Method and apparatus for purifying pyrolysis oil

Abstract

SOLUTION: The present invention provides a method and an apparatus for processing to improve the properties of pyrolysis oil and, as a result, enhancing the commercial value of the oil. The net results are creation of oil with a much lighter color in lieu of the black color, reduction or elimination of the undesired sulfury / amine aroma and reduction of the amount of PAH which is believed to be a carcinogen.SELECTED DRAWING: Figure 2

Description

[Technical Field]

[0001] The present invention relates to a black pyrolysis oil obtained by thermal treatment of vehicle tires or other waste products. (pyrolysis oil) The present invention also relates to a method and apparatus for removing polar compounds from pyrolysis oil and reducing the level of polycyclic aromatic hydrocarbons (PAHs) in the pyrolysis oil. [Background technology]

[0002] It is known to use a method of pyrolysis of hydrocarbon materials, such as discarded vehicle tires, to produce useful by-products. This not only minimizes the problem of large accumulations of discarded tires, but also produces economically valuable products. See, for example, U.S. Patent No. 6,833,485. The pyrolysis process can produce carbon products, liquid hydrocarbon products, and combustible gases.

[0003] U.S. Patent No. 6,835,861 discloses a low-energy method for the pyrolysis of hydrocarbon materials using clay and a metal catalyst. This produces solid carbonaceous material, oil, and combustible gas products. The carbon black produced by the method described in the patent was believed to be free of appreciable PAHs. The carbon char was believed to be usable as a fuel source. High-purity carbon black was believed to be usable in toners and electrical sensors. The liquid oil and gas produced by this method were believed to be easily separated from the system.

[0004] U.S. Patent Nos. 8,263,038 and 8,512,643 describe methods for removing volatiles from recycled carbon black obtained by pyrolysis of tires, in which the recycled carbon black is deagglomerated to reduce the size of the black particles, and the black particles are subjected to a countercurrent airflow to increase the processing temperature and increase the release of volatiles.

[0005] Pyrolysis oil, produced by heating rubber such as tire rubber in the absence of oxygen, produces a dark oil with a strong odor of sulfur and amines. This oil has a similar appearance to crude oil, but its composition is significantly different.

[0006] Both crude oil and pyrolysis oil contain pentane (C5), heptane (C7) and other alkane insolubles, while crude oil insolubles consist of paraffins and asphaltenes. Pyrolysis oil insolubles consist of benzoic acid and polar compounds such as oxygenates, sulfur compounds and nitrogen compounds.

[0007] Tire pyrolysis oil is currently used as crude fuel or in downwell applications to remove oil well deposits. It is known to collect oil fractions by distillation, but except for very light fractions, the distillates are black and contain an unpleasant sulfur / amine odor. It has been suggested that the black color is entrained carbon, and filtration has been attempted to remove the black color, but this has not been successful.

[0008] Despite the known prior art, there remains a very real and considerable need for solutions to the aforementioned problems. Summary of the Invention

[0009] The method and apparatus of the present invention effectively reduces the objectionable black color to a clear dark tan, preferably a clear yellow, and most preferably a bright, clear yellow. The present invention also significantly reduces the objectionable sulfur / amine odor. Finally, the preferred end product has reduced levels of PAHs, with the PAH benzo[a]pyrene at less than 1 ppm.

[0010] The temperature range for removing solvents from oil or clay residues ranges from the boiling point of the solvent to approximately the boiling point of the oil fraction. For example, for hexane, the temperature range used for processing unfractionated pyrolysis oil is about 68°C to 100°C. It has been found that exceeding this upper limit increases the cost of the process without providing comparable offsetting benefits. A preferred temperature range is 68°C to 78°C, with a most preferred temperature range being 68°C to 70°C.

[0011] An object of the present invention is to provide a method and apparatus for efficiently purifying pyrolysis oil.

[0012] It is a further object of the present invention to provide an efficient and economical means for accomplishing such purification.

[0013] Yet another object of the present invention is to produce a clear yellow pyrolysis oil, which is desirable as a treated pyrolysis oil.

[0014] Another object of the present invention is to produce pyrolysis oil that is free of objectionable sulfur / amine odors.

