Stearic acid preparation method based on DMAP compound catalyst and biuret inclusion technology

Abstract

The invention discloses a stearic acid preparation method based on a DMAP (dimethylaminopyridine) compound catalyst and a biuret inclusion technology, unique 4-dimethylaminopyridine and 1-butyl-3-methylimidazolium tetrafluoroborate are compounded to serve as a catalyst, and the product yield and content are greatly improved. The compounded catalyst can assist hydrolysis reaction under low-temperature and normal-pressure conditions, so that the reaction time is shortened, and the energy consumption is reduced. The invention accidentally finds that biuret can selectively clathrate stearic acid to obtain a high-purity stearic acid product, a three-dimensional hydrogen bond network is constructed by utilizing multiple hydrogen bond interaction between an NH group in a biuret molecule and stearic acid carboxyl, high-selectivity clathration of stearic acid is realized, and the high-selectivity clathration of stearic acid is realized. Impurities such as glycerol, monoester and the like are effectively repelled due to steric hindrance or polarity mismatching, the purity of the product can be increased from 85-90% of a crude product to more than or equal to 99% through one-step purification, the content of free glycerol is less than or equal to 0.1%, and the yield of stearic acid and fatty acid can reach 92%. The recovery rate of the biuret after thermal unpacking is greater than or equal to 90%, and green and environment-friendly effects are realized.

Description

Technical Field

[0001] The invention relates to the technical field of organic chemistry, and in particular to a method for preparing stearic acid based on a DMAP composite catalyst and biuret inclusion technology. Background Art

[0002] Stearic acid (octadecanoic acid), as a long-chain saturated fatty acid, is an important basic raw material in the field of oil and fat chemical industry. It is widely used in daily chemical products (such as soaps and moisturizers), plastic industry (as stabilizers and lubricants), food processing (emulsifiers) and pharmaceutical preparations (tablet excipients) and other fields. With the upgrading of consumption and the development of high-end manufacturing, the market demand for high-purity stearic acid (≥99%) continues to grow, especially food-grade and pharmaceutical-grade products must meet strict impurity control standards (such as free glycerol ≤0.1%, ash content ≤0.05%). However, the existing production process has significant bottlenecks in catalytic efficiency, product purity and environmental friendliness, which seriously restricts the upgrading of the industry.

[0003] Industrially, stearic acid is primarily produced through the hydrolysis of animal and vegetable oils (such as beef tallow and palm oil), with the core goal being to break the ester bonds in triglycerides. The current mainstream process still relies on alkaline catalytic hydrolysis, which, while cost-effective, has significant drawbacks. Its harsh reaction conditions require high temperatures and high pressures, and the hydrolysis reaction time is long. High temperatures can easily induce carbonization and sulfonation side reactions. Traditional stearic acid separation and purification techniques rely heavily on multi-stage solvent crystallization, a process characterized by high energy consumption and low yields. The industrial production of stearic acid has long been constrained by multiple technical bottlenecks, with core challenges centered on the imbalance between catalytic system efficiency and stability, the conflict between separation and purification energy consumption and yield, and the difficulty in balancing environmental protection and economic efficiency. Furthermore, high temperatures can induce carbonization and sulfonation side reactions. Therefore, finding an efficient, high-yield, and highly operable method for preparing stearic acid is imperative. Summary of the Invention

[0004] The object of the present invention is to provide a method for preparing stearic acid based on a DMAP composite catalyst and biuret inclusion technology.

[0005] To achieve the above objectives, the present invention adopts the following technical solutions:

[0006] The present invention discloses a method for preparing stearic acid based on a DMAP composite catalyst and biuret inclusion technology, comprising the following steps:

[0007] 1) Refined palm oil and purified water are mixed in a reaction kettle at a mass ratio of 1:1 to 3 and stirred; a composite catalyst of 4-dimethylaminopyridine (DMAP) and an ionic liquid is added, and an ultrasonic probe is immersed in the reaction solution. The ultrasonic probe is intermittently applied at a frequency of 20 to 40 Hz and a hydrolysis reaction is carried out at low temperature and normal pressure for 2 to 4 hours to produce fatty acids and glycerol;

[0008] 2) directly separating the hydrolyzate and removing glycerol to obtain a mixed fatty acid, adding a mixed solvent of water and ethanol and stirring, adding biuret and carrying out an inclusion reaction at 40-60° C. for 1-3 hours, cooling to room temperature after the reaction, and filtering and separating to obtain an inclusion complex of stearic acid and biuret;

[0009] 3) adding the inclusion complex of stearic acid and biuret to water, heating the mixture to 70-90° C. for decomposition for 1-3 hours to obtain an upper oil layer, drying the oil layer under reduced pressure to obtain high-purity stearic acid, and cooling the aqueous phase to crystallize and separate the biuret, which is then dried and recycled.

