Sorbic acid hydrolysis staged reaction method

Abstract

The invention discloses a sorbic acid hydrolysis staged reaction method, and belongs to the technical field of chemical engineering. According to the technical scheme, the method comprises the following steps: mixing beta-methylacrolein and a titanium dioxide-silicon dioxide-caprolactam composite catalyst, introducing ketene gas at 35-50 DEG C for reaction, filtering, and rectifying reaction liquid to obtain 2, 4-hexadienoic acid polyester; polyester and hydrochloric acid are added into a reaction system according to the mass ratio of 1: (1-2), the concentration of the hydrochloric acid in the system is 25-30%, and the reaction is carried out for 0.5-2 h at the temperature of 85-90 DEG C Raising the pressure to 0.1-0.4 MPa, adding hydrochloric acid which is 4.5-6 times of the mass of the polyester, enabling the concentration of the hydrochloric acid in the system to be 16-20%, and reacting for 0.5-2 hours at the temperature of 95-98 DEG C; the pressure is relieved, cooling crystallization is conducted at the speed of 0.1-0.8 DEG C / min, a hydrolysis material is obtained through separation, the hydrolysis material is washed and centrifuged, a sorbic acid crude product is obtained, and the hydrolysis yield of the crude product is larger than or equal to 90%.

Description

Technical Field

[0001] The invention discloses a method for preparing sorbic acid by hydrolyzing sorbic acid in a sorbic acid preparation process in a staged reaction, and belongs to the field of chemical production. Background Art

[0002] Sorbic acid, scientific name 2,4-hexadienoic acid, is the most widely used preservative in the world. It has high antibacterial properties and inhibits the growth and reproduction of molds. It inhibits the growth of microorganisms and plays a preservative role by inhibiting the dehydrogenase system in microorganisms. It has an inhibitory effect on molds, yeasts and many aerobic bacteria, but is almost ineffective against anaerobic spore-forming bacteria and Lactobacillus acidophilus. It is widely used in the preservation of cheese, yogurt and other cheese products, bread and pastry products, beverages, juices, jams, pickles and fish products.

[0003] Its structural characteristics are as follows:

[0004] Appearance: White needle-shaped or powdery crystals;

[0005] Solubility: slightly soluble in water, soluble in a variety of organic solvents;

[0006] CAS No.: 110-44-1;

[0007] Molecular formula: C 6 H 8 O 2 ;

[0008] Structural formula:

[0009] Molecular weight: 112.13;

[0010] Melting point (℃): 132-135;

[0011] Boiling point (℃): 228;

[0012] Flash point (℃): 127;

[0013] Relative density (g / cm 3 ):1.205;

[0014] The common method for preparing sorbic acid is to first condense ketene and crotonaldehyde to obtain polyester, and then hydrolyze with hydrochloric acid, centrifuge and wash, bleach and purify, and dry to obtain the finished sorbic acid product. Conventional methods for preparing sorbic acid by depolymerization of polyester include acid hydrolysis, alkali-acid hydrolysis, vacuum thermal cracking, etc. The vacuum thermal cracking method has high requirements for equipment, and the high temperature and high vacuum conditions make the energy consumption of this method high; the conventional acid hydrolysis method is to hydrolyze at a constant hydrochloric acid concentration, which usually cannot completely depolymerize the polyester, and produces a large amount of tar by-products, which makes the yield of this method low, and the quality of the obtained sorbic acid semi-finished product is also low.

[0015] At present, the main methods for polyester hydrolysis in industry are: intermittent method, continuous multi-stage hydrolysis, microwave-assisted hydrolysis, enzyme-catalyzed hydrolysis, etc.

[0016] Patent CN 100430362C uses an intermittent method to hydrolyze polyester: the prepared hydrochloric acid solution is pumped into the hydrolysis kettle, and the liquid level is measured. The agitator of the hydrolysis kettle is turned on, and the polyester purified in the distillation section is then placed into the hydrolysis kettle using the potential difference. The jacket steam valve of the hydrolysis kettle is opened, the temperature of the material in the kettle is heated to 96-98°C, kept warm for 30 minutes, and the steam valve is closed. The cooling water valve is opened, the temperature of the material in the kettle is reduced to below 40°C, the cooling water valve is closed, and the agitator of the hydrolysis kettle is closed to obtain crude sorbic acid. This process has a long reaction time, cumbersome operation, low production efficiency, and high cost; the purity of the sorbic acid product decreases and the color deteriorates.

