Preparation process of N, N-dimethyl propane diamine

Abstract

The invention discloses a preparation process of N, N-dimethyl propane diamine in the field of petrochemical engineering, which comprises the following steps: 1) putting a catalyst into a high-pressure reaction kettle, then adding acrylonitrile and dimethylamine, and filling into the high-pressure reaction kettle through an inlet of an ejector; 2) filling ammonia gas into the reactor after the replacement is completed, then heating the high-pressure reaction kettle through jacket steam outside the high-pressure reaction kettle, filling hydrogen into the high-pressure reaction kettle after the heating is completed, and continuously preheating the high-pressure reaction kettle until the reaction is completed; 3) the reaction liquid circulating pump sends part of the reactor outlet material to the external circulation heat exchanger and sends part of the material to the catalyst filter pump; and 4) cooling the material discharged from the external circulation heat exchanger, and returning the cooled material to the high-pressure reaction kettle for continuous reaction. The one-pot circulation process provided by the invention can avoid multi-kettle switching in the synthesis process, simplifies the process flow, reduces the equipment investment, and reduces the operation complexity.

Description

Technical Field

[0001] The present invention relates to the technical field of petrochemical engineering, and particularly to a synthesis technology of propanediamine derivatives. Technical Background

[0002] N,N-Dimethylpropylamine (DMAPA) is one of the important varieties of lower aliphatic diamines. Due to its strong polarity and active chemical properties, it can be used in a variety of organic synthesis reactions. Generally, it is mainly used as an organic synthesis intermediate to produce surfactants, dyes, ion exchange resins, etc., as an additive for epoxy resins, gasoline, oils, fibers, and leather, etc. At the same time, it can also be used as a preservative, humectant, and crosslinking agent in the plastic industry and paper industry, etc. It is a fine chemical with broad application prospects.

[0003] Currently, the industrial preparation processes of DMAPA all use dimethylamine, acrylonitrile, and hydrogen as raw materials, and adopt the Michael addition reaction of acrylonitrile and dimethylamine, and the hydrogenation reduction preparation process of dimethylaminopropionitrile. However, most of them use the batch two-step process for production, which has the disadvantages of difficult catalyst regeneration, poor product quality, complex process flow, backward overall production process, and high production cost.

[0004] Currently, the relevant patents on DMAPA mainly focus on aspects such as the type of reactor, optimization of synthesis process conditions, and selection of hydrogenation catalysts.

[0005] Chinese Patent CN105198754B discloses a batch preparation process of DMAPA. First, acrylonitrile and dimethylamine are added to a synthesis reaction kettle for reaction, and then the excess dimethylamine is removed by distillation to obtain dimethylaminopropene nitrile; then hydrogen is introduced into a high-pressure reaction kettle, and a hydrogenation catalyst is added for hydrogenation reduction reaction. After the reaction is complete, sedimentation and distillation are carried out to obtain the DMAPA product.

[0006] Chinese Patent CN101321722B proposes a method for preparing DMAPA on an industrial scale. This method first uses acrylonitrile and dimethylamine as raw materials to carry out an addition reaction in a bubble-cap column to prepare dimethylaminopropionitrile; then the concentrated dimethylaminopropionitrile product is obtained by refining at the bottom of the bubble-cap column, and finally this product is transferred to an intermittent hydrogenation reactor for catalytic hydrogenation to obtain DMAPA.

[0007] Chinese Patent CN113620813 developed a continuous process technology for microchannel amination combined with fixed-bed hydrogenation. In this method, the addition reaction of dimethylamine and acrylonitrile is first carried out in a microchannel reactor. After the reaction is completed, it is mixed with hydrogen and preheated before entering a continuous hydrogenation reactor for hydrogenation reaction. In Chinese Patent CN103333073, Meng Qingwei et al. developed a process for continuously preparing DMAPA in a double fixed-bed. Different from Patent CN113620813, in this method, the addition reaction of dimethylamine and acrylonitrile is completed in a fixed-bed reactor, and the subsequent processes are basically similar for both.

