阅读说明：本技术 一种饱和脂肪酸结晶助剂及其制备方法 (Saturated fatty acid crystallization auxiliary agent and preparation method thereof ) 是由 程瑾 李澜鹏 曹长海 李秀峥 王宜迪 于 2019-10-31 设计创作，主要内容包括：本发明涉及一种饱和脂肪酸结晶助剂及其制备方法,是将纳米SiO-2首先采用3-氨丙基三乙氧基硅烷改性,再进行超声处理,超声处理后加入长链二元酸进行改性制得的。本发明所制备结晶助剂能够有效结晶出饱和脂肪酸,避免不饱和脂肪酸结晶,实现二者的有效分离。(The invention relates to a saturated fatty acid crystallization auxiliary agent and a preparation method thereof, which is prepared by mixing nano SiO 2 Firstly, 3-aminopropyltriethoxysilane is adopted for modification, then ultrasonic treatment is carried out, and long-chain dibasic acid is added for modification after the ultrasonic treatment. The crystallization aid prepared by the invention can effectively crystallize the saturated fatty acid, avoid the crystallization of the unsaturated fatty acid and realize the effective separation of the saturated fatty acid and the unsaturated fatty acid.)

1. A preparation method of a saturated fatty acid crystallization auxiliary agent is characterized by comprising the following steps:

(1) mixing nano SiO₂Dissolving in ethanol water solution to obtain dispersion;

(2) adding 3-aminopropyltriethoxysilane into the dispersion, adjusting pH to be weakly acidic, heating for reaction, filtering, washing and drying after the reaction is finished to obtain a solid;

(3) adding an ethanol water solution into the solid, and carrying out ultrasonic treatment;

(4) and adding long-chain dibasic acid after ultrasonic treatment, stirring for reaction, and filtering, washing and drying after the reaction is finished to obtain the crystallization auxiliary agent.

2. The method of claim 1, wherein: the nano SiO in the step (1)₂Has an average particle diameter of 20 to 100nm, preferably 20 to 50 nm.

3. The method of claim 1, wherein: the volume ratio of the ethanol to the water in the ethanol water solution in the step (1) is 0.5:1-1.5:1, preferably 1:1-1.2: 1.

4. A method according to claim 1, 2 or 3, characterized in that: step (1) nanometer SiO₂The mass-to-volume ratio to the ethanol aqueous solution is 0.02:1 to 0.5:1 (g: mL), preferably 0.05:1 to 0.1:1 (g: mL).

5. The method of claim 1, wherein: the addition amount of the 3-aminopropyltriethoxysilane in the step (2) is nano SiO₂5% -15%, preferably 8% -15% by mass of (A).

6. The method of claim 1, wherein: the pH value is adjusted to 5.5-6.5, preferably 5.5-6.0 in the step (2).

7. The method of claim 1, wherein: the heating reaction temperature in the step (2) is 60-80 ℃, preferably 70-80 ℃, and the reaction time is 1-6 hours, preferably 2-5 hours.

8. The method of claim 1, wherein: the mass-to-volume ratio of the solid in the step (3) to the ethanol aqueous solution is 1:10-1:50 (g: mL), preferably 1:30-1:50 (g: mL).

9. The method according to claim 1 or 8, characterized in that: the volume ratio of the ethanol to the water in the ethanol aqueous solution in the step (3) is 1-2: 1.

10. The method of claim 1, wherein: the ultrasonic treatment power in the step (3) is 50-200W, preferably 100-200W; the temperature is 40-60 ℃, preferably 50-60 ℃; the treatment time is 15-60min, preferably 30-60 min.

11. The method of claim 1, wherein: the molecular general formula of the long-chain dicarboxylic acid in the step (4) is C_nH_2n-2O₄Wherein n is 10 to 16.

12. The method according to claim 1 or 11, characterized in that: the long-chain dibasic acid in the step (4) is nano SiO₂4% to 10%, preferably 5% to 10% by mass of (c).

13. The method of claim 1, wherein: the reaction temperature in the step (4) is 15-35 ℃, preferably 25-30 ℃, the stirring speed is 100-.