[0010] As a further improvement, the ionic liquid in step 1) of the present invention is a 4-lutidine DMAP to 1-butyl-3-methylimidazolium tetrafluoroborate ionic liquid having a mass ratio of 1:0.5 to 2.

[0011] As a further improvement, the composite catalyst in step 1) of the present invention is 0.5-3% of the mass of the refined palm oil.

[0012] As a further improvement, the temperature of the hydrolysis reaction in step 1) of the present invention is 70-90°C.

[0013] As a further improvement, the mass ratio of ethanol to water in step 2) of the present invention is 2 to 5:1.

[0014] As a further improvement, in step 2) of the present invention, the mass ratio of the mixed solvent to the refined palm oil is 1.5 to 4:1.

[0015] As a further improvement, in step 2) of the present invention, the mass ratio of biuret to refined palm oil is 0.3-0.6:1.

[0016] As a further improvement, the purity of the stearic acid prepared by the present invention can reach 99.5%, and the yield is 92%.

[0017] The present invention discloses a method for preparing stearic acid, comprising the following steps:

[0018] The beneficial effects of the present invention are as follows:

[0019] The present invention utilizes a unique combination of 4-dimethylaminopyridine and 1-butyl-3-methylimidazolium tetrafluoroborate as a catalyst, resulting in not only excellent catalytic performance but also significantly improved product yield and content. 4-Dimethylaminopyridine is a novel, highly efficient catalyst widely used in chemical synthesis. The combined catalyst can assist in the hydrolysis reaction at low temperature and atmospheric pressure, reducing reaction time and energy consumption.

[0020] This invention utilizes ultrasound to assist in the stirring process of heterogeneous materials. The intense turbulence and micro-scale mixing generated by cavitation significantly enhance molecular-scale mixing, which is crucial for rapid reactions or processes sensitive to mixing scales. For reactions limited by mass transfer, enhanced mass transfer can accelerate the primary reaction rate and inhibit side reactions. Furthermore, no acid or base is introduced during the glycerol separation step, achieving direct separation and reducing impurity sources.

[0021] The present invention unexpectedly discovered that biuret can selectively enclose stearic acid to obtain a high-purity stearic acid product. By utilizing the multiple hydrogen bonds between the NH group and the stearic acid carboxyl group in the biuret molecule, a three-dimensional hydrogen bond network is constructed to achieve high-selectivity enclosed stearic acid (selectivity coefficient ≥ 50). Impurities such as glycerol and monoesters are effectively excluded due to steric hindrance or polarity mismatch. One-step purification can increase the product purity from 85% to 90% of the crude product to ≥ 99%, with a free glycerol content of ≤ 0.1%. Compared to traditional multi-stage crystallization, biuret enclosed is completed under mild conditions, with energy consumption reduced by more than 60%, and the inclusion compound is rapidly crystallized by solvent-temperature coordinated regulation. The filtration rate is increased by 3 times, and the stearic acid yield can reach 92%. The recovery rate of biuret after hot water decomposition is ≥ 90%, and the ethanol-water mixed solvent is reused by distillation to achieve green environmental protection. DETAILED DESCRIPTION

[0022] The present invention discloses a method for preparing stearic acid based on a DMAP composite catalyst and biuret inclusion technology. The technical solution of the present invention is further described in detail below in conjunction with specific examples, but the scope of the present invention is not limited to the examples.

[0023] Example 1

[0024] 1) 1000 g of refined palm oil, 1000 g of purified water, and 5 g of a composite catalyst (4-dimethylaminopyridine:ionic liquid mass ratio = 1:0.5) were added to a reactor, stirring was started, an ultrasonic probe was inserted into the reaction solution, and intermittent ultrasonic treatment was started at a frequency of 20 Hz. The temperature was raised to 70° C. and the reaction was completed for 4 hours to obtain a mixture of fatty acids and glycerol.

[0025] 2) The obtained hydrolyzate was directly separated and glycerol was removed, and then 1500 g of a mixed solvent of ethanol and water (mass ratio of 2:1) was added, stirring was started, 300 g of biuret was added, and the temperature was raised to 40° C. for inclusion reaction. After 3 hours, the temperature was cooled to room temperature and filtered to separate the inclusion complex of stearic acid and biuret.

