1. A method for continuously and efficiently synthesizing m-phenylenediamine based on a fixed bed microreactor is characterized by comprising the following steps:

(1) dissolving m-dinitrobenzene serving as a raw material in a solvent to serve as a substrate solution to be hydrogenated;

(2) the substrate solution to be hydrogenated and hydrogen enter a micro mixer to be mixed to form a gas-liquid mixture with a good gas-liquid micro dispersion state, and then the gas-liquid mixture enters a micro packed bed reactor filled with a solid particle catalyst to react;

the reaction temperature is 40-160 ℃, and the pressure is 1-5 MPa;

the residence time of the gas-liquid mixture in the micro packed bed reactor is 10-120 s;

(3) and (3) carrying out gas-liquid separation on the gas-liquid mixture obtained after the reaction is finished, and enabling the liquid product to enter a subsequent separation and purification system.

2. The method according to claim 1, wherein in the step (1), the solvent is at least one of methanol, ethanol, propanol, isopropanol, tetrahydrofuran and pyridine.

3. The method according to claim 1 or 2, wherein in the step (1), the mass concentration of the m-dinitrobenzene in the solvent is 2 to 20 wt.%.

4. The method according to claim 3, wherein in the step (1), the mass concentration of the m-dinitrobenzene in the solvent is 5 to 10 wt.%.

5. The method of claim 1, wherein in step (2), the micromixer comprises one of a membrane dispersion reactor, a micromesh reactor, and a T-type reactor.

6. The method according to claim 1, wherein in the step (2), the reaction temperature is 40-100 ℃, and the pressure is 1.5-3 MPa;

the residence time of the gas-liquid mixture in the micro packed bed reactor is 30-100 s.

7. The method according to claim 1 or 6, wherein in the step (2), the molar ratio of m-dinitrobenzene to hydrogen in the substrate solution to be hydrogenated is 1: 6.5-15.

8. The method according to claim 7, wherein in the step (2), the molar ratio of the m-dinitrobenzene to the hydrogen in the substrate solution to be hydrogenated is 1: 7-10.

9. The method of claim 1, wherein in step (2), the size of the solid particulate catalyst is 50 to 1000 μm.

10. The method according to claim 1 or 9, wherein in the step (2), the solid particulate catalyst is at least one of a platinum carbon catalyst, a platinum/alumina catalyst, a ruthenium carbon catalyst, a nickel/alumina catalyst, a nickel/silica catalyst, and a nickel/titania catalyst.

Background

M-phenylenediamine is an important organic intermediate, and is widely used in the dye industry for synthesizing azo dyes, fur dyes, reactive dyes and sulfur dye intermediates, and can also be used for preparing materials such as hair dyes, color developers, petroleum additives, cement coagulants and the like. The m-phenylenediamine can also be synthesized with phthaloyl chloride to prepare high-temperature-resistant aromatic polyamide resin and flame-retardant fibers, and is applied to special fields of national defense, aerospace and the like. The prior m-phenylenediamine synthesis method mainly comprises an iron powder reduction method, an electrolytic reduction method and a catalytic hydrogenation method. Although the iron powder reduction method has simple process, the yield is lower, the cost is higher, and a large amount of arylamine-containing iron mud and wastewater which are difficult to treat are produced as byproducts, thereby causing serious pollution to the environment. The electrolytic reduction method has high cost and complex device, and does not have the condition of large-scale production. At present, the synthesis method of m-phenylenediamine at home and abroad mostly adopts a catalytic hydrogenation production process, m-dinitrobenzene is used as a raw material, an alcohol solvent is used as a medium, a proper catalyst is adopted, and hydrogenation reaction is carried out under the conditions of heating and pressurizing to obtain the m-phenylenediamine, the by-products obtained by the reaction are few, the yield is high, and the atom economy principle and the environmental protection requirement are met, so the method is more in line with the development requirement of a clean process. The prior process for producing m-phenylenediamine by catalytic hydrogenation in industrial production is mostly carried out in a hydrogenation kettle, and has the following defects:

