Process and system for the preparation of p-phenylenediamine-based antioxidants

Abstract

The application relates to the technical field of organic synthesis, and discloses a method and system for preparing p-phenylenediamine antidegradants. The method comprises the following steps: (1) performing a dehydration condensation reaction on RT pesi and acetone in the presence of molecular sieves to obtain a first mixed solution containing a Schiff base; (2) performing a hydrogenation reaction on the first mixed solution containing the Schiff base in the presence of a hydrogenation catalyst to obtain a second mixed solution; and (3) performing separation crystallization on the second mixed solution to obtain an antidegradant 4010NA and an antidegradant 6PPD. The method and system can coproduce the antidegradants 4010NA and 6PPD, the proportion of 4010NA and 6PPD in the products can be flexibly controlled within a certain range compared with a one-step condensation hydrogenation process, the proportion of 6PPD in the products is increased, and the prepared antidegradant products are high in purity.

Description

Methods and systems for preparing p-phenylenediamine antioxidants Technical Field

[0001] This invention relates to the field of organic synthesis technology, and specifically to a method and system for preparing p-phenylenediamine antioxidants. Background Technology

[0002] Antioxidant 6PPD, also known as antioxidant 4020, belongs to the p-phenylenediamine class of antioxidants. It is one of the high-performance, general-purpose antioxidants among amine antioxidants, exhibiting balanced anti-aging properties. It has the largest usage volume among antioxidants and holds a dominant market position. Antioxidant 4010NA, another important p-phenylenediamine antioxidant, is effective in preventing ozone aging, metal aging, and resisting flexural fatigue and cracking. It is suitable for industrial rubber products operating under static, dynamic, or intermittent conditions.

[0003] The mainstream processes for preparing antioxidants 4010NA and 6PPD are both reductive hydrocarbonation methods using ketones and RT-peptides as raw materials. The synthesis mechanisms of the two antioxidants are shown below:

[0004] Acetone and RT-peptide are condensed and hydrogenated in a one-step process to produce antioxidant 4010NA:

[0005]

[0006] In the above process, acetone undergoes self-condensation and hydrogenation to produce methyl isobutyl ketone (MIBK):

[0007]

[0008] MIBK and RT-based antioxidants are condensed and hydrogenated to produce the antioxidant 6PPD:

[0009]

[0010] The raw material ketone for preparing 4010NA is acetone, and the raw material ketone for preparing 6PPD is MIBK. MIBK is mainly obtained through the condensation and hydrogenation of acetone. Therefore, in the actual industrial production of 4010NA, 6PPD is frequently produced as a byproduct. Because no special process optimization has been performed and the 6PPD content is low, a mixed compounding method is generally used to produce a 4010NA product with approximately 95% purity. This method not only affects the quality of 4010NA but also wastes the high-value-added products MIBK and 6PPD. In existing preparation processes, due to the lack of treatment or restriction of acetone before the hydrogenation reaction, there is currently no effective method to control the product composition.

[0011] With the increasing demands for the quality and diversity of antioxidant products, there is an urgent need for an optimized and improved production process that can achieve flexible production based on actual product type requirements and obtain high-purity antioxidants 4010NA and 6PPD. Summary of the Invention

[0012] This invention addresses the problem that existing p-phenylenediamine antioxidant preparation processes struggle to co-produce 4010NA and 6PPD, and that the purity of the prepared 4010NA and 6PPD products needs further improvement. It provides a method and system for preparing p-phenylenediamine antioxidants.

[0013] To achieve the above objectives, a first aspect of the present invention provides a method for preparing a p-phenylenediamine antioxidant, comprising:

[0014] (1) In the presence of molecular sieve, acetone and RT-based products were subjected to a dehydration condensation reaction to obtain a first mixture containing Schiff base.

[0015] (2) In the presence of a hydrogenation catalyst, the first mixture containing Schiff base is subjected to a hydrogenation reaction to obtain a second mixture;

[0016] (3) The second mixture is separated and crystallized to obtain antioxidant 4010NA and antioxidant 6PPD.

[0017] A second aspect of the present invention provides a system for preparing p-phenylenediamine antioxidants, the system comprising a dehydration condensation unit A, a hydrogenation unit B, and a separation crystallization unit C connected in sequence;

[0018] The dehydration condensation unit A is used to dehydrate and condense acetone with RT-peptide to obtain a first mixture containing Schiff base.

[0019] The hydrogenation unit B is used to hydrogenate the first mixture containing Schiff base to obtain a second mixture.

[0020] The separation and crystallization unit C is used to separate and crystallize the second mixture to obtain antioxidant 4010NA and antioxidant 6PPD.

