Preparation method of high-purity oleic acid

Abstract

A preparation method of high-purity oleic acid comprises the following steps: (1) hydrolyzing natural oil to obtain crude glycerine and crude fatty acid, and separating to obtain crude glycerine and crude fatty acid; (2) carrying out reduced pressure distillation on the crude fatty acid in a first distillation tower to remove moisture and a small amount of mixed crude glycerol, heating, carrying out reduced pressure distillation in a second distillation tower, separating industrial-grade fatty acid from the tower top, and separating tar from the tower kettle; (3) adding a crystallization inducer into the industrial-grade fatty acid for freezing treatment, and separating out saturated fatty acid and crude oleic acid; and (4) rectifying the crude oleic acid to obtain high-purity oleic acid and tar. The preparation method of the high-purity oleic acid is environment-friendly and energy-saving, less in medicament addition and obviously reduced in secondary waste quantity, and the technology is safe, reliable, free of toxic and harmful substances and stable in process.

Description

Technical Field

[0001] The invention relates to a method for preparing high-purity oleic acid, and belongs to the technical field of chemical preparation. Background Art

[0002] Oleic acid, also known as octadecenoic acid, has a molecular formula of C₁₇H₃₃COOH. It is an unsaturated fatty acid containing one double bond and is widely found in natural animal and plant oils and fats as a glyceride. Pure oleic acid is a colorless and odorless liquid, while industrial oleic acid is a yellow, oily liquid. High-purity oleic acid is typically obtained by purifying industrial oleic acid.

[0003] Industrial oleic acid usually comes from animal and plant oils, which contain stearic acid, linoleic acid, linolenic acid, and other long-chain fatty acids with similar structures. It is difficult to accurately separate oleic acid from these fatty acids in industrial production.

[0004] As a raw material for the production of fine chemicals, high-purity oleic acid usually needs to have a high purity. The preparation of high-purity oleic acid can be achieved by physical or chemical methods, among which physical methods include urea complex separation, emulsification separation, solvent crystallization separation, etc.

[0005] The urea complex separation method involves dissolving urea molecules in a solvent and aligning them in a helical lattice via hydrogen bonding, forming a hexagonal cavity that serves as the host. Oleic acid, its sodium salt, or a saturated fatty acid serves as the guest, encapsulating the host cavity to form a host-guest system, or inclusion complex. Unsaturated fatty acids with two or more double bonds (such as linoleic acid and linolenic acid) or their salts, however, cannot fit within the host cavity due to their larger molecular structure due to the presence of double bonds. Under different conditions, inclusion complexes formed between urea and saturated fatty acids, and between urea and the sodium salt of oleic acid, can be separated by crystallization.

[0006] The emulsification separation method is based on the different melting points of various fatty acids, allowing different fatty acids in a fatty acid mixture to take on liquid and solid states at specific temperatures. The mixed fatty acids containing different phases are dispersed in an aqueous solution containing surfactants and electrolytes to form a multiphase dispersion system. The phases are then separated using a centrifuge according to their density, and then molecular distillation is used to further produce high-purity oleic acid.

[0007] Solvent separation utilizes the different solubilities and freezing points of various fatty acids in organic solvents to separate mixed fatty acids. Common solvent separation methods include methanol low-temperature crystallization and acetone low-temperature crystallization. Although solvent separation requires a large amount of solvent and results in high solvent losses, it offers excellent separation results, high yields, and simple equipment.

[0008] Chemical methods generally employ selective hydrogenation, which involves selecting appropriate catalysts and reaction conditions to partially hydrogenate linoleic and linolenic acids to oleic acid, while minimizing or eliminating the participation of oleic acid. Limited by catalyst selectivity, this method is difficult to control in practice, and some oleic acid is converted to stearic acid during the reaction.

