A method for synthesizing low-trans diaminodicyclohexylmethane

Abstract

The present invention relates to a method for synthesizing low-trans diaminodicyclohexylmethane (H 12 MDA). The method adds N,N,N',N'-tetramethyl-MDA compound to the raw material MDA-100, and the compound has a synergistic catalytic effect with the noble metal supported catalyst to promote the activity of the catalyst, so as to obtain H-containing catalyst with an anti-anti content as low as 10-14%. 12 MDA, while the conversion rate of MDA-100 can reach over 99%.

Description

Technical Field

[0001] The invention relates to a method for synthesizing low-trans diaminodicyclohexylmethane, and in particular to a method for preparing H12MDA by hydrogenating MDA-100. Background Art

[0002] H12MDA has three stereoisomers with different thermodynamic properties: trans-trans, cis-trans, and cis-cis. Its melting point is related to the composition of the three isomers, especially the trans-trans isomer. The lower the content of the trans-trans isomer, the lower its melting point and the better the fluidity of the product. Among them, H12MDA products with a trans-trans isomer content of about 20wt% or less are mainly used in the fields of isocyanate synthesis and epoxy curing agents. Due to the stability of the aromatic ring and the steric hindrance effect, the hydrogenation of MDA is very difficult. Most patents use loaded precious metal catalysts to carry out intermittent catalytic reactions under high temperature and high pressure in a stirred tank reactor or a fixed bed reactor to obtain satisfactory yields and trans-trans ratios.

[0003] In order to further reduce the content of trans-trans isomers, researchers in this field have conducted a lot of research work, which can be divided into two main routes:

[0004] One is to modify the catalyst with a base. For example, US 4754070 discloses a new method that can obtain a trans-trans isomer ratio of 17-24%. This method adds 0.1-15wt% of a base-modified catalyst before the catalytic reaction to modify the solid-supported rhodium-ruthenium two-component catalyst. US 6075167 provides a ruthenium-catalyzed reduction process for aromatic diamine compounds using metal nitrite as a promoter, which improves the reaction rate and reduces the generation of high-boiling point byproduct tar. US 3697449 uses an aqueous solution of 1-35% alkali metal alcohol salt or hydroxide to modify the solid-supported ruthenium catalyst, and then performs a hydrogenation reduction reaction of MDA. However, this method will cause the alkali metals in the catalytic system to continue to accumulate, and the performance of the loaded precious metal catalyst will be irreversibly damaged, thereby continuously extending the reaction time and affecting the production efficiency. At the same time, when the precious metals in the waste catalyst are recovered at the end of production, the presence of alkali metals in the catalytic system will also affect the recovery rate of the precious metals, thereby further increasing the production cost.

[0005] The second is to separate the three isomers by using appropriate separation means. For example, US4020104 uses benzaldehyde and diaminodicyclohexylmethane to react with cis-cis and cis-trans isomers to generate corresponding benzaldehyde imine compounds. The benzaldehyde imine compound undergoes an isomerization reaction under an alkali metal catalyst, such as KOH, to generate a large amount of benzaldehyde imine trans-trans isomers. Subsequently, diaminodicyclohexylmethane with a high yield of trans-trans isomers can be obtained by hydrolysis under acidic conditions. The reaction steps taken by this method are relatively large, and the conditions are harsh. At the same time, the cis-cis and cis-trans isomers in the raw materials are converted into a large amount of trans-trans isomers in the isomer reaction. Therefore, this method is only suitable for obtaining H12MDA products with a higher content of trans-trans isomers.

[0006] Therefore, there is an urgent need to study a method for effectively reducing the trans-trans isomer of H12MDA in the art while overcoming the defects of the above-mentioned existing methods. Summary of the invention

[0007] The object of the present invention is to provide a low-reaction H 12 MDA synthesis method. The method adds N,N,N',N'-tetramethyl-MDA compound to the raw material MDA-100, and the compound is synergistically catalyzed with the noble metal supported catalyst to promote the activity of the catalyst, so as to obtain H-containing catalyst with an anti-anti content as low as 10-14%. 12 MDA, while the conversion rate of MDA-100 can reach over 99%.

