Method for recovering pyrolytic oil extraction solvent

Abstract

A solvent stripping process has been developed for separating pyrolysis oil in an extract phase feed stream from an organic solvent used for extraction. The process involves using a stripping solvent in a stripping column to strip the organic solvent from the pyrolysis oil. A stripper bottoms stream comprising the pyrolysis oil and a portion of the stripping solvent can be separated into a vapor stream comprising the stripping solvent and a liquid stream comprising the pyrolysis and a portion of the stripping solvent. A stripper overhead stream comprising the stripping solvent and the organic solvent can be separated in a recovery column into a recovery column overhead stream comprising the stripping solvent and a recovery column bottoms stream comprising the organic solvent.

Description

[0001] Priority declaration

[0002] This application claims priority to U.S. Provisional Patent Application Serial No. 63 / 367,839, filed on July 7, 2022, the entire contents of which are incorporated herein by reference. Background Art

[0003] Pyrolysis is a thermal process in which solid carbonaceous biomass feedstock, i.e., "biomass", such as wood, agricultural waste / residues, algae, forestry byproducts, cellulose and lignin, municipal waste, construction / demolition debris, etc., is rapidly heated to a pyrolysis temperature of 300°C to 900°C using a pyrolysis reactor in the absence of air. Modern forms of pyrolysis or rapid thermal conversion are carried out at moderate temperatures (typically 400°C to 600°C) and short residence times of less than 5 seconds. An example is rapid thermal processing (RTP), which operates under such conditions to produce solid pyrolysis products and gaseous pyrolysis products. Gaseous pyrolysis products ("pyrolysis gases") include a non-condensable portion and a condensable portion (vapor), which can be condensed into liquid biomass-derived pyrolysis oil. Biomass-derived pyrolysis oil can be directly burned as a fuel for certain boiler and furnace applications, and can also serve as a potential feedstock in a catalytic process for producing fuel in a refinery. Biomass-derived pyrolysis oil has the potential to replace up to 60% of transportation fuels, thereby reducing dependence on conventional petroleum and lowering its environmental impact.

[0004] However, biomass-derived pyrolysis oil is a complex, highly oxygenated organic liquid, which is defined herein as containing molecules composed of hydrogen, carbon and oxygen and used as an organic liquid containing the molecules. Specifically, the oxygenated compounds in the pyrolysis oil may contain any number of parts, including but not limited to lignin fragments, aldehydes, carboxylic acids, phenols, furans, sugars, alcohols and ketones and water. Conventional biomass-derived pyrolysis oil contains 20% by weight or more of oxygen from these oxygenated hydrocarbons and 20% to 30% by weight of water with high acidity (e.g., total acid number (TAN) greater than 100). It is the presence of many of these substances that gives pyrolysis oil its characteristics, which limits its use as a biofuel. For example, biomass-derived pyrolysis oil has high acidity and low energy density, which can be largely attributed to the oxygenated hydrocarbons in the oil, which can undergo secondary reactions during storage, especially if the oil is stored at elevated temperatures.

[0005] One way to stabilize pyrolysis oil to make it more stable for biofuels and chemical conversions is to treat the oil with different solvents to selectively remove the most reactive and troublesome oxygenates from the oil. US 2019 / 0330540 teaches such an example, in which a solvent / anti-solvent scheme is designed to remove the most reactive oxygenates and sugars from pyrolysis oil. In this case, the remaining pyrolysis oil is more thermally stable and therefore more suitable for further processing into various products. However, the extraction solvent used in this method is expensive and should be recovered to improve the economic feasibility of the method. Therefore, a method for recovering an extraction organic solvent from an extraction phase feed stream comprising pyrolysis oil and an organic solvent is needed. BRIEF DESCRIPTION OF THE DRAWINGS

[0006] The accompanying drawing illustrates an embodiment of the method according to the invention. DETAILED DESCRIPTION

[0007] Pyrolysis oil can be upgraded in a hydrotreater to produce sustainable jet and diesel fuels. However, as mentioned above, due to the presence of a large oxygenate fraction in the pyrolysis oil, the oil is very thermally unstable. The maximum process temperature is currently understood to be 65°C. This thermal instability imposes significant constraints on the choice of hydrotreater as well as the separation method.