[0017] Patent CN1068564A uses 33% hydrochloric acid to acidify polyester, the mass ratio of polyester to hydrochloric acid is 1:3.5, the polyester is stirred and kept warm at 65-75°C for 1h, then heated to 80-95°C and stirred for 1.5h, and then the obtained material is separated and washed to obtain crude sorbic acid. The hydrochloric acid concentration used in this method is relatively high. On the one hand, the high-concentration hydrochloric acid volatilizes in a large amount during the reaction, which is not conducive to environmental protection treatment. On the other hand, the method uses a large amount of hydrochloric acid, and the recovery and reuse of the hydrochloric acid will also consume a large amount of high-concentration hydrochloric acid, which is not economical and has a high cost. Summary of the invention

[0018] In order to solve the above problems, the present invention adopts different reaction temperatures, reaction pressures and reaction acid concentrations in the initiation stage and the violent reaction stage to control the reaction rates at different stages of the reaction, specifically:

[0019] In the initiation stage, a higher reaction temperature and a higher acid concentration are selected to convert the raw material polyester from a high molecular compound into a low molecular compound, which is beneficial to the bond breaking of the high molecular compound, while a lower reaction temperature is beneficial to reducing the side reactions and the generation of tar by-products;

[0020] In the violent reaction stage, the further reaction and bond breaking of small molecule compounds are mainly carried out. By means of pressurization, the reaction can be carried out gently at a lower reaction acid concentration and a higher reaction temperature. The mild and controllable reaction process is more conducive to the formation of small molecule compounds into target products, and is also conducive to the conversion of isomers into sorbic acid, and the reduction of tar by-products, so that the hydrolysis reaction yield can be ≥90%, and the quality of the crude product is improved, the transmittance of the crude product is stable at ≥75%, and the isomer content is stable at 0.05% to 0.1%. The molecular weight of the tar by-products produced by hydrolysis is 200 to 500.

[0021] The present invention provides a sorbic acid hydrolysis staged reaction method, comprising the following steps:

[0022] (1) Preparation of polyester:

[0023] 500-650 parts by weight of β-methylacrolein and 3-15 parts by weight of a composite catalyst are mixed, 300-390 parts by weight of ketene gas are introduced at 35-50° C. to react for 2-4 hours, and after the reaction is completed, the mixture is filtered and the reaction liquid is distilled to obtain 2,4-hexadienoic acid polyester; the composite catalyst is composed of titanium dioxide, silicon dioxide and caprolactam;

[0024] (2) adding hydrochloric acid and the polyester obtained in step (1) into the reaction system, and starting the reaction at 85-90° C.; the concentration of hydrochloric acid in the reaction system is 25-30%;

[0025] (3) After the reaction is completed, the pressure of the reaction system is controlled to 0.1-0.4 MPa, and hydrochloric acid is added to make the concentration of hydrochloric acid in the reaction system 16-20%, and the reaction is continued at 95-98° C. for 0.5-2 h;

[0026] (4) After the reaction in step (3) is completed, the pressure is released, the temperature is lowered, and the waste liquid is separated to obtain a hydrolyzed material. The hydrolyzed material is washed and centrifuged to obtain a crude sorbic acid product.

[0027] In one embodiment, in step (1), the composite catalyst is obtained by mixing titanium dioxide, silicon dioxide, and caprolactam in a ratio of 10-20% by mass: 30-60% by mass: 25-60% by mass.

[0028] In one embodiment, in step (1), the method for preparing the composite catalyst comprises the following steps:

[0029] TiO was obtained by hydrolyzing butyl titanate in 0.1 mol / L hydrochloric acid. 2 Sol A: SiO2 was obtained by hydrolyzing ethyl orthosilicate in a mixed solution of 0.2 mol / L hydrochloric acid and ethanol. 2 Sol B; Mix A and B to obtain TiO 2 / SiO2 Sol C; adding ethanol aqueous solution to Sol C, washing and drying; then dissolving caprolactam in water to obtain solution D, dropping Sol C into solution D, washing and drying, and obtaining a titanium dioxide-silicon dioxide-caprolactam composite catalyst.

[0030] In one embodiment, in step (1), the distillation is carried out under negative pressure at a vacuum degree of 0.095 to 0.10 MPa.

[0031] In one embodiment, in step (2), the polyester and hydrochloric acid are reacted in a mass ratio of 1:1 to 1:2.

[0032] In one embodiment, in step (2), the reaction time of the reaction is 0.5 to 2 hours.

[0033] In one embodiment, in step (3), the amount of hydrochloric acid added is 4.5 to 6 times the mass of the polyester.

