MXPA00000013A - Method for demetallating petroleum streams - Google Patents

Abstract

A method of decreasing the metals content of metal containing petroleum streams (4) by forming a mixture of the petroleum fraction containing those metals and an aqueous electrolysis medium containing electron transfer agent, and passing an electric current through the mixture or through the pretreated aqueous electrolysis medium at a voltage, sufficient to remove the metals such as Ni, V and Fe from the stream (3) (i.e., to produce a petroleum fraction having decreased content of the metals). The cathodic voltage is from 0 V to -3.0 V vs. SCE. The invention provides a method of enhancing the value of petroleum feeds that traditionally have limited use in refineries due to their metals, e.g., Ni and V content.

Description

"METHOD TO DEMETHALIZE PETROLEUM CURRENTS" FIELD OF THE INVENTION The present invention relates to a method for electrochemically demetallizing the refinery feed streams.

BACKGROUND OF THE INVENTION Metal-containing petroleum streams are typically problematic in refineries as streams because the metal components contained in them have a negative impact on certain refinery operations. Therefore, demetallization has been referred to as criticism to aid in the conversion of crude fractions (see, eg, Branthaver, Western Research Institute in Ch. 12, "Influence of Metal Complexes in Fossil Fuels on Industrial Operations", Am. Chem. Soc. (1987)). These metals, for example, act as contaminants for hydroprocessing and catalytic fluid thermoformation catalysts, thereby shortening the operating length of these processes, increasing waste in gas manufacturing and decreasing the value of the coke product of the coker operations. The presence of these metals hinders the most advantageous use of the oil stream by making the heavier oil fractions (where these metal-containing structures most typically occur) less advantageous to improve, and when these resources are used they make the replacement / disposal of the catalyst is expensive. Current refinery technologies typically address the problem by using metal-containing feed streams as a less preferred option, and tolerating deactivation of the catalyst when there are no other alternatives available for the feed stream. Electrochemical processes have been used for the removal of halogenated organic compounds, eg, polychlorinated biphenyls in single-phase organic systems, see eg, US Patent Number 5,102,510 and for the removal of water-soluble metals from aqueous streams, see eg U.S. Patent Number 3,457,152. The oil streams typically do not contain halogen. The removal of metals from complex petroleum streams is more difficult because metals are associated with hydrocarbon species, and are not readily soluble in water. U.S. Patent No. 5,529,684 discloses a process for electrochemically demetallizing petroleum streams, but there is a continuing need for an effective method for the removal of these metals particularly those where improved demetallization rates are possible at higher current efficiencies. and / or lower electrolyte concentrations. The invention of the applicants addresses this need.

BRIEF DESCRIPTION OF THE DRAWINGS Figure 1 illustrates one embodiment of the process for treating an oil stream containing metals and an aqueous electrolysis medium containing the electron transfer agent by contacting both in the electrolyser. Figure 2 illustrates one embodiment of the process in which the electron transfer agent is pretreated in the electrolyser before coming into contact with the oil stream.

COMPENDIUM OF THE INVENTION The present invention provides a method for removing metals, preferably Ni and V, from petroleum streams containing these metals. In one embodiment, the process provides a process for demetallizing an oil stream by applying to a water-in-oil dispersion an oil stream containing hydrocarbon-soluble metals and an aqueous electrolysis medium containing at least one oil transfer agent. electrons and at least one electroconductive salt, an electric current sufficient to produce a stream of petroleum having a decreased metal content. In another embodiment, the invention provides a process for demetallizing a petroleum stream by contacting an aqueous electrolysis medium containing at least one electron transfer agent and at least one electroconductive salt with an electrical current sufficient to produce a medium of treated aqueous electrolysis containing a reduced electron transfer agent; and contacting the treated aqueous electrolysis medium of step (a) with a petroleum stream containing metals for a period of time sufficient to produce a stream of petroleum having a decreased metal content. The process can also be used to remove metals, such as Fe, which are more easily removed than Ni and V.

The present invention can simply comprise, consist or consist essentially of the elements described and can be implemented in the absence of an element that has not been disclosed.

