CN116836053A - Method for preparing vegetable oleic acid through repeated rectification - Google Patents

Abstract

The invention relates to a method for preparing vegetable oleic acid by multiple times of rectification. The invention comprises the following steps: in a solvent, performing saponification reaction on fatty acid methyl ester in vegetable oil under alkaline conditions to obtain a mixture, and performing freeze drying on the obtained mixture to obtain oleate; recrystallizing the obtained oleate to obtain purified oleate, redissolving in a solvent, adding a porous adsorbent, adding acid for neutralization reaction, and filtering to obtain filtrate, wherein the filtrate is primary oleic acid; rectifying the primary oleic acid; repeating the above operation at least twice to obtain medium-grade oleic acid; adding the medium-grade oleic acid into a water-containing mixed solvent containing a porous adsorbent, and crystallizing by cooling step by step to obtain the vegetable oleic acid. The method has the advantages of simple process, simple operation and lower cost, and can be used for producing the oleic acid with high quality requirement on a large scale.

Description

A method for preparing vegetable oleic acid through multiple distillations

Technical field

The present invention relates to the technical field of preparing high-purity oleic acid, and in particular refers to a method for preparing vegetable oleic acid through multiple distillations.

Background technique

Oleic acid, with the chemical formula C ₁₈ H ₃₄ O ₂ , is a monounsaturated Omega-9 fatty acid, also known as cis-9-octadecenoic acid. It is an unsaturated fatty acid containing a double bond in natural oils. Saturated fatty acids are found in natural animal and vegetable oils in the form of glycerides. Oleic acid, especially high-purity oleic acid, is an important fine chemical product and can be widely used in paints and inks, coatings, mineral flotation agents, film antistatic agents, slip agents, textile auxiliaries, explosive emulsifiers, etc.

The raw materials of industrial oleic acid in my country mainly come from animal (vegetable) oils, acidified oils (vegetable oil refining by-products), swill oil, catering industry recycled oil, tall oil, etc. Depending on the source and the preparation process used, the indicators of oleic acid will vary greatly, which leads to the diversification of applications of oleic acid products.

In recent years, the purity of oleic acid has mostly been maintained at 70%-80%. Among the known preparation methods, solvent separation, emulsification separation, chromatographic separation using adsorbents, ion exchange chromatographic separation, selective hydrogenation of linoleic acid and linolenic acid to oleic acid, etc., but these methods cannot meet the requirements of industrial large-scale To meet the requirements for preparing high-purity oleic acid, in order to expand production scale, researchers are focusing on other production methods, such as freeze pressing, crystallization filter press, distillation, organic solvent method, surfactant method, urea complex method, etc. wait. Among them, the urea complex method and the organic solvent method have high production costs; the surfactant method has a low separation degree and cannot meet industrial requirements, and has been basically eliminated; the freeze pressing method has low efficiency and a large area, and cannot achieve large-scale production. Industrial production; nowadays, the most commonly used methods for preparing high-purity oleic acid are distillation and crystallization filtration.

The distillation method achieves separation and storage based on the different carbon chain lengths and boiling points of fatty acids. Since the raw material of oleic acid is mainly a mixture of C16 and C18, C16 can be separated better by distillation method, but it is more difficult to separate the homologues of C18 distillation method, so the oil produced by distillation method The freezing point of acid is generally high, generally above 15°C. It is difficult to obtain oleic acid with a lower freezing point using this method.

The crystallization filtration method is to lower the temperature to make high-melting point hexadecanoic acid and stearic acid form crystals first, and then separate them through membrane filtration to effectively separate saturated fatty acids and low-melting unsaturated fatty acids. It is a method suitable for Industrial production method of high quality oleic acid. The crystallization filtration method is to first heat the fatty acids to ensure that all saturated fatty acids are completely dissolved, put them into a crystallization tank, crystallize and filtrate them, and then program the temperature to drop. Crystallization and filtration yield oleic acid. The process method is simple and can realize large-scale industrial production. The disadvantage is that it requires stricter process technology control, and it is easy to entrain liquid fatty acids in the hard cake, reducing the product yield.

