Novel sorbic acid crystal particle size regulation and control method

Abstract

The invention belongs to the technical field of chemical engineering, and particularly relates to a novel sorbic acid crystal particle size regulation and control method. The normal-pressure evaporation kettle is used, and the stirring mode, the stirring speed and the precipitation speed are controlled, so that the precipitation amount of sorbic acid crystals is accurately controlled; according to the invention, the crystallization process is divided into two sections through a sectional cooling mode, and two sorbic acid finished products with narrower and more uniform particle size distribution and coarse and fine particles can be obtained without screening treatment. The coarse particle sorbic acid finished product is in a square shape, the proportion of 30-50 meshes is greater than 93.3%, the proportion of 50 meshes or above is less than 3%, and the content of isomers in the finished product is less than 0.05%; the proportion of the finished sorbic acid with fine particles of 60-80 meshes is more than 82%, and the proportion of the sorbic acid with fine particles of more than 100 meshes is less than 5% The sorbic acid prepared by the method is high in purity and good in quality, a sorbic acid finished product which is narrower and more uniform in particle size distribution can be obtained without screening treatment, and different requirements of customers are met.

Description

Technical Field

[0001] The invention relates to a method for regulating and controlling the particle size of sorbic acid crystals, and belongs to the technical field of chemical industry. Background Art

[0002] Sorbic acid, scientific name 2,4-hexadienoic acid, molecular weight 112.13, melting point 132-135℃, boiling point 228℃, flash point 127℃, relative density 1.205g / cm 3 It is a white needle-shaped or powdery crystal that can be dissolved in a variety of organic solvents. Sorbic acid is an unsaturated fatty acid with conjugated dienes. It can effectively inhibit the activity of molds, yeasts and aerobic bacteria. Its effect of inhibiting the development and reproduction of harmful microorganisms is stronger than its bactericidal effect. It is a preservative recommended by the Food and Agriculture Organization of the United Nations to countries around the world. Its safety is twice that of salt. At present, sorbic acid has been widely used in the preservation and freshness of various foods, vegetables, fruits, medicines, rubber, papermaking, animal feed, cosmetics, paints, tobacco, beverages and other industries.

[0003] Sorbic acid and potassium sorbate are both commonly used food preservatives, which are widely used in the food industry. Although their mechanisms of action are similar, sorbic acid has some unique advantages over potassium sorbate. Sorbic acid is poorly soluble in water, which allows it to be used directly in oily foods and dry or semi-dry foods without pre-dissolving, simplifying the food processing process; at the same time, sorbic acid is more stable under acidic conditions, so it can play a more effective preservative role in foods with low pH values.

[0004] For sorbic acid, a narrower crystal size distribution has more advantages. Sorbic acid crystals with a narrower particle size distribution can increase the dissolution rate, improve the bioavailability of sorbic acid, make it more effectively absorbed and effective, and can also enhance the antibacterial effect, reduce agglomeration and precipitation, and improve the stability and uniformity of the product; in sustained-release preparations, sorbic acid crystals with a narrower particle size distribution can also help to more accurately control the release rate of the active ingredient, thereby extending the shelf life or efficacy time.

[0005] The ketene method is a commonly used method for the industrial production of sorbic acid internationally. The ketene method is to generate ketene by high-temperature cracking of acetic acid, which is then condensed with crotonaldehyde to form polyester, and then hydrolyzed, centrifuged, and washed to obtain a crude product. The crude sorbic acid product is then refined, neutralized, and dried to finally obtain the finished sorbic acid product. At present, the sorbic acid refining and crystallization process mainly adopts the cooling crystallization process, which is to cool the decolorized sorbic acid solution to a certain temperature at a certain rate, and then centrifugally wash, dry, and screen to obtain the sorbic acid product that meets the requirements. However, the cooling time required for this process is relatively long, and the particle size distribution of the sorbic acid after drying is uneven, and screening is required to obtain the sorbic acid product that meets the customer's particle size distribution requirements.

[0006] Patent JP1983085838A provides a method for preparing pure sorbic acid with narrow particle size distribution. Under high temperature and high pressure conditions, sorbic acid is dissolved in water, and the particle size distribution is adjusted by controlling the cooling rate and stirring rate. However, this process requires high temperature and high pressure conditions, has high requirements on equipment, and the quality of the sorbic acid finished product is poor. Patent CN103694105B provides a method for purifying sorbic acid, which uses a melt crystallization process to purify sorbic acid. The product purity is high, but the crystals of the purified sorbic acid are easy to agglomerate and the crystal form is poor after it is cooled to room temperature. Patent CN1850768A mentions a refining process for the preparation of high-purity crystalline sorbic acid. This process uses ethanol as a solvent, and uses activated carbon decolorization and cooling crystallization processes to prepare sorbic acid finished products. However, the particle size distribution of the obtained sorbic acid finished product is uneven, and screening treatment is required to meet the finished product particle size distribution requirements.

[0007] It can be seen that the conventional method for preparing the finished sorbic acid crystal has the problems of uneven particle size distribution, the need for screening treatment, long time consumption, high equipment cost, and low purity of the finished sorbic acid crystal.

[0008] Therefore, how to ensure the high purity and quality of the finished sorbic acid product while obtaining a sorbic acid product with a narrower and more uniform particle size distribution without screening treatment to meet the different needs of customers and facilitate workshop production is a technical problem to be solved urgently in this field. Summary of the invention

[0009] In order to solve the above technical problems, the present invention provides a novel method for controlling the particle size of sorbic acid crystals. According to the characteristic that sorbic acid has different solubility in ethanol solutions of different concentrations, the present invention changes the ethanol ratio in the sorbic acid decolorizing solution by controlling the amount of ethanol distilled, accurately controls the amount of sorbic acid crystal precipitation, and controls the stirring mode, stirring speed and precipitation speed so that the solute molecules have enough time to arrange, so that the sorbic acid crystal particles are arranged regularly, and finally precipitate crystals with regular shapes; at the same time, the present invention divides the crystallization process into two stages by staged cooling, avoiding secondary burst nucleation of sorbic acid at a lower temperature, which not only reduces the proportion of fine particles in the coarse particles of the sorbic acid finished product, but also obtains two types of sorbic acid finished products with narrower and more uniform coarse and fine particles without screening treatment.

