SIMULTANEOUS METAL, SULFUR AND NITROGEN REMOVAL USING SUPERCRITICAL WATER

Abstract

A process for removing metals, sulfur and nitrogen in the upgrading of hydrocarbons comprising: mixing hydrocarbons containing metals, sulfur and nitrogen with a fluid comprising water that has been heated to a temperature higher than its critical temperature in a mixing zone to form a mixture; passing the mixture to a reaction zone; reacting the mixture in the reaction zone under supercritical water conditions in the absence of externally added hydrogen for a residence time sufficient to allow upgrading reactions to occur while maintaining an effective amount of metals, derived from the hydrocarbon undergoing upgrading, in the reaction zone to catalyze the upgrading reactions; and recovering upgraded hydrocarbons having a lower concentration of metals, sulfur and nitrogen than the hydrocarbons before reaction is disclosed.

Description

FIELD OF THE INVENTION

The present invention relates to a process for simultaneous removal of metals, sulfur and nitrogen from heavy oil using supercritical water.

BACKGROUND OF THE INVENTION

Heavy oil typically contains high concentration of sulfur, metals and nitrogen. Such contaminants have very negative effects on the catalysts and equipment used in many processes for further refining to produce high value products. Hydroprocessing is currently the process of choice to remove metal and sulfur from heavy oil. Hydrotreating process typically takes place in a trickle bed or fixed-bed reactor using expensive catalyst such as Mo and requires the use, of high pressure hydrogen which becomes more and more expensive. Hydrogen-addition processes such as hydrotreating or hydrocracking require significant investments in capital and infrastructure. Hydrogen-addition processes also have high operating costs, since hydrogen production costs are highly sensitive to natural gas prices. Some remote heavy oil reserves may not even have access to sufficient quantities of low-cost natural gas to support a hydrogen plant. These hydrogen-addition processes also generally require expensive catalysts and resource intensive catalyst handling techniques, including catalyst regeneration. Therefore there is a need for improved methods/processes for heavy oil treatment to remove sulfur and metal.

One alternative to hydrotreating of heavy oil to remove sulfur and metals is to use supercritical water. However, previous processes use either catalyst or processing gas (reducing or oxidizing gas) or both to achieve simultaneous removal of sulfur and metal. Without externally supplied catalyst or hydrogen, the contaminate removal rate was not satisfactory.

U.S. Pat. Nos. 4,594,141; 4,483,761; 4,557,820; and 4,559,127 relate to the upgrading of heavy hydrocarbons using supercritical water to reduce sulfur, nitrogen and metals in the products The processes disclose use added olefin or halide components.

U.S. Pat. Nos. 3,948,754; 3,948,755 and 3,960,706 relate to a process using supercritical water for metal and sulfur removal without external supply of hydrogen using an externally supplied sulfur and nitrogen resistant catalyst.

U.S. Pat. No. 5,611,915 relates to a process to remove sulfur and nitrogen components using supercritical water using high pressure CO.

U.S. Patent Application 200310168381, U.S. Patent Application 2005/0040081 and U.S. Patent Application 200510072137 relate to a process and apparatus for treating heavy oil in such a way that vanadium contained in heavy oil is isolated during treatment with supercritical or subcritical water. Oxidizing agent is used to achieve metals removal. In addition, vanadium oxide scavenger is used to remove vanadium oxide formed from oxidation of vanadium by the oxidizing agent from reformed oils.

U.S. Pat. Nos. 3,989,618 and 4,005,005 relate to a process to upgrade heavy hydrocarbons using supercritical water without external supply of H2 or catalyst.

U.S. Pat. No. 4,446,012 relates to a process of treating heavy oil to removes metals and sulfur using sub-critical water (T=380 to 480 C and P=725 to 2175 psi) in the absence of hydrogen and catalyst.

A process according to the present invention overcomes these disadvantages by using supercritical water to upgrade a heavy hydrocarbon feedstock into an upgraded hydrocarbon product or syncrude with highly desirable properties (low sulfur content, low metals content, lower density (higher API), lower viscosity, lower residuum content, etc.). The process neither requires external supply of hydrogen nor must it use catalysts. Further, the process in the present Invention does not produce an appreciable coke by-product.

