Process and apparatus for the production of low formaldehyde acrylic acid

Abstract

The application discloses a low-aldehyde acrylic acid production method and device, relates to the technical field of acrylic acid production, and achieves the following effects: crude acrylic acid aqueous solution is obtained by absorbing acrylic acid gas generated by a reactor through an absorption tower; after the crude acrylic acid aqueous solution is deacidified and dehydrated through an azeotropic dehydration deacidification tower, the acrylic acid is refined through a multi-stage rectifying tower; heavy components in the multi-stage rectifying tower refining process are recycled through a thin film evaporator and a heavy component splitter; after aldehyde-containing acrylic acid liquid is condensed, the aldehyde-containing acrylic acid liquid is transmitted to a condensed liquid collector, and hexanediamine aqueous solution is added to the condensed liquid collector to perform a selective de-aldehyde reaction; the reaction liquid is transmitted to a third rectifying tower for separation, low-aldehyde acrylic acid is obtained, and the low-aldehyde acrylic acid is returned to the multi-stage rectifying tower for further purification, so that low-aldehyde acrylic acid products are prepared; and through the low-temperature selective reaction of hexanediamine and aldehydes, furfural and benzaldehyde are converted into high-boiling Schiff bases, and the aldehyde content of products is reduced from the source through complete separation through rectification.

Description

Technical Field

[0001] This invention belongs to the field of acrylic acid production technology, specifically relating to a method and apparatus for producing low-aldehyde acrylic acid. Background Technology

[0002] Acrylic acid, an unsaturated organic acid with carbon-carbon double bonds and carboxyl groups in its molecular structure, is chemically active and readily polymerizable, capable of generating a variety of high-value-added compounds. It is a core raw material in the fields of construction, coatings, textiles, and plastics, and occupies an important position in the petrochemical industry. Currently, the industrial production method of acrylic acid is the two-step oxidation process of propylene. The supporting purification process includes rapid cooling absorption, azeotropic distillation for acid and dehydration, removal of light components and refining, and recovery of heavy components. The acrylic acid gas generated in the reactor is absorbed by water spray in the absorption tower to obtain an acrylic acid aqueous solution. Then, azeotropic distillation is used to remove a large amount of water and acetic acid from the acrylic acid. The resulting crude acrylic acid solution is refined through a light component removal tower and a purification tower. After purification, a high-purity acrylic acid product is finally obtained.

[0003] However, in acrylic acid production, the acrylic acid components recovered by the heavy component recovery system contain light heavy component impurities such as furfural and benzaldehyde. If these impurities are not treated, they will return to the refining system through the recovery system. Since the boiling points of furfural and benzaldehyde are not much different from those of acrylic acid, they will evaporate together at the higher temperature of the heavy component recovery system. This causes furfural and benzaldehyde to accumulate in the refining and recovery systems and cannot be removed. They can only leave the production system with the product, ultimately affecting the product quality. Summary of the Invention

[0004] The purpose of this invention is to provide a method and apparatus for producing low-aldehyde acrylic acid. By selectively reacting hexamethylenediamine with aldehydes at low temperature, furfural and benzaldehyde are converted into high-boiling-point Schiff bases, which are then completely separated by distillation, thereby reducing the aldehyde content of the product from the source and solving the problems mentioned in the background art.

[0005] To achieve the above objectives, the present invention adopts the following technical solution:

[0006] A method for producing low-formaldehyde acrylic acid includes the following steps:

[0007] S1. The acrylic acid gas produced by the reactor is absorbed by an absorption tower to obtain a crude acrylic acid aqueous solution;

[0008] S2. After the crude acrylic acid aqueous solution is dehydrated and deacidified by azeotropic deacetic acid removal tower, it is purified by multi-stage distillation tower to obtain high-purity acrylic acid.

[0009] S3. The heavy components in the multi-stage distillation process are recovered by a thin-film evaporator and a heavy component decomposition device to obtain an aldehyde-containing acrylic acid liquid.

[0010] S4. After condensing the aldehyde-containing acrylic acid solution, transfer it to a condenser and add hexamethylenediamine aqueous solution to the condenser to carry out a selective dealdehyde reaction, and obtain the reaction solution.

