Method for producing and recovering levulinic acid

Abstract

The present disclosure relates to methods of producing and recovering levulinic acid.

Description

[0001] Cross-reference to related applications

[0002] This application claims the benefit of U.S. Patent Application Serial No. 63 / 466,191, filed May 12, 2023. The entire contents of that earlier application are hereby incorporated herein by reference. Technical Field

[0003] This disclosure relates to methods for producing and recycling levulinic acid. Background Technology

[0004] Solvent extraction, such as solvent extraction using alcohols, can be used during the synthesis and separation of levulinic acid. Summary of the Invention

[0005] This disclosure relates to methods for producing and recycling levulinic acid, such as methods for producing levulinic acid from cellulosic raw materials (e.g., lignocellulose).

[0006] These methods include a reactive back-extraction step, wherein after levulinic acid is extracted into an organic phase (e.g., an alcohol, such as hexanol), the organic phase is contacted with water. The levulinic acid is extracted into an aqueous phase, which can be concentrated to a relatively high concentration of levulinic acid (e.g., at least 60 wt%, at least 70 wt%, at least 80 wt%, at least 90 wt% levulinic acid) while dehydration and / or polymerization of levulinic acid derivatives (e.g., β-angelicolone) are relatively minimal (e.g., none). Furthermore, at least a portion of the levulinic acid converted to esters during organic phase extraction can be reconverted back into levulinic acid.

[0007] These methods can produce levulinic acid in higher yields compared to some other methods for producing levulinic acid. These methods can convert at least a portion of the esters of levulinic acid (e.g., hexyl levulinate) formed during the solvent extraction step back into levulinic acid. These methods can produce levulinic acid through a relatively simple purification process compared to some other methods. These methods can reduce (e.g., prevent) the formation of undesirable lactones, tarry products, and / or polymerization byproducts during separation, purification, and / or dehydration steps.

[0008] These methods can generate levulinic acid derivatives, such as esters (e.g., ethyl levulinate) and / or monomers that can be used as fuels, relatively efficiently and / or in higher yields compared to certain other methods for generating levulinic acid derivatives. These methods can consume pulp, waste paper, waste wood, and / or forest waste to generate fuels (e.g., ethyl levulinate). These methods can produce fuels with net negative carbon dioxide emissions (e.g., ethyl levulinate). Therefore, these methods can generate fuels and other derivatives relatively efficiently and / or with lower emissions compared to certain other methods for generating fuels.

[0009] In a first aspect, this disclosure provides a method for producing levulinic acid, the method comprising: contacting a first solution containing levulinic acid and an acid with an organic solvent; extracting at least a portion of the levulinic acid from the first solution into the organic solvent to form a second solution containing levulinic acid and the organic solvent; contacting the second solution with water; and extracting at least a portion of the levulinic acid from the second solution into the water to form a third solution containing levulinic acid and water. The organic solvent comprises an alcohol.

[0010] In some embodiments, the alcohol comprises C6 to C8 alcohols. In some embodiments, the alcohol comprises hexanol, heptanol, octanol, and / or isoamyl alcohol.

[0011] In some embodiments, the acid comprises sulfuric acid, nitric acid, hydrochloric acid, hydrobromic acid, and / or p-toluenesulfonic acid.

[0012] In some embodiments, the second solution further comprises an ester of levulinic acid, and contacting the second solution with water converts at least a portion of the ester of levulinic acid into levulinic acid. In some embodiments, the alcohol comprises hexanol, and the ester of levulinic acid comprises hexyl levulinate. In some embodiments, the alcohol comprises heptanol, and the ester of levulinic acid comprises heptanol levulinate. In some embodiments, the alcohol comprises octanol, and the ester of levulinic acid comprises octyl levulinate. In some embodiments, the alcohol comprises isoamyl alcohol, and the ester of levulinic acid comprises isoamyl levulinate.

[0013] In some embodiments, the first solution contains a volatile component, and the method further includes removing the volatile component from the first solution. In some embodiments, the volatile component includes formic acid, acetic acid, and furfural.

[0014] In some embodiments, the method further includes contacting the precursor material with the acid to form the first solution. In some embodiments, the acid is sulfuric acid, nitric acid, hydrochloric acid, hydrobromic acid, and / or p-toluenesulfonic acid. In some embodiments, the precursor material comprises cellulose, lignocellulose, furfural, furfuryl alcohol, sugar, and / or maleic anhydride.

[0015] In some embodiments, the method further includes evaporating a portion of the water in the third solution. In some embodiments, the concentration of levulinic acid in the third solution after evaporation is 60% to 90% by weight.