[0009] CN108530287A discloses a physical method for preparing high-purity oleic acid, comprising the following steps: S1, dissolving industrial oleic acid in an organic solvent, stirring at -20°C to 0°C until solids are completely precipitated, collecting and concentrating the liquid to obtain crude oleic acid; S2, dissolving the crude oleic acid and urea in an alcohol solution at a temperature below 60°C, keeping the temperature and cooling to crystallize, and collecting the liquid; S3, dissolving urea in a primary purified oleic acid product, keeping the temperature and cooling to crystallize, and collecting the solid; S4, dissolving the solid in an alcohol solvent to obtain a mixed solution, keeping the temperature and cooling to crystallize, collecting the solid, and dispersing the solution in water, allowing the solution to stand for separation, and collecting the oil layer to obtain high-purity oleic acid.

[0010] CN109574826A discloses a method for preparing high-purity oleic acid. The method uses vegetable oil as a raw material, obtains fatty acid methyl ester through methyl esterification, heats and refluxes with fumaric acid diester and catalyst iodine at a constant temperature, and separates unreacted saturated fatty acid methyl ester and oleic acid methyl ester by vacuum distillation. The saturated fatty acid methyl ester and oleic acid methyl ester are then included with urea and methanol, and vacuum filtration is performed to dissolve the inclusion complex, saponify, acidify, wash with water, dehydrate, dry, and filter to obtain a filtrate of high-purity saturated fatty acids and oleic acid. The filtrate is then frozen, crystallized, and filtered to remove the saturated fatty acids to obtain oleic acid with a purity of more than 99%.

[0011] CN110194716A discloses a method for preparing high-purity oleic acid, which comprises using mixed fatty acids as raw materials, dissolving the mixed fatty acids in an organic solvent to obtain a mixed solution; stirring the mixed solution at -20°C to 0°C until solids are completely precipitated, and collecting the liquid for concentration; dissolving the crude mixed fatty acid and urea in an alcohol solution, which is then kept warm, cooled, and the liquid is collected; placing the primary purified product in a freezer for dynamic crystallization; and placing the crystallized product in a filter press for pressure filtration and separation to obtain high-purity oleic acid.

[0012] Existing industrial methods for producing high-purity oleic acid mostly rely on urea complexation and solvent separation. However, the urea complexation method introduces new impurities, has high impurity levels, is complex to process, and requires a large footprint. The solvent separation method also suffers from secondary contamination and difficulty recovering the solvent. Therefore, there is a need to further improve the production process for high-purity oleic acid, providing a method that is high in purity, simple in process, and low in cost. Summary of the Invention

[0013] The present invention addresses the shortcomings of existing methods for preparing high-purity oleic acid and further improves the method based on physical fractionation. Metal chlorides are added during the separation of crude fatty acids, and combined with the optimization of the packed tower distillation process, the carryover of other unsaturated fatty acids is reduced, thereby further improving the yield and purity of oleic acid.

[0014] One aspect of the present invention discloses a method for preparing high-purity oleic acid, comprising the following steps: (1) Natural oils are hydrolyzed to obtain crude glycerol and crude fatty acids, which are then separated to obtain crude glycerol and crude fatty acids; (2) The crude fatty acids are distilled under reduced pressure in the first distillation tower to remove water and a small amount of crude glycerin, and then the temperature is raised and distilled under reduced pressure in the second distillation tower. Industrial-grade fatty acids are separated from the top of the tower, and tar is separated from the bottom of the tower. (3) Adding crystallization inducers to industrial-grade fatty acids and freezing them to separate saturated fatty acids and crude oleic acid; (4) The crude oleic acid is distilled to obtain high-purity oleic acid and tar.

[0015] The natural oil in step (1) is one or more of palm oil, camellia oil, olive oil, gutter oil, lard, mutton fat, beef tallow, and fish oil, preferably palm oil or olive oil.

[0016] The molar ratio of natural oil to water in the hydrolysis in step (1) is 0.2-1, more preferably 0.5-0.7; the hydrolysis temperature is 200-350°C, the hydrolysis pressure is 0.5-3 MPa, and the hydrolysis time is 30-90 min; more preferably, the hydrolysis temperature is 220-280°C, the hydrolysis pressure is 1-2 MPa, and the hydrolysis time is 50-70 min.

[0017] The hydrolysis in step (1) is carried out under an inert atmosphere, preferably under a nitrogen atmosphere; the separation is carried out by static stratification or solvent extraction.