In order to meet the needs of high-purity oleic acid in industrial production, it is urgent to develop a process with high product yield and high purity of oleic acid.

Contents of the invention

For this reason, the technical problem to be solved by the present invention is to overcome the technical problems of low yield and low purity of oleic acid in industrial production in the prior art.

In order to solve the above technical problems, the present invention provides a method for preparing vegetable oleic acid through multiple distillations. The invention has simple process, simple operation and low cost, and can produce high-quality oleic acid on a large scale.

The present invention is realized through the following technical solutions:

The object of the present invention is to provide a method for preparing vegetable oleic acid through multiple distillations, which includes the following steps:

(1) In a solvent, the fatty acid methyl esters in vegetable oils and fats are subjected to a saponification reaction under alkaline conditions to obtain a mixture, and the resulting mixture is freeze-dried to obtain oleate;

(2) Recrystallize the oleate salt obtained in step (1) to obtain purified oleate salt, redissolve it in a solvent, add a porous adsorbent, add acid to perform a neutralization reaction, filter the filtrate, and obtain the filtrate. It is primary oleic acid;

(3), carry out distillation treatment on the primary oleic acid described in step (2);

(4) Repeat step (3) at least twice to obtain intermediate oleic acid;

(5) Add intermediate oleic acid to a water-containing mixed solvent containing a porous adsorbent, and obtain the vegetable oleic acid by stepwise cooling and crystallization;

In step (3), in the rectification treatment, the rectification system includes dehydration and degassing, an evaporation tower, a rectification tower and an oleic acid tower; a porous adsorbent is added to the rectification tower.

In one embodiment of the present invention, in step (1), the solvent is an aqueous alcohol solution. Further, the water content is 2wt%-10wt%. Preferably it is 2wt%, 3wt%, 4wt%, 5wt%, 6wt%, 7wt%, 8wt%, 9wt%, 10wt%, etc. Or any value between any two values.

In one embodiment of the present invention, in step (1), the saponification reaction conditions are: heating temperature is 90°C-95°C, and saponification reaction time is 1-2 hours.

In one embodiment of the present invention, in step (1), the alkaline conditioner of the alkaline condition is sodium hydroxide and/or potassium hydroxide, and the pH value of the alkaline condition is 10-11.

In one embodiment of the present invention, in step (2), the porous adsorbent is prepared by the following method: dispersing gelatin into a solvent at 65°C-85°C, adding graphene oxide, and mixing to obtain gelatin-graphite oxide Alkene is stirred until a gel state is formed, and then calcined in an atmosphere containing organic gas to obtain the porous adsorbent.

In one embodiment of the invention, the solvent is water.

In one embodiment of the present invention, the mass ratio of gelatin and graphene oxide is 1:1-2. Preferably it is 1:1, 1:2, 1:1.5, etc.

In one embodiment of the present invention, the calcination conditions: temperature is 600°C-900°C; time is 3h-12h.

Further, the organic gas is one or more of methane, ethylene, and ethane.

In one embodiment of the present invention, in step (2), the amount of porous adsorbent is 20wt%-30wt%.

In one embodiment of the present invention, in step (2), the distillation pressure is 100MPa-200MPa, the temperature of the top outlet of the distillation tower in the distillation system is 195°C-200°C, and the temperature of the bottom material is 240°C. ℃ - 245 ℃; the temperature of the outlet at the top of the oleic acid tower is 160 ℃ - 165 ℃, the temperature of the oleic acid outlet in the middle of the oleic acid tower is 220 ℃ - 225 ℃, and the temperature at the bottom of the tower is 240 ℃ - 250℃. The rectification device is a conventional device in this field, including an evaporation tower, a rectification tower and an oleic acid tower in order. Among them, the oleic acid tower contains two outlets in the middle and at the top.