DETAILED DESCRIPTION OF THE INVENTION The present invention provides a method for decreasing the content of metals (particularly those typically associated with the hydrocarbon species and, therefore, hydrocarbon soluble) of a hydrocarbon oil stream, by subjecting a mixture or dispersion of the petroleum stream ( which is also referred to herein as a "fraction" or "feed") containing the metals and water, and at least one electroconductive salt, preferably a water soluble salt, and at least one transfer agent. electrons at least preferably water-soluble or solubilizable to an electric current for a sufficient period of time and to conditions sufficient to remove the metals from the stream (i.e., to produce a fraction of treated oil having a decreased content of the metals ). The removal of metals occurs from the oil phase (ie, oil). The contact is carried out under conditions to result in the passage of an electric current through it. The metal components that can be treated include the Ni and V species, since these are typically present in the petroleum streams. Transition metals such as Ni and V are frequently found, for example, in porphyrin and complexes or porphyrin-like structures, and are abundant in heavy petroleum fractions. In these feeds, these metal species tend to be found in structures that are insoluble in water or immiscible in water. The iron can also be removed by the process. Water-soluble metal salts can typically be removed from petroleum streams using electrostatic desalting processes, which involve applying an electric field to aid in the separation of water and oil phases. The water-soluble metal salts are thus extracted and removed from the oil streams. In contrast to the present invention, a high voltage is applied in a desalination apparatus in the absence or essential absence of current flow and metals that are removed are essentially insoluble in hydrocarbon. However, the hydrocarbon-soluble metal components of the petroleum stream are more difficult to treat. Oil currents are complex mixtures of many different types of reactive and non-reactive species. Since the ability to satisfactorily treat the specific components of oil streams or fractions can not easily be predicted from the reactivity and success to treat the pure components. The process of this invention can also be applied to the removal of metals that are more easily reduced than Ni and V, such as Fe. However, since other processing options are available for removal of these other metals, the process is especially advantageous for the removal of Ni, V metals since these are typically more expensive to remove. One benefit of the process of the present invention is its ability to remove metals typically contained in extractable metals typically without water, which contain residues at lower concentrations of salts and higher current deficiencies than in current processes. Examples of petroleum streams containing the metals Ni and V, or fractions that can be treated in accordance with the process of the present invention are hydrocarbon and carbonaceous petroleum streams containing fossil fuel metal such as crude oils and bitumen, as the processed / distilled streams (distillation residues) such as atmospheric and vacuum residues, feeds of the fluid catalytic thermofractifier, deasphalted oils and resins containing metal, processed waste and heavy sulfur (heavy crudes) since these typically have a high content of metals. The feed that is going to demetalize can have a metal content scale. The average vanadium in the feed is typically from about 5 parts per million to 2000 parts per million, preferably from about 20 to 1000 parts per million by weight, more preferably from about 20 to 100 parts per million. The average nickel content in the starting feed is typically from about 2 to 500 parts per million, preferably from about 2 to 250 parts per million by weight and more preferably from about 2 to 100 parts per million. For example, a heavy Arabian distillate having an initial point of 510 ° C and an end point of 627 ° C may have a typical nickel content of 8 parts per million and a vanadium content of 50 parts per million by weight . However, any nickel and / or vanadium level can be treated in accordance with the present invention. The oil feed containing metal to be treated preferably must be in a liquid fluid state at the process conditions. This can be achieved by heating the material or by treatment with an appropriate solvent. as needed. This helps maintain the mixture of the metal-containing petroleum stream and the aqueous electrolysis medium containing the electron transfer agent and the salt in a fluid form to allow the passage of an electric current. Current densities of 1 mA / cm2 of the cathode surface or a larger area are appropriate. Preferably, the oil droplets may be of sufficient size to allow the metal-containing components to achieve intimate contact with the electron transfer agent in the aqueous electrolysis medium. Droplet size particles of about 0.1 micron to 1.0 millimeter, for example, are appropriate. Desirably, the process must be carried out over a period of time and at conditions within the disclosed ranges which are sufficient to achieve a decrease, preferably a maximum decrease in the content of the metals. The contact can typically be achieved by the ultimate mixing of the petroleum stream containing the metal and the aqueous electrolysis medium (which contains the electrolyte salt of either the pretreated, ie reduced, electron transfer agent of the transfer agent. of untreated electrons, depending on the embodiment of the invention) so as to form an oil-in-water mixture or dispersion (ie, with the aqueous phase containing the electron transfer agent and the electrolyte salt as the continuous phase), using for example, a stirred batch reactor or turbulence promoters in the flow cells. Unexpectedly, introducing into the system a relatively small amount of one or more compounds that are effective in increasing the rate and / or efficiency of electron transfer can potentially increase the demetallization rate. These species or compounds are referred to herein as electron transfer agents. These agents undergo reversible electrochemical