel with acid and then neutralizing the acid with the base. The process requires temperatures of about 400° to 675° F.

The current state of the technology for desulfurization of petroleum fuel requires extremely high temperatures and pressures that require highly engineered, special equipment. Storage facilities and delivery equipment for hydrogen gas are often required components.

Sulfur continues to be a major offender in the pollution of air through the burning of fossil fuels. As concerns for the burning of fossil fuels is heightened among the major industrial countries of the world, sulfur continues to be a most undesirable component of fossil fuel burning, and consequently, permissible levels continue to be reduced.

There is a continuing need for new methods and alternate approaches for removing sulfur from petroleum fuel, and, in particular, manufacturers seek methods that are relatively simple, have low capital investment costs and are highly effective. The present invention meets or exceeds these needs.

SUMMARY OF THE INVENTION

In one aspect, the present invention provides a process for producing low sulfur petroleum fuel. The process may includes the steps of providing a petroleum fuel having a predetermined sulfur content and a predetermined Cetane Number, adding an aqueous acid solution to said fuel, adding a metal to said fuel, such as aluminum, mixing the petroleum fuel, acid solution and aluminum metal, adding sufficient aqueous base at a temperature of 100 to 120° C. to neutralize said acid, and, allowing said petroleum fuel to separate from the aqueous solution.

The petroleum fuel, which is the starting material in the process described above, may have a predetermined sulfur content of from between 20 ppm and 2000 ppm. Typically sweet crude oil from which petroleum fuel may be derived has a sulfur content of as much as 0.5% or 5000 ppm. During the petroleum refining steps, such as reforming, which lead to petroleum fuel the sulfur content is substantially reduced.

Furthermore, the Cetane Number of the petroleum fuel employed as the starting material in the present invention may be at least 40. The Cetane Number enhancing additive raises the cetane number to a value of at least 50.

The process steps disclosed in this invention may be carried out at one atmosphere of pressure.

Furthermore, the sulfur content of the starting material petroleum fuel may be reduced by at least 50%.

In another aspect, the aluminum may be in the form of powder, chips or filings or any combination thereof.

In another aspect, the aqueous acid may be selected from the group consisting of sulfuric acid, hydrochloric acid, phosphoric acid and mixtures thereof.

In a further aspect, the aqueous base used to neutralize the acid may be selected from the group consisting of sodium hydroxide, potassium hydroxide, ammonium hydroxide, sodium carbonate and sodium bicarbonate.

In another aspect of the invention, the sulfur reduction process may be followed by the addition of the Cetane Number elevating additive, which may be selected from the group consisting of alcohols, alkyl esters of inorganic acids and peroxides.

DETAILED DESCRIPTION OF THE INVENTION

Petroleum fuel may be produced from the fractional distillation of crude oil between 200° C. and 350° C. at atmospheric pressure, resulting in a mixture of hydrocarbons containing between 8 and 21 carbon atoms per molecule and being 75% saturated and 25% aromatic. The sulfur found in diesel fuel may be present as alkyl sulfides, alkyl disulfides, thiophene and thiophene derivatives along with hydrogen sulfide gas. In the present invention, these sulfur compounds may be exposed to hydrogen gas under conditions that convert organic sulfur compounds to hydrogen sulfide gas that is removed as an off-gas at elevated temperatures.

In the present invention, effective amounts of sulfuric acid may be employed so that all of the aluminum is converted to the water-soluble salt aluminum sulfate according to Scheme 1 below:

2Al+3H₂SO₄→3H₂+Al₂SO₄   Scheme 1

The hydrogen produced in Scheme 1 reacts with the sulfur compounds resulting in the cleavage of the carbon sulfur chemical bond. The net result is the formation of carbon-hydrogen and hydrogen-sulfur chemical bonds.

In Scheme 2 below ethyl mercaptan, a typical sulfur compound present in petroleum fuel, may be desulfurized resulting in the formation of the hydrocarbon and hydrogen sulfide that is readily removed from the reaction mixture under elevated temperatures.

C₂H₅SH+H₂→C₂H₆+H₂S   Scheme 2

While not wishing to be bound by theory, it is believed that the hydrogenation step of the present invention is fast and highly efficient because the sulfur compounds may be initially adsorbed onto the aluminum metal surface whereupon hydrogen gas is liberated in direct and close proximity to the sulfur compound.

Cetane Number is a measure of the ignition quality of diesel fuel. It is not a measure of overall fuel quality, but rather is a measure of the fuels ignition delay that is the time between the start of injection and start of fuel combustion. Generally, higher cetane fuels will have shorter ignition delay than lower cetane fuels.

Low Cetane Numbers will likely cause hard starting, rough operations, noise and exhaust smoke. Generally, diesel engines will operate better on fuels with cetane numbers above 50 as compared to fuels with lower cetane numbers of approximately 45 that represents the United States national average.

