CN111100034A - Method for continuously synthesizing cyanoacetic acid by using microchannel reactor - Google Patents
Method for continuously synthesizing cyanoacetic acid by using microchannel reactor Download PDFInfo
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- CN111100034A CN111100034A CN201911308500.0A CN201911308500A CN111100034A CN 111100034 A CN111100034 A CN 111100034A CN 201911308500 A CN201911308500 A CN 201911308500A CN 111100034 A CN111100034 A CN 111100034A
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- C—CHEMISTRY; METALLURGY
- C07—ORGANIC CHEMISTRY
- C07C—ACYCLIC OR CARBOCYCLIC COMPOUNDS
- C07C253/00—Preparation of carboxylic acid nitriles
- C07C253/14—Preparation of carboxylic acid nitriles by reaction of cyanides with halogen-containing compounds with replacement of halogen atoms by cyano groups
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
- B01J—CHEMICAL OR PHYSICAL PROCESSES, e.g. CATALYSIS OR COLLOID CHEMISTRY; THEIR RELEVANT APPARATUS
- B01J19/00—Chemical, physical or physico-chemical processes in general; Their relevant apparatus
- B01J19/0093—Microreactors, e.g. miniaturised or microfabricated reactors
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- C—CHEMISTRY; METALLURGY
- C07—ORGANIC CHEMISTRY
- C07C—ACYCLIC OR CARBOCYCLIC COMPOUNDS
- C07C253/00—Preparation of carboxylic acid nitriles
- C07C253/30—Preparation of carboxylic acid nitriles by reactions not involving the formation of cyano groups
Abstract
The invention provides a method for continuously synthesizing cyanoacetic acid by using a microchannel reactor, which comprises the steps of neutralization, cyaniding preheating, cyaniding reaction, cooling and acidification. In the microchannel reactor, reaction liquid is efficiently and quickly mixed and reacted, and in addition, the reaction temperature and other matched processes are accurately controlled, so that the product decomposition is effectively avoided, and the yield can be improved to 98-99.5% from 80% of a batch kettle type. More importantly, after the selectivity is improved, the purification difficulty of subsequent products is greatly reduced, and the content of chloride ions in the products is 0.05-0.12%, and the content of malonic acid is below 0.01%. The reaction time of the invention is within 20 minutes, the reaction time from neutralization to acidification is 1.9-2.5 minutes in the preferred technical scheme, and the safe amplification of the production capacity can be realized through serialization and equipment scale.
Description
Technical Field
The invention belongs to the technical field of chemical production, and particularly relates to a method for continuously synthesizing cyanoacetic acid, in particular to a method for continuously synthesizing cyanoacetic acid by using a microchannel reactor.
Background
Cyanoacetic acid is an important intermediate for the production of pharmaceuticals, fuels, and pesticides, and is used in the production of malonic acid, cyanoacetic acid esters, malonic esters, α -methyl cyanoacrylate, vitamin B6, caffeine, and cymoxanil.
Cyanoacetic acid is prepared from chloroacetic acid, first with a base such as: neutralizing sodium hydroxide or sodium carbonate to obtain sodium chloroacetate aqueous solution, adding sodium cyanide for cyanidation to obtain sodium cyanoacetate aqueous solution, adding hydrochloric acid for acidification to obtain cyanoacetic acid aqueous solution, and finally dehydrating to obtain cyanoacetic acid with different concentrations. At present, various manufacturers in China mostly adopt batch type reaction kettles for production.
The intermittent production operation is complicated, and the temperature needs to be raised and then lowered in the cyaniding process, so that the energy consumption is increased; the heat release in the cyanidation process is severe, and the temperature is not easy to control; the cyanoacetic acid product is partially hydrolyzed, resulting in poor product selectivity and reduced yield. In addition, because the production uses virulent sodium cyanide as a raw material, the intermittent production has great potential safety hazard.
