Method and system for preparing cyanogen chloride based on continuous flow of microchannel reaction device

Abstract

The invention discloses a method and a system for preparing cyanogen chloride based on continuous flow of a microchannel reaction device, under the condition of temperature control, a NaCN solution and chlorine are introduced into the microchannel reaction device for reaction, then gas-liquid separation, gas washing, drying, condensation and collection are performed to obtain a cyanogen chloride product, and a matched reaction system is provided. The microchannel reaction device is introduced into the reaction preparation process, the heat and mass transfer performance is improved through continuous flow, the heating time is shortened, and continuous production is achieved. No catalyst is used, reaction steps are simplified, and reaction cost is reduced.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of chemical synthesis, in particular to a method and system for preparing cyanogen chloride based on a micro-channel reaction device. BACKGROUND

[0002] Cyanogen chloride is a colorless to light yellow liquid, slightly sweet, highly toxic; at room temperature has a pungent odor. Density: 1.186, molecular weight: 61.47, melting point -6.5℃, boiling point 13.1℃. Soluble in water, ethanol, diethyl ether and most organic solvents, soluble in water is weakly acidic.

[0003] In the current cyanogen chloride related technology, there is still a lack of continuous preparation of cyanogen chloride reaction device, mostly using batch reaction, low production efficiency, low yield and difficult to separate in the later stage, and the preparation process has certain danger.

[0004] Therefore, there is an urgent need for a new preparation method for preparing cyanogen chloride with high yield, high yield, safe reaction and other characteristics.

[0005] The micro-channel reactor channel size is generally in microns, which greatly increases the specific surface area of the reactor to achieve the purpose of strengthening mass transfer and heat transfer. The size of the micro-channel reactor is usually 1-2 orders of magnitude smaller than the traditional reactor, but its transfer efficiency can be two orders of magnitude higher than the traditional reactor, in addition, the micro-channel reactor also has the characteristics of short conveying path, accurate control and direct amplification, etc. These characteristics make the micro-channel reactor become an ideal tool to realize fast reaction, severe exothermic reaction and even explosive reaction. SUMMARY

[0006] Based on the above deficiencies of the prior art, the technical problem solved by the present application is to provide a method for preparing cyanogen chloride based on a micro-channel reaction device with high yield, high yield and safe reaction, and to provide a reaction system. The method for preparing cyanogen chloride based on the micro-channel reaction device can improve the reaction speed, realize continuous production, improve the production capacity, and meet the safety production standard.

[0007] In order to solve the above technical problems, the present application provides a method for preparing cyanogen chloride based on a micro-channel reaction device: under temperature control conditions, NaCN solution and chlorine gas are introduced into the micro-channel reaction device for reaction, and then gas-liquid separation, gas washing, drying, condensation and collection are carried out to obtain cyanogen chloride product.

[0008] As a preferred technical solution, the method for preparing cyanogen chloride based on the micro-channel reaction device provided by the present application further includes part or all of the following technical features: As the improvement of the above technical scheme, the NaCN solution is an aqueous solution of sodium cyanide, and the mass concentration is not more than 35%, and the mass concentration is preferably 12%-18%; the molar ratio of chlorine gas to the cyanide solid in the NaCN solution is 0.7-1.5.

[0009] As the improvement of the above technical scheme, the characteristic size of the micro-channel reaction device is 0.1-10 mm, and the material is selected from strong corrosion-resistant materials, including but not limited to silicon carbide and hastelloy; during the reaction process, the reaction temperature in the micro-channel reaction device is controlled to be not more than 50°C, and the reaction time is not more than 5 minutes.

[0010] As the improvement of the above technical scheme, the gas-liquid separation process uses a gas-liquid separator, and a part of the space of the gas-liquid separator is used for temporarily storing the separated waste liquid, or a separate container is arranged in communication with the gas-liquid separator for temporarily storing the separated waste liquid; the space or the separate container for temporarily storing the waste liquid is externally provided with a heating system to control the temperature of the waste liquid to be 40°C-80°C.

[0011] As the improvement of the above technical scheme, the gas washing process uses a carbonate solution as the washing liquid, such as a potassium carbonate solution or a sodium carbonate solution, and the mass concentration of the solution is between 3% and 25%.