[0016] In some embodiments, the method further includes converting at least a portion of levulinic acid into a member selected from the group consisting of ethyl levulinate, aminolevulinic acid, succinic acid, acrylic acid, 3-hydroxypropionic acid, and diphenolic acid.

[0017] In some implementations, the method further includes separating the first solution and the second solution.

[0018] In some implementations, the method further includes separating the second solution and the third solution.

[0019] In some implementations, the ratio of water to the second solution is from 0.25:1 to 5:1 (water:second solution).

[0020] In a second aspect, this disclosure provides a method for recovering levulinic acid, the method comprising: contacting a first solution containing an organic solvent and levulinic acid and / or an ester of levulinic acid with water to form a second solution containing levulinic acid and water.

[0021] In some embodiments, the first solution contains an ester of levulinic acid, and contacting the first solution with water converts at least a portion of the ester of levulinic acid into levulinic acid.

[0022] In some embodiments, the organic solvent comprises an alcohol. In some embodiments, the ester of levulinic acid comprises an ester formed by reacting levulinic acid with the alcohol. In some embodiments, the alcohol comprises a C6 to C8 alcohol. In some embodiments, the alcohol comprises hexanol, heptanol, octanol, and / or isoamyl alcohol. In some embodiments, the alcohol comprises hexanol, and the ester of levulinic acid comprises hexyl levulinate. In some embodiments, the alcohol comprises heptanol, and the ester of levulinic acid comprises heptanol levulinate. In some embodiments, the alcohol comprises octanol, and the ester of levulinic acid comprises octyl levulinate. In some embodiments, the alcohol comprises pentanol or isoamyl alcohol, and the ester of levulinic acid comprises pentyl levulinate or isoamyl levulinate.

[0023] In some embodiments, the method further includes evaporating a portion of the water in the second solution. In some embodiments, the concentration of levulinic acid in the second solution after evaporation is 60% to 90% by weight.

[0024] In some embodiments, the method further includes converting at least a portion of levulinic acid into ethyl levulinate, aminolevulinic acid, succinic acid, acrylic acid, 3-hydroxypropionic acid, and / or diphenolic acid.

[0025] In some embodiments, the method further includes separating the first solution and the second solution.

[0026] In some implementations, the ratio of water to the first solution is from 0.25:1 to 5:1 (water:first solution).

[0027] Details of one or more embodiments of the present invention are set forth in the accompanying drawings and the following description. Other features, objects, and advantages of the invention will be apparent from the specification, drawings, and claims. Attached Figure Description

[0028] Figure 1 A flowchart of one method is described.

[0029] Figure 2 A schematic diagram of a system including a mixer is depicted.

[0030] Figure 3 A reaction scheme was described.

[0031] The same reference numerals in the various figures denote the same elements. Detailed Implementation

[0032] Figure 1 A flowchart of method 100 is depicted. In step 102, levulinic acid is produced from cellulose and / or lignocellulose raw materials by acid hydrolysis. Levulinic acid can also be produced from furfural via furfuryl alcohol, or from sugars such as glucose, sucrose, or cellobiose, or from maleic anhydride by oxidation. Cellulose and / or lignocellulose can be derived from pulp, waste paper, waste wood, and / or forest waste (e.g., softwood waste).

[0033] In step 104, solids and volatile components are removed to obtain a first mixture comprising levulinic acid and an acid (e.g., sulfuric acid). Volatile components may include formic acid, acetic acid, and furfural. Solids can be removed using any suitable method, such as by filtration, centrifugation, or sedimentation. Filtration can be performed using a filter (e.g., a coarse filter cloth with a nominal pore size of 10 micrometers), a membrane, by centrifugation, or by gravity sedimentation. Smaller colloidal particles can be further removed using a membrane filter with a smaller pore size (e.g., a membrane filter for microfiltration, ultrafiltration, or nanofiltration). Volatile components can be removed using any suitable method, such as by stripping. In some embodiments, stripping can be performed at atmospheric pressure and 100°C using excess steam or waste heat, and the stripping factor (V / F) is at most 0.9. In some embodiments, stripping can be performed under a vacuum of 100 mm Hg, and the stripping factor (V / F) is as low as 0.16 (e.g., as low as 0.1).

