A method for recycling nitromethane tail gas

Abstract

The invention discloses a method for recycling nitromethane tail gas. The method comprises the steps of passing nitromethane tail gas into an isocyanate solution or passing nitromethane tail gas into a solvent and then adding isocyanate for treatment, and then recycling the absorption liquid. The method provided by the invention can not only efficiently treat nitromethane tail gas, reduce the cost of tail gas treatment, promote the healthy and sustainable development of the nitromethane production industry, but also generate added value and further improve the economic benefits of nitromethane production enterprises.

Description

Technical Field

[0001] The invention relates to the technical field of chemical processes, and in particular to a method for resource processing of nitromethane tail gas. Background Art

[0002] As a basic chemical raw material, nitromethane is widely used in the fields of medicine, pesticides, fuel (high-energy fuel additives), etc. Its production methods mainly include natural gas nitration method and nitrite replacement method (i.e., producing nitromethane by reacting nitrite with dimethyl sulfate). At present, the domestic industrial production of nitromethane mainly adopts the nitrite replacement method. Since the nucleophilic ability of the oxygen atom on the nitro group is similar to that of the nitrogen atom, in the process of producing nitromethane by the nitrite replacement method, a large amount of nitromethane isomers - methyl nitrite are inevitably generated. The yield of nitromethane in this production process is only 50-55% (He Youlin et al., Discussion on the reaction principle and tail gas treatment of nitromethane produced by nitrite, Chemical Engineering Design, 2002, 12 (4)). The reaction is shown in formula (II):

[0003]

[0004] Methyl nitrite is colorless and odorless. If it escapes into the air, it can easily cause poisoning. It also has a wide explosion limit and is flammable and explosive. With the continuous strengthening of national environmental awareness and the continuous strengthening of national environmental protection policies and environmental law enforcement, the scientific management of tail gas in nitromethane production has increasingly become a bottleneck affecting the sustainable and stable production and operation of enterprises and a key factor in improving the core competitiveness of enterprises. At present, nitromethane production tail gas is mainly treated by alkaline aqueous solution washing. This treatment method is due to the low solubility of methyl nitrite in water, the effective reaction amount of methyl nitrite and alkali is small, and the reaction rate is very low, resulting in a small amount of methyl nitrite that can actually be absorbed and reacted in this process. A large part of methyl nitrite is still discharged with the tail gas, causing nitromethane tail gas to produce a large amount of nitrogen oxides due to the decomposition of the methyl nitrite contained, which makes it difficult to meet the national emission standards for industrial waste gas nitrogen oxides, which is not conducive to environmental protection. Patent application CN109796345A discloses a method for comprehensive utilization of tail gas produced by nitromethane by nitrite replacement method, which includes passing tail gas into alcohol, then passing the alcohol solution into a reaction solution made of ethyl acetoacetate, alcohol and catalyst, and reacting at low temperature to obtain a pharmaceutical intermediate 2-nitrosoethyl acetoacetate. This method requires the use of a large amount of catalyst, and the low temperature condition of 5-15°C needs to be controlled during the reaction, which is costly and not conducive to industrial application. Summary of the invention

[0005] In order to overcome the deficiencies of the prior art, the present invention provides a method for resource processing of nitromethane tail gas and its application.

[0006] Specifically, the nitromethane tail gas involved in the method of the present invention contains methyl nitrite, and in particular refers to the tail gas produced by the nitrite replacement method for producing nitromethane, that is, the tail gas produced by preparing nitromethane by the reaction of nitrite and dimethyl sulfate.

[0007] Specifically, the above-mentioned nitrite is sodium nitrite or potassium nitrite.

[0008] In a first aspect of the present invention, a method for resource processing of nitromethane tail gas is provided, the method comprising the following steps:

[0009] (1) first dissolving the isothiocyanate in solvent I, then introducing nitromethane tail gas to absorb it, to obtain solution I; or first introducing nitromethane tail gas into solvent I to absorb it, then adding the isothiocyanate to obtain solution I;

[0010] (2) dissolving hydrazine hydrate and a base in solvent II to obtain solution II;

[0011] (3) mixing solution II and solution I, heating and refluxing to obtain solution III;

[0012] (4) adding acid to solution III;

[0013] (5) separating and purifying the product after the reaction in step (4).