[0008] There are many methods for treating pyrolysis oil to improve its stability. An example of an extraction method includes introducing an organic solvent and water into the pyrolysis oil to force phase separation. One phase contains the pyrolysis oil and most of the organic solvent and is referred to as advanced pyrolysis oil (APO) in this article. The other phase contains water and the most hydrophilic oxygenated species. In order to make this method economically feasible, it is necessary to recover the organic solvent from the extracted APO phase.

[0009] The simplest option is a simple vacuum flash tank. However, this requires operation below 5 kPa (50 mbar) to recover acceptable amounts of organic solvent. Given the uncertainty in the composition of the bio-oil based on initial feed content and processing conditions, as well as the difficulty in developing thermodynamic models, the use of a flash tank limits process flexibility, especially if the results differ from the model. These differences will manifest as lower organic solvent recoveries from the APO, resulting in higher make-up costs.

[0010] Another possibility is a steam stripping process. However, due to the highly hydrophobic nature of some molecules present in the pyrolysis oil / organic solvent mixture, there is a risk of forming two liquid phases in the stripper. This would present significant design and operational challenges, including the potential for equipment fouling as the extracted hydrophobic molecules come out of solution.

[0011] In order to provide a suitable separation method, a solvent stripping method has been developed. The method involves stripping an organic solvent from an organic extraction oil using a stripping solvent so that the oil (comprising some residual stripping solvents) is ready for upgrading in a downstream hydrotreater. Although more expensive than flash tank substitutes due to the need for additional equipment, the stripping tower design has more process flexibility (e.g., stripping solvent rate, pressure and temperature can all be varied) than is possible in a single-stage flash tank separation. Due to the complexity of pyrolysis oil and the variability of the content of the feed to the pyrolysis process, this flexibility may be important. Even if the pyrolysis feed and / or thermodynamics do not just match modeling, the solvent stripping process also allows optimization, and it will help ensure the successful operation of the process.

[0012] The accompanying drawings illustrate one embodiment of a method 100 for recovering pyrolysis oil extraction solvent. As shown, an extract phase feed stream 115 comprising APO and an organic solvent is fed to a stripping column 110 through an inlet. Typically, the extract phase feed stream is fed near the top of the stripping column, such as above the column internals, although other locations lower in the column may be used as long as the inlet is above the inlet for the stripping solvent.

[0013] The organic solvent should be hydrophobic. The organic solvent should have an atmospheric boiling point lower than the boiling point of most components of the pyrolysis oil to limit the degradation of the thermal pyrolysis oil during solvent recovery. For example, the atmospheric boiling point of the organic solvent can be less than 200°C, or less than 190°C, or less than 180°C, or less than 170°C, or less than 160°C, or less than 150°C, or less than 140°C or less than 130°C. It is desirable that the selected organic solvent results in an overhead stream of a stripper containing 50% or more of the organic solvent and a bottom stream containing 50% or more of the pyrolysis oil. Suitable organic solvents include, but are not limited to, C4-C8 monohydric alcohols, C2-C8 alcohol esters, ethers, their derivatives, or mixtures thereof. Particularly suitable organic solvents include, but are not limited to, n-butyl acetate, ethyl acetate, propyl acetate, methyl isobutyl ketone, their derivatives, or combinations thereof.

[0014] A stripping vapor feed stream 105 is fed to the stripping column through an inlet. Typically, the stripping solvent is fed near the bottom of the stripping column 110, such as below the column internals, although other locations higher in the column may be used as long as the inlet is below the inlet for the extract phase feed stream.

[0015] The stripping solvent may be any light hydrocarbon solvent capable of solubilizing the pyrolysis oil. Suitable stripping solvents include, but are not limited to, alcohols. Suitable alcohols include, but are not limited to, methanol, ethanol, propanol, butanol, or a combination thereof.

[0016] There is evidence that APO is more stable in methanol or ethanol than in n-butyl acetate alone. This may allow operation at higher temperatures (and therefore less severe vacuum conditions), as well as longer run lengths in downstream hydroprocessing steps. Both of these would be economic benefits to the process, helping to ensure profitability for the end user.

