Production method for regulating and controlling composition of MDA product on line and production method of MDI

Abstract

The invention relates to a production method for on-line regulation and control of MDA product composition and a production method of MDI. The production method comprises the following steps: formaldehyde and aniline are subjected to a synthesis reaction in a synthesis device to obtain an aminal reaction solution, the aminal reaction solution and hydrochloric acid are subjected to a condensation reaction in a condensation device to obtain a crude product, and the crude product is subjected to post-treatment to obtain an MDA product; wherein when the MDA product is used for preparing the MDI product, the mass ratio F of the bicyclic MDI in the MDI product meets the following relational expression; the mass fraction w of aniline in the crude product is detected on line, and the following relational expression is met, x is the molar ratio of formaldehyde to aniline during feeding, and y is the molar ratio of hydrochloric acid to aniline; ; in the production process, p2 is controlled to be equal to (0.98-1.02) p1, so that the proportion of bicyclic MDA in the MDA product can be controlled online in continuous production, and bicyclic MDI and polymerized MDI with an expected proportion can be obtained when the obtained MDA product is used for preparing MDI.

Description

Technical Field

[0001] This invention relates to the field of isocyanate synthesis technology, and in particular to a production method for online control of the composition of MDA products and a production method for MDI. Background Technology

[0002] Diphenylmethane diamine (MDA) exists not only in bicyclic forms but also in tricyclic, tetracyclic, and polycyclic forms. Their distribution significantly impacts the bicyclic MDI / polymeric MDI ratio in diphenylmethane diisocyanate (MDI) prepared from MDA. Because bicyclic and polymeric MDI have different applications, market demand for them often varies regionally. Therefore, producing a specific bicyclic MDI / polymeric MDI ratio has become a current research focus.

[0003] MDA is synthesized using aniline and formaldehyde as the main raw materials, and organic or inorganic acids such as hydrochloric acid as catalysts. The reaction proceeds through a condensation reaction with gradual heating. However, the long condensation reaction time, numerous control variables, and even minor changes in process conditions can significantly affect the composition of the MDA product. Generally, a higher proportion of formaldehyde, a lower proportion of hydrochloric acid, and a faster heating rate are more conducive to the formation of polycyclic MDA. Traditional methods mostly involve adjusting these parameters to obtain an MDA product with a suitable composition, aiming to produce a specific ratio of bicyclic MDI / polymeric MDI.

[0004] For example, patent CN117865816A divides the condensation reaction into three steps and uses a characteristic index to correlate the ratios of formaldehyde, hydrochloric acid, and aniline in each step to obtain MDA products that can be directly used to produce polymeric MDI. The application of this method is limited to batch processes; its application in continuous, large-scale plants still requires verification. Patent KR100888733B1 uses a similar approach to increase the production ratio of polymeric MDI, but it is also limited to batch processes.

[0005] Patent CN118139840A posits that the molecular weight of MDA conforms to the Flory-Schulz weight distribution. It suggests altering the molecular weight distribution of pDADPM by recycling a portion of the dimer component to the synthesis step to produce polymeric MDI with desired functionality and molecular weight, without producing the second product, monomeric MDI. This method requires separating the bicyclic MDA from the product for recycling, inevitably increasing the energy consumption of the condensation process.

[0006] It is evident that existing technologies for controlling the composition of MDA products are concentrated on controlling macroscopic process conditions, and the control methods are mostly limited to intermittent processes, resulting in poor effectiveness. Summary of the Invention

[0007] Therefore, it is necessary to provide a production method for online control of the composition of MDA products and a production method for MDI to address the above problems.

[0008] A production method for online control of the composition of MDA product includes: formaldehyde and aniline undergo a synthesis reaction in a synthesis device to obtain an acetal amine reaction solution; the acetal amine reaction solution and an acid catalyst undergo a condensation reaction in a condensation device to obtain a crude product; and the crude product undergoes post-treatment to obtain the MDA product.

[0009] When preparing MDI products using the MDA product, the mass percentage F of bicyclic MDI in the MDI product satisfies the following relationship:

[0010] ;

[0011] The mass fraction w of aniline in the crude product is detected online and satisfies the following relationship, where x is the molar ratio of formaldehyde to aniline when feeding and y is the molar ratio of hydrochloric acid to aniline when feeding.

