US20100122937A1

US20100122937A1 - Method and system for removing impurities from hydrocarbon oils via lewis acid complexation

Info

Publication number: US20100122937A1
Application number: US12/274,552
Authority: US
Inventors: John Aibangbee Osaheni; Thomas Joseph Fyvie
Original assignee: General Electric Co
Current assignee: General Electric Co
Priority date: 2008-11-20
Filing date: 2008-11-20
Publication date: 2010-05-20
Also published as: CN101735854A; DE102009044586A1; JP2010121128A

Abstract

A method is provided for purifying a hydrocarbon oil comprising a quantity of impurities. A Lewis acid solution comprising a Lewis acid and an aprotic solvent is added to the hydrocarbon oil having the plurality of impurities, e.g. sulfur, vanadium, and nickel impurities, to form a mixture. Complexes are formed between the Lewis acid of the Lewis acid solution and a respective one of the impurities in the mixture. The mixture is separated into a first layer that comprises a purified fraction of the hydrocarbon oil and a second layer comprising the complexes dissolved in the aprotic solvent.

Description

FIELD OF THE INVENTION

The present invention relates to a system and process for removing impurities from hydrocarbon oils, and more particularly to a system and process for removing impurities from hydrocarbon oils via Lewis acid complexation of the impurities.

BACKGROUND OF THE INVENTION

Hydrocarbon oils represent a type of crude oil (petroleum) found throughout the world comprising a complex mixture of hydrocarbons (mostly alkanes). In most cases, hydrocarbon oils (e.g. heavy fuel oil) are processed and refined into other useful petroleum products, such as diesel fuel, gasoline, heating oil, kerosene, liquefied petroleum gas, and the like. Such other petroleum products are then used for various industrial purposes, such as for combustion fuel in a gas turbine engine.
It is well known that hydrocarbon oils, like other organic compositions derived from nature, contain contaminating compounds including vanadium, nickel, sulfur, and other elements. Sulfur impurities are of particular concern as they may be environmental pollutants subject to stringent limits and may also reduce operating efficiency of engines using fuel containing the impurities. Some fuel oils, e.g. heavy fuel oils from certain regions of the world, include notably higher levels of sulfur impurities, e.g. thiophenes and their derivatives (benzothiophenes, dibenzothiophenes, phenanthiophenes, benzonathiophenes, for example). These fuels are often differentiated by the terms “sweet” and “sour.” Crude oil may be referred to as “sweet” if it contains relatively little sulfur or “sour” if it contains substantial amounts of sulfur. Generally, the less sulfur the crude oil contains, the more valuable the crude oil. Vanadium, on the other hand, is an undesirable impurity in hydrocarbon oils because its common oxide, vanadium pentoxide, may cause severe corrosion. For example, when hydrocarbon products containing vanadium are burned, corrosion of turbine blades may occur. In addition, nickel is also known to have undesirable corrosive properties.
As the cost of fuel is on the rise, there is an increased interest in and need for utilizing lower grade fuels, such as sour crude oil and other hydrocarbon oils obtained from petroleum, oil sands, oil shale, coal, and bottoms. One known technique for removing impurities from hydrocarbon oils is referred to as hydrodesulfurization (HDS). In an HDS process, a liquid or gaseous feed is passed over a form of a molybdenum disulfide catalyst under a pressure of flowing H₂gas. In this process, thiophenes undergo hydrogenolysis to form hydrocarbons and hydrogen sulfide. Thus, thiophene itself (for example) is converted to butane and H₂S. HDS processes, however, do not effectively convert the thiophene derivatives, e.g. benzothiophene and dibenzothiophene, which are more problematic and prevalent in dirty fuels. Further, HDS processes are capital intensive as they require high temperatures and high hydrogen pressures. Moreover, HDS processes have not been shown to be useful for treating dirty fuels, but rather lighter, cleaner hydrocarbon fuels.
Further, other known methods have attempted to utilize solvent extraction techniques to remove impurities from hydrocarbon oils, such as the solvent extraction methods set forth in U.S. Pat. No. 5,753,102. U.S. Pat. No. 5,753,102 discloses utilizing a solvent allegedly having a weak dissolving power for hydrocarbons and a strong dissolving power for organic sulfur compounds to recover the organic sulfur compounds. An acid or iodine may be added to the hydrocarbon oil to increase the selectivity of the organic compounds for the solvent. Such solvent extraction techniques, however, have proven to be ineffective when attempting to purify relatively dirty oil materials having high sulfur content, e.g. greater than 1% by weight. Dirty fuels may have a sulfur content of even greater than 3% by weight. In fact, U.S. Pat. No. 5,753,102 itself shows its processes being utilized on oils having only up to 0.62% (6,280 ppm) sulfur content by weight, which is well below the sulfur content of such dirty fuels. Accordingly, there is a need for an efficient, low-cost process for the removal of sulfur compounds from high sulfur-content fuels.

