Preparation method of long-chain fatty acid

Abstract

The invention provides a preparation method of long-chain fatty acid, which comprises the following steps: mixing long-chain primary alcohol with 12-18 carbon atoms and alkali for the first time, and heating to react; and after the reaction is finished, cooling, mixing with water for the second time to form slurry, and then adding acid for acidification to obtain the long-chain fatty acid. The preparation method of the long-chain fatty acid provided by the invention has the characteristics of simple preparation process, few side reactions, easiness in purification, high product purity, high conversion rate, low cost and environmental protection.

Description

Technical Field

[0001] The invention belongs to the technical field of organic synthesis, and particularly relates to a method for preparing long-chain fatty acids. Background Art

[0002] Long-chain fatty acids are an important chemical product and intermediate chemical raw material with wide industrial applications.

[0003] CN101508639A discloses a method for preparing 4-alkyl fatty acids, which comprises using 4-alkylcyclohexanone and fatty aldehyde as raw materials, condensing, dehydrating, and hydrogenating to obtain 2-alkyl-4-alkylcyclohexanone, and then performing oxidation and decarbonylation reactions to obtain 4-alkyl fatty acids. The preparation method described in this technical solution has cumbersome steps and a complex process.

[0004] CN113004108A discloses a method for preparing an acid by oxidizing an alcohol or aldehyde with oxygen. The method comprises: using oxygen as an oxidant, an aldehyde as a raw material, and ferric nitrate, 2,2,6,6-tetramethylpiperidinium N-oxide, and an inorganic halide as catalysts in an organic solvent at room temperature under neutral conditions to oxidize the aldehyde to produce an acid; wherein the raw aldehyde is R2CHO; R2 includes a C1-C16 carbon chain, a C3-C8 carbon ring or heterocycle, an alkyl group containing fluorine, chlorine, bromine, iodine, an aromatic group, a heterocycle, an ester group, an ether bond, an alkynyl group, a double bond functional group, a terpenoid, or a steroid structure. The method is environmentally friendly, but requires a large amount of auxiliary reagents.

[0005] Existing methods for preparing fatty acids include alcohol condensation hydrogenation, strong oxidant redox methods, and indirect electrolysis, which are complex, costly, and highly polluting. Direct oxidation of alcohols with air is a green and environmentally friendly process, but it is difficult to scale up industrial production due to low conversion rates, large amounts of auxiliary reagents, and difficulty separating them.

[0006] Therefore, it is necessary to develop a method for preparing long-chain fatty acids with simple preparation process, few side reactions, easy purification, high conversion rate, and green environmental protection. Summary of the Invention

[0007] In view of the shortcomings of the prior art, the present invention aims to provide a method for preparing long-chain fatty acids, which has the characteristics of simple preparation process, few side reactions, easy purification, high product purity, high conversion rate, low cost, and environmental friendliness.

[0008] To achieve this object, the present invention adopts the following technical solutions:

[0009] The present invention provides a method for preparing a long-chain fatty acid. The method comprises the following steps: mixing a long-chain primary alcohol having 12 to 18 carbon atoms (e.g., 13, 14, 15, 16 or 17) with a base for a first time, reacting the mixture, and after the reaction, mixing the mixture with water for a second time to form a slurry, and then adding acid for acidification to obtain the long-chain fatty acid.

[0010] The present invention prepares long-chain fatty acids by melt dehydrogenating and acidifying long-chain primary alcohols with 12 to 18 carbon atoms in a single step under the action of a base. The preparation method is characterized by a simple preparation process, few side reactions, easy purification, high product purity, high conversion rate, low cost, and environmental friendliness. The present invention uses primary alcohols with an appropriate carbon chain number to prepare the corresponding fatty acids. The starting long-chain primary alcohol starting material with 12 to 18 carbon atoms has an appropriate boiling point. If the carbon chain is too small and too short, the alcohol has a low boiling point, and when the temperature rises above 220°C, the evaporation rate is high, resulting in a low yield. If the carbon chain is too small and too long, the conversion temperature is high, the conversion rate is low, and the yield is also low. Therefore, using alcohols with appropriate carbon chains to prepare the corresponding acids is a key factor in the industrial application value of this technology. Other types of alcohols, such as secondary and tertiary alcohols, can also produce fatty acids, but the technology has poor adaptability due to the multiple isomers produced.