In recent years, due to the size effect of the microchannel reactor, reactants can be mixed more sufficiently, the temperature control is accurate, side reactions and potential safety hazards caused by poor mass transfer and heat transfer are reduced, and reaction liquid continuously flows forwards, so that the occurrence of excessive reaction caused by back mixing is reduced. In addition, compared with a kettle type reactor, the micro-channel system is much smaller, and the process risk hidden trouble is greatly reduced. The microchannel reactor is in continuous production, and has simpler operation and higher controllability. These advantages have led to great attention and use of microchannel reactors in the pharmaceutical and chemical industries.
CN105481717B (applicant, chongqing violaceous chemical corporation) discloses a method for preparing cyanoacetic acid and its derivatives, wherein the cyanidation and acidification reactions are all intermittent reactions, but the acidified mixed solution is separated by a continuous chromatographic separation system filled with ammonium chromatographic separation resin to obtain cyanoacetic acid solution and sodium chloride solution, but the cyanidation and acidification reactions are all intermittent reactions, the operation steps are complex, in the reaction kettle, a large amount of heat generated by the cyanidation reaction cannot be removed in time, the cyano group is hydrolyzed, the color of the obtained product is deepened, and the yield is reduced. In addition, the product and the raw material are back-mixed, so that the local alkalinity of the reaction liquid is increased, the cyano is hydrolyzed into amide or acid under the alkaline condition, the product yield is further reduced, and the side reaction is increased.
CN 102633682B (Hebei Chengxinchi Limited liability company) discloses a process for producing cyanoacetate, the adopted raw material is chloroacetate, and a continuous cyanidation process is adopted, so that the continuous production of cyanoacetate can be realized. The disadvantages are that solid sodium chloride generated in the cyanidation process is insoluble in the used methanol solvent, and is easy to block pipelines, thereby causing production accidents, and the reaction yield is low.
CN107586263A (application named as XIONGPING) discloses an environment-friendly and clean method for continuously cyaniding and synthesizing sodium cyanoacetate and derivatives thereof, which comprises mixing a sodium chloroacetate solution and a sodium cyanide solution in a static mixer, and then flowing into a column reactor for cyanidation. Overcomes the problems of temperature runaway and boiling during the reaction process, and realizes safe, environment-friendly and clean production. However, the reaction time in the column reactor is long, and the heat generated by cyanidation cannot be quickly removed, so that the product sodium cyanoacetate cannot be further decomposed to generate impurities such as sodium malonate and the like, and the purification difficulty of downstream products cannot be reduced.
Disclosure of Invention
Aiming at the defects in the prior art, the invention provides a method for continuously synthesizing cyanoacetic acid by using a microchannel reactor, which realizes the following purposes:
(1) the method for continuously synthesizing cyanoacetic acid is provided, the reaction time is shortened, and the product yield is improved;
(2) reduce side reaction and impurity content.
In order to solve the technical problems, the invention adopts the following technical scheme:
a method for continuously synthesizing cyanoacetic acid by using a microchannel reactor comprises the following steps:
step (1) neutralization
And (3) pumping chloroacetic acid aqueous solution with a certain concentration and sodium hydroxide aqueous solution with a certain concentration into a neutralization module, and performing neutralization reaction on chloroacetic acid and sodium hydroxide. Controlling the flow rate, the proportion and the reaction temperature, and obtaining the sodium chloroacetate aqueous solution at the outlet of the module.
The molar ratio of the chloroacetic acid to the sodium hydroxide is 1: 0.8-1.2, and preferably 1: 1.00-1.05.
Controlling the flow speed and the length of the micro-channel to ensure that the residence time of the reaction liquid is 15-300 s, preferably 15-30 s.
The temperature of the module is controlled to be 15-50 ℃, and the optimal temperature is 15-35 ℃.
