A tail gas absorption system in a methyl cyanomethyl carbamate production process

Abstract

The present application relates to the technical field of tail gas treatment of pesticide compound production, and particularly relates to a tail gas absorption system in cyanamide methyl formate production process, comprising: a tail gas collecting pipeline, a pretreatment unit, a deep purification unit and a detection device; wherein the pretreatment unit comprises a dust removal tower for cooling and dedusting the tail gas; the deep purification unit comprises an absorption tower made of stainless steel, PPH or glass steel, which is used for purifying the tail gas and treating toxic and harmful substances in the waste gas; the detection device is used for real-time monitoring of tail gas emission indexes to ensure standard emission. The technical scheme can quickly and effectively adsorb and purify the tail gas generated in the cyanamide methyl formate production process, has high adsorption performance, and also has large adsorption capacity and excellent selectivity.

Description

Technical Field

[0001] This invention relates to the field of pesticide compound production tail gas treatment technology, and in particular to a tail gas absorption system in the production process of methyl cyanamide. Background Technology

[0002] Methyl cyanamide (CAS No.: 21729-98-6), with the chemical formula C3H4N2O2, is an important organic compound widely used in pesticides and fine chemicals. Methyl cyanamide is a crucial intermediate in the synthesis of fungicides such as carbendazim and benomyl. Currently, methyl cyanamide production technologies mainly include pre-filtration and post-filtration methods. In the post-filtration method, Ca(OH)2, generated during the production of cyanamide hydrazine from calcium cyanamide and water, is not filtered first; instead, it is directly added to methyl chloroformate as a deacidifying agent to produce methyl cyanamide, followed by filtration. In the pre-filtration method, after the cyanamide hydrazine solution is hydrolyzed to produce cyanamide hydrazine, the residue is first filtered to separate it. Then, the cyanamide hydrazine solution reacts with methyl chloroformate in the presence of sodium hydroxide to generate methyl cyanamide. Both methods generate a large amount of waste gas, which mainly consists of unreacted raw materials (such as methyl chloroformate, ammonia, etc.), byproducts (such as carbon dioxide, cyanamide, etc.), and small amounts of toxic and harmful substances (such as cyanide, etc.).

[0003] In existing technologies, alkaline solutions such as sodium hydroxide solution are commonly used as absorbents to absorb exhaust gases. However, high-temperature exhaust gases can cause the solute to exceed its solubility limit, or certain substances in the exhaust gas may react with the alkaline solution, resulting in the formation of a large amount of solid crystals inside the absorption tower. This can clog internal pipes, nozzles, and other components, reducing exhaust gas treatment efficiency and corroding the equipment materials. Furthermore, once crystals form, they are often difficult to remove using simple physical methods, requiring shutdown for cleaning, which increases production costs. Additionally, the varying composition of the exhaust gas makes adsorption by a single alkaline solution challenging, leading to poor exhaust gas purification effects. Summary of the Invention

[0004] To address the problems mentioned in the background section, this invention provides a tail gas absorption system for the production process of methyl cyanamide.

[0005] To achieve the above objectives, the present invention adopts the following technical solution:

[0006] A tail gas absorption system in the production process of methyl cyanamide includes: a tail gas collection pipeline, a pretreatment unit, a deep purification unit, and a detection device;

[0007] Among them, a high-altitude circular reciprocating exhaust gas collection pipe is adopted, with an interface height of 8000-10000mm. When not in use, the pipe can automatically rise to more than 1900mm to avoid collision with vehicles and operators.

[0008] The pretreatment unit includes a dust removal tower, which is used to cool and remove dust from the exhaust gas to reduce the load on the absorption tower and improve the treatment efficiency.

[0009] The deep purification unit includes an absorption tower, which is made of PPH material or fiberglass material, and is used to purify the exhaust gas and treat the toxic and harmful substances in the waste gas.

[0010] The detection device is used to monitor exhaust emission indicators in real time to ensure that emissions meet standards;

[0011] It is also equipped with leak detection devices and necessary safety facilities.

[0012] Furthermore, the dust removal tower is equipped with a cooling device and a dust filter. The cooling device is used to reduce the temperature of the exhaust gas to room temperature, and the dust filter uses a 50-300 mesh screen to capture solid particles in the exhaust gas.