[0014] Specifically, the isothiocyanate structure is shown in formula (I):

[0015]

[0016] Wherein, R1 is selected from any one of alkyl, hydroxyalkyl, aryl, and disubstituted aminoalkyl;

[0017] Preferably, the alkyl group is selected from C 1-4 Alkyl, more preferably, is selected from methyl or ethyl;

[0018] Preferably, the hydroxyalkyl group is selected from hydroxymethyl or hydroxyethyl;

[0019] Preferably, the aryl group is a phenyl group;

[0020] Preferably, the disubstituted aminoalkyl group is dimethylaminoethyl.

[0021] In some embodiments of the invention, the isothiocyanate is methyl isothiocyanate, ethyl isothiocyanate, phenyl isothiocyanate, hydroxymethyl isothiocyanate, or hydroxyethyl isothiocyanate.

[0022] Specifically, the solvent I in step (1) is preferably methanol or ethanol, more preferably ethanol.

[0023] Specifically, the solvent II in step (2) is preferably methanol or ethanol, more preferably ethanol.

[0024] Specifically, the base in step (2) is a strong base, preferably sodium hydroxide or potassium hydroxide.

[0025] Specifically, in step (3), solution II and solution I are mixed, such as by slowly dripping solution II into solution I.

[0026] Specifically, the heating reflux time in step (3) can be 0.5-3 hours, and those skilled in the art can make appropriate adjustments according to actual conditions, and the present invention does not make any specific limitations.

[0027] Specifically, the acid in step (4) is an inorganic acid, preferably concentrated hydrochloric acid or concentrated sulfuric acid.

[0028] Specifically, after adding the acid in step (4), the solution becomes acidic, such as pH=1, pH=2, etc.

[0029] Specifically, the amounts of isothiocyanate and hydrazine hydrate can be adjusted according to the content of methyl nitrite in the nitromethane tail gas.

[0030] Specifically, in the method of the present invention, the isothiocyanate can be directly used as a corresponding commercial product, or can be prepared according to a method known in the prior art.

[0031] In a specific embodiment, the operation of introducing tail gas in step (1) can be carried out in an absorption tower; subsequently, the obtained solution I is transferred into a reaction container, and then solution II is slowly added dropwise thereto. After the addition is completed, heating and reflux are performed.

[0032] Specifically, the absorption process of nitromethane tail gas in step (1) is carried out under pressurized conditions. Pressurization can accelerate the absorption rate of nitromethane tail gas, and the specific pressure can be adjusted according to the amount of nitromethane tail gas, such as adding 0.5-1 MPa of atmospheric pressure to the absorption container.

[0033] Specifically, the absorption process of nitromethane tail gas in step (1) can be carried out at a conventional production environment temperature, and the tail gas treatment temperature is not particularly limited.

[0034] Specifically, in step (1), according to the amount of nitromethane tail gas, when the absorption is completed and the nitrogen oxide emission standard is met, the tail gas treatment process is terminated. The specific reaction time is not limited. If industrial production continues, the nitromethane tail gas is continuously treated, and the isocyanate solution or solvent I can be replaced as needed.

[0035] In a specific embodiment, the reaction process of the nitromethane tail gas resource treatment method is as follows:

[0036]

[0037] In a second aspect of the present invention, there is provided application of the method described in the first aspect in the treatment of nitromethane tail gas.

[0038] In the third aspect of the present invention, a method for preparing 1-substituted-5-mercapto-tetrazolyl is provided.