[0012] ;

[0013] During the production process, control p2 = (0.98 - 1.02)p1.

[0014] In one embodiment, if p2 > 1.02p1, aniline is added to the condensation device so that p2 = (0.98 - 1.02)p1; if p2 < 0.98p1, aniline is removed from the condensation device so that p2 = (0.98 - 1.02)p1.

[0015] In one embodiment, the temperature of the condensation reaction is controlled to be below 50°C.

[0016] In one embodiment, the temperature of the condensation reaction is controlled at 45°C-48°C.

[0017] In one embodiment, the molar ratio of formaldehyde to aniline during feeding is 0.43:1-0.48:1.

[0018] In one embodiment, the molar ratio of hydrochloric acid to aniline during feeding is 0.06:1-0.3:1.

[0019] In one embodiment, the acid catalyst is selected from hydrochloric acid.

[0020] In one embodiment, in the step of synthesizing formaldehyde and aniline in a synthesis device to obtain an acetal amine reaction solution, the amount of aniline fed is reduced so that p2 > 1.02p1, and then aniline is added to the condensation device so that p2 = (0.98-1.02)p1.

[0021] In one embodiment, the condensation device is also connected to an aniline feed pipe, and when p2 > 1.02p1, aniline is added to the condensation device through the aniline feed pipe.

[0022] In one embodiment, the top of the condensation device is circulated with the stratification tank. The gas generated by the azeotropic reaction in the condensation device can be condensed and stratified in the stratification tank and then returned to the condensation device. When p2 < 0.98p1, the aniline obtained by condensation and stratification in the stratification tank is collected through the aniline discharge pipe.

[0023] A method for producing MDI, including the method for online control of the composition of MDI products.

[0024] This invention studies the formation principle of bicyclic MDA / polycyclic MDA, and then, based on this principle, correlates the proportion of bicyclic MDI in MDI with the chain growth index of polycyclic MDA to obtain a control value p1 for the chain growth index. During production, the mass fraction of aniline in the crude product obtained from the condensation reaction is monitored online and correlated with the chain growth index to obtain the actual value p2. Therefore, during production, by controlling p2 to be equal to (0.98-1.02)p1, the proportion of bicyclic MDA in the MDA product can be controlled online in continuous production. Consequently, when preparing MDI using the obtained MDA product, the desired proportions of bicyclic MDI and polymeric MDI products can be obtained. Attached Figure Description

[0025] To more clearly illustrate the technical solutions in the embodiments of this application or the conventional technology, the drawings used in the description of the embodiments or the conventional technology will be briefly introduced below. Obviously, the drawings described below are only some embodiments of this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0026] Figure 1 This is a schematic diagram of the condensation reaction between the acetal amine reaction solution of the present invention and hydrochloric acid.

[0027] In the diagram: 10. Condensation device; 11. First feed pipe; 12. Second feed pipe; 13. Aniline online detector; 14. Aniline feed pipe; 15. Separation tank; 16. Aniline outlet pipe. Detailed Implementation

[0028] To facilitate understanding of the present invention, it will be described in more detail below. However, it should be understood that the present invention can be implemented in many different forms and is not limited to the embodiments or examples described herein. Rather, these embodiments or examples are provided to make the disclosure of the present invention more thorough and complete.

[0029] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains. The terminology used herein in the specification of this invention is for the purpose of describing particular embodiments or examples only and is not intended to limit the invention. The optional scope of the term "and / or" as used herein includes any one of two or more of the related listed items, as well as any and all combinations of the related listed items, including any two related listed items, any more related listed items, or a combination of all related listed items.

[0030] In this invention, numerical ranges are involved. Unless otherwise specified, the numerical ranges are considered continuous and include the minimum and maximum values ​​of the range, as well as every value between the minimum and maximum values. Furthermore, when the range refers to integers, it includes every integer between the minimum and maximum values ​​of the range. Additionally, when multiple ranges are provided to describe features or characteristics, the ranges may be merged. In other words, unless otherwise specified, all ranges disclosed herein should be understood to include any and all subranges to which they are included.