BRIEF DESCRIPTION OF THE INVENTION

In accordance with one aspect of the present invention, there is provided a method for purifying a hydrocarbon oil having a quantity of impurities, such as impurities comprising nickel, vanadium, and sulfur. The impurities may include, for example, any ions, salts, complexes, and/or compounds including nickel, vanadium, and sulfur. The method includes adding a Lewis acid solution comprising a Lewis acid and an aprotic solvent to the hydrocarbon oil having impurities to form a mixture. In addition, the method comprises forming complexes between the Lewis acid of the Lewis acid solution and respective ones of the impurities of the hydrocarbon oil in the mixture. Further, the method includes separating the mixture into a first layer comprising a purified fraction of the hydrocarbon oil and a second layer comprising the complexes and the aprotic solvent, and thereafter recovering the first phase comprising the purified fraction of the hydrocarbon oil.
In a particular embodiment, the present invention comprises a method for purifying a hydrocarbon oil comprising a quantity of sulfur impurities. The method comprises adding a Lewis acid solution comprising a Lewis acid and an aprotic solvent to the hydrocarbon oil having sulfur impurities to form a mixture. In addition, the method comprises forming complexes between the Lewis acid of the Lewis acid solution and respective ones of the sulfur impurities of the hydrocarbon oil in the mixture. Further, the method includes separating the mixture into a first phase comprising a purified fraction of the hydrocarbon oil and a second phase comprising the complexes and the aprotic solvent, and thereafter recovering the first phase comprising the purified fraction of the hydrocarbon oil. In an embodiment, the sulfur impurities may be thiophene compounds and derivatives thereof.
In accordance with another aspect of the present invention, there is provided a system for purifying a hydrocarbon oil comprising a quantity of impurities, e.g. nickel, vanadium, and sulfur impurities. The system comprises a first vessel, a hydrocarbon oil source for delivering an amount of the hydrocarbon oil comprising a quantity of impurities to the first vessel, a Lewis acid source for delivering an amount of a Lewis acid and an aprotic solvent, if present, to the first vessel, and an aprotic solvent source for delivering an amount of the aprotic solvent to the first vessel or the Lewis acid source. In addition, the system further includes a mixer to mix the Lewis acid and the hydrocarbon oil to a degree effective to form a mixture comprising complexes between the Lewis acid and respective ones of the impurities in the hydrocarbon oil in the first vessel. Further, the system includes a separating device to separate the mixture into a first layer comprising a purified fraction of the hydrocarbon oil and a second layer comprising the complexes and the aprotic solvent in at least one of the first vessel or a second vessel. Even further, the system includes a recovering device to recover the first layer comprising the purified fraction of the hydrocarbon oil.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention can be more easily understood and the further advantages and uses thereof more readily apparent, when considered in view of the following detailed description when read in conjunction with the following figures, wherein:

FIG. 1 is a schematic illustration of a system for removing impurities in accordance with one aspect of the present invention;

FIG. 2 is a diagram showing the complexation of the Lewis acid and the sulfur impurity after mixing of the Lewis acid solution and the hydrocarbon oil in accordance with the present invention;

FIG. 3 is a flow chart showing steps for a method embodiment of the invention;

FIG. 4 is a schematic illustration of a system for deasphaltating a hydrocarbon oil sample in accordance with the present invention; and

FIG. 5 is a graph showing the residual sulfur remaining after deasphaltation and multi-stage extraction with a Lewis acid.