[0017] Ethanol is a greener solvent for n-butyl acetate recovery because it is already fully made from biomass. This is important because a significant amount of alcohol is sent to the hydrotreater to stabilize APO and can be converted into products in the process. In this scenario, the use of bioethanol will allow more tax breaks from the final transportation fuel because some tax breaks are based on the carbon intensity of the process (e.g., Low Carbon Fuel Standard (LCFS)). In addition, ethanol will be converted into ethane in the hydrotreater (rather than methanol into methane). Ethane is easier to separate from hydrogen than methane, allowing lower purge rates and hydrogen replenishment rates. Finally, ethanol has a higher flash point than methanol, thereby increasing the safety of the entire process.

[0018] Propanol and butanol are less available and therefore less likely to be used.

[0019] The operating conditions for the stripping column 110 are selected so that the organic solvent has a measurable vapor pressure, for example greater than 1 kPa. Similar to the role of steam in a steam stripper, the stripping vapor drives the gaseous organic solvent to the top of the column, which allows more organic solvent to evaporate. By controlling the rate and temperature of the stripping vapor, the amount of organic solvent removed from the APO can be precisely controlled. The resulting APO has some stripping solvent in it because the condensation of the stripping solvent provides heat for the evaporation of the organic solvent.

[0020] The operating conditions for the stripping column depend on the stripping solvent used and can be determined by one of ordinary skill in the art. For example, the stripping column can be operated at a temperature in the range of 50°C to 80°C and a pressure in the range of 5kPa to 110kPa. Suitable operating conditions for methanol include a temperature in the range of 50°C to 80°C and a pressure in the range of 15kPa to 110kPa. Suitable operating conditions for ethanol include a temperature in the range of 50°C to 80°C and a pressure in the range of 5kPa to 50kPa.

[0021] The stripper bottoms stream 120 containing less than 10 wt % of extractive solvent or less than 5 wt % and up to over 50 wt % of stripping solvent is sent to a separator 125 where a desired amount of stripping solvent 130 can be recovered and recycled back to the stripper 110. The conditions in the separator 125 can be regulated to affect stripping solvent recovery, leaving 5 wt % to 30 wt % of stripping solvent at the bottom of the separator. The goal is to leave enough stripping solvent in the APO stream 135 to provide benefits in the downstream hydroprocessor, but not too much to adversely affect project economics. Suitable separators include, but are not limited to, one or more of a flash tank, a distillation column, a stripping column, or a combination thereof, as well as other known separation unit operations.

[0022] The operating conditions for the separator depend on the type of separator and the stripping solvent used, and can be determined by one of ordinary skill in the art. For example, for methanol or ethanol, the flash tank can be operated at a temperature in the range of 50° C. to 100° C. and a pressure in the range of 5 kPa to 110 kPa.

[0023] The stripper overhead 140 containing greater than 80%, or greater than 85%, or greater than 90% organic solvent and a majority of the stripping solvent fed to 110 may be sent to a recovery column 145 to be separated into a stripping solvent stream 150 and an organic extraction solvent stream 155. For example, the recovery column may be a distillation column.

[0024] The operating conditions for the recovery tower depend on the organic solvent and stripping solvent used, and can be determined by one of ordinary skill in the art. For example, the recovery tower can be operated at a temperature in the range of 60°C to 150°C and a pressure in the range of 100kPa to 500kPa. Suitable operating conditions for methanol and n-butyl acetate include a temperature in the range of 60°C to 135°C and a pressure in the range of 100kPa to 500kPa. Suitable operating conditions for ethanol and n-butyl acetate include a temperature in the range of 75°C to 150°C and a pressure in the range of 100kPa to 500kPa.

[0025] The stripping solvent stream 150 may be recycled back to the stripping column 110. The recycling may be all or a portion of the stripping solvent stream 150. For example, a purge stream may be removed, or a portion may be sent for use elsewhere.

[0026] The organic extraction solvent stream 155 may be recycled back to an upstream pyrolysis separation process (not shown). The recycling may be all or a portion of the organic extraction solvent stream 155. For example, a purge stream may be removed, or a portion may be sent for use elsewhere.

[0027] The mass ratio of the extract phase feed stream 115 to the stripping vapor feed stream 105 may be in the range of 2:1 to 1:3, or 1:1 to 1:2.