[0008] In order to achieve the above purpose, the present invention adopts the following technical solution:

[0009] A low anti-H 12 The synthesis method of MDA is to use MDA-100 as a raw material, and obtain H12MDA with an anti-anti content of 10-14% under the action of a hydrogenation catalyst, wherein N,N,N',N'-tetramethyl-MDA compound is added to the raw material;

[0010] The structural formula of the N,N,N',N'-tetramethyl-MDA compound is as follows:

[0011]

[0012] The addition amount is 1-10wt% of the weight of the MDA-100 raw material, preferably 3-5wt%.

[0013] Preferably, the MDA-100 contains 97-100wt% of 4,4'-MDA, 0-2wt% of 2,4'-MDA and 0-1wt% of impurities, based on the weight of MDA-100; preferably 99-100wt% of 4,4'-MDA, 0-0.5wt% of 2,4'-MDA and 0-0.5wt% of impurities, based on the weight of MDA-100. Impurities such as N-methyl-4,4'-MDA.

[0014] Preferably, the hydrogenation catalyst comprises a combination of a metal and a support:

[0015] Preferably, the metal includes any one or a combination of at least two of Pt, Rh, Ru, Ir or Pd, more preferably Rh;

[0016] Preferably, the carrier comprises any one or a combination of at least two of rare earth, diatomaceous earth, alumina, activated carbon, spinel or silica-alumina, more preferably alumina;

[0017] More preferably, the metal content is 1-10 wt%, preferably 4-5 wt%, based on the weight of the hydrogenation catalyst;

[0018] More preferably, the amount of the hydrogenation catalyst is 1-10 wt %, preferably 2-3 wt %, based on the weight of MDA-100.

[0019] Preferably, the hydrogenation reaction is carried out in the presence of a solvent;

[0020] Preferably, the solvent comprises any one or a combination of at least two of cyclohexane, dioxane, tetrahydrofuran, methanol, ethanol, isopropanol, n-butanol, 2-butanol or methylcyclohexane, preferably tetrahydrofuran;

[0021] Preferably, the concentration of the raw material after mixing with the solvent is preferably 30-60wt%, more preferably 40-50wt%, based on the total weight of MDA-100 and the solvent;

[0022] Preferably, the reaction temperature is 100-250°C, preferably 150-200°C, more preferably 170-190°C; the reaction absolute pressure is 3-15MPa, preferably 5-10MPa, more preferably 6-8MPa.

[0023] Preferably, the reactor comprises a batch autoclave reactor with a catalyst filtration device;

[0024] Preferably, the catalyst filtering device is a built-in filter or an external filter, preferably a built-in filter of an autoclave.

[0025] The present invention improves the selectivity of trans-isomers in the hydrogenation reaction process by adding N,N,N',N'-tetramethyl-MDA compound to MDA-100. This is mainly due to the electron donation effect of the methyl group, which makes the benzene ring electron cloud density in N,N,N',N'-tetramethyl-MDA significantly higher than that of MDA. Therefore, during the hydrogenation reaction, the noble metal in the catalyst preferentially adsorbs N,N,N',N'-tetramethyl-MDA for catalytic hydrogenation reaction. Since most of the active metals in the catalyst are attached to the micropores of the carrier, when N,N,N',N'-tetramethyl-MDA enters the pores, the remaining effective reaction space is further reduced, which prompts the MDA hydrogenation in the reaction system to generate cis-isomers or cis-trans isomers with smaller steric hindrance, thereby achieving the purpose of reducing the content of trans-isomers in the reaction process.

[0026] The positive effects of the present invention are:

[0027] There is no need to introduce alkali to modify the catalyst structure, thus avoiding the influence of alkali metal on the recovery rate of precious metals in the waste catalyst at the end of the final reaction. In addition, there is no need to purify and separate the trans-isomers through complex separation methods, thus avoiding additional investment and production costs. At the same time, after hydrogenation of N,N,N',N'-tetramethyl-MDA, the generated N,N,N',N'-tetramethyl-HMDA can also be sold as a special polyurethane catalyst product, further increasing the added value of the product. DETAILED DESCRIPTION

[0028] The technical solution of the present invention is further described below by specific implementation methods. It should be understood by those skilled in the art that the embodiments are only to help understand the present invention and should not be regarded as specific limitations of the present invention.