In one embodiment of the present invention, in step (2), the acid is selected from hydrochloric acid.

In one embodiment of the present invention, in step (5), the water-containing mixed solvent further includes diethyl ether or acetone; the water content in the water-containing mixed solvent is 1-5 wt%. The adsorption effect of the adsorbent is used to once again play the role of impurity removal; at the same time, according to the staged cooling process during the cooling process, the impurities form crystals and precipitate on the surface of the adsorbent, separating the adsorbent, and once again achieving the removal of impurities.

In one embodiment of the present invention, in step (5), a step-by-step cooling process: the first stage temperature drops to 0°C to -10°C, the second stage temperature drops to -20°C to -15°C, the third stage temperature is -30℃ to -20℃.

The above technical solution of the present invention has the following advantages compared with the existing technology:

(1) The present invention can reduce the content of oleic acid impurities by adding porous adsorbents, utilizing porosity, increasing adsorption performance, and removing impurities in advance before distillation. At the same time, combined with multiple distillation methods, the purity of oleic acid is further improved.

(2) The method of the present invention is simple, and the device is conventional distillation equipment in this field, and the requirements for the equipment are not high; the use of organic solvents is small, except for the two organic solvents of ethanol and acetone, other organic solvents are used very rarely. Reduce costs and reduce the possibility of environmental pollution.

(3) The step-by-step cooling in the final stage of the present invention once again increases the probability of improving the purity. Through the step-by-step cooling, the oleic acid is precipitated in stages, and the purity is guaranteed.

Description of the drawings

In order to make the content of the present invention easier to understand clearly, the present invention will be further described in detail below based on specific embodiments of the present invention and in conjunction with the accompanying drawings, wherein:

Figure 1 is a device system diagram of the distillation system of the present invention.

Detailed ways

The present invention will be further described below in conjunction with the accompanying drawings and specific examples, so that those skilled in the art can better understand and implement the present invention, but the examples are not intended to limit the present invention.

Example 1

This embodiment provides a method for preparing vegetable oleic acid through multiple distillations, as follows:

(1) In an ethanol aqueous solution (water content is 5wt%), the fatty acid methyl esters in vegetable oils and fats are dissolved in a sodium hydroxide solution. The pH value of the mixed solution is 10, and the saponification reaction is performed by heating. The heating temperature is 90°C. The heating time is 1 h to obtain a reaction mixture, which is freeze-dried to obtain oleate.

(2) Recrystallize the oleate salt obtained in step (1) to obtain the purified oleate salt, redissolve it in a solvent, add 20wt% porous adsorbent, add hydrochloric acid for neutralization reaction, and filter the filtrate. The filtrate is primary oleic acid;

Among them, the preparation method of the porous adsorbent: disperse 2g of gelatin into deionized water at 85°C, add 3g of graphene oxide, mix to obtain gelatin-graphene oxide, stir until a gel state is formed, and then in a gas atmosphere containing methane The porous adsorbent was obtained by calcining at a temperature of 600°C and a time of 10 hours.

(3) Distillate the primary oleic acid described in step (2). Distillation conditions: the distillation pressure is 100MPa, the temperature of the top outlet of the distillation tower in the distillation system is 200°C, and the tower The bottom material temperature is 245°C; the top outlet temperature of the oleic acid tower is 160°C, the oleic acid outlet temperature in the middle of the oleic acid tower is 220°C, and the bottom material temperature is 250°C. Collect the oleic acid outlet The fraction at the feed port;

(4) Repeat step (3) twice, and the final collected fraction is intermediate oleic acid;

(5) Add intermediate oleic acid to a mixed solvent of water and acetone containing porous adsorbent (the volume ratio of water to acetone is 20:80), and through step-by-step cooling, the temperature in the first stage is reduced to -5°C, and the time is 20min, the second stage temperature is -18°C, the time is 40min, the third stage temperature is -25°C, crystallize overnight, filter, and take the solid phase to obtain the vegetable oleic acid, with a purity of 88% and a light color.

