Impurity removal method in isostearic acid preparation process

Abstract

The invention relates to the technical field of chemical engineering, in particular to an impurity removal method in the isostearic acid preparation process. According to the impurity removal method, in the process of preparing isostearic acid by taking monomer acid as a raw material, a catalyst is added into a reaction system, and a catalytic hydrogenation reaction is performed in the presence of hydrogen, so that impurities in the reaction system are subjected to ring-opening conversion into stearic acid, and then impurity removal is realized and high-purity isostearic acid is obtained. The monomer acid is used as a raw material, the composite catalyst is used, kettle type hydrogenation reaction is carried out, the low iodine value requirement of a hydrogenation product is met, meanwhile, the impurity stearic acid lactone difficult to separate in the monomer acid raw material is converted into stearic acid, separation and purification of isostearic acid are easy, and the purity of isostearic acid is improved.

Description

Technical Field

[0001] This invention relates to the field of chemical technology, and in particular to a method for removing impurities during the preparation of isostearic acid. Background Technology

[0002] Isostearic acid, a branched-chain fatty acid, has wide applications in cosmetics, lubricants, and plastic additives due to its unique physicochemical properties, including a low melting point, excellent oxidative stability, good solubility, and lubricity. Currently, isostearic acid on the market is mainly prepared from monomeric acids, a byproduct of dimer acid production. Through hydrogenation, the C18 branched unsaturated fatty acids in the monomeric acid are converted into saturated fatty acids, followed by purification through separation. However, as a byproduct of dimer acid production, the monomeric acid also contains C12-C22 saturated unsaturated fatty acids, cyclic acids, and C18 lactone isomers. Conventional separation methods such as crystallization, molecular distillation, or rectification can separate several key substances, but cannot separate the C18 lactone, affecting the quality of isostearic acid. Chinese patent CN 115611729 A discloses a method for extracting isostearic acid from monoacids, and isostearic acid itself. The method involves separating and enriching branched-chain fatty acids through melt crystallization or distillation, using a nickel-based catalyst to hydrogenate and saturate the branched-chain fatty acids, and then purifying them to obtain isostearic acid. However, this process has drawbacks such as high hydrogenation reaction temperature, long reaction time, high hydrogen pressure requirements, and a relatively high iodine value in the resulting product. Furthermore, stearyl lactones in the impurities cannot be removed. Summary of the Invention

[0003] To address the problem of difficult separation of impurities in the aforementioned monomeric acids and high iodine values ​​in the products, this invention provides a method for removing impurities during the preparation of isostearic acid.

[0004] To achieve the above objectives, the technical solution adopted by the present invention is as follows: A method for removing impurities during the preparation of isostearic acid involves adding a catalyst to the reaction system and carrying out a catalytic hydrogenation reaction in the presence of hydrogen. This causes impurities in the reaction system to undergo ring-opening conversion into stearic acid, thereby achieving impurity removal and obtaining high-purity isostearic acid.

[0005] To elaborate further, The raw material monomeric acid and catalyst are placed in a high-pressure reactor, purged with nitrogen, stirred and heated to 160-180°C, and then hydrogen is introduced into the reaction system to a hydrogenation pressure of 2-4 MPa for catalytic hydrogenation reaction for 2-3 hours. The hydrogenation catalysis converts the long-chain unsaturated fatty acids in the raw material into saturated fatty acids, and at the same time, the impurity stearyl lactone in the system is converted into stearic acid through ring opening. Then the temperature is lowered to 60-70°C, purged with nitrogen, and the reactor is opened and discharged. After hot filtration, impurities are removed and high-purity isostearic acid is obtained.

[0006] The raw material monobasic acid is derived from by-product monobasic acid in processing dimer acid, wherein the isomerized oleic acid content is 30%-40%, and the stearic acid lactone content is 5%-7%.

[0007] The catalyst is added in an amount of 1%-5% of the mass of the raw material.

[0008] The catalyst is catalyst A and catalyst B, wherein the mass ratio of catalyst A to catalyst B is 2:1-2:1.5, the catalyst A is a noble metal supported catalyst, and the catalyst B is kaolin.