DETAILED DESCRIPTION OF THE INVENTION

Now referring to FIG. 1, an exemplary process and system for removing a plurality of impurities from a hydrocarbon oil are depicted. Initially, a hydrocarbon oil 10 having a plurality of impurities 11 is fed from a hydrocarbon oil source 12 into a vessel or mixing tank 14. By “hydrocarbon oil,” it is meant any complex mixture having a plurality of hydrocarbons. Exemplary hydrocarbon oils suitable for the present invention include, but are not limited to, liquid oils obtained from bitumen (often called tar sands or oil sands), petroleum, oil shale, coal, as well as synthetic crude oils produced by the liquefaction of coal, heavy crude oils, and petroleum refinery residual oil fractions, such as bottoms or fractions produced by atmospheric and vacuum distillation of crude oil. The concentration of impurities 11 in the hydrocarbon oil 10 may be dependent on the geographical source of the hydrocarbon oil 10, as well as the form and prior processing (if any) of the hydrocarbon oil 10.
The impurities 11 may include any species capable of forming a complex with a Lewis acid as set forth herein. In one embodiment of the present invention, the impurities 11 may include one or more of a sulfur, nickel, or vanadium impurity. The impurities may include, for example, any ions, salts, complexes, and/or compounds including nickel, vanadium, and sulfur. In a particular embodiment, the impurities 11 comprise organic sulfur-containing compounds, such as thiophene and its derivatives. Exemplary derivatives of thiophene include various benzothiphenes, dibenzothiophenes, phenanthrothiophenes, benzonapthothiophenes, thiophene sulfides, such as aromatic and non-aromatic alkyl sulfides, and the like. As will be explained in detail below, it is believed the Lewis acids of the present invention form complexes with the impurities and may be removed from the hydrocarbon oil. In another embodiment, the impurities 11 may comprise or further comprise vanadium (in addition to sulfur impurities). In a particular embodiment, the vanadium impurities include vanadium oxides, such as for example, vanadium pentoxide. In yet another embodiment, the impurities may comprise or further comprise a nickel impurity, such as nickel, a nickel-containing compound, or a nickel-containing complex.
Optionally, a fuel solvent 16 is delivered from a solvent storage tank 18 and added to the hydrocarbon oil 10 to further liquefy or form a slurry with the hydrocarbon oil 10. In an embodiment, the ratio of the fuel solvent 16 to the hydrocarbon oil 10 may be from about 0.5:1 to about 10:1, and in a particular embodiment, is from about 1:1 to about 2:1. The fuel solvent 16 may be added to the hydrocarbon oil 10 within the hydrocarbon oil source 12 (as shown) or within the mixing tank 14. Alternatively, the mixing of the hydrocarbon oil 10 and the fuel solvent 16 may take place in any suitable vessel or static mixer to form a hydrocarbon oil-fuel solvent mixture having a desired viscosity to facilitate the Lewis acid complexation process as described herein. In one exemplary embodiment, the viscosity of the hydrocarbon oil-fuel solvent mixture may range from a viscosity of n-Pentane to a viscosity of 32.6° API gravity crude oil (from about 0.342 cSt at 17.8° C. to about 23.2 cSt at 15.6° C.). In a particular embodiment, mixtures having about a 1:1 ratio and about a 10:1 ratio of petroleum ether to Saudi heavy oil have a viscosity of approximately 0.00307 Pa-s and 0.00038 Pa-s, respectively, at room temperature. The viscosity of petroleum ether and Saudi heavy oil are about 0.00024 Pa-s and 0.03921 Pa-s, respectively. It is understood however that the hydrocarbon oil 10 may be suitable for the process without adding a fuel solvent 16 as described herein. When provided, the fuel solvent 16 may be, for example, any suitable non-polar solvent for the hydrocarbon oil 10, such as petroleum ether, hexanes, pentane, cyclohexane, heptane, and any non-polar hydrocarbon solvent with a relatively low boiling point.
To accomplish the removal of the impurities 11 from the hydrocarbon oil 10, a Lewis acid solution 20 may be added to the mixing tank 14 and combined with the hydrocarbon oil 10 having the impurities 11. In an embodiment, to form the Lewis acid solution 20, a Lewis acid 22 is delivered from a Lewis acid source 24 to a mixing tank 30 (or other suitable vessel) and an aprotic solvent 26 is delivered from an aprotic solvent source 28 to the mixing tank 30. Alternatively, the Lewis acid 22 and the aprotic solvent 26 may be independently delivered to the mixing tank 14 and mixed therein with or without the hydrocarbon oil 10, thereby eliminating the need for the mixing tank 30.
After mixing of the Lewis acid 22 and aprotic solvent 26 to provide the Lewis acid solution, the Lewis acid solution 20 may be added to the hydrocarbon oil 10 in the mixing tank 14. Each of the mixing tank 14 and the mixing tank 30 may include a mixer, e.g. an agitator or any other suitable structure as is known in the art, for mixing the components together. In addition, a heater or pressurizing unit may also be provided in the mixing tank 14 and the mixing tank 30, although it is understood that advantageously, in the present invention, added heat and pressure are not necessary for carrying out the Lewis acid complexation.
The Lewis acid 22 for the Lewis acid solution 20 may be any ion or chemical compound that can accept a pair of electrons from a corresponding Lewis base (e.g. a sulfur impurity) that acts as an electron-pair donor to a corresponding molecule. Thus, it is understood that when referring to a “Lewis acid” as used herein, it is meant to refer to any compound formed from a Lewis acid, any suitable ion that can accept a pair of electrons and act as a Lewis acid, or any adduct comprising a Lewis acid and a suitable counterion. When the Lewis acid is combined with a counterion and mixed with the hydrocarbon oil as set forth herein, the counterion may be displaced by the sulfur, vanadium, or nickel impurity, which acts as a Lewis base to form Lewis acid complexes 32 as set forth below.
In particular, while not wishing to be bound by any particular theory, it is believed the impurities in the hydrocarbon oil, e.g. sulfur, nickel, and vanadium impurities, act as hard Lewis bases that form stable complexes with the corresponding hard Lewis acids. Accordingly, the addition of hard Lewis acids to the hydrocarbon oil 10 is believed to form quick and stable complexes with the impurities 11 of the hydrocarbon oil 10. The Lewis acid complexes 32 are substantially soluble in the aprotic solvent 26, but have low to no solubility in the hydrocarbon oil 10, and thus may be removed from the hydrocarbon oil 10. Aspects of the present invention enable the removal of these complexes from the hydrocarbon oil 10, thereby providing a purified and valuable hydrocarbon oil product.
The inventors of the present invention have surprisingly found that Pearson's hard Lewis acids appear to be particularly suitable for forming complexes with the sulfur, vanadium, and nickel impurities included in hydrocarbon oils. Accordingly, in one particular embodiment of the present invention, the Lewis acid may comprise a hard Pearson Lewis acid as identified R. G. Pearson. J. Am. Chem. Soc. 1963;85:3533-3543; R. G. Pearson. Science; 1966;151:172-177; R. G. Pearson. Chem. Br.; 1967;3:103-107; R. G. Pearson, J. Chem. Ed. 1968.;45:581-587; and/or R. G. Pearson, Chemical Hardness, Wiley-VCH (1997), for example. Hard Pearson Lewis acids are generally characterized by the fact they have atomic centers of a small ionic radius; have a relatively high positive charge; do not contain electron pairs in their valence shells; have a low electron affinity; are likely to be strongly solvated; and have high energy low unoccupied molecular orbitals (LUMOs).
