Method for preparing high-purity cis-oleic acid through selective hydrogenation of vegetable oleic acid

Abstract

The invention discloses a method for preparing high-purity cis-oleic acid through selective hydrogenation of vegetable oleic acid, and belongs to the technical field of preparation of cis-oleic acid. Comprising the following steps: dissolving vegetable oleic acid in a solvent to form a mixed solution, and then introducing the mixed solution and mixed gas consisting of hydrogen and inert gas into a fixed bed reactor filled with a PdPt / C catalyst for hydrogenation reaction, thereby realizing selective hydrogenation of the vegetable oleic acid to generate high-purity cis-oleic acid. By accurately regulating and controlling the partial pressure of hydrogen in the mixed gas and the polarity type of the solvent, polyunsaturated fatty acids such as linoleic acid and the like can be efficiently hydrogenated, meanwhile, side reactions that oleic acid is excessively hydrogenated into stearic acid and a cis-structure is converted into a trans-isomer are remarkably inhibited, and finally, a cis-oleic acid product with high purity and high yield is obtained.

Description

TECHNICAL FIELD

[0001] The application relates to the technical field of cis-oleic acid preparation, and in particular to a method for preparing high-purity cis-oleic acid by selective hydrogenation of vegetable oleic acid. BACKGROUND

[0002] Cis-oleic acid (cis-C18:1) is an important monounsaturated fatty acid, which is widely used in the fields of medicine, food, cosmetics and special chemicals. The oleic acid in natural vegetable oleic acid (such as olive oil acid, rapeseed oil acid, etc.) usually coexists with other fatty acids, and may contain trans-isomers, which is difficult to directly meet the high-purity demand. At present, the preparation of high-purity cis-oleic acid mainly depends on methods such as hydrolysis, urea complexation or chromatographic separation of vegetable oleic acid, but these processes have problems such as high energy consumption, low yield or difficulty in scaling up.

[0003] The technology of preparing high-purity cis-oleic acid by selective hydrogenation of vegetable oleic acid provides a new idea for solving the above problems. Through precise control of the hydrogenation process, polyunsaturated fatty acids such as linolenic acid (C18:3) and linoleic acid (C18:2) can be selectively converted into cis-oleic acid. Compared with traditional methods, this route has potential advantages such as mild reaction conditions and easy separation of products. However, in actual industrial application, this technology still faces many challenges: first, the selectivity of conventional nickel-based or palladium-based catalysts for C=C bond hydrogenation is poor, which easily leads to over-hydrogenation to generate saturated products such as stearic acid (C18:0); second, under the hydrogenation reaction conditions, the cis-double bond of oleic acid is easy to isomerize into the thermodynamically more stable trans-structure; third, the catalyst is easy to be deactivated by carbon deposition due to the accumulation of products and raw materials, and has a short service life.

[0004] Iida et al. reported the hydrogenation reaction of soybean oil acid with 5% Pt / SiO2 as catalyst (Catalysis Communications, 2015, 62: 1-5), which can achieve 89.4% conversion rate under the condition of 0.5 MPa and 140℃, but the selectivity of cis-oleic acid is only 39.3%, and the high Pt loading leads to cost increase, which is difficult to be applied in large scale. The 0.5% Pt / γ-Al2O3 catalyst developed by Toshtay et al. (Molecular Catalysis, 2021, 513: 111819) significantly reduces the Pt loading, but only obtains 68.1% conversion rate and 49.7% cis-oleic acid selectivity under the condition of 0.5 MPa and 90℃ for hydrogenation of sunflower oil acid, and the effect of selective hydrogenation is still not satisfactory.

[0005] In summary, the existing catalytic system often presents a "seesaw" effect between conversion rate and selectivity, and it is difficult to simultaneously meet high conversion rate and high selectivity at low cost. There is still a lot of research space for the optimization and development of the method for preparing high-purity cis-oleic acid by selective hydrogenation of vegetable oil acid. Therefore, it is of great significance to develop a low-cost catalytic system with high activity, high cis-selectivity and good stability. SUMMARY

[0006] The purpose of the present application is to provide a method for preparing high-purity cis-oleic acid by selective hydrogenation of vegetable oil acid, to solve the problems raised in the background art.