[0021] Through the above technical solution, this invention adopts a multi-step reaction method. First, a water-absorbing molecular sieve is used to promote the condensation reaction of acetone and RT-based antioxidants to synthesize a Schiff base with controllable concentration. Then, hydrogenation is carried out under the action of a noble metal catalyst to obtain a mixture of antioxidant 4010NA and antioxidant 6PPD. After separation and crystallization, two high-purity antioxidant products are obtained. Compared with the one-step process of the prior art, the method for preparing p-phenylenediamine antioxidants provided by this invention can co-produce 4010NA and 6PPD, increasing the proportion of 6PPD in the product. This allows for flexible production of 4010NA and 6PPD within a certain proportion range and improves the purity of the products. The purity of the obtained antioxidant 4010NA is greater than 95% by weight, and can be as high as 99% by weight. The purity of the antioxidant 6PPD is greater than 98% by weight, and can be as high as 99% by weight. Attached Figure Description

[0022] The accompanying drawings are provided to further illustrate the invention and form part of the specification. They are used together with the following detailed description to explain the invention, but do not constitute a limitation thereof. In the drawings:

[0023] Figure 1 is a schematic diagram of the system for preparing p-phenylenediamine antioxidants according to the present invention.

[0024] Explanation of reference numerals in the attached figures

[0025] A-Dehydration condensation unit B-Hydrogenation unit C-Separation and crystallization unit

[0026] 1-Dehydration condensation reactor; 2-Storage tank; 3-Hydrogenation reactor

[0027] 4-First Separation Tower 5-Second Separation Tower 6-First Crystallizer

[0028] 7-Second Crystallizer Detailed Implementation

[0029] The endpoints and any values ​​of the ranges disclosed herein are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoint values ​​of the various ranges, the endpoint values ​​of the various ranges and individual point values, and individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed herein.

[0030] The following provides a detailed description of specific embodiments of the present invention. It should be understood that the specific embodiments described herein are for illustrative and explanatory purposes only and are not intended to limit the scope of the invention.

[0031] In a first aspect, the present invention provides a method for preparing a p-phenylenediamine antioxidant, comprising:

[0032] (1) In the presence of molecular sieve, acetone and RT-based products were subjected to a dehydration condensation reaction to obtain a first mixture containing Schiff base.

[0033] (2) In the presence of a hydrogenation catalyst, the first mixture containing Schiff base is subjected to a hydrogenation reaction to obtain a second mixture;

[0034] (3) The second mixture is separated and crystallized to obtain antioxidant 4010NA and antioxidant 6PPD.

[0035] In the existing one-step condensation hydrogenation synthesis process for antioxidant 4010NA and byproduct 6PPD, water is generated during the condensation reaction of acetone and RT-based antioxidants. This water reduces the rate of Schiff base formation and affects the catalytic activity of the noble metal catalyst. Furthermore, the one-step synthesis process has poor controllability, making it difficult to control the condensation of acetone and RT-based antioxidants as well as the self-condensation of acetone. Consequently, the composition of antioxidant 4010NA is poorly controllable. The inventors of this invention recognized the above-mentioned shortcomings and adopted an optimized and improved multi-step synthesis process. First, the raw material acetone and RT-based acetone undergo a dehydration condensation reaction. By adjusting the conditions of the condensation reaction, the ratio of the product Schiff base to 4-methyl-3-penten-2-one (a product of acetone self-condensation) can be controlled. Water-absorbing molecular sieves can be used to promote the above condensation reaction and reduce the water content of the product. Then, the product of the condensation reaction is hydrogenated, and finally, the hydrogenated product is separated and crystallized. Through the above multi-step synthesis process, 4010NA and 6PPD can be co-produced. Compared with the one-step process, the ratio of 4010NA to 6PPD in the product can be flexibly controlled within a certain range, and the proportion of 6PPD in the product can be increased, and the purity of the product is higher.

[0036] According to the present invention, in step (1), the molecular sieve can adsorb some of the water generated in the dehydration condensation reaction, which facilitates more controllable generation of Schiff bases. Preferably, the average pore size of the molecular sieve is [missing information].

[0037] According to the present invention, preferably, the molecular sieve is a 3A molecular sieve and / or a 4A molecular sieve, and more preferably a 4A molecular sieve.

[0038] In this invention, the definition of the 4A molecular sieve is relatively broad, as long as it can adsorb molecules with a diameter of less than 400 pm. It can be obtained by self-production using conventional methods or by using commercially available brand products.

[0039] According to the present invention, in step (1), the dehydration condensation reaction can be carried out by mixing acetone and RT-p-aminodiphenylamine (RT-p-aminodiphenylamine) in the presence of the molecular sieve to obtain a first mixture containing a Schiff base. The conditions for the dehydration condensation reaction include: atmospheric pressure, temperature of 60-80°C, and a total volume hourly space velocity (VHSV) of acetone and RT-p-p-aminodiphenylamine of 0.1-0.5 h⁻¹. -1 .