[0010] In order to achieve the above object, the present invention provides a novel method for controlling the particle size of sorbic acid crystals, comprising the following steps:

[0011] (1) Preparation of sorbic acid decolorizing solution:

[0012] The crude sorbic acid, the refined mother liquor and ethanol are mixed, decolorized and filtered to obtain a first sorbic acid decolorized liquid;

[0013] Wherein, the preparation method of crude sorbic acid is:

[0014] 18-25% HCl solution and 2,4-hexadienoic acid polyester are simultaneously introduced into a first-stage kettle hydrolysis kettle at a volume ratio of 1-3:1, and reacted at 80-90°C for 30-50min; pumped into a second-stage kettle hydrolysis kettle, and reacted at 70-80°C for 30-50min; pumped into a third-stage hydrolysis kettle at 60-70°C for 30-50min; pumped into a kettle cooling kettle, cooled to 40-45°C, and separated into solid and liquid to obtain crude sorbic acid;

[0015] The preparation method of the 2,4-hexadienoic acid polyester comprises: adding 500-650 parts by weight of β-methylacrolein and 3-15 parts by weight of a titanium dioxide-silicon dioxide-caprolactam composite catalyst into a reaction kettle, stirring, introducing ketene gas at a temperature of 35-50° C. to react, filtering after the reaction is completed, and subjecting the reaction liquid to negative pressure distillation to obtain the 2,4-hexadienoic acid polyester;

[0016] The preparation method of refined mother liquor is:

[0017] The crude sorbic acid and ethanol solution are mixed in a mass ratio of 1:4, heated to 70-75°C, dissolved and decolorized, cooled to 45°C at a rate of 6°C / h, then cooled to 15°C at a rate of 15°C / h, and centrifuged to obtain a refined mother liquor;

[0018] (2) Evaporation of ethanol at normal pressure:

[0019] The first sorbic acid decolorized liquid is pumped into an evaporator, and 2% to 3% of the total mass of ethanol of the decolorized liquid is evaporated at a blade tip speed of 1.4 to 1.6 m / s to obtain a second sorbic acid decolorized liquid and seed crystals for inducing crystallization;

[0020] (3) Preparation of coarse particle sorbic acid:

[0021] The second sorbic acid decolorizing solution and seed crystals for inducing crystallization are poured into a crystallization kettle, the cooling rate is controlled to be 6-8°C / h, the temperature is lowered to 40-45°C, and the third sorbic acid decolorizing solution and coarse particles are obtained by centrifugation, and the coarse particles are washed and dried to obtain coarse sorbic acid particles;

[0022] (4) Preparation of fine particle sorbic acid:

[0023] The third sorbic acid decolorized liquid is poured into a crystallization kettle, and the cooling rate is controlled to be 15-16°C / h until the temperature drops to 15-20°C. Fine particles are obtained by centrifugation, and the fine particles are washed and dried to obtain fine particle sorbic acid.

[0024] Furthermore, in step (1), the mass ratio of the crude sorbic acid, the refined mother liquor and the ethanol is 1:0.1-3:0.1-4.

[0025] Furthermore, the mixing in step (1) is carried out at 70-76°C.

[0026] Furthermore, in step (1), the decolorization is performed by adding 3% of the total mass of activated carbon; and the filtration is performed by 1 μm filtration.

[0027] Furthermore, in the first sorbic acid decolorizing solution of step (1), the mass concentration of sorbic acid is 20-50%, and the volume concentration of ethanol is 40-65%.

[0028] Furthermore, in step (2), the evaporating kettle is stirred using a propeller stirring paddle.

[0029] Furthermore, in step (2), the distillation is performed at 70-76° C. for 0.5-1 h.

[0030] Furthermore, the ethanol concentration in the second sorbic acid decolorizing solution of step (2) is 27-59%; and the particle size of the seed crystal induced crystals greater than 80 mesh accounts for more than 95%.

[0031] Furthermore, the centrifugal speed in step (3) is 1000-1200 r / min.

[0032] Furthermore, the centrifugal speed in step (4) is 1000-1200 r / min.

[0033] Furthermore, after evaporation, the crystals precipitated from the decolorized liquid are in the form of regular particles, and the proportion of crystals larger than 80 meshes is greater than 95%.

[0034] Furthermore, the coarse-grained sorbic acid is in a block shape, with 30-50 mesh accounting for more than 93.3%, and those above 50 mesh accounting for less than 3%, and the isomer content in the finished product is less than 0.05%.

[0035] Furthermore, the above-mentioned fine particle sorbic acid with a size of 60 to 80 mesh accounts for more than 82%, and the size of more than 100 mesh accounts for less than 5%.

[0036] Beneficial Effects

[0037] (1) The present invention can prepare sorbic acid finished products of coarse and fine particles, which meets the particle size requirements of different customers, and does not require screening treatment, thereby reducing process steps, facilitating factory production, and avoiding dust pollution during the production process.

[0038] (2) The particle size distribution of the coarse and fine sorbic acid finished products prepared by the present invention is narrower and more uniform, which can increase the dissolution rate of sorbic acid, reduce agglomeration and precipitation, and improve the stability and uniformity of the product.

[0039] (3) The present invention directly precipitates crystal seeds of a certain size through evaporative crystallization, thereby reducing the steps of adding crystal seeds and preparing crystal seeds, simplifying the production process, and the evaporated ethanol can be recovered and reused, thereby reducing production costs.

[0040] (4) The present invention can effectively control the particle size distribution of coarse particle sorbic acid by the staged cooling crystallization method, so that the isomer content in the coarse particle sorbic acid finished product is reduced, the product purity is improved, and the quality is improved. BRIEF DESCRIPTION OF THE DRAWINGS

[0041] Figure 1 The present invention is a flow chart of the method for controlling the particle size of sorbic acid crystals. DETAILED DESCRIPTION

[0042] The preferred embodiments of the present invention are described below. It should be understood that the embodiments are for better explaining the present invention and are not used to limit the present invention.