[0028] If desired, a condenser (not shown) will be included on the stripper overhead to maximize stripping solvent recovery for the overall process and to generate column reflux. The cooling medium for the condenser may include air, cooling water, or refrigerated water, the choice of which will be determined by an economic evaluation comparing solvent losses to the size of the steam and vacuum equipment required and the cost of the cooling medium selected.

[0029] Example

[0030] The following conditions were used to model the process shown in the accompanying figure.

[0031] Example 1

[0032] Stripping tower: 10 stages, 300mbar

[0033] Stripping vapor feed stream: 100 wt% methanol, 65°C

[0034] Extract phase feed stream: 54 wt% APO / 46 wt% n-butyl acetate, 65°C

[0035] Ratio of Stripping Vapor Feed Stream: Extraction Phase Feed Stream: 1:1, based on mass

[0036] Stripper bottom stream: 65°C

[0037] Flash tank: 65℃, 185mbar

[0038] Separator vapor stream: 95 wt% methanol

[0039] Separator liquid stream: 10 wt% methanol, 0.4 wt% n-butyl acetate, balance APO

[0040] Stripping tower overhead distillate: 95℃

[0041] Second tower: 28 stages, 10 psig

[0042] Second tower top stream: 98% methanol recovery

[0043] Second column bottom stream: 96% recovery of n-butyl acetate from the extract phase feed stream

[0044] If desired, additional recovery can be performed by, for example, adding more stages to the stripping column.

[0045] Example 2

[0046] Stripper: 11 stages, 120 mbar

[0047] Stripping vapor feed stream: 92 wt% ethanol, 6 wt% water, balance APO and n-butyl acetate, 65°C

[0048] Extract phase feed stream: 54 wt% APO / 46 wt% n-butyl acetate, 54°C Stripping vapor feed stream: extract phase feed stream ratio: 1.6:1, based on mass

[0049] Stripper bottom stream: 53°C

[0050] Flash tank: 65℃, 295mbar

[0051] Separator vapor stream: 88 wt% ethanol

[0052] Separator liquid stream: 20 wt% ethanol, 5 wt% n-butyl acetate, balance APO stripper overhead: 86°C

[0053] Second tower: 30 levels, 5 psig

[0054] Second column overhead stream: 93 wt% ethanol

[0055] Second column bottom stream: 98% recovery of n-butyl acetate from the extract phase feed stream

[0056] Example 3

[0057] Stripper: 11 stages, 295mbar

[0058] Stripping vapor feed stream: 92 wt% ethanol, 6 wt% water, balance APO and n-butyl acetate, 65°C

[0059] Extract phase feed stream: 54 wt% APO / 46 wt% n-butyl acetate, 55°C

[0060] Ratio of stripping vapor feed stream: extract phase feed stream: 1.75:1, based on mass

[0061] Stripper bottom stream: 57°C

[0062] Flash tank: 65℃, 295mbar

[0063] Separator vapor stream: 88 wt% ethanol

[0064] Separator liquid stream: 20 wt% ethanol, 5 wt% n-butyl acetate, balance APO stripper overhead: 90°C

[0065] Second tower: 30 stages, 8 psig

[0066] Second column overhead stream: 93 wt% ethanol

[0067] Second column bottom stream: 98% recovery of n-butyl acetate from the extract phase feed stream

[0068] Although at least one exemplary embodiment has been presented in the aforementioned specific embodiments of the present invention, it should be understood that there are a large number of variations. It should also be understood that an exemplary embodiment or multiple exemplary embodiments are only examples and are not intended to limit the scope, applicability or construction of the present invention in any way. On the contrary, the aforementioned specific embodiments will provide a convenient roadmap for implementing the exemplary embodiments of the present invention for those skilled in the art. It should be understood that, without departing from the scope of the present invention as set forth in the appended claims, various changes may be made to the functions and arrangements of the elements described in the exemplary embodiments.

[0069] Specific implementation plan

[0070] While the following is described in conjunction with specific embodiments, it should be understood that this description is intended to illustrate and not to limit the scope of the foregoing description and the appended claims.

