Patent Grant
9045698
The technical field generally relates to methods for removing contaminants from oils, and more particularly relates to methods for removing contaminants from oils using a base washing process followed by an acid washing process.
Renewable oils such as triglyceride oils derived from plant or animal sources and pyrolysis oils derived from lignocellulosic biomass sources are known to contain significant amounts of inorganic contaminants such as alkali and alkaline earth metals, as well as chlorides. The presence of inorganic elements in vegetable oils depends on factors such as type of soil, climatic condition, fruit maturity and extraction and pre-treatment procedures. Further, the level of chloride in lignocellulosic biomass is also dependent on the environment where the biomass is grown. Chloride is of particular concern for the hydroprocessing of these oils to produce hydrocarbon fuels due to the possibility of stress corrosion cracking and corrosion associated with the use of high chloride containing pyrolysis oils. The removal of chlorine compounds from renewable oils prior to upgrading to hydrocarbon fuels is highly desirable to mitigate against chloride induced stress corrosion cracking.
The nature of chlorine in renewable oil has a significant impact on approaches for its removal. Chloride contamination in renewable oils occurs as free chloride, complexed chloride, or organically bound chlorine. Inorganic chlorine in the form of chloride anions should be relatively easy to remove by simple hot water washing. Yet, even refined, bleached and deodorized triglyceride oils sold as food grade edible oils have been shown to contain between 1 and 6 ppm of residual chloride anion. In addition to inorganic chlorine in the form of chloride anions, chlorine could be bound covalently to organic molecules in triglyceride and pyrolysis oils. Natural chlorinated fatty acid and other organic molecules are known to be present in oils derived from marine animals and plants.
Conventional algal oil processing has not provided a satisfactorily efficient process for removing chlorine contaminants from algal oil, whether in the form or free chloride, complexed chloride, or organically bound chlorine. Further conventional algal processing has not provide a satisfactorily efficient process for removing metal contaminants from algal oil. For example, typical methods for removing metals from algal oils include the use of bleaching earths or silica absorbents. These materials are expensive, require significant material handling issue and require disposal of a large volume of solid waste.
Accordingly, it is desirable to provide methods for processing algal oils to effectively remove contaminants including metal or chlorine. Further, it is desirable to provide methods for sequentially performing a base wash and an acid wash on an algal oil during processing. Also, it is desirable to remove contaminants from algal oils before being upgraded to diesel or jet fuel. Furthermore, other desirable features and characteristics will become apparent from the subsequent detailed description and the appended claims, taken in conjunction with the accompanying drawing and the foregoing technical field and background.
Methods for processing algal oils are provided. In one embodiment, a method for removing a contaminant from an oil includes contacting the oil with a base to form an intermediate solution. Further, the method includes contacting the intermediate solution with an acid to form an acidic solution. The method separates the acidic solution into an oil portion and an aqueous waste portion including the contaminant.
In another embodiment, a method for processing an algal oil is provided. The method includes delivering the algal oil to a first mixing tank. The method further includes adding a base to the first mixing tank and mixing the algal oil and the base to form a first effluent therein. The first effluent is transferred from the first mixing tank to a second mixing tank. The method includes adding an acid to the second mixing tank and mixing the first effluent and the acid to form a second effluent therein. Further, the method separates the algal oil from the second effluent.
In another embodiment, a method is provided for processing algal oil into jet fuel. The method includes mixing the algal oil with a basic aqueous solution to form a cloudy solution including soap and mixing the cloudy solution with an aqueous acidic solution to form a clear acidic solution and soap solids. The soap solids are separated from the clear acidic solution, wherein the soap solids include the algal oil and the clear acidic solution includes the contaminant. Further, the algal oil is upgraded to form jet fuel having an aromatic concentration of greater than about 10%.
Embodiments of methods and apparatuses for processing oils will hereinafter be described in conjunction with the following drawing figure wherein:
The following detailed description is merely exemplary in nature and is not intended to limit the methods for processing algal oils. Furthermore, there is no intention to be bound by any theory presented in the preceding background or the following detailed description.
Methods for processing algal oils, and more particularly, for removing contaminants from algal oils are provided herein. The methods effectively remove chlorine and/or metals from algal oil. In exemplary methods, the algal oil is first treated with a weak base before being treated with an acid. Then a separation process, such as a centrifugal separation or phase separation, is performed to remove the treated algal oil from an aqueous mixture including the contaminant or contaminants.
A significant amount of chloride contaminants in algal oils appears to be complexed with components in the oil, such as phospholipids, which contain cationic moieties capable of forming ion pairs with the chloride ions. For most refined triglyceride oils however, only very low levels of free chloride are present. Most of the residual chlorine in these oils appears to be organically bound. It is described herein that washing with a weak base followed by acid washing is required to effectively remove residual chloride anions coordinated with cationic moieties in algal triglyceride oils.
While effective removal of chloride from triglyceride oils with high total chloride requires a combination of weak base washing and acid washing to remove both free chloride anion as well as complexed chloride, the order of washing is important. The wash with a weak base like sodium bicarbonate, potassium bicarbonate, or a weak solution of sodium hydroxide causes a strong emulsion to form with many triglyceride oils. The subsequent acid wash is required to achieve good phase separation and removal of the wash solution. As described herein, the weak base pretreatment followed by acid wash enables the reduction of chlorine in oils with high levels of contamination, such as algal oils, down to a level that is compatible with the enhanced metallurgy used in green or biodiesel refining, i.e. chloride content of less than about 50 ppm.