[0031] The process for synthesizing MDA using the acetal-amine method includes: first, formaldehyde and aniline undergo a synthesis reaction in a synthesis device to obtain an acetal-amine reaction solution; then, the acetal-amine reaction solution undergoes a condensation reaction with an acid catalyst (preferably hydrochloric acid) in a condensation device to obtain crude MDA; finally, the crude MDA undergoes post-processing to obtain the final MDA product. The post-processing step typically involves a high-temperature isomerization reaction to ensure complete conversion of the intermediate into MDA; then, the acid catalyst is neutralized with an alkaline compound such as liquid alkali; after neutralization, phase separation is performed, and the oil phase is successively subjected to water washing, distillation, or stripping to remove aniline and water, yielding a qualified MDA product.

[0032] Long-term research has revealed that the condensation reaction of aniline and formaldehyde is similar to a polymerization reaction, and the chain growth index p can be used to describe the molecular weight distribution of polycyclic products in MDA. A specific example is as follows:

[0033]

[0034] Therefore, we can conclude that a two-ring MDA has a probability p of continuing chain growth and a probability 1-p of ceasing chain growth; a three-ring MDA also has a probability p of continuing chain growth and a probability 1-p of ceasing chain growth, and so on. An n-ring MDA has a probability p of continuing chain growth and a probability 1-p of ceasing chain growth. Furthermore, the chain growth probability p can be fitted using the Flory-Schulz theory, with a goodness of fit > 0.99 for actual data. Therefore, the probability (i.e., mole fraction) of n-ring MDA in the MDA product can be summarized as p.n-2 (1-p). Furthermore, the distribution of polycyclic products in MDA can be controlled by adjusting the chain growth index p.

[0035] The molecular weight distribution of MDA also determines its functionality (functionality = molar amount of amino groups / molar amount of molecules). In the process of producing crude MDI by continuing the photochemical reaction of MDA, the amino group (-NH2) reacts with phosgene to generate the corresponding isocyanate group (-NCO). The distribution of polycyclic products remains unchanged. Therefore, the functionality of crude MDI is consistent with that of the raw material MDA.

[0036] Crude MDI produced by photochemical reaction under normal conditions has low functionality and cannot be used directly to produce rigid foam. A certain amount of bicyclic MDI needs to be separated to improve the functionality of the polymeric MDI product. Based on chain growth theory, the molecular weight distribution and functionality of crude MDI under different chain growth indices can be calculated. To obtain polymeric MDI with a suitable functionality (2.6), a portion of the bicyclic MDI must be separated. The relationship between the separation ratio (F) of this bicyclic MDI and the functionality and chain growth probability (p) of crude MDI is shown in the table below.

[0037] Table 1

[0038]

[0039] Based on the calculation results in the table above, the separation ratio F of dicyclic MDI in MDI products can be linearly fitted to the chain growth index p:

[0040]

[0041] Furthermore, long-term research has revealed that the chain growth principle in the synthesis of MDA using the acetal-amine method is as follows:

[0042]

[0043] Specifically, after adding acid catalysts such as hydrochloric acid, the acetal amine undergoes bond breaking to generate carbocation A. This carbocation A then attacks aniline to undergo addition polymerization to generate bicyclic PABA (substance 3) and polycyclic PABA (substance 4). This step is a fast reaction.

[0044] Among them, the bicyclic PABA (substance 3) undergoes bond breaking to generate aniline under the action of acid catalysts such as hydrochloric acid, while releasing methylene carbocation B. Methylene carbocation B then reacts with aniline to generate MDA (substance 6) and polycyclic MDA.

[0045] The polycyclic intermediate (substance 4) requires the breaking of individual intramolecular CN bonds, first generating a low-molecular-weight intermediate (substance 5), while simultaneously releasing a methylene carbocation B. This methylene carbocation B can react with existing aniline to form MDA (substance 6), and also with the generated MDA to continue chain growth, forming a tricyclic MDA (substance 7). More cyclic MDAs are generated sequentially through this addition polymerization process. Substance 5 repeats this process until PABA (substance 3) and the methylene carbocation B are completely consumed. The reactions that ultimately convert bicyclic PABA (substance 3) and polycyclic PABA (substance 4) into MDA are slow reactions.