[0011] S5. The reaction solution is transferred to the third distillation column for separation, and the low-aldehyde acrylic acid is returned to the multi-stage distillation column for further purification to obtain the low-aldehyde acrylic acid product.

[0012] Preferably, in step S1, the top pressure of the absorption tower is 11-15 kPaA, the reactor temperature is 60-70℃, and the concentration of the obtained crude acrylic acid aqueous solution is greater than 50%.

[0013] Preferably, in step S2, the top pressure of the deacetic acid tower is 13-17 kPaA, and the reactor temperature is 70-80°C. In the deacetic acid tower, acrylic acid, water, and toluene form a ternary azeotrope, removing water and acetic acid from the crude acrylic acid solution. The top of the deacetic acid tower is connected to a primary condenser, and the lower end of the primary condenser is connected to a secondary condenser and a second storage tank for storing toluene. The lower end of the secondary condenser is connected to a first storage tank for storing acid wastewater.

[0014] Preferably, the multi-stage distillation column is composed of a first distillation column and a second distillation column connected in series for different degrees of purification. The first distillation column is connected to the lower end of the deacetic acid removal column via a first centrifugal pump, and the lower end of the first distillation column is connected to the inlet of the second distillation column via a second centrifugal pump. The top of the second distillation column is connected to a second condenser, and the outlet of the second condenser is connected to a fourth storage tank for storing high-purity acrylic acid. The top of the first distillation column is connected to a first condenser, and the outlet of the first condenser is connected to a third storage tank. The outlet of the third storage tank is connected to both the first distillation column and the deacetic acid removal column via a third centrifugal pump. The top pressure of the first distillation column is 6-8 kPaA, and the bottom temperature is 80-90°C. The top pressure of the second distillation column is 3-4 kPaA, and the bottom temperature is 70-80°C.

[0015] Preferably, in step S3, the top pressure of the thin-film evaporator is 5-12 kPaA and the bottom temperature is 130-140°C; the top pressure of the recombinant splitter is 50-70 kPaA and the bottom temperature is 160-180°C; the inlet of the thin-film evaporator is connected to the bottom of the second distillation column via a fourth centrifugal pump; the bottom of the thin-film evaporator is connected to the inlet of the recombinant splitter via a fifth centrifugal pump; and the connecting pipe between the fifth centrifugal pump and the recombinant splitter is connected to the top of the thin-film evaporator via a reflux pipe.

[0016] Preferably, in step S4, the condenser includes a first collector and a second collector. The upper ends of both the first collector and the second collector are connected to inlet pipes for adding cooling water. The top of the thin-film evaporator is connected to the top of the first collector. The first collector is provided with an addition pipe for adding hexamethylenediamine. The lower end of the first collector is connected to the bottom of the third distillation column via a seventh centrifugal pump. The upper end of the recombinant splitter is connected to the top of the second collector. The lower end of the second collector is connected to the bottom of the third distillation column via a sixth centrifugal pump.

[0017] Preferably, the concentration of the hexamethylenediamine aqueous solution is 1%-2%, the molar ratio of hexamethylenediamine to total aldehyde in the hexamethylenediamine aqueous solution is 1.05-1.2:2, and the selective dealdehyde reaction is carried out at 35°C.

[0018] Preferably, in step S5, the bottom of the third distillation column is connected to the top of the thin-film evaporator via an eighth centrifugal pump, the top of the third distillation column is connected to a third condenser, the lower end of the third condenser is connected to a fifth storage tank for storing low-aldehyde acrylic acid, the lower end of the fifth storage tank is connected to the second distillation column, the top pressure of the third distillation column is 3-5 kPaA, and the bottom temperature is 80-90℃.

[0019] Preferably, the outlet end of the eighth centrifugal pump is connected to the interior of the distillation column through a circulation pipe, and the circulation pipe is provided with an addition pipe for adding a polymerization inhibitor. The addition amount of the polymerization inhibitor is 25 kg / h, and the polymerization inhibitor is a mixture of 1.5% phenothiazine and 0.75% copper salt.