In comparison with the traditional processes for syncrude production, advantages that may be obtained by the practice of the present invention include a high liquid hydrocarbon yield; no need for externally-supplied hydrogen; no need to provide catalyst; significant increases in API gravity in the upgraded hydrocarbon product; significant viscosity reduction in the upgraded hydrocarbon product; and significant reduction in sulfur, metals, nitrogen, TAN, and MCR (micro-carbon residue) in the upgraded hydrocarbon product.

SUMMARY OF THE INVENTION

The present invention relates to a process for removing metals, sulfur and nitrogen in the upgrading of hydrocarbons comprising: mixing hydrocarbons containing metals, sulfur and nitrogen with a fluid comprising water that has been heated to a temperature higher than its critical temperature in a mixing zone to form a mixture; passing the mixture to a reaction zone; reacting the mixture in the reaction zone under supercritical water conditions in the absence of externally added hydrogen for a residence time sufficient to allow upgrading reactions including demetalation and desulfurization to occur while maintaining an effective amount of metals, derived from the hydrocarbon undergoing upgrading, in the reaction zone to catalyze desulfurization reactions; and recovering upgraded hydrocarbons having a lower concentration of metals, sulfur and nitrogen than the hydrocarbons containing metal and sulfur.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a process flow diagram of an embodiment of the present invention.

FIG. 2 is a process flow diagram of another embodiment of the present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

The present process is related to processes described in commonly assigned U.S. patent application Ser. Nos. 11/555,048; 11/555,130; 11/555,196; and 11/555,211, all of which were filed on Oct. 31, 2006 and which are incorporated by reference herein. These patent applications relate to various aspects of heavy oil upgrading technology using supercritical water. The present disclosure also relates to processes using supercritical water to upgrade hydrocarbons.

Reactants

Water and hydrocarbons which contain metals, sulfur and nitrogen compounds, preferably heavy hydrocarbons are the two reactants employed in a process according to the present invention.

Any heavy hydrocarbon can be suitably upgraded by a process according to the present invention. Preferred are heavy hydrocarbons having an API gravity of less than 20°. Among the preferred heavy hydrocarbons are heavy crude oil, heavy hydrocarbons extracted from tar sands, commonly called tar sand bitumen, such as Athabasca tar sand bitumen obtained from Canada, heavy petroleum crude oils such as Venezuelan Orinoco heavy oil belt crudes, Boscan heavy oil, heavy hydrocarbon fractions obtained from crude petroleum oils particularly heavy vacuum gas oils, vacuum residuum as well as petroleum tar, tar sands and coal tar. Other examples of heavy hydrocarbon feedstocks which can be used are oil shale, shale oil, and asphaltenes.

Water

Any source of water may be used in the fluid comprising water in practicing the present invention. Sources of water include but are not limited to drinking water, treated or untreated wastewater, river water, lake water, seawater produced water or the like.

Mixing

In accordance with the invention, the heavy hydrocarbon feed and a fluid comprising water that has been heated to a temperature higher than its critical temperature are contacted in a mixing zone prior to entering the reaction zone. In accordance with the invention, mixing may be accomplished in many ways and is preferably accomplished by a technique that does not employ mechanical moving parts. Such means of mixing may include, but are not limited to, use of static mixers, spray nozzles, sonic or ultrasonic agitation. The oil and water should be heated and mixed so that the combined stream will reach supercritical water conditions in the reaction zone.

It was found that by avoiding excessive heating of the feed oil, the formation of byproduct such as solid residues is reduced significantly. In one embodiment, the heating sequence is designed so that the temperature and pressure of the hydrocarbons and water will reach reaction conditions in a controlled manner. This will avoid excessive local heating of oil, which will lead to solid formation and lower quality product. In order to achieve better performance, the oil should only be heated up with sufficient water present and around the hydrocarbon molecules. This requirement can be met by mixing oil with water before heating up.