[0046] Therefore, it can be seen that during the conversion of methylene carbocation B, a higher aniline concentration leads to the easier formation of low molecular weight MDA, while a lower aniline concentration leads to the easier formation of high molecular weight MDA. Thus, by adjusting the concentration of aniline in the system during the conversion of methylene carbocation B, the overall chain growth index p can be controlled, thereby controlling the proportion of bicyclic MDA in the resulting MDA product.

[0047] Research has shown that in the condensation reaction of acetal amine reaction solution and acid catalysts such as hydrochloric acid in a condensation unit to obtain crude MDA product, the mass fraction w of aniline in the crude product can be detected online. Combined with the molar ratio x of formaldehyde to aniline during the initial feeding (i.e., the molar ratio of formaldehyde and aniline when the synthesis reaction in the synthesis unit yields the acetal amine reaction solution), and the molar ratio y of hydrochloric acid to aniline during the initial feeding, the actual value p2 of the chain growth index during the production process can be obtained. The specific relationship is as follows:

[0048] .

[0049] Therefore, during the production process, it is only necessary to control p2 to be equal to (0.98-1.02)p1 to control the molecular weight distribution of MDA products online in continuous production. Thus, when preparing MDI using the obtained MDA products, the expected proportions of bicyclic MDI and polymeric MDI can be obtained.

[0050] Specifically, if the actual value of the chain growth index p2 during the production process is greater than 1.02p1, then aniline is added to the condensation unit to increase the concentration of aniline, so that p2 = (0.98-1.02)p1; if the actual value of the chain growth index p2 during the production process is less than 0.98p1, then aniline is removed from the condensation unit to reduce the concentration of aniline, so that p2 = (0.98-1.02)p1.

[0051] It should be noted that whether adding or removing aniline from the condensation unit, the addition or removal amount can be increased gradually in stages according to the actual situation. For example, when p2 > 1.02p1, first add aniline to the condensation unit, then calculate the actual value of the chain growth index p2 based on the mass fraction w of aniline in the crude product. If p2 is still greater than 1.02p1, continue to increase the aniline flow rate slightly until p2 = (0.98 - 1.02)p1. This slow increase in aniline flow rate avoids over-increasing the aniline flow rate. The addition directly changes p2 > 1.02p1 to p2 < 0.98p1; similarly, when p2 < 0.98p1, aniline in the condensation unit is extracted, and the extraction rate is gradually increased. If p2 is still less than 0.98p1 when all is extracted, heat is supplied to the condensation unit by means of steam, etc., and the heat is gradually increased to gradually increase the extraction rate until p2 = (0.98 - 1.02)p1. Thus, by gradually extracting aniline, excessive extraction is avoided, and p2 < 0.98p1 is directly changed to p2 > 1.02p1.

[0052] To control the concentration of aniline in the acetal amine reaction solution and acid catalysts such as hydrochloric acid during the condensation reaction to obtain crude MDA product, such as... Figure 1 As shown, during the condensation reaction of acetal amine reaction solution and hydrochloric acid, the reaction device includes a condensation device 10. The acetal amine reaction solution enters the condensation device 10 through the first feed pipe 11, and the acid catalyst such as hydrochloric acid enters the condensation device 10 through the second feed pipe 12. The two undergo a condensation reaction in the condensation device 10. The crude MDA product is discharged through the bottom outlet of the condensation device 10, and part of the crude MDA product is recycled to the condensation device 10.

[0053] The reaction apparatus also includes an online aniline detector 13, which can be installed on the circulation loop of the crude MDA product or directly on the condensation device 10.

[0054] Specifically, the reaction apparatus further includes an aniline feed pipe 14, which is directly connected to the condensation device 10. When the actual value of the chain growth index p2 > 1.02p1, it is used to supplement aniline into the condensation device 10, thereby increasing the concentration of aniline. The reaction apparatus also includes a layering tank 15, which is circulatedly connected to the top of the condensation device 10. At this time, the gas generated by the azeotropic reaction of aniline and water in the condensation device 10 can enter the layering tank 15, where it condenses and separates into phases. The lower layer is aniline, and the upper layer is water. The aniline and water obtained after phase separation can be recycled back to the condensation device 10. When the actual value of the chain growth index p2 < 0.98p1, aniline in the layering tank 15 can be extracted through the aniline extraction pipe 16, thereby reducing the concentration of aniline.