[0040] According to the present invention, preferably, the dehydration condensation reaction is carried out under a protective atmosphere, such as a nitrogen atmosphere, a neon atmosphere, an argon atmosphere, etc., and preferably a nitrogen atmosphere.

[0041] According to the present invention, in step (1), preferably, the molar ratio of acetone to RT-peptide is (3-5):1.

[0042] According to the present invention, in step (1), the Schiff base refers to N-isopropylidene-N'-phenyl-p-phenylenediamine obtained by dehydration condensation of acetone and RT-p-acetone.

[0043] According to the present invention, in step (1), the first mixture containing Schiff base is a liquid-phase mixture system, which, in addition to containing the Schiff base, also contains the remaining unreacted raw materials acetone, RT-paste, and 4-methyl-3-penten-2-one.

[0044] According to the present invention, in step (1), the water content in the first mixture containing Schiff base is less than 1% by weight. By utilizing the excellent water absorption properties of the molecular sieve, the water content in the reaction system can be effectively controlled, which is beneficial to the forward progress of the dehydration condensation reaction and can reduce the influence of water on the activity of the noble metal catalyst in the subsequent hydrogenation reaction.

[0045] According to the present invention, in step (2), the Schiff base in the first mixture containing the Schiff base is converted into a hydrogenation reaction. (i.e., antioxidant 4010NA), simultaneously, in step (2), the 4-methyl-3-penten-2-one in the first mixture containing Schiff base is converted to methyl isobutyl ketone by hydrogenation, then the methyl isobutyl ketone is dehydrated and condensed with RT-Plast to obtain a 6PPD precursor, and then the 6PPD precursor is hydrogenated to obtain (i.e., antioxidant 6PPD), to obtain the second mixture.

[0046] According to the present invention, in step (2), the hydrogenation reaction can be carried out by mixing the first mixture containing the Schiff base with hydrogen gas and performing the hydrogenation reaction under the action of the hydrogenation catalyst. Preferably, the conditions for the hydrogenation reaction include: a pressure of 0.4-1.5 MPa, more preferably 0.8-1.2 MPa; a temperature of 80-150°C, more preferably 90-120°C; a volume hydrogen-to-oil ratio of (100-700):1, more preferably (100-300):1; and a volume hourly space velocity (VHSV) of 0.1-0.5 h⁻¹ for the first mixture containing the Schiff base. -1 Preferably, it is 0.2-0.35h. -1 .

[0047] According to the present invention, in step (2), the hydrogenation catalyst is defined within a relatively wide range, and conventional hydrogenation catalysts used in the preparation of p-phenylenediamine antioxidants can be employed. Preferably, the hydrogenation catalyst is a supported catalyst, comprising a support and an active component; wherein the support can be selected from at least one of coconut shell activated carbon, alumina, and silica, preferably coconut shell activated carbon; more preferably, the specific surface area of ​​the coconut shell activated carbon support is 800-1200 m². 2 The catalyst has a pore volume of 0.3-2.5 g / ml, a pore size of 0.5-2.5 nm, an ash content of less than 5%, and a water absorption rate of greater than 60%. The active component can be selected from at least one of Pt, Pd, and Ni, preferably Pt. The weight ratio of the active component to the support is (0.1-5):100. Further preferably, the hydrogenation catalyst can be selected from at least one of the following: a catalyst with the brand name GX (manufactured by Hunan Minsizhuang Technology Co., Ltd.) and a catalyst with the brand name P111328 (manufactured by Shanghai Aladdin Biochemical Technology Co., Ltd.).

[0048] According to the present invention, in step (3), the separation and crystallization further includes the following steps:

[0049] (3-1) The second mixture is separated to obtain acetone, methyl isobutyl ketone and separation liquid; wherein, acetone and methyl isobutyl ketone are returned to step (1) to participate in the dehydration condensation reaction;

[0050] (3-2) The separated liquid is subjected to crystallization treatment to obtain antioxidant 4010NA and antioxidant 6PPD.

[0051] According to the present invention, in step (3-1), the separation process includes a first distillation and a second distillation performed sequentially. Specifically, the first distillation separates acetone from the second mixture, and the second distillation further separates methyl isobutyl ketone from the second mixture. The separated acetone and methyl isobutyl ketone are returned to step (1) to participate in the reaction again, thus achieving reuse.

[0052] According to the present invention, the first distillation is preferably carried out in a distillation column. Preferably, the conditions for the first distillation include: a column pressure of 0.1-0.3 MPa; a top temperature of 50-60°C and a bottom temperature of 90-100°C; and a reflux ratio of 4-5.