[0008] However, the process technologies proposed in Chinese Patents CN105198754B and CN101321722B have high operating costs and poor product quality stability in industrial production. The process technology proposed in Chinese Patent CN103333073 has a long residence time in the addition reaction stage, a large reactor size, and a high equipment investment. Although the residence time is shortened and the equipment size is reduced in the process technology of Patent CN113620813 using a microchannel reactor, the cost of the microchannel reactor is high and it is not suitable for large-scale production.

[0009] Therefore, it is very necessary to propose a new process technology for preparing dimethylpropylenediamine, which can reduce the investment in the industrial preparation process of dimethylpropylenediamine, improve the degree of automation, and make the product quality more stable. Summary of the Invention

[0010] The present invention aims at the problems existing in the prior art and provides a new preparation process for N,N-dimethylpropylenediamine.

[0011] To achieve the above object, the technical solution adopted by the present invention is as follows:

[0012] A preparation process for N,N-dimethylpropylenediamine includes the following steps:

[0013] 1) Put the prepared hydrogenation catalyst into a high-pressure reaction kettle. First add acrylonitrile and cool the high-pressure kettle, then add dimethylamine. Subsequently, fill the high-pressure reaction kettle with nitrogen to displace the air in the kettle.

[0014] 2) The outlet of the high-pressure reaction kettle is connected to a reaction liquid circulation pump. The reaction raw materials from the high-pressure reaction kettle are pressurized by the reaction liquid circulation pump and the materials at the outlet of the reaction kettle are sent to an external circulation heat exchanger and returned to the high-pressure reaction kettle through an ejector.

[0015] 3) An air inlet is opened on the side of the ejector. After the air replacement in the kettle is completed, fill the high-pressure reaction kettle with ammonia. Subsequently, heat the high-pressure reaction kettle by steam in the outer jacket of the reaction kettle. After heating is completed, fill the high-pressure reaction kettle with hydrogen and continue to preheat and maintain the temperature of the high-pressure reaction kettle until the reaction ends.

[0016] 4) Part of the reaction product coming out of the high-pressure reactor outlet is sent to the external circulation heat exchanger by the reaction liquid circulation pump. After heat exchange and temperature control, it returns to the high-pressure reactor to continue the reaction. Part is sent to the catalyst filtration pump. The material coming out of the catalyst filtration pump enters the primary filter. After filtration, the material containing the catalyst enters the catalyst metering tank to be mixed with fresh or regenerated catalyst and then sent to the high-pressure autoclave reactor; the material without the catalyst enters the secondary filter again, and the filtered crude product is sent to the crude liquid tank.

[0017] A preparation process of N,N-dimethylpropylenediamine according to the present invention is further characterized in that: by circulating and removing heat through the external circulation heat exchanger, on the one hand, the load of the jacket of the high-pressure reactor is reduced, and on the other hand, the reaction product is separated from the reaction system, which is beneficial to improving the conversion rate of the reaction raw materials.

[0018] A preparation process of N,N-dimethylpropylenediamine according to the present invention is further characterized in that: the reaction temperature of the high-pressure reactor is 40-140 °C, preferably 80-120 °C. The reaction ammonia partial pressure is 0.01-0.1 MPa, preferably 0.05-0.5 MPa; the hydrogen partial pressure is 0.1-5 MPa, preferably 0.5-3.0 MPa.

[0019] A preparation process of N,N-dimethylpropylenediamine according to the present invention is further characterized in that: the dosage of the catalyst is 0.1 wt% - 3.0 wt%, and the preferred dosage of the catalyst is 0.5 wt% - 1.5 wt%.