[0011] In the present invention, the reaction is carried out in a reactor, and the exhaust hole of the reactor is introduced into a beaker filled with water through an extension tube. The gas generated during the reaction (the gas generated is hydrogen, which is insoluble in water) is introduced into the water to generate bubbles, and at the same time, impurities contained in the gas are also washed away. After the bubbles disappear or basically disappear, heating is stopped and the reaction is considered to be completed.

[0012] Preferably, the long-chain fatty acid is a long-chain fatty acid having 12 to 18 carbon atoms (eg, 13, 14, 15, 16 or 17).

[0013] Preferably, the long-chain primary alcohol having 12 to 18 carbon atoms has a boiling point of ≥250°C at normal pressure (e.g., 255°C, 260°C, 265°C, 275°C, 280°C, or 285°C). Generally, as the carbon chain lengthens, the boiling point increases. Dodecanol has a boiling point of 259°C at normal pressure and is liquid at room temperature. The long-chain primary alcohol having 12 to 18 carbon atoms is further preferably a long-chain primary alcohol having 14 to 16 carbon atoms.

[0014] In the present invention, normal pressure means 1 atm, and room temperature means 18-25°C (eg, 19°C, 20°C, 21°C, 22°C, 23°C, or 24°C, etc.).

[0015] In the present invention, the conversion rate of preparing long-chain fatty acids is higher by selecting long-chain primary alcohols with specific structures.

[0016] Preferably, the long-chain primary alcohol having 12 to 18 carbon atoms includes tetradecanol (CH3(CH2) 13 OH), isomers of tetradecanol, hexadecanol (CH3(CH2) 15 OH) or any one or a combination of at least two of the isomers of hexadecanol, more preferably tetradecanol and hexadecanol.

[0017] Preferably, the isomers of tetradecanol include any one or a combination of at least two of 2-pentylnonanol, 2-hexyloctanol or 2-butyldecanol.

[0018] Preferably, the isomers of hexadecanol include any one of 2-heptylnonanol, 2-hexyldecanol, or 2-pentylundecanol, or a combination of at least two thereof.

[0019] Preferably, the base includes any one of sodium hydroxide and / or potassium hydroxide or a combination of at least two thereof, more preferably potassium hydroxide.

[0020] Preferably, the molar ratio of the long-chain primary alcohol having 12 to 18 carbon atoms to the base is 1:1.1 to 1:1.5, for example, 1:1.15, 1:1.2, 1:1.25, 1:1.3, 1:1.35, 1:1.4 or 1:1.45.

[0021] Preferably, the first mixing further includes mixing with a catalyst.

[0022] Preferably, the catalyst comprises any one of ZnO, Fe2O3, Al2O3, La2O3 or CeO, or a combination of at least two thereof.

[0023] Preferably, the mass of the catalyst is 1% to 5% of the mass of the long-chain primary alcohol having 12 to 18 carbon atoms, for example, 1.5%, 2%, 2.5%, 3%, 3.5%, 4% or 4.5%.

[0024] Preferably, the temperature of the first mixing is 120°C to 140°C, for example, 122°C, 124°C, 126°C, 128°C, 130°C, 132°C, 134°C, 136°C or 138°C.

[0025] In the present invention, the temperature of the first mixing is 120°C to 140°C. The first mixing is to dissolve the solid base into the system to form a single phase, allowing the reaction to proceed in a homogeneous phase. If the temperature of the first mixing is too low, the solid base is added all at once. Since the solid base is insoluble in the long-chain primary alcohol having 12 to 18 carbon atoms as the starting material, the base is likely to be deposited in the dead space of the reactor, resulting in low utilization rate.

[0026] Preferably, the reaction temperature is 220-260°C, such as 225°C, 230°C, 235°C, 240°C, 245°C, 250°C or 255°C, and more preferably 230-260°C.

[0027] Preferably, the reaction time is 6 to 12 h, for example, 6.5 h, 7 h, 7.5 h, 8 h, 8.5 h, 9 h, 9.5 h, 10 h, 10.5 h, 11 h or 11.5 h.

[0028] Preferably, the temperature of the water is 60°C to 80°C, for example, 62°C, 64°C, 66°C, 68°C, 70°C, 72°C, 74°C, 76°C or 78°C.