[0034] In step 106, levulinic acid is extracted from the first solution using solvent extraction. The first solution is contacted with an organic solvent containing an alcohol. The alcohol can be any C6 to C8 alcohol. Examples of alcohols include hexanol, heptanol, octanol, and isoamyl alcohol. Not wishing to be bound by theory, the alcohol should have relatively low solubility in the aqueous phase, which can be achieved by using a sufficiently long-chain hydrocarbon (e.g., at least six carbons). The alcohol should also have relatively high volatility, allowing for removal by stripping. Hexanol is relatively inexpensive and exhibits sufficiently low water solubility and sufficiently high volatility. Step 106 results in the formation of a second solution (organic phase) containing levulinic acid and an organic solvent, as at least a portion of the levulinic acid is extracted into the organic phase. Typically, levulinic acid is partitioned between the aqueous and organic phases. The aqueous and organic phases can be separated by gravity or centrifugation. The acid (e.g., sulfuric acid) remains in the aqueous phase. The remaining aqueous phase (raffinate) containing sulfuric acid and / or unextracted levulinic acid is separated from the second solution and recycled back to the hydrolysis reactor, where it is mixed with fresh feedstock. At least a portion of the levulinic acid in the second solution (organic phase) is converted to an ester of levulinic acid in the second solution. For example, if the organic solvent contains hexanol, at least a portion of the levulinic acid is converted to hexyl levulinate. As another example, if the organic solvent contains heptanol, at least a portion of the levulinic acid is converted to heptanol levulinate. As another example, if the organic solvent contains octanol, at least a portion of the levulinic acid is converted to octyl levulinate. As a further example, if the organic solvent contains pentanol or isopentanol, at least a portion of the levulinic acid is converted to pentyl levulinate or isopentanol levulinate.

[0035] In step 108, levulinic acid is back-extracted from the second solution into water by contacting the second solution, forming a third solution containing levulinic acid and water. Furthermore, at least a portion of the ester of levulinic acid in the second solution is converted to levulinic acid via a reaction and extracted into water. In some embodiments, at least 19% (e.g., at least 20%, at least 25%, at least 30%, at least 35%, at least 40%, at least 45%) and / or up to 49% (e.g., up to 45%, up to 40%, up to 35%, up to 30%, up to 25%, up to 20%) of the ester of levulinic acid (e.g., hexyl levulinate) in the second solution is converted to levulinic acid. In some embodiments, at least 54% (e.g., at least 55%, at least 60%, at least 65%, at least 70%, at least 75%, at least 80%, at least 85%) and / or up to 88% (e.g., up to 85%, up to 80%, up to 75%, up to 70%, up to 65%, up to 60%, up to 55%) of the ester of levulinic acid is transferred to a third solution. Step 108 can be performed in continuous countercurrent mode, continuous cocurrent mode, or batch mixing mode.

[0036] In step 110, levulinic acid in the third solution is concentrated by evaporating a portion of the water. After concentration, the concentration of levulinic acid is at least 60% by weight (e.g., at least 65% by weight, at least 70% by weight, at least 75% by weight, at least 80% by weight, at least 85% by weight, at least 90% by weight) and / or at most 95% by weight (e.g., at most 90% by weight, at most 85% by weight, at most 80% by weight, at most 75% by weight, at most 70% by weight, at most 65% by weight). It is not desirable to be bound by theory, but it is believed that the third solution can be concentrated with relatively less (e.g., no) dehydration of levulinic acid (e.g., formation of lactones) compared to concentrating levulinic acid in other solvents (e.g., organic solvents). Step 110 can be carried out in a vacuum concentration apparatus. In some embodiments, step 110 is carried out in a vacuum concentration apparatus at an absolute pressure of 100 mmHg. Furthermore, alcohols remaining in the water extract can be separated from the condensate vapor during evaporation and recycled in step 106.

[0037] In step 112, levulinic acid is converted into a high-value product. Examples of high-value products include esters that can be used as fuels, such as ethyl levulinate, aminolevulinic acid, succinic acid, acrylic acid, 3-hydroxypropionic acid, bisphenol A, and other monomers. The conversion of levulinic acid to ethyl levulinate can be carried out by reacting levulinic acid with ethanol. Excess ethanol can be removed by distillation. Step 112 can produce ethyl levulinate with a purity of at least 97% (e.g., at least 97.5%, at least 98%, at least 98.5%, at least 99%, at least 99.5%, at least 99.8%, at least 99.9%).