[0012] As the improvement of the above technical scheme, the condensation temperature is between -20°C and -6°C.

[0013] As the improvement of the above technical scheme, the product is a colorless transparent liquid, and the yield is 30-60% based on sodium cyanide.

[0014] The application also discloses a continuous flow reaction system based on a micro-channel reaction device, which comprises a liquid phase channel (1), a mass flow meter (11), a gas phase channel (2), a chlorine gas flow meter (21), a micro-channel reaction device (3), a gas-liquid separator (4), a washing tower (5), a flow-through cell (51), a pH meter (511), a washing liquid circulating pump (512), a drying tower (6), a condensation tower (7) and a product collection tank (71). The liquid phase channel (1) and the gas phase channel (2) are respectively connected to the liquid phase inlet and the gas phase inlet of the micro-channel reaction device (3); the liquid phase inlet and the gas phase inlet of the micro-channel reaction device (3) meet inside the micro-reactor; the micro-channel reaction device (3) is sequentially connected to the gas-liquid separator (4), the washing tower (5), the drying tower (6) and the condensation tower (7) after the outlet of the micro-channel reaction device (3), and the product collection tank (71) is arranged below the condensation tower; The drying tower (6) is internally provided with a drying agent; The mass flow meter (11) is arranged on the liquid phase channel (1), and the chlorine gas flow meter (21) is arranged on the gas phase channel (2) to indicate the raw material flow and assist in controlling the molar ratio. A back pressure valve (31) can be installed between the micro-channel reaction device (3) and the gas-liquid separator (4) to increase the pressure inside the micro-channel reaction device (3) and enhance the mixing effect. A part of the space of the gas-liquid separator (4) is used to temporarily store the separated waste liquid, or a separate container is provided to communicate with the gas-liquid separator (4) to temporarily store the separated waste liquid. The part of the space or the separate container for temporarily storing the waste liquid is externally provided with a heating system for controlling the temperature. The washing tower (5) is a spray tower, a bubble tower or a packed tower.

[0015] An acid-base indicator or a pH meter is installed in the flow-through cell between the washing tower (5) and the drying tower (6) to monitor the acid-base property of the gas after washing, so as to judge the washing effect.

[0016] When the system is applied to the method for preparing cyanogen chloride according to the present application, the liquid phase channel (1) delivers a NaCN solution, the gas phase channel (2) delivers chlorine gas, the NaCN solution and the chlorine gas are mixed and reacted in the micro-channel reaction device (3); the gas-liquid mixture obtained by the reaction is discharged from the micro-channel reaction device (3) and then enters the gas-liquid separator (4) to be separated into gas and liquid, and the gas phase part obtained is the crude product of cyanogen chloride; the obtained crude product of cyanogen chloride enters the washing tower (5), which is filled with an alkaline liquid to wash the acidic gas in the crude product of cyanogen chloride; the washed cyanogen chloride gas passes through the drying tower (6) which is filled with a drying agent; and the dried gas is condensed in the condensing tower (7) and collected.

[0017] The NaCN aqueous solution and the chlorine gas are mixed and reacted in the micro-channel reaction device (3) for 8-30 s, and the characteristic dimension of the micro-channel reaction device (3) is 0.1-10 mm. The material molar ratio of the chlorine gas to the sodium cyanide is 0.7-1.5, and the more preferred material molar ratio is 0.8-1.2. Taking the 15% mass concentration of the sodium cyanide solution as an example, the material molar ratio of 0.8-1.2 corresponds to a gas-liquid mass ratio of 0.174-0.260. Too much chlorine gas during the reaction will increase the side reactions and affect the washing effect of the washing device, and too little chlorine gas will also increase the side reactions and the poor flowability of the by-products, which is easy to block the reactor. The reaction temperature is controlled to be 5-40℃, and the more preferred reaction temperature is -10-30℃. Too low temperature will slow down the reaction rate, and too high temperature will produce more hydrogen cyanide, which will affect the yield.