[0013] Furthermore, the absorption tower is filled with packing particles and adsorbent, with the packing particles placed at the bottom of the absorption tower and the adsorbent placed on top of the packing particles.

[0014] Furthermore, the detection device includes at least one gas sensor and at least one temperature sensor or humidity sensor.

[0015] Furthermore, it also includes a control system, which is connected to the pretreatment unit, the deep purification unit, and the detection device. The control system is used to automatically adjust the operating parameters of the pretreatment unit and the deep purification unit based on the real-time monitoring data of the detection device in order to optimize the exhaust gas treatment effect.

[0016] Furthermore, at least one flow regulating valve is installed on the exhaust gas collection pipe to control the flow rate of the exhaust gas.

[0017] Furthermore, the filler particles include one or more of activated carbon, zeolite, bentonite, maifanite, vermiculite, sepiolite, alumina, and ceramic particles.

[0018] Furthermore, the adsorbent is prepared by the following steps:

[0019] S1. First, add the alkaline ion exchange resin to deionized water and soak for 5-10 minutes, then add it to ethanol and soak for 12-24 hours to obtain an alkaline ion exchange resin suspension for later use.

[0020] S2. Disperse mesoporous silica in ethanol, add mercaptosilane coupling agent while stirring at 200-300 rpm, react at 60-70℃ for 2-8 h, filter to remove mercaptosilane coupling agent, add cyclodextrin, react at 40-60℃ for 2-8 h, filter, wash, and dry to obtain cyclodextrin-modified mercaptoized mesoporous silica.

[0021] S3. Add the cyclodextrin-modified thiolized mesoporous silica to the alkaline ion exchange resin suspension, stir at 400-600 rpm for 20-30 min, filter, and dry at 60-80℃ to constant weight to obtain the adsorbent.

[0022] The mesoporous silica was prepared by using tetraethyl orthosilicate (TEOS) as the silicon source, hexadecyltrimethylammonium bromide (CTAB) as the template agent, and ammonia as the catalyst.

[0023] The adsorbent can be reused after being washed alternately with deionized water and ethanol 1-10 times.

[0024] Further, in step S2, the mass ratio of mesoporous silica, mercaptosilane coupling agent, and cyclodextrin is (10-15):(1-3):(5-8), and in step S3, the mass ratio of cyclodextrin-modified mercaptoized mesoporous silica to alkaline ion exchange resin suspension is (10-15):(20-30).

[0025] Furthermore, the basic ion exchange resin includes primary amine type ion exchange resin, secondary amine type ion exchange resin, tertiary amine type ion exchange resin or quaternary ammonium type ion exchange resin, and the mercaptosilane coupling agent includes 3-mercaptopropyltrimethoxysilane (silane coupling agent KH-590) or 3-mercaptopropyltriethoxysilane (silane coupling agent KH-580).

[0026] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0027] 1. The adsorbent prepared by this technical solution possesses adsorption performance and stability. It acts on harmful substances in the tail gas of methyl cyanurate production process through a combination of physical adsorption, chemical adsorption, and ion exchange, purifying the tail gas in one step. When toxic and harmful molecules in the tail gas pass through the adsorbent, they are first captured and fixed within the cyclodextrin cavity. The fixed thiolized mesoporous silica in the cavity then reacts chemically with unreacted raw materials and byproducts in the tail gas, forming covalent bonds, such as thiol bonds or thioester bonds. Furthermore, the thiolization reaction is stronger than physical adsorption; even if the concentration of compounds in the tail gas is very low, the thiolized mesoporous silica can effectively capture and fix them.

[0028] 2. Both basic ion exchange resins and mesoporous silica have high specific surface areas, providing ample surface space for adsorption, thereby enhancing physical adsorption capacity and capturing harmful substances in exhaust gases through physical adsorption. For acidic gases, basic ion exchange resins can provide basic ions for exchange, thus enhancing the adsorption capacity for acidic gases.

[0029] 3. This technical solution can rapidly and effectively adsorb and purify the tail gas generated in the production process of methyl cyanamide, and has high adsorption performance, large adsorption capacity and excellent selectivity. Detailed Implementation

[0030] The technical solution of the present invention will be clearly and completely described below with reference to the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0031] Unless otherwise specified, the raw materials used in this invention are all from commercially available conventional products, and the cyclodextrin is γ-cyclodextrin.

