CN112679358B - Method for continuously preparing 3, 5-dinitrobenzoic acid by using microchannel reactor - Google Patents
Method for continuously preparing 3, 5-dinitrobenzoic acid by using microchannel reactor Download PDFInfo
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Abstract
The invention discloses a method for continuously preparing 3, 5-dinitrobenzoic acid by using a microchannel reactor, belonging to the technical field of organic synthesis processes. The invention takes benzoic acid and concentrated nitric acid as raw materials, fuming sulfuric acid as a solvent and trifluro-ketone sulfonate as a catalyst, and continuously finishes the preparation process of 3, 5-dinitrobenzoic acid in a micro-channel reactor system. After materials are introduced into the microchannel reactor through a metering pump, a 3, 5-dinitrobenzoic acid product is obtained through preheating, mixing reaction and separation, the method can strictly control the temperature and the residence time in the reaction process, accurately control the reaction temperature to prevent temperature runaway, and improve the safety of a reaction device; the invention enhances the mass transfer effect among raw materials in a reaction system due to the strong mass transfer effect of the microchannel reactor, and greatly improves the reaction efficiency and the yield of the 3, 5-dinitrobenzoic acid.
Description
Technical Field
The invention belongs to the technical field of organic synthesis processes, and particularly relates to a method for preparing 3, 5-dinitrobenzoic acid by taking benzoic acid as a raw material and copper trifluoromethanesulfonate as a catalyst through nitration reaction, in particular to a method for continuously preparing 3, 5-dinitrobenzoic acid by taking benzoic acid as a raw material through nitration reaction in a microchannel reactor.
Background
3, 5-dinitrobenzoic acid is an important fine chemical industry, medicine, dye intermediate, mainly used for preparing diagnostic drug diatrizoic acid, diatrizoic acid is positive contrast medium for X-ray diagnosis, for preparing diatrizoate, sodium diatrizoate or compound diatrizoate injection, mainly used for urinary system radiography, also used for radiography of cardiovascular, cerebrovascular, peripheral blood vessel, bile duct, etc., and various injection radiography such as radiography of joint cavity, uterine fallopian tube and fistula, etc., so the market demand for 3, 5-dinitrobenzoic acid is increased gradually; the product can also be used as analytical reagent, intermediate of X-ray contrast agent diatrizoic acid, dye, etc., intermediate of diagnostic medicine (X-ray contrast agent) diatrizoic acid, dye, etc., reagent for resin derivatization and ampicillin determination; also can be used as a main intermediate for synthesizing anticancer substances, telmisartan and AIDS medicaments.
CS255644 discloses a method for preparing 3, 5-dinitrobenzoic acid, which is characterized in that benzoic acid is used as a raw material, concentrated sulfuric acid is used as a dehydrating agent, fuming nitric acid is used as a nitration reagent for nitration, the mass ratio of the benzoic acid to the sulfuric acid to the fuming nitric acid is 1:4.46:2.88, nitration is carried out at the temperature of below 102 ℃, the yield of the 3, 5-dinitrobenzoic acid is less than 60%, the molar ratio of the nitric acid to the benzoic acid is up to 5.47:1, and the overhigh nitric acid ratio and sulfuric acid amount are obviously not economic enough, so that the burden of three-waste treatment is too heavy, and the yield is not ideal. And (2) carrying out two-stage nitration in a mixed acid consisting of concentrated sulfuric acid and nitric acid at 70-110 ℃ and 120-140 ℃, wherein the mass ratio of benzoic acid to sulfuric acid to fuming nitric acid is 1:6.13:1.06 (the molar ratio of nitric acid to benzoic acid is 1:2.1), and the yield of the 3, 5-dinitrobenzoic acid can reach 70%.
CN111253261A discloses a method for preparing 3, 5-dinitrobenzoic acid, which is characterized in that the optimized reaction temperature of the 3, 5-dinitrobenzoic acid is 90-110 ℃, the molar ratio of nitric acid to benzoic acid is 2-4, and when the molar ratio of nitric acid to sulfuric acid to sulfur trioxide is 1: 0.439-3.265: 1, the yield can reach 66%. Different from the previous scheme, the scheme uses fuming sulfuric acid to replace concentrated sulfuric acid, greatly improves the dehydration value of the nitration reaction, is beneficial to the nitration, and is particularly beneficial to the implementation of the second nitration reaction; the micro-channel reactor is adopted to avoid secondary temperature rise in the nitration process of the benzoic acid, so that the generation of byproducts and the risk of explosion are reduced, but excessive byproducts are generated due to overhigh temperature.