reduction-oxidation (ie, they are active at redox). The electrochemical cell is typically equipped with at least two oppositely charged electrodes including cathodes (working electrodes) and anodes (counter electrodes) with the electrolyte in the system to complete the cell circuit for cell operation. For example, a plurality of work electrodes and counter electrodes placed in a package may be employed. The electrochemical cell can optionally include a reference electrode placed between the working electrodes and counter electrodes to monitor the desired working electrode voltages during the electrochemical demetallization reaction. The electrode materials useful in accordance with the present process must be resistant to degradation by and dissolution in the materials and salts that are employed during the electrochemical process. These materials must also be stable under the electric field that is imposed on them. The appropriate materials that can be used as working electrodes are those that will sustain the electrochemical demetallization and that are preferably stable and economical, including lead, cadmium, zinc, tin, mercury and alloys thereof, and carbon and other materials suitable for the removal of metals, eg, Ni and V. Other suitable electrodes known in the art can be used for removal of other metals . Suitable three-dimensional electrodes, such as carbon or metal foams, are included as suitable electrodes. Appropriate materials that can be used as counter electrodes must be resistant to degradation and corrosion in the presence of products produced in the electrochemical process. Other conventional electrodes known to those skilled in the art to be stable in aqueous solutions containing an electrolyte salt and the electron transfer agent of the types used herein may also be used. As noted above, the process of the present invention is carried out in an electrochemical cell containing an aqueous electrolysis medium which is capable of conducting the electric current and supporting the electrochemical demetallization in the presence of an electroconductive salt and a composed of electron transfer. The aqueous electrolysis medium is the continuous phase in the present electrochemical process and is brought into contact with the petroleum stream containing metals as the dispersed phase in the aqueous electrolysis medium. The salt and the electron transfer agent must be sufficiently soluble or solubilizable in the aqueous electrolysis medium to provide sufficient conductivity and sufficient reaction regimes. Useful materials such as electron transfer agents are capable of undergoing reversible electrochemical reduction / oxidation during the demetallization of the petroleum stream, and are sufficiently soluble or solubilizable in the acidic electrolysis medium to provide the desired reaction rate. These representative examples of the compounds include the organic, organometallic and inorganic species. The electron transfer agents can be any water-soluble or water-soluble chemical species that exhibits reversible electrochemical redox behavior within the potential range of 0 to -3.0 V versus SCE. A person ordinarily skilled in the art will recognize that this is appropriately determined for a material by measuring the cyclic voltammograms of the species in an aqueous electrolyte and determining whether the species exhibits reversible electrochemical redox at this potential scale. In the process of the present invention, the electron accepted by the electron transfer agent would not be donated to the anode during electrolysis, but rather to the species to be treated within the petroleum stream. The chemical species that could be considered as electron transfer agents for the process include both the organic species and metal complexes that undergo reversible redox, as described above. For example, in the organic category are species such as quinones, anthroquinones, benzoquinones, naphthaquinones, xanthones, italic acids, sulfonates, tosylates, carboxylates and benzophenones with appropriate substituents to aid water solubility and to tune the properties of redox to the desired potential scale. Many types of metal complexes, for example, trisbipyridyl, trisphenanthroline and dithiocarbamate complexes of the transition metals, could be considered for this process. The derivation of the coordination groups to increase the solubility in water and to affect the redox potentials could be carried out by a person ordinarily skilled in the art. A large scale of potential electron transfer agents is possible, being avoided only by water solubility or solubilizability and its reversible redox behavior in the desired potential scale. The ratio of the electron transfer agent to the salt can be selected by a person skilled in the art to influence both the demetallization regime and the efficiency depending on the specific materials used., its concentrations and processing conditions. The salt of the electrolyte in the aqueous electrolysis medium is desirably a salt that dissolves or dissociates in water to produce electrically conductive ions, but does not undergo redox within the range of applied potentials used. Suitable organic electrolytes include quaternary carbyl and hydrocarbyl onium salts, e.g. alkylammonium salts. Inorganic electrolytes include, e.g. NaOH, KOH and sodium phosphate. Mixtures thereof can also be used. Suitable onium ions include bis-phosphonium, sulfonium, and ammonium. The carbyl and hydrocarbyl residues are preferably alkyl. The quaternary alkylammonium ions include tetramethylammonium, tetraethylammonium and tetrabutylammonium. Optionally, the additives known in the art for improving the operation of the electrodes of the system can be added, such as surfactants, detergents, emulsifying agents and anodic depolarizing agents. Typically, a salt concentration of 1 percent to 50 percent by weight in the aqueous electrolysis medium, preferably from 5 percent to 25 percent by weight, is appropriate with the use of lower amounts of salt anticipating in the presence of the electron transfer agent. The pH of the solution must be selected with respect to the specific electron transfer agent and salt used, and may also vary with the metals to be removed.