14. A saturated fatty acid crystallization aid characterized in that it is prepared by the process according to any one of claims 1 to 13.

15. Use of a saturated fatty acid crystallization aid according to claim 14, wherein: the method is used for separating saturated fatty acid and unsaturated fatty acid from vegetable oil fatty acid under low-temperature freezing condition.

16. Use according to claim 15, characterized in that: the vegetable oil fatty acid is one or more of soybean oleic acid, corn oleic acid and cotton seed oleic acid.

17. Use according to claim 15, characterized in that: the mass percentage of the crystallization aid and the vegetable oil fatty acid is 5-20%, preferably 10-20%.

18. Use according to claim 15, characterized in that: the freezing temperature is-5 ℃ to-14 ℃, the stirring speed is 100 and 500rpm, and the crystallization time is 5 to 15 hours.

Technical Field

The invention belongs to the technical field of fatty acid, and particularly relates to a saturated fatty acid crystallization auxiliary agent and a preparation method thereof.

Background

Vegetable oil fatty acid is generally mixed fatty acid containing both saturated fatty acid and unsaturated fatty acid, and the common methods for separating saturated fatty acid from unsaturated fatty acid at present include molecular distillation, freeze-squeezing, solvent freeze-separation, adsorption separation, supercritical fluid extraction, and the like.

In order to remove saturated fatty acids, it is conventional to freeze mixed fatty acids directly to induce crystallization of saturated fatty acids, followed by separation and removal. However, saturated fatty acids tend to directionally precipitate crystals at low temperatures and form a three-dimensional network structure, and gaps of the network structure wrap a large amount of liquid, so that solid-liquid separation is very difficult, and a large pressure difference is generally required. Sometimes such a network may extend through a substantial part of the volume occupied by the liquid. When separation is carried out under a large pressure difference, the net structure is gradually destroyed and dispersed into very fine crystal particles, which easily block the filter medium and cause difficulty in separation.

CN105316107A discloses a method for separating oleic acid and linoleic acid from tea seed oil, which is to saponify and acidify the tea seed oil to prepare mixed fatty acid, and to remove saturated fatty acid by solvent freezing crystallization pretreatment. However, the solvent freezing separation method has large energy consumption in freezing and solvent recovery, and the organic solvent has strong volatility and has high requirements on equipment, production environment and operation.

CN103074158A discloses a method for separating unsaturated fatty acid, which comprises freezing and crystallizing mixed fatty acid containing unsaturated fatty acid at low temperature of 0-minus 5 ℃, filtering and separating; then absorbing the separated liquid product by adopting an oil absorption material at the low temperature of 0 to minus 5 ℃; and finally, centrifuging the product obtained after adsorption at a low temperature of between 0 and-5 ℃ in different rotating speed gradients, and centrifuging to obtain the high-concentration unsaturated fatty acid. The method directly carries out freezing crystallization, if certain crystallization requirements are met, the time consumption is long, the filtrate needs to be subjected to a subsequent separation process, and the crystallization process is complex.

Disclosure of Invention

Aiming at the defects of the prior art, the invention provides a saturated fatty acid crystallization auxiliary agent and a preparation method thereof. The invention adopts 3-aminopropyl triethoxysilane and long-chain dibasic acid to nano SiO₂The prepared crystallization auxiliary agent can effectively crystallize the saturated fatty acid, avoid the crystallization of the unsaturated fatty acid and realize the effective separation of the saturated fatty acid and the unsaturated fatty acid.

The preparation method of the saturated fatty acid crystallization auxiliary agent provided by the invention comprises the following steps:

（1）mixing nano SiO₂Dissolving in ethanol water solution to obtain dispersion;

(2) adding 3-aminopropyltriethoxysilane into the dispersion, adjusting pH to be weakly acidic, heating for reaction, filtering, washing and drying after the reaction is finished to obtain a solid;

(3) adding an ethanol water solution into the solid, and carrying out ultrasonic treatment;

(4) and adding long-chain dibasic acid after ultrasonic treatment, stirring for reaction, and filtering, washing and drying after the reaction is finished to obtain the crystallization auxiliary agent.