[0039] Specifically, the product separated and purified in step (5) is 1-substituted-5-mercapto-tetrazolyl, the structure of which is In particular, 1-methyl-5-mercapto-tetrazolyl has the structure 1-Phenyl-5-mercapto-tetrazolyl 1-Hydroxymethyl-5-mercapto-tetrazolyl 1-Hydroxyethyl-5-mercapto-tetrazolyl 1-(2-Dimethylaminoethyl)-1H-5-mercapto-tetrazolyl

[0040] Tetrazol compounds are widely used as organic synthesis intermediates in the fields of medicine, energetic materials, agriculture, preparation of coordination polymers, solid catalysts, photosensitive materials, etc. In some embodiments of the present invention, examples of 1-substituted-5-mercapto-tetrazolyl are 1-methyl-5-mercapto-tetrazolyl, 1-phenyl-5-mercapto-tetrazolyl, 1-hydroxymethyl-5-mercapto-tetrazolyl, 1-hydroxyethyl-5-mercapto-tetrazolyl, etc. and their salts, which can be used as important pharmaceutical intermediates, such as for the synthesis and preparation of cephalosporin drugs, especially 1-methyl-5-mercapto-tetrazolyl, which is an important raw material for a variety of third, fourth and fifth generation cephalosporin antibiotics, and is mainly used as an intermediate for more than ten cephalosporin drugs such as cefoperazone sodium, cefmandole, cefmenoxime hydrochloride, cefmetazole, cefotetan, cefpiramide, and cefadroxil; 1-phenyl-5-mercapto-tetrazolyl can be used as an electroplating additive, a photographic antifogging agent, a stabilizer for electronic chemicals, etc. With the popularity of cephalosporin antibiotics, the demand for 1-methyl-5-mercapto-tetrazolyl will increase. For example, 1-phenyl-5-mercapto-tetrazolyl is used as an intermediate for statins.

[0041] Therefore, the nitromethane tail gas resource treatment method of the present invention can not only efficiently treat nitromethane tail gas, reduce the tail gas treatment cost, solve the environmental protection problems that restrict the long-term development of enterprises, promote the healthy and sustainable development of the nitromethane production industry, and form an industrial chain between chemical production and pharmaceutical processing, but also use waste gas resources to produce high value-added products such as 1-substituted-5-mercapto-tetrazole, especially 1-methyl-5-mercapto-tetrazole, 1-phenyl-5-mercapto-tetrazole, etc., in addition to filling the gap in the pharmaceutical market, but also can further improve the economic benefits of nitromethane production enterprises.

[0042] In a fourth aspect of the present invention, there is provided application of the method described in the first aspect in the preparation of 1-substituted-5-mercapto-tetrazole or its salt using nitromethane tail gas.

[0043] Specifically, the 1-substituted-5-mercapto-tetrazolyl has the structure of the above-mentioned general formula (III) of the present invention, especially 1-methyl-5-mercapto-tetrazolyl, 1-phenyl-5-mercapto-tetrazolyl, 1-hydroxymethyl-5-mercapto-tetrazolyl, and 1-hydroxyethyl-5-mercapto-tetrazolyl.

[0044] Specifically, the salt of 1-substituted-5-mercapto-tetrazole may be an alkali metal salt thereof, such as 1-substituted-5-mercapto-tetrazole potassium salt, 1-substituted-5-mercapto-tetrazole sodium salt and the like.

[0045] In a fifth aspect of the present invention, a method for preparing a cephalosporin antibiotic compound or a pharmaceutically acceptable salt thereof is provided, comprising the following steps:

[0046] (1) first dissolving the isothiocyanate in solvent I, then passing nitromethane tail gas into it for absorption, to obtain solution I; or first passing nitromethane tail gas into solvent I for absorption, then adding the isothiocyanate, to obtain solution I;

[0047] (2) dissolving hydrazine hydrate and a base in solvent II to obtain solution II;

[0048] (3) mixing solution II and solution I, heating and refluxing to obtain solution III;

[0049] (4) adding acid to solution III;

[0050] (5) separating and purifying the product after the reaction in step (4) to obtain 1-substituted-5-mercapto-tetrazole;

[0051] (6) Using the obtained product 1-substituted-5-mercapto-tetrazolyl to synthesize a cephalosporin antibiotic compound or a pharmaceutically acceptable salt thereof.