[0015] It is yet another object of the present invention to reduce the amount of PAHs present in the treated oil.

[0016] It is yet another object of the present invention to provide a desirable bright yellow pyrolysis oil while eliminating undesirable sulfur / amine odors and reducing PAHs to increase the commercial value of the pyrolysis oil.

[0017] These and other objects of the present invention will become readily apparent upon reference to the following detailed description and appended claims. [Brief explanation of the drawings]

[0018] [Figure 1] FIG. 1 is a schematic diagram of an apparatus configuration that can be used in the present invention using a distillation-elution method.

[0019] [Figure 2] FIG. 2 is a schematic diagram of an apparatus that uses the forced flow-elution method and can be used in the present invention.

[0020] [Figure 3] FIG. 3 is a graph showing weight percent versus temperature versus derivative weight percent for clay during drying. DETAILED DESCRIPTION OF THE INVENTION

[0021] The present invention provides a method and apparatus for removing polar compounds. Removal is achieved by adjusting conditions so that the polar compounds bind with activated attapulgite, also known as palygorskite. Many other materials have been tried without significant success. These materials include, but are not limited to, bentonite, montmorillonite, activated carbon, charcoal, carbon black, and diatomaceous earth, but they also failed to produce the desired results.

[0022] The present invention also contemplates a method and apparatus for regenerating clay using a polar solvent and then reactivating it. Reactivation can be accomplished using the same apparatus and method as for leaching, but with the polar solvents described above.

[0023] In the method of the present invention, the polarity of the unfractionated pyrolysis oil or pyrolysis oil fraction is first adjusted, and the contaminants are adsorbed onto clay, followed by elution and separation of the clean oil from the conditioning solvent.

[0024] The polarity can be adjusted by diluting with a non-polar solvent. The non-polar solvent can be an alkane or a combination of several alkanes. The alkane can have 4 to 10 carbons (butane, pentane, hexane, heptane, octane, nonane, or decane), preferably pentane, hexane, and heptane (C5-C7), with the most preferred alkane being hexane (C6). If desired, a combination of two or more alkanes can be used in this process.

[0025] Unwanted components are adsorbed onto the attapulgite. These include polar compounds, such as alkane insolubles, such as benzoic acid, quinolones, steric acid oxygenates, sulfur-containing compounds, and nitrogen-containing compounds. The method and apparatus of the present invention removes the polar compounds. This is accomplished by precipitating the insolubles, filtering or centrifuging them, and binding the polar compounds with activated attapulgite clay. Removal of the polar compounds not only eliminates the black color and unpleasant odor, but also allows the pyrolysis oil to maintain its physical and chemical properties. The clean oil is then eluted in a nonpolar solvent. The solvent is then separated from the oil by evaporation. The column is then cleaned for reuse with, for example, acetone, methanol, tetrahydrofuran, or dimethylformamide, or other polar solvents.

[0026] Heavy pyrolysis oil is known to contain a variety of polycyclic aromatic hydrocarbons (PAHs), of which benzo[a]pyrene is the most carcinogenic of this group of compounds. The present invention was found to clarify the oil color, reduce odor, and reduce PAH levels.

[0027] The method of the present invention involves the precipitation and adsorption of black matter from oil using an alkane or mixture of alkanes selected from the group consisting of C4 to C10 (butane, pentane, hexane, heptane, octane, nonane, and decane). Preferred alkanes are those selected from the group consisting of C5 to C7 alkanes (pentane, hexane, and heptane). The most preferred alkane is hexane.

[0028] The oil to be loaded onto the column is diluted with an alkane solvent in a volume ratio of about 1:2 to 1:30 (oil to alkane), preferably about 1:4 to 1:15, and most preferably about 1:6 to 1:10. The diluted oil is aged at room temperature for at least 30 minutes to allow sedimentation. The aged diluted oil may be filtered or centrifuged to remove sediment before loading onto the column, or it may be loaded onto the column without removing the sediment. The oil is slowly loaded onto the top of the bed, and fluid is collected from the bottom of the column. For example, this would require a column flow rate of about 0.22 liters per hour per liter of void volume (equivalent to a column flow rate of 4 liters per hour using a column with a void volume of about 18.2 liters). The flow rate ranges from about 0.1 to 0.6 liters per hour per liter of void volume, preferably from about 0.2 to 0.4 liters per hour per liter of void volume, and most preferably from about 0.3 to 3.5 liters per hour per liter of void volume.