[0053] According to the present invention, the second distillation is preferably carried out in a distillation column. Preferably, the conditions for the second distillation include: a column pressure of 0.1-0.3 MPa; a top temperature of 110-120°C and a bottom temperature of 140-150°C; and a reflux ratio of 4-5.

[0054] According to the present invention, the main components of the separated liquid obtained after the separation treatment are antioxidant 4010NA and antioxidant 6PPD. Preferably, the sum of the contents of acetone and methyl isobutyl ketone in the separated liquid is less than 15% by weight.

[0055] According to the present invention, in step (3-2), the crystallization process includes a first crystallization and a second crystallization performed sequentially. Specifically, the antioxidant product 4010NA is separated through the first crystallization, and the antioxidant product 6PPD is separated through the second crystallization.

[0056] According to the present invention, in order to obtain better crystallization separation effect, preferably, the temperature of the first crystallization is 50-60℃; and the temperature of the second crystallization is 30-40℃.

[0057] The method for preparing p-phenylenediamine antioxidants provided by this invention has strong continuous operation and can flexibly produce 4010NA and 6PPD within a certain ratio range according to product type requirements. Compared with the existing one-step condensation and hydrogenation synthesis process, the conversion rate of raw material RT-p-propane is higher, the problem of by-product water can be solved, the reaction conditions are milder, and the product quality is better. It can achieve a product purity of 4010NA greater than 95% by weight and a product purity of 6PPD greater than 98% by weight.

[0058] A second aspect of the present invention provides a system for preparing p-phenylenediamine antioxidants, as shown in FIG1. ​​The system includes a dehydration condensation unit A, a hydrogenation unit B, and a separation crystallization unit C connected in sequence.

[0059] The dehydration condensation unit A is used to dehydrate and condense acetone with RT-peptide to obtain a first mixture containing Schiff base.

[0060] The hydrogenation unit B is used to hydrogenate the first mixture containing Schiff base to obtain a second mixture.

[0061] The separation and crystallization unit C is used to separate and crystallize the second mixture to obtain antioxidant 4010NA and antioxidant 6PPD.

[0062] According to the present invention, in the system for preparing p-phenylenediamine antioxidants, the dehydration condensation unit A includes a dehydration condensation reactor 1 and a storage tank 2 connected in sequence. The dehydration condensation reactor 1 can be any reactor capable of performing a dehydration condensation reaction between acetone and RT-peptide; the present invention does not particularly limit its application. The storage tank 2 is used to store the first mixture containing the Schiff base.

[0063] According to the present invention, in the system for preparing p-phenylenediamine antioxidants, the hydrogenation unit B includes a hydrogenation reactor 3, and the hydrogenation reactor 3 is connected to the storage tank 2. The hydrogenation reactor 3 can be any reactor capable of hydrogenating liquid-phase raw materials with hydrogen gas; the present invention does not impose any particular limitation on it.

[0064] According to the present invention, in the system for preparing p-phenylenediamine antioxidants, the separation and crystallization unit C includes a first separation tower 4, a second separation tower 5, a first crystallizer 6, and a second crystallizer 7 connected in sequence; wherein, the first separation tower 4 is connected to the hydrogenation reactor 3.

[0065] In this invention, the first separation tower 4 and the second separation tower 5 are preferably distillation towers, used to sequentially distill and separate acetone and methyl isobutyl ketone from the second mixture obtained after hydrogenation, and obtain a separated liquid after separation.

[0066] In this invention, the first crystallizer 6 and the second crystallizer 7 are preferably external circulation cooling crystallizers, used to sequentially crystallize and separate antioxidant 4010NA and antioxidant 6PPD from the separation liquid to obtain a high-purity antioxidant product.

[0067] According to the present invention, preferably, the first separation tower 4 and the second separation tower 5 are respectively connected to the dehydration condensation reactor 1. Specifically, the top outlets of the first separation tower 4 and the second separation tower 5 are respectively connected to the inlet of the dehydration condensation reactor 1, for returning the acetone and methyl isobutyl ketone separated by distillation to the dehydration condensation reactor 1 to continue participating in the dehydration condensation reaction, thereby achieving reuse.

[0068] The system for preparing p-phenylenediamine antioxidants provided by this invention, through separately set dehydration condensation unit A and hydrogenation unit B, can achieve flexible production of 4010NA and 6PPD within a certain ratio range according to product type requirements. Furthermore, in the separation and crystallization unit C, different products can be thoroughly separated by crystallization based on differences in product solubility and melting point, resulting in high-purity products.

[0069] The following describes, with reference to Figure 1, a method for preparing p-phenylenediamine antioxidants using the system provided by the present invention.