The reactor of the 3, 5-dinitrobenzoic acid preparation process disclosed in the patent or reported in the literature is mostly a reaction bottle or a reaction kettle with stirring, and the reaction mode is a batch operation mode and is carried out at normal pressure or near normal pressure. In the preparation process of 3, 5-dinitrobenzoic acid, benzoic acid is dissolved in a solvent, the nitration reaction is a liquid-liquid reaction system, liquid-liquid mass transfer obstacles often exist in the reaction process, and a high-temperature and high-pressure reaction system is often needed to promote the mass transfer in the reaction system. The reaction for preparing 3, 5-dinitrobenzoic acid can be carried out only when the reactant is fully contacted with the nitrating agent, and ideal liquid-liquid phase mass transfer is difficult to realize by the paddle stirring action in a bottle type (kettle type) reactor, so the preparation method has low reaction efficiency and long reaction time. The preparation of 3, 5-dinitrobenzoic acid by nitrating benzoic acid with nitric acid is an exothermic reaction, the heat release is about 296kJ/mol, and for a stirring reactor which is operated in an intermittent mode under the condition of normal pressure or near normal pressure, the heat exchange area is small, the heat exchange capability is low, the stable temperature control effect is poor, and the 'temperature runaway' risk is high; the system is open, the dead angle of the device is large, the process control is in an intermittent fluctuation state, and the stability and safety of the device are determined to be low.
The invention utilizes the continuous flow microchannel reaction technology to carry out nitration reaction and continuous synthesis of 3, 5-dinitrobenzoic acid products, can solve a plurality of defects of the prior art in many aspects, and is a breakthrough to the reaction process of the conventional kettle type stirring reactor. The micro-channel reactor is a special-shaped pipeline type reactor with enhanced mass and heat transfer processes, and the micro-channel reactor has ideal performance of a plug flow reactor by specially designing a micro-channel structure and can be used for continuous synthesis of 3, 5-dinitrobenzoic acid. The microchannel reactor has the advantages of miniaturized pipeline size, extremely large specific surface area, higher mass and heat transfer characteristics, capability of skipping direct amplification through a step-by-step amplification test, flexible preparation and high safety performance.
Disclosure of Invention
Aiming at the defects of the process, the invention provides a method for continuously preparing 3, 5-dinitrobenzoic acid by using a microchannel reactor, which can strengthen mass transfer and heat transfer, accurately control reaction temperature and reaction time, prevent the temperature runaway phenomenon and the generation of byproducts and improve conversion rate and yield due to the structural characteristics of narrow reaction space and large specific surface area of the microchannel reactor. Meanwhile, the microchannel reactor has the characteristics of large liquid holdup, short reaction retention time, strong mass transfer and heat transfer effects, no dead volume and the like, and improves the safety of the benzoic acid nitration reaction.
On the basis, concentrated nitric acid (98%) is selected as a nitrating agent, so that the generation amount of waste acid is reduced, and the complete conversion of the raw materials is ensured under the condition of the nitrating agent with the concentration. The research of the invention finds that: when concentrated nitric acid is used for nitration, about 1% of 3, 4-dinitrobenzoic acid by-product is always generated, and the impurity is difficult to remove to below 0.1% by a conventional recrystallization method, although the 3, 5-dinitrobenzoic acid with the purity can meet the requirements of general chemical engineering application, the rigorous requirements of medical intermediates are difficult to achieve, and the value of the common chemical product is far lower than that of the medical intermediate (the price of the common chemical product is more than one time different), so that the trace impurity which is difficult to remove has serious adverse effect on the added value of the product. In the exploration process, the invention unexpectedly discovers that the generation of the 3, 4-dinitrobenzoic acid impurity can be inhibited by adding trace copper trifluorosulfonate during nitration, the HPLC content is only about 0.03 percent, and the requirement of a key intermediate of the raw material medicine on the impurity is completely met (generally, the requirement of a single impurity is less than 0.1 percent). Therefore, the invention has the unexpected discovery that the purity of the product is qualitatively improved, and the purity is as high as 99.8 percent, and compared with the prior art, the invention has obvious technical progress.