In one embodiment, the Lewis acid 22 comprises one or more cations (which are also considered Pearson Hard Lewis acids) selected from the group consisting of H⁺, Li⁺, Na⁺, K⁺, Be²⁺, Mg²⁺, Ca²⁺, Sr²⁺, Sn²⁺, Al³⁺, Se³⁺, Ga³⁺, In³⁺, La³⁺, Ce³⁺, Cr³⁺, Co³⁺, Fe³⁺, As³⁺, Ir³⁺, Si⁴⁺, Ti⁴⁺, Zr⁴⁺, Th⁴⁺, U⁴⁺, Pu⁴⁺, I⁷⁺, I⁵⁺, and Cl⁷⁺. Any suitable counterion may be utilized in forming a metal salt with the Lewis acid 22. In another embodiment, the Lewis acid may be one or more species (which are also considered Pearson Hard Lewis acids)selected from the group consisting of VO²⁺, UO₂ ²⁺, (CH3)₂Sn²⁺, BeMe₂, AlCl₃, GaCl₃, FeCl₃, AlH₃, BF₃, BCl₃, B(OR)₃, Al(CH₃)₃, Ga(CH₃)₃, In(CH₃)₃, RPO₂ ⁺, ROPO₂ ⁺, SO₃, R₃C⁺, RCO⁺, CO₂, NC⁺. In a particular embodiment, the Lewis acid 22 comprises one or more of AlCl₃, GaCl₃, FeCl₃. The inventors have surprisingly found that AlCl₃, GaCl₃, FeCl₃, and combinations thereof provide excellent results for the complexation of impurities in hydrocarbon oil samples particularly in forming complexes with thiophene compounds and their derivatives, which act as corresponding hard Pearson Lewis bases. It is believed that the Lewis acids, e.g. AlCl₃, GaCl₃, FeCl₃, form complexes with a respective one of the impurities 11, e.g. a sulfur-containing compound according to the following formula.
In yet another embodiment, the Lewis acid 22 may be a species having the formula HX, wherein X is a halide. In yet another embodiment, the Lewis acid may comprise one or more borderline Pearson Lewis acids from the group consisting of Fe²⁺, Co²⁺, Ni²⁺, Cu²⁺, Zn²⁺, Pb²⁺, Sn²⁺, Sb³⁺, Bi³⁺, Ir³⁺, B(CH₃)₃, SO₂, Ru²⁺, R₃C⁺, and benzene⁺.
Without competing moieties, a stoichiometric amount of the Lewis acid 22 relative to the impurities 11 in the hydrocarbon oil 10 may be provided in the mixing tank 14 for complexation with the impurities 11 of the hydrocarbon oil 10. However, due to such other competing impurities and components in the hydrocarbon oil 10, in an embodiment, a stoichiometric excess of the Lewis acid 22 is provided to further increase the likelihood of complexation of substantially all of the impurities in the hydrocarbon oil 10 with the Lewis acid 22. In a particular embodiment, the Lewis acid 22 is provided in a slight stoichiometric excess relative to the impurities 11 in the hydrocarbon oil 10. In another embodiment, the Lewis acid 22 is provided at up to 300% (3 times) of a stoichiometric amount relative to the impurities 11 to increase the likelihood that the Lewis acid 22 will form complexes with all to substantially all of the sulfur, vanadium, and/or nickel impurities in the hydrocarbon oil sample.
The aprotic solvent 26 may be any suitable solvent that may easily form two phases due to differences in solubility or densities with the hydrocarbon oil 10 when sufficiently mixed therewith and allowed to separate. Moreover, the aprotic solvent 26 is selected to solvate the positively charged species of the Lewis acid 22 via the negative dipole(s) of the aprotic solvent 26. In an embodiment, the aprotic solvent 26 may be acetonitrile, nitromethane, 1,2-dichloroethane, or combinations thereof.
As shown in FIG. 2, once the hydrocarbon oil 10 and Lewis acid solution 20 are combined in the mixing tank 14 and are mixed to form a mixture 38, the Lewis acid complexes 32 will begin to form between the Lewis acid 22 and respective ones of the impurities 11 of the hydrocarbon oil 10. In addition, as shown, the mixture 38 comprising the Lewis acid solution 20 and the hydrocarbon oil 10 will begin to form two distinct phases. A first layer 34 (supernatant layer) comprises the hydrocarbon oil 10 (and any added fuel solvent 16 if present) while a second layer 36 comprises the Lewis acid complexes 32 and the aprotic solvent 26. To encourage the formation of the Lewis acid complexes 32, and to promote the separation of the mixture 38 into the first layer 34 and the second layer 36, the mixture 38 may be delivered to another suitable vessel, e.g. vessel 40, for separation of the mixture 38, such as by centrifugation (via a separating device such as a centrifuge). Alternatively, the centrifugation may take place in the mixing tank 14 or any other suitable location. Further alternatively, any other suitable method and apparatus for further separating the mixture 38 into the two distinct phases (the first layer 34 and the second layer 36) may be utilized, which may take place in the mixing tank, vessel 40, or any other suitable vessel.
After separation, the mixture 38 now more definitively comprises the first layer 34 (supernatant layer) including a first purified fraction 44 of the hydrocarbon oil 10 and the second layer 36 (bottom layer) comprising the Lewis acid complexes 32 as shown in FIG. 2. The first layer 34 comprising the first purified fraction 44 may be recovered by any suitable extraction method or apparatus (recovery device) known in the art, such as by decantation or via a separatory funnel. Thereafter, the first layer 34 may be delivered from the particular vessel, e.g. vessel 40, to a storage tank 42. If any fuel solvent 16, e.g. petroleum ether, was originally added to the hydrocarbon oil 10, the fuel solvent 16 may be removed from the first purified fraction 44 in the storage tank 42 by any suitable method, such as by evaporation.
It is understood that other non-sulfur, non-nickel, or non-vanadium impurities in the hydrocarbon oil 10 may inhibit or otherwise slow the complexation of species of the Lewis acid 22 and respective impurities 11. Thus, in one exemplary embodiment, it may be desirable to repeat the processes to further purify the first purified fraction 44 as if the first purified fraction 44 were the original starting material for the process, e.g. hydrocarbon oil 10, provided from the hydrocarbon oil source 12. Thus, in one embodiment, the first purified fraction 44 may be redirected to the mixing tank 14 and combined with yet another amount of the Lewis acid solution 20 in the mixing tank 14 as shown by arrow 46 and processed in the same manner as the hydrocarbon oil 10 as described herein. The first purified fraction 44 may be combined with the hydrocarbon oil 10 or processed without any additional amount of the hydrocarbon oil 10.
In another embodiment, the first purified fraction 44 may be processed as described herein for hydrocarbon oil 10 utilizing separate equipment, e.g. further mixing tanks and vessels. It is understood that the above-described Lewis complexation process may be performed once or repeated a number of times to provide a purified hydrocarbon oil product having reduced to minimal amounts of impurities. As would be appreciated by one skilled in the art, the number of times the process is performed is generally dependent on the desired purity of the final hydrocarbon product. In an embodiment, further purified fractions, e.g. a second purified fraction 52 (formed from removing impurities from the first purified fraction 44) may be delivered (shown by arrow 54) to a suitable storage vessel, e.g. vessel 56, for storage of the further purified hydrocarbon oil material. In this way, mixing with other “dirtier” less purified fractions of the hydrocarbon oil 10 is prevented.