[0029] The clay to oil to be clarified ratio ranges from about 4:1 to 20:1 by weight, or preferably from about 6:1 to 15:1 by weight, and most preferably from about 6:1 to 10:1 by weight, with higher weights resulting in improved recovery.

[0030] Figure 1 illustrates another method for processing pyrolysis oil, referred to herein as the "distillation-elution method." This method is slightly preferable to the forced flow-elution method described herein in connection with Figure 2. One advantage over the forced flow-elution method is that the distillation-elution method uses less solvent, making it more economical to use.

[0031] While either the method and apparatus of Figure 1 or Figure 2 effectively practice the present invention, Figure 1 is preferred. The distillation-elution method and apparatus (shown in Figure 1) uses less solvent in the elution phase to elute material from the column and less solvent in the wash phase. Also, because the column is eluted and washed with distilled solvent, it typically operates at a higher temperature than the forced-flow elution method. This improves the efficiency of elution and washing.

[0032] Regarding the elution of oil, there are two effective and alternative procedures for washing the column. In the first example, hexane is pumped to the top of the bed, for example, and allowed to move downward by gravity. The flow rate through the column is controlled to approximately 4 liters per hour using a valve at the bottom of the column, washing up to 30 bed volumes of bed. The eluate contains the extracted oil and hexane. The oil and hexane are collected in a container and separated from each other by distillation at a temperature high enough to evaporate the hexane (68°C), but not so high as to evaporate the oil. The reclaimed oil is recovered in the distillation bottoms. The column is then washed and prepared for the next operating cycle.

[0033] In a second example elution process, freshly distilled hexane is sent to the top of the column using a distillation system in which the elution bottoms of the column are heated to a temperature high enough to vaporize the hexane (68°C) but not high enough to vaporize the oil.

[0034] The evaporation temperature of the specific solvent used for elution or washing and the specific pyrolysis oil fraction is (1) a temperature between the boiling point of the specific solvent and a temperature 32°C higher than the boiling point of the most volatile compound in the specific pyrolysis oil fraction, or (2) preferably a temperature between the boiling point of the specific solvent and a temperature 10°C higher than the boiling point of the most volatile compound in the oil fraction, or (3) most preferably a temperature between the boiling point of the specific solvent and a temperature 2°C higher than the boiling point of the most volatile compound in the oil fraction.

[0035] For example, for hexane used to clarify unfractionated pyrolysis oil, the ranges are (1) 68° C. to 100° C., or (2) preferably 68° C. to 78° C., or (3) most preferably 68° C. to 70° C. Ranges for other alkanes are known to those skilled in the art and can be readily determined.

[0036] In this way, the solvent is continuously pumped to the top of the column, and the flow rate through the column is controlled using a valve at the bottom of the column to about 4 liters per hour, washing up to 30 bed volumes of the bed.

[0037] The difference between this process and known standard column chromatography processes is that the distillation-elution method of the present invention uses less solvent and higher temperatures. A Soxhlet is used to continuously soak a solid (clay in this case) to remove bound or trapped material. It is not suitable for the present process because it does not flow solvent through the material in a top-down manner, as required for chromatography. In an alternative process, a fiber thimble allows the residue to flow down the side of the crucible. This minimizes contact between the clay and the extract, as some of the extract is carried to the bottom of the vessel without being retained there.

[0038] The process of the present invention has been found to be more effective at removing polars from the oil during washing and removing polars from the column.