In the invention, the nano SiO in the step (1)₂Has an average particle diameter of 20 to 100nm, preferably 20 to 50 nm. The volume ratio of ethanol to water in the ethanol aqueous solution is 0.5:1 to 1.5:1, preferably 1:1 to 1.2: 1. Nano SiO₂The mass-to-volume ratio to the ethanol aqueous solution is 0.02:1 to 0.5:1 (g: mL), preferably 0.05:1 to 0.1:1 (g: mL).

In the invention, the adding amount of the 3-aminopropyltriethoxysilane in the step (2) is nano SiO₂5% -15%, preferably 8% -15% by mass of (A).

In the present invention, the pH adjustment in step (2) is weakly acidic, specifically 5.5 to 6.5, preferably 5.5 to 6.0.

In the invention, the heating reaction temperature in the step (2) is 60-80 ℃, preferably 70-80 ℃, and the reaction time is 1-6h, preferably 2-5 h.

According to the invention, the filtration in the step (2) adopts filtration modes such as suction filtration, centrifugation and the like. Washing is carried out by respectively washing with distilled water and absolute ethyl alcohol for multiple times to mainly remove free reactants. The drying temperature is 80-100 ℃, and the drying time is 2-6 h.

In the present invention, the mass-to-volume ratio of the solid in step (3) to the aqueous ethanol solution is 1:10 to 1:50 (g: mL), preferably 1:30 to 1:50 (g: mL). The volume ratio of ethanol to water in the ethanol water solution is 1-2: 1.

In the invention, the ultrasonic treatment power in the step (3) is 50-200W, preferably 100-200W; the temperature is 40-60 ℃, preferably 50-60 ℃; the treatment time is 15-60min, preferably 30-60 min.

In the present invention, step (4)The molecular general formula of the long-chain dicarboxylic acid is C_nH_2n-2O₄Wherein n is 10 to 16. The dosage of the long-chain dicarboxylic acid is nano SiO₂4% to 10%, preferably 5% to 10% by mass of (c).

In the present invention, the reaction temperature in step (4) is 15-35 deg.C, preferably 25-30 deg.C, the stirring speed is 100-400rpm, preferably 200-300rpm, and the reaction time is 2-6h, preferably 2-5 h.

In the invention, after the reaction in the step (4) is finished, filtration is carried out by adopting filtration modes such as suction filtration and the like. The washing is carried out for a plurality of times by respectively washing distilled water and absolute ethyl alcohol, and mainly removing free reactants. The drying temperature is 80-100 ℃, and the drying time is 2-6 h.

The saturated fatty acid crystallization auxiliary agent is prepared by the method. The prepared crystallization aid is used for separating saturated fatty acid and unsaturated fatty acid in vegetable oil fatty acid under the condition of low-temperature freezing. The vegetable oil fatty acid is one or more of soybean oleic acid, corn oleic acid, cotton seed oleic acid and the like. The mass percentage of the crystallization auxiliary agent and the vegetable oil fatty acid is 5-20%, preferably 10-20%, the freezing temperature is-5 ℃ to-14 ℃, the stirring speed is 100-500rpm, and the crystallization time is 5-15 h.

Compared with the prior art, the invention has the following beneficial effects:

(1) the nano SiO is modified by adopting a combined mode of 3-aminopropyltriethoxysilane modification-ultrasonic treatment-long-chain dicarboxylic acid modification₂The crystallization auxiliary agent is prepared by modification, so that saturated fatty acid can be effectively crystallized, and the crystallization of unsaturated fatty acid is avoided, thereby realizing the effective separation of the saturated fatty acid and the unsaturated fatty acid.

(2) Adopts 3-aminopropyl triethoxysilane and long-chain dibasic acid to nano SiO₂Modified, two substances and SiO₂The formed functional group is beneficial to forming epiphytic crystal, thereby avoiding the wall sticking of the crystal and the generation of a large amount of fine crystal and pseudo crystal in the crystallization process and avoiding the liquid package of the crystal.

(3) The crystallization auxiliary agent prepared by the invention can be used for freezing crystallization of low-concentration raw materials, does not need additional solvent and solvent separation process, and has the advantages of easily obtained raw materials and good crystallization effect.