[0009] The catalyst A is a noble metal supported catalyst, the carrier is activated carbon, and the active component is at least one of Ag, Pt and Pd elements, and the loading amount is 0.5%-1%. Beneficial effects: The composite catalyst used in the application has higher efficiency in hydrogenation conversion of long-chain unsaturated fatty acid into saturated fatty acid, and the obtained hydrogenation product has lower iodine value. Meanwhile, stearic acid lactone in the system is converted into easily separated stearic acid, and the separation and purification difficulty of isostearic acid is reduced. BRIEF DESCRIPTION OF DRAWINGS

[0010] Figure 1 The product gas chromatogram provided for Example 1 of the application.

[0011] Figure 2 The product gas chromatogram provided for Comparative Example 2 of the application. DETAILED DESCRIPTION

[0012] In order to further understand the application, the preferred embodiments of the application are described below in combination with examples.

[0013] In the monobasic acid hydrogenation reaction in the preparation process of the application, the mutual promotion and synergistic effect of the composite catalysts can meet the requirement of low iodine value of the product, and can convert stearic acid lactone which is difficult to separate by conventional means into stearic acid which is easy to separate, thereby reducing the difficulty of subsequent separation process and reducing the process cost.

[0014] In the examples and comparative examples, the by-product monobasic acid obtained from the production of dimer acid by a certain company in Zhejiang is used as the raw material, wherein the stearic acid lactone content is 5%-7%.

[0015] In the following examples, the SiO2 content of kaolin is not less than 45%, and the Al2O 3 not less than 35%.

[0016] For determination of the content of hydrogenation product components, refer to AOCS Official Method Ce 1b-89.

[0017] Example 1 Impurity removal method in isostearic acid preparation process, comprising the following steps: (1) 180g of pretreated monomer acid, 3.6g of noble metal catalyst, and 1.8g of kaolin were added into a high-pressure reaction kettle, and nitrogen was replaced for three times and hydrogen was replaced for three times.

[0018] The noble metal catalyst is a Pd / C catalyst, and the loading amount is 0.5% (2) Hydrogen was introduced into the above reaction system to a pressure of 2.5MPa, the stirring speed was opened to 1000rpm, and the temperature was raised to 160℃ for 2h of heat preservation reaction; (3) After the reaction was completed, the temperature was cooled to 70℃, and after nitrogen replacement, the kettle was opened for filtration to obtain a hydrogenation product, and the catalyst was recovered (see Figure 1 ).

[0019] From Figure 1 It can be seen that no stearic acid lactone peak appears after hydrogenation reaction and chromatographic determination, that is, the purpose of impurity removal by hydrogenation is achieved.

[0020] Example 2 Impurity removal method in isostearic acid preparation process, comprising the following steps: (1) 180g of pretreated monomer acid, 7.2g of noble metal catalyst, and 3.6g of kaolin were added into a high-pressure reaction kettle, and nitrogen was replaced for three times and hydrogen was replaced for three times.

[0021] The noble metal catalyst is a Pd / C catalyst, and the loading amount is 1% (2) Hydrogen was introduced into the above reaction system to a pressure of 2.5MPa, the stirring speed was opened to 1000rpm, and the temperature was raised to 180℃ for 2h of heat preservation reaction; (3) After the reaction was completed, the temperature was cooled to 70℃, and after nitrogen replacement, the kettle was opened for hot filtration to obtain a hydrogenation product, and the catalyst was recovered.

[0022] Example 3 Impurity removal method in isostearic acid preparation process, comprising the following steps: (1) 180g of pretreated monomer acid, 3.6g of noble metal catalyst, and 1.8g of kaolin were added into a high-pressure reaction kettle, and nitrogen was replaced for three times and hydrogen was replaced for three times.

[0023] The noble metal catalyst is a Pd / C catalyst, and the loading amount is 1.5% (2) Hydrogen was introduced into the above reaction system to a pressure of 2MPa, the stirring speed was opened to 1000rpm, and the temperature was raised to 180℃ for 2h of heat preservation reaction; (3) After the reaction was completed, the temperature was cooled to 70℃, and after nitrogen replacement, the kettle was opened for filtration to obtain a hydrogenation product, and the catalyst was recovered.

[0024] Example 4 The impurity removal method in the preparation process of isostearic acid comprises the following steps: (1) 180g of pretreated monomer acid, 3.6g of noble metal catalyst, and 2.7g of kaolin were added to a high-pressure reaction kettle, and nitrogen was replaced three times and hydrogen was replaced three times.