[0070] Acetone and RT peroxide are mixed at a molar ratio of (3-5):1 and then introduced into dehydration condensation unit A. The mixture first enters a molecular sieve (with an average pore size of...). The dehydration condensation reaction was carried out in reactor 1 under a nitrogen atmosphere (reaction temperature 60-80℃, total volume hourly space velocity of acetone and RT-peptide 0.1-0.5 h⁻¹). -1 The process involves obtaining a first mixture containing Schiff bases (wherein the water content is less than 1% by weight) and sending it to storage tank 2. The first mixture containing Schiff bases then enters hydrogenation unit B from storage tank 2, where it mixes with hydrogen gas in hydrogenation reactor 3 and undergoes a hydrogenation reaction under the action of a hydrogenation catalyst (pressure 0.4-1.5 MPa; temperature 80-150℃; hydrogen-to-oil ratio 100-700; volume hourly space velocity of the first mixture containing Schiff bases 0.1-0.5 h⁻¹). -1 The first mixture is then fed into a second separation column (4) to obtain a second mixture. This second mixture enters the separation and crystallization unit C, where it first undergoes first distillation in a first separation column 4 (pressure 0.1-0.3 MPa; top temperature 50-60℃, bottom temperature 90-100℃; reflux ratio 4-5) to separate acetone. Then, it enters a second separation column 5 (pressure 0.1-0.3 MPa; top temperature 110-120℃, bottom temperature 90-100℃; reflux ratio 4-5) to separate methyl isobutyl ketone. The separated acetone and methyl isobutyl ketone... The acetone is returned from the top of the first separation tower 4 and the second separation tower 5 to the dehydration condensation reactor 1 to continue participating in the dehydration condensation reaction, and a separated liquid is obtained at the bottom of the second separation tower 5 (wherein the sum of the contents of acetone and methyl isobutyl ketone is less than 15% by weight); the separated liquid enters the first crystallizer 6 (crystallization temperature is 50-60℃) for the first crystallization, and high-purity antioxidant product 4010NA is obtained; the remaining liquid phase enters the second crystallizer 7 (crystallization temperature is 30-40℃) for the second crystallization, and high-purity antioxidant product 6PPD is obtained.

[0071] The present invention will be described in detail below through embodiments. In the following embodiments and comparative examples,

[0072] 3A molecular sieve: grade XFF23-102485, purchased from Jiangsu Xianfeng Nanomaterials Technology Co., Ltd., with an average pore size of [missing information].

[0073] 4A molecular sieve: grade XFF20-102487, purchased from Jiangsu Xianfeng Nanomaterials Technology Co., Ltd., with an average pore size of [missing information].

[0074] Hydrogenation catalyst: Grade P111328, purchased from Shanghai Aladdin Biochemical Technology Co., Ltd.

[0075] Example 1

[0076] (1) As shown in Figure 1, acetone and RT-peptide are mixed at a molar ratio of 3:1 and then fed into dehydration condensation unit A. First, the mixture enters dehydration condensation reactor 1, which is filled with 4A molecular sieves, and the dehydration condensation reaction is carried out under a nitrogen atmosphere (reaction temperature is 80℃, and the total volume hourly space velocity of acetone and RT-peptide is 0.3 h⁻¹). -1 The first mixture containing Schiff base (in which the water content is less than 1% by weight) is obtained and sent to storage tank 2.

[0077] The composition of the first mixture containing Schiff base and the relevant results of the dehydration condensation reaction are shown in Table 1;

[0078] (2) The first mixture containing Schiff bases described above enters the hydrogenation unit B from the storage tank 2, where it is mixed with hydrogen gas in the hydrogenation reactor 3 and undergoes a hydrogenation reaction under the action of a hydrogenation catalyst (pressure 1.0 MPa, temperature 90°C, hydrogen-to-oil ratio 400:1, volume hourly space velocity of the first mixture containing Schiff bases 0.25 h⁻¹). -1 ), to obtain the second mixture;

[0079] The composition of the resulting second mixture is shown in Table 2;

[0080] (3-1) The second mixture mentioned above enters the separation and crystallization unit C. First, it enters the first distillation column 4 (column pressure: 0.1 MPa; top temperature: 56℃; bottom temperature: 90℃; reflux ratio: 4) for first distillation. Then, it enters the second distillation column 5 (column pressure: 0.1 MPa; top temperature: 112℃; bottom temperature: 140℃; reflux ratio: 4.5) for second distillation. The separated acetone and methyl isobutyl ketone are returned from the top of the first distillation column 4 and the second distillation column 5 to the dehydration condensation reactor 1 to continue participating in the dehydration condensation reaction. The separated liquid is obtained at the bottom of the second separation column 5 (wherein, the sum of the contents of acetone and methyl isobutyl ketone is 12.9% by weight).

[0081] (3-2) The above separated liquid is fed into the first crystallizer 6 (crystallization temperature is 60℃) for the first crystallization to obtain antioxidant product 4010NA. The remaining liquid phase is fed into the second crystallizer 7 (crystallization temperature is 40℃) for the second crystallization to obtain antioxidant product 6PPD.