[0034] In one embodiment, in step (4), the temperature is lowered to 40°C at a rate of 0.1-0.8°C / min, the waste liquid is separated to obtain a hydrolyzed material, the hydrolyzed material is washed with water, 1.5 times with 70% ethanol solution, and then washed with 0.5 times with water, and centrifuged at 1500-2500 rpm for 5-10 minutes to obtain a crude sorbic acid product.

[0035] The present invention also provides an application of the method in preparing crude sorbic acid.

[0036] Beneficial Effects

[0037] (1) In the initiation stage of the hydrolysis reaction, by using high concentration of hydrochloric acid and high reaction temperature, the high molecular weight polyester is efficiently decomposed into small molecular weight compounds, and the reaction process control is more stable, the generation of side reactions is reduced, and the generation of by-products is reduced;

[0038] (2) During the violent reaction stage of the hydrolysis process, the pressure rises and the hydrochloric acid concentration decreases during the reaction, making the conversion of small molecule compounds into target products more gentle. At the same time, a higher reaction temperature is selected to accelerate the reaction rate, make the reaction more thorough, reduce side reactions, and be more conducive to the conversion of isomers into target products during the reaction process. The crude sorbic acid content is stabilized at 93-95%, the isomer content in the crude sorbic acid is stabilized at 0.05-0.1%, and the hydrolysis yield is ≥90%;

[0039] (3) The molecular weight of the tar after centrifugal washing of the hydrolyzed crude product is between 200 and 500. The tar is more easily soluble in alcohol. The centrifugal washing effect is good, the quality of the crude product is improved, and the amount of tar after hydrolysis is reduced by 10% compared with the conventional process. The transmittance of the crude product is ≥75%. BRIEF DESCRIPTION OF THE DRAWINGS

[0040] Figure 1 The figure is a process flow chart of the staged reaction method for hydrolysis of sorbic acid. DETAILED DESCRIPTION

[0041] The following examples and comparative examples are provided with the measurement / calculation methods involved:

[0042] 1. Determination of sorbic acid and its isomers in crude products

[0043] (1) The chromatographic column is Agilent Eclipse XDB-C18;

[0044] (2) Weigh 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;

[0045] (3) Calculate the content of sorbic acid and its isomers in the crude product by the area percentage method.

[0046] 2. Determination of transmittance of crude sorbic acid by UV spectrophotometer

[0047] The reference substance method is used to prepare the test solution and the reference substance solution respectively. The solvents used are exactly the same. The amount of the measured component contained in the reference substance solution should be 100% ± 10% of the specified amount of the measured component in the test solution. After measuring the absorbance of the test solution and the reference substance solution at the specified wavelength, calculate the concentration of the measured solution in the test sample according to the following formula:

[0048] Cx=(Ax / Ar)Cr

[0049] Where Cx is the concentration of the test solution; Ax is the absorbance of the test solution; Cr is the concentration of the reference solution; Ar is the absorbance of the reference solution.

[0050] 3. Tar molecular weight determination

[0051] Gel Permeation Chromatography (GPC) was used to measure:

[0052] (1) Preparation of calibration standard substances: Select a polymer with a known molecular weight as a calibration standard substance and prepare a set of standard substance solutions with different molecular weights;

[0053] (2) Sample pretreatment: dissolve the sample to be tested in an appropriate solvent and perform necessary pretreatment steps, such as filtering to remove impurities;

[0054] (3) Instrument debugging: Debug various parameters of the GPC instrument, such as flow rate, temperature, etc., to ensure that the instrument operates in the best condition;

[0055] (4) Sample injection: The calibration standard and the sample to be tested are injected into the column of the GPC instrument in sequence;

[0056] (5) Column separation: In the GPC column, polymers in the solution will be separated in the column due to their different molecular weights;

[0057] (6) Detection: At the outlet of the column, use an appropriate detector to measure the response signal of the solution, such as refractive index, light scattering, or viscosity;

[0058] (7) Data processing: Based on the measurement results and response signals of the calibration standard substances, data processing is performed using computational analysis software to draw a molecular weight distribution curve or calculate the average molecular weight.

[0059] 4. Calculation of hydrolysis yield

[0060] Crude sorbic acid mass × crude sorbic acid content / polyester mass × 100%.