[0018] In step (2), the temperature of the first distillation tower is 60-95°C, and the pressure is 10-50KPa, more preferably 65-75°C, and the pressure is 20-30KPa; the temperature of the second distillation tower is 150-200°C, and the pressure is 0.1-1KPa, more preferably 0.2-0.5KPa.

[0019] The crystallization inducing agent in step (3) is a methanol solution containing urea and metal chloride.

[0020] In step (3), the mass concentration of urea in the methanol solution is 10-20wt%, and the mass content of the metal chloride is 1-10wt%; the mass ratio of the urea to the metal chloride is 1-4, more preferably 2-3; the metal chloride is a chloride of an alkali metal or an alkaline earth metal, preferably one of sodium chloride, potassium chloride, magnesium chloride, and calcium chloride.

[0021] The mass ratio of the crystallization inducer to the industrial-grade fatty acid in step (3) is 1-10:100, more preferably 2-5:100; the temperature of the freezing treatment is 20-60°C, more preferably 30-50°C.

[0022] The distillation in step (4) is carried out in a distillation tower, which is a packed tower; the packing is acid-modified alumina / MOFs; the mass ratio of acid-modified alumina to MOFs is 1-5:1, more preferably 2-3:1; preferably, the acid-modified alumina is alumina treated by phosphoric acid impregnation; preferably, the impregnation uses a 1-20wt% phosphoric acid aqueous solution, and the impregnation is carried out for 10-30 minutes at a liquid-solid mass ratio of 100:30-50; the MOFs is Zn-2-methylimidazole; the top temperature of the distillation tower is 200-300°C, and the distillation tower operates under normal pressure or reduced pressure, and the pressure under the reduced pressure state is 0.01-0.09MPa.

[0023] The high-purity oleic acid prepared by the method of the present invention has a purity of 99.5 wt % or more, more preferably 99.7 wt % or more; the yield of oleic acid by the method is 73 % or more, more preferably 75 % or more.

[0024] The present invention adds a crystallization inducer during the separation process of crude fatty acids to adjust the precipitation speed of saturated fatty acids, reduce the precipitation speed of saturated fatty acids, make the precipitation of saturated fatty acids more stable, reduce unsaturated fatty acids in the precipitate, and thus improve the yield of oleic acid; the composition of the filler is optimized in the distillation process, which not only improves the separation efficiency of linoleic acid and linolenic acid, but also fully separates the crystallization inducer added during the freezing treatment process, and further improves the yield and purity of oleic acid.

[0025] The technical effect of the present invention: The high-purity oleic acid preparation method disclosed in the present invention is environmentally friendly and energy-saving, with less addition of reagents and significantly reduced secondary waste. The technology is safe and reliable, does not produce toxic substances, and has a stable process. DETAILED DESCRIPTION

[0026] The following examples are intended to further illustrate the present invention, but are not intended to limit the present invention.

[0027] Example 1: A method for preparing high-purity oleic acid comprises the following steps: (1) Palm oil was used as the raw material and hydrolyzed for 30 min under nitrogen atmosphere at 280°C and 1.0 MPa to obtain crude glycerol and crude fatty acids, which were then allowed to stand for separation to obtain crude glycerol and crude fatty acids; (2) The crude fatty acids are distilled under reduced pressure in the first distillation tower to remove water and a small amount of crude glycerin, and then the temperature is raised and distilled under reduced pressure in the second distillation tower. Industrial-grade fatty acids are separated from the top of the tower, and tar is separated from the bottom of the tower. The temperature of the first distillation tower is 75°C and the pressure is 30 kPa; the temperature of the second distillation tower is 150°C and the pressure is 0.2 kPa. (3) adding a crystallization inducer to the industrial-grade fatty acid and subjecting it to a freezing treatment to separate saturated fatty acids and crude oleic acid; the crystallization inducer is a methanol solution having a urea concentration of 15 wt% and a potassium chloride content of 5 wt%; the mass ratio of the crystallization inducer to the industrial-grade fatty acid is 1:100; and the freezing treatment temperature is 50°C; (4) Crude oleic acid is distilled in a packed tower to obtain high-purity oleic acid and tar; the packing is phosphoric acid-modified alumina / Zn-2-methylimidazole; the mass ratio of the acid-modified alumina to the Zn-2-methylimidazole is 5:1; the top temperature of the packed tower is 260°C, and the distillation tower is operated at atmospheric pressure.