[0043] The experiments and test methods involved in the following embodiments are as follows:

[0044] 1. Determination of sorbic acid isomers: liquid chromatography

[0045] (1) The chromatographic column used in the present invention is Agilent Eclipse XDB-C18;

[0046] (2) Weigh about 0.15 g of sample, add acetonitrile and ultrasonically dissolve, dilute with water to a 100 mL volumetric flask, filter through a 0.45 μm filter membrane and inject, then start the chromatograph. After all operating conditions of the instrument are stable, inject the sample solution into the injection valve with a micro-syringe. After all components have flowed out, use a chromatographic workstation or integrator to process the results;

[0047] (3) Calculate the content of sorbic acid isomers using the area percentage method.

[0048] 2. Test method for particle size of sorbic acid finished product

[0049] The present invention uses a sieving method to test the particle size of the finished sorbic acid product: the sieves are arranged up and down in the order of aperture size, the apertures of the sieves used are 30 meshes, 50 meshes, 60 meshes, 80 meshes and 100 meshes respectively, a powder sample is placed on the uppermost layer, vibrates for 10 minutes at a vibration frequency of 3000 times / min, the weight of the powder on each sieve number is weighed, and the percentage of different particle sizes on each sieve number is obtained.

[0050] 3. Methods for washing coarse and fine particles of sorbic acid

[0051] (1) The centrifuge speed is increased to 700 r / min, and feeding begins. Feeding is performed for 20 to 25 s each time, with an interval of 20 s in between, and a total of 10 times of feeding. After that, the speed is increased to 1000 r / min, and the mother liquor is centrifuged for 2.5 min;

[0052] (2) Wash the material three times with process water, with water intake for 30 seconds each time, centrifugation for 10 seconds, and then continuous centrifugation for about 3 minutes. The speed slowly decreases. After 4 minutes, the speed drops to about 100r / min and the material is unloaded. The material unloaded from the first car is the tail material, which contains a large amount of washing water and is sent to the decolorization section for decolorization. The damp products unloaded from the second car can be dried.

[0053] 4. Methods for drying coarse and fine particles of sorbic acid

[0054] Feed the vacuum dryer, close the feed port, close the air valve, turn on the hot water pump, turn on the vacuum pump, start the dryer, control the drying temperature during the process, dry for 3.5 to 4 hours, turn off the hot water pump, open the cooling water valve, the vacuum degree remains unchanged, the temperature drops below 45°C, close the cooling water valve and the vacuum valve, open the air valve, and pour out the finished product.

[0055] 5. Test method for the crystal form of sorbic acid finished product

[0056] The present invention uses electron microscopy to test the crystal form of the finished sorbic acid crystal: the microscopic morphology, grain size and crystal form of the crystal structure are observed by a high-resolution transmission electron microscope or a scanning electron microscope.

[0057] Raw materials and equipment involved in the embodiments:

[0058] The preparation steps of the refined mother liquor and crude sorbic acid involved in the following examples can refer to the Chinese invention patent application document with publication number CN112876347A. The specific preparation method is as follows:

[0059] (1) A 30% by mass HCl aqueous solution and water in a volume ratio of 2:1 are simultaneously introduced into a mixer to obtain an 18% by mass HCl solution;

[0060] (2) 18% HCl solution and polyester in a volume ratio of 1:1 are simultaneously introduced into a first-stage hydrolysis kettle, the material stays in the first-stage hydrolysis kettle for 30 minutes, and the reaction temperature is 80° C.; a delivery pump is used to continuously pump the solid-liquid mixture into a second-stage hydrolysis kettle, the material stays in the second-stage hydrolysis kettle for 30 minutes, and the reaction temperature is 70° C.; a delivery pump is used to continuously pump the solid-liquid mixture into a third-stage hydrolysis kettle, the material stays in the third-stage hydrolysis kettle for 30 minutes, and the reaction temperature is 60° C.;

[0061] The polyester is 2,4-hexadienoic acid polyester: 500-650 parts by weight of β-methylacrolein and 3-15 parts by weight of a titanium dioxide-silicon dioxide-caprolactam composite catalyst are added to a reaction kettle, stirred, and ethylene ketone gas is introduced at a temperature of 35-50° C. to react. After the reaction is completed, the reaction solution is filtered, and the 2,4-hexadienoic acid polyester is obtained after negative pressure distillation;

[0062] (3) The gas phase of the multi-stage hydrolysis reaction is all absorbed by water, and the solid-liquid mixture after the hydrolysis reaction is continuously pumped from the three-stage kettle hydrolysis kettle to the kettle cooling kettle through a delivery pump, and a solid-liquid separation operation is performed at 40° C., and crude sorbic acid is obtained after centrifugal washing;

[0063] (4) The crude sorbic acid and 45% (V / V) ethanol solution were mixed at a mass ratio of 1:4 and then heated to 70-75°C. After the sorbic acid was completely dissolved, 3% of the total solution mass of activated carbon was added for decolorization. After decolorization for half an hour, the decolorized solution was uniformly cooled to 45°C at a rate of 6°C / h, cooled to 15°C at a rate of 15°C / h, and centrifuged at a speed of 1000 r / min to separate and obtain a refined mother liquor.

[0064] In addition, the refined mother liquor can also be directly taken from the production workshop of Nantong Acetic Acid Chemical Co., Ltd. In this case, the refined mother liquor contains 40% by mass of ethanol and 2-3% by mass of sorbic acid;

[0065] The crude sorbic acid can also be directly obtained from the workshop of Nantong Acetic Acid Chemical Co., Ltd. In this case, the crude product has a sorbic acid content of 91-93%, a tar content of 2-3%, an isomer content of 0.2-0.5%, and a moisture content of 5-7%.

[0066] The molecular formula and structural formula of sorbic acid involved in the embodiments are:

[0067] The molecular formula of sorbic acid is C6H8O2.