[0020] A preparation process of N,N-dimethylpropylenediamine according to the present invention is further characterized in that: the hydrogenation catalyst is Raney nickel, Raney copper, Pt / C, Pd / C and cobalt composite nanocatalyst, preferably Raney nickel or Raney copper composite nanocatalyst. The hydrogenation catalyst can select commercially available catalysts with a wide application range and reliable and mature technology in the market.

[0021] A preparation process of N,N-dimethylpropylenediamine according to the present invention is further characterized in that: the ejector is preferably a jet ejector. The ejector generally consists of parts such as a nozzle, a receiving chamber, a mixing chamber and a diffuser chamber.

[0022] A preparation process of N,N-dimethylpropylenediamine according to the present invention is further characterized in that: an air inlet is opened on the side of the ejector, and an ammonia gas inlet and a hydrogen gas inlet are provided.

[0023] The positive effects of the technology of the present invention are as follows:

[0024] 1. The one-pot circulation process proposed by the process of the present invention can avoid multi-reactor switching in the synthesis process, simplify the process flow, reduce equipment investment, and reduce operation complexity.

[0025] 2. The circulation loop formed by the high-pressure reactor, reaction liquid circulation pump, external circulation heat exchanger, and jet injector in the process of the present invention enables more precise control of parameters such as temperature, residence time, and pressure, enhances the controllability of the reaction process, and improves the effectiveness of the utilization of various resources in the reaction process.

[0026] 3. The process of the present invention is provided with an external circulation heat exchanger, which can reduce the reaction temperature of the high-pressure reactor to a controllable range, avoid the "temperature runaway" of the reactor caused by local hot spots, reduce the generation of heavy components, and thus ensure the yield and quality of the reaction products.

[0027] 4. The application of the jet injector improves the mixing, diffusion, mass transfer, and heat transfer efficiency of the materials in the reactor, enables the materials in the high-pressure reactor to be fully mixed evenly, enhances the conversion rate of the reaction raw materials, and increases the yield of the target product. At the same time, it effectively reduces the reaction by-products, reduces the difficulty of the subsequent separation and purification process, reduces the production cost, and is suitable for industrial production.

[0028] The following further elaborates on the present invention in conjunction with the attached drawings and specific embodiments, but does not limit the scope of use of the present invention. Description of the Drawings

[0029] Figure 1 It is a process flow diagram for the preparation of N,N-dimethylpropylenediamine of the present invention.

[0030] The reference numerals shown therein are: 1 - jet injector, 2 - high-pressure reactor, 3 - reaction liquid circulation pump, 4 - external circulation heat exchanger, 5 - catalyst filtration pump, 6 - primary filter, 7 - catalyst metering tank, 8 - secondary filter, 9 - crude liquid tank, 10 - reaction liquid storage tank, 11 - catalyst preparation tank, 12 - ammonia gas inlet, 13 - hydrogen gas inlet. Specific Embodiments

[0031] The following further elaborates on the present invention in conjunction with the attached Figure 1 drawings. At the same time, the embodiments of the present invention only illustrate the specific circumstances of the implementation of the present invention and do not limit this embodiment.

[0032] As shown in the figure, the DMAPA preparation process of the present invention includes the following steps:

[0033] (1) Load the prepared composite nano-catalyst into the high-pressure reactor 2. First, pump acrylonitrile at room temperature, and then pass chilled water through the coil in the high-pressure reactor 2 to cool down the high-pressure reactor (1 - 10 °C), and then pump in dimethylamine with a slight excess. Fill the reactor with nitrogen to displace the air in the reactor. The percentage of the catalyst in the total mass of the reaction materials is 0.5 wt% - 1.5 wt%, and the molar ratio of the reaction raw materials acrylonitrile and dimethylamine is 1.1 - 1.6;