the m-dinitrobenzene catalytic hydrogenation reaction is a typical gas-liquid-solid three-phase reaction, and when the reaction is carried out in an intermittent reaction kettle, high pressure and long reaction time are usually required for ensuring the full contact among three phases and the full performance of the hydrogenation reaction, so that the reaction efficiency is low, and meanwhile, the increase of azo compounds is caused by low mass transfer efficiency, thereby influencing the purity of products; meanwhile, the amount of catalyst required for reaction in the batch type reaction kettle is large and easy to lose. CN102070464A discloses a method for preparing m-phenylenediamine by hydrogenation of m-dinitrobenzene as a raw material in a batch reactor, wherein a palladium catalyst is adopted in the method, the hydrogenation reaction is completed for several hours at the temperature of 40-60 ℃ and under the pressure of 0.25-0.6 MPa, but the catalyst required by the reaction is large in amount, the purity of the obtained m-phenylenediamine is low, and the m-phenylenediamine can be used in the next production process only by refining. In view of the drawbacks of the batch reactor hydrogenation process, scientists have proposed a method for continuously and efficiently synthesizing m-phenylenediamine based on a microreactor. Compared with an intermittent reaction kettle, the micro-reactor has the advantages of high mixing efficiency, good mass and heat transfer performance, good safety and the like, is applied to the field of organic synthesis, can realize the continuity of the reaction process, reduce the volume of the reactor, accurately control the reaction conditions and improve the yield and selectivity of the reaction. Therefore, the method for continuously synthesizing the m-phenylenediamine by catalytic hydrogenation is developed based on the microreactor technology, can reduce a reactor system, inhibit the generation of byproducts, improve the process safety and improve the product quality, and has important economic, safe and environmental protection values.

The patent specification with publication number CN 111302949A discloses a process for preparing phenylenediamine by a micro-reaction technology, and the inventive concept and the technical route are as follows: 1. metering the nitroaromatic hydrocarbon to be reduced, a solvent, a catalyst and hydrogen, and then continuously feeding the obtained product into a hydrogenation microreactor to carry out hydrogenation reduction reaction, wherein the method comprises the following specific steps: firstly, preparing a catalyst, nitroaromatic to be reduced and a solvent into a suspension, metering the suspension, continuously feeding the suspension into a hydrogenation microreactor, and simultaneously continuously feeding hydrogen into the hydrogenation microreactor; 2. and (3) allowing the reaction liquid obtained in the hydrogenation microreactor to enter a hydrogenation ageing device for ageing, and detecting that the reaction liquid is at an end point when no nitro compound exists. In the aspect of specific parameters, the hydrogen consumption is large, and the molar ratio of hydrogen to nitroaromatic is preferably 8-12: 1; the reaction temperature is high, preferably 80-100 ℃. In addition, according to the method of the patent technology, the catalyst is added into the substrate solution to form the suspension for reaction, so that the problems of catalyst sedimentation, material back-mixing and the like inevitably exist in the reaction process can be reasonably presumed, and the specific implementation method of the method clearly describes the operation steps of subsequently separating and recovering the catalyst, which is tedious.

Disclosure of Invention

Aiming at the technical problems and the defects in the field, the invention provides a method for continuously and efficiently synthesizing m-phenylenediamine based on a fixed bed microreactor, wherein a micro packed bed reactor filled with a solid particle catalyst is used as the fixed bed microreactor, and compared with the traditional batch reactor, the reactor has the advantages of high mass and heat transfer efficiency, continuous operation, capability of accurately controlling reaction time, small floor area, convenience in amplification, environmental friendliness, safety and the like; the method has the advantages of convenient operation, controllable heat release, short reaction period, environmental protection and safety, and the obtained product has high purity and less content of azo by-products.

A method for continuously and efficiently synthesizing m-phenylenediamine based on a fixed bed microreactor comprises the following steps:

(1) dissolving m-dinitrobenzene serving as a raw material in a solvent to serve as a substrate solution to be hydrogenated;

(2) the substrate solution to be hydrogenated and hydrogen enter a micro mixer to be mixed to form a gas-liquid mixture with a good gas-liquid micro dispersion state, and then the gas-liquid mixture enters a micro packed bed reactor filled with a solid particle catalyst to react;

the reaction temperature is 40-160 ℃, and the pressure is 1-5 MPa;

the residence time of the gas-liquid mixture in the micro packed bed reactor is 10-120 s;

(3) and (3) carrying out gas-liquid separation on the gas-liquid mixture obtained after the reaction is finished, and enabling the liquid product to enter a subsequent separation and purification system.