[0028] Example 2: A method for preparing high-purity oleic acid comprises the following steps: (1) Camellia oleifera seed oil was used as the raw material and hydrolyzed for 60 min under nitrogen atmosphere at 220°C and 1.5 MPa to obtain crude glycerol and crude fatty acids, which were then allowed to stand for separation to obtain crude glycerol and crude fatty acids; (2) The crude fatty acids are distilled under reduced pressure in the first distillation tower to remove water and a small amount of crude glycerin, and then the temperature is raised and distilled under reduced pressure in the second distillation tower. Industrial-grade fatty acids are separated from the top of the tower, and tar is separated from the bottom of the tower. The temperature of the first distillation tower is 65°C and the pressure is 20 kPa; the temperature of the second distillation tower is 200°C and the pressure is 0.5 kPa. (3) adding a crystallization inducer to the industrial-grade fatty acid and subjecting it to a freezing treatment to separate saturated fatty acids and crude oleic acid; the crystallization inducer is a methanol solution containing 15 wt% urea and 5 wt% sodium chloride; the mass ratio of the crystallization inducer to the industrial-grade fatty acid is 2:100; and the freezing treatment temperature is 30°C; (4) Crude oleic acid is distilled in a packed tower to obtain high-purity oleic acid and tar; the packing is phosphoric acid-modified alumina / Zn-2-methylimidazole; the mass ratio of the acid-modified alumina to the Zn-2-methylimidazole is 3:1; the top temperature of the packed tower is 280°C, and the distillation tower is operated at a pressure of 0.03 MPa.

[0029] Example 3: A method for preparing high-purity oleic acid comprises the following steps: (1) Olive oil was used as raw material and hydrolyzed for 60 min under nitrogen atmosphere, 350°C, and 1.0 MPa to obtain crude glycerol and crude fatty acids, which were then allowed to stand and separate to obtain crude glycerol and crude fatty acids; (2) The crude fatty acids are distilled under reduced pressure in the first distillation tower to remove water and a small amount of crude glycerin, and then the temperature is raised and distilled under reduced pressure in the second distillation tower. Industrial-grade fatty acids are separated from the top of the tower, and tar is separated from the bottom of the tower. The temperature of the first distillation tower is 70°C and the pressure is 20 kPa; the temperature of the second distillation tower is 200°C and the pressure is 1 kPa. (3) adding a crystallization inducer to the industrial-grade fatty acid and subjecting it to a freezing treatment to separate saturated fatty acids and crude oleic acid; the crystallization inducer is a methanol solution containing 15 wt% urea and 5 wt% calcium chloride; the mass ratio of the crystallization inducer to the industrial-grade fatty acid is 1:100; and the freezing treatment temperature is 40°C; (4) Crude oleic acid is distilled in a packed tower to obtain high-purity oleic acid and tar; the packing is phosphoric acid-modified alumina / Zn-2-methylimidazole; the mass ratio of the acid-modified alumina to the Zn-2-methylimidazole is 2:1; the top temperature of the packed tower is 280°C, and the distillation tower is operated at atmospheric pressure.

[0030] Comparative Example 1: The other steps are the same as those in Example 1, except that in step (3), the crystallization inducer is a methanol solution of urea, the crystallization inducer is a methanol solution with a urea mass concentration of 15 wt%, the mass ratio of the crystallization inducer to the industrial-grade fatty acid is 1:100, and the temperature of the freezing treatment is 50°C.

[0031] Comparative Example 2: The other steps are the same as those in Example 1, except that the distillation tower in step (4) is a plate tower.

[0032] Comparative Example 3: The other steps are the same as those in Example 1, with the only difference being that the distillation tower in step (4) is a packed tower, and the packing is alumina.