[0068] Sorbic acid structure:

[0069]

[0070] Figure 1 Flow chart of the method for controlling the particle size of sorbic acid crystals of the present invention, as shown in Figure 1 As shown, the present invention performs a first program cooling after a certain amount of ethanol is evaporated from the sorbic acid decolorization liquid to precipitate crystal seeds, so as to prepare a coarse particle sorbic acid product, and then uses the decolorization liquid after the coarse particle sorbic acid is precipitated to perform a second program cooling to prepare a fine particle sorbic acid product, and the remaining decolorization liquid enters the next batch of refining process.

[0071] Embodiment 1:

[0072] (1) Preparation of sorbic acid decolorizing solution:

[0073] The crude sorbic acid, refined mother liquor and ethanol were mixed at a mass ratio of 1:1.84:1.16 at 75°C until completely dissolved, and then 3% (120kg) of the total mass of activated carbon was added for decolorization for 30 minutes, and the mixture was filtered through a plate and frame filter press and a precision filter with a filtration accuracy of 1μm to prepare about 4t of the first sorbic acid decolorized liquid; after testing, the mass concentration of sorbic acid in the obtained first sorbic acid decolorized liquid was 25%, and the volume concentration of ethanol was 48%;

[0074] (2) Evaporation of ethanol at normal pressure:

[0075] 4 tons of the first sorbic acid decolorized liquid is pumped into a normal pressure evaporator, the stirring is a propulsion stirring paddle, the blade tip speed of the normal pressure evaporator is controlled to be 1.5 m / s, and after heating to 70°C, evaporate at 70°C for 1 hour, slowly evaporate 120 kg of ethanol, and the volume concentration of ethanol in the decolorized liquid after evaporation drops to about 46.2%, and obtain a second sorbic acid decolorized liquid, in which a small amount of crystals are precipitated, and the precipitated crystals are regular granular, and the proportion of crystals above 80 mesh is greater than 95%; the precipitated crystals can be used as seed crystals in a primary crystallization kettle to induce crystallization;

[0076] (3) Preparation of coarse particle sorbic acid:

[0077] The second sorbic acid decolorizing solution and a small amount of precipitated crystals in step (2) are poured into a primary crystallization kettle, and the temperature is uniformly reduced to 45° C. at a rate of 6° C. / h, and centrifuged at a speed of 1000 r / min to obtain a third sorbic acid decolorizing solution and coarse particles, and the coarse particles are washed and dried to prepare a coarse particle sorbic acid finished product in the form of a block;

[0078] (4) Preparation of fine particle sorbic acid:

[0079] The third sorbic acid decolorized liquid in step (3) is poured into a secondary crystallization kettle, and the temperature is uniformly reduced to 15°C at a rate of 15°C / h, and centrifuged at a speed of 1000r / min to obtain fine particles. The fine particles are washed and dried to prepare a fine particle sorbic acid product, and the remaining decolorized liquid enters the next batch of refining process.

[0080] The experimental results are as follows:

[0081] The isomer content of the coarse sorbic acid product obtained in step (3) is 0.013%, and the coarse sorbic acid product has a particle size of 30 to 50 meshes accounting for 96%, 50 meshes or more accounting for 2%, and 30 meshes or less accounting for 2%; the coarse sorbic acid crystals are uniformly block-shaped and have no agglomeration;

[0082] The fine-particle sorbic acid product obtained in step (4) has a particle size of less than 60 mesh accounting for 8%, 60-80 mesh accounting for 83%, 80-100 mesh accounting for 7%, and above 100 mesh accounting for 2%; the fine-particle sorbic acid crystals are in an uneven block shape, with some agglomerates, and the proportion of crystals with agglomeration phenomenon in the fine-particle sorbic acid crystals is 3.0%.

[0083] Embodiment 2:

[0084] (1) Preparation of sorbic acid decolorizing solution:

[0085] The crude sorbic acid, refined mother liquor and ethanol were mixed at a mass ratio of 1:0.65:0.35 at 75°C until completely dissolved, and then 3% (120kg) of the total mass of activated carbon was added for decolorization for 30 minutes, and the mixture was filtered through a plate and frame filter press and a precision filter with a filtration accuracy of 1μm to prepare about 4t of the first sorbic acid decolorized liquid; after testing, the mass concentration of sorbic acid in the obtained first sorbic acid decolorized liquid was 47%, and the volume concentration of ethanol was 60%;

[0086] (2) Evaporation of ethanol at normal pressure:

[0087] 4 tons of the first sorbic acid decolorized liquid is pumped into a normal pressure evaporator, the stirring is a propulsion stirring paddle, the blade tip speed of the normal pressure evaporator is controlled to be 1.5 m / s, and after heating to 70°C, evaporation is performed at 70°C for 40 minutes, and 80 kg of ethanol is slowly evaporated. After evaporation, the volume concentration of ethanol in the decolorized liquid drops to about 59%, and a second sorbic acid decolorized liquid is obtained, in which a small amount of crystals are precipitated, and the precipitated crystals are regular granular, and the proportion of crystals above 80 mesh is greater than 95%; the precipitated crystals can be used as seed crystals in a primary crystallization kettle to induce crystallization;

[0088] (3) Preparation of coarse particle sorbic acid:

[0089] The second sorbic acid decolorizing solution and a small amount of precipitated crystals in step (2) are poured into a primary crystallization kettle, and the temperature is uniformly reduced to 45° C. at a rate of 8° C. / h, and centrifuged at a speed of 1000 r / min to obtain a third sorbic acid decolorizing solution and coarse particles, and the coarse particles are washed and dried to prepare a square coarse particle sorbic acid finished product;

[0090] (4) Preparation of fine particle sorbic acid:

[0091] The decolorized liquid after the coarse particle sorbic acid is precipitated in step (3) is poured into a secondary crystallization kettle, and the temperature is uniformly reduced to 15°C at a rate of 16°C / h, centrifuged at a speed of 1000r / min, washed and dried to obtain a fine particle sorbic acid product, and the remaining decolorized liquid enters the next batch of refining process.