[0025] The noble metal catalyst is a Pb / C catalyst with a loading of 0.5% (2) Hydrogen was introduced into the above reaction system to a pressure of 3MPa, the stirring speed was opened to 1000rpm, and the temperature was raised to 180℃ and kept for 2h; (3) After the reaction was completed, the temperature was cooled to 70℃, and after nitrogen replacement, the kettle was opened for filtration to obtain the hydrogenation product, and the catalyst was recovered.

[0026] In order to verify that the method of the present application has better effect, the following is taken as a reference to Example 1, and further explained in combination with multiple comparative examples.

[0027] Comparative Example 1 The difference from Example 1 is that in this comparative example, an equal amount of nickel-based catalyst is used instead of the composite catalyst of Example 1, and the other operations are the same as Example 1.

[0028] Comparative Example 2 The difference from Example 1 is that in this comparative example, kaolin is not added, and the other operations are the same as Example 1 (see Figure 2 ).

[0029] From Figure 2 It can be seen that after hydrogenation, a stearic acid lactone peak appears at a retention time of 22.8min as determined by chromatography, so it can be seen that impurity removal has not been achieved.

[0030] Comparative Example 3 The difference from Example 1 is that in this comparative example, the amount of kaolin added is 1.4g, and the other operations are the same as Example 1.

[0031] Comparative Example 4 The difference from Example 1 is that in this comparative example, the reaction temperature is 140℃, and the other operations are the same as Example 1.

[0032] Comparative Example 5 The difference from Example 1 is that in this comparative example, the reaction pressure is 1.5Mpa, and the other operations are the same as Example 1.

[0033] The lactone content of the hydrogenation product prepared in each of the above examples and comparative examples was detected by gas chromatography normalization method (referring to AOCS Official Method Ce 1b-89), as shown in Table 1.

[0034] Table 1

[0035] "\ " in the table is not detected.

[0036] From the data in Table 1, it can be seen that, relative to the comparative example, the present application uses Pd / C as the catalyst and kaolin as the monomer acid hydrogenation catalyst, the reaction temperature is 160-180℃, the hydrogen pressure is 2-3Mpa, the rotation speed is 1000rpm, and the reaction time is 2-3h, and the content of stearic acid lactone in the obtained product is less than 0.1%, and this process method, relative to the existing process, not only improves the product quality, but also reduces the process difficulty.

Claims

1. A method for removing impurities during the preparation of isostearic acid, characterized in that: A catalyst is added to the reaction system, and a catalytic hydrogenation reaction is carried out in the presence of hydrogen to open the ring of impurities in the reaction system and convert them into stearic acid, thereby achieving impurity removal and obtaining high-purity isostearic acid.

2. The method for removing impurities during the preparation of isostearic acid according to claim 1, characterized in that: The raw material monomeric acid and catalyst are placed in a high-pressure reactor, purged with nitrogen, stirred and heated to 160-180°C, and then hydrogen is introduced into the reaction system to a hydrogenation pressure of 2-4 MPa for catalytic hydrogenation reaction for 2-3 hours. The hydrogenation catalysis converts the long-chain unsaturated fatty acids in the raw material into saturated fatty acids, and at the same time, the impurity stearyl lactone in the system is converted into stearic acid through ring opening. Then the temperature is lowered to 60-70°C, purged with nitrogen, and the reactor is opened and discharged. After hot filtration, impurities are removed and high-purity isostearic acid is obtained.

3. The method for removing impurities during the preparation of isostearic acid according to claim 1 or 2, characterized in that: The raw material monoacid is derived from the monomeric acid byproduct of the processing of dimer acid, wherein the content of isomeric oleic acid is 30%~40% and the content of stearic acid lactone is 5%~7%.

4. The method for removing impurities during the preparation of isostearic acid according to claim 1 or 2, characterized in that: The catalyst is added at a rate of 1% to 5% of the raw material mass.

5. The method for preparing isostearic acid according to claim 4, characterized in that: The catalyst is catalyst A and catalyst B, wherein the mass ratio of catalyst A to catalyst B is 2:1 to 2:1.5, catalyst A is a noble metal supported catalyst, and catalyst B is kaolin.

6. The method for preparing isostearic acid according to claim 5, characterized in that: Catalyst A is a noble metal supported catalyst, with activated carbon as the support and at least one of Ag, Pt, and Pd elements as the active component, with a loading of 0.5% to 1%.

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