Example 2

This embodiment provides a method for preparing vegetable oleic acid through multiple distillations, as follows:

(1) In an ethanol aqueous solution (water content is 10wt%), the fatty acid methyl esters in vegetable oils and fats are dissolved in a potassium hydroxide solution. The pH value of the mixed solution is 11, and the saponification reaction is carried out by heating. The heating temperature is 95°C. The heating time is 2 h to obtain a reaction mixture, which is freeze-dried to obtain oleate.

(2) Recrystallize the oleate salt obtained in step (1) to obtain purified oleate salt, redissolve it in a solvent, add 25wt% porous adsorbent, add hydrochloric acid for neutralization reaction, and filter the filtrate. The filtrate is primary oleic acid;

Among them, the preparation method of the porous adsorbent: disperse 2g of gelatin into deionized water at 85°C, add 3g of graphene oxide, mix to obtain gelatin-graphene oxide, stir until a gel state is formed, and then in a gas atmosphere containing methane The porous adsorbent was obtained by calcining at a temperature of 600°C and a time of 4 hours.

(3) Distillate the primary oleic acid described in step (2). Distillation conditions: the distillation pressure is 200MPa, the temperature of the top outlet of the distillation tower in the distillation system is 200°C, and the tower The bottom material temperature is 240°C; the top outlet temperature of the oleic acid tower is 160°C, the oleic acid outlet temperature in the middle of the oleic acid tower is 220°C, and the bottom material temperature is 240°C. Collect the oleic acid outlet The fraction at the feed port.

(4) Repeat step (3) twice, and the final collected fraction is intermediate oleic acid.

(5) Add intermediate oleic acid to a mixed solvent of water and acetone containing porous adsorbent (the volume ratio of water to acetone is 20:80), and through step-by-step cooling, the temperature in the first stage is reduced to -3°C, and the time is 20min, the second stage temperature is -15°C, the time is 30min, the third stage temperature is -30°C, crystallize overnight, filter, and take the solid phase to obtain the vegetable oleic acid, with a purity of 86% and a light color.

Example 3

This embodiment provides a method for preparing vegetable oleic acid through multiple distillations, as follows:

(1) In an ethanol aqueous solution (water content is 5wt%), the fatty acid methyl esters in vegetable oils and fats are dissolved in a sodium hydroxide solution. The pH value of the mixed solution is 10, and the saponification reaction is performed by heating. The heating temperature is 90°C. The heating time is 1 h to obtain a reaction mixture, which is freeze-dried to obtain oleate.

(2) Recrystallize the oleate salt obtained in step (1) to obtain the purified oleate salt, redissolve it in a solvent, add 20wt% porous adsorbent, add hydrochloric acid for neutralization reaction, and filter the filtrate. The filtrate is primary oleic acid;

Among them, the preparation method of the porous adsorbent: disperse 2g of gelatin into deionized water at 85°C, add 3g of graphene oxide, mix to obtain gelatin-graphene oxide, stir until a gel state is formed, and then in a gas atmosphere containing methane The porous adsorbent was obtained by calcining at a temperature of 900°C and a time of 3 hours.

(3) Distillate the primary oleic acid described in step (2). Distillation conditions: the distillation pressure is 100MPa, the temperature of the top outlet of the distillation tower in the distillation system is 200°C, and the tower The bottom material temperature is 245°C; the top outlet temperature of the oleic acid tower is 160°C, the oleic acid outlet temperature in the middle of the oleic acid tower is 220°C, and the bottom material temperature is 250°C. Collect the oleic acid outlet The fraction at the feed port;

(4) Repeat step (3) twice, and the final collected fraction is intermediate oleic acid;

(5) Add intermediate oleic acid to a mixed solvent of water and acetone containing porous adsorbent (the volume ratio of water to acetone is 20:80), and through step-by-step cooling, the temperature in the first stage is reduced to -5°C, and the time is 20min, the second stage temperature is -18°C, the time is 40min, the third stage temperature is -25°C, crystallize overnight, filter, and take the solid phase to obtain the vegetable oleic acid, with a purity of 87% and a light color.