[0092] The experimental results are as follows:

[0093] The isomer content of the coarse sorbic acid product obtained in step (3) is 0.016%, and the coarse sorbic acid product has a particle size of 30 to 50 meshes accounting for 95.1%, particles above 50 meshes accounting for 2.5%, and particles below 30 meshes accounting for 2.4%; the coarse sorbic acid crystals are uniformly block-shaped without agglomeration;

[0094] The fine-particle sorbic acid product obtained in step (4) has a particle size of less than 60 mesh accounting for 7%, 60-80 mesh accounting for 86%, 80-100 mesh accounting for 3%, and above 100 mesh accounting for 4%; the fine-particle sorbic acid crystals are in an uneven block shape, with some agglomerates, and the proportion of crystals with agglomeration phenomenon in the fine-particle sorbic acid crystals is 3.2%.

[0095] Embodiment 3:

[0096] (1) Preparation of sorbic acid decolorizing solution:

[0097] The crude sorbic acid, refined mother liquor and ethanol were mixed at a mass ratio of 1:0.21:1.37 at 75°C until completely dissolved, and then 3% (120kg) of the total mass of activated carbon was added for decolorization for 30 minutes, and the mixture was filtered through a plate and frame filter press and a precision filter with a filtration accuracy of 1μm to prepare about 4t of the first sorbic acid decolorized liquid; after testing, the mass concentration of sorbic acid in the obtained first sorbic acid decolorized liquid was 36%, and the volume concentration of ethanol was 54%;

[0098] (2) Evaporation of ethanol at normal pressure:

[0099] 4 tons of the first sorbic acid decolorized liquid is pumped into a normal pressure evaporator, the stirring is a propulsion stirring paddle, the blade tip speed of the normal pressure evaporator is controlled to be 1.5 m / s, and after heating to 70°C, evaporation is performed at 70°C for 50 minutes, and 100 kg of ethanol is slowly evaporated. After evaporation, the volume concentration of ethanol in the decolorized liquid drops to about 52.5%, and a second sorbic acid decolorized liquid is obtained, in which a small amount of crystals are precipitated, and the precipitated crystals are regular granular, and the proportion of crystals above 80 mesh is greater than 95%; the precipitated crystals can be used as seed crystals in a primary crystallization kettle to induce crystallization;

[0100] (3) Preparation of coarse particle sorbic acid:

[0101] The second sorbic acid decolorizing solution and a small amount of precipitated crystals in step (2) are poured into a primary crystallization kettle, and the temperature is uniformly reduced to 45° C. at a rate of 7° C. / h, and centrifuged at a speed of 1000 r / min to obtain a third sorbic acid decolorizing solution and coarse particles, and the coarse particles are washed and dried to prepare a block-shaped coarse particle sorbic acid finished product;

[0102] (4) Preparation of fine particle sorbic acid:

[0103] The third sorbic acid decolorized liquid in step (3) is poured into a secondary crystallization kettle, uniformly cooled to 15°C at a rate of 16°C / h, centrifuged at a speed of 1000r / min, washed and dried to obtain a fine particle sorbic acid product, and the remaining decolorized liquid enters the next batch of refining process.

[0104] The experimental results are as follows:

[0105] The isomer content of the coarse sorbic acid product obtained in step (3) is 0.011%, and the coarse sorbic acid product has a particle size of 30 to 50 meshes accounting for 93.3%, particles above 50 meshes accounting for 2.8%, and particles below 30 meshes accounting for 3.7%; the coarse sorbic acid crystals are uniformly block-shaped without agglomeration;

[0106] The fine-particle sorbic acid product obtained in step (4) has a particle size of less than 60 mesh accounting for 7.1%, 60-80 mesh accounting for 82%, 80-100 mesh accounting for 7.7%, and above 100 mesh accounting for 3.2%; the fine-particle sorbic acid crystals are in an uneven block shape, with some agglomerates, and the proportion of crystals with agglomeration phenomenon accounts for 3.6% of the fine-particle sorbic acid crystals.

[0107] Comparative Example 1:

[0108] Compared with Example 1, the ethanol evaporation amount was changed in this comparative example, and the other aspects were consistent with Example 1:

[0109] (1) Preparation of sorbic acid decolorizing solution:

[0110] The crude sorbic acid, refined mother liquor and ethanol were mixed at a mass ratio of 1:1.84:1.16 at 75°C until completely dissolved, and then 3% (120kg) of the total mass of activated carbon was added for decolorization for 30 minutes, and the mixture was filtered through a plate and frame filter press and a precision filter with a filtration accuracy of 1μm to prepare about 4t of the first sorbic acid decolorized liquid; after testing, the mass concentration of sorbic acid in the obtained first sorbic acid decolorized liquid was 25%, and the volume concentration of ethanol was 48%;

[0111] (2) Evaporation of ethanol at normal pressure:

[0112] 4 tons of the first sorbic acid decolorized liquid is pumped into a normal pressure evaporator, the stirring is a propulsion stirring paddle, the blade tip speed of the normal pressure evaporator is controlled to be 1.5 m / s, and after heating to 70°C, evaporate at 70°C for 2h, 100min, and 80min, respectively, and slowly evaporate 180kg, 160kg, and 140kg of ethanol, respectively. After evaporation, the volume concentration of ethanol in the decolorized liquid decreases to about 45.3%, 45.6%, and 45.9%, respectively, to obtain a second sorbic acid decolorized liquid, in which a small amount of crystals are precipitated, the precipitated crystals are regular granular, and the proportion of crystals above 80 mesh is greater than 95%; the precipitated crystals can be used as seed crystals in a primary crystallization kettle to induce crystallization;

[0113] (3) Preparation of coarse particle sorbic acid:

[0114] The second sorbic acid decolorizing solution and a small amount of precipitated crystals in step (2) are poured into a primary crystallization kettle, and the temperature is uniformly reduced to 45° C. at a rate of 6° C. / h, and centrifuged at a speed of 1000 r / min to obtain a third sorbic acid decolorizing solution and coarse particles, and the coarse particles are washed and dried to prepare a coarse particle sorbic acid finished product in the form of a block;

[0115] (4) Preparation of fine particle sorbic acid:

[0116] The third sorbic acid decolorized liquid in step (3) is poured into a secondary crystallization kettle, uniformly cooled to 15°C at a rate of 15°C / h, centrifuged at a speed of 1000r / min, washed and dried to obtain a fine particle sorbic acid product, and the remaining decolorized liquid enters the next batch of refining process.