[0038] In some embodiments, step 102 may produce levulinic acid at a concentration of at least 7% by weight (e.g., at least 8% by weight, at least 9% by weight, at least 10% by weight, at least 11% by weight, at least 12% by weight, at least 13% by weight, at least 14% by weight, at least 15% by weight, at least 16% by weight, at least 17% by weight, at least 18% by weight, at least 19% by weight, at least 20% by weight, at least 21% by weight, at least 22% by weight, at least 23% by weight, at least 24% by weight) and / or at most 25% by weight (e.g., at most 24% by weight, at most 23% by weight, at most 22% by weight, at most 21% by weight, at most 20% by weight, at most 19% by weight, at most 18% by weight, at most 17% by weight, at most 16% by weight, at most 15% by weight, at most 14% by weight, at most 13% by weight, at most 12% by weight, at most 11% by weight, at most 10% by weight, at most 9% by weight, at most 8% by weight). Examples of acids used include mineral acids such as sulfuric acid, nitric acid, hydrochloric acid, hydrobromic acid, and p-toluenesulfonic acid. In some embodiments, the concentration of the acid is at least 2% by weight (e.g., at least 3% by weight, at least 4% by weight, at least 5% by weight, at least 6% by weight, at least 7% by weight, at least 8% by weight, at least 9% by weight) and / or at most 10% by weight (e.g., at most 9% by weight, at most 8% by weight, at most 7% by weight, at most 6% by weight, at most 5% by weight, at most 4% by weight, at most 3% by weight). Step 102 can be carried out in a continuous backmixing reactor. Step 102 can be carried out at a temperature of at least 185°C (e.g., at least 190°C, at least 195°C, at least 200°C, at least 205°C) and / or at most 210°C (e.g., at most 205°C, at most 200°C, at most 195°C, at most 190°C). Not wanting to be bound by theory, it is believed that temperatures below 195°C and above 185°C can increase the yield of formic acid, a byproduct produced in conjunction with levulinic acid. Step 102 can be carried out for at least 10 minutes (e.g., at least 15 minutes, at least 20 minutes, at least 25 minutes) and / or at most 30 minutes (e.g., at most 25 minutes, at most 20 minutes, at most 15 minutes). In some embodiments, step 102 can be carried out in a continuous backmixing reactor with 3.5% sulfuric acid at 195°C for up to 30 minutes.

[0039] Figure 2A schematic diagram of a system 200 for use in step 108 is depicted. An organic feed stream 220 and a fresh water stream 230 contact each other in a mixer 210. The organic feed stream 220 typically contains hexanol, levulinic acid, and hexyl levulinate. In the mixer 210, at least a portion of the hexyl levulinate from the organic feed stream 220 is converted to levulinic acid by reacting with water. Furthermore, at least a portion of the levulinic acid (free levulinic acid from the organic feed stream 220 and / or levulinic acid formed by the hydrolysis of hexyl levulinate) enters the aqueous phase. An organic output stream 240 and a water output stream exit the mixer 210. The organic output stream 240 contains hexanol and may further contain unhydrolyzed hexyl levulinate and / or levulinic acid. The water output stream 250 contains water and levulinic acid. Hexyl levulinate is insoluble in the aqueous phase, therefore the water output stream 250 does not contain hexyl levulinate. Organic feed stream 220 corresponds to the second solution in step 108, and water output stream 250 corresponds to the third solution in step 108. Hexyl levulinate can remain in the organic phase and be recycled back to step 106.

[0040] Mixer 210 can be a continuous multi-stage centrifugal contactor, such as a Podbielniak machine; a continuous mixer-sedimenter, such as a Robatel machine; or a stirred tank batch contactor, in which the phases are mixed and settled in the same container. Gravity settling can also be used to separate the water output stream 250 from the organic output stream 240. A liquid-packed tower (e.g., a tower packed with packing or trays) can also be used to separate the water output stream 250 from the organic output stream 240. The flow of the organic feed stream 220 and the fresh water stream 230 can be countercurrent, cocurrent, and / or can be batch contact.

[0041] The concentration of levulinic acid in the water output stream 250 (corresponding to the third solution generated in step 108) may be at least 7% by weight (e.g., up to 7.5% by weight, up to 8% by weight, at least 8.5% by weight, at least 9% by weight, at least 9.5% by weight) and / or up to 12% by weight (e.g., up to 11.5% by weight, up to 11% by weight, up to 10.5% by weight, up to 10% by weight, up to 9.5% by weight, up to 9% by weight, up to 8.5% by weight). The ratio of fresh water flow 230 to organic feed flow 220 (corresponding to the amount of water added to the second solution in step 108) is at least 0.25:1 (e.g., at least 0.3:1, at least 0.4:1, at least 0.5:1, at least 0.6:1, at least 0.7:1, at least 0.75:1, at least 0.8:1, at least 0.9:1, at least 1:1, at least 1.5:1, at least 2:1, at least 2.5:1, at least 3:1, at least 3.5). Water:organic phase ratios of at least 4:1, at least 4.5:1, and / or up to 5:1 (e.g., up to 4.5:1, up to 4:1, up to 3.5:1, up to 3:1, up to 2.5:1, up to 2:1, up to 1.5:1, up to 1:1, up to 0.9:1, up to 0.8:1, up to 0.75:1, up to 0.7:1, up to 0.6:1, up to 0.5:1, up to 0.4:1, up to 0.3:1). It is not desirable to be bound by theory; it is believed that the amount of water used should be minimized while maintaining relatively high levels of extractable levulinic acid. Due to water extraction, given an appropriate number of extraction stages (e.g., at least four stages) and / or an appropriate ratio of fresh water stream 230 to organic feed stream 220 (e.g., 1.4), at least a portion (e.g., at least 50% and / or up to 90%) of levulinic acid from organic feed stream 220 can be extracted into water output stream 250.

