Method and apparatus for clarification of 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 method and apparatus for changing a black pyrolysis oil obtained by heat-treating vehicle tires or other waste into a lighter and more yellow color. 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 pyrolysis oil.

Background Art

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

[0003] U.S. Patent No. 6,835,861 discloses a low-energy method of pyrolyzing hydrocarbon materials using clay and metal catalysts. This produces solid carbonaceous substances, oil, and combustible gas products. The carbon black produced by the method described in the patent was thought to contain no detectable amount of PAHs. Carbon char was thought to be usable as a fuel source. High-purity carbon black was thought to be usable in toners and electrical sensors. The liquid oil and gas produced by this method were thought to be easily separable 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 these methods, the recycled carbon black is deagglomerated to reduce the size of the black particles, and a countercurrent airflow is applied to the black particles to raise the treatment temperature and increase the release of volatiles.

[0005] The pyrolysis oil produced by heating rubber, such as tire rubber, in an oxygen-free environment yields a black oil with a strong sulfur and amine odor. This oil closely resembles crude oil in appearance, but its composition is significantly different.

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

[0007] Tire pyrolysis oil is currently used either as crude fuel or in downwell applications to remove sediment from oil wells. While it is known that the oil fraction can be collected by distillation, the distillate, with the exception of very light fractions, is black and contains an unpleasant sulfur / amine odor. The black color has been suggested to be due to accompanying carbon, and attempts at filtration to remove the black color have been unsuccessful.

[0008] Despite the existence of publicly known prior art, there is still a very real and considerable demand for solutions to the aforementioned problems. [Overview of the project]

[0009] The method and apparatus of the present invention effectively reduce the undesirable black color to a transparent dark yellowish-brown, preferably a transparent yellow, and most preferably a bright transparent yellow. The present invention also has the effect of significantly reducing the undesirable sulfur / amine odor. Finally, the preferred final product has a reduced PAH level, with PAH benzo[a]pyrene at less than 1 ppm.

[0010] The temperature for removing the solvent from the oil or clay residue is generally within the range from the boiling point of the solvent to the boiling point of the oil fraction. For example, in the case of hexane, the temperature range used for treating unfractionated pyrolysis oil is approximately 68°C to 100°C. It has been found that exceeding this upper limit increases the cost of the process without yielding the equivalent benefits that would otherwise be offset. A preferred temperature range is 68°C to 78°C, and the most preferred range is 68°C to 70°C.

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

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

[0013] Another object of the present invention is to produce a desired clear yellow pyrolysis oil as the treated pyrolysis oil.

[0014] Another object of the present invention is to produce pyrolysis oil without unpleasant sulfur / amine odor.

[0015] Another object of the present invention is to reduce the amount of PAH present in the treated oil.

[0016] Another object of the present invention is to provide a desirable bright yellow pyrolysis oil and to remove undesirable sulfur / amine odors and reduce PAHs in order to enhance the commercial value of the pyrolysis oil.

[0017] These and other objects of the present invention will be readily apparent by referring to the detailed description below and the appended claims. [Brief explanation of the drawing]

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

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

[0020] [Figure 3] Figure 3 is a graph showing the relationship between weight percentage, temperature, and derivative weight percentage for clay during drying. [Modes for carrying out the invention]

[0021] This 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. Numerous other materials were tried, but without significant success. These materials included, but were not limited to, bentonite, montmorillonite, activated carbon, charcoal, carbon black, and diatomaceous earth, but they did not produce the desired results.

[0022] The present invention also intends a method and apparatus for regenerating clay using a polar solvent and then reactivating it. Reactivation can be achieved using the same apparatus and method as for elution, but using the polar solvent described above.

[0023] In the method of the present invention, first the polarity of the unfractionated pyrolysis oil or pyrolysis oil fraction is adjusted, contaminants are adsorbed onto clay, and then the clean oil is eluted and separated from the adjusted solvent.