[0029] Preferably, the mass ratio of the long-chain primary alcohol having 12 to 18 carbon atoms to water is 1:1 to 1:2, for example, 1:1.1, 1:1.2, 1:1.3, 1:1.4, 1:1.5, 1:1.6, 1:1.7, 1:1.8 or 1:1.9.

[0030] Preferably, the acid is a sulfuric acid solution.

[0031] Preferably, the concentration of the sulfuric acid solution is 2 to 6 mol / L, for example, 2.5 mol / L, 3 mol / L, 3.5 mol / L, 4 mol / L, 4.5 mol / L, 5 mol / L or 5.5 mol / L.

[0032] Preferably, the acid is added to a pH of 1 to 2, such as 1.1, 1.2, 1.3, 1.4, 1.5, 1.6, 1.7, 1.8 or 1.9.

[0033] Preferably, the acidification further includes the steps of water washing and reduced pressure distillation.

[0034] Preferably, the volume ratio of the oil phase to the water phase in the water washing is 1.8-2.2:1, for example, 1.85:1, 1.9:1, 1.95:1, 2.0:1, 2.05:1, 2.1:1 or 2.15:1, etc.

[0035] Preferably, the temperature of the reduced pressure distillation is 160-180°C (for example, 162°C, 164°C, 166°C, 168°C, 170°C, 172°C, 174°C, 176°C or 178°C, etc.), and the pressure is 0.001-0.01MPa (for example, 0.002MPa, 0.003MPa, 0.004MPa, 0.005MPa, 0.006MPa, 0.007MPa, 0.008MPa or 0.009MPa, etc.).

[0036] Preferably, the preparation method specifically includes the following steps: heating a long-chain primary alcohol with 12 to 18 carbon atoms to 120 to 140°C under stirring, adding a base and a catalyst in sequence for the first mixing, heating to 220 to 260°C for reaction, cooling after the reaction, mixing with water for the second time to form a slurry, and then adding acid for acidification to form an upper organic phase and a lower aqueous solution, washing the upper organic phase with water and performing reduced pressure distillation to obtain the long-chain fatty acid.

[0037] Preferably, the stirring speed is 300-400 r / min, for example, 320 r / min, 330 r / min, 340 r / min, 350 r / min, 360 r / min, 370 r / min, 380 r / min or 390 r / min.

[0038] Preferably, the heating rate is 3 to 8°C / min, for example, 3.5°C / min, 4°C / min, 4.5°C / min, 5°C / min, 5.5°C / min, 6°C / min, 6.5°C / min, 7°C / min or 7.5°C / min.

[0039] Preferably, the cooling is to a temperature ≤ 80°C, such as 30°C, 40°C, 50°C, 60°C or 70°C.

[0040] In the present invention, the cooling function is to ensure operational safety. The lower aqueous solution includes sulfate (such as sodium sulfate and / or potassium sulfate) and a small amount of catalyst metal ions, which can be distilled to produce sulfate byproducts in industrial production.

[0041] Compared with the prior art, the present invention has the following beneficial effects:

[0042] Long-chain fatty acids are prepared in a single step by melt dehydrogenation and acidification of long-chain primary alcohols having 12 to 18 carbon atoms in the presence of an alkali. The preparation method is characterized by a simple preparation process, few side reactions, easy purification, high product purity, high conversion rate, low cost, and environmental friendliness. The long-chain fatty acid preparation method of the present invention has a conversion rate of ≥74.9%, and the purity of the produced long-chain fatty acids is ≥91.0%. Preferably, the conversion rate is ≥93.5%, and the purity of the produced long-chain fatty acids is ≥98.3%. DETAILED DESCRIPTION

[0043] The technical solution of the present invention is further described below by way of specific embodiments. It should be understood by those skilled in the art that the embodiments are merely to help understand the present invention and should not be regarded as specific limitations of the present invention.