[0071] The first embodiment of the present invention is a method for recovering a pyrolysis oil extraction solvent, the method comprising introducing an extraction phase feed stream containing pyrolysis oil and an organic solvent into a stripping tower through an extraction phase feed stream inlet; introducing a stripping vapor feed stream containing a stripping solvent into the stripping tower at a point lower than the extraction phase feed stream inlet, thereby forming a stripping tower top stream containing an organic solvent and a stripping solvent and a stripping tower bottom stream containing pyrolysis oil and a stripping solvent. One embodiment of the present invention is one, any one or all of the first embodiment of this paragraph to the previous embodiment of this paragraph, and further comprises separating the stripping tower top stream into a recovery tower top stream containing a stripping solvent and a recovery tower bottom stream containing an organic solvent in a recovery tower. One embodiment of the present invention is one, any one or all of the first embodiment of this paragraph to the previous embodiment of this paragraph, and further comprises separating the stripping tower bottom stream into a separator vapor stream containing a stripping solvent and a separator liquid stream containing pyrolysis oil in a separator. One embodiment of the present invention is one, any or all of the first embodiment of this paragraph to the previous embodiment of this paragraph, further comprising recycling the recovery tower top stream to the stripping tower as part of the stripping vapor feed stream; or recycling the recovery tower bottom stream to the pyrolysis oil extraction process; or both. One embodiment of the present invention is one, any or all of the first embodiment of this paragraph to the previous embodiment of this paragraph, further comprising recycling the separator vapor stream to the stripping tower as part of the stripping vapor feed stream. One embodiment of the present invention is one, any or all of the first embodiment of this paragraph to the previous embodiment of this paragraph, wherein the organic solvent comprises n-butyl acetate, ethyl acetate, propyl acetate, methyl isobutyl ketone, or a combination thereof. One embodiment of the present invention is one, any or all of the first embodiment of this paragraph to the previous embodiment of this paragraph, wherein the stripping solvent comprises methanol, ethanol, propanol, butanol, or a combination thereof. One embodiment of the present invention is one, any or all of the first embodiment of this paragraph to the previous embodiment of this paragraph, wherein the separator is a flash tank, a distillation tower, a stripping tower, or a combination thereof. One embodiment of the present invention is one, any or all of the first embodiment of this paragraph to the previous embodiments of this paragraph, wherein the flash tank is operated at a temperature in the range of 50°C to 100°C and a pressure in the range of 5kPa to 110kPa. One embodiment of the present invention is one, any or all of the first embodiment of this paragraph to the previous embodiments of this paragraph, wherein the stripping column is operated at a temperature in the range of 50°C to 80°C and a pressure in the range of 5kPa to 110kPa.An embodiment of the present invention is one, any one or all of the first embodiment of this paragraph to the previous embodiments of this paragraph, wherein the recovery column is operated at a temperature in the range of 60°C to 150°C and a pressure in the range of 100 kPa to 500 kPa. An embodiment of the present invention is one, any one or all of the first embodiment of this paragraph to the previous embodiments of this paragraph, wherein the mass ratio of the extract phase feed stream to the stripping vapor feed stream is in the range of 2:1 to 1:3.

[0072] A second embodiment of the present invention is a method for recovering a pyrolysis oil extraction solvent, the method comprising introducing an extraction phase feed stream comprising pyrolysis oil and an organic solvent into a stripping tower through an extraction phase feed stream inlet; introducing a stripping vapor feed stream comprising a stripping solvent into the stripping tower at a point lower than the extraction phase feed stream inlet, thereby forming a stripping tower top stream comprising an organic solvent and a stripping solvent and a stripping tower bottom stream comprising pyrolysis oil and a stripping solvent; separating the stripping tower bottom stream into a vapor stream comprising a stripping solvent and a liquid stream comprising pyrolysis oil in a flash tank; and separating the stripping tower top vapor into a recovery tower top stream comprising a stripping solvent and a recovery tower bottom stream comprising an organic solvent in a recovery tower. One embodiment of the present invention is one, any or all of the second embodiment of this paragraph to the previous embodiment of this paragraph, further comprising recycling the top stream of the recovery tower to the stripping tower as part of the stripping vapor feed stream; or recycling the vapor stream from the flash tank to the stripping tower as part of the stripping vapor feed stream; or both. One embodiment of the present invention is one, any or all of the second embodiment of this paragraph to the previous embodiment of this paragraph, further comprising recycling the bottom stream of the recovery tower to the pyrolysis oil extraction process. One embodiment of the present invention is one, any or all of the second embodiment of this paragraph to the previous embodiment of this paragraph, wherein the stripping solvent comprises methanol, ethanol, propanol, butanol or a combination thereof. One embodiment of the present invention is one, any or all of the second embodiment of this paragraph to the previous embodiment of this paragraph, wherein the organic solvent comprises n-butyl acetate, ethyl acetate, propyl acetate, methyl isobutyl ketone or a combination thereof. One embodiment of the present invention is one, any or all of the second embodiment of this paragraph to the previous embodiment of this paragraph, wherein the flash tank is operated at a temperature in the range of 50°C to 100°C and a pressure in the range of 5kPa to 110kPa. One embodiment of the present invention is one, any or all of the second embodiment of this paragraph to the previous embodiment of this paragraph, wherein the stripping tower is operated at a temperature in the range of 50°C to 80°C and a pressure in the range of 5kPa to 110kPa; or the recovery tower is operated at a temperature in the range of 60°C to 150°C and a pressure in the range of 100kPa to 500kPa; or both. One embodiment of the present invention is one, any or all of the second embodiment of this paragraph to the previous embodiment of this paragraph, wherein the mass ratio of the extract phase feed stream to the stripping vapor stream is in the range of 2:1 to 1:3.