[0033] The purity and yield of the high-purity oleic acid obtained in the examples and comparative examples were evaluated, and the results are shown in Table 1.

[0034] Table 1

[0035] According to the properties of the high-purity oleic acid obtained in the examples and comparative examples, it can be seen that the high-purity oleic acid obtained by the method described in the present application has a very high purity and a high oleic acid yield.

[0036] It should be clear to those skilled in the art that the above embodiments are merely exemplary of the technical solutions of the present invention and are not intended to limit the scope of protection of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative work are within the scope of protection of the present invention.

Claims

1. A method for preparing high-purity oleic acid, comprising the following steps: (1) Natural oils are hydrolyzed to obtain crude glycerol and crude fatty acids, which are then separated to obtain crude glycerol and crude fatty acids; (2) The crude fatty acids are distilled under reduced pressure in the first distillation tower to remove water and a small amount of crude glycerin, and then the temperature is raised and distilled under reduced pressure in the second distillation tower. Industrial-grade fatty acids are separated from the top of the tower, and tar is separated from the bottom of the tower. (3) Adding crystallization inducers to industrial-grade fatty acids and freezing them to separate saturated fatty acids and crude oleic acid; (4) The crude oleic acid is distilled to obtain high-purity oleic acid and tar.

2. The method according to claim 1, characterized in that The natural oil in step (1) is one or more of palm oil, camellia oil, olive oil, gutter oil, lard, mutton fat, beef tallow, and fish oil, preferably palm oil or olive oil.

3. The method according to claim 1, characterized in that The molar ratio of natural oil to water in the hydrolysis in step (1) is 0.2-1, more preferably 0.5-0.7; the hydrolysis temperature is 200-350°C, the hydrolysis pressure is 0.5-3 MPa, and the hydrolysis time is 30-90 min; more preferably, the hydrolysis temperature is 220-280°C, the hydrolysis pressure is 1-2 MPa, and the hydrolysis time is 50-70 min.

4. The method according to claim 1, characterized in that The hydrolysis in step (1) is carried out under an inert atmosphere, preferably under a nitrogen atmosphere; the separation is carried out by static stratification or solvent extraction.

5. The method according to claim 1, characterized in that In step (2), the temperature of the first distillation tower is 60-95°C, and the pressure is 10-50KPa, more preferably 65-75°C, and the pressure is 20-30KPa; the temperature of the second distillation tower is 150-200°C, and the pressure is 0.1-1KPa, more preferably 0.2-0.5KPa.

6. The method according to claim 1, characterized in that The crystallization inducing agent in step (3) is a methanol solution containing urea and metal chloride.

7. The method according to claim 1, characterized in that In step (3), the mass concentration of urea in the methanol solution is 10-20wt%, and the mass content of the metal chloride is 1-10wt%; the mass ratio of the urea to the metal chloride is 1-4, more preferably 2-3; the metal chloride is a chloride of an alkali metal or an alkaline earth metal, preferably one of sodium chloride, potassium chloride, magnesium chloride, and calcium chloride.

8. The method according to claim 1, characterized in that The mass ratio of the crystallization inducer to the industrial-grade fatty acid in step (3) is 1-10:100, more preferably 2-5:100; the temperature of the freezing treatment is 20-60°C, more preferably 30-50°C.

9. The method according to claim 1, characterized in that The distillation in step (4) is carried out in a distillation tower, which is a packed tower; the packing is acid-modified alumina / MOFs; the mass ratio of acid-modified alumina to MOFs is 1-5:1, more preferably 2-3:1; preferably, the acid-modified alumina is alumina impregnated with phosphoric acid, and the MOFs is Zn-2-methylimidazole; the top temperature of the distillation tower is 200-300°C, and the distillation tower is operated under normal pressure or reduced pressure, and the pressure under the reduced pressure is 0.01-0.09 MPa.

10. The method according to claim 1, characterized in that The high-purity oleic acid obtained by the method has a purity of more than 99.5wt%, and more preferably a purity of more than 99.7%; the yield of oleic acid is more than 73%, and more preferably more than 75%.

Images