[0007] To achieve the above-mentioned purpose, the present application provides a method for preparing high-purity cis-oleic acid by selective hydrogenation of vegetable oil acid, which comprises the following steps: dissolving vegetable oil acid in a solvent to form a mixed solution with a mass concentration of 10-50wt.%, and then passing the mixed solution and a mixed gas composed of hydrogen and inert gas into a fixed bed reactor containing a PdPt / C catalyst to perform a hydrogenation reaction. By adjusting the polarity type of the solvent and the partial pressure of hydrogen in the mixed gas, selective hydrogenation of vegetable oil acid to produce high-purity cis-oleic acid is realized.

[0008] Preferably, the vegetable oil acid is one or more of palm kernel oil oleic acid, soybean oil oleic acid, rapeseed oil oleic acid, linseed oil oleic acid, and sunflower seed oil oleic acid.

[0009] Preferably, the solvent is one or more of acetone, acetonitrile, ethanol, isopropanol, and tetrahydrofuran.

[0010] Preferably, the total pressure of the mixed gas is 0.3-1.0MPa, wherein the volume percentage of hydrogen is 5%-80%, and the inert gas is one or more of nitrogen, argon, and helium.

[0011] Preferably, before the hydrogenation reaction, the PdPt / C catalyst is reduced in situ in the fixed bed reactor for 2-6h at a reduction temperature of 300-500℃.

[0012] Preferably, during the hydrogenation reaction, the temperature is 40-100℃, the mass space velocity is 7.8-15.6h -1 , and the volume flow ratio of the mixed gas to the mixed solution is 50-200:1.

[0013] Preferably, the total metal loading of Pd and Pt in the PdPt / C catalyst is 0.5wt.%, and the molar ratio of Pd to Pt is 1:1.

[0014] Therefore, the application provides a method for preparing high-purity cis-oleic acid by selectively hydrogenating plant oil acid, which realizes efficient conversion of polyunsaturated fatty acid into high-purity cis-oleic acid by accurately regulating the hydrogen partial pressure in the mixed gas and the polarity type of the solvent, and the catalysis of the PdPt / C composite catalyst, and has the following core beneficial effects: (1) Inhibition of side reactions: the inert gas molecules in the mixed gas can effectively separate the hydrogen molecules, increase the difficulty of the hydrogen molecules reaching the catalyst and the surface of the reactants, and reduce the collision frequency of the hydrogen molecules and the reactants, thereby significantly inhibiting the excessive hydrogenation reaction of oleic acid (cis-C18:1) into stearic acid (C18:0), and inhibiting the isomerization side reaction of the cis double bond to the trans isomer.

[0015] (2) Improving cis selectivity: the selected polar solvent can surround and stabilize the semi-hydrogenated intermediate (C18:1) generated in the hydrogenation reaction through electrostatic interaction, effectively inhibiting the rotation of the carbon-carbon single bond of the intermediate, thereby generating cis-oleic acid (cis-C18:1) with high selectivity.

[0016] (3) Excellent comprehensive performance: the method of the application can realize an unsaturated fatty acid conversion rate of ≥90%, a cis-oleic acid selectivity of ≥80%, and high product purity; at the same time, it has the advantages of clean process, high reaction efficiency, strong adaptability of raw materials, controllable catalyst cost (low metal loading), good stability, etc., and is suitable for large-scale industrial production, and can meet the application needs of high-end markets for high-purity cis-monounsaturated fatty acids.

[0017] The technical solutions of the application will be further described in detail below with reference to the drawings and examples. BRIEF DESCRIPTION OF DRAWINGS

[0018] Figure 1 A schematic diagram of the reaction device used in the application. DETAILED DESCRIPTION

[0019] The technical solutions of the application will be further described in detail below with reference to the drawings and examples. Figure 1 It should be understood that these examples are only used to illustrate the application and are not used to limit the scope of the application, and any changes, modifications, substitutions, combinations, simplifications made without deviating from the spirit and principles of the application are equivalent replacement methods and are included in the protection scope of the application. In addition, it should be understood that after reading the content of the application, those skilled in the art can make various modifications or modifications to the application, and these equivalent forms also fall within the scope defined by the appended claims, and belong to the protection scope of the application.

