Patent Publication Number: US-8529687-B2

Title: Oxidation of asphaltenes

Description:
FIELD 
     This disclosure relates generally to the processing of asphaltenes, such as by oxidation. 
     BACKGROUND 
     Asphaltenes are high molecular weight hydrocarbons having a chemical structure that can include stacked sheets of fused aromatic rings. Due to their high molecular weight (e.g., greater than about 1,000 daltons) asphaltenes are found within the least volatile fraction after distillation of crude oil. Asphaltenes also can be found in oil sands along with minerals and other hydrocarbons. 
     High molecular weight hydrocarbons, such as asphaltenes, typically are not suitable for use as fuel oil (e.g., as a replacement for diesel fuel used in the transportation industry), as a solvent to reduce the viscosity of other fluids so that they can be transported through a pipeline, or as feedstock for the production of petroleum-derived organic chemicals. Conventionally, the high molecular weight hydrocarbons produced during refinement processes are either discarded or broken down into lower molecular weight hydrocarbons using a process generally known as “cracking.” For example, hydrogen can be added (e.g., by subjecting the high molecular weight hydrocarbons to a hydrotreating process) or carbon can be subtracted (e.g., by subjecting the high molecular weight hydrocarbons to a coking process). Hydrotreating typically includes reacting the high molecular weight hydrocarbons at high pressures in the presence of catalysts. Coking typically includes breaking down the high molecular weight hydrocarbons into two or more fractions, such as a light paraffinic or aromatic liquid fraction and a heavy solid coke fraction. 
     Conventional cracking processes can be used to derive value from high molecular weight hydrocarbons, but they typically are expensive due to high energy demands and the cost of capital equipment and catalysts. With regard to the heaviest fraction, which requires the most processing, conventional cracking processes often prove to be uneconomical. In addition, conventional cracking processes typically are ineffective at breaking down large asphaltene molecules and often result in the precipitation of such molecules or in the production of petroleum coke. 
     Although cracking processes have not been developed specifically for use on asphaltenes, some processes have been developed for use on asphaltene-containing heavy hydrocarbon mixtures. These processes include the Taciuk kiln process (as shown, for example, in U.S. Pat. No. 6,589,417) and non-Taciuk pyrolysis (as shown, for example, in U.S. Pat. No. 5,961,786). Both of these processes involve endothermic reactions that require significant energy. Typically, these processes burn a portion of the hydrocarbons to sustain the reactions. The remainder often is less than 50% of the original material. Moreover, carrying out these processes usually requires the use of furnaces and other expensive capital equipment. 
     Some references disclose the oxidation of aromatic hydrocarbons, including polycyclic aromatic hydrocarbons, in the context of remediation. These references include U.S. Pat. No. 5,849,201 (the &#39;201 patent) and International Patent Publication No. WO 01/32936 (the &#39;936 publication). The &#39;201 patent discloses the “rapid remediation of aromatic hydrocarbons, and especially polycyclic aromatic hydrocarbons (PAHs), in contaminated materials, such as soils, sludges, tars, sands and liquids using catalysts in conjunction with ozone, oxidants and surfactants.” The &#39;936 publication discloses the remediation of PAHs by chemical oxidation followed by biological treatment. The processes disclosed in these references involve total oxidation of aromatic hydrocarbons into very low molecular weight products, such as carbon dioxide. Since virtually all of the energy contained in the aromatic hydrocarbons is consumed, these processes generally are not suitable for use in upgrading asphaltenes to form useful hydrocarbon products. 
     SUMMARY 
     Disclosed herein are embodiments of a method for processing asphaltenes, such as by oxidation. Oxidation of the asphaltenes can be performed, for example, at a relatively mild temperature, such as a temperature from about 25° C. to about 95° C. The pressure also can be near ambient. 