Cyaniding preheating of step (2)
And (2) feeding the sodium chloroacetate aqueous solution obtained in the step (1) into a cyaniding preheating module, and simultaneously pumping a sodium cyanide aqueous solution with a certain concentration. Controlling the flow rate and proportion of sodium cyanide and the length of the micro-channel, and raising the temperature of the outlet feed liquid to the spontaneous reaction temperature through a circulating temperature control system.
The molar ratio of the sodium cyanide to the chloroacetic acid is 0.8-1.2: 1, and preferably 1.00-1.05: 1.
The length of the micro-channel is controlled, so that the residence time of the reaction liquid is 15-300 s, preferably 15-30 s.
The temperature of the outlet feed liquid is controlled to be 50-100 ℃, and the optimal temperature is 80-95 ℃.
Step (3) cyanation reaction
And (3) allowing the reaction liquid obtained in the step (2) to enter a cyanidation reaction module, controlling the length of the microchannel, removing the generated reaction heat through a circulating temperature control system, and obtaining a sodium cyanoacetate aqueous solution at the outlet of the module.
The length of the micro-channel is controlled, so that the residence time of the reaction liquid is 15-300 s, preferably 30-60 s.
The temperature of the module is controlled to be 80-120 ℃, and preferably 95-102 ℃.
Cooling in step (4)
And (4) allowing the sodium cyanoacetate aqueous solution obtained in the step (3) to enter a cooling module, controlling the length of the micro-channel, and cooling by a circulating temperature control system to enable the temperature of the outlet feed liquid to reach the acidification temperature.
The temperature of the module is controlled to be 15-50 ℃, and preferably 15-35 ℃.
The length of the micro-channel is controlled, so that the residence time of the reaction liquid is 15-300 s, preferably 15-32 s.
And controlling the outlet temperature of the cooling module to be below 20-35 ℃.
Step (5) acidification
And (4) feeding the sodium cyanoacetate aqueous solution cooled in the step (4) into an acidification module, simultaneously pumping hydrochloric acid with a certain concentration, controlling the concentration, flow rate and proportion of the hydrochloric acid, removing the generated reaction heat through a circulating temperature control system, and obtaining the aqueous solution of cyanoacetic acid at an outlet.
The temperature of the module is controlled to be 15-25 ℃.
Controlling the length of the micro-channel to ensure that the residence time of the reaction liquid is 14-18 s and the liquid holdup is 19-21 ml;
the molar ratio of the hydrochloric acid to the chloroacetic acid in the step (5) is 0.98-1.02: 1.
Step (6) post-treatment
And (5) dehydrating, desalting and separating the effluent obtained in the step (5) to obtain cyanoacetic acid aqueous solutions with different concentrations.
The further preferred technical scheme is as follows:
a method for continuously synthesizing cyanoacetic acid by using a microchannel reactor comprises the following steps:
step (1) neutralization
And (3) pumping chloroacetic acid aqueous solution with a certain concentration and sodium hydroxide aqueous solution with a certain concentration into a neutralization module, and performing neutralization reaction on chloroacetic acid and sodium hydroxide. Controlling the flow rate, the proportion and the reaction temperature, and obtaining the sodium chloroacetate aqueous solution at the outlet of the module.
The molar ratio of chloroacetic acid to sodium hydroxide is 1: 1.00-1.05.
Controlling the flow rate and the length of the micro-channel to ensure that the residence time of the reaction liquid is 25-30s and the liquid holdup of the module is 20 ml;
controlling the temperature of the module to be 15-35 ℃;
the concentration of the chloroacetic acid aqueous solution is 3-5mmol/ml, and the concentration of the sodium hydroxide aqueous solution is 7.8-8.2 mmol/ml; the flow rate of the chloroacetic acid aqueous solution is 29-31ml/min, and the flow rate of the sodium hydroxide aqueous solution is 12-19 ml/min.
Cyaniding preheating of step (2)
And (2) feeding the sodium chloroacetate aqueous solution obtained in the step (1) into a cyaniding preheating module, and simultaneously pumping a sodium cyanide aqueous solution with a certain concentration. Controlling the flow rate and proportion of sodium cyanide and the length of the micro-channel, and raising the temperature of the outlet feed liquid to the spontaneous reaction temperature through a circulating temperature control system.