[0039] Consider an example operating cycle for the system of Figure 1. The system shown in Figure 1 uses evaporation and gravity to deliver the solution, using approximately 10 to 15 times less solvent than the forced-flow elution method shown in Figure 2, which will be described later. To achieve the same level of purification in this example distillation-elution method, the oil and hexane are most preferably mixed in a ratio of 1:6 to 1:10 before being loaded onto the column. The oil and hexane are mixed in vessel 13 and allowed to stand for approximately two hours or more. Solids that settle in vessel 13 can be removed by filtration or centrifugation, or they can be left suspended in the fluid. Liquid is gravity-fed to column 17 through valve 24 at a column flow rate of approximately 0.22 liters per hour per liter of void volume. Bottom valve 26 remains closed for a contact time of approximately one to two hours. Valve 26 is opened, and a quantity of hexane equivalent to the oil and hexane mixture in tank 20 is maintained at its boiling temperature, which for hexane is at least 68°C, by heat exchanger 14. Hexane vapor travels through line 16 and is condensed by condenser 10. The condensed hexane drips through valve 24 into column 17, through column 17, and then through valve 26 into tank 20. The flow rate is controlled using valve 26 to preferably provide a column flow rate of about 0.1 to 0.6 liters per hour per liter of void volume. The oil elution process is complete after about 10 to 30 column bed volumes of hexane have been eluted through column 17.

[0040] At this point, valve 23 is opened, and valves 24 and 26 are closed. The contents of tank 20 are heated to at least 68°C to completely remove the hexane from tank 20 by evaporation. The hexane is evaporated in tank 20, passes through line 16 and open valve 23, and is condensed by condensers 10 and 12 and sent to tank 18. The product oil in tank 20 is then drained to tank 21 via valve 25. Valve 25 is then closed, and tank 21 is replaced with a clean tank. Valves 24 and 26 are closed to isolate column 17, and residual hexane is removed from the clay by heating the column using heat exchanger 15 and evaporating the residual hexane through condenser 11 and into tank 18.

[0041] Next, the column is washed with a polar solvent. A preferred solvent for washing the clay is acetone. In the case of acetone, it is transferred to tank 20 while valves 23, 25, and 26 are closed. Valve 24 is open to condenser 10. Tank 20 is heated to the boiling point of acetone using exchanger 14. The acetone evaporates from tank 20 and passes through line 16, then condenses in condenser 10, passes through valve 24, and drips onto column 17. Bottom valve 26 is open, allowing dripping into tank 20. This continues for approximately 30 bed volumes (the volume of clay in the column is the bed volume). For this part of the process, tanks 18 and 21 are replaced with clean tanks. Valves 24 and 26 are closed, and valve 23 is open. Tank 20 continues to be heated until the acetone is completely evaporated. The acetone vapor travels through line 16 and is condensed through condensers 10 and 12. The recovered acetone is collected in tank 18. Waste collected in tank 20 is discharged through valve 25 to tank 21 for disposal or repurposing. The tank is then cleaned and initially prepared for the next batch.

[0042] FIG. 2 shows a schematic diagram of an example of a forced elution apparatus that can be used in the method of the present invention. In this example, the oil to hexane ratio is 1:16. The oil-hexane mixture is placed in vessel 40 and allowed to sit for approximately two hours. Solids that settle in vessel 40 can be removed by filtration or centrifugation, or can remain suspended in the fluid. The liquid is pumped by pump 31 through valve 33 onto column 22. The oil is slowly pumped to the top of the bed, and fluid is collected from the bottom of column 22 at a column flow rate of approximately 0.22 liters per hour per liter of void volume (equivalent to a column flow rate of 4 liters per hour using a column with a void volume of approximately 18.2 liters). Once the material is loaded onto column 22, column bottom valve 36 is closed for approximately one to two hours to allow sufficient contact time between the liquid and the clay. Next, valve 36 is opened, valve 33 is rotated open, and pump 31 pumps hexane from tank 41 onto column 22 at a column flow rate of approximately 0.22 liters per hour per liter of void volume (equivalent to a column flow rate of 4 liters per hour using a column with a void volume of approximately 18.2 liters). Next, with valve 36 open, valve 37 closed, and valve 35 in the open position, the column is washed with approximately 30 times the oil-hexane volume loaded onto the column from tank 41, with hexane entering tank 27. Tank 27 is heated to approximately 68°C by heating jacket 28, and the vapor is condensed by condenser 44. The hexane is collected in tank 45 until only oil remains in tank 27. The clarified oil is then sent through valve 37 to tank 29. Valves 33, 35, 36, and 37 are closed, and valve 32 is open. Jacket 42 can be heated and jacket 43 can be cooled to remove residual hexane from column 22 and dry the clay. Tank 45 holds any recovered hexane, which is eventually pumped by pump 30 through valve 38 to tank 41 for reuse.