[0117] The results are shown in Table 1:

[0118] Table 1 Results of coarse and fine particle sorbic acid products prepared in Comparative Example 1

[0119]

[0120] Comparative Example 2:

[0121] Compared with Example 1, the blade tip speed of this comparative example is changed, and the other aspects are consistent with Example 1:

[0122] (1) Preparation of sorbic acid decolorizing solution:

[0123] The crude sorbic acid, refined mother liquor and ethanol were mixed at a mass ratio of 1:1.84:1.16 at 75°C until completely dissolved, and then 3% (120kg) of the total mass of activated carbon was added for decolorization for 30 minutes, and the mixture was filtered through a plate and frame filter press and a precision filter with a filtration accuracy of 1μm to prepare about 4t of the first sorbic acid decolorized liquid; after testing, the mass concentration of sorbic acid in the obtained first sorbic acid decolorized liquid was 25%, and the volume concentration of ethanol was 48%;

[0124] (2) Evaporation of ethanol at normal pressure:

[0125] 4 tons of the first sorbic acid decolorized liquid was pumped into a normal pressure evaporator, and the stirring was carried out by a propulsion stirring paddle. The blade tip speeds of the normal pressure evaporator were controlled to be 0.5 m / s, 1.0 m / s, and 2 m / s, respectively. After heating to 70°C, the liquid was evaporated at 70°C for 1 hour, and 120 kg of ethanol was slowly evaporated. After evaporation, the ethanol content in the decolorized liquid dropped to about 41%, and a second sorbic acid decolorized liquid was obtained, in which a small amount of crystals were precipitated. The precipitated crystals were in the shape of regular particles, and the proportion of crystals above 80 mesh was greater than 95%. The precipitated crystals could be used as seed crystals in a primary crystallization kettle to induce crystallization;

[0126] (3) Preparation of coarse particle sorbic acid:

[0127] The second sorbic acid decolorizing solution and a small amount of precipitated crystals in step (2) are poured into a primary crystallization kettle, and the temperature is uniformly reduced to 45° C. at a rate of 6° C. / h, and centrifuged at a speed of 1000 r / min to obtain a third sorbic acid decolorizing solution and coarse particles, and the coarse particles are washed and dried to prepare a coarse particle sorbic acid finished product in the form of a block;

[0128] (4) Preparation of fine particle sorbic acid:

[0129] The third sorbic acid decolorized liquid in step (3) is poured into a secondary crystallization kettle, uniformly cooled to 15°C at a rate of 15°C / h, centrifuged at a speed of 1000r / min, washed and dried to obtain a fine particle sorbic acid product, and the remaining decolorized liquid enters the next batch of refining process.

[0130] The results are shown in Table 2:

[0131] Table 2 Results of coarse and fine particle sorbic acid products prepared in Comparative Example 2

[0132]

[0133] Comparative Example 3:

[0134] Compared with Example 1, the stirring method was changed from a propeller stirring paddle to an anchor stirring paddle, and the rest was the same as Example 1:

[0135] (1) Preparation of sorbic acid decolorizing solution:

[0136] The crude sorbic acid, refined mother liquor and ethanol were mixed at a mass ratio of 1:1.84:1.16 at 75°C until completely dissolved, and then 3% (120kg) of the total mass of activated carbon was added for decolorization for 30 minutes, and the mixture was filtered through a plate and frame filter press and a precision filter with a filtration accuracy of 1μm to prepare about 4t of the first sorbic acid decolorized liquid; after testing, the mass concentration of sorbic acid in the obtained first sorbic acid decolorized liquid was 25%, and the volume concentration of ethanol was 48%;

[0137] (2) Evaporation of ethanol at normal pressure:

[0138] 4 tons of the first sorbic acid decolorized liquid is pumped into a normal pressure evaporator, the stirring is an anchor-type stirring paddle, the blade tip speed of the normal pressure evaporator is controlled to be 1.5 m / s, and after heating to 70°C, evaporate at 70°C for 1 hour, slowly evaporate 120 kg of ethanol, and the ethanol content in the decolorized liquid after evaporation drops to about 41%, and obtain a second sorbic acid decolorized liquid, in which a small amount of crystals are precipitated, and the precipitated crystals are regular granular, and the proportion of crystals above 80 mesh is greater than 95%; the precipitated crystals can be used as seed crystals in a primary crystallization kettle to induce crystallization;

[0139] (3) Preparation of coarse particle sorbic acid:

[0140] The second sorbic acid decolorizing solution and a small amount of precipitated crystals in step (2) are poured into a primary crystallization kettle, and the temperature is uniformly reduced to 45° C. at a rate of 6° C. / h, and centrifuged at a speed of 1000 r / min to obtain a third sorbic acid decolorizing solution and coarse particles, and the coarse particles are washed and dried to prepare a coarse particle sorbic acid finished product in the form of a block;

[0141] (4) Preparation of fine particle sorbic acid:

[0142] The third sorbic acid decolorized liquid in step (3) is poured into a secondary crystallization kettle, uniformly cooled to 15°C at a rate of 15°C / h, centrifuged at a speed of 1000r / min, washed and dried to obtain a fine particle sorbic acid product, and the remaining decolorized liquid enters the next batch of refining process.

[0143] The stirring of the atmospheric pressure evaporator is propulsion stirring, which can generate greater shear force and disturbance force, thereby achieving more complete mixing and stirring effects; anchor stirring does not generate large shear force when stirring low-viscosity liquids, and cannot make the precipitate evenly distributed.

