Tail gas absorption system in production process of methyl cyanamide formate

Abstract

The invention relates to the technical field of pesticide compound production tail gas treatment, in particular to a tail gas absorption system in a methyl cyanamide formate production process, which comprises a tail gas collection pipeline, a pretreatment unit, a deep purification unit and a detection device, wherein the pretreatment unit comprises a dust removal tower and is used for cooling and removing dust from tail gas; the deep purification unit comprises an absorption tower, and the absorption tower is made of stainless steel, PPH or glass fiber reinforced plastic and is used for purifying tail gas and treating toxic and harmful substances in the waste gas; and the detection device is used for monitoring tail gas emission indexes in real time to ensure up-to-standard emission. According to the technical scheme, the tail gas generated in the production process of the methyl cyanamide formate can be quickly and effectively adsorbed and purified, and the tail gas adsorbent has efficient adsorption performance, large adsorption capacity and excellent selectivity.

Description

Technical Field

[0001] The invention relates to the technical field of tail gas treatment in pesticide compound production, and in particular to a tail gas absorption system in a methyl cyanamide formate production process. Background Art

[0002] Methyl cyanamide formate (CAS No.: 21729-98-6), with the chemical formula C3H4N2O2, is an important organic compound widely used in the fields of pesticides and fine chemicals. Methyl cyanamide formate is an important intermediate in the synthesis of fungicides carbendazim and benomyl. At present, the production technology of methyl cyanamide formate mainly includes the first filtration method and the second filtration method. The second filtration method is to use the Ca(OH)2 produced by the preparation of calcium hydrogen cyanamide from lime nitrogen and water without filtering it first, but directly add it to methyl chloroformate as a deacidifying agent to produce methyl cyanamide formate, and then filter it. The first filtration method is to filter and separate the residue after the calcium hydrogen cyanamide solution is prepared by hydrolysis of lime nitrogen, and then react the calcium hydrogen cyanamide solution with methyl chloroformate in the presence of sodium hydroxide to produce methyl cyanamide formate. Both methods will generate a large amount of waste gas, the waste gas components of which mainly include incompletely reacted raw materials (such as methyl chloroformate, ammonia, etc.), by-products (such as carbon dioxide, cyanamide, etc.) and a small amount of toxic and harmful substances (such as cyanide, etc.).

[0003] In the prior art, alkaline solutions such as sodium hydroxide solutions are usually used as absorption liquids to absorb tail gas. However, high-temperature tail gas can cause its solutes to exceed the solubility limit, or certain substances in the tail gas react with the alkaline solution, resulting in a large amount of solid crystals in the absorption tower, clogging pipes, nozzles and other components inside the equipment, reducing the efficiency of tail gas treatment, and corroding the material of the equipment. In addition, once crystals are formed, it is often difficult to remove them by simple physical methods, and the equipment needs to be shut down for cleaning, which increases production costs. At the same time, the content of each component in the tail gas is different, and it is difficult to adsorb a single alkaline solution, resulting in poor tail gas purification effect. Summary of the invention

[0004] In order to solve the problems mentioned in the above background technology, the present invention provides a tail gas absorption system in the production process of methyl cyanamide formate.

[0005] In order to achieve the above object, the present invention adopts the following technical solutions:

[0006] A tail gas absorption system in a cyanamide methyl formate production process, comprising: 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 pipeline is used, with an interface height of 8000-10000mm. The pipeline can automatically rise to more than 1900mm when not in use to avoid collision with vehicles and operators;

[0008] The pre-treatment unit includes a dust removal tower, which is used to cool and remove dust from the tail gas to reduce the load of 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 exhaust gas;

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

[0011] Leak detection devices and necessary safety facilities are also provided.

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

[0013] Furthermore, the absorption tower is filled with filling particles and adsorbents, the filling particles are placed at the bottom of the absorption tower, and the adsorbent is placed on the upper layer of the filling 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, and is used to automatically adjust the working parameters of the pretreatment unit and the deep purification unit according to the real-time monitoring data of the detection device to optimize the exhaust gas treatment effect.