In yet another embodiment, to improve the efficiency of the Lewis acid 22 in complexing with the impurities 11 in the hydrocarbon oil 10, the hydrocarbon oil may first be deasphalted using a portion of a fuel solvent 16 described above, such as petroleum ether or hexanes. Hydrocarbon oils, such as the hydrocarbon oil 10, are known to contain amounts of asphaltenes, which contain heteroatoms that may interfere with the removal of the impurities 11 by competing for the Lewis acid 22. By removal of at least some of the asphaltenes prior to the addition of the Lewis acid 22 to the hydrocarbon oil 10, the efficiency and amount of Lewis acid complexation between the Lewis acid 22 and the impurities 11 may be improved and increased respectively. As shown in FIG. 4, for example, an amount of the fuel solvent 16 is added to an amount of a hydrocarbon oil 10 in a vessel 60 to form a mixture 62. In one embodiment, the ratio of the aprotic solvent 26 to the hydrocarbon oil 10 may be from 0.5:1 to 10:1, and in a particular embodiment is from 1:1 to 2:1. The mixture 62 may then be centrifuged in the vessel 60 (or any other suitable vessel, e.g. vessel 64).
After centrifugation, a pre-treated hydrocarbon oil 66 is formed comprising precipitates 68, typically in the form a semi-solid residue comprising a plurality of asphaltenes, and typically high molecular weight asphaltenes. Alternatively, the precipitates 68 may be removed from the pre-treated hydrocarbon oil 66 by filtration, decantation, and the like. The pre-treated hydrocarbon oil 66 may be removed from the precipitates 68 (or vice-versa) as shown by arrow 70. The pre-treated hydrocarbon oil 66 may then be directed to the mixing tank 14 as a further source of hydrocarbon oil for the system and processed as described above and shown in FIG. 1. In addition, the precipitates 68 may be directed to the vessel 40 (or any other suitable location) as shown by arrow 72 for regeneration and recovery of the Lewis acid 22 with an acid 48 as described herein.
In another embodiment, with reference to FIGS. 1-2, once the first layer 34 (supernatant layer) has been removed containing the first purified fraction 44 (or further purified fraction), the second layer 36 comprising the Lewis acid complexes 32 and the aprotic solvent 26 remaining in the vessel 40 may be treated with an acid 48 delivered from an acid source 50. For ease of reference, the acid 48 is shown as being added to the vessel 40. However, it is understood that the acid 48 may be added to the second layer 36 (or to precipitates 68) at any suitable location to prepare the components for mixing by any suitable method. The purpose of the acid 48 is to regenerate the Lewis acid 22 and enable at least some of the Lewis acid 22 to be recycled and reused for the purification of further hydrocarbon oil material. In one embodiment, the acid 48 is HCL having a concentration in the range of from about 0.001 M to about 3.5 M.
It is believed that after the acid 48 is added to the remaining material (e.g. second layer 36 or precipitates 68) in the vessel 40 (after removal of the purified fraction), the acid 48 will compete with the Lewis acid 22 for complexation with the impurities 11. The acid 48, for example, will be preferably substituted for the Lewis acid 22 in the Lewis acid complexes 32, and thus the Lewis acid 22 will be freed for reuse if so desired in accordance with the present invention. The Lewis acid 22 may be recovered by any suitable method known in the art, for example, by distillation from the vessel 40. Once recovered, the Lewis acid 22 may be directed to the mixing tank 14 as shown by line 58, may be directed back to the Lewis acid source 24 (not shown), or may be directed to any other desired location for use or storage thereof.
The present invention is effective to remove a substantially higher number of impurities than other known techniques, such as HDS and solvent extraction. The formation of highly soluble complexes with a Lewis acid substantially aids in the removal of the impurities from hydrocarbon oils having trace amounts of nickel and vanadium 1-4 wt % sulfur impurities. In an aspect of the present invention, any of the processes and systems described herein are capable of removing substantially all of the sulfur impurities from a hydrocarbon oil having greater than about 1% by weight sulfur with an effective amount of Lewis acid. In another aspect of the present invention, the processes and systems described herein are capable of removing substantially all of the sulfur impurities (e.g. to a level of less than about 1% by weight) from a hydrocarbon oil material having greater than 3% sulfur content. Aspects of the present invention are particularly useful for gas turbine applications where it is often desirable to lower the sulfur impurity content from 4% by weight sulfur (or greater) to less than about 1% by weight sulfur. Accordingly, in one aspect, the present invention provides an efficient, low-cost process for the removal of sulfur impurities, e.g. thiophenes and their derivatives, from high sulfur-content fuels.
FIG. 3 depicts an embodiment of a method according to an aspect of the present invention. As shown, there is illustrated a method 100 for purifying a hydrocarbon oil 10 comprising a quantity of impurities 11. The method 100 comprises step 102 of adding a Lewis acid solution 20 comprising a Lewis acid 22 and an aprotic solvent 26 to the hydrocarbon oil 10 to form a mixture 38. The method further comprises step 104 of forming Lewis acid complexes 32 between the Lewis acid 22 and respective ones of the impurities 11 of the hydrocarbon oil 10 in the mixture 38. Next, the method comprises step 106 of separating the mixture into a first layer 34 comprising a first purified fraction 44 of the hydrocarbon oil 10 and a second layer 36 comprising the Lewis acid complexes 32 and the aprotic solvent 26. After the two layers have been substantially formed, the method further comprises step 108 of recovering the first layer 34 comprising the first purified fraction 44.
In one embodiment, a stoichiometric excess of the Lewis acid 22 in the Lewis acid solution 20 is provided. In addition, the method may further comprise, after step 108 of recovering the first layer 34, repeating the steps 102-108 on the first purified fraction 44 removed during step 108 to generate at least a second purified fraction of the hydrocarbon oil 10. Further, the method may comprise after step 108, recovering the Lewis acid 22 by adding an acid 48 to the second layer 36 comprising the Lewis acid complexes 32 and reusing the Lewis acid 22 recovered by the acid 48 to remove impurities in a subsequent hydrocarbon oil sample.
In a particular embodiment, the method 100 may be modified such that the hydrocarbon oil 10 is pre-treated to remove competing asphaltene compounds from the hydrocarbon oil 10. In this embodiment, prior to step 102 of adding a Lewis acid solution 20 comprising a Lewis acid 22 and an aprotic solvent 26 to the hydrocarbon oil 10 to form a mixture 38, the method comprises adding an amount of the fuel solvent 16 to an amount of the hydrocarbon oil 10 to form a mixture, centrifuging the mixture to form precipitates 68 in the mixture and a supernatant comprising a pre-treated hydrocarbon oil 66 and transferring the pre-treated hydrocarbon oil (without the precipitates) 66 for use in step 102.