[0082] The purity of the obtained antioxidant products 4010NA and 6PPD is shown in Table 3.

[0083] Example 2

[0084] (1) As shown in Figure 1, acetone and RT-peptide are mixed at a molar ratio of 5:1 and then fed into dehydration condensation unit A. First, the mixture enters dehydration condensation reactor 1, which is filled with 4A molecular sieves, and the dehydration condensation reaction is carried out under a nitrogen atmosphere (reaction temperature is 80℃, and the total volume hourly space velocity of acetone and RT-peptide is 0.3 h⁻¹). -1 The first mixture containing Schiff base (in which the water content is less than 1% by weight) is obtained and sent to storage tank 2.

[0085] The composition of the first mixture containing Schiff base and the relevant results of the dehydration condensation reaction are shown in Table 1;

[0086] (2) The first mixture containing Schiff base is introduced from storage tank 2 into hydrogenation unit B, where it is mixed with hydrogen in hydrogenation reactor 3 and subjected to hydrogenation reaction under the action of hydrogenation catalyst (pressure 1 MPa, temperature 90°C, hydrogen-to-oil ratio 350:1, volume hourly space velocity of the first mixture containing Schiff base 0.30 h⁻¹). -1 ), to obtain the second mixture;

[0087] The composition of the resulting second mixture is shown in Table 2;

[0088] (3-1) The second product mentioned above enters the separation and crystallization unit C. First, it enters the first distillation column 4 (column pressure: 0.1 MPa; column top temperature: 56℃; column bottom temperature: 90℃; reflux ratio: 4) for first distillation. Then, it enters the second distillation column 5 (column pressure: 0.1 MPa; column top temperature: 112℃; column bottom temperature: 140℃; reflux ratio: 4.5) for second distillation. The separated acetone and methyl isobutyl ketone are returned from the top of the first distillation column 4 and the second distillation column 5 to the dehydration condensation reactor 1 to continue to participate in the dehydration condensation reaction. The separated liquid is obtained at the bottom of the second separation column 5 (wherein, the sum of the contents of acetone and methyl isobutyl ketone is 14% by weight).

[0089] (3-2) The above separated liquid is fed into the first crystallizer 6 (crystallization temperature is 60℃) for the first crystallization to obtain antioxidant product 4010NA. The remaining liquid phase is fed into the second crystallizer 7 (crystallization temperature is 40℃) for the second crystallization to obtain antioxidant product 6PPD.

[0090] The purity of the obtained antioxidant products 4010NA and 6PPD is shown in Table 3.

[0091] Example 3

[0092] (1) As shown in Figure 1, acetone and RT-peptide are mixed at a molar ratio of 3:1 and then fed into dehydration condensation unit A. First, the mixture enters dehydration condensation reactor 1, which is filled with 4A molecular sieves, and the dehydration condensation reaction is carried out under a nitrogen atmosphere (reaction temperature is 60℃, and the total volume hourly space velocity of acetone and RT-peptide is 0.3h). -1 The first mixture containing Schiff base (in which the water content is less than 1% by weight) is obtained and sent to storage tank 2.

[0093] The composition of the first mixture containing Schiff base and the relevant results of the dehydration condensation reaction are shown in Table 1;

[0094] (2) The first mixture containing Schiff base is introduced from storage tank 2 into hydrogenation unit B, where it is mixed with hydrogen in hydrogenation reactor 3 and subjected to hydrogenation reaction under the action of hydrogenation catalyst (pressure 1.2 MPa, temperature 100 °C, hydrogen-to-oil ratio 400:1, volume hourly space velocity of the first mixture containing Schiff base 0.25 h⁻¹). -1 ), to obtain the second mixture;

[0095] The composition of the resulting second mixture is shown in Table 2;

[0096] (3-1) The second product mentioned above enters the separation and crystallization unit C. First, it enters the first distillation column 4 (column pressure: 0.1 MPa; column top temperature: 56℃; column bottom temperature: 90℃; reflux ratio: 4) for first distillation. Then, it enters the second distillation column 5 (column pressure: 0.1 MPa; column top temperature: 112℃; column bottom temperature: 140℃; reflux ratio: 4.5) for second distillation. The separated acetone and methyl isobutyl ketone are returned from the top of the first distillation column 4 and the second distillation column 5 to the dehydration condensation reactor 1 to continue to participate in the dehydration condensation reaction. The separated liquid is obtained at the bottom of the second separation column 5 (wherein, the sum of the contents of acetone and methyl isobutyl ketone is 7% by weight).

[0097] (3-2) The above separated liquid is fed into the first crystallizer 6 (crystallization temperature is 60℃) for the first crystallization to obtain antioxidant product 4010NA. The remaining liquid phase is fed into the second crystallizer 7 (crystallization temperature is 40℃) for the second crystallization to obtain antioxidant product 6PPD.

