Fatty acid recovery and separation process

Abstract

A zero-discharge, low-temperature process for the recovery and separation of mixtures of mono- and di-acids (fatty acids) is disclosed that provides for the recovery and separation of mixtures of mono- and di-acids (fatty acids) in high yield and purity in a substantially short period of time.

Description

[Technical field]

[0001] The present invention relates to a novel process for the recovery and separation of fatty acids. More particularly, the present invention relates to a process for the separation and recovery of acids synthesized by oxidation of fatty acids oxidized using oxygen or ozone, which highly improves the yield and purity of the product. [Background technology]

[0002] Fatty acids are oxidized using strong oxidizing agents such as H2O2 and other agents to create low purity mixed acids with low yields of 60-80%. However, for cosmetic applications such as azelaic acid, a high purity product is desirable. Traditionally, this mixture of acids is separated by steam distillation at high temperatures or solvent extraction. However, for large scale operations involving very large volumes of solvent, steam distillation has significant limitations. High temperature processing is also less desirable for large scale operations.

[0003] One paper by Brenna et al. (Molecules 2020,25(8),1882;https: / / doi.org / 10.3390 / molecules25081882) reported the separation of a mixture of azelaic acid and pelargonic acid by repartitioning a mixture of ethyl acetate and hot acid (1:1 mixture of EtOAc and water at 50 °C for 1 h) to obtain an aqueous phase from which azelaic acid crystallized upon cooling. After three extraction cycles, azelaic acid could be recovered as a pure compound (>99% purity) in 73% yield. Pelargonic acid was isolated from the organic phase in 77% separation yield and 91% purity. The method requires cooling crystallization and is energy intensive.

[0004] One patent document, GB813842A, discloses a two-step oxidation of oleic acid using molecular oxygen followed by nitric acid to obtain a mixture of mono- and di-carboxylic acids (pelargonic acid and azelaic acid), which are then treated with various kinds of solvents for extraction, separation and purification. The recovery of the product in this method uses water for extraction, and the solubility in water is low at low temperatures, making the recovery of the product impossible.

[0005] Another patent document GB585315A discloses the formation of a mixture of pelargonic and azelaic acids in the oxidation of oleic acid with H2SO4, MnO2 and HNO3, the oxidation products being steam distilled. The use of acids and bases results in the wastewater containing dissolved solids, which require further treatment. The use of metal oxide catalysts requires additional steps to convert it into separable products. The recovery of azelaic acid does not occur from the aliphatic esters, but requires an additional extraction step.

[0006] Another patent document US2998439A discloses a process for the separation and recovery of monobasic and dibasic acids, for example the separation of pelargonic acid and azelaic acid, which uses the steps of countercurrently extracting a mixture of monobasic and dibasic acids between a polar solvent and a nonpolar solvent at a temperature of about 85°C above the dissociation temperature of the acid complex, with the ratio of the polar solvent feed rate to the acid feed rate being greater than about 5 and the ratio of the nonpolar solvent feed rate to the acid feed rate being about 1, cooling the polar solution and recovering the dibasic acid contained therein by crystallization, distilling the nonpolar solution, and separating the nonpolar solvent from the monobasic acid contained therein by distillation.

[0007] The polar solvent is water and the non-polar solvent can be any aliphatic hydrocarbon solvent with a boiling point up to 200° C. In this prior art, water and a hydrocarbon solvent with a boiling point up to 200° C. are used to recover azelaic acid. Moreover, temperatures above the dissociation temperature of the product are included, which actually creates new impurities.

[0008] Thus, there remains a need in the art to provide an acid recovery and separation process that is carried out at low temperatures, preferably at room temperature. Thus, there remains a need in the art to provide an acid recovery and separation process that is carried out at low temperatures, preferably at room temperature. It would be an additional commercially advantageous feature of the process if it provided a pure product in high yield. Summary of the Invention

[0009] (Objective of the Invention) The primary objective of the present invention is to provide an ambient temperature process for acid recovery and separation that provides the acid in high purity and high yield.

[0010] SUMMARY OF THEINVENTION Thus, to achieve the objectives of the present invention, the process for recovering and separating a mixture of mono-acids and di-acids comprises: a) dissolving a mixture of a first acid and a second acid to be recovered and separated in a specific ratio in a mixture of water and a first polar solvent; b) evaporating the first polar solvent to obtain an aqueous suspension of the acid; c) adding a second polar solvent to the suspension of step (b), wherein the boiling point of the first polar solvent is lower than the boiling point of the second polar solvent; obtaining separation of water and a solution of one acid in the second solvent; and d) evaporating the second solvent and adding a non-polar solvent to result in precipitation of the first or second acid and a solution of the first or second acid in the non-polar solvent; and e) filtering the solution of step d) to separate the first precipitated acid from the second acid remaining in the non-polar solvent.