[0034] (2) The reaction materials from the high-pressure reactor 2 enter the reaction liquid circulation pump 3. After being pressurized by the reaction liquid circulation pump 3, they are temperature-controlled through the external circulation heat exchanger 4 and then enter from the top inlet of the jet injector 1 after heat exchange and temperature control. An air inlet is provided on the side of the injector. When the ammonia gas inlet 12 is opened, gaseous ammonia enters the injector to mix and react with the liquid-phase materials. The reacted materials return to the top inlet of the jet injector 1 after passing through the high-pressure reactor 2, the reaction liquid circulation pump 3, and the external circulation heat exchanger 4. The proportion of ammonia gas introduced is controlled. After the introduction is completed, the hydrogen gas inlet 13 is opened. Gaseous hydrogen enters the injector 1 through the jet injector inlet pipe to fully mix and react with the slurry-like reaction raw materials and catalyst mixture. The mixed and reacted materials return to the top inlet of the jet injector 1 after passing through the high-pressure reactor 2, the reaction liquid circulation pump 3, and the external circulation heat exchanger 4. Hydrogen gas is also introduced in proportion. After cyclic reaction until the introduction of hydrogen ends, a reaction liquid containing DMAPA is obtained. The partial pressure of ammonia gas in the high-pressure reactor 2 is 0.05 - 0.5 MPa, and the partial pressure of hydrogen gas is 0.5 - 3.0 MPa.

[0035] (3) The high-pressure reactor 2 is equipped with an external jacket, and steam is introduced into the jacket. During the process of filling ammonia gas, the temperature of the reactor is increased in a programmed manner to maintain the temperature of the reactor at 40 - 80 °C. After the ammonia gas filling is completed, during the process of filling hydrogen gas, the temperature of the reactor continues to rise to the reaction temperature and is maintained until the reaction is completed. The reaction temperature is 80 °C - 120 °C, the programmed heating rate is 30 °C - 45 °C / h, and the reaction time is 1 - 3 h. Steam or cooling water can be introduced into the jacket of the reactor, enabling the jacket to have both heating and cooling functions;

[0036] (4) The reaction products and catalyst slurry from the high-pressure reactor 2 are partially sent to the external circulation heat exchanger 4 after passing through the reaction liquid circulation pump 3. The external circulation heat exchanger 4 controls the temperature through heat exchange to keep the reaction temperature stable. The materials finally enter the jet injector 1 and return to the high-pressure reactor 2 for continuous reaction, and part of them go to the catalyst filtration pump 5. The reaction products and catalyst slurry from the catalyst filtration pump 5 enter the primary filter 6 through a pipeline. In the primary filter 6, the reaction clear liquid and the catalyst slurry are separated by solid-liquid separation. The concentrated catalyst slurry enters the catalyst metering tank 7, is mixed evenly with the fresh or regenerated catalyst from the catalyst preparation tank 11, and then is sent to the high-pressure reactor 2 for continuous reaction. When the activity of the catalyst decreases significantly and the catalyst inside the high-pressure reactor 2 needs to be replaced as a whole, the reaction liquid in the reactor needs to be sent to the reaction liquid temporary storage tank 10 through the reaction liquid circulation pump 3, and after the catalyst is updated, the reaction is restarted in a cycle. The primary filter 6 is one of a disc filter, a mesh filter, or a basket filter;

[0037] (5) The reaction clear liquid from the primary filter 6 enters the secondary filter 8 with a higher filtration accuracy through the pipeline again. In the secondary filter 8, the reaction clear liquid is filtered with high precision again. The filtered reaction clear liquid is sent to the crude liquid tank 9 as the crude reaction product, and then a qualified DMAPA product is obtained through the refining unit. The catalyst obtained by filtration is sent to the catalyst regeneration unit as waste catalyst. The secondary filter 8 is one of a disk filter, a mesh filter or a basket filter, with a higher filtration accuracy;