Diesel fuels are blend of distillate fuels and cracked petroleum hydrocarbons. The cracked hydrocarbons are low in cetane number due to high aromatic content. To meet the cetane Number demands of most diesel engines, cetane improvers are added to the blend.

Cetane improvers modify fuel combustion in the engine. They encourage early and uniform ignition of the fuel. Typically alkyl nitrate additives can increase cetane by about 3 to 5 numbers. Most cetane improvers contain alkyl nitrates that break down providing additional oxygen for better combustion.

Experimental

The present invention is a process that may be carried out in two phases. The first phase may include receiving petroleum fuel to be treated. The fuel temperature may be 80 to 100° C. The fuel then may be mixed with an aqueous solution of sulfuric acid followed by the addition of elemental aluminum. This step may be carried out at atmospheric pressure. This phase may take 10 hours depending on the incoming level of sulfur fuel and the quantity of fuel being treated.

In a second phase, the fuel may be mixed with an aqueous solution of base to neutralize unreacted acid. The reaction mixture may be heated to a temperature of about 100° C. and mixing its continued for 3 to 4 hours. As a next step, the resulting fuel may be sent to a separator where the fuel naturally separates from the water phase.

An additional step may be employed to raise the Cetane Number. At least one additive may be added to the fuel. The additive may be an alcohol such as methanol, an alkyl esters of inorganic acids such as alkyl nitrates, butyl nitrates, amyl nitrates, isobutyl nitrate or a peroxides or combinations thereof.

The process may reduce sulfur content by at least 50% and raise the Cetane Number to a value higher than 50.

The present process is a simple and inexpensive treatment of petroleum fuel to improve its ignition quality and provide cleaner fuels.

While the invention has been described in detail with reference to specific embodiments thereof, it will be apparent to one skilled in the art that various changes and modifications can be made therein without departing from the scope and spirit thereof. Although the present invention has been described herein with reference to particular means, materials and embodiments, the present invention is not intended to be limited to the particulars disclosed herein; rather, the present invention extends to all functionally equivalent structures, methods and uses, such as those within the scope of one with average skill in the art.

Claims

1. A process for producing low sulfur petroleum, the process comprising the steps of:

a. providing a petroleum feedstock;

b. adding effective amount of aqueous acid solution to the petroleum;

c. adding effective amount of metal to the petroleum;

d. mixing the petroleum, the acid solution and the metal;

e. adding effective amounts of aqueous base to neutralize the acid; and

f. separating the resulting petroleum from the aqueous solution.

2. The process according to claim 1 wherein the metal is aluminum.

3. The process according to claim 1 further comprising the step of adding at least one Cetane number elevating additive.

4. The process according to claim 3 wherein the at least one Cetane number elevating additive is selected from the group consisting of alcohols, alkyl esters of inorganic acids, and peroxides.

5. The process according to claim 1 wherein said sulfur content is reduced by at least 50%.

6. The process according to claim 2 wherein said aluminum metal is selected from the group consisting of aluminum powder, aluminum chips, and aluminum filings.

7. The process according to claim 1 wherein said aqueous acid is selected from the group consisting of sulfuric acid, hydrochloric acid, and phosphoric acid.

8. The process according to claim 1 wherein said aqueous base is selected from the group consisting of sodium hydroxide, potassium hydroxide, ammonium hydroxide, sodium carbonate and sodium bicarbonate.

9. The process according to claim 1 wherein said process steps are carried out at a pressure of one atmosphere.

10. A method for producing clean petroleum fuel, the method comprises the steps of:

a. providing a crude oil;

b. reducing the sulfur content of the oil; and

c. elevating the Cetane number of the oil, wherein the method steps are carried out at a pressure of one atmosphere.

11. The method of claim 10 wherein the step of reducing the sulfur content further comprises the steps of:

d. adding effective amount of aqueous acid solution to the oil;

e. adding effective amount of metal to the oil;

f. mixing the oil, the acid solution and the metal;

g. adding effective amounts of aqueous base to neutralize the acid; and

h. separating the resulting oil from the aqueous solution.

12. The method according to claim 11 wherein the metal in step (e) is aluminum.

13. The method according to claim 10, wherein the step of elevating the Cetane number comprises the step of adding at least one Cetane number elevating additive.

14. The method according to claim 13 wherein the at least one Cetane number elevating additive is selected from the group consisting of alcohols, alkyl esters of inorganic acids, and peroxides.

15. The method according to claim 12 wherein the aluminum metal is selected from the group consisting of aluminum powder, aluminum chips, and aluminum filings.

16. The method according to claim 11 wherein the aqueous acid in step (d) is selected from the group consisting of sulfuric acid, hydrochloric acid, and phosphoric acid.

17. The method according to claim 11 wherein the aqueous base in step (g) is selected from the group consisting of sodium hydroxide, potassium hydroxide, ammonium hydroxide, sodium carbonate and sodium bicarbonate.

18. A petroleum fuel produced by the method according to claim 10.