EXAMPLE 1

A 0.5M solution of Lewis acid was prepared by dissolving 11.3 g of AlCl₃in 192 g of nitromethane (density of Nitromethane=1.136 g/cc). 6 g of a 3 wt. % dibenzothiophene (DBT) solution in petroleum ether (density of PE=0.7 g/cc) was weighed into a 15 ml centrifuge tube. 3 g of the 0.5M Lewis acid solution was added. The tube turned yellowish-green upon vigorous shaking for 1 to 5 minutes. The tube was centrifuged at 2100 rpm for 10 minutes. The top phase was (supernatant) was clear and the bottom phase became dark green. Both phases were analyzed for sulfur using X-ray fluorescence (XRF) shown in Table 1 below. After the initial test, 3.72 g additional Lewis acid (LA) (0.5M) was added to the supernatant to further remove the residual sulfur, thereby demonstrating that the limitation to complete removal is the amount of Lewis acid supplied.

EXAMPLE 2

6 g of a 3 wt. % benzothiophene (BzT) solution in petroleum ether (density of PE=0.7 g/cc) was weighed into a 15 ml centrifuge tube. 3.2 g of the 0.5M Lewis acid solution was added. The tube turned orange and then dark red upon vigorous shaking for 1 to 5 minutes. The tube was centrifuged at 2100 rpm for 10 minutes. The top phase was (supernatant) was clear and the bottom phase was dark red. Both phases were analyzed for sulfur using X-ray fluorescence (XRF). After the initial test, 4.01 g additional Lewis acid (LA) (0.5M) was added to the supernatant to further remove the residual sulfur, thereby again demonstrating that the limitation to complete removal is the amount of Lewis acid supplied.
The results of the Examples 1 and 2 are summarized in Table 1 below.

	TABLE 1

		ΔS removed
		Top Phase
	Sample description	(supernatant)

	1a. DBT	37.7%
	2a. BzT	53.3%
	1b. DBT + 3.72 g LA	80.8%
	2b BzT + 4 g LA	91.9%

EXAMPLE 3

To show the benefits of the pre-treatment of a hydrocarbon oil on the reduction of sulfur-containing impurities, in a 50 cc centrifuge tube, 10 g of petroleum ether was added to a 5 g sample of Shuquaiq crude oil. The amount was calculated to provide 2.3 moles of AlCl₃per mole of sulfur-impurities. The contents of the centrifuge tube was shaken vigorously for about 2 minutes and then centrifuged at 3000 rpm for 10 minutes. The supernatant was decanted off and the petroleum ether was allowed to evaporate until a constant weight was obtained. Thereafter, to the supernatant, 18 g of 0.5M AlCl₃in nitromethane solution (Lewis acid solution) was added. The contents of the centrifuge tube were shaken vigorously for about 2 minutes and then centrifuged at 3000 rpm for 10 minutes. The supernatant was decanted off and the nitromethane was allowed to evaporate until a constant weight was obtained. The wt % of residual sulfur in the Shuquaiq crude oil sample was then calculated to be about 1.6% S by X-ray fluorescence.
In comparison, a neat Shuquaiq crude oil sample (neat-de-asphalting) was not pre-treated with petroleum ether. To a 5 g Shuquaiq crude oil sample in a 50 cc centrifuge tube, 5 g of a 0.5M AlCl₃in nitromethane solution (Lewis acid solution) was added. The contents of the centrifuge tube were shaken vigorously for about 2 minutes and then centrifuged at 3000 rpm for 10 minutes. The supernatant was decanted off and the nitromethane was allowed to evaporate until a constant weight was obtained. The wt % of residual sulfur in the Shuquaiq crude oil sample was then calculated to be about 1.9% S by X-ray fluorescence. Thus, pre-treatment or dilution with petroleum ether aids in sulfur removal from hydrocarbon oil samples.