Example 4

This embodiment provides a method for preparing vegetable oleic acid through multiple distillations, as follows:

(1) In an ethanol aqueous solution (water content is 2wt%), the fatty acid methyl esters in vegetable oils and fats are dissolved in a sodium hydroxide solution. The pH value of the mixed solution is 10, and the saponification reaction is performed by heating. The heating temperature is 90°C. The heating time is 1 h to obtain a reaction mixture, which is freeze-dried to obtain oleate.

(2) Recrystallize the oleate salt obtained in step (1) to obtain the purified oleate salt, redissolve it in a solvent, add 20wt% porous adsorbent, add hydrochloric acid for neutralization reaction, and filter the filtrate. The filtrate is primary oleic acid;

Among them, the preparation method of the porous adsorbent: disperse 2g of gelatin into deionized water at 85°C, add 3g of graphene oxide, mix to obtain gelatin-graphene oxide, stir until a gel state is formed, and then in a gas atmosphere containing methane The porous adsorbent was obtained by calcining at a temperature of 800°C and a time of 12 hours.

(3) Distillate the primary oleic acid described in step (2). Distillation conditions: the distillation pressure is 200MPa, the temperature of the top outlet of the distillation tower in the distillation system is 200°C, and the tower The bottom material temperature is 245°C; the top outlet temperature of the oleic acid tower is 160°C, the oleic acid outlet temperature in the middle of the oleic acid tower is 220°C, and the bottom material temperature is 250°C. Collect the oleic acid outlet The fraction at the feed port;

(4) Repeat step (3) twice, and the final collected fraction is intermediate oleic acid;

(5) Add intermediate oleic acid to a mixed solvent of water and acetone containing porous adsorbent (the volume ratio of water to acetone is 20:80), and through step-by-step cooling, the temperature in the first stage is reduced to -5°C, and the time is 20min, the second stage temperature is -18°C, the time is 45min, the third stage temperature is -30°C, crystallize overnight, filter, and take the solid phase to obtain the vegetable oleic acid, with a purity of 89% and a light color.

Example 5

This embodiment provides a method for preparing vegetable oleic acid through multiple distillations, as follows:

(1) In an ethanol aqueous solution (water content is 3wt%), the fatty acid methyl esters in vegetable oils and fats are dissolved in a sodium hydroxide solution. The pH value of the mixed solution is 10, and the saponification reaction is performed by heating. The heating temperature is 90°C. The heating time is 2 h to obtain a reaction mixture, which is freeze-dried to obtain oleate.

(2) Recrystallize the oleate salt obtained in step (1) to obtain the purified oleate salt, redissolve it in a solvent, add 20wt% porous adsorbent, add hydrochloric acid for neutralization reaction, and filter the filtrate. The filtrate is primary oleic acid;

Among them, the preparation method of the porous adsorbent: disperse 2g of gelatin into deionized water at 65°C, add 2g of graphene oxide, mix to obtain gelatin-graphene oxide, stir until a gel state is formed, and then in a gas atmosphere containing ethylene Calcining was carried out at a temperature of 900°C and a time of 5 hours to obtain the porous adsorbent.