[0018] A flow meter is installed on the liquid phase channel (1), and a chlorine flow meter is installed on the gas phase channel (2). A portion of the space of the gas-liquid separator (4) is used to temporarily store the separated waste liquid, or a separate container connected to the gas-liquid separator (4) is provided for temporarily storing the separated waste liquid. A heating system is provided outside this portion of the space or the separate container for temporarily storing the waste liquid to control the temperature of the waste liquid at 40℃~80℃. A portion of the cyanide gas dissolved in the water is evaporated by heating. After a certain interval, such as half an hour, most of the liquid is discharged and then continues to accumulate, and so on.

[0019] The obtained crude cyanogen chloride product enters a washing tower (5), which contains an alkaline solution to wash away acidic gases such as hydrochloric acid and hydrogen cyanide from the crude cyanogen chloride product. The washing tower (5) can be a spray tower, a packed tower, or a combination of both. It uses a carbonate solution, such as potassium carbonate solution or sodium carbonate solution, with a mass concentration between 3% and 25%. A pH meter can be installed inside the washing tower (5) to determine when the washing solution is depleted and needs to be replaced. Alternatively, a pH meter can be omitted, and the timing of washing solution replacement can be determined solely by the flow-through tank described below.

[0020] A flow tank (51) is provided between the washing tower (5) and the drying tower (6) to allow the washed gas to pass through. The flow tank (51) is filled with an acid-base indicator or equipped with a pH meter to monitor the acidity or alkalinity of the washed gas and thus judge the washing effect. When the liquid in the flow tank is acidic, it indicates that the washing effect is not good and the washing effect needs to be strengthened, such as replacing the washing liquid or increasing the amount of washing liquid sprayed.

[0021] The washed cyanide gas passes through a drying tower (6), which contains desiccants such as anhydrous calcium chloride and molecular sieves.

[0022] The dried gas is condensed and collected by the condenser tower (7). The condensation temperature is set between -20℃ and -6℃, and the optimal condensation temperature is between -10℃ and -7℃. If the condensation temperature is too high, the product gas will not be able to be condensed and collected well. If the temperature is too low, the product gas will solidify, increasing the collection difficulty and increasing the wall thickness between the condenser and the refrigerant, thus reducing the heat transfer efficiency.

[0023] A tail gas treatment device must be installed after the condenser tower (7) to treat the uncondensed gas and prevent it from being directly discharged into the air and causing harm to the surrounding people or environment.

[0024] All equipment and pipelines through which gases pass during the reaction should ideally be made of corrosion-resistant materials such as PTFE, silicon carbide, Hastelloy, or glass to facilitate long-term use. Using stainless steel will generate ferric and ferrous ions, significantly impacting product yield.

[0025] Compared with the prior art, the technical solution of the present invention has the following beneficial effects: This invention improves the heat and mass transfer performance of the reaction process by introducing a microchannel reaction device into the preparation process of cyanogen chloride, thereby accelerating the reaction rate, enabling continuous production, and increasing the production capacity to a certain extent. At the same time, the introduction of the microchannel reaction device improves the safety of the preparation process. In addition, this invention provides suitable reaction condition parameters, which improves the reaction yield.

[0026] The above description is merely an overview of the technical solution of the present invention. In order to better understand the technical means of the present invention and to implement it in accordance with the contents of the specification, and to make the above and other objects, features and advantages of the present invention more apparent and understandable, the following detailed description is provided in conjunction with preferred embodiments. Attached Figure Description

[0027] To more clearly illustrate the technical solutions of the embodiments of the present invention, the accompanying drawings of the embodiments will be briefly described below.

[0028] Figure 1 This is a schematic diagram of the continuous flow reaction system of the microchannel reaction device for preparing cyanogen chloride as described in Example 1. The reaction system includes: a liquid phase channel (1), a mass flow meter (21), a gas phase channel (2), a chlorine flow meter (21), a microchannel reaction device (3), a gas-liquid separator (4), a washing tower (5), a flow cell (51), a pH meter (511), a washing liquid circulation pump (512), a drying tower (6), a condensing tower (7), and a product collection tank (71). Detailed Implementation

[0029] The following detailed description of specific embodiments of the present invention is part of this specification. The principles of the present invention are illustrated through examples, and other aspects, features and advantages of the present invention will become apparent from this detailed description.