[0044] Example 1

[0045] The present embodiment provides a method for preparing a long-chain fatty acid, which comprises the following steps: adding tetradecanol (425 g, 1.98 mol, 500 mL) into a reactor equipped with a stirring system, a temperature control system, a vent, and a solid feeding port, wherein the vent is connected to a beaker filled with water through an extension tube, the sealing cover of the solid feeding port is closed, stirring and heating are started at a stirring speed of 350 r / min and a heating rate of 5°C / min, the temperature is raised to 120°C, potassium hydroxide (134 g, 2.39 mol) is slowly added from the solid feeding port and mixed, and then a catalyst (ZnO, 8.5 g) is added and mixed, the solid feeding port is closed, stirring is continued, and the temperature is raised to 250°C for reaction, and the reaction ends when the bubbles generated by the extension tube in the beaker filled with water disappear. The reaction is carried out for 12 hours. Stop stirring, cool naturally, and when the temperature drops to 80°C, mix with 80°C water (425g, 425mL) to form a slurry, and transfer it to a 2L volumetric flask. Use electromagnetic stirring and add 4mol / L sulfuric acid solution dropwise for acidification to pH 1 to form an upper organic phase and a lower aqueous solution. Wash the upper organic phase with water and perform vacuum distillation. The volume ratio of the oil phase to the aqueous phase in the water washing is 2:1. The temperature of the vacuum distillation is 165°C and the pressure is 0.002MPa to obtain the long-chain fatty acid.

[0046] The molar ratio of tetradecanol to potassium hydroxide is 1:1.2.

[0047] The mass of the catalyst is 2% of the mass of tetradecanol.

[0048] The mass ratio of the tetradecanol to water is 1:1.

[0049] Example 2

[0050] The present embodiment provides a method for preparing a long-chain fatty acid, which comprises the following steps: adding hexadecanol (481 g, 1.98 mol, 500 mL) into a reactor equipped with a stirring system, a temperature control system, a vent, and a solid feeding port, wherein the vent is connected to a beaker filled with water through an extension tube, the sealing cover of the solid feeding port is closed, stirring and heating are started at a stirring speed of 400 r / min and a heating rate of 3°C / min, the temperature is raised to 130°C, potassium hydroxide (145 g, 2.58 mol) is slowly added from the solid feeding port and mixed, and then a catalyst (Fe2O3, 5 g) is added and mixed, the solid feeding port is closed, stirring is continued, and the temperature is raised to 230°C for reaction, and the reaction ends when the bubbles generated by the extension tube in the beaker filled with water disappear. The reaction is carried out for 10 hours. Stop stirring, cool naturally, and when the temperature drops to 70°C, mix with 70°C water (720g, 720mL) to form a slurry, and transfer it to a 2L volumetric flask. Use electromagnetic stirring and add 2mol / L sulfuric acid solution dropwise for acidification to pH 2 to form an upper organic phase and a lower aqueous solution. Wash the upper organic phase with water and perform vacuum distillation. The volume ratio of the oil phase to the aqueous phase in the water washing is 2:1. The temperature of the vacuum distillation is 170°C and the pressure is 0.002MPa to obtain the long-chain fatty acid.

[0051] The molar ratio of hexadecanol to potassium hydroxide is 1:1.3.

[0052] The mass of the catalyst is 1% of the mass of hexadecanol.

[0053] The mass ratio of the hexadecanol to water is 1:1.5.

[0054] Example 3

[0055] The present embodiment provides a method for preparing a long-chain fatty acid, which comprises the following steps: adding tetradecanol (425 g, 1.98 mol, 500 mL) into a reactor equipped with a stirring system, a temperature control system, a vent, and a solid feeding port, wherein the vent is connected to a beaker filled with water through an extension tube, the sealing cover of the solid feeding port is closed, stirring and heating are started at a stirring speed of 300 r / min and a heating rate of 8°C / min, the temperature is raised to 140°C, potassium hydroxide (155 g, 2.76 mol) is slowly added from the solid feeding port and mixed, and then a catalyst (Al2O3, 20 g) is added and mixed, the solid feeding port is closed, stirring is continued, and the temperature is raised to 240°C for reaction. The reaction ends when the bubbles generated by the extension tube in the beaker filled with water disappear, and the reaction is carried out for 6 hours. Stop stirring, cool naturally, and when the temperature drops to 60°C, mix with 60°C water (850g, 850mL) to form a slurry, and transfer it to a 2L volumetric flask. Use electromagnetic stirring and add 6mol / L sulfuric acid solution dropwise for acidification to pH 1 to form an upper organic phase and a lower aqueous solution. Wash the upper organic phase with water and perform vacuum distillation. The volume ratio of the oil phase to the aqueous phase in the water washing is 2:1. The temperature of the vacuum distillation is 180°C and the pressure is 0.002MPa to obtain the long-chain fatty acid.

[0056] The molar ratio of tetradecanol to potassium hydroxide is 1:1.4.