In addition to chloride contamination, algal oils may include metal or alkali earth metals contaminants such as aluminum, calcium, magnesium, sodium, and potassium. It has been determined that the process including a weak base pretreatment followed by an acid wash treatment is effective in removing metal contaminants. Such treatment reduces metal content in oils from an initial content in the range of 100 ppm to 1000 ppm to a metal content of less than 10 ppm, such as less than 5 ppm.
Referring now to
As shown, a base solution 20 is fed into the first mixing tank 16. An exemplary base solution 20 is 2% sodium bicarbonate, 2% potassium bicarbonate, or a dilute solution of sodium hydroxide having approximately the same pH as a 2% sodium bicarbonate solution. An exemplary base solution 20 has a pH of about 7.5 to about 10.5, such as about 9.5. Further, in the exemplary embodiment substantially equal amounts of the feed oil 12 and the base solution 20 are fed into the first mixing tank.
The feed oil 12 and the base solution 20 are mixed in the mixing tank 16 at an elevated temperature. Specifically, the feed oil 12 and the base solution 20 are mixed at a temperature range of about 40° C. to about 80° C., such as about 50° C. to about 60° C., for example at about 55° C. The feed oil 12 and the base solution 20 are typically introduced to the mixing tank 16 at the desired temperature, though the feed oil 12 and the base solution 20 may be heated in the mixing tank 16.
During mixing in the mixing tank 16, the feed oil 12 and the base solution 20 form an intermediate solution 24. Typically, the intermediate solution 24 is a cloudy solution including soap. The intermediate solution 24 may be agitated in the mixing tank 16 for a selected time period, such as for up to 12 hours. When the contaminant is chloride, it is believed that contact with the base solution 20 causes the chloride to be unassociated as it reaches equilibrium with the bicarbonate or hydroxide ions, e.g., the chloride will be free in the oil, not bound. Specifically, chloride ions are displaced from ion pairs or micelles by the bicarbonate or hydroxide.
After mixing, the intermediate solution 24 is removed from the mixing tank 16 as an effluent stream 28. In the embodiment of
As shown, an acidic solution 48 is also fed into the second mixing tank 44. An exemplary acidic solution 48 is a 2% concentration of sulfuric acid solution. In an exemplary embodiment, a sufficient amount of the acidic solution 48 should be added so that the resulting solution 52 formed in the second mixing tank 44 has a pH of no more than about 2. The solution 52 is mixed in the mixing tank for a selected period of time, such as for about 4 to about 12 hours.
In an exemplary embodiment, an elevated temperature is maintained during contact between the remaining oil 40 (or the effluent stream 28) and the acidic solution 48 in the second mixing tank 44. For example, the remaining oil 40 (or the effluent stream 28) and the acidic solution 48 are mixed at a temperature range of about 40° C. to about 80° C., such as about 50° C. to about 60° C., for example at about 55° C. The remaining oil 40 (or the effluent stream 28) and the acidic solution 48 are typically introduced to the second mixing tank 44 at the desired temperature, though they may be heated in the second mixing tank 44.
Contacting the remaining oil 40 (or the effluent stream 28) with the acidic solution 48 causes the formation of solution 52 as a clear acidic solution and soap solids mixture. Specifically, the soap is hydrolyzed by the acidic solution 48. The clear acidic solution and soap solids mixture 52 is removed from the second mixing tank 44 and fed to a separation unit 56, such as a centrifuge. In the separation unit 56, oil and water are separated into a product oil stream 60, e.g., a de-contaminated triglyceride oil and an aqueous waste stream 64 including the contaminant(s). If the aqueous waste stream 36 was formed by separation unit 32, it may be mixed with the aqueous waste stream 64. The aqueous waste stream 64 or streams 36 and 64 are washed with water in washing tank 68 to remove any polar organics before the waste 72 is discharged.
Example 1 is provided in accordance with the method provided in
Example 2 is provided in accordance with the method provided in
At parallel steps 204 and 205, the algal slurry is processing to form an algal crude oil. For example, at step 204, the algal slurry is processed by hydrothermal liquefaction. In exemplary embodiments, the hydrothermal liquefaction process occurs at a temperature above about 350° C. and at a pressure greater than about 172.36 bar (2500 psig). The hydrothermal liquefaction process produces crude algal oil at step 206. Specifically, the hydrothermal liquefaction process produces a bio-oil that has a significant aromatic content, such as greater than about 10%. At alternative step 205, a solvent extraction process is performed to form the crude algal oil at step 206. Known exemplary processes for extracting algal oil use hexane, petroleum ether, or benzene and ether. Solvent extraction processes can derive more than 95% of the total oil present in the algae.
Thereafter, the base wash pretreatment and acid wash treatment discussed in relation to
Example 3 is provided in accordance with the method of
Example 4 is provided in accordance with the method of
As described herein, methods for removing contaminants from oils, such as algal oils have been provided. In exemplary embodiments, a method has been described for forming synthetic jet fuel from algal oil through hydrothermal liquefaction, base wash pretreatment, acid wash treatment and catalytic upgrading though any suitable methods for processing oils may utilize the contaminant removal process disclosed herein.
While at least one exemplary embodiment has been presented in the foregoing detailed description, it should be appreciated that a vast number of variations exist. It should also be appreciated that the exemplary embodiment or exemplary embodiments are only examples, and are not intended to limit the scope, applicability, or configuration of the claimed subject matter in any way. Rather, the foregoing detailed description will provide those skilled in the art with a convenient road map for implementing an exemplary embodiment or embodiments. It being understood that various changes may be made in the function and arrangement of elements described in an exemplary embodiment without departing from the scope set forth in the appended claims.
This invention was made with U.S. Government support under contract number DE-EE0003046 under the National Advanced Algal Biofuels & Bioproducts Consortia. The Government has certain rights in this invention.
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