[0043] The evaporation temperature of the particular solvent used for elution or purification and the particular pyrolysis oil fraction is (1) a temperature between the boiling point of the particular solvent and a temperature 32°C higher than the boiling point of the most volatile compound in the particular pyrolysis oil fraction, or (2) preferably a temperature between the boiling point of the particular solvent and a temperature 10°C higher than the boiling point of the most volatile compound in the oil fraction, or (3) most preferably a temperature between the boiling point of the particular solvent and a temperature 2°C higher than the boiling point of the most volatile compound in the oil fraction.

[0044] For example, when hexane is used to clarify unfractionated pyrolysis oil, the ranges are (1) 68°C to 100°C, or (2) preferably 68°C to 78°C, or (3) most preferably 68°C to 70°C.

[0045] The column bed used in the examples, capable of processing 4 liters of oil, was approximately 18 inches in diameter, 24 inches high, and had a volume of approximately 34 liters. The bed was filled with approximately 16 kilograms, or approximately 32 liters, of clay and wet with approximately 20 liters of hexane. The column configuration consisted of screen plates and glass wool at the top and bottom, with a valve at the bottom to control the flow.

[0046] As shown in Figure 2, valve 38 is opened and the contents of tank 45 are pumped through pump 30 into tank 41. Once the transfer is complete, valve 38 is closed. Tank 41 is replaced with a tank containing acetone. Acetone is pumped from tank 41 using pump 31 through valve 33 and fed into column 22. The acetone extracts the material in column 22 and sends it through open valve 36 to tank 27.

[0047] The material collected in tank 27 is evaporated, and the acetone is collected in tank 45. Vapors passing through open valve 35 are condensed by cooling jacket 44, and the acetone is collected until only a waste residue remains in tank 27. The temperature range for the cleaning process is as described above. The waste from tank 27 is discharged via valve 37 to tank 29 for disposal or repurposing. The tank is then refilled to its initial condition for the next operating cycle.

[0048] Attapulgite clay has been found to function more efficiently when activated. Activation can be achieved by drying it at 150°C until the weight stops changing. Referring to Figure 3, a TGA was used to reach a suitable temperature of up to 700°C at a ramp rate of 10°C / min. While the clay can be dried at temperatures above 150°C, at these temperatures the clay tends to decompose and lose much of its performance. Figure 3 shows the thermogravimetric analysis (TGA) results of the attapulgite test, showing the weight loss rate as a function of temperature. This profile indicates the temperatures at which free water and hydration water are generated. It was found that evaporating the hydration water at high temperatures reduced the clay's capacity in the purification residue.

[0049] When purifying the clay for reuse, it is preferred to use a polar solvent such as selected from the group consisting of acetone, methanol, tetrahydrofuran, dimethylformamide, or another solvent suitable for the purpose. Currently, the preferred polar solvent for this purpose is acetone. For purification, a valve at the bottom of the column is used to control the flow rate through the column to about 4 liters per hour, washing the bed with up to 30 bed volumes.

[0050] After the process is complete, the clay may be regenerated by washing with a polar solvent.

[0051] Although the preferred alkanes are those having 4 to 10 carbons, it will be understood that they may be used individually in the process, for example, hexane and butane may be used in combination. Also, while the preferred alkanes are used individually to derive hexane, other alkanes within the preferred group having 4 to 10 carbons may be used individually.

[0052] While particular embodiments of the present invention have been described above for purposes of illustration, it will be apparent to those skilled in the art that many modifications may be made to the details thereof without departing from the invention as defined in the appended claims.

Claims

1. 1. A method for treating pyrolysis oil, comprising: (a) eluting clean oil with an alkane, (b) mixing the pyrolysis oil with alkanes; (c) allowing the mixture obtained in step (b) to stand for at least 30 minutes; (d) feeding the mixture from step (c) into a column by gravity, thereby binding the unwanted components, including the insoluble compounds, to the activated attapulgite clay in the column, or filtering or centrifuging the mixture from step (c) to remove solids, thereby feeding the mixture by gravity into a column, thereby binding the unwanted components, including the insoluble compounds, to the activated attapulgite clay in the column; and (e) recovering the clean oil-dissolved alkane from the column; (f) separating the clean oil from alkanes; A method comprising:

2. 10. The method of claim 1, comprising using an alkane selected from the group consisting of alkanes containing 4 to 10 carbons.