[0020] The term "embodiment" is mentioned herein means that the specific features, structures or properties described in connection with the embodiment can be included in at least one embodiment of the present application. The term "embodiment" appearing in various places in the specification does not necessarily refer to the same embodiment, nor does it particularly limit the independence or association between other embodiments. In principle, in the present application, as long as there is no technical contradiction or conflict, the technical features mentioned in each embodiment can be combined in any way to form a corresponding implementable technical solution.

[0021] Unless otherwise defined, the meanings of the technical terms used herein are the same as those commonly understood by those skilled in the art to which the present application belongs; the use of related terms herein is only for the purpose of describing specific embodiments, and is not intended to limit the present application.

[0022] Unless otherwise specified, the reagents, instruments, equipment, etc. used in the present application are the reagents, instruments and equipment commonly used by those skilled in the art; the test standards use the national standards or international standards commonly used in the art, and no redundant description is made here.

[0023] As Figure 1 shown, the reaction device used for the following examples and comparative examples is shown in the figure, the mixed solution is delivered by a metering pump, mixed with a mixed gas controlled by a flow meter at the inlet of the reactor, and then enters the catalyst bed to occur hydrogenation reaction, and the product is collected after cooling and separation. This device is the existing device in the art, and no redundant specific statement is made here.

[0024] Example 1: Palm kernel oil oleic acid was dissolved in ethanol to obtain a palm kernel oil oleic acid solution with a mass concentration of 10 wt.%, and the palm kernel oil oleic acid solution was injected into a fixed bed reactor containing PdPt / C catalyst (total metal loading 0.5 wt.%, Pd and Pt molar ratio 1:1) with a mixed gas of 40 vol.% hydrogen and 60 vol.% argon for hydrogenation reaction. The volume flow ratio of the mixed gas to the palm kernel oil oleic acid solution was 100:1, the total pressure of the mixed gas was 0.3 MPa, the hydrogenation reaction temperature was 80°C, the mass space velocity was 9.5 h -1 .

[0025] Before the hydrogenation reaction, the PdPt / C catalyst was loaded into the fixed bed reactor, argon was first introduced as an inert gas to replace the air in the system, then switched to a hydrogen atmosphere, and heated to 400°C for 2h in situ reduction. After reduction, the temperature was lowered to the hydrogenation reaction temperature, the hydrogen and argon mixed gas atmosphere was switched, and then the subsequent hydrogenation reaction was started. The specific reaction results are shown in Table 1.

[0026] Example 2: The difference between this example and example 1 is that the volume percentage of hydrogen in the mixed gas is 20%, the volume percentage of argon is 80%, and other reaction parameters and conditions are unchanged, which are not repeated here. The specific reaction results are shown in Table 1.

[0027] Example 3: The difference between this example and example 1 is that the plant oil acid is soybean oil oleic acid, and other reaction parameters and conditions are unchanged, which are not repeated here. The specific reaction results are shown in Table 1.

[0028] Example 4: The difference between this example and example 1 is that the solvent is acetone, and other reaction parameters and conditions are unchanged, which are not repeated here. The specific reaction results are shown in Table 1.

[0029] Example 5: The difference between this example and example 1 is that the weight hourly space velocity is 11.1h -1 , and other reaction parameters and conditions are unchanged, which are not repeated here. The specific reaction results are shown in Table 1.

[0030] Example 6: The palm kernel oil oleic acid is dissolved in ethanol to obtain a palm kernel oil oleic acid solution with a mass concentration of 20wt.%, and the palm kernel oil oleic acid solution is injected into a fixed bed reactor containing PdPt / C catalyst (total metal loading 0.5wt.%, Pd and Pt molar ratio 1:1) with a mixed gas of volume percentage of 10% hydrogen and volume percentage of 90% argon for hydrogenation reaction. The volume flow ratio of the mixed gas to the palm kernel oil oleic acid solution is 100:1, the total pressure of the mixed gas is 1.0MPa, the reaction temperature is 90℃, and the weight hourly space velocity is 9.5h -1 .