[0052] Specifically, the conditions of steps (1)-(5) are as described in the first and third aspects of the present invention.

[0053] In some embodiments of the present invention, cefmenoxime hydrochloride can be prepared using 1-methyl-5-mercapto-tetrazolyl prepared by the present invention with reference to "Li Aijun, Zhou Xueqin, Li Wei, et al. Synthesis of cefmenoxime hydrochloride [J]. Chinese Journal of Antibiotics, 2005, 30 (3)".

[0054] Specifically, the above-mentioned cephalosporin antibiotic compound can be selected from: any one of cefoperazone, cefmenoxime, cefmandole, cefuroxime, ammonia cephalosporin, cefadroxil, hydroxypyraclostrobin, cefazolin, ceftriaxone, cefmetazole, cefotetan, cefpiramide, iodine cephalosporin, benzopyran cephalosporin, naphthyridine cephalosporin, etc.

[0055] In a sixth aspect of the present invention, there is provided use of nitromethane tail gas in medicine and synthesis using the method described in the fifth aspect, specifically, for example, in the synthesis of cephalosporin antibiotic compounds or pharmaceutically acceptable salts thereof.

[0056] Beneficial Effects

[0057] 1. The method for resource recovery of nitromethane tail gas provided by the present invention can efficiently treat nitromethane tail gas, reduce the cost of tail gas treatment, solve the problem of rapid purification and absorption of nitromethane tail gas in the prior art, reduce the emission of nitrogen oxides in the tail gas, and is beneficial to environmental protection.

[0058] 2. The present invention promotes the healthy and sustainable development of the nitromethane production industry, and can also generate added value, further improving the economic benefits of nitromethane production enterprises. The nitromethane tail gas resource treatment method of the present invention has a simple process, reduces the investment in tail gas treatment, and reduces production costs.

[0059] 3. The present invention obtains the pharmaceutical intermediate 1-substituted-5-mercapto-tetrazolyl by absorbing nitromethane tail gas, which can be used as an important intermediate for producing cephalosporins, statins and other drugs, and is widely used in the pharmaceutical industry. This method solves the problem of using the absorption liquid, meets the needs of the pharmaceutical industry, and avoids waste of resources. The comprehensive utilization method of tail gas of the present invention realizes efficient co-production, is easy to industrialize, and will be conducive to the development of the green industrial chain. DETAILED DESCRIPTION

[0060] Unless otherwise defined, all scientific and technical terms used in the present invention have the same meanings as commonly understood by one of ordinary skill in the art to which the present invention relates.

[0061]

[00136] Various publications, patents, and published patent specifications are cited herein, the disclosures of which are incorporated by reference in their entireties.

[0062] 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 only 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.

[0063] Example 1

[0064] (1) dissolving 14.6 g (0.2 mol) of methyl isothiocyanate in 80 g of anhydrous ethanol to obtain solution A;

[0065] (2) Transfer solution A to a laboratory micro-absorption tower, start the absorption tower circulation pump, and pass the nitromethane tail gas produced by the nitrite replacement method into the absorption tower at a flow rate of 0.1 L / min for absorption. When the weight of solution A no longer increases, stop passing the tail gas, and transfer the resulting solution I to a reaction bottle;

[0066] (3) Dissolve 12.5 g (0.2 mol) of 80% hydrazine hydrate and 13.2 g (0.2 mol) of 85% KOH in 90 g of anhydrous ethanol to obtain solution II;

[0067] (4) Slowly drip solution II into solution I, heat to 75°C and reflux for 1 h to obtain solution III;

[0068] (5) Solution III was cooled, concentrated hydrochloric acid was added dropwise until pH = 2, and the by-product potassium chloride was removed by filtration. The filtrate was evaporated and concentrated, and then cooled to precipitate crystals. The filter cake was filtered and dried to obtain the product 1-methyl-5-mercaptotetrazole with a purity of 99.6% and a yield of 85.1%.

