Fumaric acid preparation process based on free radical steady-state dynamic compensation and feed-grade fumaric acid

Abstract

The application discloses a fumaric acid preparation process based on free radical steady-state dynamic compensation and feed grade fumaric acid. The process comprises the following steps: maleic anhydride is hydrolyzed to generate maleic acid in constant mass liquid phase; mother liquor is pumped in a proportion of 10% to 40% of the total weight of fresh pure water and the mother liquor for recycling, and the COD value (COD ad ) of the recycled mother liquor excluding the oxygen demand of the reaction substrate is calculated as a feedforward control index; in the isomerization reaction stage, the calculated COD ad value is used to dynamically link and increase the dosing amount of sodium bromide and ammonium persulfate catalyst to offset the consumption of effective free radicals in the system by external impurities, maintain the free bromine radical in a steady state, and finally obtain fumaric acid through physical cooling crystallization and centrifugal separation. The application not only realizes high proportion of environmental protection recycling of the crystallization mother liquor, but also effectively inhibits the generation of color by-products, so that the main content purity of the output feed grade fumaric acid is stable ≥ 99.5%, the color number is strictly controlled ≤ 20, the quality fluctuation of multiple batches of circulation is suppressed, and the crystallization yield is stabilized.

Description

Technical Field

[0001] This invention relates to the fields of fine chemical synthesis and feed additive manufacturing technology, specifically to a fumaric acid preparation process based on free radical steady-state dynamic compensation and feed-grade fumaric acid. Background Technology

[0002] Fumaric acid (fumaric acid, C4H4O4), a dicarboxylic acid, is widely used as an acidity regulator in the feed additive industry. The production of high-purity feed-grade fumaric acid typically requires meeting relevant industry or national standards (e.g., the purity of the main content ≥ 99.5% and color number ≤ 20 as specified in NY / T920-2004).

[0003] The current mainstream technical route for preparing fumaric acid involves thermodynamically hydrolyzing maleic anhydride in an aqueous phase to generate maleic acid, followed by a cis-trans isomerization reaction under the action of a redox catalyst (such as a mixture of sodium bromide and ammonium persulfate). This reaction is typically carried out at 90°C to 100°C.

[0004] To reduce wastewater treatment costs, recycling the mother liquor generated after fumaric acid crystallization is a current optimization strategy. However, existing technologies face insurmountable technical bottlenecks when implementing high-proportion recycling of the crystallization mother liquor: with an increase in recycling batches, the product color darkens rapidly, purity decreases significantly, and crystallization yield becomes extremely unstable. These quality fluctuations make long-term continuous operation of high-proportion mother liquor recycling difficult in industrial practice. Summary of the Invention

[0005] To address the problems of increased product color, decreased purity, and yield fluctuations caused by the reuse of crystallization mother liquor in existing technologies, the present invention aims to provide a fumaric acid preparation process based on free radical steady-state dynamic compensation.

[0006] The inventors of this invention unexpectedly discovered through in-depth research into microscopic reaction kinetics that byproduct impurities enriched in the crystallization mother liquor can quench and consume a large number of effective free radicals in the reaction system. When dealing with mother liquor reuse, if the catalyst dosage is not dynamically adjusted according to the amount of impurities introduced, incomplete isomerization reaction and co-precipitation of color-developing byproducts will inevitably occur. Based on this microscopic mechanism, the process of this invention uses "COD brought in by reuse" as a feedforward control index, and combines it with a fluid dynamic density calibration water volume balancing and catalyst dynamic compensation mechanism. Under the high steric hindrance state of solid-liquid two-phase mixing, the process achieves the reuse of crystallization mother liquor while ensuring the purity of fumaric acid product ≥ 99.5% and color number ≤ 20.