FIG. 1 shows an embodiment of a process according to the invention. Water is heated up to supercritical conditions by Heater 1, then the supercritical water mixed with heavy oil feed in the mixer. The temperature of heavy oil feed can be kept in the range of about 100° C. to 200° C. to avoid thermal cracking but still high enough to maintain reasonable pressure drop. In an embodiment in which after mixing with heavy oil, the temperature of the water-oil mixture would be lower than critical temperature of water, Heater 2 is used to raise the temperature of the mixture stream to above the critical temperature of water. In this embodiment, the heavy oil is first partially heated up by water, then the water-oil mixture is heated to supercritical conditions by the second heater (Heater 2). Where after mixing with heavy oil, the temperature of the water-oil mixture is higher than the critical temperature of water, a second heater would not be used.

Other methods of mixing and heating sequences based on the above teachings may be used to accomplish these objectives as will be recognized by those skilled in the art.

Reaction Conditions

After the reactants have been mixed, they are passed into a reaction zone in which they are allowed to react under temperature and pressure conditions of supercritical water, i.e. supercritical water conditions, in the absence of externally added hydrogen, for a residence time sufficient to allow upgrading reactions to occur. The reaction is preferably allowed to occur in the absence of externally added catalysts or promoters.

“Hydrogen” as used herein in the phrase, “in the absence of externally added hydrogen” means hydrogen gas. This phrase is not intended to exclude all sources of hydrogen that are available as reactants. Other molecules such as saturated hydrocarbons may act as a hydrogen source during the reaction by donating hydrogen to other unsaturated hydrocarbons. In addition, H₂ may be formed in-situ during the reaction through steam reforming of hydrocarbons and water-gas-shift reaction.

The reaction zone preferably comprises a reactor, which is equipped with a means for collecting the reaction products (syncrude, water, and gases), and a section, preferably at the bottom, where any metals or solids (the “dreg stream”) may accumulate.

Supercritical water conditions include a temperature from 374° C. (the critical temperature of water) to 1000° C., preferably from 374° C. to 600° C. and most preferably from 374° C. to 400° C., a pressure from 3,205 (the critical pressure of water) to 10,000 psia, preferably from 3,205 psia to 7,200 psia and most preferably from 3,205 to 4,000 psia, an oil/water volume ratio from 1:0.1 to 1:10, preferably from 1:0.5 to 1:3 and most preferably about 1:1 to 1:2.

The reactants are allowed to react under these conditions for a sufficient time to allow upgrading reactions to occur. Preferably, the residence time will be selected to allow the upgrading reactions to occur selectively and to the fullest extent without having undesirable side reactions of coking or residue formation. Reactor residence times may be from 1 minute to 6 hours, preferably from 8 minutes to 2 hours and most preferably from 10 to 40 minutes.

The present process includes the feature of maintaining an effective amount of metals, derived from the hydrocarbon undergoing upgrading, in the reaction zone to catalyze desulfurization reactions. Since the metals removed from heavy oil will serve as catalyst for sulfur removal, it is important to maintain metal concentrations inside the reactor. With reference to the embodiment shown in FIG. 1, such requirement is met by using a CSTR (continuous stirred tank reactor) type reactor. For CSTR metals formed through metals removal reactions are well mixed with feed stream and catalyze sulfur removal reactions, and therefore high removal rate of both metal and sulfur can be achieved.

FIG. 2 shows another method of maintaining an effective amount of metal in the reaction zone. In this embodiment part of dreg stream which contains high concentration of metals is recycled back to maintain adequate metal concentration in the reactor. The metal concentration inside the reactor can be controlled by adjusting recycle ratio. Such recycle strategy can also be used to control metal concentration when a CSTR is used. The dreg stream may either be withdrawn from anywhere it forms, for example from the reactor or from a high pressure separator shown in FIG. 2.