[0069] This embodiment is different from the conventional treatment of three wastes in which the target product is precipitated as crystals, which easily generates new wastewater. In this embodiment, the by-product potassium chloride is precipitated as crystals, and the resource-recyclable product is present in the filtrate. The filtrate is evaporated and concentrated to recover the solvent and by-product methanol, and then cooled and crystallized to obtain the target product. Almost no secondary waste liquid is generated, which is a new breakthrough in solving the bottleneck problem of nitromethane tail gas emissions in a completely green and environmentally friendly way.

[0070] Example 2

[0071] (1) dissolving 14.6 g (0.2 mol) of methyl isothiocyanate in 80 g of anhydrous methanol to obtain solution A;

[0072] (2) Transfer solution A to a laboratory micro-absorption tower, start the absorption tower circulation pump, and pass the nitromethane tail gas produced by the nitrite replacement method into the absorption tower at a flow rate of 0.1 L / min for absorption. When the weight of solution A no longer increases, stop passing the tail gas, and transfer the resulting solution I to a reaction bottle;

[0073] (3) Dissolve 12.5 g (0.2 mol) of 80% hydrazine hydrate and 13.2 g (0.2 mol) of 85% KOH in 90 g of anhydrous methanol to obtain solution II;

[0074] (4) Solution II was slowly dripped into solution I and heated to 75°C and refluxed for 1 h to obtain solution III;

[0075] (5) Solution III was cooled, hydrochloric acid was added dropwise until pH = 2, the by-product potassium chloride was removed by filtration, the filtrate was evaporated and concentrated, the temperature was lowered to precipitate crystals, and the filter cake was dried to obtain 1-methyl-5-mercaptotetrazole with a purity of 99.1% and a yield of 82.3%.

[0076] Example 3

[0077] (1) dissolving 14.6 g (0.2 mol) of methyl isothiocyanate in 80 g of anhydrous ethanol to obtain solution A;

[0078] (2) Transfer solution A to a laboratory micro-absorption tower, start the absorption tower circulation pump, and pass the nitromethane tail gas produced by the nitrite replacement method into the absorption tower at a flow rate of 0.1 L / min for absorption, increase the atmospheric pressure by 0.5 MPa, accelerate the absorption of the nitromethane tail gas, and stop passing the tail gas when the weight of solution A no longer increases, and transfer the resulting solution I to a reaction bottle;

[0079] (3) Dissolve 12.5 g (0.2 mol) of 80% hydrazine hydrate and 13.2 g (0.2 mol) of 85% KOH in 90 g of anhydrous ethanol to obtain solution II;

[0080] (4) Solution II was slowly dripped into solution I and heated to 75°C and refluxed for 1 h to obtain solution III;

[0081] (5) Solution III was cooled, hydrochloric acid was added dropwise until pH = 2, the by-product potassium chloride was removed by filtration, the filtrate was evaporated and concentrated, the temperature was lowered to precipitate crystals, and 1-methyl-5-mercaptotetrazole was obtained by filtration and drying. The purity was 99.7% and the yield was 86.2%.

[0082] Example 4

[0083] (1) 80 g of anhydrous ethanol was placed in a laboratory micro-absorption tower, and the circulation pump of the absorption tower was turned on. The nitromethane tail gas produced by the nitrite replacement method was passed into the absorption tower at a flow rate of 1 L / min for absorption, and the atmospheric pressure was increased by 1 MPa. When the weight of solution A no longer increased, the tail gas was stopped, and the absorption solution A was transferred to a reaction bottle;

[0084] (2) Dissolve 14.6 g (0.2 mol) of methyl isothiocyanate in absorption liquid A to obtain solution I;

[0085] (3) Dissolve 12.5 g (0.2 mol) of 80% hydrazine hydrate and 13.2 g (0.2 mol) of 85% KOH in 90 g of anhydrous ethanol to obtain solution II;

[0086] (4) Solution I was slowly dripped into solution II and heated to 75°C and refluxed for 1 h to obtain solution III;

[0087] (5) Solution III was cooled, hydrochloric acid was added dropwise until the pH value was less than 2, the by-product potassium chloride was removed by filtration, the filtrate was evaporated and concentrated, the temperature was lowered to precipitate crystals, and 1-methyl-5-mercaptotetrazole was obtained by filtration and drying. The purity was 99.6% and the yield was 85.0%.