[0007] The first aspect of this invention provides a process for preparing fumaric acid based on free radical steady-state dynamic compensation, the process comprising the following continuous operation steps: Step S1 Raw material input and hydrolysis: Maleic anhydride is input into the reactor, and fresh pure water is added to carry out the hydrolysis reaction to obtain an aqueous solution of maleic acid; wherein, the total mass of the aqueous phase is controlled to be 1.3 to 1.7 times the mass of maleic anhydride; Step S2: Mother liquor reuse and impurity load calculation: Pump the previous batch of crystallization mother liquor into the reactor, controlling the reuse weight of the crystallization mother liquor to be 10% to 40% of the total weight of fresh pure water and crystallization mother liquor; determine the volumetric chemical oxygen demand (COD) of this batch of crystallization mother liquor to be reused. ml and the density ρ of the mother liquor ml The total oxygen demand load (COD) is calculated based on the estimated total volume of the system and then applied to the system. ad ; Step S3: Dynamic compensation of the catalyst: Under heating conditions in the reaction system, sodium bromide and ammonium persulfate are added to the reactor, respectively; the amount of catalyst added is related to the COD calculated in step S2. ad The values ​​show a positive correlation; Step S4 Isomerization reaction: Maintain the heating state of the reaction system to carry out the cis-trans isomerization reaction. As fumaric acid is generated and precipitated, the system is transformed into a solid-liquid two-phase suspension slurry. Maintain high torque stirring to overcome the steric hindrance of the solid phase. The reaction time lasts for 350 to 480 minutes. Step S5 Cooling, Crystallization and Separation: After the reaction is completed, the system is physically cooled to allow fumaric acid to crystallize out. The cooling rate is controlled at 1℃ / min to 2.5℃ / min to reduce the overall temperature of the system to 25℃ or below. Subsequently, the fumaric acid product is collected by centrifugation, and the crystallization mother liquor generated during separation is transferred to the next production batch in step S2 for recycling.

[0008] Further, in step S2: when the calculated COD amount carried over to the current batch of the circulating system is obtained... ad When the concentration reaches or exceeds 10500 mg / L, the circulation pipeline of the crystallization mother liquor is blocked, and the batch of mother liquor is discharged from the reaction system for treatment; and 3.75 tons of fresh pure water are added in full in the next batch of production.

[0009] Furthermore, the amount of catalyst added in step S3 is determined according to the following formula:

[0010] Where a, b, c, and d are constant proportionality coefficients, and their values ​​range as follows: a is 0.0065. a) up to 0.0070; b) up to 0.24 to 0.26; c) up to 0.0185 to 0.0190; d) up to 0.58 to 0.62.

[0011] Furthermore, during the hydrolysis reaction in step S1 and the isomerization reaction in step S4, the temperature of the reaction system inside the reactor is maintained at 90°C to 100°C.

[0012] Furthermore, the reactor is a reactor with an external heat exchange jacket, through which a heat source is introduced to provide heating, and through which a cooling medium is introduced to control the cooling rate.

[0013] Furthermore, in step S2, the total oxygen demand (COD) load of the system is applied. ad The calculation formula is:

[0014] Where m ml To apply the mother liquor mass, ρ ml To apply the density of the mother liquor; where, V_ total The estimated total volume of the isomerization reaction system at 100 °C is calculated either by reading the actual volume from the calibrated level gauge inside the reactor at 100 °C, or by using a formula:

[0015] Where m anh m_ represents the total mass of maleic anhydride. aq ρ represents the total mass of the aqueous phase. mix The average density constant of the system is 1.10 kg / L to 1.15 kg / L.

[0016] Furthermore, the high-torque stirring device inside the reactor is an anchor-type stirring paddle or a ribbon-type stirring paddle, configured to maintain uniform dispersion of the solid phase and provide strong shear when the isomerization reaction system is transformed into a solid-liquid two-phase suspension slurry in step S4.

[0017] Furthermore, after centrifugation in step S5, the fumaric acid crystals are washed with deionized water. The entire amount of the deionized water washing liquid is collected and replaced with an equal mass of fresh pure water in the next batch of the aqueous phase. Excess crystallization mother liquor is discharged to maintain the balance of aqueous phase materials in the system.

[0018] The second aspect of this invention provides a feed-grade fumaric acid prepared by the above-mentioned process based on free radical steady-state dynamic compensation. According to the analytical method specified in the standard "NY / T 920-2004 Feed-grade Fumaric Acid", its main content purity is ≥ 99.5% and its color number is ≤ 20 by platinum-cobalt colorimetry.