[0026] 3) adding the inclusion compound of stearic acid and biuret to water and heating the mixture to 70° C. for 3 hours, separating the mixture into layers to obtain an upper stearic acid oil layer, and drying the layer under reduced pressure at 70° C. to obtain high-purity stearic acid with a yield of 88% and a purity of 99.2%. The aqueous phase is cooled and crystallized to separate the biuret, which is then dried and recycled.

[0027] Example 2

[0028] 1) 1000 g of refined palm oil, 2000 g of purified water, and 15 g of a composite catalyst (4-dimethylaminopyridine:ionic liquid mass ratio = 1:1.5) were added to a reactor, stirring was started, an ultrasonic probe was inserted into the reaction solution, and intermittent ultrasonic treatment was started at a frequency of 30 Hz. The temperature was raised to 80° C. and the reaction was completed for 2 hours to obtain a mixture of fatty acids and glycerol.

[0029] 2) The obtained hydrolyzate was directly separated and glycerol was removed, and then 3000 g of a mixed solvent of ethanol and water (mass ratio of 3:1) was added, stirring was started, 450 g of biuret was added, and the temperature was raised to 50° C. for inclusion reaction. After 2 hours, the temperature was cooled to room temperature and filtered to separate the inclusion complex of stearic acid and biuret.

[0030] 3) adding the inclusion compound of stearic acid and biuret to water and heating the mixture to 80° C. for 2 hours, separating the mixture into layers to obtain an upper stearic acid oil layer, and drying the layer under reduced pressure at 70° C. to obtain high-purity stearic acid with a yield of 92% and a purity of 99.5%. The aqueous phase is cooled and crystallized to separate the biuret, which is then dried and recycled.

[0031] Example 3

[0032] 1) 1000 g of refined palm oil, 3000 g of purified water, and 30 g of a composite catalyst (4-dimethylaminopyridine:ionic liquid mass ratio = 1:2) were added to a reactor, stirring was started, an ultrasonic probe was inserted into the reaction solution, and intermittent ultrasonic treatment was started at a frequency of 40 Hz. The temperature was raised to 90° C. and the reaction was completed for 3 hours to obtain a mixture of fatty acids and glycerol.

[0033] 2) The obtained hydrolyzate was directly separated and glycerol was removed, and then 4000 g of a mixed solvent of ethanol and water (mass ratio of 5:1) was added, stirring was started, 600 g of biuret was added, and the temperature was raised to 60° C. for inclusion reaction. After 1 hour, the temperature was cooled to room temperature and filtered to separate the inclusion complex of stearic acid and biuret.

[0034] 3) adding the inclusion compound of stearic acid and biuret to water and heating the mixture to 90° C. for 1 hour, separating the mixture into layers to obtain an upper stearic acid oil layer, and drying the layer under reduced pressure at 70° C. to obtain high-purity stearic acid with a yield of 83% and a purity of 99%. The aqueous phase is cooled and crystallized to separate the biuret, which is then dried and recycled.

[0035] Comparative Example 1

[0036] Only 1.5 g of 4-dimethylaminopyridine was added in the first step of the reaction. Other conditions were the same as those in Example 2. The reaction time was extended to 6 hours to complete the reaction. The recovery rate of stearic acid was 75% and the purity was 80%.

[0037] It can be seen that, compared with Example 2, in Control Example 1, a single catalyst is used instead of a composite high-efficiency catalyst, resulting in poor catalytic effect, low degree of hydrolysis, long reaction time, and a decrease in the recovery rate of stearic acid of only 85%.

[0038] Comparative Example 2

[0039] Ultrasonic assistance was removed from the system, and only conventional stirring was used. Other conditions were the same as in Example 2, except that the reaction temperature was increased to 100° C. and the reaction time was extended to 8 hours. The recovery rate of stearic acid was 73% and the purity was 78%.

[0040] It can be seen that compared with Example 2, in Control Example 2, no ultrasonic assistance was used during the reaction process, resulting in difficulty in mass transfer in the heterogeneous system, prolonged reaction time, and reduced conversion rate, resulting in a low yield of stearic acid and a purity of only 78%.

[0041] Comparative Example 3

[0042] The subsequent purification of stearic acid used a urea bag and technology, and the other conditions were the same as in Example 2. The stearic acid recovery yield was 75% and the purity was 82%.

[0043] Visible, reference example 3 is contrasted with embodiment 2, and what used in inclusion stearic acid in reference example 3 is urea inclusion, and its stearic acid inclusion rate is lower than biuret, causes its yield reduction to be only 75%, purity is only 82%, and in crystallization recovery process, energy consumption is higher (needing lower crystallization temperature).Its circulation repeatedly utilizes the rate of recovery of rear urea and greatly declines, is far less than biuret.