[0011] In a preferred embodiment, the water and the first polar solvent are mixed in a specific ratio ranging from 5:95 to 15:85.

[0012] In a preferred embodiment, the first polar solvent is selected from acetone, isopropyl alcohol, acetonitrile, tetrahydrofuran, methanol, ethanol, dioxane, and the like.

[0013] In another preferred embodiment, the second polar solvent is selected from ethylene dichloride or an aliphatic ester, preferably ethyl acetate, butyl acetate and propyl acetate.

[0014] In yet another preferred embodiment, the non-polar solvent is selected from n-hexane, diethyl ether, butyl ether, pet ether, cyclopentyl methyl ether, n-pentane, and the like. [Brief description of the drawings]

[0015] [Figure 1] FIG. 1 shows a flow chart of the recovery and separation process for the mixture of mono- and di-acids. [Diagram 2] FIG. 2 shows the 1H NMR data of azelaic acid in DMSO-d6. [Diagram 3] FIG. 3 shows the 13C NMR data of azelaic acid in DMSO-d6. [Figure 4] FIG. 4 shows the 1H NMR data of pelargonic acid in DMSO-d6. [Diagram 5] FIG. 5 shows the 13C NMR data of pelargonic acid in DMSO-d6. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0016] The present invention will now be described in detail with reference to certain preferred and alternative embodiments so that its various aspects may be more fully understood and appreciated.

[0017] In describing the present invention, the terms "nonanoic acid" and "pelargonic acid" are used interchangeably and have the same meaning throughout the specification. Thus, to achieve the objectives of the present invention, the present invention provides a process for the recovery and separation of a mixture of mono- and di-acids, comprising the steps of: a) dissolving the mixture of the first acid and the second acid to be recovered and separated in a mixture of water and a first polar solvent in a ratio of 5:95; b) evaporating the first polar solvent to obtain an aqueous suspension of the acid; c) adding a second polar solvent to the suspension of step (b), wherein the boiling point of the first polar solvent is lower than the boiling point of the second polar solvent; obtaining separation of water and a solution of one acid in the second solvent; d) evaporating the second solvent and adding a non-polar solvent, resulting in precipitation of the first or second acid and a solution of the first or second acid in the non-polar solvent; and e) filtering the solution of step d) to separate the first precipitated acid from the second acid remaining in the non-polar solvent.

[0018] In another embodiment, the water and the first polar solvent are mixed in a specific ratio ranging from 5:95 to 15:85.

[0019] Specifically, water and the first polar solvent are mixed in specific ratios of 5:95, 8:92, 10:90, and 15:85.

[0020] In a preferred embodiment, the first polar solvent is selected from acetone, isopropyl alcohol, acetonitrile, tetrahydrofuran, methanol, ethanol, dioxane, and the like.

[0021] In another preferred embodiment, the second polar solvent is selected from ethylene dichloride or an aliphatic ester, preferably ethyl acetate, butyl acetate and propyl acetate.

[0022] In yet another preferred embodiment, the non-polar solvent is selected from n-hexane, diethyl ether, butyl ether, pet ether, cyclopentyl methyl ether, n-pentane, and the like.

[0023] Nonanoic acid is synthesized together with azelaic acid in the oxidation of oleic acid, but the two acids need to be separated to obtain them in high purity. The process of the present invention achieves both the objectives of high yield and high purity in a short period of time.

[0024] In one embodiment of the present invention, the process is carried out in batch or continuous mode.

[0025] Step (a) of the process is carried out at room temperature (20-30°C) and step (d) is carried out at a temperature ranging between 50 and 120°C.

[0026] The process overcomes the drawbacks of the prior art processes by being carried out at low temperatures ranging from 20° C. to 50° C., so that no impurities are formed and the acid is obtained with a purity of at least 90%.

[0027] In a preferred embodiment, the first and second acids recovered and separated are selected from a combination of at least two acids, such as azelaic acid, pelargonic acid, dodecanoic acid, 3-hydroxynonanoic acid, and tridecanedioic acid.

[0028] The process provides acid yields ranging from 80-100% and acid purities ranging from 90-99.0%.

[0029] In one embodiment, batch as well as continuous separation is carried out at room temperature using extraction and decantation techniques. Continuous separation protocols require smaller equipment sizes than batch processes. Separation of both products is carried out in pure form in a short time with complete recovery and recycling of the solvent. This process provides pure acid in less than 20 minutes versus several hours reported in the prior art. The average time for the prior art processes is about 6 hours.

[0030] In a preferred embodiment, the continuous separation protocol is 90% more energy efficient than conventional batch operations. The purity of azelaic acid and pelargonic acid recovered after separation is 90-99% without the need for further purification, see Figures 2, 3, 4 and 5.