[0019] Compared with the prior art, the technical solution of the present invention has the following beneficial effects: (1) The inventors of this invention have for the first time revealed the competitive annihilation mechanism of impurities on free radicals in the mother liquor recycling process. This invention adopts the input oxygen demand index and strictly introduces the mother liquor density to eliminate dimensional errors, accurately quantifying the impurity load introduced into the reaction system, and providing an accurate feedforward adjustment basis for the control system.

[0020] (2) This invention constructs a dynamic linkage compensation mechanism for the catalyst. Faced with the increase in impurities caused by the high proportion of mother liquor reuse, the system provides a corresponding incremental catalyst according to the compensation equation, effectively suppressing the generation of colored by-products. It overcomes the defect that the product color becomes darker due to the high proportion of mother liquor reuse, and maintains the high purity and low color number of the product while reusing wastewater.

[0021] (3) This invention has made a breakthrough in recognizing the physical limit of the extremely low solubility of fumaric acid at 100 °C (only about 9.8 g / 100 g water). In a solid-liquid slurry system with a solid-liquid content of up to 40%, this invention clearly combines high-torque stirring with a gentle programmed cooling crystallization strategy, eliminating the risk of rapid cooling and wall formation and the encapsulation of impurities by fine crystal bursts, and smoothing out the quality fatigue fluctuations of multiple batches of cycles. Detailed Implementation

[0022] The present invention will be further illustrated by way of embodiments below, but the present invention is not limited to the scope of the embodiments described herein.

[0023] This invention provides a process for preparing fumaric acid based on free radical steady-state dynamic compensation, the process comprising the following continuous operation steps: Step S1 Raw material input and hydrolysis: Maleic anhydride is input into a reactor equipped with an anti-corrosion inner coating and a high-torque stirring device, and an aqueous phase is added to carry out a hydrolysis reaction to obtain an aqueous solution of maleic acid; wherein, the total mass of the aqueous phase is controlled to be 1.3 to 1.7 times the mass of maleic anhydride added; Step S2: Mother liquor reuse and impurity load calculation: The aqueous phase consists of fresh pure water and the mother liquor from the previous batch of crystallization separation; the reuse mass of the mother liquor is controlled to account for 10% to 40% of the total mass of the aqueous phase; the volumetric chemical oxygen demand (COD) of the batch of mother liquor to be reused is determined. ml and the density ρ of the mother liquor ml Based on the theoretical total volume of the entire reaction system for this batch, the total oxygen demand load introduced into the system is calculated and denoted as COD. ad ; Step S3: Dynamic compensation of the catalyst: Under heating conditions, sodium bromide and ammonium persulfate are added to the reactor, respectively; the mass of the catalyst added is equal to the COD calculated in step S2. ad The values ​​show a positive correlation and are compensated for. Step S4 Isomerization reaction: The reaction system is heated to 90°C to 100°C for the cis-trans isomerization reaction. As the solubility limitation of the isomerization product fumaric acid restricts its precipitation, the system transforms into a solid-liquid two-phase suspension slurry with a solid content exceeding 30%. During this period, the high-torque stirring device is continuously operated to overcome the steric hindrance of the solid phase. The isomerization reaction lasts for 350 to 480 minutes. S5 Cooling Crystallization and Separation: After the reaction is completed, the cooling rate is controlled by an external jacket at 1 ℃ / min to 2.5 ℃ / min to perform programmed cooling crystallization, reducing the overall temperature of the system to 25 ℃ or below; then, centrifugation is performed to collect the fumaric acid crystal product, and the crystallization mother liquor generated during separation is collected for recycling in the next batch of step S2.