In order to achieve the purpose, the invention adopts the technical scheme that:
a method for continuously preparing 3, 5-dinitrobenzoic acid by using a microchannel reactor comprises the following steps:
(1) mixing raw materials of benzoic acid and fuming sulfuric acid (104%) according to a certain proportion at room temperature by taking a micro-channel system as a reactor, and preparing a mixed solution of the benzoic acid and the fuming sulfuric acid under continuous stirring; and respectively taking the concentrated nitric acid (containing copper triflate with the molar weight equivalent to 0.5-1% of benzoic acid) and the concentrated nitric acid as reaction materials, and respectively introducing the reaction materials into a preheating module in the microchannel reactor through a metering pump for preheating, wherein the preheating temperature is controlled by an external heat exchanger.
Wherein the molar ratio of the benzoic acid to the fuming sulfuric acid in the step (1) is 1: 4-9, the molar ratio of the benzoic acid to the concentrated nitric acid is 1: 2-4.5, and the preheating and reaction temperature is 60-80 ℃.
(2) The flow (3-15 ml/min) of materials is controlled by a metering pump, the preheated materials synchronously enter the microchannel reactor modules with different channel structures for mixing and reaction, after the reaction process is completed, reaction liquid flows out from an outlet of the microchannel reactor, enters a closed pressure container for collecting reaction liquid, enters a post-treatment process and analyzes the product by using high performance liquid chromatography.
Wherein the residence time in the microchannel reactor is 30-300 s, and the reaction pressure is 5-15 bar.
The synthesis of 3, 5-dinitrobenzoic acid is carried out under the process condition, the conversion rate of benzoic acid is 90-100%, and the selectivity of 3, 5-dinitrobenzoic acid is 80.52-99.39%. The yield of the 3, 5-dinitrobenzoic acid is 69.00-95.23%.
The micro-channel system comprises different functional areas such as a preheating area, a reaction area, a quenching area and the like.
The micro-channel module micro-structure comprises one or a mixture of a straight-flow channel, a flat pipeline with a rectangular cross section, a round-cake type pulse variable-diameter rectangular flat pipeline, an oblique-cake type pulse variable-diameter rectangular flat pipeline, an enhanced mixed round-cake type rectangular flat pipeline, an enhanced mixed oblique-cake type rectangular flat pipeline and a micro-channel with a 3g-Heart Cell structure.
In the process of carrying out benzoic acid nitration reaction in a continuous flow microchannel reactor in a continuous reaction mode, the raw materials are pumped into a microchannel reaction system by a metering pump, the temperature of the reactor is accurately controlled by a regulation circulation condenser, and the actual reaction temperature is measured by a thermocouple on a microchannel circuit. The material conveying pipeline is internally provided with a pressure gauge, a safety valve, a one-way valve and the like. In the reaction process, the molar ratio among the materials is changed by adjusting the flow of the metering pump, and the pressure in the reaction system is monitored and measured in real time through the pressure gauge. The raw materials are respectively preheated in the microchannel reactor, then are mixed and reacted, and after a certain residence time (from a few seconds to a few minutes), a reaction product is obtained at a discharge port.
Compared with the prior art, the invention has the following main advantages:
1. the invention adopts a continuous preparation method, the reaction time is shortened from traditional hours to dozens of seconds to several minutes, the preparation period is short, the reaction process is more stable, and the reaction efficiency is obviously improved.
2. The selected microchannel reactor can enhance the mass transfer and heat transfer performance, keep the reaction temperature constant, avoid the temperature runaway phenomenon, reduce the generation of by-products and improve the safety of the reaction process.
3. The invention has simple operation, wide application range and flexible preparation, and can be expanded by the parallel construction of reaction devices.
4. The invention creatively introduces the catalyst copper triflate, inhibits the generation amount of the byproduct 3, 4-dinitrobenzoic acid, and improves the selectivity and the yield of the product 3, 5-dinitrobenzoic acid.
Drawings
FIG. 1 is a process flow diagram for preparing 3, 5-dinitrobenzoic acid by benzoic acid continuous nitration reaction.