The molar ratio of the sodium cyanide to the chloroacetic acid is 1.00-1.05: 1.
And controlling the length of the micro-channel to ensure that the residence time of the reaction liquid is 20-28 s.
Controlling the temperature of the outlet feed liquid to be 80-95 ℃, and preferably 85-90 ℃;
the liquid holdup of the module is 20-30ml,
the concentration of the sodium cyanide aqueous solution is 6.8-7.2 mmol/ml; the flow rate is 14-22 ml/min;
step (3) cyanation reaction
And (3) allowing the reaction liquid obtained in the step (2) to enter a cyanidation reaction module, controlling the length of the microchannel, removing the generated reaction heat through a circulating temperature control system, and obtaining a sodium cyanoacetate aqueous solution at the outlet of the module.
Controlling the length of the micro-channel to ensure that the residence time of the reaction liquid is 32-43 s.
The temperature of the module is controlled to be 95-102 ℃, and the liquid holdup of the module is 30-50 ml.
Cooling in step (4)
And (4) allowing the sodium cyanoacetate aqueous solution obtained in the step (3) to enter a cooling module, controlling the length of the micro-channel, and cooling by a circulating temperature control system to enable the temperature of the outlet feed liquid to reach the acidification temperature.
Controlling the temperature of the module to be 15-35 ℃, and controlling the liquid holdup of the module to be 29-31 ml;
the length of the micro-channel is controlled to ensure that the residence time of the reaction liquid is 36-32 s.
Step (5) acidification
And (4) feeding the sodium cyanoacetate aqueous solution cooled in the step (4) into an acidification module, simultaneously pumping hydrochloric acid with a certain concentration, controlling the concentration, flow rate and proportion of the hydrochloric acid, removing the generated reaction heat through a circulating temperature control system, and obtaining the aqueous solution of cyanoacetic acid at an outlet.
The temperature of the module is controlled to be 15-50 ℃, and preferably 15-25 ℃.
The length of the micro-channel is controlled, so that the residence time of the reaction liquid is 10-300 s, preferably 15-30 s.
The molar ratio of the hydrochloric acid to the chloroacetic acid in the step (5) is 0.8-1.2: 1, and preferably 0.98-1.02: 1.
The concentration of the hydrochloric acid is 10-11 mmol/ml; the flow rate is 9.3-14.5 ml/min;
step (6) post-treatment
And (5) dehydrating, desalting and separating the effluent obtained in the step (5) to obtain cyanoacetic acid aqueous solutions with different concentrations.
The preferable technical scheme has the technical effects that: the concentration of the cyanoacetic acid aqueous solution is 70-90%, the content of chloride ions is 0.05-0.12%, the content of malonic acid is less than 0.01%, the yield of the cyanoacetic acid is 98-99.5% (calculated by chloroacetic acid), and the reaction time from neutralization to acidification is 1.9-2.5 minutes.
The concentration of each raw material solution is not limited in the invention, and the proper concentration is calculated according to the production condition. Unless otherwise specified, are commercially available.
The residence time of the reaction liquid in the microchannel is controlled by the liquid inlet quantity of the feed liquid and the internal capacity of the microchannel reactor. The liquid inlet of the feed liquid is controlled by respective independent metering pumps, and the flow range can be adjusted within 1-100 ml/min. The plates of the microchannels may be increased or decreased depending on the experimental situation by connecting them in series.
The reaction temperature of the microchannel reactor of the invention is controlled by a temperature control medium coupled to the microchannel reactor, the medium circulating through the sandwich of the microchannel reactor. And the medium temperature of each module is coordinately controlled through a circulating temperature control system. Under preferred conditions, the heat generated by the media-transfer reaction in the cyanidation reaction module can be used to preheat the module, thereby reducing energy consumption.