[0144] The experimental results are as follows: the isomer content in the coarse-grained sorbic acid finished product is 0.053%, of which 69% have a particle size of 30-50 mesh, 24.3% have a particle size of more than 50 mesh, and 6.7% have a particle size of less than 30 mesh; of the fine-grained sorbic acid finished product, 10.2% have a particle size of less than 60 mesh, 83% have a particle size of 60-80 mesh, 4.6% have a particle size of 80-100 mesh, and 2.2% have a particle size of more than 100 mesh.

[0145] Comparative Example 4:

[0146] Compared with Example 1, the cooling rate of the first-stage crystallization kettle was changed, and the others were consistent with Example 1:

[0147] (1) Preparation of sorbic acid decolorizing solution:

[0148] The crude sorbic acid, refined mother liquor and ethanol were mixed at a mass ratio of 1:1.84:1.16 at 75°C until completely dissolved, and then 3% (120kg) of the total mass of activated carbon was added for decolorization for 30 minutes, and the mixture was filtered through a plate and frame filter press and a precision filter with a filtration accuracy of 1μm to prepare about 4t of the first sorbic acid decolorized liquid; after testing, the mass concentration of sorbic acid in the obtained first sorbic acid decolorized liquid was 25%, and the volume concentration of ethanol was 48%;

[0149] (2) Evaporation of ethanol at normal pressure:

[0150] 4 tons of the first sorbic acid decolorized liquid was pumped into a normal pressure evaporator, the blade tip speed of the normal pressure evaporator was controlled to be 1.5 m / s, and after the temperature was raised to 70°C, the liquid was evaporated at 70°C for 1 hour, and 120 kg of ethanol was slowly evaporated. After evaporation, the ethanol content in the decolorized liquid dropped to about 41%, and a second sorbic acid decolorized liquid was obtained, in which a small amount of crystals were precipitated. The precipitated crystals were in the shape of regular particles, and the proportion of crystals above 80 mesh was greater than 95%; the precipitated crystals could be used as seed crystals in a primary crystallization kettle to induce crystallization;

[0151] (3) Preparation of coarse particle sorbic acid:

[0152] The second sorbic acid decolorizing solution and a small amount of precipitated crystals in step (2) are poured into a primary crystallization kettle, and the temperature is uniformly reduced to 45° C. at a rate of 10° C. / h, 12° C. / h, 14° C. / h, and 16° C. / h, respectively, and centrifuged at a speed of 1000 r / min to obtain a third sorbic acid decolorizing solution and coarse particles, and the coarse particles are washed and dried to prepare a square-shaped coarse particle sorbic acid finished product;

[0153] (4) Preparation of fine particle sorbic acid:

[0154] The third sorbic acid decolorized liquid in step (3) is poured into a secondary crystallization kettle, uniformly cooled to 15°C at a rate of 15°C / h, centrifuged at a speed of 1000r / min, washed and dried to obtain a fine particle sorbic acid product, and the remaining decolorized liquid enters the next batch of refining process.

[0155] The results are shown in Table 3:

[0156] Table 3 Results of coarse and fine particle sorbic acid products prepared in Comparative Example 4

[0157]

[0158] Comparative Example 5:

[0159] Compared with Example 1, the cooling rate of the secondary crystallization kettle was changed, and the others were consistent with Example 1:

[0160] (1) Preparation of sorbic acid decolorizing solution:

[0161] The crude sorbic acid, refined mother liquor and ethanol were mixed at a mass ratio of 1:1.84:1.16 at 75°C until completely dissolved, and then 3% (120kg) of the total mass of activated carbon was added for decolorization for 30 minutes, and the mixture was filtered through a plate and frame filter press and a precision filter with a filtration accuracy of 1μm to prepare about 4t of the first sorbic acid decolorized liquid; after testing, the mass concentration of sorbic acid in the obtained first sorbic acid decolorized liquid was 25%, and the volume concentration of ethanol was 48%;

[0162] (2) Evaporation of ethanol at normal pressure:

[0163] 4 tons of the first sorbic acid decolorized liquid was pumped into a normal pressure evaporator, the blade tip speed of the normal pressure evaporator was controlled to be 1.5 m / s, and after the temperature was raised to 70°C, the liquid was evaporated at 70°C for 1 hour, and 120 kg of ethanol was slowly evaporated. After evaporation, the ethanol content in the decolorized liquid dropped to about 41%, and a second sorbic acid decolorized liquid was obtained, in which a small amount of crystals were precipitated. The precipitated crystals were in the shape of regular particles, and the proportion of crystals above 80 mesh was greater than 95%; the precipitated crystals could be used as seed crystals in a primary crystallization kettle to induce crystallization;

[0164] (3) Preparation of coarse particle sorbic acid:

[0165] The second sorbic acid decolorizing solution and a small amount of precipitated crystals in step (2) are poured into a primary crystallization kettle, and the temperature is uniformly reduced to 45° C. at a rate of 6° C. / h, and centrifuged at a speed of 1000 r / min to obtain a third sorbic acid decolorizing solution and coarse particles, and the coarse particles are washed and dried to prepare a coarse particle sorbic acid finished product in the form of a block;

[0166] (4) Preparation of fine particle sorbic acid:

[0167] The third sorbic acid decolorized liquid in step (3) is poured into a secondary crystallization kettle, and the temperature is uniformly reduced to 15°C at a rate of 6°C / h, 8°C / h, 10°C / h, 12°C / h, and 14°C / h, respectively, and centrifuged at a speed of 1000 r / min, washed, and dried to prepare a fine particle sorbic acid product, and the remaining decolorized liquid enters the next batch of refining process.