FIG. 2 is a diagram of a continuous flow microchannel reactor apparatus used in the present invention: 1. 2-raw material, 3, 4-raw material pump, 5, 6-preheating zone, 7-micro channel, 8-quenching zone and 9-product collection.
FIG. 3 is a channel structure diagram of a microchannel used in the present invention.
The device comprises a 3 a-straight-flow channel, a 3 b-rectangular flat pipeline micro-channel, a 3 c-round cake type pulse variable-diameter rectangular flat pipeline, a 3 d-oblique square cake type pulse variable-diameter rectangular flat pipeline, a 3 e-reinforced mixed round cake type rectangular flat pipeline, a 3 f-reinforced mixed oblique square cake type rectangular flat pipeline and a 3g-Heart Cell structure micro-channel.
Detailed Description
The invention is further illustrated by the following examples, which are not intended to limit the scope of the invention.
The following examples were carried out in a microchannel reactor according to the requirements of the process of the present invention.
Example 1
The microchannel reactor apparatus of the present invention, which is assembled from 3a (front) +3b (back) channel structures, is divided into a preheating zone, a reaction zone, and a quenching zone, connected according to FIG. 2. The reaction residence time is controlled for 180s by adjusting the flow rate of the pump (5-15ml/min) and the length of the micro-channel, the preheating temperature and the reaction temperature are set to be 60 ℃, and the reaction pressure is 5 bar. The mixed solution of benzoic acid and fuming sulfuric acid (104%) is fed into preheating zone A of the device through metering pump 1, and concentrated nitric acid (98%) is fed into preheating zone B of the device through pump 2, after two materials are fully preheated respectively, they are fed into reaction zone to make mixing reaction. Wherein, the benzoic acid and the concentrated nitric acid are continuously discharged from an outlet according to the molar ratio of 1:3, 3, 5-dinitrobenzoic acid, the reaction liquid is quenched by ice water, then crystallized and filtered to obtain a crude product, and part of refined 3, 5-dinitrobenzoic acid is obtained by washing with water and ethanol. And (4) analyzing the trace amount of the fine product by HPLC, wherein the peak time of the fine product is consistent with that of the standard product. The results of the experiments conducted with different amounts of oleum are shown in the following table:
TABLE 1 Experimental results for the continuous preparation of 3, 5-dinitrobenzoic acid with different amounts of sulfuric acid (without copper triflate)
NBA is m-nitrobenzoic acid, 3,5- (DNBA) is 3, 5-dinitrobenzoic acid, 3,4- (DNBA) is 3, 4-dinitrobenzoic acid, 2,4- (DNBA) is 2, 4-dinitrobenzoic acid, and 2,5- (DNBA) is 2, 5-dinitrobenzoic acid.
Under the condition of unchanged process conditions in the above examples, the copper triflate catalyst was added to concentrated nitric acid, and the experimental results are shown in the following table:
TABLE 2 Experimental results for the continuous preparation of 3, 5-dinitrobenzoic acid with different sulfuric acid dosages (containing copper triflate)
Example 2
The microchannel reactor apparatus (3a +3c) of the present invention is divided into a preheating zone, a reaction zone and a quenching zone, connected according to FIG. 2. The reaction residence time is controlled to be 210s by adjusting the flow of the pump and the length of the micro-channel, the flow rate of the pump is 5-15ml/min, the preheating temperature and the reaction temperature are set to be 65 ℃, and the reaction pressure is 5 bar. The mixed solution of benzoic acid and fuming sulfuric acid (104%) is fed into preheating zone A of the device through metering pump 1, and concentrated nitric acid (98%) is fed into preheating zone B of the device through pump 2, after two materials are fully preheated respectively, they are fed into reaction zone to make mixing reaction. Wherein the molar ratio of the benzoic acid to the sulfuric acid is 1:6. Continuously discharging the 3, 5-dinitrobenzoic acid product from an outlet, quenching the reaction liquid with ice water, crystallizing, filtering to obtain a crude product, washing with water and ethanol to obtain partial refined 3, 5-dinitrobenzoic acid, and analyzing the trace refined product by HPLC, wherein the peak time of the refined product is consistent with that of the standard product. The results of the experiments conducted in the discussion of the amount of nitric acid are shown in the following table:
TABLE 3 Experimental results for the continuous preparation of 3, 5-dinitrobenzoic acid with different reaction material ratios (without copper triflate)