The invention does not limit the model, material and the like of the microchannel reactor. Any microchannel reactor can be used to implement the subject technology.
In the step of cyanoacetic acid synthesis, the most critical is the cyanidation process. In the reaction kettle, the reaction liquid is heated to a certain temperature to initiate the reaction, and then the heat generated by the reaction can keep the reaction continuously. . In the microchannel reactor, a large amount of heat generated by the reaction can be removed in time, and product back mixing is avoided, so that the product quality and yield can be effectively improved.
The invention pumps prepared chloroacetic acid aqueous solution and sodium hydroxide aqueous solution into a neutralization module of a microchannel reactor respectively for neutralization reaction, and obtains sodium chloroacetate aqueous solution by controlling the proportion and the reaction temperature. And respectively pumping the sodium chloroacetate aqueous solution and the sodium cyanide aqueous solution into a cyanidation reaction preheating module, controlling the flow rate and the reaction ratio, and circularly heating to reach the spontaneous reaction temperature. And then the reaction liquid enters a cyanidation reaction module, and reaction heat is removed through circulating temperature reduction, and the temperature is controlled within a proper range. After cyaniding is finished, the reaction liquid is cooled through the cooling module, then enters the acidification module, and meanwhile, hydrochloric acid is pumped in to adjust the proportion of the hydrochloric acid, and the aqueous solution of cyanoacetic acid is obtained at an outlet.
Compared with the prior art, the invention has the following beneficial effects:
1. in the microchannel reactor, reaction liquid is efficiently and quickly mixed and reacted, and in addition, the reaction temperature and other matched processes are accurately controlled, so that the product decomposition is effectively avoided, and the yield can be improved to 98-99.5% from 80% of a batch kettle type. More importantly, after the selectivity is improved, the purification difficulty of subsequent products is greatly reduced, and the content of chloride ions in the products is 0.05-0.12%, and the content of malonic acid is below 0.01%.
2. The reaction time of the invention is within 20 minutes, the reaction time from neutralization to acidification is 1.9-2.5 minutes in the preferred technical scheme, and the safe amplification of the production capacity can be realized through serialization and equipment scale.
3. The batch production is changed into continuous production, so that the process flow and the operation difficulty can be greatly simplified, and the occupied area is greatly reduced compared with a kettle type.
4. The liquid holdup in the microchannel reactor is greatly reduced relative to an intermittent kettle, and the potential safety hazard caused by violent exothermic reaction and materials is greatly reduced.
5. The method has the defects of complex operation, low equipment utilization rate, high energy consumption, poor reaction selectivity and potential safety hazard in the process in the intermittent cyanoacetic acid production.
Drawings
FIG. 1 is a schematic view of continuous synthesis of cyanoacetic acid in micro-channel of the present invention
The specific implementation mode is as follows:
the present invention is further described with reference to specific examples, which are provided for illustrative purposes only and are not intended to limit the scope of the present invention.
The microchannel reactor used in the following examples is a corning glass microchannel reactor, which is made of glass. The reagents and starting materials used are commercially available without specific reference.
The concentrations of the starting materials in the examples are molar concentrations (mmol/ml ).
The yields in the examples were calculated on chloroacetic acid as starting material.
Example 1
(1) Neutralization
And respectively pumping a chloroacetic acid aqueous solution with the concentration of 5mmol/ml and a sodium hydroxide aqueous solution with the concentration of 8mmol/ml into a neutralization module at the flow rates of 30ml/min and 18.75ml/min respectively, wherein the molar ratio of chloroacetic acid to sodium hydroxide is 1:1. The temperature of the module is controlled to be 20-25 ℃. The module liquid hold-up was 20ml and the reaction time was about 25 s.