     In some embodiments, the asphaltenes are separated from an asphaltene-containing composition prior to oxidation. The separated asphaltenes can comprise, for example, from about 0% to about 30% non-asphaltene hydrocarbons prior to being oxidized. In other embodiments, the asphaltenes are oxidized within the asphaltene-containing composition. Oxidation products resulting from the oxidation of the separated asphaltenes can be combined with any other desired hydrocarbons or combinations of hydrocarbons to form useful compositions, such as fuel oil and feedstock for the production of petroleum-derived organic chemicals. The disclosed embodiments can be performed as batch or semi-batch processes or substantially continuously. In some embodiments, the asphaltene-containing composition is oil sand. For example, asphaltenes can be processed within or separated from a mixture of hydrocarbons derived from oil sand. The other hydrocarbons in the mixture of hydrocarbons also can be broken down into more useful products. For example, these other hydrocarbons can be separately broken down and then combined with one or more of the asphaltene oxidation products. Alternatively, the asphaltene oxidation products can be mixed with the other hydrocarbons before the other hydrocarbons are processed. The asphaltene oxidation products may act as a solvent to reduce the viscosity of the other hydrocarbons, such as to allow the other hydrocarbons to be transported through a pipeline. 
     Oxidation of the asphaltenes can proceed to a degree that is effective to facilitate use or further processing of the asphaltenes, but that does not result in complete oxidation of the asphaltenes to solely carbon oxides, such as carbon monoxide and carbon dioxide. There are various methods for assessing the degree of oxidation. For example, oxidation of the asphaltenes can include breaking from about 2% to about 50% of the aromatic rings in the asphaltenes. Similarly, the average molecular weight of the oxidation products can be, for example, from about 10% to about 50% of the average molecular weight of the asphaltenes. 
     In some embodiments, oxidation includes introducing an oxidizing agent into the asphaltenes. Oxidation also can include microbial oxidation of the asphaltenes. A catalyst also can be added to catalyze oxidation of the asphaltenes. Suitable oxidizing agents for use in various embodiments include, for example, permanganate compounds, cerium compounds, chromate compounds, dichromate compounds, peroxide compounds, ozone, tetroxide compounds, nitrate compounds, nitrite compounds, persulfate compounds, peroxy acids, halogen-containing compounds (e.g., hypochlorite, chlorite, chlorate, perchlorate and analogous halogen-containing compounds) and derivatives and combinations thereof. Oxidation also can include introducing Fenton&#39;s Reagent into the asphaltenes. Suitable catalysts include catalysts comprising vanadium, titanium, tungsten, molybdenum, ruthenium and combinations thereof. For example, suitable catalysts can comprise oxides of these elements. The oxidizing agent can be introduced at any amount sufficient to achieve the desired result. For example, the oxidizing agent can be introduced at a molar ratio between about 0.01 part oxidizing agent to 1 part asphaltenes and about 0.5 part oxidizing agent to 1 part asphaltenes. 
     When introduced into an asphaltene-containing composition, the oxidizing agent can be selected to preferentially oxidize the asphaltenes over other hydrocarbons in the composition. Useful oxidizing agents for preferentially oxidizing the asphaltenes include persulfate compounds, peroxy acids, periodic acids, ozone, and derivatives and combinations thereof Useful catalysts for catalyzing the preferential oxidation of asphaltenes include catalysts comprising ruthenium. For example, suitable catalysts can comprise oxides of ruthenium. 
     The oxidation products resulting from oxidation of the asphaltenes may, and typically do, have a viscosity lower than the viscosity of the asphaltenes prior to oxidation. In some embodiments, the viscosity of the asphaltenes is measured to determine a quantity of oxidizing agent to be added to the asphaltenes. For example, the viscosity of the asphaltenes can be measured while introducing the oxidizing agent or between the introduction of aliquots of the oxidizing agent. 