[0031] Before hydrogenation reaction, the PdPt / C catalyst is subjected to in-situ reduction reaction in the fixed bed reactor, and the specific process of in-situ reaction is the same as that of example 1, which is not repeated here. The specific reaction results are shown in Table 1.

[0032] Example 7: The difference between this example and example 6 is that the plant oil acid is linseed oil oleic acid, and other reaction parameters and conditions are unchanged, which are not repeated here. The specific reaction results are shown in Table 1.

[0033] Example 8: Palm kernel oil oleic acid was dissolved in ethanol to obtain a palm kernel oil oleic acid solution with a mass concentration of 20 wt.%, and the palm kernel oil oleic acid solution was injected into a fixed bed reactor filled with a PdPt / C catalyst (total metal loading of 0.5 wt.%, Pd to Pt molar ratio of 1:1) to perform a hydrogenation reaction with a mixed gas of 50 vol.% hydrogen and 50 vol.% argon. The volume flow ratio of the mixed gas to the palm kernel oil oleic acid solution was 100:1, the total pressure of the mixed gas was 1.0 MPa, the reaction temperature was 80°C, and the mass space velocity was 9.5 h-1. -1 .

[0034] Before the hydrogenation reaction, the PdPt / C catalyst was subjected to an in-situ reduction reaction in the fixed bed reactor, and the specific process of the in-situ reaction was the same as that of Example 1, which is not repeated here. The specific reaction results are shown in Table 1.

[0035] Example 9: Palm kernel oil oleic acid was dissolved in ethanol to obtain a palm kernel oil oleic acid solution with a mass concentration of 40 wt.%, and the palm kernel oil oleic acid solution was injected into a fixed bed reactor filled with a PdPt / C catalyst (total metal loading of 0.5 wt.%, Pd to Pt molar ratio of 1:1) to perform a hydrogenation reaction with a mixed gas of 70 vol.% hydrogen and 30 vol.% argon. The volume flow ratio of the mixed gas to the palm kernel oil oleic acid solution was 100:1, the total pressure of the mixed gas was 1.0 MPa, the reaction temperature was 90°C, and the mass space velocity was 9.5 h-1. -1 .

[0036] Before the hydrogenation reaction, the PdPt / C catalyst was subjected to an in-situ reduction reaction in the fixed bed reactor, and the specific process of the in-situ reaction was the same as that of Example 1, which is not repeated here. The specific reaction results are shown in Table 1.

[0037] Example 10: The difference between this example and Example 9 is only that the vegetable oil acid is linseed oil oleic acid, and other reaction parameters and conditions remain unchanged, which are not repeated here. The specific reaction results are shown in Table 1.

[0038] Comparative Example 1: Palm kernel oil oleic acid was dissolved in ethanol to obtain a palm kernel oil oleic acid solution with a mass concentration of 10 wt.%, and the palm kernel oil oleic acid solution was injected into a fixed bed reactor filled with a PdPt / C catalyst (total metal loading of 0.5 wt.%, Pd to Pt molar ratio of 1:1) to perform a hydrogenation reaction with pure hydrogen. The volume flow ratio of the pure hydrogen to the palm kernel oil oleic acid solution was 100:1, the hydrogen pressure was 0.3 MPa, the reaction temperature was 80°C, and the mass space velocity was 9.5 h-1. -1 .

[0039] Before the hydrogenation reaction, the PdPt / C catalyst was subjected to an in-situ reduction reaction in a fixed bed reactor. The in-situ reaction was the same as that of Example 1, and thus will not be repeated here. The specific reaction results are shown in Table 1.

[0040] Comparative Example 2: Palm kernel oil oleic acid was dissolved in ethanol to obtain a palm kernel oil oleic acid solution with a mass concentration of 20 wt.%. The palm kernel oil oleic acid solution and pure hydrogen were injected into a fixed bed reactor containing a PdPt / C catalyst (total metal loading of 0.5 wt.%, Pd to Pt molar ratio of 1:1) to perform a hydrogenation reaction. The volume flow ratio of pure hydrogen to palm kernel oil oleic acid solution was 100:1, the hydrogen pressure was 1.0 MPa, the reaction temperature was 80°C, and the mass space velocity was 9.5 h -1 .