(2) Cyanidation preheating
And (2) enabling the reaction liquid obtained in the step (1) to enter a cyaniding preheating module, and simultaneously pumping a sodium cyanide aqueous solution with the concentration of 6.92mmol/ml, wherein the flow rate of the sodium cyanide aqueous solution is 21.7 ml/min. The molar ratio of the sodium cyanide to the chloroacetic acid is 1:1. The temperature of the outlet feed liquid is increased to 80-85 ℃ by a circulating temperature control system. The liquid holdup of the module was 30ml and the time for the reaction liquid to flow through the module was about 26 seconds.
(3) Cyanidation reaction
And (3) enabling the reaction liquid obtained in the step (2) to enter a cyanidation reaction module, controlling the temperature of the module to be 95-100 ℃, controlling the liquid holdup of the module to be 50ml, and controlling the reaction time to be about 43 s.
(4) Cooling down
And (4) allowing the sodium cyanoacetate aqueous solution obtained in the step (3) to enter a cooling module, wherein the module is controlled at a temperature of 15-20 ℃. The liquid holdup of the module is 30ml, the time for the reaction liquid to flow through the module is about 26s, and the outlet temperature is controlled below 20 ℃.
(5) Acidification
And (4) feeding the sodium cyanoacetate aqueous solution cooled in the step (4) into an acidification module, and simultaneously pumping hydrochloric acid with the concentration of 10.16mmol/ml, the flow rate of 14.5ml/min and the molar ratio of the hydrochloric acid to chloroacetic acid of 0.98: 1. The generated reaction heat is removed through a circulating temperature control system, and the module control temperature is 15-25 ℃. The module had a liquid hold-up of 20ml and a reaction time of about 14 s.
(6) Post-treatment
And (5) dehydrating, desalting and separating the effluent obtained in the step (5) to obtain a cyanoacetic acid aqueous solution with the concentration of 70%. The content of cyanoacetic acid in the detection solution is 70.2%, the content of chloride ions is 0.12%, the content of malonic acid is less than 0.01%, and the calculated yield is about 98%.
Example 2
(1) Neutralization
And respectively pumping chloroacetic acid aqueous solution with the concentration of 3.17mmol/ml and sodium hydroxide aqueous solution with the concentration of 8mmol/ml into a neutralization module at the flow rates of 30ml/min and 12.5ml/min respectively, wherein the molar ratio of chloroacetic acid to sodium hydroxide is 1: 1.05. The temperature of the module is controlled to be 25-35 ℃. The module had a liquid hold-up of 20ml and a reaction time of about 28 s.
(2) Cyanidation preheating
And (2) feeding the reaction liquid obtained in the step (1) into a cyaniding preheating module, and simultaneously pumping a sodium cyanide aqueous solution with the concentration of 6.92 mmol/ml. The NaCN flow rate was 14 ml/min. The molar ratio of the sodium cyanide to the chloroacetic acid is 1.02: 1. The temperature of the outlet feed liquid is increased to 80-85 ℃ by a circulating temperature control system. The liquid holdup of the module was 20ml and the time for the reaction liquid to flow through the module was about 21 seconds.
(3) Cyanidation reaction
And (3) allowing the reaction liquid obtained in the step (2) to enter a cyanidation reaction module, wherein the temperature of the module is controlled to be 95-100 ℃. The module liquid hold-up was 30ml and the reaction time was about 32 s.
(4) Cooling down
And (4) allowing the sodium cyanoacetate aqueous solution obtained in the step (3) to enter a cooling module, wherein the module is controlled at a temperature of 25-35 ℃. The liquid holdup of the module is 30ml, the time for the reaction liquid to flow through the module is about 32s, and the outlet temperature is controlled below 35 ℃.
(5) Acidification
And (4) feeding the sodium cyanoacetate aqueous solution cooled in the step (4) into an acidification module, and simultaneously pumping hydrochloric acid with the concentration of 10.16mmol/ml, wherein the flow rate is about 9.36ml/min, and the molar ratio of the hydrochloric acid to chloroacetic acid is 1:1. The generated reaction heat is removed through a circulating temperature control system, and the module control temperature is 15-25 ℃. The module liquid hold-up was 20ml and the reaction time was about 18 s.