[0031] Figure 2 shows the structure of azelaic acid. 1H NMR (400 MHz, DMSO-d6) δ = 11.96 (s, 2H), 2.17-2.20 (m, 4H), 1.45-1.50 (t, J = 6.4 Hz, 4H), 1.25 (br.s, 6H).

[0032] Figure 3 shows 13 C NMR (101 MHz, DMSO-d6) δ = 174.9, 34.0, 28.8, 24.9.

[0033] It can be seen from Figures 1 and 2 that only the azelaic acid peak was observed.

[0034] Figure 4 shows the structure of pelargonic acid. 1 H NMR (400MHz, DMSO-d6) δ = 10.51 (s, 1H), 2.35 (t, J = 7.57Hz, 2H), 1.61 (quin, J = 7.38Hz, 2H), 1.26-1.32 (m, 10H), 0.86-0.88 (m, 3H).

[0035] Figure 5 shows the structure of pelargonic acid. 13 C NMR (400 MHz, DMSO-d6) δ = 180.3, 34.0, 31.7, 29.0, 24.6, 22.6, 14.0.

[0036] From Figures 4 and 5, it can be inferred that only the peak for pelargonic acid is present.

[0037] Figure 1 shows a continuous process for the recovery and separation of fatty acids: a mixture of products resulting from the oxidation of oleic acid (containing significant proportions of azelaic and nonanoic acids) and water at room temperature is pumped independently by two different pumps into a Tee-mixer followed by a tubular reactor. The outlet of the tubular reactor is connected to another Tee-mixer and then to a tubular reactor where ethyl acetate is pumped alone. The outlet from the tubular reactor is fed into a continuous decanter from which the aqueous layer is decanted and the organic layer consisting of ethyl acetate is continuously fed to recover the ethyl acetate and PET ether is continuously added to the decanted mass to precipitate the azelaic acid. The precipitated mass is filtered to obtain azelaic acid powder and nonanoic acid remaining in the mother liquor.

[0038] example The following examples are illustrative and should not be construed as limiting the scope of the invention.

[0039] Example 1: Comparative Example: 2 g of a mixture of azelaic acid and nonanoic acid in water was taken. Up to 70% of the water could be evaporated under vacuum for 2 hours. When a non-polar solvent, i.e., PET ether (60 mL), was added to the remaining mass, some of the azelaic acid and nonanoic acid remaining in the PET ether solution precipitated along with the inseparable water fraction. The yields of recovered azelaic acid and nonanoic acid were 61% and 68%, respectively. The time required for separation of the mixed acids was 5-10 minutes, and the purity of azelaic acid and nonanoic acid was 98% and 78%, respectively.

[0040] Example 2: Comparative Example: This separation was carried out at 0°C. Quantitative amounts of water (50 mL) and ethyl acetate (50 mL) were added to 2 g of the mixture of azelaic acid and nonanoic acid. The aqueous layer was then decanted and the ethyl acetate was evaporated. A non-polar solvent, i.e., PET ether (60 mL), was added to the mixture of azelaic acid and nonanoic acid, which remained in the PET ether solution and precipitated. Nonanoic acid was quantitatively recovered by evaporating the PET ether. The yields of pure azelaic acid and nonanoic acid obtained by this method were 84% and 87%, respectively.

[0041] Example 3 (batch mode): This separation was carried out at 50°C. A quantitative amount of water (50 mL) and ethyl acetate (50 mL) were added to 2 g of the mixture of azelaic acid and nonanoic acid. The aqueous layer was then decanted and the ethyl acetate was evaporated. The mixture of azelaic acid and nonanoic acid was added with PET ether (60 mL), a non-polar solvent, which resulted in the precipitation of the azelaic acid and nonanoic acid remaining in the PET ether solution. The yields of pure azelaic acid and nonanoic acid obtained by this method were 86% and 92%, respectively.

[0042] Example 4 (batch mode): Using the mass obtained in Example 3, 20 ml of a non-polar solvent, i.e., PET ether, was added to the mixture of azelaic acid and nonanoic acid, which precipitated the remaining azelaic acid and nonanoic acid in the PET ether solution. Nonanoic acid was quantitatively recovered by evaporating the PET ether. The yields of pure azelaic acid and nonanoic acid obtained by this method were 90% and 86%, respectively.

[0043] Example 5 (Batch mode): Using the mass obtained in Example 3, 40 ml of a non-polar solvent i.e. PET ether was added to the mixture of azelaic acid and nonanoic acid, which resulted in the precipitation of azelaic acid and nonanoic acid remaining in the PET ether solution. The yields of pure azelaic acid and nonanoic acid obtained by this method were 88% and 90%, respectively.