[0041] Before the hydrogenation reaction, the PdPt / C catalyst was subjected to an in-situ reduction reaction in a fixed bed reactor. The in-situ reaction was the same as that of Example 1, and thus will not be repeated here. The specific reaction results are shown in Table 1.

[0042] Comparative Example 3: The difference between Comparative Example 3 and Comparative Example 1 was that the hydrogen pressure was 0.12 MPa, and the other reaction parameters and conditions were unchanged, and thus will not be repeated here. The specific reaction results are shown in Table 1.

[0043] Comparative Example 4: The difference between Comparative Example 4 and Comparative Example 2 was that the hydrogen pressure was 0.5 MPa, and the other reaction parameters and conditions were unchanged, and thus will not be repeated here. The specific reaction results are shown in Table 1.

[0044] Comparative Example 5: Palm kernel oil oleic acid was dissolved in ethanol to obtain a palm kernel oil oleic acid solution with a mass concentration of 10 wt.%. The palm kernel oil oleic acid solution and pure hydrogen were injected into a fixed bed reactor containing a PdPt / C catalyst (total metal loading of 0.5 wt.%, Pd to Pt molar ratio of 1:1) to perform a hydrogenation reaction. The volume flow ratio of pure hydrogen to palm kernel oil oleic acid solution was 50:1, the hydrogen pressure was 0.12 MPa, the reaction temperature was 80°C, and the mass space velocity was 9.5 h -1 .

[0045] Before the hydrogenation reaction, the PdPt / C catalyst was subjected to an in-situ reduction reaction in a fixed bed reactor. The in-situ reaction was the same as that of Example 1, and thus will not be repeated here. The specific reaction results are shown in Table 1.

[0046] Comparative Example 6: Palm kernel oil oleic acid was dissolved in ethanol to obtain a solution of palm kernel oil oleic acid with a mass concentration of 20 wt.%, and the solution of palm kernel oil oleic acid was injected into a fixed bed reactor containing a PdPt / C catalyst (total metal loading 0.5 wt.%, Pd to Pt molar ratio 1:1) for hydrogenation reaction. The volume flow ratio of pure hydrogen to the solution of palm kernel oil oleic acid was 50:1, the hydrogen pressure was 0.5 MPa, the reaction temperature was 80°C, and the mass space velocity was 9.5 h -1 .

[0047] Before the hydrogenation reaction, the PdPt / C catalyst was subjected to an in-situ reduction reaction in the fixed bed reactor, and the specific process of the in-situ reaction was the same as that of Example 1, which is not repeated here. The specific reaction results are shown in Table 1.

[0048] Comparative Example 7: The difference from Example 1 is only that the solvent is cyclohexane, and other reaction parameters and conditions remain unchanged, which are not repeated here. The specific reaction results are shown in Table 1.

[0049] Table 1: Comparison of hydrogenation results of different examples and comparative examples

[0050] As can be seen from the data in Table 1, in all the representative plant oil acid selective hydrogenation processes of Examples 1-10, by using the mixed gas regulation system to control the hydrogen partial pressure and combining the use of polar solvents, the selectivity of cis-oleic acid (cis-C18:1) can be more than 80% while maintaining the conversion rate of plant oil acid to be more than 90%, which is significantly better than the level of the prior art.

[0051] The results of Comparative Examples 1-2 show that under the same reaction conditions, using pure hydrogen can improve the conversion rate, but the selectivity of cis-oleic acid is significantly reduced. Comparative Examples 3-4 further show that even if the pressure of pure hydrogen is adjusted to the same hydrogen partial pressure as the mixed gas, it is still impossible to achieve the same level of high cis-oleic acid selectivity. Comparative Examples 1 and 3 compared the reaction effects of different pressures under pure hydrogen conditions, and found that the selectivity of cis-oleic acid was only 31.9%. Comparative Examples 5-6 reduced the volume flow ratio of pure hydrogen to plant oil acid while maintaining the same hydrogen partial pressure as the mixed gas, but the selectivity of cis-oleic acid hardly improved. When non-polar solvent cyclohexane was used in Comparative Example 7, the conversion rate increased slightly, but the selectivity of cis-oleic acid was 52.6%, which was lower than the cis-oleic acid selectivity of all examples.