Reaction Product Separation

After the reaction has progressed sufficiently, a single phase reaction product is withdrawn from the reaction zone, cooled, and separated into gas, effluent water, and upgraded hydrocarbon phases. This separation is preferably done by cooling the stream and using one or more two-phase separators, three-phase separators, or other gas-oil-water separation device known in the art. However, any method of separation can be used in accordance with the invention.

The composition of gaseous product obtained by treatment of the heavy hydrocarbons in accordance with the process of the present invention will depend on feed properties and typically comprises light hydrocarbons, water vapor, acid gas (CO₂ and H₂S), methane and hydrogen. The effluent water may be used, reused or discarded. It may be recycled to e.g. the feed water tank, the feed water treatment system or to the reaction zone.

The upgraded hydrocarbon product, which is sometimes referred to as “syncrude” herein may be upgraded further or processed into other hydrocarbon products using methods that are known in the hydrocarbon processing art.

The process of the present invention may be carried out either as a continuous or semi-continuous process or a batch process or as a continuous process. In the continuous process the entire system operates with a feed stream of oil and a separate feed stream of water and reaches a steady state; whereby all the flow rates, temperatures, pressures, and composition of the inlet, outlet, and recycle streams do not vary appreciably with time. For continuous operations such as those shown in FIG. 1 and FIG. 2, oil feed will be heated up very quickly by supercritical water, and a preferred means for achieving simultaneous removal of metals, sulfur and nitrogen is using a reactor with backmixing behavior or to recycle some of the reactor bottoms (dreg stream) so that the metals removed from the feed oil will serve as catalyst for sulfur removal reactions.

While not being bound to any theory of operation, it is believed that a number of upgrading reactions are occurring simultaneously at the supercritical water conditions used in the present process. In a preferred embodiment of the invention the major chemical/upgrading reactions are believed to be:

Thermal Cracking: C_xH_y→lighter hydrocarbons

Steam Reforming: C_xH_y+2xH₂O=xCO₂+(2x+y/2)H₂

Water-Gas-Shift: CO+H₂O=CO₂+H₂

Demetalization: C_xH_yNi_w+H₂O/H₂→NiO/Ni(OH)₂+lighter hydrocarbons

Desulfurization: C_xH_yS_z+H₂O/H₂=H₂S+lighter hydrocarbons

The exact pathway may depend on the reactor operating conditions (temperature, pressure, O/W volume ratio), reactor design (mode of contact/mixing, sequence of heating), and the hydrocarbon feedstock.

The following Examples are illustrative of the present invention, but are not intended to limit the invention in any way beyond what is contained in the claims which follow.

EXAMPLE 1

Experimental Process Description

A bomb reactor was loaded with a water and a heavy oil feed with API=12.8, which was a heavy crude oil which was diluted with a diluent hydrocarbon at a ratio of 5:1 (20 vol % of diluent). The reactor was immersed in a sand bath at reaction temperature so the temperature inside the reactor was quickly raised to ˜400° C., typically in 3 to 5 minutes. The reaction time was 30 minutes, and after reaction the reactor was quickly cooled down. The upgraded oil product and water were then recovered from the bomb reactor.

The properties of the heavy crude feed were as follows: 12.8 API gravity at 60/60; 1329 CST viscosity @40° C.; 13.04 wt % MCRT; 3.54 wt % sulfur; 0.56 wt % nitrogen; 3.05 mg KOH/gm acid number; 1.41 wt % water; 371 ppm Vanadium; and 86 ppm Nickel.

After the super critical water treatment upgraded product (syncrude) had the following properties: 19.2 API gravity at 60/60; 3.15 wt % MCRT; 0.54 wt % sulfur; 0.21 wt % nitrogen; 5.16 ppm Vanadium; and 1.09 ppm Nickel. Substantial reductions in metals and sulfur were observed, with simultaneous increase in the API gravity and a significant decrease in the viscosity of the original crude oil feedstock.