Detailed Description

The method and effects of the present invention will be further described in detail with reference to specific examples. The embodiments are implemented on the premise of the technical scheme of the invention, and detailed implementation modes and specific operation processes are given, but the protection scope of the invention is not limited by the following embodiments.

The experimental procedures in the following examples are, unless otherwise specified, conventional in the art. The test materials used in the following examples were purchased from biochemical reagent stores unless otherwise specified.

The fatty acid content of the invention is analyzed by gas phase. Gas phase analysis conditions: an Agilent GC-2010 gas chromatograph is provided with a FID detector; the chromatographic column is SP-2560 type capillary column, 100m × 0.25mm × 0.20 μm. The sample inlet temperature is 280 ℃; the sample volume is 1 mu L; split-flow sample injection with a split-flow ratio of 200: 1; the initial column temperature is 180 ℃, the temperature is raised to 290 ℃ at the heating rate of 8 ℃/min, and the temperature is kept for 5 min; the detector temperature was 280 ℃.

Example 1

SiO with the grain diameter of 30nm₂Dissolving in ethanol water solution with volume ratio of ethanol to water of 1:1 to obtain nanometer SiO₂The mass-to-volume ratio of the dispersion to the ethanol aqueous solution was 0.05g:1mL, and a dispersion was prepared. Adding 3-aminopropyl triethoxysilane into the dispersion liquid in nano SiO₂8% of the mass, the pH was adjusted to 5.8, and the reaction was carried out at 75 ℃ for 3 hours. And after the reaction is finished, performing suction filtration, washing for 3 times by using distilled water and absolute ethyl alcohol respectively, and drying for 6 hours in an oven at the temperature of 80 ℃ to obtain a solid. Adding ethanol water solution with volume ratio of ethanol to water of 1:1 into solid, wherein the solid-liquid mass volume ratio of the solid to the ethanol water solution is 1g:30mL, and performing ultrasonic treatment at 50 deg.C with power of 100W for 30 min. Adding tridecylic acid with nano SiO 2 content₂10 percent of the mass, stirring and reacting for 2 hours at 25 ℃, the stirring speed is 200rpm, after the reaction is finished, pumping filtration is carried out, distilled water and absolute ethyl alcohol are respectively used for washing for 3 times, and the mixture is placed in an oven at 80 ℃ for drying for 6 hours to obtain the modified nano SiO₂Particles, i.e. crystallization aids.

3100-3700cm^-1Nearby peaks ascribed to-OH and-NHStretching vibration peak of the radical. After modification, 3400cm^-1The near-OH stretching vibration peak is obviously weakened, which shows that the nano SiO₂The hydrophilicity decreased during the modification and, at the same time, at 2800cm^-1The peak oscillation of methylene group shows that the 3-aminopropyl triethoxysilane is bonded to the nano SiO by chemical bond₂The surface of the particles. Nano SiO modified by long-chain binary acid₂At 3100cm^-1the-NH stretching vibration peak near the point is obviously strengthened and is 1622 cm^-1C = O stretching vibration peak appears, 1532 cm appears in fingerprint area^-1C-N stretching vibration peak sum 1290 cm^-1Vibration peaks of-NH and-CN indicate that amide bond is formed in the modification reaction, and modified SiO₂The long-chain dibasic acid is grafted successfully.

Example 2

SiO with the particle size of 20nm₂Dissolving in ethanol water solution with volume ratio of ethanol to water of 1.5:1 to obtain nanometer SiO₂The mass-to-volume ratio of the dispersion to the ethanol aqueous solution was 0.1g:1mL, and a dispersion was prepared. Adding 3-aminopropyl triethoxysilane into the dispersion liquid in nano SiO₂8% of the mass, the pH was adjusted to 5.8, and the reaction was carried out at 75 ℃ for 3 hours. And after the reaction is finished, performing suction filtration, washing for 3 times by using distilled water and absolute ethyl alcohol respectively, and drying for 6 hours in an oven at the temperature of 80 ℃ to obtain a solid. Adding ethanol water solution with volume ratio of ethanol to water of 1:1 into solid, wherein the solid-liquid mass ratio of the solid to the ethanol water solution is 1g:30mL, and performing ultrasonic treatment at 50 deg.C with power of 100W for 30 min. Adding tridecylic acid with nano SiO 2 content₂10 percent of the mass of the modified nano SiO, stirring and reacting for 2 hours at 25 ℃, stirring at the speed of 200rpm, filtering after the reaction is finished, washing for 3 times by using distilled water and absolute ethyl alcohol respectively, and drying for 6 hours in an oven at 80 ℃ to obtain the modified nano SiO₂Particles, i.e. crystallization aids.