The reaction temperatures will vary with the specific oil stream due to its viscosity and the type of the electrolyte and its pH. However, temperatures may appropriately vary from about room temperature to about 371 ° C, preferably from 38 ° C to 149 ° C, and pressures from 0 atmosphere to 210 atmospheres, preferably from 1 atmosphere to 3 atmospheres. An increase in temperature can be used to facilitate the removal of the metal species. Within the conditions of the process that is disclosed, a liquid or fluid or fluid medium phase must be maintained. After demetallization, the oil stream of the product contains a reduced level of metals, e.g. content of Ni and / or of V and / or Fe. Although the actual amount removed will vary according to the starting feed, on average the vanadium levels of more than about 15 parts per million by weight, preferably less of about 4 parts per million and average nickel levels of less than about 10 parts per million, preferably less than about 2 parts per million can be achieved of course. More than 30 percent by weight of vanadium and total nickel can be removed in this way.

The decreased product of the metal contaminant (eg improved) can be used in refining operations that are deleteriously affected by higher levels of metals, for example, thermofraction or catalytic fluid hydroprocessing, or a product can be mixed with other streams of metal content higher or lower to obtain a desired level of metal contaminants. A benefit of the present invention is that the process can be operated under ambient temperature and atmospheric pressure even when they can be used if a higher temperature and pressure is necessary. Its most basic form is carried out in the electrochemical cell by electrolytic means, that is, in a non-electrostatic mode, as the passage of the current is required (e.g., relatively low voltage / high current). The cell can either divide or not divide. These systems include the stirred batch or flow through the reactors. The foregoing may be purchased commercially or made using technology known in the art. The cathode voltage will vary depending on the metal to be removed from the electron transfer agent. The cathodic voltage is within the range of 0 to -3.0 V versus Satured Calomel Electrode (SCE), preferably from -1.0 to -2.5 V based on the characteristics of the specific oil fraction. Although a direct current is typically used, the operation of the electrode can be improved by using an alternative current or other voltage / current waveforms. One embodiment of the electrochemical process of the present invention (depicted in Figure 1) is carried out in an electrochemical cell in an oil stream containing hydrocarbon soluble metals, in contact with an aqueous electrolysis medium containing less an electrolyte salt of the electron transfer agent, preferably soluble in the aqueous medium where a voltage is applied to the cathodes and anodes oppositely charged in the electrochemical cell. After the treatment, the improved (demetalated) petroleum stream is separated from the aqueous electrolysis medium and the metals are removed from the aqueous electrolysis medium before recycling the aqueous electrolysis medium to treat the oil feed containing additional metals. Thus, in the first embodiment, the petroleum stream containing the metals and the aqueous electrolysis medium containing the electrolyte salt and the electron transfer agent are combined and subjected to the application of an appropriate cathodic voltage for produce demetallization. Figure 1 exemplifies this modality. In another embodiment of the process of the present invention, the aqueous electrolysis medium (which contains the electron transfer agent) is subjected to separate electrochemical treatment in an electrochemical cell where a voltage is applied to the oppositely charged electrodes to produce a reduced electron transfer agent (i.e. in an electrochemical reduction step). The electrochemically pretreated aqueous electrolysis medium containing the electrolyte salt and the reduced electron transfer agent is then contacted with the petroleum stream containing the metals to form an oil-in-water dispersion for a time and at conditions sufficient to produce a stream of treated oil having a decreased metal content. The improved (ie, demetalated) petroleum stream can be separated from the aqueous electrolysis medium containing the electrolyte salt and the oxidized electron transfer agent, and the recycled aqueous electrolysis medium to the electrochemical treatment step. Beneficially in this embodiment, the petroleum stream is not taken in contact with the anode and the cathode (ie, the demetallization treatment occurs separately from the electrochemical treatment step). Figure 2 exemplifies this modality. In the Figures, the letter boxes designate process steps and the numbered arrows designate the process streams. Figure 1 depicts one embodiment of the process of the present invention. In Figure 1, the petroleum stream containing metals (1) and the aqueous electrolysis medium containing the electron transfer agent and salt (5) are contacted in Contactor A. This contact can be achieved by means of devices as aligned static mixers, a mixer tank, a sonification mixer, etc. The resulting oil-in-water dispersion (2) of fine oil droplets dispersed in the aqueous electrolysis medium is then passed to electrolyser B, where the electrochemical demetalization is carried out. A variety of devices ranging from a single continuously stirred tank (CSTR) of the type of an electrochemical cell to a cascade of plug flow electrolysers can be used. The recirculation of current (3) through step B (not shown in the Figure) may be required to achieve the desired demetallization levels and would be considered as an optimization of the process. The electrolyser B consists of at least one cathode and an anode properly positioned to achieve the passage of electric current to appropriate cathode potentials and to result in the demetallization of the oil stream. The treated stream (3) leaving the electrolyser B, is an oil-in-water dispersion wherein the oil component has a decreased metal content. The stream (3) is passed to at least a separate C, where the oil and the aqueous electrolyte phases are separated. This step can be achieved in a variety of ways: a large holding tank, a gravity settler / coalescing agent, an electrostatic coalescing agent, etc. The stream (4) of demetallized petroleum can be passed for further processing in the refinery. The stream of the aqueous electrolyte (5) still containing the salt and the electron transfer agent is recycled back to Contactor A to mix with the petroleum stream containing the additional metals. The optional D separator is included to indicate that metals removed from the petroleum stream can be recovered from the aqueous phase by conventional methods such as precipitation, flocculation, filtration or electrochemical electroplating. The stream 6 represents only a small fraction of the total recirculating electrolyte in stream (6) and as such, is actually a purge stream. The addition of the replenishment current of the new electrolyte and the electron transfer agent to maintain steady-state operation must be taken into account as an optimization of the process. Figure 2 represents a second embodiment of the process of the present invention. The feeding to the process is the same as in Figure 1, that is, a stream of oil containing metals (1). A is a mixer, but this time, the aqueous electrolysis medium containing the salt and the electron transfer agent (4) is electrochemically pretreated in the electrolyser C, and comes out as stream 6 which is the salt containing the medium of aqueous electrolysis and electron transfer agent electrochemically reduced. The treatment in the electrolyzer C produces an electron transfer reagent that is reduced, that is, it has electrons accepted at the cathode (and can transfer these electrons to the acceptor molecules in the petroleum stream during mixing). In Figure 1 above, in contrast, the electron transfer agent is first mixed with the petroleum stream and then both the aqueous electrolysis medium and the petroleum phases are subjected to electrochemical treatment. In the alternative embodiment in Figure 2, only the current of the aqueous electrolyte is subjected to direct electrochemical reduction in the electrolyzer C. By eliminating the passage of the oil stream through the electrolyzer C, an improvement in the electrode life is anticipated and the elimination of electrode fouling. The potentially smaller size of the stream (4) of the aqueous electrolysis medium relative to the oil-in-water dispersion stream (2) could also offer opportunities for a more compact and less expensive C electrolyzer. In Figure 2, stream (2) is an oil-in-water dispersion wherein the oil stream has undergone indirect reduction and demetallization by contact with the pre-reduced electron transfer agent. In Separator B (equivalent to C in Figure 1) the demetallized oil stream (3) is separated from the stream of the aqueous electrolysis medium (4) which is recycled through the electrolyser C. In the stream (4) ) the electron transfer agent is in its oxidized form and the mode can accept electrons by passing it through electrolyzer C. In stream (5), the electron transfer agent is in its reduced form and can donate electrons to the oil stream (1) in contact A. Current 6 and Separator D are as in Figure 1