[0057] The mass of the catalyst is 4.7% of the mass of tetradecanol.

[0058] The mass ratio of the tetradecanol to water is 1:2.

[0059] Example 4

[0060] This embodiment provides a method for preparing a long-chain fatty acid, which differs from Example 1 only in that the mass of potassium hydroxide is adjusted to 165 g, and the molar ratio of tetradecanol to potassium hydroxide is 1:1.48. Other steps are the same as in Example 1.

[0061] Example 5

[0062] This embodiment provides a method for preparing a long-chain fatty acid, which differs from Example 1 only in that the mass of potassium hydroxide is adjusted to 165 g, and the molar ratio of tetradecanol to potassium hydroxide is 1:1.12. Other steps are the same as in Example 1.

[0063] Example 6

[0064] This embodiment provides a method for preparing long-chain fatty acids, which differs from Example 1 only in that the catalyst (ZnO) is replaced with a catalyst (La2O3) of the same mass, and the rest is the same as Example 1.

[0065] Example 7

[0066] This embodiment provides a method for preparing long-chain fatty acids, which is the same as Example 1 except that the reaction temperature is adjusted to 260° C.

[0067] Example 8

[0068] This embodiment provides a method for preparing long-chain fatty acids, which is the same as Example 1 except that the reaction temperature is adjusted to 220°C.

[0069] Example 9

[0070] This embodiment provides a method for preparing a long-chain fatty acid, which is the same as that of Example 1 except that tetradecanol is replaced with dodecanol of the same mass.

[0071] Example 10

[0072] This embodiment provides a method for preparing a long-chain fatty acid, which is the same as that of Example 1 except that tetradecanol is replaced with octadecyl alcohol of the same mass.

[0073] Example 11

[0074] This embodiment provides a method for preparing a long-chain fatty acid, which is the same as Example 1 except that potassium hydroxide is replaced with sodium hydroxide in an equal molar amount.

[0075] Example 12

[0076] This comparative example provides a method for preparing a long-chain fatty acid, which differs from Example 1 only in that no catalyst (ZnO) is added, and other conditions are the same as those in Example 1.

[0077] Comparative Example 1

[0078] This comparative example provides a method for preparing a long-chain fatty acid, which differs from Example 1 only in that the tetradecanol is replaced with decanol of the same mass, and other conditions are the same as those in Example 1.

[0079] The conversion rate of long-chain primary alcohol or decanol having 12 to 18 carbon atoms as a raw material into long-chain fatty acids and the purity of the obtained long-chain fatty acids in the preparation methods of long-chain fatty acids provided in the above examples and comparative examples were tested.

[0080] The test results are shown in Table 1.

[0081] Table 1

[0082] Conversion rate (%) purity(%) Example 1 96.0 98.7 Example 2 95.4 99.2 Example 3 93.5 98.3 Example 4 96.5 98.4 Example 5 96.1 98.5 Example 6 94.7 98.2 Example 7 97.8 99.0 Example 8 81.5 93.8 Example 9 74.9 92.1 Example 10 87.4 91.0 Example 11 83.3 98.4 Example 12 89.0 98.1 Comparative Example 1 69.0 88.2

[0083] As can be seen from the contents of Table 1, the conversion rate of the long-chain fatty acid preparation method described in Examples 1-11 is ≥74.9%, and the purity of the obtained long-chain fatty acids is ≥91.0%. The conversion rate of the long-chain fatty acid preparation method described in Example 1-7 is ≥93.5%, and the purity of the obtained long-chain fatty acids is ≥98.3%.

[0084] From the comparison between Examples 1 and 6, it can be seen that when the catalyst (ZnO) is replaced with the catalyst (La2O3) of the same mass, the effects of the catalysts zinc oxide and lanthanum oxide are similar, and both have good catalytic effects.

[0085] Compared with Example 1, if the reaction temperature is lower (Example 8), the conversion rate and purity decrease. Therefore, it can be seen that the reaction temperature in the range of 230-260°C is more effective.

[0086] Comparison of Examples 1, 9, and 10 shows that if tetradecanol is replaced with the same mass of dodecanol (Example 9) or tetradecanol is replaced with the same mass of octadecanol (Example 10), both the conversion rate and the purity decrease. This shows that the effect is better when long-chain primary alcohols with 14-16 carbon atoms are selected.