Under the condition of unchanged process conditions in the above examples, the copper triflate catalyst was added to concentrated nitric acid, and the experimental results are shown in the following table:
TABLE 4 Experimental results for the continuous preparation of 3, 5-dinitrobenzoic acid with different reaction material ratios (containing copper triflate)
Example 3
The microchannel reactor apparatus (3a +3d) of the present invention is divided into a preheating zone, a reaction zone and a quenching zone, connected according to FIG. 2. The reaction residence time is controlled to be 240s by adjusting the flow of the pump and the length of the micro-channel, the flow rate of the pump is 5-15ml/min, the preheating temperature and the reaction temperature are set to be 70 ℃, and the reaction pressure is 10 bar. The mixed solution of benzoic acid and fuming sulfuric acid (104%) is fed into preheating zone A of the device through metering pump 1, and concentrated nitric acid (98%) is fed into preheating zone B of the device through pump 2, after two materials are fully preheated respectively, they are fed into reaction zone to make mixing reaction. Wherein the molar ratio of the benzoic acid to the sulfuric acid is 1:5, and the molar ratio of the benzoic acid to the nitric acid is 1:4. Continuously discharging the 3, 5-dinitrobenzoic acid product from an outlet, quenching the reaction liquid with ice water, crystallizing, filtering to obtain a crude product, washing with water and ethanol to obtain partial refined 3, 5-dinitrobenzoic acid, and analyzing 2 trace refined products by HPLC, wherein the peak time of the refined products is consistent with that of the standard products. The results of the experimental work on reaction temperature are shown in the following table:
TABLE 5 Experimental results for the continuous preparation of 3, 5-dinitrobenzoic acid at different reaction temperatures (without copper triflate)
Under the condition of unchanged process conditions in the above examples, the copper triflate catalyst was added to concentrated nitric acid, and the experimental results are shown in the following table:
TABLE 6 Experimental results for the continuous preparation of 3, 5-dinitrobenzoic acid at different reaction temperatures (containing copper triflate)
Example 4
The microchannel reactor apparatus (3a +3e) of the present invention is divided into a preheating zone, a reaction zone and a quenching zone, connected according to FIG. 2. The reaction residence time is controlled to be 270s by adjusting the flow of the pump and the length of the micro-channel, the flow rate of the pump is 5-15ml/min, the preheating temperature and the reaction temperature are set to be 80 ℃, and the reaction pressure is 10 bar. The mixed solution of benzoic acid and fuming sulfuric acid (104%) is fed into preheating zone A of the device through metering pump 1, and concentrated nitric acid (98%) is fed into preheating zone B of the device through pump 2, after two materials are fully preheated respectively, they are fed into reaction zone to make mixing reaction. Wherein the molar ratio of the benzoic acid to the sulfuric acid is 1:5, and the molar ratio of the benzoic acid to the nitric acid is 1: 2.5. Continuously discharging the 3, 5-dinitrobenzoic acid product from an outlet, quenching the reaction liquid with ice water, crystallizing, filtering to obtain a crude product, washing with water and ethanol to obtain partial refined 3, 5-dinitrobenzoic acid, and analyzing 2 trace refined products by HPLC, wherein the peak time of the refined products is consistent with that of the standard products. The results of the experiments, discussing different residence times, are shown in the following table:
TABLE 7 results of experiments on the continuous preparation of 3, 5-dinitrobenzoic acid with different residence times (without copper triflate)
Under the condition of unchanged process conditions in the above examples, the copper triflate catalyst was added to concentrated nitric acid, and the experimental results are shown in the following table:
TABLE 8 Experimental results for the continuous preparation of 3, 5-dinitrobenzoic acid with different residence times (containing copper triflate)
Example 5