     The oxidizing agent and the asphaltenes may be mixed by any suitable methods. For example, a solvent or miscibility agent can be introduced into the asphaltenes prior to or while oxidizing the asphaltenes. The solvent or miscibility agent can include, for example, citric acid, formic acid, an alkyl ester, a dialkyl ether, an alcohol or a derivative or combination thereof. In some embodiments, the solvent or miscibility agent is introduced at a molar ratio between about 0.02 part solvent or miscibility agent to 1 part asphaltenes and about 0.2 part solvent or miscibility agent to 1 part asphaltenes. The oxidation products also may act as a solvent or miscibility agent for the asphaltenes and the oxidizing agent. For example, in some embodiments, the oxidation products include one or more fatty acid, ester or ketone. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a schematic diagram representing embodiments of a method for processing oil sands, including oxidation of separated asphaltenes to produce a solvent for transporting a non-asphaltene hydrocarbon component of the oil sands. 
     
    
    
     DETAILED DESCRIPTION 
     Unless otherwise explained, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this disclosure belongs. The singular terms “a,” “an,” and “the” include plural referents unless the context clearly indicates otherwise. Similarly, the word “or” is intended to include “and” unless the context clearly indicates otherwise. The term “includes” means “comprises.” The method steps described herein, such as the separation steps and the mixing steps, can be partial, substantial or complete unless indicated otherwise. 
     Disclosed herein are embodiments of a method for processing asphaltenes. Asphaltenes are found within many natural materials, including crude oil and oil sands. Although historically difficult to process using conventional methods, asphaltenes are a rich source of energy. Embodiments of the disclosed method can be used to process asphaltenes to form more useful products. Many of these embodiments are particularly well suited for processing asphaltenes within oil sands. 
     Some embodiments of the disclosed method include oxidizing asphaltenes to produce lower molecular weight oxidation products. The oxidization products typically are in a form suitable for use as fuel oil (e.g., as a replacement for diesel fuel used in the transportation industry), as a solvent to reduce the viscosity of other fluids so that they can be transported through a pipeline, or as feedstock for the production of petroleum-derived organic chemicals. For example, the oxidation products typically have a lower boiling point and a lower viscosity than the asphaltenes from which they were derived. 
     A variety of techniques can be used to oxidize asphaltenes. In some embodiments, an oxidizing agent is introduced into the asphaltenes. Suitable oxidizing agents include, for example, permanganate compounds, cerium compounds, chromate compounds, dichromate compounds, peroxide compounds, ozone, tetroxide compounds, nitrate compounds, nitrite compounds, persulfate compounds, peroxy acids, halogen-containing compounds (e.g., hypochlorite, chlorite, chlorate, perchlorate and analogous halogen-containing compounds) and derivatives and combinations thereof. The oxidizing agent can be introduced at any amount sufficient to achieve the desired result. For example, the oxidizing agent can be introduced at a molar ratio between about 0.005 part oxidizing agent to 1 part asphaltenes and about 1 part oxidizing agent to 1 part asphaltenes, such as between about 0.01 part oxidizing agent to 1 part asphaltenes and about 0.5 part oxidizing agent to 1 part asphaltenes or between about 0.05 part oxidizing agent to 1 part asphaltenes and about 0.25 part oxidizing agent to 1 part asphaltenes. 
     Oxidation of asphaltenes also can include adding a catalyst or a reagent comprising a catalyst. Suitable catalysts include catalysts comprising vanadium, titanium, tungsten, molybdenum, ruthenium and combinations thereof. In some embodiments, the catalysts are metal oxides, such as oxides of vanadium, titanium, tungsten, molybdenum or ruthenium. Suitable reagents comprising a catalyst include Fenton&#39;s Reagent. 
     Excess heat typically is not required to carry out the oxidation of asphaltenes in embodiments of the disclosed method. The activity of certain oxidizing agents, however, may be facilitated by mild heating. For example, in some embodiments, the oxidation of asphaltenes is carried out at a temperature sufficiently elevated to facilitate oxidation. This can be a temperature, for example, from about 25° C. to about 250° C., such as from about 25° C. to about 95° C. or from about 35° C. to about 65° C. 