[0038] Example 1

[0039] Charge the prepared composite nano-catalyst into the high-pressure reactor. The percentage of the catalyst in the total mass of the reaction materials is 1.2 wt%. First, pump acrylonitrile at room temperature, and then pump dimethylamine after cooling the reactor by passing chilled water through the coil in the reactor. The molar ratio of acrylonitrile to dimethylamine is 1.2. Charge nitrogen into the reactor to displace the air in the reactor. The reaction materials from the high-pressure reactor enter the reaction liquid circulation pump. After being pressurized by the reaction liquid circulation pump, they are temperature-controlled through the external circulation heat exchanger and then enter from the top inlet of the jet ejector. There is an air inlet on the side of the ejector. Open the ammonia gas inlet, and gaseous ammonia enters the ejector to mix and react with the liquid-phase materials. The reacted materials return to the top inlet of the ejector after passing through the high-pressure reactor, the reaction liquid circulation pump, and the external circulation heat exchanger. Control the proportion of ammonia gas introduced, and set the partial pressure of ammonia gas to 0.1 MPa. After the introduction is completed, pass steam into the jacket of the high-pressure reactor, and the reactor is heated up in a programmed manner. It is heated up to 50 °C in 0.5 h. At this time, open the hydrogen gas inlet, and gaseous hydrogen enters the ejector through the hydrogen inlet pipe of the ejector to fully mix and react with the slurry-like reaction raw materials and catalyst and other materials. During the charging of hydrogen gas, the reactor is continuously heated up to 100 °C in 1.5 h, and hydrogen gas is also introduced in proportion, and the partial pressure of hydrogen gas is maintained at 2.0 MPa, and the reaction lasts for 2 h. After the reaction, a reaction liquid containing DMAPA is obtained. The conversion rate of acrylonitrile is 100%, and the yield of DMAPA is 94.5%. The reaction product and catalyst slurry from the high-pressure reactor pass through the reaction liquid circulation pump. Part goes to the external circulation heat exchanger and finally enters the ejector and returns to the high-pressure reactor to continue the reaction, and part goes to the catalyst filtration pump. The reaction product and catalyst slurry from the catalyst filtration pump enter the disk primary filter through the pipeline. In the primary filter, the reaction clear liquid and the catalyst slurry are separated from solid to liquid. The concentrated catalyst slurry enters the catalyst metering tank and is mixed evenly with the fresh or regenerated catalyst from the catalyst preparation tank and then sent to the high-pressure reactor to continue the reaction. The reaction clear liquid from the primary filter enters the secondary filter with a higher filtration accuracy through the pipeline. In the secondary high-precision filter, the reaction clear liquid is filtered again. The filtered reaction clear liquid is sent to the crude liquid tank as the crude reaction product, and then a qualified DMAPA product is obtained through the refining unit. The catalyst obtained by filtration is sent to the catalyst regeneration unit as waste catalyst;