[0030] Example 1 The reaction system includes: a liquid phase channel (1), a gas phase channel (2), a microchannel reaction device (3), a gas-liquid separator (4), a scrubbing tower (5), a drying tower (6), and a condensing tower (7).

[0031] The liquid phase channel (1) and the gas phase channel (2) are respectively connected to the liquid phase inlet and the gas phase inlet of the microchannel reaction device (3); after the outlet of the microchannel reaction device (3), the gas-liquid separator (4), the washing tower (5), the flow pool (51), the drying tower (6) and the condensing tower (7) are connected in sequence, and the product collection tank (71) is connected below the condensing tower (7).

[0032] The liquid phase channel (1) is circulated with a sodium cyanide aqueous solution of 15% by mass, and a mass flow meter is installed on the liquid phase channel (1) to provide feedback on the sodium cyanide solution flow rate; the gas phase channel (2) is circulated with chlorine gas, and a chlorine gas mass flow meter is installed on the gas phase channel (2) to provide feedback on the chlorine gas flow rate; the microchannel reaction device (3) has a characteristic dimension of 5mm, a liquid holding capacity of about 350ml, is made of silicon carbide, and has a cooling circulation system on its outside; the gas-liquid separator (4) has a 3L volume space at the bottom for temporarily storing the separated liquid. The washing tower (5) has an outer jacket for heating; the washing tower (5) is connected to a potassium carbonate spray circulation system, using an 8% mass concentration potassium carbonate solution, and the washing tower has an outer jacket for cooling; the washing tower (5) is connected to a flow tank (51), which is made of glass and contains a 0.1% mass concentration methyl orange indicator, and a pH meter (511) is installed below the indicator liquid surface; the drying tower (6) is filled with anhydrous calcium chloride as a desiccant; the condensing tower (7) is a tubular condensing tower with a heat exchange area of ​​1.5m². 2 The condensing medium is a mixture of ethylene glycol and water in a 1:1 volume ratio. The bottom of the condensing tower is connected to a product collection tank (71) with a jacket to ensure constant temperature. The final exhaust gas enters the tail gas scrubbing tower for treatment.

[0033] Before the reaction begins, the temperature control system is turned on, and the temperature of the microchannel reactor (3) is set to 5°C, the temperature of the gas-liquid separator (4) to 60°C, the temperature of the scrubbing tower (5) to 20°C, the temperature of the condensing tower (7) to -9°C, and the temperature of the collection tank (71) to -6°C. After the temperature reaches the set temperature, the potassium carbonate spray system of the scrubbing tower (5) is turned on, and then a sodium cyanide solution with a mass concentration of 15% is introduced from the liquid phase channel (1) to fill the pipe and microreactor. The flow rate is controlled at 9.75 kg / h. After 1 minute, chlorine gas is introduced from the gas phase channel (2), and the chlorine gas flow rate is adjusted to stabilize. When the gas-liquid molar ratio is stable, the chlorine gas flow rate is 2.12 kg / h. During the reaction, when the pH of the scrubbing liquid inside the scrubbing tower (5) is lower than 7 or the indicator in the flow tank (51) turns red, the scrubbing liquid is replaced. The reaction continues for 80 minutes. During the operation, the temperature of the microchannel reactor (3) gradually rises and eventually stabilizes, with a maximum temperature of 30°C. The final product was a colorless and transparent liquid, with a yield of 44.5% based on sodium cyanide.

[0034] The product is first tested for free chlorine using a colorimetric reaction, and then its purity is determined by titration. If the free chlorine test fails, the free chloride ions will affect the purity titration, making it impossible to accurately measure the product purity.

[0035] The method for detecting free chlorine is as follows: add 25 mL of deionized water to a 100 mL Erlenmeyer flask, then add 1 mL of a mixture of 10% KI and 0.5% starch indicator. Use a pipette to draw 0.2 mL of the product to be tested and place it into the Erlenmeyer flask. The solution is qualified if it is colorless.

[0036] The purity testing method is as follows: place the product to be tested at -10℃ and cool for 10 minutes; weigh a 50mL ground glass sampling bottle containing 25mL of 10% NaOH solution on a balance and then place it at -10℃ to cool for 3 minutes; use a pipette to draw 0.3mL of the cooled sample into the ground glass sampling bottle.