     Some disclosed embodiments include the use of microbial oxidation. For example, an enzyme and live organisms can be added to asphaltenes within or separated from an asphaltene-containing composition. Microbial oxidation processes often are more selective than other oxidation processes. Thus, it also may be possible to preferentially oxidize asphaltenes within a mixture of hydrocarbons. Suitable organisms for the preferential oxidation of asphaltenes include bacteria (e.g.,  Pseudomonas, Aeromonas, Moraxella  and  Flavobacteria ), fungi (e.g.,  Oomycetes, Zygomycota  and  Ascomycota ) and microalgae (e.g.,  Porphyridium, Diatoms, Chlorella  and  Dunaliella ). 
     Since asphaltenes typically are viscous, a solvent or miscibility agent can be added to facilitate mixing between the asphaltenes and the oxidizing agent. Asphaltenes are hydrophobic, whereas most oxidizing agents are hydrophilic. Therefore, some suitable solvents and miscibility agents include both hydrophilic and hydrophobic portions. Suitable solvents and miscibility agents include, for example, citric acid, formic acid, alkyl esters, dialkyl ethers, alcohols (e.g., methanol and ethanol) and derivatives and combinations thereof. The solvent or miscibility agent can be introduced, for example, at a molar ratio between about 0.01 part solvent or miscibility agent to 1 part asphaltenes and about 1 part solvent or miscibility agent to 1 part asphaltenes, such as between about 0.02 part solvent or miscibility agent to 1 part asphaltenes and about 0.2 part solvent or miscibility agent to 1 part asphaltenes or between about 0.05 part solvent or miscibility agent to 1 part asphaltenes and about 0.1 part solvent or miscibility agent to 1 part asphaltenes. 
     In some embodiments, certain oxidation products may act as solvents or miscibility agents that facilitate mixing between the asphaltenes and the oxidizing agent. For example, the oxidation products can include fatty acids, esters or ketones, which have both hydrophilic and hydrophobic portions. The formation of these products may reduce the need for added solvent or miscibility agent. To maximize this benefit, some embodiments include processing the asphaltenes in a substantially continuous process in which new oxidation products are substantially continuously formed to act as solvents or miscibility agents for further oxidation. Of course, the process also can be performed as a batch or semi-batch process. 
     Oxidation may reduce the energy value of asphaltenes. Thus, in some disclosed embodiments, the degree of oxidation is limited to an amount sufficient to form useful products. Limiting the oxidation provides controlled product formation and reduces processing costs. In some disclosed embodiments, oxidation includes breaking from about 1% to about 95% of the aromatic rings in the asphaltenes, such as from about 2% to about 50% or from about 5% to about 25%. The average molecular weight of the oxidation products can be from about 5% to about 75% of the average molecular weight of the asphaltenes, such as from about 10% to about 50% or from about 15% to about 30%. 
     The degree of oxidation can be controlled, for example, by controlling the quantity of oxidizing agent added to the separated asphaltenes. In some embodiments, the oxidizing agent is introduced into the separated asphaltenes slowly while the physical properties of the mixture are monitored. For example, a certain quantity of oxidizing agent can be added followed by mixing and a measurement of a physical property of the mixture, such as the viscosity of the mixture. This process then can be repeated until the desired degree of oxidation is achieved. 
     If added to a mixture of hydrocarbons including low molecular weight hydrocarbons in addition to asphaltenes, certain oxidizing agents will preferentially oxidize the low molecular weight hydrocarbons before the asphaltenes. Low molecular weight hydrocarbons typically are already in a usable form, so oxidizing these materials is not desirable. Therefore, some embodiments of the disclosed method include separating asphaltenes from other hydrocarbons prior to oxidation. For example, some embodiments include separating a hydrocarbon mixture from oil sand and then separating asphaltenes from this hydrocarbon mixture. Information regarding these separation steps can be found, for example, in U.S. Pat. No. 6,007,709 and U.S. patent application Ser. No. 11/371,327 (the &#39;327 application), which are incorporated herein by reference. The separated asphaltenes can comprise, for example, from about 0% to about 40% non-asphaltene hydrocarbons prior to being oxidized, such as from about 0% to about 30% or from about 0% to about 20%. 