[0061] The 36.5% (AR) hydrochloric acid involved in the following examples was purchased from Sinopharm Chemical Reagent Co., Ltd.; the polyester was produced in the workshop, and the following preparation steps can be referred to the Chinese invention patent with publication number CN 103613747 A:

[0062] 500-650 parts by weight of β-methylacrolein and 3-15 parts by weight of a composite catalyst of titanium dioxide-silicon dioxide-caprolactam (mass percentage 10-20%: 30-60%: 25-60%) are added to a reaction kettle, stirred, and 300-390 parts by weight of ketene gas are introduced at a temperature of 35-50° C. to react for 2-4 hours. After the reaction is completed, the reaction solution is filtered and subjected to negative pressure distillation at a vacuum degree of 0.095-0.10 MPa to obtain 2,4-hexadienoic acid polyester.

[0063] In a specific embodiment of the present invention, polyester can be prepared according to the following method:

[0064] (1) Preparation of titanium dioxide-silicon dioxide-caprolactam composite catalyst:

[0065] 8.8083 g of butyl titanate was hydrolyzed in 103.6 mL of 0.1 mol / L hydrochloric acid to obtain TiO 2 Sol A; 21.5544 g of ethyl orthosilicate was hydrolyzed in a mixed solution of 12.8 mL of 0.2 mol / L hydrochloric acid and 15.4 mL of ethanol to obtain SiO 2 Sol B: A and B were mixed and stirred for 0.5 hours to obtain colorless, clear and transparent TiO 2 / SiO 2Sol C; 11.7099 g of caprolactam was dissolved in 780 g of water to obtain a solution D, and Sol C was dropped into the solution D, washed and dried to obtain a titanium dioxide - silicon dioxide - caprolactam composite catalyst;

[0066] (2) Add 550 kg of β-methylacrolein and 5 kg of the titanium dioxide-silicon dioxide-caprolactam composite catalyst obtained in step (1) into a reaction kettle, stir, heat to 40° C., and introduce 330 kg of ethylene ketone gas for reaction. After the reaction is completed, filter the catalyst, and distill the reaction solution under a vacuum degree of 0.098 MPa to obtain 2,4-hexadienoic acid polyester.

[0067] The above method is not intended to limit the present invention, and the polyester may also be commercially available.

[0068] Example 1: A stepwise reaction method for hydrolysis of sorbic acid

[0069] The specific implementation is as follows:

[0070] (1) Initiation section:

[0071] 300 g of polyester and high-concentration hydrochloric acid with a mass fraction of 25% (w / w) were added to the hydrolysis kettle in a mass ratio of 1:1. The hydrochloric acid content in the reaction system was monitored by an online hydrochloric acid concentration detector to stabilize the hydrochloric acid concentration at 25%. The temperature was raised to 85° C. under normal pressure to start the reaction, and the reaction time was 0.5 h.

[0072] (2) Violent reaction stage:

[0073] Slowly increase the pressure of the reaction system in step (1) to 0.1 MPa, and add low-concentration hydrochloric acid 4.5 times the mass of the polyester thereto, monitor the hydrochloric acid content in the reaction system by an online hydrochloric acid concentration detector, and gradually reduce the hydrochloric acid concentration in the system to 16%, control the entire reaction temperature to 95°C, and the reaction time to 0.5 h;

[0074] (3) After the reaction is completed, the pressure is released, and the temperature is uniformly lowered to 40° C. at a rate of 0.1° C. / min. The hydrolyzed material is separated to obtain a hydrolyzed material. The hydrolyzed material is washed with water, filtered, and washed with a 70% (v / v) ethanol aqueous solution 1.5 times the amount of the hydrolyzed material (after ethanol washing, the material contains tar by-products). After filtering out the ethanol solution containing the tar by-products, the material is washed with 0.5 times the amount of water of the hydrolyzed material. After washing, the material is centrifuged at 2000 rpm for 5 min to finally obtain a crude sorbic acid product.

[0075] The results show:

[0076] (1) The hydrolysis yield of the process is 90.5%, the transmittance of crude sorbic acid is 79.8%, the content of crude sorbic acid is 93.9%, and the isomer content is 0.1%.

[0077] (2) The ethanol solution containing the tar by-product in step (3) is evaporated to dryness to obtain concentrated tar. The tar molecular weight is measured to be 250.

[0078] It can be seen that the hydrolysis reaction of the present invention is thorough, the molecular weight of the obtained tar is small, the low molecular weight tar is more easily dissolved in ethanol during the washing process, and the tar is removed as the ethanol evaporates, so that the quality of the crude sorbic acid is further improved.