[0024] The polarity can be adjusted by dilution with a nonpolar solvent. The nonpolar solvent may be an alkane or a combination of several alkanes. The alkanes may have 4 to 10 carbon atoms (butane, pentane, hexane, heptane, octane, nonane, or decane), preferably pentane, hexane, and heptane (C5-C7), with hexane (C6) being the most preferred alkane. If necessary, combinations of two or more alkanes may be used in this method.

[0025] The unwanted components are adsorbed onto attapulgite. These unwanted components include alkane-insoluble substances of polar compounds such as benzoic acid, quinolone, steric acid oxygenates, sulfur-containing compounds, and nitrogen-containing compounds. The method and apparatus of the present invention remove polar compounds. This is achieved by precipitating the insoluble substances and filtering or centrifuging them, and binding the polar compounds to the activated attapulgite clay. By removing the polar compounds, not only are the black color and unpleasant odor removed, but the pyrolysis oil maintains its physical and chemical properties. Thereafter, the clean oil is eluted into a nonpolar solvent. Next, the solvent is separated from the oil by evaporation. Thereafter, the column is cleaned for reuse, for example, with acetone, methanol, tetrahydrofuran, or dimethylformamide, or other polar solvents.

[0026] Heavy fractions of pyrolysis oil are known to contain various polycyclic aromatic hydrocarbons (PAHs), among which benzo[a]pyrene is the most carcinogenic in this group of compounds. It has been found that the invention of the present application makes the color of the oil transparent, reduces the odor, and reduces the level of PAHs.

[0027] The method of the present invention includes precipitating, adsorbing, and removing black substances from oil by using an alkane or alkane mixture 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 into the column is diluted with an alkane solvent in a volume ratio of approximately 1:2 to 1:30 (oil to alkane), preferably about 1:4 to 1:15, most preferably about 1:6 to 1:10. The diluted oil is left to stand at room temperature for at least 30 minutes to allow precipitation. The settled diluted oil may be filtered or centrifuged to remove the precipitate before being loaded into the column, or it may be loaded into the column without removing the precipitate. The oil is slowly loaded to the top of the bed, and the 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 for every liter of void capacity (equivalent to a column flow rate of 4 liters per hour when using a column with a void capacity of about 18.2 liters). The flow rate is in the range of approximately 0.1 to 0.6 liters per hour per liter of void volume, preferably in the range of approximately 0.2 to 0.4 liters per hour per liter of void volume, and most preferably in the range of 0.3 to 3.5 liters per hour per liter of void volume.

[0029] The ratio of clay to purified oil is approximately 4:1 to 20:1 by weight, preferably approximately 6:1 to 15:1 by weight, and most preferably approximately 6:1 to 10:1 by weight. Higher weight results in better recovery.

[0030] Figure 1 shows another method for treating pyrolysis oil (referred to herein as the “distillation-elution method”). This method is slightly preferred over the forced-flow-elution method described herein in relation to Figure 2. One advantage of the distillation-elution method over the forced-flow-elution method is that it is more economically advantageous because it uses less solvent.

[0031] Both the methods and apparatus shown in Figures 1 and 2 effectively implement the present invention, but Figure 1 is preferred. The distillation-elution method and apparatus (shown in Figure 1) uses less solvent in the elution phase to elute the material from the column and uses less solvent in the washing phase. Also, since the column is eluted and washed with the 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 oil elution, there are two effective and alternative procedures for cleaning the column. In the first method, hexane is delivered to the top of the bed, for example by a pump, and then moved downwards 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, cleaning beds up to 30 bed volumes. 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 sufficient to evaporate the hexane (68°C) but not high enough to evaporate the oil. The recycled oil is recovered in the distillation bottoms. The column is then cleaned and prepared for the next operating cycle.

[0033] In the second elution process example, a distillation system is used to send the freshly distilled hexane to the top of the column. In this system, the elution bottom of the column is heated to a temperature sufficient to evaporate the hexane (68°C) but not high enough to evaporate the oil.