[0040] Example 2

[0041] Charge the prepared composite nano-catalyst into a high-pressure reactor. The percentage of the catalyst in the total mass of the reaction materials is 1.5 wt%. At room temperature, first pump acrylonitrile into the reactor, and then pass chilled water through the coil in the reactor to cool down the reactor. After that, pump in dimethylamine. The molar ratio of acrylonitrile to dimethylamine is 1.6. Charge nitrogen into the reactor to displace the air in the reactor. The reaction materials from the high-pressure reactor enter the reaction liquid circulation pump. After being pressurized by the reaction liquid circulation pump, they are temperature-controlled through an external circulation heat exchanger and then enter from the top inlet of the jet ejector. An air inlet is opened on the side of the ejector. Open the ammonia gas inlet, and gaseous ammonia enters the ejector to mix and react with the liquid-phase materials. The reacted materials return to the top inlet of the ejector after passing through the high-pressure reactor, the reaction liquid circulation pump, and the external circulation heat exchanger. Control the proportion of ammonia gas introduced, and set the partial pressure of ammonia gas to 0.5 MPa. After the introduction is completed, pass steam into the jacket of the high-pressure reactor, and the reactor is heated up in a programmed manner. It is heated up to 80 °C in 1 h. At this time, open the hydrogen gas inlet, and gaseous hydrogen enters the ejector through the hydrogen inlet pipe of the ejector to mix and react fully with the slurried reaction raw materials and catalyst mixture. During the charging process of hydrogen gas, the reactor is continuously heated up to 120 °C in 1 h, and hydrogen gas is also introduced in proportion. The partial pressure of hydrogen gas is maintained at 3.0 MPa, and the reaction lasts for 3 h. After the reaction is completed, a reaction liquid containing DMAPA is obtained. The conversion rate of acrylonitrile is 100%, and the yield of DMAPA is 91.6%. The reaction products and catalyst slurry from the high-pressure reactor pass through the reaction liquid circulation pump. Part of them goes to the external circulation heat exchanger and finally enters the ejector to return to the high-pressure reactor for continuous reaction, and part of them goes to the catalyst filtration pump. The reaction products and catalyst slurry from the catalyst filtration pump enter the disk-type primary filter through the pipeline. In the primary filter, the reaction clear liquid and the catalyst slurry are separated by solid-liquid separation. The concentrated catalyst slurry enters the catalyst metering tank and is mixed evenly with the fresh or regenerated catalyst from the catalyst preparation tank and then sent to the high-pressure reactor for continuous reaction. The reaction clear liquid from the primary filter enters the secondary filter with higher filtration accuracy through the pipeline. In the secondary high-precision filter, the reaction clear liquid is filtered again. The filtered reaction clear liquid is sent to the crude liquid tank as the crude reaction product and is subsequently refined in the refining unit to obtain a qualified DMAPA product. The filtered catalyst is sent to the catalyst regeneration unit as waste catalyst.

[0042] Example 3

[0043] Load the prepared composite nano-catalyst into the high-pressure reactor. The percentage of the catalyst in the total mass of the reaction materials is 0.5 wt%. At room temperature, first pump acrylonitrile into the reactor. Then, after cooling the reactor by passing chilled water through the coil in the reactor, pump in dimethylamine. The molar ratio of acrylonitrile to dimethylamine is 1.1. Charge nitrogen into the reactor to displace the air inside the reactor. The reaction materials from the high-pressure reactor enter the reaction liquid circulation pump. After being pressurized by the reaction liquid circulation pump, they are temperature-controlled through an external circulation heat exchanger and then enter from the top inlet of the jet injector. There is an air inlet on the side of the injector. Open the ammonia gas inlet, and gaseous ammonia enters the injector to mix and react with the liquid-phase materials. The reacted materials return to the top inlet of the injector after passing through the high-pressure reactor, the reaction liquid circulation pump, and the external circulation heat exchanger. Control the ammonia gas input ratio and set the partial pressure of ammonia to 0.05 MPa. After the input is completed, pass steam into the jacket of the high-pressure reactor, and the reactor is heated up programmatically. It is heated to 40 °C in 0.5 h. At this time, open the hydrogen gas inlet, and gaseous hydrogen enters the injector through the injector inlet pipe to fully mix and react with the slurried reaction raw materials and catalyst mixture. During the hydrogen charging process, the reactor is continuously heated to 80 °C in 1 h, and hydrogen is also input in proportion, with the partial pressure of hydrogen maintained at 1.0 MPa, and the reaction lasts for 1 h. After the reaction is completed, a reaction liquid containing DMAPA is obtained, with the acrylonitrile conversion rate being 100% and the DMAPA yield being 88.1%. The reaction products and catalyst slurry from the high-pressure reactor pass through the reaction liquid circulation pump. Part of them goes to the external circulation heat exchanger and finally enters the injector to return to the high-pressure reactor for further reaction, and part goes to the catalyst filtration pump. The reaction products and catalyst slurry from the catalyst filtration pump enter the disc-type primary filter through the pipeline. In the primary filter, the reaction clear liquid and the catalyst slurry are separated from solid to liquid. The concentrated catalyst slurry enters the catalyst metering tank and is mixed evenly with the fresh or regenerated catalyst from the catalyst preparation tank and then sent to the high-pressure reactor for further reaction. The reaction clear liquid from the primary filter enters the secondary filter with higher filtration accuracy through the pipeline. In the secondary high-precision filter, the reaction clear liquid is filtered again. The filtered reaction clear liquid is sent to the crude liquid tank as the crude reaction product and is subsequently refined through the refining unit to obtain the qualified DMAPA product. The filtered catalyst is sent to the catalyst regeneration unit as waste catalyst.