[0055] Furthermore, according to the principle of chain growth, the composition of the MDA product can only be changed by adjusting the system before substances 4 and 5 are completely converted. To achieve this, after adding hydrochloric acid, it is preferable to control the condensation reaction temperature below 50°C, more preferably between 40°C and 48°C, and even more preferably between 45°C and 48°C. This can inhibit the rapid conversion of substances 4 and 5, and maintaining a certain concentration is beneficial to maintaining the effectiveness of the regulation.

[0056] Furthermore, the molar ratio of formaldehyde to aniline is controlled at 0.43:1-0.48:1 during feeding, and the reaction temperature is preferably controlled at 75℃-95℃. This helps to control the generation of N-methyl MDA and N-formyl MDA impurities, thereby obtaining MDA products with low color, low N-methyl impurities, and low N-formyl impurities. Consequently, when using MDA to prepare MDI, MDI products with low hydrolytic chlorine and low color can be obtained.

[0057] Furthermore, controlling the molar ratio of acid catalyst to aniline to 0.06:1-0.3:1 during feeding helps to avoid excessive consumption of hydrochloric acid and obtain a better reaction rate.

[0058] The acid catalyst can be selected from organic acids and / or inorganic acids such as hydrochloric acid, sulfuric acid, phosphoric acid, and methanesulfonic acid, with hydrochloric acid being preferred.

[0059] Since adding aniline to the condensation device can reduce energy consumption, the present invention preferably reduces the amount of aniline fed in the step of synthesizing formaldehyde and aniline in the synthesis device to obtain acetal amine reaction solution, so that p2 > 1.02p1, and then adds aniline to the condensation device so that p2 = (0.98-1.02)p1.

[0060] The present invention also provides a method for producing MDI, including the online control method for the composition of MDA product, wherein the MDA product is then subjected to a phosgenation reaction with phosgene to remove HCl, excess phosgene and solvent to obtain the MDI product.

[0061] Since the production method of the present invention can control the molecular weight distribution in the MDA product online, when preparing MDI using the obtained MDA product, the expected proportions of bicyclic MDI and polymeric MDI can be obtained.

[0062] The technical solution of the present invention will be further described below through specific embodiments. However, those skilled in the art will understand that the following embodiments are only for illustrating the present invention and should not be regarded as limiting the scope of the present invention. Unless otherwise specified, specific conditions in the embodiments are performed under conventional conditions or conditions recommended by the manufacturer. Reagents or instruments used without specified manufacturers are all commercially available conventional products.

[0063] Comparative Example 1:

[0064] The proportion of bicyclic MDI products should be controlled at 30%, and the feeding should be based on empirical values, as follows:

[0065] Based on experience, the feed ratios were determined to be: formaldehyde / aniline molar ratio of 0.44 and hydrochloric acid / aniline molar ratio of 0.11. Formaldehyde and aniline were added in a single step during the acetal amine synthesis process, while hydrochloric acid was added in the condensation unit; no additional aniline was added. The acetal amine reaction temperature was 88℃, and the condensation reaction temperature was 45℃. The feed flow rates were 10.0 kg / h for 37% formaldehyde, 16.1 kg / h for aniline, and 3.8 kg / L for 30% hydrochloric acid.

[0066] After 72 hours of stable operation, the composition of the MDA product is shown in Table 2.

[0067] Table 2

[0068]

[0069] MDI was synthesized via photochemical reaction using this MDA product:

[0070] First, MDA and chlorobenzene are mixed in a static mixer, then reacted with phosgene solution in a dynamic mixer. The phosgene-to-amine molar ratio is controlled at 5.2:1, the temperature at 82℃, and the pressure at 15 bar (absolute pressure). The material obtained from the cold reactor enters the hot reactor for thermophosgenation, with the temperature controlled at 108℃ and the pressure at 2.8 bar (absolute pressure). The resulting material contains phosgene and the solvent chlorobenzene in addition to MDI. Phosgene is first removed at 180℃ and 2.5 bar (absolute pressure), followed by three stages of solvent removal. The first stage solvent removal tower has a temperature and pressure of 160℃ and 0.8 bar (absolute pressure), the second stage has a temperature and pressure of 170℃ and 0.09 bar (absolute pressure), and the third stage has a temperature and pressure of 210℃ and 0.01 bar (absolute pressure), yielding crude MDI product. Crude MDI is distilled to obtain polymeric MDI products with qualified functionality, and also to obtain bicyclic MDI products (including pure 4,4-MDI products and 4,4 / 2,4 mixed products), of which bicyclic MDI products account for 43% of all products.