(3) Distillate the primary oleic acid described in step (2). Distillation conditions: the distillation pressure is 100MPa, the temperature of the top outlet of the distillation tower in the distillation system is 200°C, and the tower The bottom material temperature is 245°C; the top outlet temperature of the oleic acid tower is 160°C, the oleic acid outlet temperature in the middle of the oleic acid tower is 220°C, and the bottom material temperature is 250°C. Collect the oleic acid outlet The fraction at the feed port;

(4) Repeat step (3) three times, and the final collected fraction is intermediate oleic acid;

(5) Add intermediate oleic acid to a mixed solvent of water and acetone containing porous adsorbent (the volume ratio of water to acetone is 20:80), and through step-by-step cooling, the temperature in the first stage is reduced to -10°C, and the time is 35min, the second stage temperature is -18°C, the time is 30min, the third stage temperature is -25°C, crystallize overnight, filter, and take the solid phase to obtain the vegetable oleic acid, with a purity of 88% and light color.

Example 6

This embodiment provides a method for preparing vegetable oleic acid through multiple distillations, as follows:

(1) In an ethanol aqueous solution (water content is 5wt%), the fatty acid methyl esters in vegetable oils and fats are dissolved in a sodium hydroxide solution. The pH value of the mixed solution is 10, and the saponification reaction is performed by heating. The heating temperature is 90°C. The heating time is 1 h to obtain a reaction mixture, which is freeze-dried to obtain oleate.

(2) Recrystallize the oleate salt obtained in step (1) to obtain the purified oleate salt, redissolve it in a solvent, add 20wt% porous adsorbent, add hydrochloric acid for neutralization reaction, and filter the filtrate. The filtrate is primary oleic acid;

Among them, the preparation method of the porous adsorbent: disperse 2g of gelatin into deionized water at 85°C, add 3g of graphene oxide, mix to obtain gelatin-graphene oxide, stir until a gel state is formed, and then in a gas atmosphere containing methane The porous adsorbent was obtained by calcining at a temperature of 900°C and a time of 5 hours.

(3) Distillate the primary oleic acid described in step (2). Distillation conditions: the distillation pressure is 100MPa, the temperature of the top outlet of the distillation tower in the distillation system is 200°C, and the tower The bottom material temperature is 245°C; the top outlet temperature of the oleic acid tower is 160°C, the oleic acid outlet temperature in the middle of the oleic acid tower is 220°C, and the bottom material temperature is 250°C. Collect the oleic acid outlet The fraction at the feed port;

(4) Repeat step (3) twice, and the final collected fraction is intermediate oleic acid;

(5) Add intermediate oleic acid to a mixed solvent of water and acetone containing porous adsorbent (the volume ratio of water to acetone is 20:80), and through step-by-step cooling, the temperature in the first stage is reduced to -5°C, and the time is 20min, the second stage temperature is -18°C, the time is 40min, the third stage temperature is -25°C, crystallize overnight, filter, and take the solid phase to obtain the vegetable oleic acid, with a purity of 85% and a light color.

Comparative Example 1 (compared with Example 1, the difference is that no adsorbent is used)

This comparative example provides a method for preparing vegetable oleic acid through multiple distillations, as follows:

(1) In an ethanol aqueous solution (water content is 5wt%), the fatty acid methyl esters in vegetable oils and fats are dissolved in a sodium hydroxide solution. The pH value of the mixed solution is 10, and the saponification reaction is performed by heating. The heating temperature is 90°C. The heating time is 1 h to obtain a reaction mixture, which is freeze-dried to obtain oleate.

(2) Recrystallize the oleate salt obtained in step (1) to obtain purified oleate salt, redissolve it in a solvent, add hydrochloric acid to perform a neutralization reaction, and filter the filtrate, which is primary oleic acid;

(3) Distillate the primary oleic acid described in step (2). Distillation conditions: the distillation pressure is 100MPa, the temperature of the top outlet of the distillation tower in the distillation system is 200°C, and the tower The bottom material temperature is 245°C; the top outlet temperature of the oleic acid tower is 160°C, the oleic acid outlet temperature in the middle of the oleic acid tower is 220°C, and the bottom material temperature is 250°C. Collect the oleic acid outlet The fraction at the feed port;

(4) Repeat step (3) twice, and the final collected fraction is intermediate oleic acid;

(5) Add intermediate oleic acid to a mixed solvent of water and acetone containing porous adsorbent (the volume ratio of water to acetone is 20:80), and through step-by-step cooling, the temperature in the first stage is reduced to -5°C, and the time is 20min, the second stage temperature is -18°C, the time is 40min, the third stage temperature is -25°C, crystallize overnight, filter, and take the solid phase to obtain the vegetable oleic acid, with a purity of 80% and a slightly darker color.