[0024] Further, in step S2: the total oxygen demand (COD) load brought into the system is applied. ad The conversion formula is as follows

[0025] Where m ml To apply the mother liquor mass, ρ ml To apply the density of the mother liquor; where, V_ total The estimated total volume of the isomerization reaction system at 100 °C is calculated either by reading the actual volume from the calibrated level gauge inside the reactor at 100 °C, or by using a formula:

[0026] Where m anh m_ represents the total mass of maleic anhydride. aq ρ represents the total mass of the aqueous phase. mix The average density constant of the system is 1.10 kg / L to 1.15 kg / L.

[0027] Furthermore, the mass of catalyst added in step S3 is determined according to the following formula:

[0028] Wherein, a, b, c, and d are constant proportionality coefficients, and their values ​​range from 0.0065 to 0.0070; b from 0.24 to 0.26; c from 0.0185 to 0.0190; and d from 0.58 to 0.62.

[0029] Furthermore, after centrifugation in step S5, the fumaric acid crystals are washed with deionized water. The deionized water washing liquid is collected in its entirety and used to replace an equal mass of fresh pure water for balancing the aqueous phase in the next batch in step S2. The excess mother liquor remaining in this batch is discharged to maintain the overall aqueous phase material balance of the system.

[0030] Raw material specifications and testing standards The specifications of the main chemical raw materials used in the embodiments and comparative examples of this invention are as follows: Maleic anhydride: Industrial grade, main content purity ≥ 99.5%.

[0031] Water used for reaction and washing: deionized water or pure water.

[0032] Catalysts: Industrial grade sodium bromide (purity ≥ 99.0%), industrial grade ammonium persulfate (purity ≥ 99.0%).

[0033] Testing standards: The purity and color of the main content of fumaric acid products shall be determined by the analytical methods (such as the platinum-cobalt colorimetric method) specified in the standard "NY / T 920-2004 Feed Grade Fumaric Acid".

[0034] In all embodiments and comparative examples, 2500 parts by weight of maleic anhydride was used as the reference raw material, and the mass of fresh pure water and recycled mother liquor in the reactor was controlled at 3750 parts by weight.

[0035] Example 1 Step S1: Add 2500 parts by mass of maleic anhydride to a reactor equipped with a jacket and an anchor-type high-torque stirrer. Based on the mass of the mother liquor used, add 3375 parts by mass of pure water. Start stirring and heating to hydrolyze the maleic anhydride into an aqueous maleic acid solution, maintaining the system temperature at 90°C.

[0036] Step S2: Take the crystallization mother liquor from the previous batch and determine its COD. ml The concentration was 19500 mg / L, and the density ρ was measured. ml = 1.15 g / mL. Pump this mother liquor into the reactor until it accounts for 10% of the total weight of fresh pure water and crystallization mother liquor. Using the density equation and the estimated total volume V... total Conversion, applying the COD imported into the system ad The concentration was 1950 mg / L.

[0037] Step S3: Calculate and add 17.5 parts by mass of sodium bromide and 48.2 parts by mass of ammonium persulfate according to the linkage formula (where a = 0.0068, b = 0.256, c = 0.0188, d = 0.61).

[0038] Step S4: Maintain heating to carry out the isomerization reaction. As the system becomes a thick white solid-liquid suspension, maintain anchor stirring and strong shear for 350 minutes.

[0039] Step S5: After the reaction is complete, the cooling rate is controlled at approximately 2 °C / min using a jacket to cool the system to 25 °C for crystallization. After centrifugation, the system is washed with 500 parts by mass of deionized water. The washing solution is incorporated into the system as makeup water for the next batch, and any excess residual mother liquor is discharged.

[0040] Example 2 Step S1: Add 2500 parts by weight of maleic anhydride, add 3000 parts by weight of pure water, and heat to hydrolyze.

[0041] Step S2: Take the COD of the mother liquor ml The concentration was measured to be 21200 mg / L, and the density ρ was measured. ml = 1.18 g / mL, pumped into the reactor to make it account for 20% of the total weight of the aqueous phase. Using the density equation and the estimated total volume V... total Conversion, input COD into the system ad The concentration was 4240 mg / L.

[0042] Step S3: Maintain the system at 90℃ ~ 100℃, and add 18.1 parts by mass of sodium bromide and 49.5 parts by mass of ammonium persulfate according to the aforementioned formula.