[0079] Example 2: A stepwise reaction method for hydrolysis of sorbic acid

[0080] The specific implementation is as follows:

[0081] (1) Initiation section:

[0082] 300 g of polyester and high-concentration hydrochloric acid with a mass fraction of 28% (w / w) were added to the hydrolysis kettle in a mass ratio of 1:1. The hydrochloric acid content in the reaction system was monitored by an online hydrochloric acid concentration detector to stabilize the hydrochloric acid concentration at 28%. The temperature was raised to 88° C. at normal pressure to start the reaction, and the reaction time was 1 hour.

[0083] (2) Violent reaction stage:

[0084] Slowly increase the pressure of the reaction system in step (1) to 0.25 MPa, and add low-concentration hydrochloric acid 5 times the mass of the polyester thereto, monitor the hydrochloric acid content in the reaction system by an online hydrochloric acid concentration detector, and gradually reduce the hydrochloric acid concentration in the system to 18%, control the entire reaction temperature to 96.5°C, and the reaction time to 1 h;

[0085] (3) After the reaction is completed, the pressure is released, and the temperature is uniformly lowered to 40° C. at a rate of 0.5° C. / min. The hydrolyzed material is separated to obtain a hydrolyzed material. The hydrolyzed material is washed with water, filtered, and washed with a 70% (v / v) ethanol aqueous solution 1.5 times the amount of the hydrolyzed material (after ethanol washing, the material contains tar by-products). After filtering out the ethanol solution containing the tar by-products, the material is washed with 0.5 times the amount of water of the hydrolyzed material. After washing, the material is centrifuged at 2000 rpm for 5 min to finally obtain a crude sorbic acid product.

[0086] The results show:

[0087] (1) The hydrolysis yield of the process is 91.1%, the transmittance of crude sorbic acid is 77.6%, the content of crude sorbic acid is 93.4%, and the isomer content is 0.08%.

[0088] (2) evaporating the ethanol solution containing the tar by-product in step (3) to obtain concentrated tar, and the tar molecular weight is measured to be 300.

[0089] It can be seen that the hydrolysis reaction of the present invention is thorough, the molecular weight of the obtained tar is small, the low molecular weight tar is more easily dissolved in ethanol during the washing process, and the tar is removed as the ethanol evaporates, so that the quality of the crude sorbic acid is further improved.

[0090] Example 3: A stepwise reaction method for hydrolysis of sorbic acid

[0091] The specific implementation is as follows:

[0092] (1) Initiation section:

[0093] 300 g of polyester and high-concentration hydrochloric acid with a mass fraction of 30% (w / w) were added to the hydrolysis kettle in a mass ratio of 1:2. The hydrochloric acid content in the reaction system was monitored by an online hydrochloric acid concentration detector to stabilize the hydrochloric acid concentration at 30%. The temperature was raised to 90° C. under normal pressure to start the reaction, and the reaction time was 2 h.

[0094] (2) Violent reaction stage:

[0095] Slowly increase the pressure of the reaction system in step (1) to 0.4 MPa, and add low-concentration hydrochloric acid 5 times the mass of the polyester thereto, monitor the hydrochloric acid content in the reaction system by an online hydrochloric acid concentration detector, and gradually reduce the hydrochloric acid concentration in the system to 20%, control the entire reaction temperature to 98° C., and the reaction time to 2 h;

[0096] (3) After the reaction is completed, the pressure is released, and the temperature is uniformly lowered to 40° C. at a rate of 0.8° C. / min. The hydrolyzed material is separated to obtain a hydrolyzed material. The hydrolyzed material is washed with water, filtered, and washed with a 70% (v / v) ethanol aqueous solution 1.5 times the amount of the hydrolyzed material (after ethanol washing, the material contains tar by-products). After filtering out the ethanol solution containing the tar by-products, the material is washed with 0.5 times the amount of water of the hydrolyzed material. After washing, the material is centrifuged at 2000 rpm for 5 min to finally obtain a crude sorbic acid product.

[0097] The results show:

[0098] (1) The hydrolysis yield of the process is 90.7%, the transmittance of crude sorbic acid is 75%, the content of crude sorbic acid is 94.4%, and the isomer content is 0.05%.

[0099] (2) evaporating the ethanol solution containing the tar by-product in step (3) to obtain concentrated tar, and measuring the molecular weight of the tar to be 500.

[0100] It can be seen that the hydrolysis reaction of the present invention is thorough, the molecular weight of the obtained tar is small, the low molecular weight tar is more easily dissolved in ethanol during the washing process, and the tar is removed as the ethanol evaporates, so that the quality of the crude sorbic acid is further improved.