[0029] Unless otherwise specified, the raw materials used in the following examples or comparative examples are all commercially available industrial-grade conventional raw materials. The main raw materials and testing instrument information are as follows:

[0030] 4wt% Rh / Al2O3 and 5wt% Rh / Al2O3 catalysts were purchased from Johnson Matthey, and wt% refers to the metal content.

[0031] Tetrahydrofuran was purchased from Komiou Company with analytical grade.

[0032] MDA-100 comes from Wanhua WANAMINE MDA-100, in which the content of 4,4'-MDA is 99.5wt%, the content of N-methyl-4,4'-MDA is 0.35wt%, and the content of 2,4'-MDA is 0.15wt%.

[0033] N,N,N',N'-tetramethyl-MDA was prepared in-house, with a purity of more than 98 wt%. The preparation process was as follows: 20 g MDA-100, 80 g tetrahydrofuran and 4 g Pt / C catalyst (Pt loading was 4 wt%, based on the dry weight of the catalyst; the water content of the catalyst was 50 wt%, based on the total weight of the catalyst) were added to a 500 ml high-pressure reactor, and after being replaced three times with 1 MPa (absolute pressure) of N2, the pressure was replaced three times with 1 MPa (absolute pressure) of H2, and then the pressure was increased to 3 MPa (absolute pressure) with H2. Stirring was started to increase the temperature. When the reaction temperature increased to 80°C, H2 was continuously introduced into the reactor to ensure that the reaction pressure was maintained at 5 MPa (absolute pressure). At the same time, 50 g of formaldehyde aqueous solution (formaldehyde concentration was 37 wt%) was pumped into the reactor at a feed rate of 2 g / min through a horizontal flow pump. After the reaction was continued for 2 hours, the reactor was cooled and depressurized. When the temperature of the reactor drops to 30°C, the crude product liquid is filtered and separated from the catalyst through a built-in filter using N2 at no more than 0.6MPa (absolute pressure). Excess water and formaldehyde are removed from the crude product liquid at 20KPa and 80°C to obtain N,N,N',N'-tetramethyl-MDA product, which has a purity greater than 98wt% as determined by gas chromatography.

[0034] Gas chromatography analysis method: Agilent 7890 series, DB-5 capillary column was used, the FID detector temperature was 300°C, the initial column temperature was 160°C, increased to 300°C at 10°C / min, and stayed for 20 minutes.

[0035] Example 1

[0036] In a 1L autoclave with a built-in filter, 6g of 4wt% Rh / Al2O3 catalyst and 10g of N,N,N',N'-tetramethyl-MDA were added, and 200g of MDA-100 and 200g of tetrahydrofuran were added at the same time. After being replaced with 1MPa (absolute pressure) of N2 three times, it was replaced with 1MPa (absolute pressure) of H2 three times, and then the H2 pressure was supplemented to 5MPa (absolute pressure). The temperature was raised to 190°C. During the reaction, H2 was continuously introduced into the reactor through a hydrogen flow controller to ensure that the reaction pressure was maintained at 6MPa (absolute pressure). When the hydrogen flow rate reading of the hydrogen flow controller was lower than 100sccm, the introduction of H2 was stopped. When the pressure drop of the reactor was less than 0.01MPa / min, the reaction was stopped, and the reactor was cooled and depressurized. When the temperature of the reactor drops to 50°C, N2 with an absolute pressure not exceeding 0.6MPa is used to filter and separate the product liquid from the catalyst through a built-in filter, and the product liquid is analyzed by gas chromatography. When the product liquid is filtered clean, 200g MDA-100, 200g tetrahydrofuran and 10g N,N,N',N'-tetramethyl-MDA are added, and the above steps are repeated to recycle the catalyst. The reaction results are shown in Table 1.