[0016] Furthermore, at least one flow regulating valve is provided on the tail gas collection pipeline to control the flow of the tail gas.

[0017] Further, the filling particles include one or more of activated carbon, zeolite, bentonite, medical stone, vermiculite, sepiolite, alumina and ceramic particles.

[0018] Further, the adsorbent comprises the following steps to prepare:

[0019] S1. First add the alkaline ion exchange resin into deionized water, soak for 5-10 min, then add into ethanol, soak for 12-24 h, and obtain the alkaline ion exchange resin suspension for standby use;

[0020] S2, dispersing mesoporous silica in ethanol, adding a mercaptosilane coupling agent at a stirring speed of 200-300 rpm, reacting at 60-70° C. for 2-8 hours, filtering to remove the mercaptosilane coupling agent, adding cyclodextrin, reacting at 40-60° C. for 2-8 hours, filtering, washing, and drying to obtain cyclodextrin-modified mercapto-modified mesoporous silica;

[0021] S3. Add the thiolated mesoporous silica modified with cyclodextrin into the alkaline ion exchange resin suspension, stir at a speed of 400-600 rpm for 20-30 min, filter, and dry at 60-80° C. to constant weight to obtain an adsorbent.

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

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

[0024] Furthermore, 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 mercapto-modified mesoporous silica and alkaline ion exchange resin suspension is (10-15):(20-30).

[0025] Furthermore, the alkaline ion exchange resin includes a primary amine type ion exchange resin, a secondary amine type ion exchange resin, a tertiary amine type ion exchange resin or a 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 present invention has the following beneficial effects:

[0027] 1. The adsorbent prepared by this technical solution has adsorption performance and stability. It acts on harmful substances in the tail gas of the methyl cyanamide production process through physical adsorption, chemical adsorption and ion exchange, and purifies the tail gas at one time. When the toxic and harmful molecules in the tail gas pass through the adsorbent, they are first captured and fixed in the cavity of cyclodextrin. The thiolated mesoporous silica fixed in the cavity reacts chemically with the incompletely reacted raw materials, by-products, etc. in the tail gas to form covalent bonds, such as thiol bonds or thioester bonds. In addition, the thiol reaction is stronger than physical adsorption. Even if the concentration of the compound in the tail gas is very low, the thiolated mesoporous silica can effectively capture and fix it.

[0028] 2. Both alkaline ion exchange resin and mesoporous silica have high specific surface area, providing a large amount of surface area for adsorption, thereby enhancing the physical adsorption capacity and capturing harmful substances in tail gas through physical adsorption. For acidic gases, alkaline ion exchange resin can provide alkaline ions for exchange, thereby enhancing the adsorption capacity of acidic gases.

[0029] 3. This technical solution can quickly and effectively adsorb and purify the tail gas generated by the production process of methyl cyanamide formate, has efficient adsorption performance, and also has a large adsorption capacity and excellent selectivity. DETAILED DESCRIPTION

[0030] The technical solution of the present invention will be clearly and completely described below in conjunction with the embodiments of the present invention. Obviously, the described embodiments are part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

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

[0032] Preparation Example 1

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

[0034] S1, add 10kg of primary amine type ion exchange resin into 10kg of deionized water, soak for 5min, then add into 10kg of ethanol, soak for 12h, and obtain a primary amine type ion exchange resin suspension for standby use;

[0035] S2, dispersing 10 kg of mesoporous silica in 30 kg of anhydrous ethanol, adding 1 kg of silane coupling agent KH-590 at a stirring speed of 200 rpm, reacting at 60° C. for 2 h, filtering to remove the silane coupling agent KH-590, adding 5 kg of cyclodextrin, reacting at 40° C. for 2 h, filtering, washing, and drying at 60° C. to constant weight to obtain cyclodextrin-modified thiolated mesoporous silica;