[0032] Preparation Example 1

[0033] The adsorbent is prepared by the following steps:

[0034] S1. First, add 10 kg of primary amine ion exchange resin to 10 kg of deionized water and soak for 5 min. Then add 10 kg of ethanol and soak for 12 h to obtain a suspension of primary amine ion exchange resin for later use.

[0035] S2. Disperse 10 kg of mesoporous silica in 30 kg of anhydrous ethanol. Add 1 kg of silane coupling agent KH-590 while stirring at 200 rpm. React at 60 °C for 2 h. Filter to remove silane coupling agent KH-590. Add 5 kg of cyclodextrin. React at 40 °C for 2 h. Filter, wash, and dry at 60 °C to constant weight to obtain cyclodextrin-modified thiolized mesoporous silica.

[0036] S3. Add 10 kg of cyclodextrin-modified thiolized mesoporous silica to 20 kg of primary amine ion exchange resin suspension, stir at 400 rpm for 20 min, filter, and dry at 60 °C to constant weight to obtain the adsorbent.

[0037] Preparation Example 2

[0038] The adsorbent is prepared by the following steps:

[0039] S1. First, add 10 kg of primary amine ion exchange resin to 10 kg of deionized water and soak for 10 min. Then add 10 kg of ethanol and soak for 18 h to obtain a suspension of primary amine ion exchange resin for later use.

[0040] S2. 12 kg of mesoporous silica was dispersed in 30 kg of anhydrous ethanol. 2 kg of silane coupling agent KH-590 was added while stirring at 250 rpm. The mixture was reacted at 65 °C for 5 h. The silane coupling agent KH-590 was removed by filtration. 6.5 kg of cyclodextrin was added and the mixture was reacted at 50 °C for 5 h. The mixture was then filtered, washed, and dried at 60 °C to constant weight to obtain cyclodextrin-modified thiolized mesoporous silica.

[0041] S3. Add 12 kg of cyclodextrin-modified thiolized mesoporous silica to 25 kg of primary amine ion exchange resin suspension, stir at 500 rpm for 25 min, filter, and dry at 70 °C to constant weight to obtain the adsorbent.

[0042] Preparation Example 3

[0043] The adsorbent is prepared by the following steps:

[0044] S1. First, add 10 kg of primary amine ion exchange resin to 10 kg of deionized water and soak for 10 min. Then add 10 kg of ethanol and soak for 24 h to obtain a suspension of primary amine ion exchange resin for later use.

[0045] S2. 15 kg of mesoporous silica was dispersed in 30 kg of anhydrous ethanol. 3 kg of silane coupling agent KH-590 was added while stirring at 300 rpm. The mixture was reacted at 70 °C for 8 h. The silane coupling agent KH-590 was removed by filtration. 8 kg of cyclodextrin was added and the mixture was reacted at 60 °C for 8 h. The mixture was then filtered, washed, and dried at 60 °C to constant weight to obtain cyclodextrin-modified thiolized mesoporous silica.

[0046] S3. Add 15 kg of cyclodextrin-modified thiolized mesoporous silica to 30 kg of primary amine ion exchange resin suspension, stir at 600 rpm for 30 min, filter, and dry at 80 °C to constant weight to obtain the adsorbent.

[0047] Example 1

[0048] A tail gas absorption system for the production process of methyl cyanamide includes a tail gas collection pipeline, a pretreatment unit, a deep purification unit, a detection device, and a control system.

[0049] The exhaust gas collection pipe is made of stainless steel and is equipped with two flow regulating valves, located before the inlet of the pretreatment unit and the inlet of the deep purification unit, respectively, to control the flow rate of the exhaust gas.

[0050] The pretreatment unit includes a dust collection tower, the tower body of which is made of stainless steel;

[0051] The dust removal tower is equipped with a cooling device, which uses a cooling water circulation system to reduce the exhaust gas temperature to room temperature. The dust removal filter screen uses a 200-mesh screen.

[0052] The deep purification unit includes an absorption tower made of PPH material. The absorption tower is filled with activated carbon, zeolite and bentonite as packing particles and placed at the bottom of the tower. The adsorbent prepared in Preparation Example 1 is placed on the upper layer.