[0042] Figure 3 A reaction scheme for the conversion of levulinic acid to esters in the presence of alcohols is described. When n=1, levulinic acid is converted to hexyl levulinate in hexanol. When n=2, levulinic acid is converted to heptyl levulinate in heptanol. When n=3, levulinic acid is converted to octyl levulinate in octanol. As mentioned above, it is not desirable to be bound by theory, but it is believed that back-extraction of levulinic acid from alcohols (e.g., hexanol, heptanol, octanol) to the aqueous phase can convert at least a portion of the esters (e.g., hexyl levulinate, heptyl levulinate, octyl levulinate) to levulinic acid.

[0043] In some embodiments, the aqueous phase does not contain sulfuric acid. In other embodiments, the aqueous phase contains sulfuric acid (e.g., a catalytic amount of sulfuric acid). It is not intended to be theoretically rigorous, but it is believed that the presence of sulfuric acid may facilitate the hydrolysis of hexyl levulinate to levulinic acid.

[0044] Example

[0045] Example 1

[0046] Mix 51 kg of a hexanol solution containing 2.29 kg (4.5 wt%) of levulinic acid and an estimated 1.82 kg (2.1 wt%) of hexyl levulinate with 51 kg of fresh water in a 200 L HDPE drum container. Batch mix the liquids for 1 hour using a 0.25 HP drum mixer with a 2-inch three-blade impeller. Allow the liquids to settle and stand overnight to separate.

[0047] Carefully pump out the top layer of hexanol and skim it off, collecting it separately using the tubing attached to the pump. Then pump the lower aqueous layer out of the container and allow it to settle in a separatory funnel. Remove any remaining hexanol by skimming off the remaining aqueous phase.

[0048] The final mass of the water extract was 50.9 kg, and the final mass of the hexanol raffinate was 47.5 kg. The mass balance was 96.5%. The initial mass of levulinic acid introduced into the organic phase was determined to be 2.29 kg by high-performance liquid chromatography (HPLC). After separation, analysis of the organic raffinate phase by gas chromatography (GC) showed that the amount of levulinic acid in the organic phase was 1.002 kg (2.1 wt%). HPLC analysis of the water extract phase showed that the amount of levulinic acid in the aqueous phase was 1.6 kg (3.12 wt%). Therefore, the total amount of levulinic acid increased from 2.29 kg to 2.59 kg, indicating an increase of 0.3 kg (13%).

[0049] The initial mass of hexyl levulinate in the organic phase was estimated to be 1.82 kg using the material balance difference. During back-extraction, the total amount of levulinic acid increased by 296.4 g, indicating that 510.9 g of hexyl levulinate was hydrolyzed. Therefore, the estimated mass of hexyl levulinate in the organic raffinate was 1.31 kg (1.82 kg minus 0.51 kg). The aqueous phase contained no hexyl levulinate because it is insoluble in water. The estimated loss of hexyl levulinate was 0.51 kg. The increase of 0.3 kg in levulinic acid is in good agreement with the equivalent loss of 0.51 kg in hexyl levulinate. Therefore, water extraction resulted in the hydrolysis of approximately 28% (0.51 / 1.82) of the hexyl levulinate in the organic phase. 47.8% of the levulinic acid initially present in the organic phase as free and esterified levulinic acid (hexyl levulinate) was extracted into the aqueous phase. For a single batch extraction stage, the extraction rate of levulinic acid (47.8%) was unexpectedly high.

[0050] The aqueous extract was then processed using a Buchi R-220 20L floor-standing rotary evaporator vacuum evaporator. The rotary evaporator removed a portion of the water to concentrate the aqueous phase. After concentrating the aqueous phase 10-fold, evaporation was temporarily stopped, and the concentrate was filtered through a 1.5-micron microfiber glass filter. A small amount of precipitate was filtered out. The concentrate was further concentrated to a final concentration of 947.6 g / L levulinic acid (approximately 90% by weight levulinic acid). The concentrate also contained 10% by weight formic acid and trace amounts of sulfuric acid. The concentrations were determined by HPLC. No significant loss of levulinic acid was observed due to polymerization. The maximum loss of levulinic acid during evaporation was 5.4%. The aqueous phase was able to be concentrated to a relatively high levulinic acid concentration and a sufficiently low water concentration, making it suitable as a feedstock for further chemical conversions such as esterification (e.g., by reaction with ethanol to ethyl levulinate).