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

[0037] Preparation Example 2

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

[0039] S1, add 10kg of primary amine type ion exchange resin into 10kg of deionized water, soak for 10min, then add into 10kg of ethanol, soak for 18h, and obtain a primary amine type ion exchange resin suspension for standby use;

[0040] S2, dispersing 12 kg of mesoporous silica in 30 kg of anhydrous ethanol, adding 2 kg of silane coupling agent KH-590 at a stirring speed of 250 rpm, reacting at 65 ° C for 5 hours, filtering to remove the silane coupling agent KH-590, adding 6.5 kg of cyclodextrin, reacting at 50 ° C for 5 hours, filtering, washing, and drying at 60 ° C to constant weight to obtain cyclodextrin-modified thiolated mesoporous silica;

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

[0042] Preparation Example 3

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

[0044] S1, add 10kg of primary amine type ion exchange resin into 10kg of deionized water, soak for 10min, then add into 10kg of ethanol, soak for 24h, and obtain a primary amine type ion exchange resin suspension for standby use;

[0045] S2, dispersing 15 kg of mesoporous silica in 30 kg of anhydrous ethanol, adding 3 kg of silane coupling agent KH-590 at a stirring speed of 300 rpm, reacting at 70° C. for 8 h, filtering to remove the silane coupling agent KH-590, adding 8 kg of cyclodextrin, reacting at 60° C. for 8 h, filtering, washing, and drying at 60° C. to constant weight to obtain cyclodextrin-modified thiolated mesoporous silica;

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

[0047] Example 1

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

[0049] The tail gas collection pipeline 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 of the tail gas;

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

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

[0052] The deep purification unit comprises an absorption tower, the tower body is made of PPH, the absorption tower is filled with activated carbon, zeolite and bentonite as filling particles, which are placed at the bottom of the tower, and the adsorbent prepared in Preparation Example 1 is placed on the upper layer;

[0053] The detection device includes two gas sensors, which are used to detect toxic gases and combustible gases in the exhaust gas, respectively, and 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 adopts PLC (Programmable Logic Controller), which is connected with the pretreatment unit, deep purification unit and detection device. According to the real-time monitoring data of the detection device, the control system automatically adjusts the working parameters of the pretreatment unit and the deep purification unit.

[0055] Example 2

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

[0057] Example 3

[0058] The difference between this embodiment and embodiment 1 is that the adsorbent prepared in preparation example 3 is used, and the rest is the same as embodiment 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, and the rest 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, and 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 primary amine type ion exchange resin is used as the adsorbent, and the rest is the same as 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, and the rest is the same as Example 3.

[0067] The waste gas produced by our factory on a certain day was 0.0187t, and the specific content is shown in Table 1:

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

[0069]

[0070]

[0071] After the system treatment of Example 1, the contents are 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 (except nitrogen) 3.58 Particles 1.24 Other substances 75.01

[0074] The treated tail gas was collected and tested according to GB 37823-2019 "Pharmaceutical Industry Air Pollutant Emission Standards" to see if the tail gas met the standards. The results are shown in Table 3:

[0075] Table 3. Atmospheric pollutant indicators of treated waste gas

[0076] Pollutant Name <![CDATA[Mass concentration (mg / m 3 )]]> Particles 8.45 NMHC 19.17 TVOC 27.54 Benzene 1.20 Phosgene 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] The waste gas generated in the factory on a certain day was collected again, randomly divided into four parts, and then treated by the systems of Comparative Examples 1-4 respectively. The results are shown in Table 4:

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

[0079]

[0080] Comparative Example 1 uses 30% sodium hydroxide solution as an adsorbent, which has a certain removal effect on acidic substances (such as methyl chloroformate and methyl cyanamide formate) in the waste gas, but the overall effect is not as good as the adsorbent in the embodiment. Comparative Example 2 uses only mesoporous silica as an adsorbent, and the adsorption effect is not as good as the adsorbent in the embodiment, which may be because although mesoporous silica has a certain adsorption capacity, it lacks synergistic effects with other components. Comparative Example 3 uses only primary amine type ion exchange resin as an adsorbent, which may be because the primary amine type 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 uses only cyclodextrin as an adsorbent, and the effect is not ideal. Although cyclodextrin has certain adsorption and inclusion capabilities, it has limited treatment effects on waste gas in the production process of methyl cyanamide formate when used alone.