[0073] Although there is no further detailed description, it is believed that those skilled in the art can utilize the present invention to the greatest extent by using the foregoing description and can easily determine the essential characteristics of the present invention without departing from the spirit and scope of the present invention to make various changes and modifications of the present invention and adapt it to various usages and conditions. Therefore, the aforementioned preferred specific embodiments should be understood as merely illustrative and not to limit the rest of the present disclosure in any way, and are intended to cover various modifications and equivalent arrangements included within the scope of the appended claims.

[0074] In the foregoing, all temperatures are set forth in degrees Celsius and all parts and percentages are by weight unless otherwise indicated.

Claims

1. A method for recovering a pyrolysis oil extraction solvent, the method comprising: introducing an extract phase feed stream (115) comprising pyrolysis oil and an organic solvent into the stripping column (110) through an extract phase feed stream inlet; as well as A stripping vapor feed stream (105) comprising a stripping solvent is introduced into the stripping column (110) at a point below the extract phase feed stream inlet, thereby forming a stripping column overhead stream (140) comprising the organic solvent and the stripping solvent and a stripping column bottom stream (120) comprising the pyrolysis oil and the stripping solvent.

2. The method according to claim 1, further comprising: The stripping column overhead stream (140) is separated in a recovery column (145) into a recovery column overhead stream (150) comprising the stripping solvent and a recovery column bottoms stream (155) comprising the organic solvent.

3. The method according to any one of claims 1 to 2, further comprising: The stripper bottoms stream (120) is separated in a separator (125) into a separator vapor stream (130) comprising the stripping solvent and a separator liquid stream (135) comprising the pyrolysis oil.

4. The method according to claim 2, further comprising: Recycling the recovery column overhead stream (150) to the stripping column (110) as part of the stripping vapor feed stream (105); or Recycling the recovery tower bottom stream (155) to the pyrolysis oil extraction process; or Both.

5. The method according to claim 3, further comprising: The separator vapor stream (130) is recycled to the stripping column (110) as part of the stripping vapor feed stream (105).

6. The method according to any one of claims 1 to 2, wherein the organic solvent comprises n-butyl acetate, ethyl acetate, propyl acetate, methyl isobutyl ketone, or a combination thereof.

7. The method of any one of claims 1 to 2, wherein the stripping solvent comprises methanol, ethanol, propanol, butanol, or a combination thereof.

8. The method of claim 3, wherein the separator (125) is a flash tank, a distillation column, a stripping column, or a combination thereof.

9. The method according to any one of claims 1 to 2, wherein: The separator is a flash tank operated at a temperature in the range of 50°C to 100°C and a pressure in the range of 5 kPa to 110 kPa; or The stripping column is operated at a temperature in the range of 50°C to 80°C and a pressure in the range of 5kPa to 110kPa; or The recovery column is operated at a temperature in the range of 60°C to 150°C and a pressure in the range of 100 kPa to 500 kPa; or A combination of them.

10. The process according to any one of claims 1 to 2, wherein the mass ratio of the extract phase feed stream to the stripping vapor feed stream is in the range of 2:1 to 1:3.

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