[0020] The present invention also provides a production apparatus for low-aldehyde acrylic acid, for implementing the production method of low-aldehyde acrylic acid described above. The apparatus includes an absorption tower connected to a reactor, the outlet end of the absorption tower being connected to an acetic acid removal tower, the lower end of the acetic acid removal tower being connected to a multi-stage distillation tower, the liquid outlet end of the multi-stage distillation tower being connected to a thin-film evaporator, the liquid outlet end of the thin-film evaporator being connected to a recombination and decomposition device, the thin-film evaporator and the recombination and decomposition device being connected to a third distillation tower via a condenser, the upper end of the third distillation tower being connected to the multi-stage distillation tower via a reflux mechanism, and the top of the multi-stage distillation tower being connected to a storage device for collecting the low-aldehyde acrylic acid product.

[0021] The method and apparatus for producing low-formaldehyde acrylic acid proposed in this invention have the following advantages compared with the prior art:

[0022] 1. This invention is based on a two-step propylene oxidation method. First, crude acrylic acid aqueous solution is obtained through an absorption tower, followed by acetic acid removal and multi-stage distillation to obtain high-purity acrylic acid. The distilled heavy fraction is then recovered as aldehyde-containing acrylic acid solution through a thin-film evaporator and a heavy fraction decomposition device. Hexamethylenediamine aqueous solution is added to the aldehyde-containing acrylic acid solution for low-temperature selective aldehyde removal. The reaction solution is separated by a third distillation tower, and the low-aldehyde acrylic acid is returned to the purification system for further purification to obtain the product. This invention achieves targeted removal of aldehyde impurities and efficient recovery of acrylic acid, solving the problem of aldehyde accumulation and making it suitable for continuous industrial production.

[0023] 2. This invention can directly process heavy components to recover acrylic acid without major modifications to the original refining system. It is compatible with existing two-step propylene oxidation production equipment, and the modification cost is low.

[0024] 3. This invention maximizes the recovery of acrylic acid while removing aldehydes, reduces raw material loss and unit consumption, and has a low process temperature, simple process, and significantly lower energy consumption than crystallization processes. Attached Figure Description

[0025] Figure 1 This is a flowchart of the method of the present invention;

[0026] Figure 2 This is a system block diagram of the device of the present invention;

[0027] In the diagram: 1. Absorption tower; 2. Ninth centrifugal pump; 3. First storage tank; 4. Second storage tank; 5. Secondary condenser; 6. First condenser; 7. Deacetic acid tower; 8. First centrifugal pump; 9. Third centrifugal pump; 10. Third storage tank; 11. First condenser; 12. First distillation tower; 13. Second centrifugal pump; 14. Second distillation tower; 15. Fourth centrifugal pump; 16. Second condenser; 17. Fourth storage tank; 18. Thin-film evaporator; 19. First liquid collector; 20. Seventh centrifugal pump; 21. Fifth centrifugal pump; 22. Recombinant decomposition unit; 23. Second liquid collector; 24. Sixth centrifugal pump; 25. Eighth centrifugal pump; 26. Third distillation tower; 27. Fifth storage tank; 28. Third condenser. Detailed Implementation

[0028] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. The specific embodiments described herein are merely used to explain the present invention and are not intended to limit the present invention. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0029] This invention provides, for example Figure 1-2 The method for producing low-formaldehyde acrylic acid shown includes the following steps:

[0030] S1. The acrylic acid gas produced by the reactor is absorbed by absorption tower 1 to obtain a crude acrylic acid aqueous solution. The top pressure of absorption tower 1 is 11-15 kPaA, the reactor temperature is 60-70℃, and the concentration of the obtained crude acrylic acid aqueous solution is greater than 50%. Under these temperature and pressure conditions, water spraying can efficiently absorb the gaseous acrylic acid in the reactor, avoid high-temperature polymerization of acrylic acid, ensure that the crude acrylic acid concentration is >50%, increase the crude acrylic acid concentration, reduce the subsequent distillation load, and reduce energy consumption and material loss. This reactor is a two-step gas-phase catalytic oxidation reactor for propylene, and the reactor uses a tubular fixed-bed reactor.