[0053] The detection device includes two types of gas sensors, which are used to detect toxic gases and combustible gases in the exhaust gas, respectively. It also includes a temperature sensor and a humidity sensor to monitor the temperature and humidity of the exhaust gas in real time.

[0054] The control system uses a PLC (Programmable Logic Controller) and is connected to the pretreatment unit, the deep purification unit, and the detection device. Based on the real-time monitoring data from the detection device, the control system automatically adjusts the operating parameters of the pretreatment unit and the deep purification unit.

[0055] Example 2

[0056] The difference between this embodiment and Example 1 is that the adsorbent prepared in Example 2 is used, while the rest is the same as in Example 1.

[0057] Example 3

[0058] The difference between this embodiment and Example 1 is that the adsorbent prepared in Example 3 is used, while the rest is the same as in Example 1.

[0059] Comparative Example 1

[0060] The difference between this comparative example and Example 1 is that only 30% sodium hydroxide solution is used as the adsorbent; otherwise, it is the same as Example 1.

[0061] Comparative Example 2

[0062] The difference between this comparative example and Example 2 is that only mesoporous silica is used as the adsorbent, while the rest is the same as Example 2.

[0063] Comparative Example 3

[0064] The difference between this comparative example and Example 3 is that only a primary amine ion exchange resin is used as the adsorbent; otherwise, they are the same as in Example 3.

[0065] Comparative Example 4

[0066] The difference between this comparative example and Example 3 is that only cyclodextrin is used as the adsorbent, while the rest is the same as Example 3.

[0067] On a certain day, our factory generated 0.0187 tons of waste gas, the specific contents of which are shown in Table 1.

[0068] Table 1. Content of various substances in exhaust gas

[0069]

[0070]

[0071] After systematic processing in Example 1, the contents were obtained as shown in Table 2:

[0072] Table 2. Content of various substances in the treated waste gas

[0073] name content(%) Methyl chloroformate 0.58 carbon dioxide 18.24 Acetylene 0.07 cyanamide 0.01 Methyl cyanamide 1.28 Nitrogen-containing substances (excluding nitrogen gas) 3.58 Particulate matter 1.24 Other substances 75.01

[0074] The treated exhaust gas was collected and tested to determine whether it met the standards according to GB 37823-2019 "Emission Standard of Air Pollutants for Pharmaceutical Industry". The results are shown in Table 3.

[0075] Table 3. Air pollutant indicators of treated exhaust gas

[0076] Pollutant Name <![CDATA[Mass concentration (mg / m 3 )]]> Particulate matter 8.45 NMHC 19.17 TVOC 27.54 benzene series compounds 1.20 Phosphorus Not detected hydrogen cyanide 0.81 benzene 0.36 formaldehyde 0.05 chlorine 0.27 hydrogen chloride 10.56 hydrogen sulfide Not detected ammonia 11.25

[0077] Waste gas generated by the factory on a certain day was collected again, randomly divided into four portions, and then treated using the systems of comparative examples 1-4 respectively. The results are shown in Table 4:

[0078] Table 4. Content (%) of various substances in the exhaust gas before and after treatment in Comparative Examples 1-4

[0079]

[0080] Comparing Tables 1-4, Comparative Example 1, using a 30% sodium hydroxide solution as an adsorbent, showed some removal effect on acidic substances (such as methyl chloroformate and methyl cyanamide) in the waste gas, but its overall effect was not as good as the adsorbent in the examples. Comparative Example 2, using only mesoporous silica as an adsorbent, also showed a less effective adsorption than the adsorbent in the examples, possibly because while mesoporous silica has a certain adsorption capacity, it lacks synergistic effects with other components. Comparative Example 3, using only primary amine ion exchange resin as an adsorbent, may be because primary amine ion exchange resin has limited adsorption capacity for certain substances and needs to be used in combination with other components to achieve the best effect. Comparative Example 4, using only cyclodextrin as an adsorbent, also showed unsatisfactory results. Although cyclodextrin has certain adsorption and inclusion capabilities, its effect on treating waste gas from the methyl cyanamide production process is limited when used alone.