[0098] The purity of the obtained antioxidant products 4010NA and 6PPD is shown in Table 3.

[0099] Example 4

[0100] (1) As shown in Figure 1, acetone and RT-peptide are mixed at a molar ratio of 3:1 and fed into dehydration condensation unit A. First, the mixture enters dehydration condensation reactor 1, which is packed with 3A molecular sieve catalyst, and the dehydration condensation reaction is carried out under a nitrogen atmosphere (reaction temperature is 80℃, and the total volume hourly space velocity of acetone and RT-peptide is 0.3h). -1 ), to the first mixture containing Schiff base (wherein the water content is less than 2% by weight), and sent to storage tank 2;

[0101] The composition of the first mixture containing Schiff base and the relevant results of the dehydration condensation reaction are shown in Table 1;

[0102] (2) The first mixture containing Schiff base is introduced from storage tank 2 into hydrogenation unit B, where it is mixed with hydrogen in hydrogenation reactor 3 and subjected to hydrogenation reaction under the action of hydrogenation catalyst (pressure 1.0 MPa, temperature 80℃, hydrogen-to-oil ratio 400:1, volume hourly space velocity of the first mixture containing Schiff base 0.25 h⁻¹). -1 ), to obtain the second mixture;

[0103] The composition of the resulting second mixture is shown in Table 2;

[0104] (3-1) The second mixture mentioned above enters the separation and crystallization unit C, and first enters the first distillation column 4 (column pressure 0.1MPa; column top temperature 56℃, column bottom temperature 90℃; reflux ratio 4) for first distillation, and then enters the second distillation column 5 (column pressure 0.1MPa; column top temperature 112℃, column bottom temperature 140℃; reflux ratio 4.5) for second distillation. The separated acetone and methyl isobutyl ketone are returned from the top of the first distillation column 4 and the second distillation column 5 to the dehydration condensation reactor 1 to continue to participate in the dehydration condensation reaction, and the separated liquid is obtained at the bottom of the second separation column 5 (wherein, the sum of the contents of acetone and methyl isobutyl ketone is 5% by weight).

[0105] (3-2) The above separated liquid is fed into the first crystallizer 6 (crystallization temperature is 60℃) for the first crystallization to obtain antioxidant product 4010NA. The remaining liquid phase is fed into the second crystallizer 7 (crystallization temperature is 40℃) for the second crystallization to obtain antioxidant product 6PPD.

[0106] The purity of the obtained antioxidant products 4010NA and 6PPD is shown in Table 3.

[0107] Comparative Example 1

[0108] The method is the same as in Example 1, except that in step (3-2), the separated liquid is introduced into a distillation column, and atmospheric pressure distillation separation is performed using the boiling point difference between 4010NA and 6PPD (column pressure 0.1MPa; top temperature 180℃, bottom temperature 200℃; reflux ratio 4). Other steps and conditions are the same as in Example 1, yielding antioxidant products 4010NA and 6PPD.

[0109] The product composition and reaction results of each step are shown in Table 1-3.

[0110] Comparative Example 2

[0111] Acetone and RT-peptide were mixed at a molar ratio of 3:1. A Pt / C catalyst (Pt weight accounted for 0.25% of the total catalyst weight) was loaded into a fixed-bed reactor. The mixture of acetone and RT-peptide was added to carry out a condensation hydrogenation reaction (reaction temperature 100℃, pressure 1.0MPa, hydrogen-to-oil ratio 400:1) to obtain a reaction solution.

[0112] The above reaction liquid was separated into gas and liquid phases, and then passed through a recovery tower to recover acetone and methyl isobutyl ketone, respectively. Finally, it entered a distillation tower for further distillation (tower pressure 0.1 MPa; top temperature 180℃, bottom temperature 200℃; reflux ratio 4) to obtain the antioxidant product. In the obtained antioxidant product, the weight ratio of 4010NA to 6PPD was 4:1; the purity of antioxidant product 4010NA was 90.2% by weight, and the purity of antioxidant product 6PPD was 97.1% by weight.

[0113] Table 1

[0114]

[0115] Note: The percentage content of each component in Table 1 is by weight.

[0116] Table 2

[0117]

[0118] Note: The high-boiling-point substances in Table 2 are the products obtained by hydrogenation of the self-condensation product of methyl isobutyl ketone and RT-perose.

[0119] Table 3

[0120]

[0121] As can be seen from the results of Examples 1-4 and Comparative Examples 1-2 above, the method for preparing p-phenylenediamine antioxidants of the present invention can produce two high-purity antioxidant products by adjusting the ratio of acetone and RT-peptide and performing a two-step reaction of condensation and hydrogenation. Moreover, it can controllably produce products 4010NA and 6PPD within a certain ratio range (for example, the weight ratio of 4010NA to 6PPD in Examples 1-4 is in the range of (1.6-3):1). Compared with the one-step process (for example, Comparative Example 2), the proportion of 6PPD in the product can be higher.