EXAMPLE 4

The above Lewis acid solution (0.5M AlCl₃in nitromethane) in Example 3 was added to the Shuquaiq oil samples in a single stage. However, it is contemplated that the Lewis acid solution may be added to any hydrocarbon oil sample in multiple stages. Accordingly, for comparative purposes, for the petroleum ether pre-treated Shuquaiq oil sample of Example 2, the 0.5M AlCl₃in nitromethane solution was provided to a hydrocarbon oil sample (e.g. a source sample and subsequent supernatant samples) in 3 successive aliquots of 2 g of the 0.5M AlCl₃in nitromethane solution. In between each aliquot of the AlCl₃in nitromethane solution, the contents of the centrifuge tube were shaken vigorously for about 2 minutes and then centrifuged at 3000 rpm for 10 minutes. The supernatant was decanted off and the nitromethane was allowed to evaporate until a constant weight was obtained. The respective residual sulfur wt % before Stage 1 (deasphaltation), and in Stage 1, Stage 2, and Stage 3 were approximately 3.5%, 2.3%, 1.9%, and 1.3% respectively as shown in FIG. 5.

EXAMPLE 5

To investigate the impact of the choice of solvent, Lewis acid concentration, and the type of oil (Shuquaiq crude oil vs. heavy fuel oil), 6 different samples were investigated. The results of this experiment are shown in Table 2 below. In sample 1, 10 g of a heavy oil sample and 20 g of petroleum ether were added in a first 50 cc centrifuge tube. In sample 2, 10 g of a heavy oil sample and 20 g of hexanes were added in a second 50 cc centrifuge tube. In sample 3, 10 g of a heavy oil sample and 20 g of petroleum ether were added in a first 50 cc tube. In sample 4, 10 g of a Shuquaiq crude oil and 20 g of petroleum ether were added in a first 50 cc centrifuge tube. In sample 5, 10 g of a Shuquaiq crude oil and 20 g of hexanes were added in a second 50 cc centrifuge tube. In sample 6, 10 g of a Shuquaiq crude oil and 20 g of petroleum ether were added in a first 50 cc tube.
To each of samples 1-6, at least a 12 g solution of a 2.8 M solution of FeCl₃in nitromethane (Lewis acid solution) was then added. The contents of each centrifuge tube were shaken vigorously for about 2 minutes and then centrifuged at 3000 rpm for 10 minutes. The supernatant was decanted off and the fuel solvent (petroleum ether or hexanes) were allowed to evaporate until a constant weight was obtained. Samples 3 and 6, however, were also provided with excess FeCl₃(3× amount). The results are provided below in Table 2. The percentage values (by weight) correspond to the residual sulfur remaining in the hydrocarbon oil samples after treatment. In particular, the results show that the use of hexanes (isomers of hexane) can improve the reduction of residual sulfur over the use of petroleum ether. Further, providing an excess of the Lewis acid appears to significantly reduce the amount of residual sulfur in the sample after processing. This is likely due to the amount of competing counterions in the hydrocarbon oil samples for the Lewis acid. The excess Lewis acid, therefore, renders it more likely that the Lewis acid will form a complex with a particular impurity.

TABLE 2

	Heavy fuel oil	Shuquaiq crude
Solvent/Lewis Acid Solution Used	(sample #)	oil (sample #)

Petroleum ether w/ FeCl₃in	1.50% S (1)	1.08% S (4)
nitromethane
Hexanes w/ FeCl₃in nitromethane	1.30% S (2)	0.95% S (5)
Petroleum ether w/ excess FeCl₃in	0.67% S (3)	0.40% S (6)
nitromethane

EXAMPLE 6

To show the effect of the Lewis acid in reducing vanadium and nickel levels in a hydrocarbon oil, in a first sample (a) and to a 50 cc centrifuge tube was added 10 g of Shuquaiq crude oil (containing 58 ppm V, 16.6 ppm Ni) and 20 g of petroleum ether was added. Thereafter, 12 g of a 2.8M solution of FeCl₃in nitromethane (Lewis acid solution) was added. The contents of the centrifuge tube were shaken vigorously for about 2 minutes and then centrifuged at 3000 rpm for 10 minutes. The supernatant was decanted off and the petroleum ether was allowed to evaporate until a constant weight was obtained. The resulting clean oil was analyzed by ICP/MS (ASTM D5673) for residual vanadium and nickel content and the results are shown by row (a) of Table 3 below.
In a second sample (b) and to a 50 cc centrifuge tube was added 10 g of Shuquaiq crude oil (containing 58 ppm V, 16.6 ppm Ni) and 20 g of hexanes. Thereafter, 12 g of a 2.8M solution of FeCl₃in nitromethane (Lewis acid solution) was added. The contents of the centrifuge tube were shaken vigorously for about 2 minutes and then centrifuged at 3000 rpm for 10 minutes. The supernatant was decanted off and the hexanes were allowed to evaporate until a constant weight was obtained. The resulting clean oil was analyzed by ICP/MS (ASTM D5673) for residual vanadium and nickel content and the results are shown by row (b) of Table 3 below.
In a third sample (c) and to a 50 cc centrifuge tube was added 10 g of heavy fuel oil (HFO) (34.3 ppm V; 9.6 ppm Ni) and 20 g of petroleum ether was added. 10 g of a 2.8M solution of FeCl₃in nitromethane (Lewis acid solution) was added. The contents of the centrifuge tube were shaken vigorously for about 2 minutes and then centrifuged at 3000 rpm for 10 minutes. The supernatant was decanted off and the petroleum ether was allowed to evaporate until a constant weight was obtained. The resulting clean oil was analyzed by ICP/MS (ASTM D5673) for residual vanadium and nickel content and the results are shown by row (c) of Table 3 below.