[0031] S2. After the crude acrylic acid aqueous solution is dehydrated and deacidified by azeotropic deacetic acid removal tower 7, it is purified by multi-stage distillation tower to obtain high-purity acrylic acid. The bottom of the absorption tower 1 is connected to the deacetic acid removal tower 7 through the ninth centrifugal pump 2. The top pressure of the deacetic acid removal tower 7 is 13-17 kPaA, and the bottom temperature is 70-80℃. In the deacetic acid removal tower 7, acrylic acid, water and toluene form a ternary azeotrope, removing water and acetic acid from the crude acrylic acid solution, thereby reducing the water and acetic acid content in the crude acrylic acid and increasing the acrylic acid concentration to over 80%. The top of the deacetic acid removal tower 7 is connected to a primary condenser 6. The lower end of the primary condenser 6 is connected to a secondary condenser 5 and a second storage tank 4 for storing toluene. The lower end of the secondary condenser 5 is connected to a first storage tank 3 for storing acid wastewater, realizing solvent recovery and wastewater classification treatment.

[0032] The multi-stage distillation column consists of a first distillation column 12 and a second distillation column 14 connected in series for different degrees of purification. The first distillation column 12 is connected to the lower end of the deacetic acid removal column 7 via a first centrifugal pump 8. The lower end of the first distillation column 12 is connected to the inlet of the second distillation column 14 via a second centrifugal pump 13. The top of the second distillation column 14 is connected to a second condenser 16. The outlet of the second condenser 16 is connected to a fourth storage tank 17 for storing high-purity acrylic acid. The top of the first distillation column 12 is connected to a first condenser 11. The outlet of the first condenser 11 is connected to a third storage tank 10. The outlet of the third storage tank 10 is connected to the first distillation column 12 and the deacetic acid column 7 via a third centrifugal pump 9. The top pressure of the first distillation column 12 is 6-8 kPaA and the bottom temperature is 80-90℃. The top pressure of the second distillation column 14 is 3-4 kPaA and the bottom temperature is 70-80℃. The first distillation column 12 and the second distillation column 14 are connected in series for purification. Light components and heavy components are removed stepwise by gradient temperature and pressure to gradually improve the purity of acrylic acid and ensure the basic purity index of the product.

[0033] S3. The heavy components from the multi-stage distillation process are recovered via a thin-film evaporator 18 and a heavy component decomposer 22 to obtain an aldehyde-containing acrylic acid solution. The top pressure of the thin-film evaporator 18 is 5-12 kPaA, and the bottom temperature is 130-140℃. The top pressure of the heavy component decomposer 22 is 50-70 kPaA, and the bottom temperature is 160-180℃, which facilitates efficient decomposition of heavy components and recovery of acrylic acid at the corresponding temperature and pressure, while separating some heavy component impurities. The inlet of the thin-film evaporator 18 is connected to the bottom of the second distillation column 14 via a fourth centrifugal pump 15, and the bottom of the thin-film evaporator 18 is connected to the inlet of the heavy component decomposer 22 via a fifth centrifugal pump 21. The connecting pipe between the fifth centrifugal pump 21 and the heavy component decomposer 22 is connected to the top of the thin-film evaporator 18 via a reflux pipe. This connection method can maximize the recovery of acrylic acid from the distilled heavy components, reduce production unit consumption, and provide high-quality raw materials for subsequent formaldehyde removal.

[0034] S4. After condensing the aldehyde-containing acrylic acid solution, transfer it to a condenser and add hexamethylenediamine aqueous solution to the condenser to carry out a selective dealdehyde reaction, and obtain the reaction solution.

[0035] The condenser includes a first collector 19 and a second collector 23. The upper ends of both the first collector 19 and the second collector 23 are connected to inlet pipes for adding cooling water. The top of the thin-film evaporator 18 is connected to the top of the first collector 19. The first collector 19 is equipped with an addition pipe for adding hexamethylenediamine. The lower end of the first collector 19 is connected to the bottom of the third distillation column 26 through a seventh centrifugal pump 20. The upper end of the recombinant splitter 22 is connected to the top of the second collector 23. The lower end of the second collector 23 is connected to the bottom of the third distillation column 26 through a sixth centrifugal pump 24. The first collector 19 and the second collector 23 collect the recovered acrylic acid from the thin-film evaporator 18 and the recombinant splitter 22, respectively. The hexamethylenediamine is precisely added through the matching addition pipe to ensure that the formaldehyde removal reaction proceeds uniformly. This achieves segmented collection and stable reaction of recovered acrylic acid, avoids uneven material mixing, and improves the controllability and efficiency of the formaldehyde removal reaction.