The conception and the technical route of the invention are as follows: 1. firstly, mixing a substrate solution to be hydrogenated containing m-dinitrobenzene with hydrogen in a micro mixer to form a gas-liquid mixture with good gas-liquid micro dispersion state; 2. the obtained gas-liquid mixture enters a micro packed bed reactor filled with solid particle catalyst for reaction, the catalyst is not carried out by reaction liquid, the product is still the gas-liquid mixture, and the solid particle catalyst does not need to be separated; 3. the reaction temperature required by the micro packed bed reactor is lower, the generation of azo compounds can be effectively reduced, the yield and purity of the target product can be extremely high at the reaction temperature as low as 40 ℃, and the yield of the m-phenylenediamine can reach 97.5%.

On the basis of the conception and the technical route, aiming at the gas-liquid mixture and the fixed bed microreactor, the invention further optimizes and controls the reaction temperature, the reaction pressure and the residence time of the gas-liquid mixture in the fixed bed microreactor filled with the catalyst, which are adaptive to the gas-liquid mixture and the fixed bed microreactor, and realizes the maximum reaction efficiency, the product yield and the purity. In the method, high-yield m-phenylenediamine can be obtained in a short time at a reaction temperature as low as 40 ℃ in the catalytic hydrogenation reaction process in the fixed bed microreactor, and the energy consumption is obviously reduced on the premise of keeping high reaction efficiency.

The method utilizes the high-efficiency mass transfer performance of the micro packed bed reactor filled with the solid particle catalyst, effectively inhibits the generation of azo by-products and m-nitroaniline by strengthening gas-liquid-solid mass transfer in the hydrogenation reaction process, and reduces the reaction retention time to be within 2 minutes from a plurality of hours required by the reaction kettle; meanwhile, the reaction residence time distribution, the reaction temperature and the reaction pressure are well controlled, the reaction conversion rate and the product purity are remarkably improved, the obtained reaction conversion rate is close to 100%, and the highest m-phenylenediamine yield can reach 98.5%. The method can effectively solve the problems of low production efficiency, poor product purity, complex device operation and the like in the hydrogenation kettle process, realizes continuous automatic operation in the reaction process, and has the advantages of high yield, good safety and the like.

In the step (1), the solvent is preferably at least one of methanol, ethanol, propanol, isopropanol, tetrahydrofuran and pyridine.

The concentration of m-dinitrobenzene in the substrate solution to be hydrogenated influences the reaction conversion rate and the product purity. In the process system of the present invention, in the step (1), the mass concentration of the m-dinitrobenzene in the solvent is preferably from 2 wt% to 20 wt%, and more preferably from 5 wt% to 10 wt%.

In the step (2), the micro mixer preferably comprises one of a membrane dispersion reactor, a micro-sieve reactor and a T-shaped reactor, and can also be other micro reactors capable of realizing uniform mixing of a gas-liquid system.

Preferably, in the step (2), the reaction temperature is 40-100 ℃, and the pressure is 1.5-3 MPa;

the residence time of the gas-liquid mixture in the micro packed bed reactor is 30-100 s. The method has the advantages of lower reaction temperature, extremely high reaction efficiency, product yield and purity at low reaction temperature and in short reaction time.

In the step (2), the molar ratio of m-dinitrobenzene to hydrogen in the substrate solution to be hydrogenated is preferably 1: 6.5-15, and more preferably 1: 7-10.

In the technical scheme that the conventional catalyst and reaction liquid form suspension, the subsequent step of separating and recycling the catalyst is involved, and if the size of the catalyst is too small, the problems of incomplete separation of the catalyst and reaction products, high recycling difficulty and the like can be caused. The invention adopts a fixed bed micro-reactor, and does not relate to the subsequent separation process of the catalyst and the reaction product, so the size of the catalyst can be smaller, and the reaction efficiency, the product yield and the purity are higher. Preferably, in the step (2), the size of the solid particle catalyst is 50-1000 microns, and the solid particle catalyst can be matched with parameters such as reaction temperature, reaction pressure, residence time and the like in the catalytic hydrogenation process to perform synergistic action, so that the reaction efficiency, the product yield and the purity are further improved.

In the step (2), the solid particulate catalyst is preferably at least one of a platinum carbon catalyst, a platinum/alumina catalyst, a ruthenium carbon catalyst, a nickel/alumina catalyst, a nickel/silica catalyst, and a nickel/titania catalyst.