[0168] The results are shown in Table 4:

[0169] Table 4 Results of coarse and fine particle sorbic acid products prepared in Comparative Example 5

[0170]

[0171] Comparative Example 6:

[0172] Compared with Example 1, the step-by-step cooling is changed to non-step-by-step cooling, and the rest is the same as Example 1:

[0173] (1) Preparation of sorbic acid decolorizing solution:

[0174] The crude sorbic acid, refined mother liquor and ethanol were mixed at a mass ratio of 1:1.84:1.16 at 75°C until completely dissolved, and then 3% (120kg) of the total mass of activated carbon was added for decolorization for 30 minutes, and filtered through a plate and frame filter press and a precision filter with a filtration accuracy of 1μm to prepare about 4t of the first sorbic acid decolorized liquid; after testing, the mass concentration of sorbic acid in the obtained first sorbic acid decolorized liquid was 25%, and the volume concentration of ethanol was 48%;

[0175] (2) Evaporation of ethanol at normal pressure:

[0176] 4 tons of the first sorbic acid decolorized liquid is pumped into a normal pressure evaporator, the stirring is a propulsion stirring paddle, the blade tip speed of the normal pressure evaporator is controlled to be 1.5 m / s, and after heating to 70°C, evaporate at 70°C for 1 hour, slowly evaporate 120 kg of ethanol, and the volume concentration of ethanol in the decolorized liquid after evaporation drops to about 46.2%, and obtain a second sorbic acid decolorized liquid, in which a small amount of crystals are precipitated, and the precipitated crystals are regular granular, and the proportion of crystals above 80 mesh is greater than 95%; the precipitated crystals can be used as seed crystals in a primary crystallization kettle to induce crystallization;

[0177] (3) Preparation of sorbic acid:

[0178] The second sorbic acid decolorized liquid and a small amount of precipitated crystals in step (2) are poured into a primary crystallization kettle, uniformly cooled to 45°C at a rate of 6°C / h, cooled to 15°C at a rate of 15°C / h, centrifuged at a speed of 1000 r / min, washed, dried and sieved to prepare coarse and fine particle sorbic acid products, and the remaining decolorized liquid enters the next batch of refining process.

[0179] The experimental results are as follows:

[0180] The isomer content of the prepared coarse particle sorbic acid product is 0.071%, the particle size below 30 mesh accounts for 3.7%, 30-50 mesh accounts for 51.9%, and 50-60 mesh accounts for 18.2%. The coarse particle sorbic acid crystals are uniformly square, partially agglomerated, and the proportion of agglomerated crystals to the coarse particle sorbic acid crystals is 6.7%;

[0181] Among the prepared fine particle sorbic acid products, 60-80 mesh accounts for 10.4%, and above 80 mesh accounts for 15.8%; the fine particle sorbic acid crystals are uneven blocks, with some agglomerates, and the proportion of agglomerated crystals accounts for 8.4% of the fine particle sorbic acid crystals.

[0182] Although the present invention has been disclosed as above in the form of a preferred embodiment, it is not intended to limit the present invention. Anyone familiar with this technology can make various changes and modifications without departing from the spirit and scope of the present invention. Therefore, the scope of protection of the present invention should be based on the definition of the claims.

Claims

1. A method for regulating the particle size of sorbic acid crystals, characterized in that: Includes steps: (1) Preparation of sorbic acid decolorizing solution: The crude sorbic acid, the refined mother liquor and ethanol are mixed, decolorized and filtered to obtain a first sorbic acid decolorized liquid; Wherein, the preparation method of crude sorbic acid is: 18-25% HCl solution and 2,4-hexadienoic acid polyester are simultaneously introduced into a first-stage kettle hydrolysis kettle at a volume ratio of 1-3:1, and reacted at 80-90°C for 30-50min; pumped into a second-stage kettle hydrolysis kettle, and reacted at 70-80°C for 30-50min; pumped into a third-stage hydrolysis kettle at 60-70°C for 30-50min; pumped into a kettle cooling kettle, cooled to 40-45°C, and separated into solid and liquid to obtain crude sorbic acid; The preparation method of refined mother liquor is: The crude sorbic acid and ethanol solution are mixed in a mass ratio of 1:4, heated to 70-75°C, decolorized after dissolution, cooled to 45°C at a rate of 6°C / h, then cooled to 15°C at a rate of 15°C / h, and centrifuged to obtain a refined mother liquor; (2) Evaporation to remove ethanol at normal pressure: The first sorbic acid decolorized liquid is pumped into an evaporator, and 2% to 3% of the total mass of ethanol of the decolorized liquid is evaporated at a blade tip speed of 1.4 to 1.6 m / s to obtain a second sorbic acid decolorized liquid and seed crystals for inducing crystallization; (3) Preparation of coarse particle sorbic acid: The second sorbic acid decolorizing solution and seed crystals for inducing crystallization are poured into a crystallization kettle, the cooling rate is controlled to be 6-8°C / h, the temperature is lowered to 40-45°C, and the third sorbic acid decolorizing solution and coarse particles are obtained by centrifugation, and the coarse particles are washed and dried to obtain coarse sorbic acid particles; (4) Preparation of fine particle sorbic acid: The third sorbic acid decolorized liquid is poured into a crystallization kettle, and the cooling rate is controlled to be 15-16°C / h until the temperature drops to 15-20°C. Fine particles are obtained by centrifugation, and the fine particles are washed and dried to obtain fine particle sorbic acid.

2. The method according to claim 1, characterized in that The mass ratio of the crude sorbic acid, the refined mother liquor and the ethanol in step (1) is 1:0.1-3:0.1-4.

3. The method according to claim 1, characterized in that The mixing in step (1) is carried out at 70-76°C.

4. The method according to claim 1, characterized in that In step (1), the decolorization is performed by adding 3% of the total weight of activated carbon; and the filtration is performed by 1 μm filtration.

5. The method according to claim 1, characterized in that The mass concentration of sorbic acid in the first sorbic acid decolorizing solution of step (1) is 20-50%, and the volume concentration of ethanol is 40-65%.

6. The method according to claim 1, characterized in that In step (2), the evaporator is stirred using a propeller stirring paddle.

7. The method according to claim 1, characterized in that In step (2), the distillation is carried out at 70-76° C. for 0.5-1 h.

8. The method according to claim 1, characterized in that The ethanol concentration in the second sorbic acid decolorizing solution of step (2) is 27-59%; and the particle size greater than 80 mesh accounts for more than 95% in the seed crystal induced crystallization.

9. The method according to claim 1, characterized in that: The centrifugal speed in step (3) is 1000-1200r / min.

10. The method according to claim 1, characterized in that The centrifugal speed in step (4) is 1000-1200r / min.

Images