[0071] Comparative Example 2:

[0072] The proportion of bicyclic MDI was controlled at 30%. Based on experience, adjustments were made to proportion 1, keeping the formaldehyde flow rate and reaction temperature constant. The hydrochloric acid / aniline molar ratio was decreased to 0.08, and the formaldehyde / aniline molar ratio was increased to 0.48. The feed flow rates were: 37% formaldehyde 10 kg / h, aniline 23.9 kg / h, and 30% hydrochloric acid 2.5 kg / L.

[0073] After 72 hours of stable operation, the composition of the MDA product is shown in Table 3.

[0074] Table 3

[0075]

[0076] MDI was synthesized by photochemical reaction using this MDA product according to the method of Comparative Example 1. After removing phosgene and solvent, the crude MDI was separated by distillation to obtain polymeric MDI product with qualified functionality. At the same time, bicyclic MDI product (including pure 4,4-MDI product and 4,4 / 2,4 mixed product) was also obtained, with the bicyclic MDI product accounting for 25.7% of all products.

[0077] Example 1:

[0078] The proportion of dicyclic MDI products should be controlled at 30%, according to The chain growth probability p1 is determined to be 0.292.

[0079] Following the method described in Comparative Example 2, with the reaction temperature remaining constant, after 1 hour of stable feeding into the condensation unit, online detection showed that the mass fraction of aniline in the crude MDA product was 28.4%. The calculated chain growth probability p2 was 0.305. At this point, online control was implemented. Since p2 > p1, aniline was added to the condensation unit at a flow rate of 0.2 kg / h. After 15 minutes, p2 decreased to 0.302, and the mass fraction of aniline increased to 28.8%. The aniline flow rate was further increased to 0.57 kg / h. After 15 minutes, p2 decreased to 0.295, and the mass fraction of aniline increased to 29.3%. The aniline flow rate was further increased to 0.7 kg / h. After 30 minutes, p2 decreased to 0.292, reaching the target value, and the mass fraction of aniline was 29.5%.

[0080] After 72 hours of stable operation, the composition of the MDA product is shown in Table 4.

[0081] Table 4

[0082]

[0083] Using this MDA product, MDI was synthesized by photochemical reaction according to the method of Comparative Example 1. After removing phosgene and solvent, the crude MDI was separated by distillation to obtain a polymeric MDI product with qualified functionality. At the same time, bicyclic MDI products (including pure 4,4-MDI product and 4,4 / 2,4 mixed product) were also obtained, with the bicyclic MDI product accounting for 30% of all products.

[0084] Example 2:

[0085] The proportion of dicyclic MDI products is controlled at 35%, according to The chain growth probability p1 is determined to be 0.277.

[0086] During feeding, the initial hydrochloric acid / aniline molar ratio was set to 0.07, and the formaldehyde / aniline molar ratio was set to 0.44. The reaction temperature remained constant, and the feed flow rates were: 10 kg / h for 37% formaldehyde, 26.1 kg / h for aniline, and 2.4 kg / L for 30% hydrochloric acid.

[0087] After the condensation unit had been feeding steadily for 1 hour, the mass fraction of aniline in the crude MDA product was detected online and found to be 31.5%. The calculated chain growth probability p2 is 0.269. The reflux flow rate in the condensation unit is 2.9 kg / h. At this point, online control is implemented. Since p2 < p1, all aniline in the stratification tank is extracted at a flow rate of 0.24 kg / h. After 15 minutes, p2 rises to 0.272, and the aniline mass fraction is 31.3%.

[0088] Due to insufficient reflux provided by the heat of reaction, steam was introduced into the bottom heater at a rate of 2.7 kg / h, increasing the reflux rate to 6.1 kg / h. Simultaneously, all aniline in the stratification tank was extracted at a rate of 0.51 kg / h. After stabilizing for 30 minutes, p2 rose to 0.276, and the aniline mass fraction was 31.1%. Steam was then added to a rate of 4.2 kg / h, increasing the reflux rate to 7.8 kg / h. All aniline in the stratification tank was extracted at a rate of 0.60 kg / h. After stabilizing for 30 minutes, p2 rose to 0.278, and the aniline mass fraction was 30.9%.