[0044] The above are only the preferred embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principle of the present invention shall be included within the protection scope of the present invention.

Claims

1. A preparation process of N,N-dimethylpropylenediamine, comprising the following steps: 1) Put the prepared hydrogenation catalyst into a high-pressure reactor, first add acrylonitrile, cool the high-pressure reactor, then add dimethylamine, and then fill the high-pressure reactor with nitrogen to displace the air in the reactor; 2) The outlet of the high-pressure reactor is connected to a reaction liquid circulation pump. The reaction raw materials from the high-pressure reactor are pressurized by the reaction liquid circulation pump, and the materials at the outlet of the reactor are sent to an external circulation heat exchanger and then returned to the high-pressure reactor through an ejector; 3) An air inlet is opened on the side of the ejector. After the air in the reactor is displaced, ammonia is filled into the high-pressure reactor, and then the high-pressure reactor is heated by steam in the outer jacket of the reactor. After heating, hydrogen is filled into the high-pressure reactor and the high-pressure reactor is continuously preheated and maintained at a constant temperature until the reaction ends; 4) Part of the reaction products coming out of the outlet of the high-pressure reactor are sent to the external circulation heat exchanger by the reaction liquid circulation pump, and after heat exchange and temperature control, they are returned to the high-pressure reactor to continue the reaction. Part is sent to a catalyst filtration pump, and the materials coming out of the catalyst filtration pump enter a primary filter. After filtration, the catalyst-containing materials enter a catalyst metering tank, are mixed with fresh or regenerated catalyst, and are sent to a high-pressure kettle reactor; The catalyst-free materials enter a secondary filter again, and the filtered crude product is sent to a crude liquid tank.

2. The preparation process of N,N-dimethylpropylenediamine according to claim 1, characterized in that: The reaction temperature of the high-pressure reactor is 40 - 140 °C, the reaction ammonia partial pressure is 0.01 - 0.1 MPa; the hydrogen partial pressure is 0.1 - 5 MPa.

3. The preparation process of N,N-dimethylpropylenediamine according to claim 2, characterized in that: The reaction temperature of the high-pressure reactor is 80 - 120 °C. The reaction ammonia partial pressure is 0.05 - 0.5 MPa; the hydrogen partial pressure is 0.5 - 3.0 MPa.

4. The preparation process of N,N-dimethylpropylenediamine according to claim 1, characterized in that: The dosage of the catalyst is 0.1 wt% - 3.0 wt%, and preferably the dosage of the catalyst is 0.5 wt% - 1.5 wt%.

5. The preparation process of N,N-dimethylpropylenediamine according to claim 1 is acidic, characterized in that: The hydrogenation catalyst is Raney nickel, Raney copper, Pt / C, Pd / C and cobalt composite nano-catalyst, and preferably Raney nickel or Raney copper composite nano-catalyst.

6. The preparation process of N,N-dimethylpropylenediamine according to claim 1, characterized in that: The ejector is a jet ejector.

7. The preparation process of N,N-dimethylpropylenediamine according to claim 1, characterized in that: The ejector consists of parts such as a nozzle, a receiving chamber, a mixing chamber and a diffuser chamber.

8. The preparation process of N,N-dimethylpropylenediamine according to claim 1, characterized in that: An air inlet is opened on the side of the ejector, and an ammonia inlet and a hydrogen inlet are provided.

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