(6) Post-treatment
And (5) dehydrating, desalting and separating the effluent obtained in the step (5) to obtain a cyanoacetic acid aqueous solution. The content of cyanoacetic acid in the detection solution is 70.5%, the content of chloride ions is 0.1%, the content of malonic acid is less than 0.01%, and the calculated yield is about 98.5%.
Example 3
(1) Neutralization
And respectively pumping chloroacetic acid aqueous solution with the concentration of 3.17mmol/ml and sodium hydroxide aqueous solution with the concentration of 8mmol/ml into a neutralization module at the flow rates of 30ml/min and 12.1ml/min respectively, wherein the molar ratio of chloroacetic acid to sodium hydroxide is 1: 1.02. The temperature of the module is controlled to be 15-25 ℃. The module had a liquid hold-up of 20ml and a reaction time of about 29 s.
(2) Cyanidation preheating
And (2) feeding the reaction liquid obtained in the step (1) into a cyaniding preheating module, and simultaneously pumping a sodium cyanide aqueous solution with the concentration of 6.92 mmol/ml. The NaCN flow rate was 14.4 ml/min. The molar ratio of the sodium cyanide to the chloroacetic acid is 1.05: 1. The temperature of the outlet feed liquid is increased to 90-95 ℃ by a circulating temperature control system. The liquid holdup of the module was 20ml and the time for the reaction liquid to flow through the module was about 21 seconds.
(3) Cyanidation reaction
And (3) allowing the reaction liquid obtained in the step (2) to enter a cyanidation reaction module, wherein the temperature of the module is controlled to be 97-102 ℃. The module liquid hold-up was 30ml and the reaction time was about 32 s.
(4) Cooling down
And (4) allowing the sodium cyanoacetate aqueous solution obtained in the step (3) to enter a cooling module, wherein the module is controlled at a temperature of 15-20 ℃. The liquid holdup of the module is 30ml, the time for the reaction liquid to flow through the module is about 32s, and the outlet temperature is controlled below 20 ℃.
(5) Acidification
And (4) feeding the sodium cyanoacetate aqueous solution cooled in the step (4) into an acidification module, and simultaneously pumping hydrochloric acid with the concentration of 10.16mmol/ml, wherein the flow rate is about 9.54ml/min, and the molar ratio of the hydrochloric acid to chloroacetic acid is 1.02: 1. The generated reaction heat is removed through a circulating temperature control system, and the module control temperature is 15-25 ℃. The module liquid hold-up was 20ml and the reaction time was about 18 s.
(6) Post-treatment
And (5) dehydrating, desalting and separating the effluent obtained in the step (5) to obtain a cyanoacetic acid aqueous solution. The content of cyanoacetic acid in the solution is detected to be 90%, the content of chloride ions is detected to be 0.05%, the content of malonic acid is detected to be less than 0.01%, and the calculated yield is about 99.5%.
Compared with the chemical reaction carried out by the conventional reactor, the microchannel reactor has the following advantages:
(1) the width and depth of the channel in the reactor are small, the diffusion distance of reactants is shortened, the mass transfer speed is high, and the reactants can be fully mixed in a short time in the flowing process.
(2) The micro-channel has large specific surface area and high heat exchange efficiency, and even if the reaction is violent in exothermic reaction, a large amount of reaction heat released instantly can be removed in time, so that the reaction temperature is maintained in a proper range.
(3) The reaction is carried out in the microchannel reactor, the required raw materials are few, the dosage of toxic and harmful raw materials can be reduced, and the use is safer. The environmental pollutants generated in the reaction process are few, and the method is an environment-friendly and safe production platform.
(4) When the synthesis reaction is carried out in the microchannel reactor, the reactant ratio, the temperature, the pressure and the reaction time can be accurately controlled by adjusting the flow rate and the channel length.