In the step (3), the yield of m-phenylenediamine in the gas-liquid mixture obtained after the reaction is finished is not lower than 95 wt%.

In the step (3), the gas obtained by gas-liquid separation contains hydrogen, can enter a tail gas treatment system, and can be recycled, for example, the hydrogen can be used for mixing with the substrate solution to be hydrogenated in the step (2).

Compared with the prior art, the invention has the main advantages that:

1) before and after the catalytic hydrogenation reaction, the conveyed materials are only gas-liquid mixtures all the time. In the process of continuously synthesizing m-phenylenediamine by catalytic hydrogenation, the gas-liquid-solid contact area in the micro packed bed reactor is large, the mass and heat transfer efficiency is high, and the catalyst inactivation caused by violent heat release can be avoided;

2) the reaction temperature required by the micro packed bed reactor is lower, so that the generation of azo compounds can be effectively reduced;

3) the reaction time is accurate and controllable, the generation of m-nitroaniline and azo compounds is inhibited, and the yield of m-phenylenediamine is not lower than 95 percent and even can reach more than 98 percent;

4) the reactor has small volume and high safety.

Drawings

FIG. 1 is a schematic flow chart of a method for continuously and efficiently synthesizing m-phenylenediamine based on a fixed-bed microreactor according to the present invention;

in the figure: 1-micro mixer; 2-a micro packed bed reactor packed with solid particulate catalyst; and 3-a gas-liquid separation tank.

Detailed Description

The invention is further described with reference to the following drawings and specific examples. It should be understood that these examples are for illustrative purposes only and are not intended to limit the scope of the present invention. The following examples are conducted under conditions not specified, usually according to conventional conditions, or according to conditions recommended by the manufacturer.

The invention relates to a method for continuously and efficiently synthesizing m-phenylenediamine based on a fixed bed microreactor, which comprises the following steps of:

(1) m-dinitrobenzene is taken as a raw material, dissolved in a solvent to be used as a substrate solution to be hydrogenated, namely a m-dinitrobenzene solution,

(2) the m-dinitrobenzene solution and hydrogen enter a micro mixer 1 to be mixed to form a gas-liquid mixture with good gas-liquid micro dispersion state, and then the gas-liquid mixture enters a micro packed bed reactor 2 filled with a solid particle catalyst to be reacted;

the reaction temperature is 40-160 ℃, and the pressure is 1-5 MPa;

the residence time of the gas-liquid mixture in the micro packed bed reactor is 10-120 s;

(3) and (3) carrying out gas-liquid separation on the gas-liquid mixture obtained after the reaction in a gas-liquid separation tank 3, wherein the gas containing hydrogen can enter a tail gas treatment system, and the liquid product containing m-phenylenediamine can enter a subsequent separation and purification system.

Example 1

According to the method, an ethanol solution of m-dinitrobenzene is prepared, the concentration is 20 wt%, and the molar ratio of hydrogen to m-dinitrobenzene is controlled to be 8: 1; the solution and hydrogen were mixed in an inlet T-type micromixer, the resulting gas-liquid mixture was passed through a packed bed packed with a platinum alumina catalyst (catalyst size 200 μm), the reaction temperature was set at 40 ℃, the reaction pressure was 5.0MPa, the residence time was 120s, the reaction product was collected at the outlet of the packed bed reactor, and the obtained product was analyzed, with the conversion of m-dinitrobenzene being 100%, the yield of m-phenylenediamine being 97.5%, and the content of azo and other impurities being 2.16%.

Example 2

According to the method, an experiment is carried out, a methanol solution of m-dinitrobenzene is prepared, the concentration is 5 wt%, and the molar ratio of hydrogen to m-dinitrobenzene is controlled to be 10: 1; the solution and hydrogen were mixed in an inlet membrane dispersion micromixer, the resulting gas-liquid mixture was passed through a packed bed packed with a ruthenium-carbon catalyst (catalyst size 600 μm), the reaction temperature was set at 70 ℃, the reaction pressure was 2.0MPa, the residence time was 70s, the reaction product was collected at the outlet of the packed bed reactor, and the obtained product was analyzed, with the conversion of m-dinitrobenzene being 100%, the yield of m-phenylenediamine being 96.7%, and the content of azo-like impurities being 3.27%.