Example 3

SiO with the grain diameter of 50nm₂Dissolving in ethanol water solution with volume ratio of ethanol to water of 1.1:1 to obtain nanometer SiO₂The mass-to-volume ratio of the dispersion to the ethanol aqueous solution was 0.08g:1mL, and a dispersion was prepared. Adding 3-aminopropyltriethoxysilane into the dispersion liquid in the amount ofNano SiO₂8% of the mass, the pH was adjusted to 5.8, and the reaction was carried out at 75 ℃ for 3 hours. And after the reaction is finished, performing suction filtration, washing for 3 times by using distilled water and absolute ethyl alcohol respectively, and drying for 6 hours in an oven at the temperature of 80 ℃ to obtain a solid. Adding ethanol water solution with volume ratio of ethanol to water of 1:1 into solid, wherein the solid-liquid mass ratio of the solid to the ethanol water solution is 1g:30mL, and performing ultrasonic treatment at 50 deg.C with power of 100W for 30 min. Adding tridecylic acid with nano SiO 2 content₂10 percent of the mass of the modified nano SiO, stirring and reacting for 2 hours at 25 ℃, stirring at the speed of 200rpm, filtering after the reaction is finished, washing for 3 times by using distilled water and absolute ethyl alcohol respectively, and drying for 6 hours in an oven at 80 ℃ to obtain the modified nano SiO₂Particles, i.e. crystallization aids.

Example 4

SiO with the grain diameter of 30nm₂Dissolving in ethanol water solution with volume ratio of ethanol to water of 1:1 to obtain nanometer SiO₂The mass-to-volume ratio of the dispersion to the ethanol aqueous solution was 0.05g:1mL, and a dispersion was prepared. Adding 3-aminopropyl triethoxysilane into the dispersion liquid in nano SiO₂10% by mass, the pH was adjusted to 6.0, and the reaction was carried out at 70 ℃ for 5 hours. And after the reaction is finished, performing suction filtration, washing for 3 times by using distilled water and absolute ethyl alcohol respectively, and drying for 6 hours in an oven at the temperature of 80 ℃ to obtain a solid. Adding ethanol water solution with volume ratio of ethanol to water of 1:1 into solid, wherein the solid-liquid mass ratio of the solid to the ethanol water solution is 1g:30mL, and performing ultrasonic treatment at 50 deg.C with power of 100W for 30 min. Adding tridecylic acid with nano SiO 2 content₂10 percent of the mass, stirring and reacting for 2 hours at 25 ℃, the stirring speed is 200rpm, after the reaction is finished, pumping filtration is carried out, distilled water and absolute ethyl alcohol are respectively used for washing for 3 times, and the mixture is placed in an oven at 80 ℃ for drying for 6 hours to obtain the modified nano SiO₂Particles, i.e. crystallization aids.