EXAMPLE 2

The following procedure was performed using a continuous system. The feed oil was heated to 130° C. before entering a mixer. The heated crude was injected into a stream of supercritical water at temperature of 400° C. The water to oil ratio (volume at room temperature) was 3:1. The oil-supercritical water mixture was then injected into a reactor at temperature of 400° C. and pressure of 3400 psig. The upgraded product, which formed a homogeneous phase with supercritical water, was withdrawn from the top of the reactor and send to high pressure separator which was operated at the same pressure but lower temperature to achieve oil-water separation. The dreg stream was removed from reactor bottom.

The properties of the feed crude in Example 2 were as follows: 8 API gravity at 60/60; 65689 CST viscosity @40° C.;. 15.7 wt % MCRT; 4.17 wt % sulfur; 0.68 wt % nitrogen; 5.8 mg KOH/gm acid number; 435 ppm Vanadium; and 104 ppm Nickel.

After the super critical water treatment upgraded product (syncrude) had the following properties: 20.5 API gravity at 60/60; 10.9 CST viscosity @400° C., 2.2 wt % MCRT; 3.17 wt % sulfur; 0.29 wt % nitrogen; 40.9 ppm Vanadium; and 5.9 ppm Nickel.

EXAMPLE 3

The procedure of Example 2 was repeated except that the properties of the feed crude were as follows: 8 API gravity at 60/60; 20,400 CST viscosity @40° C.; 13 wt % MCRT; 5 wt % sulfur; 0.48 wt % nitrogen; 3.8 mg KOH/gm acid number; 215 ppm Vanadium; and 80 ppm Nickel.

After the super critical water treatment upgraded product (syncrude) had the following properties: 18 API gravity at 60/60; 21 CST viscosity @40° C. 3 wt % MCRT; 4 wt % sulfur; 0.27 wt % nitrogen; 41 ppm Vanadium; and 8 ppm Nickel.

For Examples 2 and 3, substantial reductions in metals, nitrogen and sulfur were observed, with simultaneous increase in the API gravity and a significant decrease in the viscosity of the original crude oil feedstock.

There are numerous variations on the present invention which are possible in light of the teachings,and supporting examples described herein. It is therefore understood that within the scope of the following claims, the invention may be practiced otherwise than as specifically described or exemplified herein.

Claims

1. A process for removing metals, sulfur and nitrogen in the upgrading of hydrocarbons comprising:

(a) mixing hydrocarbons containing metals, sulfur and nitrogen with a fluid comprising water that has been heated to a temperature higher than its critical temperature in a mixing zone to form a mixture;

(b) passing the mixture to a reaction zone;

(c) reacting the mixture in the reaction zone under supercritical water conditions in the absence of externally added hydrogen for a residence time sufficient to allow upgrading reactions to occur while maintaining an effective amount of metals, derived from the hydrocarbon undergoing upgrading, in the reaction zone to catalyze the upgrading reactions; and

(d) recovering upgraded hydrocarbons having a lower concentration of metals, sulfur and nitrogen than the hydrocarbons of step (a).

2. A process according to claim 1, wherein the hydrocarbons are heavy hydrocarbons selected from the group consisting of whole heavy petroleum crude oil, tar sand bitumen, heavy hydrocarbon fractions obtained from crude petroleum oils, heavy vacuum gas oils, vacuum residuum, petroleum tar, coal tar and their mixtures.

3. A process according to claim 1, wherein the fluid comprising water enters the mixing zone at a temperature sufficiently higher than the critical temperature of water so as to cause the resulting mixture to have a temperature higher than the critical temperature of water.

4. A process according to claim 3, wherein the temperature of the fluid comprising water is from 400° C. to 600° C.

5. A process according to claim 1, wherein the hydrocarbons in step (a) are at a temperature of from 100° C. to 200° C.

6. A process according to claim 1, wherein the supercritical water conditions include a temperature from 374° C. to 1000° C., a pressure from 3,205 psia to 10,000 psia an oil/water volume ratio from 1:0.1 to 1:5 and where the residence time is from 1 minute to 6 hours.

7. A process according to claim 1, wherein the supercritical water conditions include a temperature from 374° C. to 600° C., a pressure from 3,205 psia to 7,200 psia, an oil/water volume ratio from 1:0.5 to 1:3 and where the residence time is from 8 minutes to 2 hours.