[0037] Allow the sample bottle containing the sample to equilibrate at room temperature for 3 minutes, carefully wipe off any moisture from the outside of the bottle, weigh it accurately, and calculate the sample mass.

[0038] Wash the sample from the sampling bottle into a 300mL Erlenmeyer flask, add 10mL of formaldehyde and 10mL of nitric acid, titrate with silver nitrate until obvious clumping occurs, then add excess silver nitrate (2-3)mL, then add 3mL of ammonium ferric sulfate indicator, and titrate with 0.1mol / L ammonium thiocyanate standard solution until the solution turns light red as the endpoint. The purity of the product is obtained by calculation.

[0039] The test results showed that the free chlorine content was within acceptable limits, and the product purity was 97.1%.

[0040] Example 2 The reaction equipment is the same as in Example 1.

[0041] Before the reaction begins, the temperature control system is turned on, and the temperature of the microreactor (3) is set to -5℃, the temperature of the gas-liquid separator (4) is set to 65℃, the washing tower (5) is not used for cooling, the temperature of the condenser (7) is set to -10℃, and the temperature of the collection tank (71) is set to -6℃. After the temperature reaches the set temperature, the potassium carbonate spray system of the washing tower (5) is turned on, and then a sodium cyanide solution with a mass concentration of 15% is introduced from the liquid phase channel (1) to fill the pipe and the microreactor. The flow rate is controlled at 9.0 kg / h. After 1 minute, chlorine gas is introduced from the gas phase channel (2), and the chlorine gas flow rate is adjusted to stabilize. When the gas-liquid molar ratio is stable, the chlorine gas flow rate is 2.37 kg / h. During the reaction, when the pH of the washing liquid inside the washing tower (5) is lower than 7 or the indicator in the flow tank (51) turns red, the washing liquid is replaced. The reaction continues for 120 minutes. During the operation, the temperature of the microreactor (3) gradually rises and eventually stabilizes, with a maximum temperature of 40℃. The final product was a colorless and transparent liquid with a purity of 96.1% and a yield of 55.2% based on sodium cyanide.

[0042] The methods for detecting the free chlorine and purity of the product are the same as in Example 1.

[0043] Example 3 The reaction equipment is the same as in Example 1.

[0044] Before the reaction begins, the temperature control system is turned on, and the temperature of the microreactor (3) is set to 20°C, the temperature of the gas-liquid separator (4) is set to 85°C, the cooling of the scrubbing tower (5) is not activated, the temperature of the condensing tower (7) is set to -16°C, and the temperature of the collection tank (71) is set to -6°C. After the temperature reaches the set temperature, the potassium carbonate spray system of the scrubbing tower (5) is turned on, and then a sodium cyanide solution with a mass concentration of 15% is introduced from the liquid phase channel (1) to fill the pipe and the microreactor. The flow rate is controlled at 6.5 kg / h. After 1 minute, chlorine gas is introduced from the gas phase channel (2), and the chlorine gas flow rate is adjusted to stabilize. When the gas-liquid molar ratio is stable, the chlorine gas flow rate is 1.2 and the chlorine gas flow rate is 1.34 kg / h. During the reaction, when the pH of the scrubbing liquid inside the scrubbing tower (5) is lower than 7 or the indicator in the flow tank (51) turns red, the scrubbing liquid is replaced. The reaction continues for 160 minutes. During the operation, the temperature of the microreactor (3) gradually rises and eventually stabilizes, with a maximum temperature of 60°C. The final product was a slightly yellow, transparent liquid with a purity of 95%; the yield, calculated based on sodium cyanide, was 39.3%.

[0045] The methods for detecting the free chlorine and purity of the product are the same as in Example 1.

[0046] All the raw materials listed in this invention, as well as the upper and lower limits and ranges of the raw materials and the upper and lower limits and ranges of the process parameters (such as temperature, time, etc.), can realize this invention. Examples are not listed one by one here.