[0122] The preferred embodiments of the present invention have been described in detail above; however, the present invention is not limited thereto. Within the scope of the inventive concept, various simple modifications can be made to the technical solutions of the present invention, including combinations of various technical features in any other suitable manner. These simple modifications and combinations should also be considered as the content disclosed in the present invention and are all within the protection scope of the present invention.

Claims

1. A method for preparing p-phenylenediamine antioxidants, characterized in that, include: (1) In the presence of molecular sieve, acetone and RT-Plast are subjected to dehydration condensation reaction to obtain a first mixture containing Schiff base; (2) In the presence of a hydrogenation catalyst, the first mixture containing Schiff base is subjected to a hydrogenation reaction to obtain a second mixture; (3) The second mixture is separated and crystallized to obtain antioxidant 4010NA and antioxidant 6PPD; The conditions for the dehydration condensation reaction include: a temperature of 60-80°C and a total volume hourly space velocity (VHSV) of 0.1-0.5 h⁻¹ for acetone and RT-peptide. -1 The water content in the first mixture containing Schiff base is less than 2% by weight; the conditions for the hydrogenation reaction include: pressure of 0.4-1.5 MPa; temperature of 80-150℃; hydrogen-to-oil ratio of (100-700):1; and volume hourly space velocity of the first mixture containing Schiff base of 0.1-0.5 h⁻¹. -1 The separation and crystallization process includes: (3-1) separating the second mixture to obtain acetone, methyl isobutyl ketone and a separation liquid; wherein, acetone and methyl isobutyl ketone return to step (1) to participate in the dehydration condensation reaction; (3-2) crystallizing the separation liquid to obtain antioxidant 4010NA and antioxidant 6PPD; the sum of the contents of acetone and methyl isobutyl ketone in the separation liquid is less than 15% by weight; the crystallization process includes a first crystallization and a second crystallization performed sequentially.

2. The method according to claim 1, wherein, In step (1), the average pore size of the molecular sieve is 3-5 Å; and / or, the molecular sieve is a 3A molecular sieve and / or a 4A molecular sieve.

3. The method according to claim 2, wherein, The molecular sieve is a 4A molecular sieve.

4. The method according to any one of claims 1-3, wherein, In step (1), the molar ratio of acetone to RT-permethrin is (3-5):

1.

5. The method according to any one of claims 1-3, wherein, In step (2), the conditions for the hydrogenation reaction include: pressure of 0.8-1.2 MPa; temperature of 90-120℃; hydrogen-to-oil ratio of (100-300):1; and volume hourly space velocity (VHSV) of the first mixture containing Schiff base of 0.2-0.35 h⁻¹. -1 .

6. The method according to any one of claims 1-3, wherein, The separation process includes a first distillation and a second distillation performed sequentially.

7. The method according to claim 6, wherein, The conditions for the first distillation include: a column pressure of 0.1-0.3 MPa; a top temperature of 50-60°C and a bottom temperature of 90-100°C; and a reflux ratio of 4-5; and / or the conditions for the second distillation include: a column pressure of 0.1-0.3 MPa; a top temperature of 110-120°C and a bottom temperature of 140-150°C; and a reflux ratio of 4-5.

8. The method according to claim 1, wherein, The temperature of the first crystallization is 50-60℃; and / or the temperature of the second crystallization is 30-40℃.

9. A system for preparing p-phenylenediamine antioxidants, characterized in that, The system includes a dehydration condensation unit (A), a hydrogenation unit (B), and a separation and crystallization unit (C) connected in sequence. The dehydration condensation unit (A) is used to dehydrate and condense acetone with RT-peptide to obtain a first mixture containing a Schiff base. The hydrogenation unit (B) is used to hydrogenate the first mixture containing the Schiff base to obtain a second mixture. The separation and crystallization unit (C) is used to separate and crystallize the second mixture to obtain antioxidant 4010NA and antioxidant 6PPD. The dehydration condensation unit (A) includes a dehydration condensation reactor (1) and a storage tank (2) connected in sequence. The hydrogenation unit (B) includes a hydrogenation reactor (3), which is connected to the storage tank (2). The separation and crystallization unit (C) includes a first separation tower (4), a second separation tower (5), a first crystallizer (6), and a second crystallizer (7) connected in sequence. The first separation tower (4) is connected to the hydrogenation reactor (3).

10. The system according to claim 9, wherein, The first separation tower (4) and the second separation tower (5) are respectively connected to the dehydration condensation reactor (1).

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