Comparative Example 2 (compared with Example 1, the difference is that the distillation is done once)

This comparative example provides a method for preparing vegetable oleic acid through multiple distillations, as follows:

(1) In an ethanol aqueous solution (water content is 5wt%), the fatty acid methyl esters in vegetable oils and fats are dissolved in a sodium hydroxide solution. The pH value of the mixed solution is 10, and the saponification reaction is performed by heating. The heating temperature is 90°C. The heating time is 1 h to obtain a reaction mixture, which is freeze-dried to obtain oleate.

(2) Recrystallize the oleate salt obtained in step (1) to obtain the purified oleate salt, redissolve it in a solvent, add 20wt% porous adsorbent, add hydrochloric acid for neutralization reaction, and filter the filtrate. The filtrate is primary oleic acid;

Among them, the preparation method of the porous adsorbent: disperse 2g of gelatin into deionized water at 85°C, add 3g of graphene oxide, mix to obtain gelatin-graphene oxide, stir until a gel state is formed, and then in a gas atmosphere containing methane The porous adsorbent was obtained by calcining at a temperature of 600°C and a time of 10 hours.

(3) Distillate the primary oleic acid described in step (2). Distillation conditions: the distillation pressure is 100MPa, the temperature of the top outlet of the distillation tower in the distillation system is 200°C, and the tower The bottom material temperature is 245°C; the top outlet temperature of the oleic acid tower is 160°C, the oleic acid outlet temperature in the middle of the oleic acid tower is 220°C, and the bottom material temperature is 250°C. Collect the oleic acid outlet The fraction collected at the feed port is intermediate oleic acid;

(5) Add intermediate oleic acid to a mixed solvent of water and acetone containing porous adsorbent (the volume ratio of water to acetone is 20:80), and through step-by-step cooling, the temperature in the first stage is reduced to -5°C, and the time is 20min, the second stage temperature is -18°C, the time is 40min, the third stage temperature is -25°C, crystallize overnight, filter, and take the solid phase to obtain the vegetable oleic acid, with a purity of 75% and a light color.

Comparative Example 3 (compared with Example 1, the difference is that the temperature reduction in step (5) is not divided into stages)

This comparative example provides a method for preparing vegetable oleic acid through multiple distillations, as follows:

(1) In an ethanol aqueous solution (water content is 5wt%), the fatty acid methyl esters in vegetable oils and fats are dissolved in a sodium hydroxide solution. The pH value of the mixed solution is 10, and the saponification reaction is performed by heating. The heating temperature is 90°C. The heating time is 1 h to obtain a reaction mixture, which is freeze-dried to obtain oleate.

(2) Recrystallize the oleate salt obtained in step (1) to obtain the purified oleate salt, redissolve it in a solvent, add 20wt% porous adsorbent, add hydrochloric acid for neutralization reaction, and filter the filtrate. The filtrate is primary oleic acid;

Among them, the preparation method of the porous adsorbent: disperse 2g of gelatin into deionized water at 85°C, add 3g of graphene oxide, mix to obtain gelatin-graphene oxide, stir until a gel state is formed, and then in a gas atmosphere containing methane The porous adsorbent was obtained by calcining at a temperature of 600°C and a time of 10 hours.