[0043] Step S4: Keep the agitator running in the white solid-liquid suspension system to maintain phase homogeneity, and continue the isomerization reaction for 380 minutes.

[0044] Step S5: Control the cooling rate to approximately 2 ℃ / min for cooling crystallization, centrifuge to separate, wash with 500 parts by mass of pure water, and discharge the residual mother liquor.

[0045] Example 3 Step S1: Add 2500 parts by mass of maleic anhydride, add 2625 parts by mass of pure water, and heat to hydrolyze.

[0046] Step S2: Take the COD of the mother liquor ml The concentration was measured to be 24000 mg / L, and the density ρ was measured. ml= 1.19 g / mL), pumped into the reactor to make it account for 30% of the total weight of the aqueous phase. Using the density equation and the estimated total volume V... total Conversion, input COD into the system ad It is 7200 mg / L.

[0047] Step S3: Maintain the system at 90℃ ~ 100℃, and add 18.8 parts by mass of sodium bromide and 51.3 parts by mass of ammonium persulfate according to the aforementioned formula.

[0048] Step S4: Maintain the stirrer in shear mode in the solid-liquid suspension system for 420 minutes for the isomerization reaction.

[0049] Step S5: Control the cooling rate to approximately 1.8 ℃ / min for cooling crystallization, centrifuge to separate, wash with 500 parts by mass of pure water, and discharge the residual mother liquor.

[0050] Example 4 Step S1: Add 2500 parts by weight of maleic anhydride and reduce the amount of pure water to 2250 parts by weight.

[0051] Step S2: Take the crystallization mother liquor (COD) ml = 26200 mg / L, density ρml = 1.21 g / mL), pump in 1500 parts by mass to make it account for 40% of the total aqueous phase. Calculate COD ad It is 10480 mg / L.

[0052] Step S3: Maintain the system at 90℃ ~ 100℃, and add 19.6 parts by mass of sodium bromide and 53.3 parts by mass of ammonium persulfate according to the formula in the same group.

[0053] Step S4: Keep the high-torque stirring device running continuously in the solid-liquid suspension system for isomerization for 480 minutes.

[0054] Step S5: Control the cooling rate to 1.5 ℃ / min for cooling crystallization, centrifuge, wash with 500 parts by weight of pure water, and discharge the residual mother liquor. Example 5 Following the process flow and parameters of Example 4, 10 consecutive batches of isomerization reactions were performed. In the first batch, pure water was used as the aqueous phase. Starting from the second batch, the aqueous phase required for each hydrolysis reaction included the deionized water washing liquid from the previous batch and a proportionally supplemented crystallization separation mother liquor. Excess crystallization mother liquor from each batch was discharged to the wastewater treatment system.

[0055] The results showed that after 10 consecutive batch cycles, the CODad concentration in the reaction system gradually stabilized at around 9800 mg / L after the 6th batch, without nonlinear infinite accumulation. Through catalytic feedforward control of this process, the product purity from the 1st to the 10th batch remained within a stable range of 99.51% to 99.65%, the color number was stably controlled between 15 and 20, and the single-batch crystallization yield remained constant between 94.5% and 95.2%. This process achieved stable product quality over a long period and with multiple batch cycles.

[0056] Comparative Example 1 did not reuse the mother liquor for crystallization. Hydrolysis was performed by directly adding 3750 parts by mass of fresh pure water to 2500 parts by mass of maleic anhydride. In step S3, only the basic amount of catalyst (17.0 parts by mass of sodium bromide and 47.0 parts by mass of ammonium persulfate) was added. The remaining steps were the same as in Example 1.

[0057] Comparative Example 2 Steps S1 and S2 are performed in the same manner as in Example 4. In step S3, no catalyst increment compensation is performed; only the basic amount of catalyst (17.0 parts by mass of sodium bromide and 47.0 parts by mass of ammonium persulfate) is added. In step S4, even though the isomerization reaction time is extended from 480 minutes to 600 minutes, the purity of the final reaction product is still only 98.2%, with a color number as high as 65.