[0036] The concentration of the hexamethylenediamine aqueous solution is 1%-2%, and the molar ratio of hexamethylenediamine to total aldehyde in the hexamethylenediamine aqueous solution is 1.05-1.2:2. The selective dealdehyde reaction is carried out at 35°C. At low temperature, hexamethylenediamine preferentially undergoes nucleophilic addition with aldehydes to form Schiff bases and does not react with acrylic acid, thus ensuring the selectivity and conversion rate of the dealdehyde reaction and avoiding the effect of excessive or insufficient hexamethylenediamine on the dealdehyde removal effect.

[0037] S5. The reaction liquid is transferred to the third distillation column 26 for separation, and the low-aldehyde acrylic acid is returned to the multi-stage distillation column for further purification to obtain the low-aldehyde acrylic acid product.

[0038] The bottom of the third distillation column 26 is connected to the top of the thin-film evaporator 18 via the eighth centrifugal pump 25. The top of the third distillation column 26 is connected to the third condenser 28. The lower end of the third condenser 28 is connected to the fifth storage tank 27 for storing low-aldehyde acrylic acid. The lower end of the fifth storage tank 27 is connected to the second distillation column 14. The top pressure of the third distillation column 26 is 3-5 kPaA, and the bottom temperature is 80-90℃. Utilizing the boiling point difference between acrylic acid and Schiff base, low-aldehyde acrylic acid is collected from the top of the column, and the bottom material is returned to the thin-film evaporator 18 for recycling. This achieves efficient separation of acrylic acid and dealdehyde by-products, and the recycling further improves the material utilization rate.

[0039] The outlet of the eighth centrifugal pump 25 is connected to the interior of the distillation column through a circulation pipe, and the circulation pipe is equipped with an addition pipe for adding a polymerization inhibitor. The addition amount of the polymerization inhibitor is 25 kg / h. The polymerization inhibitor is a mixture of 1.5% phenothiazine and 0.75% copper salt. The polymerization inhibitor inhibits the high-temperature polymerization of acrylic acid and the formation of acrylamide with hexamethylenediamine, avoids system polymerization blockage, ensures stable operation of the device, prevents the generation of by-products, and maintains product purity.

[0040] The above production method is based on the two-step oxidation of propylene. First, crude acrylic acid aqueous solution is obtained through absorption tower 1. Acetic acid is removed and high-purity acrylic acid is obtained through multi-stage distillation. The distilled heavy fraction is recovered as aldehyde-containing acrylic acid liquid through thin film evaporator 18 and heavy fraction decomposition unit 22. Hexamethylenediamine aqueous solution is added to the aldehyde-containing acrylic acid liquid for low-temperature selective aldehyde removal. The reaction liquid is separated by third distillation tower 26. Low-aldehyde acrylic acid is returned to the purification system for purification to obtain the product. This process can achieve targeted removal of aldehyde impurities and efficient recovery of acrylic acid, solve the problem of aldehyde accumulation, and is suitable for continuous industrial production.

[0041] This invention also provides a production apparatus for low-aldehyde acrylic acid, used to implement the above-described method for producing low-aldehyde acrylic acid, such as... Figure 2As shown, the device includes an absorption tower 1 connected to a reactor. The outlet of the absorption tower 1 is connected to an acetic acid removal tower 7. The lower end of the acetic acid removal tower 7 is connected to a multi-stage distillation tower. The liquid outlet of the multi-stage distillation tower is connected to a thin-film evaporator 18. The liquid outlet of the thin-film evaporator 18 is connected to a recombination and decomposition device 22. The thin-film evaporator 18 and the recombination and decomposition device 22 are connected to a third distillation tower 26 via a condenser. The upper end of the third distillation tower 26 is connected to the multi-stage distillation tower via a reflux mechanism. The reflux mechanism includes a third condenser 28 connected to the top of the third distillation tower 26. The lower end of the third condenser 28 is connected to a fifth storage tank 27 for storing low-aldehyde acrylic acid. The lower end of the fifth storage tank 27 is connected to a second distillation tower 14. The top of the multi-stage distillation tower is connected to a storage device for collecting low-aldehyde acrylic acid products. The storage device is a fourth storage tank 17. The device has a compact structure, requires minimal modification, is compatible with existing production lines, and enables automated and continuous production of low-aldehyde acrylic acid.