[0101] Example 4: A stepwise reaction method for hydrolysis of sorbic acid

[0102] The specific implementation is as follows:

[0103] (1) Initiation section:

[0104] 300 g of polyester and high-concentration hydrochloric acid with a mass fraction of 30% (w / w) were added to the hydrolysis kettle in a mass ratio of 1:1, and the hydrochloric acid content in the reaction system was monitored by an online hydrochloric acid concentration detector to stabilize the hydrochloric acid concentration at 30%. The temperature was raised to 85° C. under normal pressure to start the reaction, and the reaction time was 1 hour;

[0105] (2) Violent reaction stage:

[0106] Slowly increase the pressure of the reaction system in step (1) to 0.4 MPa, and add low-concentration hydrochloric acid 6 times the mass of the polyester thereto, monitor the hydrochloric acid content in the reaction system by an online hydrochloric acid concentration detector, and gradually reduce the hydrochloric acid concentration in the system to 16%, control the entire reaction temperature to 98° C., and the reaction time to 1 h;

[0107] (3) After the reaction is completed, the pressure is released, and the temperature is uniformly lowered to 40° C. at a rate of 0.5° C. / min. The hydrolyzed material is separated to obtain a hydrolyzed material. The hydrolyzed material is washed with water, filtered, and washed with a 70% (v / v) ethanol aqueous solution 1.5 times the amount of the hydrolyzed material (after ethanol washing, the material contains tar by-products). After filtering out the ethanol solution containing the tar by-products, the material is washed with 0.5 times the amount of water of the hydrolyzed material. After washing, the material is centrifuged at 2000 rpm for 5 min to finally obtain a crude sorbic acid product.

[0108] The results show:

[0109] (1) The hydrolysis yield of the process is 91.2%, the transmittance of crude sorbic acid is 79.5%, the content of crude sorbic acid is 93.5%, and the isomer content is 0.06%.

[0110] (2) The ethanol solution containing the tar by-product in step (3) is evaporated to dryness to obtain concentrated tar. The tar molecular weight is measured to be 230.

[0111] It can be seen that the hydrolysis reaction of the present invention is thorough, the molecular weight of the obtained tar is small, the low molecular weight tar is more easily dissolved in ethanol during the washing process, and the tar is removed as the ethanol evaporates, so that the quality of the crude sorbic acid is further improved.

[0112] Comparative Example 1: A Sorbic Acid Hydrolysis Staged Reaction Method

[0113] The specific implementation method is the same as that of Example 1, except that the conventional intermittent method is used for hydrolysis. The specific operation steps are as follows:

[0114] (1) 300 g of polyester and high-concentration hydrochloric acid with a mass fraction of 21% (w / w) were added to a hydrolysis kettle in a mass ratio of 1:1, and the hydrochloric acid content in the reaction system was monitored by an online hydrochloric acid concentration detector to stabilize the hydrochloric acid concentration at 21%. The temperature was raised to 90° C. under normal pressure to start the reaction, and the reaction time was 1 hour;

[0115] (2) The kettle temperature is controlled between 90 and 96° C. After the reaction is completed, the kettle temperature is uniformly lowered to 40° C. at a rate of 0.1 to 0.8° C. / min. The hydrolyzed material is separated from the hydrochloric acid waste liquid to obtain a hydrolyzed material. The hydrolyzed material is washed with water, filtered, and washed with 1.5 times the amount of 70% (v / v) ethanol aqueous solution of the hydrolyzed material (after ethanol washing, the material contains tar by-products). After filtering out the ethanol solution containing the tar by-products, the material is washed with 0.5 times the amount of water of the hydrolyzed material. After washing, the material is centrifuged at 2000 rpm for 5 min to finally obtain a crude sorbic acid product.

[0116] The results show:

[0117] The ethanol solution containing the tar byproduct in step (2) is evaporated to dryness to obtain concentrated tar. The results are shown in Table 1 and Table 2:

[0118] Table 1 Crude sorbic acid prepared by conventional batch hydrolysis and different reaction temperatures

[0119]

[0120]

[0121] Table 2 Crude sorbic acid prepared by conventional batch hydrolysis and different cooling crystallization rates

[0122]

[0123] Note: The cooling crystallization rate has no effect on the hydrolysis yield and tar molecular weight of crude sorbic acid and is not the subject of investigation, so no specific value is given here.