Example 5

SiO with the grain diameter of 30nm₂Dissolving in ethanol water solution with volume ratio of ethanol to water of 1:1 to obtain nanometer SiO₂The mass-to-volume ratio of the dispersion to the ethanol aqueous solution was 0.05g:1mL, and a dispersion was prepared. Adding 3-aminopropyl triethoxysilane into the dispersion liquid in nano SiO₂15% by mass, adjusting the pH to 5.5Reacting at 80 ℃ for 2 h. And after the reaction is finished, performing suction filtration, washing for 3 times by using distilled water and absolute ethyl alcohol respectively, and drying for 6 hours in an oven at the temperature of 80 ℃ to obtain a solid. Adding ethanol water solution with volume ratio of ethanol to water of 1:1 into solid, wherein the solid-liquid mass volume ratio of the solid to the ethanol water solution is 1g:30mL, and performing ultrasonic treatment at 50 deg.C with power of 100W for 30 min. Adding tridecylic acid with nano SiO 2 content₂10 percent of the mass of the modified nano SiO, stirring and reacting for 2 hours at 25 ℃, stirring at the speed of 200rpm, filtering after the reaction is finished, washing for 3 times by using distilled water and absolute ethyl alcohol respectively, and drying for 6 hours in an oven at 80 ℃ to obtain the modified nano SiO₂Particles, i.e. crystallization aids.

Example 6

SiO with the grain diameter of 30nm₂Dissolving in ethanol water solution with volume ratio of ethanol to water of 1:1 to obtain nanometer SiO₂The mass-to-volume ratio of the dispersion to the ethanol aqueous solution was 0.05g:1mL, and a dispersion was prepared. Adding 3-aminopropyl triethoxysilane into the dispersion liquid in nano SiO₂8% of the mass, the pH was adjusted to 5.8, and the reaction was carried out at 75 ℃ for 3 hours. And after the reaction is finished, performing suction filtration, washing for 3 times by using distilled water and absolute ethyl alcohol respectively, and drying for 6 hours in an oven at the temperature of 80 ℃ to obtain a solid. Adding an ethanol water solution with the volume ratio of ethanol to water of 2:1 into the solid, wherein the solid-liquid mass volume ratio of the solid to the ethanol water solution is 1g:40mL, and carrying out ultrasonic treatment at 50 ℃ with the power of 200W for 45 min. Adding tridecylic acid with nano SiO 2 content₂10 percent of the mass of the modified nano SiO, stirring and reacting for 2 hours at 25 ℃, stirring at the speed of 200rpm, filtering after the reaction is finished, washing for 3 times by using distilled water and absolute ethyl alcohol respectively, and drying for 6 hours in an oven at 80 ℃ to obtain the modified nano SiO₂Particles, i.e. crystallization aids.

Example 7

SiO with the grain diameter of 30nm₂Dissolving in ethanol water solution with volume ratio of ethanol to water of 1:1 to obtain nanometer SiO₂The mass-to-volume ratio of the dispersion to the ethanol aqueous solution was 0.05g:1mL, and a dispersion was prepared. Adding 3-aminopropyl triethoxysilane into the dispersion liquid in nano SiO₂8% of the mass, the pH was adjusted to 5.8, and the reaction was carried out at 75 ℃ for 3 hours. After the reaction is finished, pumpingFiltering, washing with distilled water and anhydrous ethanol for 3 times, respectively, and drying in an oven at 80 deg.C for 6 hr to obtain solid. Adding an ethanol water solution with the volume ratio of ethanol to water of 1.5:1 into the solid, wherein the solid-liquid mass volume ratio of the solid to the ethanol water solution is 1g:50mL, and carrying out ultrasonic treatment at 60 ℃ with the power of 150W for 60 min. Adding tridecylic acid with nano SiO 2 content₂10 percent of the mass of the modified nano SiO, stirring and reacting for 2 hours at 25 ℃, stirring at the speed of 200rpm, filtering after the reaction is finished, washing for 3 times by using distilled water and absolute ethyl alcohol respectively, and drying for 6 hours in an oven at 80 ℃ to obtain the modified nano SiO₂Particles, i.e. crystallization aids.