Claims (10)
1. A method for continuously synthesizing cyanoacetic acid by using a microchannel reactor is characterized by comprising the following steps: the method comprises the steps of neutralization, cyaniding preheating, cyaniding reaction, cooling and acidification.
2. The method for continuously synthesizing cyanoacetic acid by using the microchannel reactor as claimed in claim 1, wherein: in the neutralization step, chloroacetic acid aqueous solution and sodium hydroxide aqueous solution are pumped into a neutralization module, and chloroacetic acid and sodium hydroxide are subjected to neutralization reaction to prepare sodium chloroacetate aqueous solution; the molar ratio of chloroacetic acid to sodium hydroxide is 1: 0.8-1.2, the residence time of the reaction liquid is 15-300 s, and the temperature of the module is controlled to be 15-50 ℃.
3. The method for continuously synthesizing cyanoacetic acid by using the microchannel reactor as claimed in claim 2, wherein: the mol ratio of chloroacetic acid to sodium hydroxide is 1: 1.00-1.05; the residence time of the reaction liquid is 15-30 s; the temperature of the module is controlled to be 15-35 ℃.
4. The method for continuously synthesizing cyanoacetic acid by using the microchannel reactor as claimed in claim 2, wherein: the cyaniding preheating step includes that sodium chloroacetate aqueous solution enters a cyaniding preheating module, and sodium cyanide aqueous solution with a certain concentration is pumped in; the molar ratio of the sodium cyanide to the chloroacetic acid is 0.8-1.2: 1; the residence time of the reaction liquid is 15-300 s; and controlling the temperature of the outlet feed liquid to be 50-100 ℃.
5. The method for continuously synthesizing cyanoacetic acid by using the microchannel reactor as claimed in claim 4, wherein: the molar ratio of the sodium cyanide to the chloroacetic acid is 1.00-1.05: 1; the residence time of the reaction liquid is 15-30 s; the temperature of the outlet feed liquid is controlled to be 80-95 ℃.
6. The method for continuously synthesizing cyanoacetic acid by using the microchannel reactor as claimed in claim 1, wherein: the cyaniding reaction is carried out, namely the mixed solution after cyaniding preheating enters a cyaniding reaction module to carry out cyaniding reaction, so that the retention time of the reaction solution is 15-300 s; the temperature of the module is controlled to be 80-120 ℃.
7. The method for continuously synthesizing cyanoacetic acid by using the microchannel reactor as claimed in claim 6, wherein: the cyanidation reaction is carried out, so that the retention time of the reaction liquid is 30-60 s; the control temperature of the module is 95-102 ℃.
8. The method for continuously synthesizing cyanoacetic acid by using the microchannel reactor as claimed in claim 1, wherein: cooling, wherein the temperature of the outlet feed liquid reaches the acidification temperature; controlling the temperature of the module to be 15-50 ℃; the residence time of the reaction solution is 15-300 s.
9. The method for continuously synthesizing cyanoacetic acid by using the microchannel reactor as claimed in claim 1, wherein: cooling, wherein the temperature of the module is controlled to be 15-35 ℃, and the residence time of the reaction liquid is 15-32 s;
and controlling the outlet temperature of the cooling module to be below 20-35 ℃.
10. The method for continuously synthesizing cyanoacetic acid by using the microchannel reactor as claimed in claim 1, wherein: acidifying, namely feeding the cooled sodium cyanoacetate aqueous solution into an acidification module, and simultaneously pumping hydrochloric acid with a certain concentration, wherein the temperature of the module is controlled to be 15-25 ℃; the residence time of the reaction liquid is 14-18 s, and the liquid holdup is 19-21 ml; the molar ratio of the hydrochloric acid to the chloroacetic acid is 0.98-1.02: 1.
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| CN112279782A (en) * | 2020-10-22 | 2021-01-29 | 京博农化科技有限公司 | Preparation method of 2- (2-methylphenoxymethyl) benzoyl nitrile |
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