(3) Distillate the primary oleic acid described in step (2). Distillation conditions: the distillation pressure is 100MPa, the temperature of the top outlet of the distillation tower in the distillation system is 200°C, and the tower The bottom material temperature is 245°C; the top outlet temperature of the oleic acid tower is 160°C, the oleic acid outlet temperature in the middle of the oleic acid tower is 220°C, and the bottom material temperature is 250°C. Collect the oleic acid outlet The fraction at the feed port;

(4) Repeat step (3) twice, and the final collected fraction is intermediate oleic acid;

(5) Add intermediate oleic acid to a mixed solvent of water and acetone containing porous adsorbent (the volume ratio of water to acetone is 20:80), lower the temperature to -25°C, crystallize overnight, filter, and take the solid phase to obtain The vegetable oleic acid has a purity of 79% and a light color.

Obviously, the above-mentioned embodiments are only examples for clear explanation and are not intended to limit the implementation. For those of ordinary skill in the art, other changes or modifications may be made based on the above description. An exhaustive list of all implementations is neither necessary nor possible. The obvious changes or modifications derived therefrom are still within the protection scope of the present invention.

Claims (9)

1. A method for preparing vegetable oleic acid through multiple distillations, which is characterized in that it includes the following steps: (1) In a solvent, the fatty acid methyl esters in vegetable oils and fats are subjected to a saponification reaction under alkaline conditions to obtain a mixture, and the resulting mixture is freeze-dried to obtain oleate; (2) Recrystallize the oleate salt obtained in step (1) to obtain purified oleate salt, redissolve it in a solvent, add a porous adsorbent, add acid to perform a neutralization reaction, filter the filtrate, and obtain the filtrate. It is primary oleic acid; (3), carry out distillation treatment on the primary oleic acid described in step (2); (4) Repeat step (3) at least twice to obtain intermediate oleic acid; (5) Add intermediate oleic acid to a water-containing mixed solvent containing a porous adsorbent, and obtain the vegetable oleic acid by stepwise cooling and crystallization. 2. The method according to claim 1, characterized in that, in step (1), the conditions of the saponification reaction: the heating temperature is 90°C-95°C, and the saponification reaction time is 1-2 hours. 3. The method according to claim 1, characterized in that, in step (1), the alkaline conditioner of the alkaline condition is sodium hydroxide and/or potassium hydroxide, and the pH value of the alkaline condition is 10 -11. 4. The method according to claim 1, characterized in that in step (2), the porous adsorbent is prepared by the following method: dispersing gelatin into a solvent of 65°C-85°C, adding graphene oxide, Gelatin-graphene oxide is obtained by mixing, stirred until a gel state is formed, and then calcined in an atmosphere containing organic gas to obtain the porous adsorbent. 5. The method according to claim 4, wherein the mass ratio of gelatin and graphene oxide is 1:1-2. 6. The method according to claim 4, characterized in that the calcination conditions: temperature is 600°C-900°C; time is 3h-12h. 7. The method according to claim 1, characterized in that in step (2), the amount of porous adsorbent is 20wt%-30wt%. 8. The method according to claim 1, characterized in that, in step (3), the rectification pressure is 100MPa-200MPa, and the temperature of the top outlet of the rectification tower in the rectification system is 195°C-200°C, The material temperature at the bottom of the tower is 240°C-245°C; the temperature of the outlet at the top of the oleic acid tower is 160°C-165°C, the temperature of the oleic acid outlet in the middle of the oleic acid tower is 220°C-225°C, and the temperature at the bottom of the tower The material temperature is 240℃-250℃. 9. The method according to claim 1, wherein in step (5), the water-containing mixed solvent further includes diethyl ether or acetone; the water content in the water-containing mixed solvent is 1-5 wt%. The method according to claim 1, characterized in that in step (5), the step-by-step cooling process: the temperature in the first stage is reduced to 0°C to -10°C, and the temperature in the second stage is -20°C to -15°C, The third stage temperature is -30℃ to -20℃.