Example 8

SiO with the grain diameter of 30nm₂Dissolving in ethanol water solution with volume ratio of ethanol to water of 1:1 to obtain nanometer SiO₂The mass-to-volume ratio of the dispersion to the ethanol aqueous solution was 0.05g:1mL, and a dispersion was prepared. Adding 3-aminopropyl triethoxysilane into the dispersion liquid in nano SiO₂8% of the mass, the pH was adjusted to 5.8, and the reaction was carried out at 75 ℃ for 3 hours. And after the reaction is finished, performing suction filtration, washing for 3 times by using distilled water and absolute ethyl alcohol respectively, and drying for 6 hours in an oven at the temperature of 80 ℃ to obtain a solid. Adding ethanol water solution with volume ratio of ethanol to water of 1:1 into solid, wherein the solid-liquid mass volume ratio of the solid to the ethanol water solution is 1g:30mL, and performing ultrasonic treatment at 50 deg.C with power of 100W for 30 min. Adding tridecylic acid with nano SiO 2 content₂5 percent of the mass of the modified nano SiO, stirring and reacting for 5 hours at 26 ℃, stirring at the speed of 240rpm, filtering after the reaction is finished, washing for 3 times by using distilled water and absolute ethyl alcohol respectively, and drying for 6 hours in an oven at 80 ℃ to obtain the modified nano SiO₂Particles, i.e. crystallization aids.

Example 9

SiO with the grain diameter of 30nm₂Dissolving in ethanol water solution with volume ratio of ethanol to water of 1:1 to obtain nanometer SiO₂The mass-to-volume ratio of the dispersion to the ethanol aqueous solution was 0.05g:1mL, and a dispersion was prepared. Adding 3-aminopropyl triethoxysilane into the dispersion liquid in nano SiO₂And 8 percent of the mass, adjusting the pH value to 5.8, and carrying out water bath reaction for 3 hours at the temperature of 75 ℃. After the reaction is finished, performing suction filtration, and using distilled water and anhydrous waterWashing with ethanol for 3 times, and drying in 80 deg.C oven for 6 hr to obtain solid. Adding ethanol water solution with volume ratio of ethanol to water of 1:1 into solid, wherein the solid-liquid mass volume ratio of the solid to the ethanol water solution is 1g:30mL, and performing ultrasonic treatment at 50 deg.C with power of 100W for 30 min. Adding tridecylic acid with nano SiO 2 content₂8 percent of the mass of the modified nano SiO, stirring and reacting for 3 hours at 30 ℃, stirring at the speed of 300rpm, filtering after the reaction is finished, washing for 3 times by using distilled water and absolute ethyl alcohol respectively, and drying for 6 hours in an oven at 80 ℃ to obtain the modified nano SiO₂Particles, i.e. crystallization aids.

Example 10

SiO with the grain diameter of 30nm₂Dissolving in ethanol water solution with volume ratio of ethanol to water of 1:1 to obtain nanometer SiO₂The mass-to-volume ratio of the dispersion to the ethanol aqueous solution was 0.05g:1mL, and a dispersion was prepared. Adding 3-aminopropyl triethoxysilane into the dispersion liquid in nano SiO₂And 8 percent of the mass, adjusting the pH value to 5.8, and carrying out water bath reaction for 3 hours at the temperature of 75 ℃. And after the reaction is finished, performing suction filtration, washing for 3 times by using distilled water and absolute ethyl alcohol respectively, and drying for 6 hours in an oven at the temperature of 80 ℃ to obtain a solid. Adding ethanol water solution with volume ratio of ethanol to water of 1:1 into solid, wherein the solid-liquid mass volume ratio of the solid to the ethanol water solution is 1g:30mL, and performing ultrasonic treatment at 50 deg.C with power of 100W for 30 min. Then adding hexadecanedioic acid, the dosage of which is nano SiO₂10 percent of the mass of the modified nano SiO, stirring and reacting for 2 hours at 25 ℃, stirring at the speed of 200rpm, filtering after the reaction is finished, washing for 3 times by using distilled water and absolute ethyl alcohol respectively, and drying for 6 hours in an oven at 80 ℃ to obtain the modified nano SiO₂Particles, i.e. crystallization aids.