[0042] To verify the effectiveness of using the above-described apparatus in preparing low-aldehyde acrylic acid, the following examples and comparative examples are provided:

[0043] Example 1

[0044] A method for producing low-formaldehyde acrylic acid includes the following steps:

[0045] 1. The acrylic acid gas produced by the reactor is absorbed by an absorption tower with a top pressure of 13 kPaA and a reactor temperature of 65°C to obtain a crude acrylic acid aqueous solution with a concentration of 52%.

[0046] 2. The crude acrylic acid aqueous solution is dehydrated and deacidified by azeotropic deacetic acid removal in a deacetic acid removal tower to obtain an acrylic acid solution with a concentration of 82%. The top pressure of the deacetic acid removal tower is 15 kPaA and the bottom temperature is 75℃. It is then purified by multi-stage distillation towers. The top pressure of the first distillation tower is 7 kPaA and the bottom temperature is 85℃; the top pressure of the second distillation tower is 3.5 kPaA and the bottom temperature is 75℃, to obtain high-purity acrylic acid with a concentration of 99.5%.

[0047] 3. The heavy components in the multi-stage distillation process are recovered by a thin-film evaporator and a heavy component decomposition unit to obtain an aldehyde-containing acrylic acid solution with a concentration of 95.2% and an aldehyde content of 4.36%. The top pressure of the thin-film evaporator is 8 kPaA and the bottom temperature is 135℃; the top pressure of the heavy component decomposition unit is 60 kPaA and the bottom temperature is 170℃.

[0048] 4. After condensing the aldehyde-containing acrylic acid solution, transfer it to a condenser and add hexamethylenediamine aqueous solution to the condenser to carry out a selective aldehyde removal reaction. The aldehyde removal reaction temperature is 35℃, the reaction time is 30 minutes, the concentration of hexamethylenediamine aqueous solution is 1.5%, and the molar ratio of hexamethylenediamine to total aldehyde is 1.1:2; thus obtaining the reaction solution.

[0049] S5. The reaction solution is transferred to the third distillation column for separation. The top pressure of the third distillation column is 4 kPaA, the bottom temperature is 85℃, and the amount of polymerization inhibitor added is 25 kg / h. The resulting low-aldehyde acrylic acid is returned to the multi-stage distillation column for further purification to obtain the low-aldehyde acrylic acid product.

[0050] Example 2

[0051] The similarities will not be repeated here. The difference from Example 1 is that in step 3, the concentration of recovered acrylic acid is 96.1% and the aldehyde content is 2.85%, while the other parameters remain unchanged.

[0052] Example 3

[0053] The similarities will not be repeated here. The difference from Example 1 is that in step 4, the molar ratio of hexamethylenediamine to total aldehyde is 1.05:2, while the other parameters remain unchanged.

[0054] Comparative Example 1

[0055] Using the existing two-step propylene oxidation method, the recombinant component recovers acrylic acid and returns it directly to the refining system without undergoing hexamethylenediamine dealdehyde treatment. The remaining parameters are the same as in Example 1.

[0056] The component contents of the raw materials, amine-treated materials, and final products in Example 1 are shown in Table 1 below:

[0057] Table 1

[0058]

[0059] As shown in Table 1, the aldehyde content in the material after amine treatment significantly decreased from 4.361% in the raw material to 0.004%, and the aldehyde content in the final product was further controlled to 0.085%. Therefore, the present invention uses hexamethylenediamine at low temperature to achieve efficient and selective removal of aldehyde impurities from acrylic acid in heavy components. At the same time, the purity of acrylic acid in the final product reached 99.800%, no hexamethylenediamine acrylamide byproduct was detected, and the contents of impurities such as moisture, acrylic acid dimer, and polymerization inhibitor were all at low levels. This indicates that the present invention can ensure the high purity of acrylic acid products while efficiently removing aldehydes, and will not produce harmful byproducts or affect product quality.