[0058] Comparative Example 3 Step S1: Add 2500 parts by weight of maleic anhydride, add 3562.5 parts by weight of pure water, and heat to hydrolyze.

[0059] Step S2: Take the mother liquor (COD / mL, measured to be 19000 mg / L, density ρ / mL = 1.13 g / mL), pump it into the reaction vessel to make it account for 5% of the total weight of the aqueous phase. The converted COD / mL is 950 mg / L.

[0060] Step S3: Add 17.2 parts by mass of sodium bromide and 47.6 parts by mass of ammonium persulfate according to the aforementioned formula.

[0061] Step S4: The isomerization reaction lasts for 330 minutes.

[0062] Step S5: Cool to crystallize, centrifuge, and wash with 500 parts by weight of pure water. Collect the product and send it for testing.

[0063] Comparative Example 4 Step S1: Add 2500 parts by mass of maleic anhydride, reduce the amount of fresh pure water in the system to 2250 parts by mass to balance the mass, and then heat to hydrolyze.

[0064] Step S2: Select the crystallization mother liquor (with a measured COD / mL of 30,000 mg / L and a measured density ρ / mL of 1.25 g / mL) due to excessive circulation and high impurity accumulation, and pump it into the reactor proportionally to make it account for 40% of the total weight of the aqueous phase. Calculate COD / mL to be 12,000 mg / L.

[0065] Step S3: Add 20.0 parts by mass of sodium bromide and 54.2 parts by mass of ammonium persulfate according to the aforementioned formula.

[0066] Step S4: The isomerization reaction lasts for 500 minutes.

[0067] Step S5: Cool to crystallize, centrifuge, and wash with 500 parts by weight of pure water. Collect the product and send it for testing.

[0068] Comparative Example 5 The formulation and catalytic feedforward control parameters of Example 4 were completely replicated, but the cooling rate was not controlled during the cooling and crystallization stage in step S5. The overall temperature of the system was rapidly reduced from 100 °C to 25 °C within 30 minutes by fully opening the freezing medium in the external jacket.

[0069] The results showed that due to the excessively rapid overall cooling of the system leading to excessive local supercooling, a crystalline scale with a thickness of 3-5 cm was formed on the inner wall of the reactor. Simultaneously, due to the explosive secondary nucleation under high supercooling, a large number of fine crystals precipitated within the reaction system, physically entraining and encapsulating residual color-developing byproducts and impurities from the mother liquor within the crystals. After centrifugation and washing with deionized water, the purity of the main content of the product was only 98.70%, and the color number determined by the platinum-cobalt colorimetric method was as high as 45.

[0070] The foregoing has shown and described the basic principles, main features, and advantages of the present invention. Those skilled in the art should understand that the present invention is not limited to the above embodiments. The embodiments and descriptions in the specification are merely illustrative of the principles of the invention. Various changes and modifications can be made to the invention without departing from its spirit and scope, and all such changes and modifications fall within the scope of the present invention as claimed. The scope of protection of this invention is defined by the appended claims and their equivalents.

Claims

1. A process for preparing fumaric acid based on free radical steady-state dynamic compensation, characterized in that, The process includes the following continuous operation steps: Step S1 Raw material input and hydrolysis: Maleic anhydride is input into the reactor, and fresh pure water is added to carry out the hydrolysis reaction to obtain an aqueous solution of maleic acid; wherein, the total mass of the aqueous phase is controlled to be 1.3 to 1.7 times the mass of maleic anhydride; Step S2: Mother liquor reuse and impurity load calculation: Pump the previous batch of crystallization mother liquor into the reactor, controlling the reuse weight of the crystallization mother liquor to be 10% to 40% of the total weight of fresh pure water and crystallization mother liquor; determine the volumetric chemical oxygen demand (COD) of this batch of crystallization mother liquor to be reused. ml and the density ρ of the mother liquor ml The total oxygen demand load (COD) is calculated based on the estimated total volume of the system and then applied to the system. ad ; Step S3: Dynamic compensation of the catalyst: Under heating conditions in the reaction system, sodium bromide and ammonium persulfate are added to the reactor, respectively; the amount of catalyst added is related to the COD calculated in step S2. ad The values ​​show a positive correlation; Step S4 Isomerization reaction: Maintain the heating state of the reaction system to carry out the cis-trans isomerization reaction. As fumaric acid is generated and precipitated, the system is transformed into a solid-liquid two-phase suspension slurry. Maintain high torque stirring to overcome the steric hindrance of the solid phase. The reaction time lasts for 350 to 480 minutes. Step S5 Cooling, Crystallization and Separation: After the reaction is completed, the system is physically cooled to allow fumaric acid to crystallize out. The cooling rate is controlled at 1℃ / min to 2.5℃ / min to reduce the overall temperature of the system to 25℃ or below. Subsequently, the fumaric acid product is collected by centrifugation, and the crystallization mother liquor generated during separation is transferred to the next production batch in step S2 for recycling.