Example 11

SiO with the grain diameter of 30nm₂Dissolving in ethanol water solution with volume ratio of ethanol to water of 1:1 to obtain nanometer SiO₂The mass-to-volume ratio of the dispersion to the ethanol aqueous solution was 0.05g:1mL, and a dispersion was prepared. Adding 3-aminopropyl triethoxysilane into the dispersion liquid in nano SiO₂And 8 percent of the mass, adjusting the pH value to 5.8, and carrying out water bath reaction for 3 hours at the temperature of 75 ℃. After the reaction is finished, the mixture is filtered, and washed by distilled water and absolute ethyl alcohol respectively 3And then, drying the mixture in an oven at the temperature of 80 ℃ for 6 hours to obtain a solid. Adding ethanol water solution with volume ratio of ethanol to water of 1:1 into solid, wherein the solid-liquid mass volume ratio of the solid to the ethanol water solution is 1g:30mL, and performing ultrasonic treatment at 50 deg.C with power of 100W for 30 min. Then adding deca-carbon dibasic acid with the dosage of nano SiO₂10 percent of the mass of the modified nano SiO, stirring and reacting for 2 hours in a water bath at normal temperature of 25 ℃, stirring at the speed of 200rpm, filtering after the reaction is finished, washing for 3 times by using distilled water and absolute ethyl alcohol respectively, and drying for 6 hours in an oven at 80 ℃ to obtain the modified nano SiO₂Particles, i.e. crystallization aids.

Comparative example 1

The preparation process and the operating conditions were the same as in example 1, except that an aqueous ethanol solution was used instead of the aqueous ethanol solution.

Comparative example 2

The preparation process and the operating conditions were the same as in example 1, except that an aqueous solution was used instead of the aqueous ethanol solution.

Comparative example 3

The preparation process and the operating conditions were the same as in example 1, except that the ultrasonic treatment was directly carried out without the treatment in step (2).

Comparative example 4

The preparation process and the operation conditions are the same as those of the example 1, except that the pH is not adjusted in the step (2), the pH is natural, and the reaction is stirred at room temperature.

Comparative example 5

The preparation process and the operation conditions are the same as those of the example 1, except that the modification is not carried out in the step (3), and the step (4) is directly carried out.

Comparative example 6

The preparation process and the operation conditions are the same as those of the example 1, except that the crystallization auxiliary agent is obtained after the treatment of the step (3) without adopting the modification of the step (4).

Examples 1 to 11 and comparative examples 1 to 6 were used for low-temperature freeze crystallization of saturated fatty acids. The vegetable oil fatty acid is soybean oleic acid, corn oleic acid and cotton seed oleic acid, and the composition of the vegetable oil fatty acid is shown in table 1.

TABLE 1 vegetable oil fatty acid composition

As can be seen from table 1, the content of saturated fatty acids in oleic acid of soybean was 15.08%, and the content of unsaturated fatty acids was 84.92%; the content of saturated fatty acid in the oleic acid of the corn is 13.57 percent, and the content of unsaturated fatty acid is 86.43 percent; the content of saturated fatty acid in the cottonseed oleic acid is 24.23%, and the content of unsaturated fatty acid in the cottonseed oleic acid is 75.77%.

Heating and melting the vegetable oil acid at 50 ℃ for 30min, adding a crystallization aid according to the mass percent of the crystallization aid and the vegetable oil fatty acid of 10%, freezing at-10 ℃ at a low temperature, stirring at a speed of 100rpm, crystallizing for 10h, gradually saturating and growing crystals to form large-particle crystals, filtering at positive pressure, and carrying out gas phase analysis on the obtained filter residue and filtrate product, wherein the sum of the saturated fatty acid and the unsaturated fatty acid is 100%, and the results are shown in Table 2.

TABLE 2 analysis results of vegetable oleic acids after freeze crystallization

As can be seen from Table 2, the content of saturated fatty acid in the frozen and crystallized filtrate of each vegetable oleic acid is obviously reduced, and the content of unsaturated fatty acid in the filter residue is less than 8.58%. It can be seen from the comparative examples that the crystallization aid of the invention is not used or unmodified nano SiO is directly used₂And (3) performing freezing crystallization, wherein the crystals seriously wrap unsaturated fatty acid, so that the separation efficiency of saturated fatty acid and unsaturated fatty acid is poor, and the content of the unsaturated fatty acid in filter residue is more than or equal to 12.79%. Therefore, the crystallization auxiliary agent can effectively crystallize the saturated fatty acid and avoid the crystallization of the unsaturated fatty acid, thereby realizing the effective separation of the saturated fatty acid and the unsaturated fatty acid.