[0034] The evaporation temperatures of the specific solvent used for elution or washing and the specific pyrolysis oil fraction are (1) 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 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 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 purify unfractionated pyrolysis oil, the range is (1) 68°C to 100°C, or (2) preferably 68°C to 78°C, or (3) most preferably 68°C to 70°C. The ranges for other alkanes are known to those skilled in the art and can be easily determined.

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

[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 a higher temperature. Soxhlet is used to continuously immerse a solid (clay in the present invention) to remove bound or trapped substances. It is unsuitable for the process of the present invention because it does not allow the solvent to flow through the substance in a top-down manner, as required in chromatography. In another process, a fiber thimble can be used to allow the residue to flow out to the side of the crucible. This minimizes contact between them, as some of the extract is carried to the bottom of the container without getting stuck in the clay.

[0038] The process of the present invention has been found to be more effective in removing polar substances from oil during cleaning and from columns.

[0039] Consider an example of the operating cycle of the system shown in Figure 1. The system shown in Figure 1 uses evaporation and gravity to deliver the solution and uses about one-tenth to one-fifteenth the amount of solvent as the forced flow elution method shown in Figure 2, which will be described later. To achieve a similar level of purification in this example of a distillation-elution method, the oil and hexane are mixed in a ratio most preferably 1:6 to 1:10 before being loaded into the column. The oil and hexane are mixed in container 13 and left to stand for about two hours or more. The solid that settles in container 13 may be removed by filtration or centrifugation, or it may be left suspended in the fluid. The liquid is supplied to column 17 through valve 24 by gravity at a column flow rate of about 0.22 liters per hour per liter of void volume. The bottom valve 26 remains closed for a contact time of about one to two hours. Valve 26 is opened, and an amount of hexane equivalent to the oil-hexane mixture in tank 20 is maintained by heat exchanger 14 at its boiling point, which is at least 68°C for hexane. The hexane vapor travels through tube 16 and is condensed by condenser 10. The condensed hexane drips through valve 24 into column 17, and then through column 17 into tank 20 via valve 26. The flow rate is controlled using valve 26, preferably to about 0.1 to 0.6 liters per hour per void volume of column flow rate. The oil elution process is completed after about 10 to 30 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 hexane from tank 20 by evaporation. The hexane evaporates in tank 20, passes through tube 16 and the open valve 23, and is condensed by condensers 10 and 12 and sent to tank 18. Next, the generated oil in tank 20 is discharged to tank 21 through valve 25. Valve 25 is then closed and tank 21 is replaced with a clean tank. The residual hexane is removed from the clay by isolating column 17 by closing valves 24 and 26 and heating the column using heat exchanger 15, which evaporates the residual hexane through condenser 11 into tank 18.

[0041] Next, the column is washed with a polar solvent. The 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 in the closed position. Valve 24 is open to condenser 10. Tank 20 is heated to the boiling point of acetone using a changer 14. The acetone evaporates from tank 20, passes through tube 16, then condenses in condenser 10, passes through valve 24, and drips onto column 17 and passes through column 17. The bottom valve 26 is open, allowing dripping into tank 20. This continues for about 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 has completely evaporated. The acetone vapor moves through tube 16 and condenses through condenser 10 and condenser 12. The recovered acetone is collected in tank 18. The waste collected in tank 20 is discharged through valve 25 into tank 21 for disposal or use for another purpose. The tanks are then cleaned and prepared for the next batch.