2. The fumaric acid preparation process based on free radical steady-state dynamic compensation according to claim 1, characterized in that, In step S2: when the calculated COD amount carried over to the current batch of the circulating system is obtained... ad When the concentration reaches or exceeds 10500 mg / L, the circulation pipeline of the crystallization mother liquor is blocked, and the batch of mother liquor is discharged from the reaction system for treatment; and 3.75 tons of fresh pure water are added in full in the next batch of production.

3. The fumaric acid preparation process based on free radical steady-state dynamic compensation according to claim 1, characterized in that, The amount of catalyst added in step S3 is determined according to the following formula: Where a, b, c, and d are constant proportionality coefficients, and their values ​​range as follows: a is 0.0065 a) up to 0.0070; b) up to 0.24 to 0.26; c) up to 0.0185 to 0.0190; d) up to 0.58 to 0.

62.

4. The fumaric acid preparation process based on free radical steady-state dynamic compensation according to claim 1, characterized in that, During the hydrolysis reaction in step S1 and the isomerization reaction in step S4, the temperature of the reaction system in the reactor is maintained at 90°C to 100°C.

5. The fumaric acid preparation process based on free radical steady-state dynamic compensation according to claim 1, characterized in that, The reactor is a reactor with an external heat exchange jacket. A heat source is introduced through the jacket to provide heating, and a cooling medium is introduced through the jacket to control the cooling rate.

6. The fumaric acid preparation process based on free radical steady-state dynamic compensation according to claim 6, characterized in that, In step S2, the total oxygen demand (COD) load of the system is applied. ad The calculation formula is: Where m ml To apply the mother liquor mass, ρ ml To apply the density of the mother liquor; Among them, V_ total The estimated total volume of the isomerization reaction system at 100℃ is calculated either by reading the actual volume from the calibrated level gauge inside the reactor at 100℃, or by using a formula: Where m anh m_ represents the total mass of maleic anhydride. aq ρ represents the total mass of the aqueous phase. mix The average density constant of the system is 1.10 kg / L to 1.15 kg / L.

7. The fumaric acid preparation process based on free radical steady-state dynamic compensation according to any one of claims 1 to 6, characterized in that, The high-torque stirring device in the reactor is an anchor-type stirring paddle or a ribbon-type stirring paddle, configured to maintain uniform dispersion of the solid phase and provide strong shear when the isomerization reaction system is transformed into a solid-liquid two-phase suspension slurry in step S4.

8. The fumaric acid preparation process based on free radical steady-state dynamic compensation according to claim 1, characterized in that, After centrifugation in step S5, the fumaric acid crystals are washed with deionized water. The entire volume of the deionized water washing liquid is collected and added to the next batch of the aqueous phase to replace an equal mass of fresh pure water. Excess crystallization mother liquor is discharged to maintain the balance of aqueous phase materials in the system.

9. A feed-grade fumaric acid, characterized in that, The fumaric acid is prepared by the process based on free radical steady-state dynamic compensation as described in any one of claims 1 to 8; its main content purity is ≥ 99.5% and its color number is ≤ 20 by the analytical method specified in the standard "NY / T 920-2004 Feed Grade Fumaric Acid".

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