[0047] The above description is merely a preferred embodiment of the present invention, and should not be construed as limiting the scope of the invention. It should be noted that those skilled in the art can make various improvements and modifications without departing from the principles of the present invention, and these improvements and modifications are also considered to be within the scope of protection of the present invention.

Claims

1. A method for preparing cyanogen chloride using a microchannel reactor in a continuous flow process, characterized in that: Under temperature control, NaCN solution and chlorine gas are introduced into a microchannel reactor to react, followed by gas-liquid separation, gas washing, drying, and condensation to obtain cyanogen chloride product.

2. The method for continuous flow preparation of cyanogen chloride based on a microchannel reactor as described in claim 1, characterized in that: The NaCN solution is an aqueous solution of sodium cyanide with a mass concentration of no more than 35%; the molar ratio of chlorine gas and sodium cyanide solid in the NaCN solution is 0.7~1.

5.

3. The method for continuous flow preparation of cyanogen chloride based on a microchannel reactor as described in claim 1, characterized in that: The microchannel reaction device has a characteristic size of 0.1~10mm and is made of highly corrosion-resistant materials, including but not limited to silicon carbide and Hastelloy. During the reaction, the reaction temperature in the microchannel reaction device is controlled to not exceed 50℃ and the reaction interval is not more than 5 minutes.

4. The method for continuous flow preparation of cyanogen chloride based on a microchannel reactor as described in claim 1, characterized in that: The gas-liquid separation process uses a gas-liquid separator. A portion of the space in the gas-liquid separator is used to temporarily store the separated waste liquid, or a separate container connected to the gas-liquid separator is provided for temporarily storing the separated waste liquid. A heating system is provided outside this portion of the space or the separate container for temporarily storing the waste liquid to control the temperature of the waste liquid at 40℃~80℃.

5. The method for continuous flow preparation of cyanogen chloride based on a microchannel reactor as described in claim 1, characterized in that: The gas washing process uses a carbonate solution as the washing liquid, with a solution mass concentration between 3% and 25%.

6. The method for continuous flow preparation of cyanogen chloride based on a microchannel reactor as described in claim 1, characterized in that: The condensation temperature is between -20°C and -6°C.

7. The method for continuous flow preparation of cyanogen chloride based on a microchannel reactor as described in claim 1, characterized in that: The carbonate solution is one of potassium carbonate solution, potassium bicarbonate solution, sodium carbonate solution, or sodium bicarbonate solution, or a mixture thereof.

8. The method for continuous flow preparation of cyanogen chloride based on a microchannel reactor as described in claim 1, characterized in that: The product is a colorless and transparent liquid with a yield of 25% to 60% based on sodium cyanide.

9. A continuous flow reaction system based on a microchannel reactor, characterized in that: It includes a liquid phase channel (1), a gas phase channel (2), a microchannel reaction device (3), a gas-liquid separator (4), a scrubbing tower (5), a drying tower (6), and a condensing tower (7). The liquid phase channel (1) and the gas phase channel (2) are respectively connected to the liquid phase inlet and the gas phase inlet of the microchannel reactor (3); the liquid phase inlet and the gas phase inlet of the microchannel reactor (3) converge inside the microreactor; after the outlet of the microchannel reactor (3), the gas-liquid separator (4), the washing tower (5), the drying tower (6) and the condensing tower (7) are connected in sequence, and a product collection tank (71) is set below the condensing tower; The drying tower (6) is filled with desiccant; a chlorine flow meter (11) is installed on the liquid phase channel (1), and a chlorine flow meter (21) is installed on the gas phase channel (2); A portion of the space in the gas-liquid separator (4) is used to temporarily store the separated waste liquid, or a separate container connected to the gas-liquid separator (4) is provided for temporarily storing the separated waste liquid. A heating system is provided outside this portion of the space or the separate container for temporarily storing the waste liquid to control the temperature. The scrubbing tower (5) is a spray tower, a bubble tower or a packed tower.

10. The continuous flow reaction system based on a microchannel reaction device as described in claim 9, characterized in that: A back pressure valve (31) may be installed between the microchannel reaction device (3) and the gas-liquid separator (4); a flow pool is provided between the washing tower (5) and the drying tower (6), which contains an acid-base indicator or a pH meter.

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