[0060] The component contents of the raw materials, amine-treated materials, and final products in Example 2 are shown in Table 2 below:

[0061] Table 2

[0062]

[0063] The data in Table 2 show that after amine treatment, the aldehyde content in the material decreased significantly from 2.850% in the raw material to 0.002%, and the aldehyde content in the final product was further controlled to 0.067%. This indicates that the present invention has a stable and efficient aldehyde removal effect on the recovery of acrylic acid from heavy components with different initial aldehyde contents. The purity of acrylic acid in the final product reached 99.826%, and no hexamethylenediamine acrylamide byproducts were detected. The content of other impurities was low and stable, further proving that the process of the present invention has wide applicability, stable and reliable operation, and can stably prepare high-purity acrylic acid products with low aldehyde content.

[0064] The purity of acrylic acid, total aldehyde content, aldehyde removal efficiency, and byproduct (hexamethylenediamine acrylamide) of Examples 1, 2, 3, and Comparative Example 1 were tested. The test results are shown in Table 3 below:

[0065] Table 3

[0066]

[0067] As shown in Table 3, after low-temperature selective dealdehyde removal with hexamethylenediamine in Examples 1-3, the aldehyde content decreased from 4.361% and 2.850% of the raw materials to 0.085% and 0.067% of the products, respectively, with a dealdehyde removal efficiency of 95.1% and 96.8%. Comparative Example 1 had no dealdehyde removal step and the aldehyde content was as high as 650 ppm. The dealdehyde removal effect of the present invention is significantly better. The acrylic acid purity of the examples reached 99.80%~99.83%, which is higher than that of Comparative Example 1, and there were no amide byproducts, resulting in more stable product purity.

[0068] In summary, by using hexamethylenediamine for low-temperature selective aldehyde removal coupled with distillation separation, heavy components can be directly processed to recover acrylic acid, completely solving the problem of aldehyde accumulation. The aldehyde removal efficiency is ≥95%, the aldehyde content of the product is <100ppm, and the purity of acrylic acid is ≥99.8%. At the same time, the process is simple, requires little modification, has low energy consumption, low investment, and no by-products. Its comprehensive performance is significantly better than traditional processes and existing patented technologies, making it suitable for large-scale industrial production.

[0069] Finally, it should be noted that the above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art can still modify the technical solutions described in the foregoing embodiments or make equivalent substitutions for some of the technical features. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for producing low-formaldehyde acrylic acid, characterized in that: Includes the following steps: S1. The acrylic acid gas produced by the reactor is absorbed by an absorption tower to obtain a crude acrylic acid aqueous solution; S2. After the crude acrylic acid aqueous solution is dehydrated and deacidified by azeotropic deacetic acid removal tower, it is purified by multi-stage distillation tower to obtain high-purity acrylic acid. S3. The heavy components in the multi-stage distillation process are recovered by a thin-film evaporator and a heavy component decomposition device to obtain an aldehyde-containing acrylic acid liquid. S4. After condensing the aldehyde-containing acrylic acid solution, transfer it to a condenser and add hexamethylenediamine aqueous solution to the condenser to carry out a selective dealdehyde reaction, and obtain the reaction solution. S5. The reaction solution is transferred to the third distillation column for separation, and the low-aldehyde acrylic acid is returned to the multi-stage distillation column for further purification to obtain the low-aldehyde acrylic acid product.

2. The method for producing low-formaldehyde acrylic acid according to claim 1, characterized in that: In step S1, the top pressure of the absorption tower is 11-15 kPaA, the reactor temperature is 60-70℃, and the concentration of the obtained crude acrylic acid aqueous solution is greater than 50%.

3. The method for producing low-formaldehyde acrylic acid according to claim 1, characterized in that: In step S2, the top pressure of the deacetic acid tower is 13-17 kPaA, and the reactor temperature is 70-80℃. In the deacetic acid tower, acrylic acid, water, and toluene form a ternary azeotrope, removing water and acetic acid from the crude acrylic acid solution. The top of the deacetic acid tower is connected to a primary condenser, and the lower end of the primary condenser is connected to a secondary condenser and a second storage tank for storing toluene. The lower end of the secondary condenser is connected to a first storage tank for storing acid wastewater.