[0051] Example 2 - Podbeilniak

[0052] Several water extraction experiments were conducted using a pilot-scale Podbeilniak A-25 centrifugal contactor (POD). This extraction machine uses centrifugal force and rotary pumping action for mixer-sedimentation operation, replacing gravity for separation and multi-stage countercurrent mixing. The device has two inlet nozzles and two outlet nozzles. The machine body rotates to induce centrifugal mixing and sedimentation of the immiscible organic and aqueous phases. The A-25 POD is designed to correspond to approximately four ideal stages of mixing and sedimentation.

[0053] In a series of experiments, a POD was used with a range of organic feed to water extractant flow rates. An organic feed (organic input stream) containing levulinic acid and hexyl levulinate dissolved in hexanol was fed into the POD's inlet nozzle at a specified flow rate using a calibrated metering pump. Simultaneously, a fresh water extractant phase (fresh water input stream) was fed into another inlet nozzle.

[0054] In each stage within the machine, the aqueous extract phase is continuously mixed with a water-immiscible organic (hexanol) phase, and the immiscible layers are separated by centrifugation. The hexanol phase contains esterified levulinic acid (hexyl levulinate) as the dissolved component and free, unesterified levulinic acid. The aim is to extract as much free and esterified levulinic acid as possible. Since hexyl levulinate is insoluble in the aqueous phase, the hexyl levulinate in the organic phase is hydrolyzed to produce levulinic acid, which is then extracted into the aqueous phase.

[0055] The volumetric flow rate of the organic feed varied between 0.405 and 0.597 L / min. The aqueous (fresh water) extract phase was fed at a flow rate ranging from 0.467 to 0.8 LPM. The flow rate ratio of organic feed to water extract ranged from 1.13 to 1.37. In all seven experiments, the concentrations of levulinic acid and hexyl levulinate in the organic feed, as measured by GC, were 35.4 g / L and 79.8 g / L, respectively. The outlet concentrations in the organic raffinate (organic output stream), as measured by GC, ranged from 5.41 to 5.89 g / L for levulinic acid and from 54.52 to 57.44 g / L for hexyl levulinate. The outlet concentrations in the water extract, as measured by HPLC, ranged from 30.87 g / L to 35.15 g / L for levulinic acid. Hexyl levulinate is insoluble in the aqueous medium. The parameters and contents of each feed stream are summarized in Table 1. Mass flow rate is calculated based on the flow meter calibration curve. The amounts of levulinic acid and hexyl levulinate, expressed in grams, are calculated by multiplying the concentration in g / L by the volumetric flow rate. Total levulinate corresponds to the amounts of levulinic acid and hexyl levulinate. Total levulinic acid equivalent is calculated as the amount of levulinic acid and the amount of hexyl levulinate converted using the molecular weights of levulinic acid and hexyl levulinate.

[0056] Table 1. Summary of Input and Output Streams

[0057]

[0058] Table 2 summarizes the experimental results. In all experiments, the percentage of hexyl levulinate decomposed ranged from 30% to 34%, and the total levulinic acid fraction extracted into the aqueous phase ranged from 51% to 55% of the levulinic acid equivalent entering the machine. The aqueous phase not only hydrolyzed a significant portion of the hexyl levulinate fed into the equipment but also extracted a relatively high percentage of usable levulinic acid in the form of an aqueous extract.

[0059] Table 2. Summary of Results

[0060]

[0061] Contact with the aqueous phase appears to both hydrolyze hexyl levulinate and extract the resulting levulinic acid along with the free levulinic acid. Given that only four stages are available, this technique results in a high percentage of levulinic acid being extracted into the aqueous extract phase.

[0062] Example 3 - Podbeilniak

[0063] Several water extraction experiments were conducted using a pilot-scale Podbeilniak A-25 centrifugal contactor (POD), as described in Example 2.

[0064] The volumetric flow rate of the organic feed hexanol varied between 0.60 and 0.62 LPM. The water (fresh water) extract phase was fed at a volumetric flow rate ranging from 0.63 to 0.66 LPM. The inlet flow rate was fed via a calibrated metering pump. The flow rate-to-volume ratio of the organic feed to the water extract ranged from 1.0 to 1.1. The outlet flow rate was measured by timed volumetric collection. The outlet flow rate of the organic raffinate ranged from 0.61 to 0.63 LPM, and the outlet flow rate of the water extract ranged from 0.61 to 0.65 LPM. The total mass balance in all tests was 98.9% or higher. A summary of each feed stream is presented in Table 3. The results are summarized in Table 4.