[0037] Table 1 Reaction results of Example 1

[0038]

[0039] Example 2

[0040] In a 1L autoclave with a built-in filter, 4g of 5wt% Rh / Al2O3 catalyst and 6g of N,N,N',N'-tetramethyl-MDA were added, and 200g of MDA-100 and 134g of tetrahydrofuran were added at the same time. After being replaced with 1MPa (absolute pressure) of N2 three times, it was replaced with 1MPa (absolute pressure) of H2 three times, and then the H2 pressure was supplemented to 6MPa (absolute pressure). The temperature was raised to 170°C. During the reaction, H2 was continuously introduced into the reactor through a hydrogen flow controller to ensure that the reaction pressure was maintained at 8MPa (absolute pressure). When the hydrogen flow rate reading of the hydrogen flow controller was lower than 100sccm, the introduction of H2 was stopped. When the pressure drop of the reactor was less than 0.01MPa / min, the reaction was stopped, and the reactor was cooled and depressurized. When the temperature of the reactor drops to 50°C, N2 with an absolute pressure not exceeding 0.6MPa is used to filter and separate the product liquid from the catalyst through a built-in filter, and the product liquid is analyzed by gas chromatography. When the product liquid is filtered clean, 200g MDA-100, 134g tetrahydrofuran and 6g N,N,N',N'-tetramethyl-MDA are added, and the above steps are repeated to recycle the catalyst. The reaction results are shown in Table 2.

[0041] Table 2 Reaction results of Example 2

[0042]

[0043]

[0044] Comparative Example 1

[0045] Except for not adding N,N,N',N'-tetramethyl-MDA, the other reaction conditions were the same as in Example 1. The reaction results are shown in Table 3.

[0046] Table 3 Reaction results of comparative example 1

[0047]

[0048] Comparative Example 2

[0049] Except that 40 g of N,N,N',N'-tetramethyl-MDA was added in each batch, the other reaction conditions were the same as those in Example 2. The reaction results are shown in Table 4.

[0050] Table 4 Reaction results of comparative example 2

[0051]

Claims

1. A low anti-H 12 MDA synthesis method, using MDA-100 as raw material, under the action of hydrogenation catalyst, obtains H with an anti-anti content of 10-14% 12 MDA, where Adding N,N,N',N'-tetramethyl-MDA compound to the raw material, the addition amount is 1-10wt% of the weight of the MDA-100 raw material; the hydrogenation catalyst is a noble metal supported catalyst, including a combination of a metal and a carrier, the metal is selected from at least one of Pt, Rh, Ru, Ir or Pd, and the content of the metal is 1-10wt% based on the weight of the hydrogenation catalyst; The structure of the N,N,N',N'-tetramethyl-MDA compound is shown below:

2. The method according to claim 1, characterized in that The amount of the N,N,N',N'-tetramethyl-MDA compound added is 3-5wt% of the weight of the MDA-100 raw material.

3. The method according to claim 1, characterized in that The MDA-100 contains 97-100 wt % of 4,4'-MDA, 0-2 wt % of 2,4'-MDA and 0-1 wt % of impurities, based on the weight of MDA-100.

4. The method according to claim 1, characterized in that: The carrier is selected from at least one of rare earth, diatomaceous earth, alumina, activated carbon, spinel or silica-alumina.

5. The method according to claim 1 or 4, characterized in that: The amount of the hydrogenation catalyst is 1-10 wt % based on the weight of MDA-100.

6. The method according to any one of claims 1 to 4, characterized in that: The hydrogenation reaction is carried out in the presence of a solvent.

7. The method according to claim 6, characterized in that The solvent is selected from at least one of cyclohexane, dioxane, tetrahydrofuran, methanol, ethanol, isopropanol, n-butanol, 2-butanol or methylcyclohexane.

8. The method according to claim 7, characterized in that The concentration of the raw materials after mixing with the solvent is 30-60wt%, based on the total weight of MDA-100 and the solvent.

9. The method according to any one of claims 1 to 4, characterized in that: The reaction temperature is 100-250°C, and the reaction absolute pressure is 3-15MPa.

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