Claims (9)

R E I V I N D I C A C I O N S

1. A process for demetallizing an oil stream comprising: applying to an oil-in-water dispersion an oil stream containing hydrocarbon-soluble metals and an aqueous electrolysis medium containing at least one electron transfer agent, and so less a redox-stable electroconductive salt, an electric current sufficient to produce a petroleum stream having a decreased metal content.

2. The process of claim 1, wherein the electron transfer agent is selected from the organic species and metal complexes capable of undergoing reversible electrochemical reduction / oxidation.

3. The process of claim 1, wherein the electric current is at a cathodic voltage of 0 to -3.0 V versus SCE. A process for demetallizing an oil stream comprising: (a) contacting an aqueous electrolysis medium containing at least one electron transfer agent capable of undergoing reversible redox electrochemistry and at least one electroconductive salt with a electrical current sufficient to produce a treated aqueous electrolysis medium containing a reduced electron transfer agent. (b) contacting the treated aqueous electrolysis medium of step (a) with a petroleum stream containing metals for a period of time sufficient to produce a stream of petroleum having a decreased metal content. The process of claim 4, wherein the electric current is at a cathode voltage of 0 to -3.0 V versus SCE. The process of claim 4, wherein the contact of step (b) produces an oil-in-water dispersion of the petroleum stream containing metals in the aqueous electrolysis medium. The process of claim 4, wherein the contact of step (b) results in the production of an oxidized electron transfer agent in the aqueous electrolysis medium. The process of claim 4, further comprising recovering and treating the aqueous electrolysis medium containing the electron transfer agent and the electroconductive salt to regenerate the reduced electron transfer agent. 9. The process of claim 4, further comprising making the aqueous electrolysis medium recycle to jog a stream of petroleum containing additional metals.