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

[0082] In the description of the specification, the description with reference to the terms "preparation example", "embodiment", "various embodiments" and the like means that the specific features, structures, materials or characteristics described in conjunction with the embodiment or preparation example are included in at least one embodiment or preparation example of the present invention. In this specification, the schematic representation of the above terms does not necessarily refer to the same embodiment or preparation example. Moreover, the specific features, structures, materials or characteristics described can be combined in any one or more embodiments or preparation examples in a suitable manner.

[0083] The above description is only a preferred specific implementation manner of the present invention, but the protection scope of the present invention is not limited thereto. Any technician familiar with the technical field can make equivalent replacements or changes according to the technical scheme and inventive concept of the present invention within the technical scope disclosed by the present invention, which should be covered by the protection scope of the present invention.

Claims

1. A tail gas absorption system in a cyanamide methyl formate production process, characterized in that: include: Tail gas collection pipeline, pretreatment unit, deep purification unit and detection device; The pre-treatment unit includes a dust removal tower for cooling and dust removal of the tail 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 treat the toxic and harmful substances in the exhaust gas; The detection device is used to monitor exhaust emission indicators in real time to ensure that emissions meet standards.

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

3. A tail gas absorption system in a cyanamide methyl formate production process according to claim 1, characterized in that: The absorption tower is filled with filling particles and adsorbents. The filling particles are placed at the bottom of the absorption tower, and the adsorbent is placed on the upper layer of the filling particles.

4. A tail gas absorption system in a cyanamide methyl formate production process 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.

5. A tail gas absorption system in a cyanamide methyl formate production process 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, and is used to automatically adjust the working parameters of the pretreatment unit and the deep purification unit according to the real-time monitoring data of the detection device to optimize the exhaust gas treatment effect.

6. The tail gas absorption system in a cyanamide methyl formate production process according to claim 1, characterized in that: At least one flow regulating valve is provided on the tail gas collection pipeline to control the flow of the tail gas.

7. The tail gas absorption system in a cyanamide methyl formate production process according to claim 3, characterized in that: The filler particles include one or more of activated carbon, zeolite, bentonite, medical stone, vermiculite, sepiolite, alumina and ceramic particles.

8. The tail gas absorption system in a cyanamide methyl formate production process according to claim 3, characterized in that: The adsorbent is prepared by the following steps: S1. First add the alkaline ion exchange resin into deionized water, soak for 5-10 min, then add into ethanol, soak for 12-24 h, and obtain the alkaline ion exchange resin suspension for standby use; S2, dispersing mesoporous silica in ethanol, adding a mercaptosilane coupling agent at a stirring speed of 200-300 rpm, reacting at 60-70° C. for 2-8 hours, filtering to remove the mercaptosilane coupling agent, adding cyclodextrin, reacting at 40-60° C. for 2-8 hours, filtering, washing, and drying to obtain cyclodextrin-modified mercapto-modified mesoporous silica; S3. Add the thiolated mesoporous silica modified with cyclodextrin into the alkaline ion exchange resin suspension, stir at a speed of 400-600 rpm for 20-30 min, filter, and dry at 60-80° C. to constant weight to obtain an adsorbent.

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

10. The tail gas absorption system in the production process of methyl cyanamide formate according to claim 8, characterized in that: The basic ion exchange resin includes a primary amine type ion exchange resin, a secondary amine type ion exchange resin, a tertiary amine type ion exchange resin or a quaternary ammonium type ion exchange resin, and the mercaptosilane coupling agent includes 3-mercaptopropyltrimethoxysilane or 3-mercaptopropyltriethoxysilane.

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