[0065] Table 3. Summary of Input and Output Streams

[0066]

[0067] Table 4. Summary of Results

[0068]

[0069] Example 4 - ROBATEL

[0070] Water extraction experiments were conducted using a pilot-scale ROBATEL SX 6-0 mixer-settler apparatus. This apparatus comprises four sequential mixer-settler stages combined in a single module. In each stage, the aqueous extract phase is continuously mixed with a water-immiscible organic (hexanol) phase and separated by gravity. The hexanol phase contains esterified levulinic acid (hexyl levulinate) and free levulinic acid. The aim was to extract as much free and esterified levulinic acid as possible. Since hexyl levulinate is insoluble in the aqueous phase, the hexyl levulinate in the organic phase was to be hydrolyzed to produce levulinic acid, which could then be extracted into the aqueous phase.

[0071] An organic mixture containing levulinic acid and hexyl levulinate dissolved in hexanol was fed into the inlet nozzle of the ROBATEL apparatus at a calibrated flow rate of 1.31 L / min (LPM) using a metering pump. GC analysis revealed that the organic mixture contained 70.7 g / L levulinic acid and 15.3 g / L hexyl levulinate. Fresh water was then fed into another inlet nozzle of the ROBATEL apparatus at a calibrated rate of 1.63 LPM using a metering pump. The outlet flow rates of the organic and aqueous phases from the apparatus were measured using timed volumetric collection. The apparatus was brought to equilibrium by allowing three times its volume of aqueous and organic phases to flow through it at a constant flow rate. The apparatus volume was approximately 225 L. After reaching steady state, the flow rates of the organic and water outlet streams were measured, and samples of both streams were analyzed. The overall mass balance closure for the entire test was 97.4%. Gas chromatography revealed that the effluent organic stream contained 2.84 g / L levulinic acid and 12.45 g / L hexyl levulinate. HPLC analysis of the effluent revealed that it contained 57.8 g / L of levulinic acid but no hexyl levulinate, which is insoluble in the aqueous phase. A summary of each stream is presented in Table 5.

[0072] Table 5. Summary of Input and Output Streams

[0073]

[0074] Calculations of hexyl levulinate entering and leaving the equipment showed a loss of 3.1 g / min. This represents 16% hydrolysis of hexyl levulinate entering the equipment in the organic phase. The aqueous phase leaving the equipment extracted 88% of the free or esterified levulinate entering the equipment. The overall mass balance closure was 97.4%.

[0075] Contact with the aqueous phase appears to both hydrolyze hexyl levulinate and extract the resulting levulinic acid along with free levulinic acid. Considering that the device consists of only four mixer-settler stages, the aqueous phase not only hydrolyzes a significant portion of the hexyl levulinate fed into the device but also extracts a high percentage of usable levulinic acid into the aqueous solution.

[0076] Example 5 - ROBATEL

[0077] Water extraction experiments were conducted using a ROBATEL SX 6-0 mixer-sedimentation apparatus, as described in Example 4.

[0078] In each test, the water used to extract levulinic acid and hexyl levulinate was immiscible with hexanol solution. Hexanol inlet flow rate ranged from 0.55 to 0.84 LPM, and fresh water feed flow rate ranged from 0.71 to 1.11 LPM. The organic feed to water extract flow rate ratio ranged from 1.2 to 1.5. Both feeds were input via calibrated metering pumps. Outlet flow rates were measured using timed volumetric collection. The organic output flow rate ranged from 0.56 to 0.86 L / min, and the water extract flow rate ranged from 0.7 to 1.08 L / min. In all experiments, the total mass balance was 98.7% or higher. The hexanol feed contained 34.28 to 37.88 g / L levulinic acid and 2.03 to 3.99 g / L hexyl levulinate, as measured by GC. Organic and aqueous phase outlet flow rates from the apparatus were measured using timed volumetric collection. The equipment was brought to equilibrium by allowing three times its volume of aqueous and organic phases to flow through it at a constant flow rate. Once steady state was achieved, the flow velocities of the organic and water outlet flows were measured, and samples of both flows were analyzed. A summary of each flow is presented in Table 6. The results are summarized in Table 7.

[0079] Table 6. Summary of Input and Output Streams

[0080]

[0081] Table 7. Summary of Results

[0082]

[0083] In all experiments, the degree of hydrolysis of hexyl levulinate ranged from 19% to 36%. The extraction efficiency of levulinic acid into the aqueous extraction phase ranged from 73% to 88% across the four mixer-sediment stages.