TABLE 3

Sample ID	Nickel (ppm)	Vanadium (ppm)

(a) Shuquaiq/PE	0.28	0.73
(b) Shuquaiq/Hexanes	0.27	0.64
(c) HFO/PE	0.03	0.16

While various embodiments of the present invention have been shown and described herein, it will be understood that such embodiments are provided by way of example only and not of limitation. Numerous variations, changes and substitutions will occur to those skilled in the art without departing from the teaching of the present invention. Accordingly, it is intended that the invention be interpreted within the full spirit and scope of the appended claims.

Claims

1. A method for purifying a hydrocarbon oil comprising a quantity of impurities, the method comprising:

(a) adding a Lewis acid solution comprising a Lewis acid and an aprotic solvent to the hydrocarbon oil to form a mixture;

(b) forming complexes between the Lewis acid of the Lewis acid solution and respective ones of the impurities of the hydrocarbon oil in the mixture;

(c) separating the mixture into a first layer comprising a purified fraction of the hydrocarbon oil and a second layer comprising the complexes and the aprotic solvent; and

(d) recovering the first layer comprising the purified fraction of the hydrocarbon oil.

2. The method of claim 1, wherein the impurities comprise at least one of sulfur, nickel, or vanadium.

3. The method of claim 1, wherein a stoichiometric excess of the Lewis acid is provided relative to the impurities in the hydrocarbon oil.

4. The method of claim 1, further comprising, after said recovering, repeating (a) through (d) for the first layer comprising the purified fraction of the hydrocarbon oil to obtain a second purified fraction of the hydrocarbon oil.

5. The method of claim 1, further comprising, after said recovering, recapturing the Lewis acid by adding an acid to the second layer comprising the complexes.

6. The method of claim 1, further comprising mixing the hydrocarbon oil with a solvent to form a fuel-solvent mixture prior to said forming complexes.

7. The method of claim 1, wherein the Lewis acid comprises a hard Pearson Lewis acid.

8. The method of claim 7, wherein the Lewis acid comprises at least one of AlCl₃, GaCl₃, FeCl₃, or combinations thereof.

9. The method of claim 1, wherein the impurities comprise at least one of thiophenes or derivatives thereof.

10. The method of claim 9, wherein the impurities comprise at least one of benzothiophenes, dibenzothiophenes, phenanthiophenes, benzonathiophenes, thiophene sulfides, or derivatives thereof.

11. The method of claim 1, wherein the hydrocarbon oil comprises at least one of a heavy fuel oil and a liquid oil, and wherein the liquid oil is obtained from at least one of bitumen, petroleum, oil shale, coal, or synthetic crude oil.

12. The method of claim 1, wherein the aprotic solvent comprises at least one of acetonitrile, nitromethane, 1,2-dichloroethane, or combinations thereof.

13. The method of claim 1, further comprising:

prior to said adding (a), adding an amount of the fuel solvent to an amount of the hydrocarbon oil to form a mixture;

centrifuging the mixture to form a precipitate in the mixture and a supernatant comprising a pre-treated hydrocarbon oil; and

transferring the pre-treated hydrocarbon oil for use in said adding (a).

14. A method for purifying a hydrocarbon oil comprising a quantity of sulfur impurities, the method comprising:

(b) forming complexes between the Lewis acid of the Lewis acid solution and respective ones of the sulfur impurities of the hydrocarbon oil in the mixture;

15. A system for purifying a hydrocarbon oil comprising a quantity of impurities comprising:

a first vessel;

a hydrocarbon oil source for delivering an amount of the hydrocarbon oil comprising a quantity of impurities to the first vessel;

a Lewis acid source for delivering an amount of a Lewis acid and an aprotic solvent, if present, to the first vessel;

an aprotic solvent source for delivering an amount of the aprotic solvent to at least one of the first vessel or the Lewis acid source;

a mixer to mix the Lewis acid and the hydrocarbon oil to a degree effective to form a mixture comprising complexes between the Lewis acid and respective ones of the impurities in the hydrocarbon oil in the first vessel;

a separating device to separate the mixture into a first layer comprising a purified fraction of the hydrocarbon oil and a second layer comprising the complexes and the aprotic solvent in at least one of the first vessel or a second vessel; and

a recovering device to recover the first layer comprising the purified fraction of the hydrocarbon oil.

16. The system of claim 15, wherein the impurities comprise at least one of sulfur, nickel, or vanadium.

17. The system of claim 15, wherein an amount of the Lewis acid is in a stoichiometric excess of the Lewis acid relative to the impurities in the hydrocarbon oil.

18. The system of claim 17, wherein the Lewis acid comprises a hard Pearson Lewis acid.

19. The system of claim 18, wherein the Lewis acid comprises at least one of AlCl₃, GaCl₃, FeCl₃, or mixtures thereof.

20. The system of claim 15, wherein the impurities comprise thiophenes and derivatives thereof.

21. The system of claim 20, wherein the impurities comprise at least one of benzothiophenes, dibenzothiophenes, phenanthiophenes, benzonathiophenes, thiophene sulfides, or derivatives thereof.

22. The system of claim 15, wherein the hydrocarbon oil comprises at least one of a heavy fuel oil and a liquid oil, and wherein the liquid oil is obtained from at least one of bitumen, petroleum, oil shale, coal, or synthetic crude oil.

23. The system of claim 15, wherein the aprotic solvent comprises at least one of acetonitrile, nitromethane, 1,2-dichloroethane, or combinations thereof.