[0081] In summary, the adsorbent in the embodiments effectively removes harmful substances from the exhaust gas through the synergistic effect of physical and chemical adsorption.

[0082] In the description of this specification, the terms "preparation example," "example," "various examples," etc., refer to specific features, structures, materials, or characteristics described in connection with that example or preparation example, which are included in at least one example or preparation example of the present invention. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same example or preparation example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more examples or preparation examples.

[0083] The above description is only a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any equivalent substitutions or modifications made by those skilled in the art within the scope of the technology disclosed in the present invention, based on the technical solution and inventive concept of the present invention, should be covered within the scope of protection of the present invention.

Claims

1. A tail gas absorption system in the production process of methyl cyanurate, characterized in that, include: Exhaust gas collection pipe, pretreatment unit, deep purification unit and detection device; The pretreatment unit includes a dust removal tower, which is used to cool and remove dust from the exhaust gas. The deep purification unit includes an absorption tower, which is made of stainless steel, PPH or fiberglass, and is used to purify the exhaust gas and remove toxic and harmful substances from the waste gas. The detection device is used to monitor exhaust emission indicators in real time to ensure that emissions meet standards; The absorption tower is filled with packing particles and adsorbent. The packing particles are placed at the bottom of the absorption tower, and the adsorbent is placed on top of the packing particles. The adsorbent is prepared by the following steps: S1. First, add the alkaline ion exchange resin to deionized water and soak for 5-10 minutes, then add it to ethanol and soak for 12-24 hours to obtain an alkaline ion exchange resin suspension for later use. S2. Disperse mesoporous silica in ethanol, add mercaptosilane coupling agent while stirring at 200-300 rpm, react at 60-70℃ for 2-8 h, filter to remove mercaptosilane coupling agent, add cyclodextrin, react at 40-60℃ for 2-8 h, filter, wash, and dry to obtain cyclodextrin-modified mercaptoized mesoporous silica. S3. Add the cyclodextrin-modified thiolized mesoporous silica to the alkaline ion exchange resin suspension, stir at 400-600 rpm for 20-30 min, filter, and dry at 60-80℃ to constant weight to obtain the adsorbent.

2. The tail gas absorption system in the production process of methyl cyanurate according to claim 1, characterized in that, The dust removal tower is equipped with a cooling device and a dust filter. The cooling device is used to reduce the temperature of the exhaust gas to room temperature, and the dust filter uses a 50-300 mesh screen to capture solid particles in the exhaust gas.

3. The tail gas absorption system in the production process of methyl cyanurate according to claim 1, characterized in that, The detection device includes at least one gas sensor and at least one temperature sensor or humidity sensor.

4. The tail gas absorption system in the production process of methyl cyanurate according to claim 1, characterized in that, It also includes a control system, which is connected to the pretreatment unit, the deep purification unit, and the detection device. The control system is used to automatically adjust the operating parameters of the pretreatment unit and the deep purification unit based on the real-time monitoring data of the detection device in order to optimize the exhaust gas treatment effect.

5. The tail gas absorption system in the production process of methyl cyanurate according to claim 1, characterized in that, At least one flow regulating valve is installed on the exhaust gas collection pipe to control the flow rate of the exhaust gas.

6. The tail gas absorption system in the production process of methyl cyanurate according to claim 1, characterized in that, The filler particles include one or more of activated carbon, zeolite, bentonite, maifanite, vermiculite, sepiolite, alumina, and ceramic particles.

7. The tail gas absorption system in the production process of methyl cyanurate according to claim 1, characterized in that, In step S2, the mass ratio of mesoporous silica, mercaptosilane coupling agent, and cyclodextrin is (10-15):(1-3):(5-8). In step S3, the mass ratio of cyclodextrin-modified mercaptoized mesoporous silica to alkaline ion exchange resin suspension is (10-15):(20-30).

8. The tail gas absorption system in the production process of methyl cyanurate according to claim 1, characterized in that, Basic ion exchange resins include primary amine type ion exchange resins, secondary amine type ion exchange resins, tertiary amine type ion exchange resins, or quaternary ammonium type ion exchange resins, and mercaptosilane coupling agents include 3-mercaptopropyltrimethoxysilane or 3-mercaptopropyltriethoxysilane.

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