[0089] After 72 hours of stable operation, the composition of the MDA product is shown in Table 5.

[0090] Table 5

[0091]

[0092] Using this MDA product, MDI was synthesized by photochemical reaction according to the method of Comparative Example 1. After removing phosgene and solvent, the crude MDI was separated by distillation to obtain a polymeric MDI product with qualified functionality. At the same time, bicyclic MDI products (including pure 4,4-MDI product and 4,4 / 2,4 mixed product) were also obtained, with the bicyclic MDI product accounting for 34% of all products.

[0093] As can be seen from the comparative examples, it is difficult to control the composition of MDA products by using empirical values ​​to control the feeding, and thus it is difficult to control the separation ratio of MDI products, with large differences. However, by using the method of the present invention for online control, the composition of MDA products can be precisely controlled, thereby obtaining MDI products with the expected separation ratio.

[0094] The technical features of the above embodiments can be combined in any way. For the sake of brevity, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0095] The embodiments described above are merely illustrative of several implementations of the present invention, and while the descriptions are relatively specific and detailed, they should not be construed as limiting the scope of the invention patent. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of the present invention, and these all fall within the protection scope of the present invention. Therefore, the protection scope of this invention patent should be determined by the appended claims.

Claims

1. A method for producing an MDA product composition on-line regulated, comprising: Formaldehyde and aniline are subjected to a condensation reaction in a synthesis device to obtain an acetal amine reaction liquid, the acetal amine reaction liquid is subjected to a condensation reaction with an acid catalyst in a condensation device to obtain a crude product, and the crude product is subjected to post-treatment to obtain an MDA product; Characterized in that, when the MDA product is used to prepare an MDI product, the mass proportion F of dicyclic MDI in the MDI product satisfies the following relationship: ； The mass fraction w of aniline in the crude product is detected online, and satisfies the following relationship, wherein x is the molar ratio of formaldehyde to aniline when feeding, and y is the molar ratio of hydrochloric acid to aniline when feeding; ； During production, p2=(0.98-1.02)p1 is controlled.

2. The method of producing an MDA product according to claim 1, wherein If p2>1.02p1, aniline is supplemented into the condensation device to make p2=(0.98-1.02)p1; if p2<0.98p1, aniline in the condensation device is extracted to make p2=(0.98-1.02)p1.

3. The method of claim 1, wherein the MDA product composition is produced on-line. The temperature of the condensation reaction is controlled to be below 50°C.

4. The method of producing an MDA product according to claim 3, wherein The temperature of the condensation reaction is controlled to be 45-48°C.

5. The method of claim 1, wherein the MDA product composition is produced on-line. The molar ratio of formaldehyde to aniline when feeding is 0.43:1-0.48:

1. The molar ratio of acid catalyst to aniline when feeding is 0.06:1-0.3:

1.

6. The method of producing an MDA product according to claim 1, wherein The acid catalyst is selected from hydrochloric acid.

7. The method of claim 1, wherein the MDA product composition is produced on-line. In the step of obtaining an acetal amine reaction liquid by subjecting formaldehyde and aniline to a condensation reaction in a synthesis device, the amount of aniline feeding is reduced to make p2>1.02p1, and then aniline is supplemented into the condensation device to make p2=(0.98-1.02)p1.

8. The method of producing an MDA product according to any one of claims 1 to 7, wherein The condensation device is also connected to an aniline feeding pipe, and when p2>1.02p1, aniline is supplemented into the condensation device through the aniline feeding pipe.

9. The method of producing an MDA product according to any one of claims 1 to 7, wherein The top of the condensation device is connected to a layered tank in circulation, and the gas generated by azeotropy in the condensation device can be refluxed to the condensation device after being condensed and layered in the layered tank, and when p2<0.98p1, the aniline condensed and layered in the layered tank is extracted through an aniline discharging pipe.

10. A method for producing MDI, characterized by, The production method for online regulating the composition of an MDA product according to any one of claims 1-9.

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