The microchannel reaction device (3g +3f) is divided into a preheating zone, a reaction zone and a quenching zone, the reaction residence time is controlled to be 300s by adjusting the flow of a pump and the length of a channel of a microchannel according to the connection of a figure 2, the flow rate of the pump is controlled to be 5-15ml/min, the preheating temperature and the reaction temperature are set to be 75 ℃, and the reaction pressure is 10 bar. The mixed solution of benzoic acid and fuming sulfuric acid (104%) is fed into preheating zone A of the device through metering pump 1, and concentrated nitric acid (98%) is fed into preheating zone B of the device through pump 2, after two materials are fully preheated respectively, they are fed into reaction zone to make mixing reaction. Wherein the molar ratio of the benzoic acid to the sulfuric acid is 1:4, and the molar ratio of the benzoic acid to the nitric acid is 1:2. Continuously discharging the 3, 5-dinitrobenzoic acid product from an outlet, quenching the reaction liquid with ice water, crystallizing, filtering to obtain a crude product, washing with water and ethanol to obtain partial refined 3, 5-dinitrobenzoic acid, and analyzing the trace refined product by HPLC, wherein the peak time of the refined product is consistent with that of the standard product. The results of the experiments, investigating the amount of catalyst, are shown in the following table:
TABLE 9 Experimental results for continuous preparation of 3, 5-dinitrobenzoic acid with different amounts of catalyst
The increase of the copper trifluorosulfonate catalyst can reduce the generation of the by-product 3, 4-dinitrobenzoic acid and reduce the selectivity, but because the unit price is expensive, the addition of the catalyst is more suitable under the condition of considering the cost, and the dosage is 0.5-1.0 percent.
The invention creatively discovers that even under the condition of higher yield (such as about 90%) of the 3, 5-dinitrobenzoic acid, the impurity of the 3, 4-dinitrobenzoic acid is still contained in the product at about 1%, and the purity requirement is difficult to meet. Other catalysts have been tried in the present invention, but the effect is not obvious, so the catalyst is selected to be copper triflate. The method adds the copper triflate catalyst into the reaction system, not only slightly improves the yield of the 3, 5-dinitrobenzoic acid, but also can obviously inhibit the generation of 3, 4-dinitrobenzoic acid impurities, thereby greatly improving the purity of the target product, and the purity can reach more than 99.8 percent.
The foregoing is only a preferred embodiment of the present invention, and it should be noted that, for those skilled in the art, various modifications and decorations can be made without departing from the principle of the present invention, and these modifications and decorations should also be regarded as the protection scope of the present invention.
Claims (3)
1. A method for continuously preparing 3, 5-dinitrobenzoic acid by using a microchannel reactor is characterized by comprising the following steps:
(1) in a reactor with a micro-channel structure, respectively taking a mixed solution of benzoic acid and fuming sulfuric acid at room temperature and concentrated nitric acid as reaction materials, and respectively introducing the reaction materials into a preheating module in the reactor with the micro-channel structure through a metering pump for preheating; wherein the molar ratio of the benzoic acid to the fuming sulfuric acid is 1: 4-9, and the molar ratio of the benzoic acid to the concentrated nitric acid is 1: 2.5-4.5; the concentrated nitric acid contains a copper triflate catalyst, and the addition amount of the copper triflate is 0.5-1% of the molar mass of the benzoic acid;
(2) controlling the flow of the materials by a metering pump, synchronously feeding the preheated materials into a reactor module of a micro-channel structure for mixing and reacting, wherein the retention time in the micro-channel structure is 2-4.5min, the reaction temperature is 50-90 ℃, the reaction pressure is 5-15 bar, after the reaction process is finished, the product flows out of an outlet of the reactor, and the reaction liquid is collected and enters a post-treatment process to obtain the 3, 5-dinitrobenzoic acid.
2. The method for continuously preparing 3, 5-dinitrobenzoic acid using a microchannel reactor as claimed in claim 1, wherein the preheating temperature in step (1) is 60 to 80 ℃.
3. The method for continuously preparing 3, 5-dinitrobenzoic acid by using the microchannel reactor as claimed in claim 1, wherein the microchannel structure used comprises a straight-flow channel, a flat channel having a rectangular cross section, and one or more of a flat rectangular flat channel of a disk type pulse diameter-changing type, a flat rectangular flat channel of an oblique disk type pulse diameter-changing type, a reinforced mixed rectangular flat channel of a disk type, a reinforced mixed rectangular flat channel of an oblique disk type, and a microchannel of a 3g-Heart Cell structure.
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