Example 3

According to the method, an experiment is carried out, a tetrahydrofuran solution of m-dinitrobenzene is prepared, the concentration is 15 wt%, and the molar ratio of hydrogen to m-dinitrobenzene is controlled to be 6.5: 1; the solution and hydrogen are mixed in an inlet micromesh micromixer, the formed gas-liquid mixture passes through a micro packed bed filled with a nickel silicon dioxide catalyst (the size of the catalyst is 50 microns), the reaction temperature is set to be 100 ℃, the reaction pressure is 2MPa, the residence time is 50s, a reaction product is collected at the outlet of the micro packed bed reactor, and the obtained product is analyzed, so that the conversion rate of the m-dinitrobenzene is 100%, the yield of the m-phenylenediamine is 96.7%, and the content of impurities such as azo compounds is 2.87%.

Example 4

According to the method, an experiment is carried out, a methanol solution of m-dinitrobenzene is prepared, the concentration is 15 wt%, and the molar ratio of hydrogen to m-dinitrobenzene is controlled to be 15: 1; the solution and hydrogen are mixed in an inlet T-shaped micro mixer, the formed gas-liquid mixture passes through a micro packed bed filled with a platinum-carbon catalyst (the size of the catalyst is 1000 microns), the reaction temperature is set to be 80 ℃, the reaction pressure is set to be 2.5MPa, the residence time is 80s, reaction products are collected at the outlet of the micro packed bed reactor, and the obtained products are analyzed, so that the conversion rate of the m-dinitrobenzene is 100 percent, the yield of the m-phenylenediamine is 98.5 percent, and the content of impurities such as azo compounds is 1.21 percent.

Example 5

According to the method, an experiment is carried out, a methanol solution of m-dinitrobenzene is prepared, the concentration is 10 wt%, and the molar ratio of hydrogen to m-dinitrobenzene is controlled to be 9: 1; the solution and hydrogen are mixed in an inlet T-shaped micro mixer, the formed gas-liquid mixture passes through a micro packed bed filled with a nickel-carbon catalyst (the size of the catalyst is 800 microns), the reaction temperature is set to be 80 ℃, the reaction pressure is 4MPa, the retention time is 70s, a reaction product is collected at the outlet of the micro packed bed reactor, and the obtained product is analyzed, so that the conversion rate of the m-dinitrobenzene is 100 percent, the yield of the m-phenylenediamine is 97.3 percent, and the content of impurities such as azo is 2.48 percent.

Example 6

According to the method, an experiment is carried out, an isopropanol solution of m-dinitrobenzene is prepared, the concentration is 10 wt%, and the molar ratio of hydrogen to m-dinitrobenzene is controlled to be 8: 1; the solution and hydrogen are mixed in an inlet membrane dispersion micro mixer, the formed gas-liquid mixture passes through a micro packed bed filled with a nickel titanium dioxide catalyst (the size of the catalyst is 300 microns), the reaction temperature is set to be 90 ℃, the reaction pressure is 2MPa, the retention time is 50s, a reaction product is collected at the outlet of the micro packed bed reactor, and the obtained product is analyzed, so that the conversion rate of the m-dinitrobenzene is 100 percent, the yield of the m-phenylenediamine is 96.8 percent, and the content of impurities such as azo is 2.99 percent.

Example 7

According to the method, an experiment is carried out, a methanol solution of m-dinitrobenzene is prepared, the concentration is 10 wt%, and the molar ratio of hydrogen to m-dinitrobenzene is controlled to be 10: 1; the solution and hydrogen are mixed in an inlet T-shaped micro mixer, the formed gas-liquid mixture passes through a micro packed bed filled with a nickel alumina catalyst (the size of the catalyst is 600 microns), the reaction temperature is set to be 110 ℃, the reaction pressure is 1MPa, the retention time is 80s, a reaction product is collected at the outlet of the micro packed bed reactor, and the obtained product is analyzed, so that the conversion rate of the m-dinitrobenzene is 100 percent, the yield of the m-phenylenediamine is 95.3 percent, and the content of impurities such as azo compounds is 4.42 percent.

Furthermore, it should be understood that various changes and modifications can be made by one skilled in the art after reading the above description of the present invention, and equivalents also fall within the scope of the invention as defined by the appended claims.