4. The method for producing low-formaldehyde acrylic acid according to claim 1, characterized in that: The multi-stage distillation column consists of a first distillation column and a second distillation column connected in series for different degrees of purification. The first distillation column is connected to the lower end of the deacetic acid removal column via a first centrifugal pump. The lower end of the first distillation column is connected to the inlet of the second distillation column via a second centrifugal pump. The top of the second distillation column is connected to a second condenser. The outlet of the second condenser is connected to a fourth storage tank for storing high-purity acrylic acid. The top of the first distillation column is connected to a first condenser. The outlet of the first condenser is connected to a third storage tank. The outlet of the third storage tank is connected to both the first distillation column and the deacetic acid removal column via a third centrifugal pump. The top pressure of the first distillation column is 6-8 kPaA, and the bottom temperature is 80-90°C. The top pressure of the second distillation column is 3-4 kPaA, and the bottom temperature is 70-80°C.

5. The method for producing low-formaldehyde acrylic acid according to claim 1, characterized in that: In step S3, the top pressure of the thin-film evaporator is 5-12 kPaA and the bottom temperature is 130-140℃. The top pressure of the recombinant splitter is 50-70 kPaA and the bottom temperature is 160-180℃. The inlet of the thin-film evaporator is connected to the bottom of the second distillation column through a fourth centrifugal pump. The bottom of the thin-film evaporator is connected to the inlet of the recombinant splitter through a fifth centrifugal pump. The connecting pipe between the fifth centrifugal pump and the recombinant splitter is connected to the top of the thin-film evaporator through a reflux pipe.

6. The method for producing low-formaldehyde acrylic acid according to claim 5, characterized in that: In step S4, the condenser includes a first collector and a second collector. The upper ends of both the first collector and the second collector are connected to inlet pipes for adding cooling water. The top of the thin-film evaporator is connected to the top of the first collector. The first collector is provided with an addition pipe for adding hexamethylenediamine. The lower end of the first collector is connected to the bottom of the third distillation column through a seventh centrifugal pump. The upper end of the recombinant splitter is connected to the top of the second collector. The lower end of the second collector is connected to the bottom of the third distillation column through a sixth centrifugal pump.

7. The method for producing low-formaldehyde acrylic acid according to claim 1, characterized in that: The concentration of the hexamethylenediamine aqueous solution is 1%-2%, and the molar ratio of hexamethylenediamine to total aldehyde in the hexamethylenediamine aqueous solution is 1.05-1.2:2, and a selective dealdehyde reaction is carried out at 35°C.

8. The method for producing low-formaldehyde acrylic acid according to claim 1, characterized in that: In step S5, the bottom of the third distillation column is connected to the top of the thin-film evaporator via an eighth centrifugal pump. The top of the third distillation column is connected to a third condenser. The lower end of the third condenser is connected to a fifth storage tank for storing low-aldehyde acrylic acid. The lower end of the fifth storage tank is connected to the second distillation column. The top pressure of the third distillation column is 3-5 kPaA, and the bottom temperature is 80-90℃.

9. A method for producing low-formaldehyde acrylic acid according to claim 8, characterized in that: The outlet end of the eighth centrifugal pump is connected to the interior of the distillation column through a circulation pipe, and the circulation pipe is equipped with an addition pipe for adding a polymerization inhibitor. The addition amount of the polymerization inhibitor is 25 kg / h, and the polymerization inhibitor is a mixture of 1.5% phenothiazine and 0.75% copper salt.

10. A production apparatus for low-formaldehyde acrylic acid, used to implement the production method of low-formaldehyde acrylic acid according to any one of claims 1-9, characterized in that: The apparatus includes an absorption tower connected to a reactor, the outlet of which is connected to an acetic acid removal tower, the lower end of which is connected to a multi-stage distillation tower, the liquid outlet of which is connected to a thin-film evaporator, the liquid outlet of which is connected to a recombination and decomposition device, the thin-film evaporator and the recombination and decomposition device being connected to a third distillation tower via a condenser, the upper end of which is connected to the multi-stage distillation tower via a reflux mechanism, and the top of which is connected to a storage device for collecting low-aldehyde acrylic acid products.

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