[0084] The aqueous phase not only hydrolyzes a significant portion of the hexyl levulinate fed into the equipment, but also extracts a high percentage of usable levulinic acid in aqueous solution form.

[0085] Many embodiments of the invention have been described. However, it should be understood that various modifications can be made without departing from the spirit and scope of the invention. Therefore, other embodiments are within the scope of the claims.

Claims

1. A method of producing levulinic acid, the method comprising: contacting a first solution comprising levulinic acid and an acid with an organic solvent; extracting at least a portion of the levulinic acid from the first solution into the organic solvent, forming a second solution comprising the levulinic acid and the organic solvent; contacting the second solution with water; and extracting at least a portion of the levulinic acid from the second solution into water, forming a third solution comprising the levulinic acid and water, wherein the organic solvent comprises an alcohol.

2. The method of claim 1, wherein the alcohol comprises a C6 to C8 alcohol.

3. The method of claim 1 or 2, wherein the alcohol comprises at least one member selected from the group consisting of hexanol, heptanol, octanol, pentanol, and isoamyl alcohol.

4. The method of any one of claims 1-3, wherein the acid comprises a member selected from the group consisting of sulfuric acid, nitric acid, hydrochloric acid, hydrobromic acid, and p-toluenesulfonic acid.

5. The method of any one of claims 1-4, wherein: the second solution further comprises an ester of levulinic acid; and contacting the second solution with water converts at least a portion of the ester of levulinic acid to levulinic acid.

6. The method of claim 5, wherein the alcohol comprises hexanol and the ester of levulinic acid comprises hexyl levulinate.

7. The method of any one of claims 1-6, wherein the first solution comprises a volatile component, and the method further comprises removing the volatile component from the first solution.

8. The method of any one of claims 1-7, further comprising contacting a precursor material with the acid to form the first solution.

9. The method of claim 8, wherein the precursor material comprises at least one member selected from the group consisting of cellulose, lignocellulose, furfural, furfuryl alcohol, a sugar, and maleic anhydride.

10. The method of any one of claims 1-9, further comprising evaporating a portion of the water in the third solution.

11. The method of claim 10, wherein the concentration of levulinic acid in the third solution after evaporation is 60% to 90% by weight.

12. The method of claim 10 or 11, further comprising converting at least a portion of the levulinic acid to a member selected from the group consisting of ethyl levulinate, amino levulinic acid, succinic acid, acrylic acid, 3-hydroxypropionic acid, and diphenolic acid.

13. The method of any one of claims 1-12, further comprising separating the first solution and the second solution.

14. The method of any one of claims 1-13, further comprising separating the second solution and the third solution.

15. The method of any one of claims 1-14, wherein the ratio of water to second solution is 0.25: 1 to 5: 1 water:second solution.

16. A method of recovering levulinic acid, the method comprising: contacting a first solution with water, the first solution comprising an organic solvent and at least one member selected from the group consisting of levulinic acid and an ester of levulinic acid; and ​ forming a second solution comprising levulinic acid and water.

17. The method of claim 16, wherein the first solution comprises an ester of the levulinic acid, and contacting the first solution with water converts at least a portion of the ester of the levulinic acid to levulinic acid.

18. The method of claim 16 or 17, wherein the organic solvent comprises an alcohol.

19. The method of claim 18, wherein the ester of the levulinic acid comprises an ester formed from the reaction of levulinic acid with the alcohol.

20. The method of claim 18 or 19, wherein the alcohol comprises a C6 to C8 alcohol.

21. The method of any one of claims 18-20, wherein the alcohol comprises at least one member selected from the group consisting of hexanol, heptanol, octanol, pentanol, and isoamyl alcohol.

22. The method of any one of claims 18-21, wherein the alcohol comprises hexanol, and the ester of the levulinic acid comprises hexyl levulinate.

23. The method of any one of claims 16-22, further comprising evaporating a portion of the water in the second solution.

24. The method of claim 23, wherein the concentration of levulinic acid in the second solution after evaporation is from 60% to 90% by weight.

25. The method of claim 23 or 24, further comprising converting at least a portion of the levulinic acid to a member selected from the group consisting of ethyl levulinate, amino levulinic acid, succinic acid, acrylic acid, 3-hydroxypropionic acid, and diphenolic acid.

26. The method of any one of claims 16-25, further comprising separating the first solution and the second solution.

27. The method of any one of claims 16-26, wherein the ratio of water to first solution is from 0.25: 1 to 5: 1 water: first solution.

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