[0044] Comparative Example 4

[0045] 1) 1000 g of refined palm oil, 2000 g of purified water, and 15 g of sodium hydroxide were added to an autoclave, stirred, heated to 160° C., and reacted under a pressure of 1.0 MPa for 6 hours to obtain a mixture of fatty acids and glycerol.

[0046] 2) 15% hydrochloric acid was added to adjust the pH to 6 and the glycerol was removed by separation.

[0047] 3) The crude product was put into n-hexane-methanol for precipitation, and stearic acid was obtained by multi-stage solvent crystallization and filtration. The yield was only 65% ​​and the purity was 70%.

[0048] It can be seen that, compared with Example 2, Control Example 4 uses a traditional alkaline catalyst, and does not use a composite high-efficiency catalyst, the catalytic effect is poor, the reaction conditions are harsh, high temperature and high pressure are required, and the reaction time is long, the degree of hydrolysis is not high, hydrochloric acid is used to adjust the pH, unnecessary impurities are introduced, and the subsequent separation and purification process does not use biuret inclusion technology, the energy consumption is high, and continuous production is difficult, resulting in a significant decrease in its yield, only 65%, and the purity is not high, only 70%.

[0049] Finally, it should be noted that the above examples are merely specific implementation examples of the present invention. Obviously, the present invention is not limited to the above examples and is subject to numerous variations. All variations that can be directly derived or conceived by a person of ordinary skill in the art from the disclosure of the present invention should be considered within the scope of protection of the present invention.

Claims

1. A method for preparing stearic acid based on a DMAP composite catalyst and biuret inclusion technology, characterized in that: The following steps are involved: 1) Refined palm oil and purified water are mixed in a reaction kettle at a mass ratio of 1:1 to 3 and stirred; a composite catalyst of 4-dimethylaminopyridine (DMAP) and an ionic liquid is added, and an ultrasonic probe is immersed in the reaction solution. The ultrasonic probe is intermittently applied at a frequency of 20 to 40 Hz and a hydrolysis reaction is carried out at low temperature and normal pressure for 2 to 4 hours to produce fatty acids and glycerol; 2) directly separating the hydrolyzate and removing glycerol to obtain a mixed fatty acid, adding a mixed solvent of water and ethanol and stirring, adding biuret and carrying out an inclusion reaction at 40-60° C. for 1-3 hours, cooling to room temperature after the reaction, and filtering and separating to obtain an inclusion complex of stearic acid and biuret; 3) adding the inclusion complex of stearic acid and biuret to water, heating the mixture to 70-90° C. for decomposition for 1-3 hours to obtain an upper oil layer, drying the oil layer under reduced pressure to obtain high-purity stearic acid, and cooling the aqueous phase to crystallize and separate the biuret, which is then dried and recycled.

2. The method for preparing stearic acid based on DMAP composite catalyst and biuret inclusion technology according to claim 1, wherein The ionic liquid in step 1) is a mixture of 4-lutidine DMAP and 1-butyl-3-methylimidazolium tetrafluoroborate in a mass ratio of 1:0.5-2.

3. The method for preparing stearic acid based on DMAP composite catalyst and biuret inclusion technology according to claim 1, wherein The composite catalyst in step 1) is 0.5-3% of the mass of the refined palm oil.

4. The method for preparing stearic acid based on DMAP composite catalyst and biuret inclusion technology according to claim 1, 2 or 3, wherein The temperature of the hydrolysis reaction in step 1) is 70-90°C.

5. The method for preparing stearic acid based on DMAP composite catalyst and biuret inclusion technology according to claim 4, wherein The mass ratio of ethanol to water in the step 2) is 2 to 5:

1.

6. The method for preparing stearic acid based on DMAP composite catalyst and biuret inclusion technology according to claim 5, wherein In the step 2), the mass ratio of the mixed solvent to the refined palm oil is 1.5 to 4:

1.

7. The method for preparing stearic acid based on DMAP composite catalyst and biuret inclusion technology according to claim 6, wherein In the step 2), the mass ratio of biuret to refined palm oil is 0.3-0.6:

1.

8. The method for preparing stearic acid based on DMAP composite catalyst and biuret inclusion technology according to claim 1 or 2 or 3 or 4 or 5 or 6, wherein: The purity of the prepared stearic acid can reach 99.5%, and the yield is 92%.