3. 10. The method of claim 1, comprising using a mixture of two or more alkanes selected from the group consisting of alkanes containing from 4 to 10 carbons.

4. 10. The method of claim 1, comprising using an alkane selected from the group consisting of alkanes containing 5 to 7 carbons.

5. The method of claim 1, comprising using hexane as the alkane.

6. 10. The method of claim 1, comprising mixing the pyrolysis oil and alkane in a ratio of about 1:2 to 1:30 of the pyrolysis oil to the alkane.

7. 7. The method of claim 6, comprising mixing the pyrolysis oil and alkane in a ratio of about 1:4 to 1:15 of pyrolysis oil to alkane.

8. 8. The method of claim 7, comprising mixing the pyrolysis oil and alkane in a ratio of about 1:6 to 1:10 of pyrolysis oil to alkane.

9. 10. The method of claim 1, wherein the separation of the clean oil and alkanes is accomplished by evaporation.

10. Condensing the vaporized alkane; introducing the condensed alkane into a first vessel; the clean oil being in a second container; the second container being substantially free of alkanes; 10. The method of claim 9, comprising:

11. regenerating the clay with a polar solvent; reactivating the regenerated clay; and 10. The method of claim 9, comprising:

12. 10. The method of claim 1, comprising a weight ratio of said clay to said pyrolysis oil of from 4:1 to 20:

1.

13. 13. The method of claim 12, comprising a weight ratio of said clay to said pyrolysis oil of from 6:1 to 15:

1.

14. 10. The method of claim 1, further comprising purifying the clay prior to subjecting the pyrolysis oil to a next cycle of treatment.

15. 15. The method of claim 14, comprising purifying the clay using a polar solvent.

16. 16. The method of claim 15, comprising using acetone as the polar solvent for clay purification.

17. 16. The method of claim 15, comprising using as the polar solvent for clay purification one selected from the group consisting of methanol, tetrahydrofuran, and dimethylformamide.

18. The method of claim 17, wherein hexane is used as the alkane, and step (f) comprises heating the hexane to a temperature between 68°C and 100°C to evaporate the hexane.

19. The method of claim 17, wherein hexane is used as the alkane, and step (f) comprises heating the hexane to a temperature between 68°C and 78°C to evaporate the hexane.

20. The method of claim 17, wherein hexane is used as the alkane, and step (f) comprises heating the hexane to a temperature between 68°C and 70°C to evaporate the hexane.

21. The method of claim 1, comprising using hexane as the alkane.

22. 22. The method of claim 21, wherein step (d) comprises flowing the mixture through the column at a column flow rate of between 0.1 and 0.6 liters per hour per liter of column void volume.

23. 22. The method of claim 21, wherein step (d) comprises flowing the mixture through the column at a column flow rate of 0.2 to 0.4 liters per hour per liter of column void volume.

24. 22. The method of claim 21, wherein step (d) comprises flowing the mixture through the column at a column flow rate of between 0.3 and 3.5 liters per hour per liter of column void volume.

25. 10. The method of claim 1, wherein step (f) comprises separating the clean oil and alkane by heating the alkane to a temperature high enough to vaporize the alkane, but not high enough to vaporize the clean oil.

26. 10. The method of claim 1, wherein step (f) comprises separating the clean oil and alkane by heating the alkane to a temperature between the boiling point of the alkane and 32° C. above the boiling point of the most volatile compound in the particular pyrolysis oil fraction.

27. 10. The method of claim 1, wherein step (f) comprises separating the clean oil and alkane by heating the alkane to a temperature between the boiling point of the alkane and 10° C. above the boiling point of the most volatile compound in the particular pyrolysis oil fraction.

28. 10. The method of claim 1, wherein step (f) comprises separating the clean oil and alkane by heating the alkane to a temperature between the boiling point of the alkane and 2° C. above the boiling point of the most volatile compound in the particular pyrolysis oil fraction.

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