[0124] It can be seen that after the conventional intermittent method is used for hydrolysis, at different reaction temperatures, the hydrolysis yield of crude sorbic acid decreases, the transmittance of crude sorbic acid decreases, the isomer content increases, the hydrolysis reaction is not complete, the molecular weight of the washed tar is large, and the quality of crude sorbic acid cannot be improved;

[0125] After hydrolysis by conventional intermittent method, the transmittance of crude sorbic acid decreased and the isomer content increased at different cooling and crystallization rates, and the quality of crude sorbic acid could not be improved.

[0126] Comparative Example 2: A Sorbic Acid Hydrolysis Staged Reaction Method

[0127] Specific implementation method The method is the same as Example 1, except that the concentration of hydrochloric acid in the first stage of the stepwise reaction is adjusted to 22%, 30%, 32%, and 35%, and other conditions remain unchanged to prepare crude sorbic acid.

[0128] result:

[0129] Table 3 Crude sorbic acid prepared by different hydrochloric acid concentrations in the first stage reaction in Comparative Example 2

[0130]

[0131]

[0132] It can be seen that after adjusting the hydrochloric acid concentration in the first stage of the reaction, the hydrolysis yield of crude sorbic acid decreased, the transmittance of crude sorbic acid decreased, the isomer content increased, the hydrolysis reaction was not complete, the molecular weight of the washed tar was large, and the quality of crude sorbic acid could not be improved.

[0133] Comparative Example 3: A Sorbic Acid Hydrolysis Staged Reaction Method

[0134] Specific implementation method The same as Example 1, except that the first stage reaction temperature of the staged reaction is adjusted to 75°C, 80°C, 90°C, 92°C, 95°C, 97°C, and other conditions remain unchanged to prepare crude sorbic acid.

[0135] result:

[0136] Table 4 Crude sorbic acid prepared at different first stage reaction temperatures in Comparative Example 3

[0137]

[0138] It can be seen that after adjusting the temperature of the first stage reaction, the hydrolysis yield of crude sorbic acid is reduced, the transmittance of crude sorbic acid is reduced, the isomer content is increased, the hydrolysis reaction is not complete, the molecular weight of the washed tar is large, and the quality of crude sorbic acid cannot be improved.

[0139] Comparative Example 4: A Sorbic Acid Hydrolysis Staged Reaction Method

[0140] Specific implementation method is the same as Example 2, except that the second stage reaction temperature of the staged reaction is adjusted to 70°C, 72°C, 75°C, 80°C, 92°C, 95°C, 98°C, and other conditions remain unchanged to prepare crude sorbic acid.

[0141] result:

[0142] Table 5 Crude sorbic acid prepared at different second stage reaction temperatures in Comparative Example 4

[0143]

[0144]

[0145] It can be seen that after adjusting the reaction temperature of the second stage, the overall crude sorbic acid hydrolysis yield decreased, the transmittance of the crude sorbic acid decreased, the isomer content increased, the centrifugal washing effect was poor, the molecular weight of the washed tar was large, and the quality of the crude sorbic acid could not be improved.

[0146] Comparative Example 5: A Sorbic Acid Hydrolysis Staged Reaction Method

[0147] Specific implementation method The method is the same as Example 2, except that the concentration of hydrochloric acid in the second stage of the stepwise reaction is adjusted to 14%, 16%, 20%, 22%, 25%, and 27%, and other conditions remain unchanged to prepare crude sorbic acid.

[0148] result:

[0149] Table 6 Crude sorbic acid prepared by different hydrochloric acid concentrations in the second stage reaction in Comparative Example 5

[0150]

[0151] It can be seen that after adjusting the hydrochloric acid concentration in the second stage, the hydrolysis yield of crude sorbic acid is reduced, the transmittance of crude sorbic acid is reduced, the isomer content is increased, the hydrolysis reaction is not complete, the molecular weight of the washed tar is large, and the quality of crude sorbic acid cannot be improved.

[0152] Comparative Example 6: A Sorbic Acid Hydrolysis Staged Reaction Method

[0153] Specific implementation method The same as Example 4, except that the mass ratio of the polyester in the first stage of the stepwise reaction to the high concentration hydrochloric acid with a mass fraction of 30% is set to 1:0.5, 1:1.5, 1:2.5, and other conditions remain unchanged to prepare crude sorbic acid.

[0154] result:

[0155] Table 7 Crude sorbic acid prepared by mass ratio of different polyesters and 30% high concentration hydrochloric acid in Comparative Example 6

[0156]

[0157]

[0158] It can be seen that after adjusting the mass ratio of the polyester in the first stage reaction and the high concentration hydrochloric acid with a mass fraction of 30%, the transmittance of the crude sorbic acid decreased, the isomer content increased, the hydrolysis reaction was not complete, the molecular weight of the washed tar was large, and the quality of the crude sorbic acid could not be improved.