[0087] Comparison of Examples 1 and 11 shows that if potassium hydroxide is replaced with the same molar amount of sodium hydroxide, the conversion rate decreases. This shows that the effect is better when potassium hydroxide is selected as the base.

[0088] Compared with Example 1, if the catalyst (ZnO) is not added (Example 12), the conversion rate is reduced, which shows that the effect is better under the catalysis of the catalyst.

[0089] Compared with Example 1, if tetradecanol is replaced with decanol of the same mass (Comparative Example 1), both the conversion rate and purity are reduced. This shows that the effect of selecting long-chain primary alcohols with 12 to 18 carbon atoms is better.

[0090] The applicant declares that the present invention uses the above-mentioned embodiments to illustrate the method for preparing a long-chain fatty acid, but the present invention is not limited to the above-mentioned embodiments, that is, it does not mean that the present invention must rely on the above-mentioned embodiments to be implemented. Those skilled in the art should understand that any improvements to the present invention, equivalent replacements of various raw materials for the products of the present invention, addition of auxiliary ingredients, selection of specific methods, etc., are all within the scope of protection and disclosure of the present invention.

Claims

1. A method for preparing long-chain fatty acids, characterized in that: The preparation method comprises the following steps: mixing a long-chain primary alcohol having 12 to 18 carbon atoms and a base for the first time, reacting the mixture, and mixing the mixture with water for the second time after the reaction to form a slurry, and then adding acid for acidification to obtain the long-chain fatty acid.

2. The preparation method according to claim 1, characterized in that The long-chain primary alcohol having 12 to 18 carbon atoms has a boiling point of ≥250°C at normal pressure and is liquid at room temperature; Preferably, the long-chain primary alcohol having 12 to 18 carbon atoms includes any one of tetradecanol, an isomer of tetradecanol, hexadecanol, or an isomer of hexadecanol, or a combination of at least two thereof.

3. The preparation method according to claim 1 or 2, characterized in that The base includes sodium hydroxide and / or potassium hydroxide; Preferably, the molar ratio of the long-chain primary alcohol having 12 to 18 carbon atoms to the base is 1:1.1 to 1:1.

5.

4. The preparation method according to any one of claims 1 to 3, characterized in that The first mixing also includes mixing with a catalyst; Preferably, the catalyst comprises any one or a combination of at least two of ZnO, Fe2O3, Al2O3, La2O3 or CeO; Preferably, the mass of the catalyst is 1% to 5% of the mass of the long-chain primary alcohol having 12 to 18 carbon atoms; Preferably, the temperature of the first mixing is 120-140°C.

5. The preparation method according to any one of claims 1 to 4, characterized in that The reaction temperature is 220-260°C; Preferably, the reaction time is 6 to 12 hours.

6. The preparation method according to any one of claims 1 to 5, characterized in that The temperature of the water is 60-80°C; Preferably, the mass ratio of the long-chain primary alcohol having 12 to 18 carbon atoms to water is 1:1 to 1:

2.

7. The preparation method according to any one of claims 1 to 6, characterized in that The acid is a sulfuric acid solution; Preferably, the concentration of the sulfuric acid solution is 2-6 mol / L.

8. The preparation method according to any one of claims 1 to 7, characterized in that The acid addition is to add acid until the pH value is 1-2.

9. The preparation method according to any one of claims 1 to 8, characterized in that The acidification step further includes washing with water and distilling under reduced pressure; Preferably, the volume ratio of the oil phase to the water phase in the water washing is 1.8-2.2:1; Preferably, the temperature of the reduced pressure distillation is 160-180° C., and the pressure is 0.001-0.01 MPa.

10. The preparation method according to any one of claims 1 to 9, characterized in that: The preparation method specifically comprises the following steps: heating a long-chain primary alcohol having 12 to 18 carbon atoms to 120 to 140° C. under stirring, successively adding a base and a catalyst for a first mixing, heating to 220 to 260° C. for reaction, cooling after completion of the reaction, mixing with water for a second time to form a slurry, then acidifying with acid to form an upper organic phase and a lower aqueous solution, washing the upper organic phase with water and performing reduced pressure distillation to obtain the long-chain fatty acid; Preferably, the stirring speed is 300-400 r / min; Preferably, the heating rate is 3-8°C / min; Preferably, the cooling is to a temperature of ≤80°C.