[0044] Example 6 (Batch mode): Using the mass obtained in Example 3, 80 ml of a non-polar solvent i.e. PET ether was added to the mixture of azelaic acid and nonanoic acid, which resulted in the precipitation of azelaic acid and nonanoic acid remaining in the PET ether solution. The yields of pure azelaic acid and nonanoic acid obtained by this method were 89% and 91%, respectively.

[0045] Example 7 (Batch mode): Using the mass obtained in Example 3, 100ml of non-polar solvent i.e. PET ether was added to the mixture of azelaic acid and nonanoic acid, which resulted in precipitation of the remaining azelaic acid and nonanoic acid in the PET ether solution. The yields of pure azelaic acid and nonanoic acid obtained by this method were 84% and 88%, respectively.

[0046] Example 8 (Batch mode): Using the mass obtained in Example 3, 120 ml of a non-polar solvent i.e. PET ether was added to the mixture of azelaic acid and nonanoic acid, which resulted in the precipitation of azelaic acid and nonanoic acid remaining in the PET ether solution. The yields of pure azelaic acid and nonanoic acid obtained by this method were 88% and 91%, respectively.

[0047] Example 9 (Continuous Mode): In the continuous mode of operation, the mixture of acids dissolved in the solvent obtained in Example 3 was sent to a continuous distillation unit for recovering the organic solvent, and the high boiling residue (mixture of acids and water) continuously collected at the bottom of the distillation column was passed through a liquid-liquid extractor for extraction with polar solvent ethyl acetate (20 volumes relative to oleic acid). After the extraction was completed, the organic phase was continuously separated using a decanter and then sent to another distillation column, the organic solvent was recovered from the top, while the bottom mixture of acids was continuously fed into a tubular reactor together with non-polar solvent pet ether (20 volumes relative to oleic acid) to promote the precipitation of azelaic acid and nonanoic acid remaining in the solvent. Filtration of the discharge stream gave azelaic acid as the main product, and nonanoic acid in the mother liquor was transferred to the non-polar solvent. The yields of azelaic acid and nonanoic acid were 89% and 78%, respectively.

[0048] As shown in Examples 3 to 9 above, the purity of azelaic acid and nonanoic acid is 98%±0.5% and 78.5%±0.5%, respectively.

[0049] (Advantages of the Invention) Low temperature process ·Zero discharge process All solvents are recycled The process provides high yield and purity of the product -The time consumption of the process is greatly reduced

Claims

1. 1. A method for recovering and separating a mixture of mono-acids and di-acids, comprising the steps of: a) dissolving the mixture of the recovered and separated first and second acids in a mixture of water and a first polar solvent; b) evaporating the first polar solvent to obtain an aqueous suspension of acid; c) adding a second polar solvent to the suspension of step (b), wherein the boiling point of the first polar solvent is lower than the boiling point of the second polar solvent; obtaining separation of water and a solution of an acid in the second solvent; d) evaporating the second polar solvent and adding a non-polar solvent to result in precipitation of the first or second acid and a solution of the first or second acid in the non-polar solvent; and e) filtering the solution of step d) to obtain the first acid and the second acid separately.

2. 2. The method of claim 1, wherein the mixture of water and first polar solvent is in a ratio ranging from 5:95 to 15:

85.

3. 10. The method of claim 1 which is a batch or continuous process.

4. 2. The method of claim 1, wherein step (a) is carried out at a temperature in the range of 20-30°C and step (d) is carried out at a temperature in the range of 50°C to 120°C.

5. 2. The method of claim 1, wherein the first acid recovered and separated is azelaic acid.

6. 2. The method of claim 1, wherein the second acid recovered and separated is selected from the group consisting of nonanoic acid, dodecanoic acid, 3-hydroxynonanoic acid, tridecanedioic acid, or mixtures thereof.

7. 2. The method of claim 1, wherein the first polar solvent is selected from acetone, isopropyl alcohol, acetonitrile, tetrahydrofuran, methanol, ethanol, and dioxane.

8. 2. The process according to claim 1, wherein the second polar solvent is selected from ethylene dichloride or an aliphatic ester, preferably ethyl acetate, butyl acetate or propyl acetate.

9. 2. The method of claim 1, wherein the non-polar solvent is selected from n-hexane, diethyl ether, butyl ether, pet ether, cyclopentyl methyl ether, n-pentane.

10. 10. The method of claim 1, wherein the yield of the first acid is in the range of 61 to 90%.

11. 10. The process of claim 1, wherein the yield of the second acid is in the range of 68 to 92%.

12. 2. The method of claim 1, wherein the purity of the first acid is in the range of 98-99%.

13. 2. The method of claim 1, wherein the purity of the second acid is in the range of 78-79%.

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