[0159] Comparative Example 7: A Sorbic Acid Hydrolysis Staged Reaction Method

[0160] Specific implementation method The same as Example 4, except that the reaction time of the staged reaction is 0.25h, 1.5h, 3h, and other conditions remain unchanged to prepare crude sorbic acid.

[0161] result:

[0162] Table 8 Crude sorbic acid prepared by different segmented reaction times in Comparative Example 7

[0163]

[0164] It can be seen that after adjusting the reaction time of the segmented reaction, the hydrolysis yield of the crude sorbic acid is reduced, the transmittance of the crude sorbic acid is reduced, the isomer content is increased, the hydrolysis reaction is not complete, the molecular weight of the washed tar is large, and the quality of the crude sorbic acid cannot be improved.

[0165] Comparative Example 8: A Sorbic Acid Hydrolysis Staged Reaction Method

[0166] The specific implementation method is the same as Example 4, except that the cooling crystallization rates are 0.5°C / min, 1°C / min, and 2°C / min, and other conditions remain unchanged to prepare crude sorbic acid.

[0167] result:

[0168] Table 9 Results of crude sorbic acid prepared at different cooling crystallization rates in Comparative Example 8

[0169]

[0170] It can be seen that after adjusting the cooling crystallization rate, the transmittance of the crude sorbic acid decreased, and the quality of the crude sorbic acid could not be further improved.

[0171] 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 sorbic acid hydrolysis staged reaction method, characterized in that: The steps include: (1) Preparation of polyester: After mixing 500-650 parts by weight of β-methylacrolein and 3-15 parts by weight of a composite catalyst, 300-390 parts by weight of ethylene ketone gas is introduced at 35-50° C. to react for 2-4 hours; after the reaction is completed, the reaction liquid obtained after filtration is distilled to obtain 2,4-hexadienoic acid polyester; the composite catalyst is composed of titanium dioxide, silicon dioxide and caprolactam; (2) adding hydrochloric acid and the polyester obtained in step (1) to the reaction system so that the concentration of hydrochloric acid in the reaction system is 25-30%, mixing and reacting at 85-90° C.; (3) After the reaction is completed, the pressure of the reaction system is controlled to be 0.1-0.4 MPa, and hydrochloric acid is added to make the concentration of hydrochloric acid in the reaction system 16-20%, and the reaction is continued at 95-98° C. for 0.5-2 h; (4) After the reaction in step (3) is completed, the pressure is released, the temperature is lowered, and the waste liquid is separated to obtain a hydrolyzed material. The hydrolyzed material is washed and centrifuged to obtain a crude sorbic acid product.

2. The method according to claim 1, characterized in that In step (1), the composite catalyst is obtained by mixing titanium dioxide, silicon dioxide and caprolactam in a mass percentage ratio of 10-20%: 30-60%: 25-60%.

3. The method according to claim 2, characterized in that In step (1), the preparation method of the composite catalyst comprises the following steps: TiO2 sol A is obtained by hydrolyzing butyl titanate in 0.1 mol / L hydrochloric acid; SiO2 sol B is obtained by hydrolyzing ethyl orthosilicate in a mixed solution of 0.2 mol / L hydrochloric acid and ethanol; A and B are mixed to obtain TiO2 / SiO2 sol C; An ethanol aqueous solution is added to the sol C, and the mixture is washed and dried; caprolactam is then dissolved in water to obtain a solution D, and the sol C is dropped into the solution D, and the mixture is washed and dried to obtain a titanium dioxide-silicon dioxide-caprolactam composite catalyst.

4. The method according to claim 1, characterized in that: In step (1), the distillation is carried out under negative pressure at a vacuum degree of 0.095 to 0.10 MPa.

5. The method according to claim 4, characterized in that In step (2), the polyester and hydrochloric acid are reacted in a mass ratio of 1:1 to 1:

2.

6. The method according to claim 5, characterized in that In step (2), the reaction time of the reaction is 0.5 to 2 hours.

7. The method according to claim 6, characterized in that In step (3), the amount of hydrochloric acid added is 4.5 to 6 times the mass of the polyester.

8. The method according to claim 7, characterized in that In step (4), the cooling rate is 0.1 to 0.8°C / min.

9. The method according to claim 7, characterized in that: In step (4), the centrifugation is at 1500-2500 rpm for 5-10 min.

10. Use of the method according to any one of claims 1 to 9 in the preparation of crude sorbic acid.

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