     After being separated, the asphaltenes can be oxidized to form oxidation products, which then can be combined with other hydrocarbons, such as other hydrocarbons from the hydrocarbon mixture. These other hydrocarbons may undergo separate processing, if necessary. In some embodiments, the oxidation products are mixed with other hydrocarbons as a solvent to reduce the viscosity of the other hydrocarbons. This can be useful if the other hydrocarbons are viscous and need to be transported through a pipeline. For example, the bitumen separated from oil sands typically is viscous and must be mixed with a solvent before being transported through a pipeline. The oxidation products can take the place of all or a portion of the solvent. 
       FIG. 1  shows one example of a method for processing oil sands. The method begins with oil sand mining. Oil sand  10  resulting from the oil sand mining is transported to a treatment location where it undergoes froth flotation and separation, which typically involves mixing the oil sand with hot water  12  to form a mixture and then introducing gas into the mixture. The hydrocarbons rise with bubbles of the gas to produce a hydrocarbon-rich froth  14  over a hydrocarbon-depleted aqueous phase  16 . The hydrocarbon-depleted aqueous phase  16  is sent to disposal or further treatment. The hydrocarbon-rich froth  14  is mixed with a paraffinic hydrocarbon solvent  18  and subjected to one or more settling stages. The paraffinic hydrocarbon solvent  18  causes precipitation of asphaltenes in the mixture. After settling, bitumen  20  is separated from a tailings stream  22  comprising precipitated asphaltenes, residual solids, residual water and solvent. The tailings stream  22  then flows into a tailings solvent recovery unit (TSRU), which separates a recovered solvent stream  24  from a TSRU tailings stream  26 . The recovered solvent stream  24  can be recycled back to the froth treatment stage. 
     The TSRU tailings stream  26  typically includes asphaltenes, minerals, water and some residual solvent. The asphaltenes  28  can be recovered by the one of the processes disclosed in the &#39;327 application. Such processes can include flotation, gravity settling and/or hydrophobic agglomeration. These processes result in the separation of minerals  30 . Once separated, the asphaltenes  28  are mixed with an oxidizing agent  32  to produce oxidation products  34 . The oxidation products  34  have a reduced viscosity and can act as a solvent for the bitumen  20 . The oxidation products  34  are mixed with the bitumen  20  to form a diluted bitumen mixture  36  with a sufficiently low viscosity to be transported through a pipeline. If additional viscosity reduction is required, a return solvent  38  can be mixed into the diluted bitumen mixture  36 . 
     Asphaltenes also can be oxidized without first being separated from other hydrocarbons. In such embodiments, it can be useful to use an oxidizing agent that preferentially oxidizes the asphaltenes over the other hydrocarbons. A catalyst also can be used to promote the preferential oxidation of asphaltenes over the other hydrocarbons. Examples of oxidizing agents that are well-suited for preferentially oxidizing asphaltenes include strongly electrophilic oxidizing agents, such as persulfate compounds, peroxy acids, periodic acids, ozone, and derivatives and combinations thereof. Examples of catalysts that are useful for catalyzing the preferential oxidation of asphaltenes include catalysts comprising ruthenium. For example, suitable catalysts can comprise oxides of ruthenium. 
     In view of the many possible embodiments to which the principles of the disclosed invention may be applied, it should be recognized that the illustrated embodiments are only preferred examples of the invention and should not be taken as limiting the scope of the invention. Rather, the scope of the invention is defined by the following claims. We therefore claim as our invention all that comes within the scope and spirit of these claims.