8. A process according to claim 1, wherein the supercritical water conditions include a temperature from 374° C. to 400° C. a pressure from 3,205 psia to 4,000 psia, an oil/water volume ratio from 1:1 to 1:2 and where the residence time is from 10 to 40 minutes.

9. A process according to claim 1, wherein the mixture in the reaction zone is reacted in the absence of any externally supplied catalyst or promoter.

10. A process according to claim 1, further comprising the step of heating the mixture formed in step (a) to a temperature higher than the supercritical temperature of water before passing the mixture to the reaction zone.

11. A process for removing metals and sulfur in the upgrading of hydrocarbons comprising:

(a) mixing hydrocarbons containing metals and sulfur with a fluid comprising water having a temperature higher than the critical temperature of water in a mixing zone to form a mixture having a temperature higher than the critical temperature of water;

(b) passing the mixture to a reaction zone;

(c) reacting the mixture in the reaction zone under supercritical water conditions in the absence of externally added hydrogen for a residence time sufficient to allow upgrading reactions including demetalation and desulfurization to occur while maintaining an effective amount of metals, derived from the hydrocarbon undergoing upgrading, in the reaction zone to catalyze desulfurization reactions; and

(d) recovering upgraded hydrocarbons having a lower concentration of metals and sulfur than the hydrocarbons of step (a)

12. A process according to claim 11, wherein the hydrocarbons are heavy hydrocarbons selected from the group consisting of whole heavy petroleum crude oil, tar sand bitumen, heavy hydrocarbon fractions obtained from crude petroleum oils, heavy vacuum gas oils, vacuum residuum, petroleum tar, coal tar and their mixtures

13. A process according to claim 11, wherein the fluid comprising water enters the mixing zone at a temperature sufficiently higher than the critical temperature of water so as to cause the resulting mixture to have a temperature higher than the critical temperature of water.

14. A process according to claim 13, wherein the temperature of the fluid comprising water is from 400° C. to 600° C.

15. A process according to claim 11, wherein the heavy hydrocarbons in step (a) are at a temperature of from 100° C. to 200° C.

16. A process according to claim 10, wherein the supercritical water conditions include a temperature from 374° C. to 1000° C., a pressure from 3,205 psia to 10,000 psia an oil/water volume ratio from 1:0.1 to 1:5 and where the residence time is from 1 minute to 6 hours.

17. A process according to claim 10, wherein the supercritical water conditions include a temperature from 374° C. to 600° C., a pressure from 3,205 psia to 7,200 psia, an oil/water volume ratio from 1:0.5 to 1:3 and where the residence time is from 8 minutes to 2 hours.

18. A process according to claim 10, wherein the supercritical water conditions include a temperature from 374° C. to 400° C., a pressure from 3,205 psia to 4,000 psia, an oil/water volume ratio from 1:1 to 1:2 and where the residence time is from 10 to 40 minutes.

19. A process according to claim 10, further comprising the step of heating the mixture formed in step (a) to a temperature higher than the critical temperature of water before passing the mixture to the reaction zone.

20. A process for removing metals and sulfur in the upgrading of hydrocarbons comprising:

(a) mixing hydrocarbons containing metals and sulfur with a fluid comprising water that has been heated to a temperature higher than its critical temperature in a mixing zone to form a mixture;

(b) passing the mixture to a reaction zone;

(c) reacting the mixture in the reaction zone under supercritical water conditions in the absence of externally added hydrogen for a residence time sufficient to allow upgrading reactions including demetalation and desulfurization to occur while maintaining an effective amount of metals, derived from the hydrocarbon undergoing upgrading, in the reaction zone to catalyze desulfurization reactions;

(d) separating a dreg stream containing metals from the reaction product;

(e) passing at least a portion of the dreg stream to the reaction zone; and

(g) recovering upgraded hydrocarbons having a lower concentration of metals and sulfur than the hydrocarbons of step (a).