[0052] That is, the comparative example 1-6 uses pure hydrogen as the reaction gas, even if adjusting the hydrogen pressure or volume flow ratio, the cis-oleic acid selectivity is only 25.6%~35.5%, indicating that the introduction of inert gas in the mixed gas is the key factor to inhibit the side reaction and improve the selectivity. The comparative example 7 uses non-polar solvent cyclohexane, although the C18:1 selectivity reaches 91.7%, but the cis-oleic acid selectivity is only 52.6%, far lower than the level of the example, proving that the polar solvent has an irreplaceable role in stabilizing the semi-hydrogenation intermediate and improving the cis-selectivity.

[0053] In summary, by accurately regulating the hydrogen partial pressure of the mixed gas and the solvent polarity, the present application realizes the efficient selective hydrogenation of linolenic acid, linoleic acid and other highly unsaturated fatty acids, thereby obtaining high-purity cis-oleic acid.

[0054] Finally, it should be noted that: the above examples are only used to illustrate the technical solutions of the present application rather than limit it, although the present application has been described in detail with reference to the preferred embodiments, those skilled in the art should understand that: it can still modify or equivalently replace the technical solutions of the present application, and these modifications or equivalent replacements also cannot make the modified technical solutions deviate from the spirit and scope of the technical solutions of the present application.

Claims

1. A process for the production of high purity cis-oleic acid by selective hydrogenation of a vegetable oil acid, characterized in that: The vegetable oil acid is dissolved in a solvent to form a mixed solution with a mass concentration of 10-50 wt.%, and then the mixed solution is introduced into a fixed bed reactor containing a PdPt / C catalyst together with a mixed gas composed of hydrogen and an inert gas to perform a hydrogenation reaction, so that high-purity cis-oleic acid is generated by selectively hydrogenating the vegetable oil acid by adjusting the type of polarity of the solvent and the partial pressure of hydrogen in the mixed gas.

2. The method for preparing high purity cis-oleic acid by selective hydrogenation of vegetable oil acid according to claim 1, characterized in that: The vegetable oil acid is one or more of palm kernel oil oleic acid, soybean oil oleic acid, rapeseed oil oleic acid, linseed oil oleic acid, and sunflower seed oil oleic acid.

3. The method for preparing high purity cis-oleic acid by selective hydrogenation of vegetable oil acid according to claim 1, characterized in that: The solvent is one or more of acetone, acetonitrile, ethanol, isopropanol, and tetrahydrofuran.

4. The method for preparing high purity cis-oleic acid by selective hydrogenation of vegetable oil acid according to claim 1, characterized in that: The total pressure of the mixed gas is 0.3-1.0 MPa, wherein the volume percentage of hydrogen is 5%-80%, and the inert gas is one or more of nitrogen, argon, and helium.

5. The method for preparing high purity cis-oleic acid by selective hydrogenation of vegetable oil acid according to claim 1, characterized in that: Before the hydrogenation reaction, the PdPt / C catalyst is reduced in situ in the fixed bed reactor for 2-6 h at a reduction temperature of 300-500℃.

6. The method for preparing high purity cis-oleic acid by selective hydrogenation of vegetable oil acid according to claim 1, characterized in that: The temperature during the hydrogenation reaction is 40-100℃, the mass space velocity is 7.8-15.6h -1 , and the volume flow ratio of the mixed gas to the mixed solution is 50-200:

1.

7. The method for preparing high purity cis-oleic acid by selective hydrogenation of vegetable oil acid according to claim 1, characterized in that: The total metal loading of Pd and Pt in the PdPt / C catalyst is 0.5 wt.%, and the molar ratio of Pd to Pt is 1:1.

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