[0042] Figure 2 schematically shows an example of a forced elution apparatus usable in the method of the present invention. In this example, the oil-to-hexane ratio is 1:16. The oil-hexane mixture is in a container 40 and left standing for about 2 hours. The solid that settles in the container 40 may be removed by filtration or centrifugation, or it may remain suspended in the fluid. The liquid is pumped onto the column 22 by a pump 31 through a valve 33. The oil is slowly pumped to the top of the bed, and the fluid is recovered from the bottom of the column 22 at a column flow rate of about 0.22 liters per hour per liter of void volume (corresponding to a column flow rate of 4 liters per hour when using a column with a void volume of about 18.2 liters). Once the material is loaded onto the column 22, the column bottom valve 36 is closed for about 1 to 2 hours to allow sufficient contact time between the liquid and the clay. Next, valve 36 is opened, valve 33 is turned open, and pump 31 pumps hexane from tank 41 onto column 22 at a rate of approximately 0.22 liters per hour per liter of void capacity (equivalent to a column flow rate of 4 liters per hour if a column with a void capacity of approximately 18.2 liters is used). Next, valve 36 is opened, valve 37 is closed, and valve 35 is in the open position, allowing water to enter tank 27, and the column is washed with approximately 30 times the volume of oil-hexane loaded into the column from tank 41. Tank 27 is heated to approximately 68°C by the heating jacket 28, and the vapor is condensed by the condenser 44. Hexane is recovered into tank 45 until only oil remains in tank 27. Next, the purified oil is sent to tank 29 through valve 37. Valves 33, 35, 36, and 37 are closed, and valve 32 is open. Jacket 42 is heated and jacket 43 is cooled to remove residual hexane from column 22 and dry the clay. Tank 45 holds all the recovered hexane, which is eventually pumped by pump 30 through valve 38 to tank 41 for reuse.

[0043] The evaporation temperatures of the specific solvent used for elution or purification and the specific pyrolysis oil fraction are (1) 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 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 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.

[0044] For example, when hexane is used to purify unfractionated pyrolysis oil, the range is (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 example, capable of processing 4 liters of oil, was approximately 18 inches in diameter, 24 inches high, and had a capacity of approximately 34 liters. The bed was filled with approximately 16 kilograms, or approximately 32 liters, of clay and wetted with approximately 20 liters of hexane. The column configuration consisted of screen plates and glass wool at the top and bottom, with a flow control valve at the bottom.

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

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

[0048] Attapulgite clay was found to function more efficiently after activation. Activation can be achieved by drying it at 150°C until its weight no longer changes. Referring to Figure 3, using TGA, suitable temperatures up to 700°C could be reached with a ramp rate of 10°C / min. While the clay can be dried at temperatures above 150°C, at such temperatures the clay tends to decompose and lose much of its performance. Figure 3 shows the results of thermogravimetric analysis (TGA) of the attapulgite test, showing the weight loss rate as a function of temperature. This profile shows the temperatures at which free water and hydration water are generated. It was found that evaporating the high-temperature hydration water reduced the volume of clay in the purification residue.

[0049] When purifying clay for reuse, it is preferable to use a polar solvent 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. During purification, a valve at the bottom of the column is used to control the flow rate through the column to approximately 4 liters per hour, and the beds are washed with a maximum bed volume of 30.

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

[0051] Preferred alkanes have 4 to 10 carbon atoms, but it will be understood that in the process they may be used individually, for example, hexane and butane may be used in combination. Also, although preferred alkanes were used individually for the purpose of deriving hexane, other alkanes from the preferred group having 4 to 10 carbon atoms may be used individually.

[0052] While specific embodiments of the present invention have been described for illustrative purposes, it will be apparent to those skilled in the art that many modifications can be made in detail 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 an alkane; (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 alkane in which the clean oil is dissolved 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 from 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 the 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 the alkane in a ratio of about 1:4 to 1:15 of the pyrolysis oil to the alkane.

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

9. 10. The method of claim 1, comprising separating the clean oil and alkanes by evaporation.

10. Condensing the evaporated 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 causing flow of 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 causing flow of the mixture through the column at a column flow rate of between 0.2 and 0.4 liters per hour per liter of column void volume.

24. 22. The method of claim 21, wherein step (d) comprises causing flow of 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. 2. The method of claim 1, wherein step (f) comprises effecting separation of 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. 2. The method of claim 1, wherein step (f) comprises effecting separation of 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. 2. The method of claim 1, wherein step (f) comprises effecting separation of the clean oil and alkane by heating the alkane to a temperature between the boiling point of the alkane and 10° C. higher than the boiling point of the most volatile compound in the particular pyrolysis oil fraction.

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

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