[0088] Example 5

[0089] (1) dissolving 20.6 g of hydroxyethyl isothiocyanate in 80 g of anhydrous ethanol to obtain solution A;

[0090] (2) Transfer solution A to a laboratory micro-absorption tower, start the absorption tower circulation pump, and pass the nitromethane tail gas produced by the nitrite replacement method into the absorption tower at a flow rate of 0.1 L / min for absorption. When the weight of solution A no longer increases, stop passing the tail gas, and transfer the resulting solution I to a reaction bottle;

[0091] (3) Dissolve 12.5 g (0.2 mol) of 80% hydrazine hydrate and 9.4 g (0.2 mol) of 85% NaOH in 90 g of anhydrous ethanol to obtain solution II;

[0092] (4) Solution II was slowly dripped into solution I and heated to 70°C and refluxed for 2 h to obtain solution III;

[0093] (5) Solution III was cooled, concentrated sulfuric acid was added dropwise until the pH value was less than 2, and after evaporation and concentration, anhydrous ethanol was added, and the by-products were removed by filtration. The filtrate was evaporated and concentrated, cooled, and crystals were precipitated. The crystals were filtered and dried to obtain 1-hydroxyethyl-5-mercaptotetrazole with a purity of 99.6% and a yield of 83.4%.

[0094] Example 6

[0095] (1) 80 g of anhydrous ethanol was transferred into a laboratory micro-absorption tower, and the circulation pump of the absorption tower was turned on. The nitromethane tail gas produced by the nitrite replacement method was passed into the absorption tower at a flow rate of 0.5 L / min for absorption, and an atmospheric pressure of 1 MPa was added. When the weight no longer increased, the tail gas was stopped, and the resulting solution I was transferred into a reaction bottle;

[0096] (2) Dissolve 27.0 g (0.2 mol) of phenyl isothiocyanate in solution I;

[0097] (3) Dissolve 12.5 g (0.2 mol) of 80% hydrazine hydrate and 9.4 g (0.2 mol) of 85% NaOH in 90 g of anhydrous ethanol to obtain solution II;

[0098] (4) Solution II was slowly dripped into solution I and heated to 70°C and refluxed for 1 h to obtain solution III;

[0099] (5) Solution III was cooled, concentrated sulfuric acid was added dropwise until pH = 1, and after evaporation and concentration, anhydrous ethanol was added, and by-products were removed by filtration. The filtrate was evaporated and concentrated, cooled, and crystals were precipitated. 1-phenyl-5-mercaptotetrazole was obtained by filtration and drying. The purity was 99.3% and the yield was 82.7%.

[0100] Example 7

[0101] (1) dissolving 26.0 g (0.2 mol) of 2-dimethylaminoethyl isothiocyanate in 80 g of anhydrous ethanol to obtain solution A;

[0102] (2) Transfer solution A to a laboratory micro-absorption tower, start the absorption tower circulation pump, and pass the nitromethane tail gas produced by the nitrite replacement method into the absorption tower at a flow rate of 0.1 L / min for absorption. When the weight of solution A no longer increases, stop passing the tail gas, and transfer the resulting solution I to a reaction bottle;

[0103] (3) Dissolve 12.5 g (0.2 mol) of 80% hydrazine hydrate and 9.4 g (0.2 mol) of 85% NaOH in 90 g of anhydrous ethanol to obtain solution II;

[0104] (4) Solution I was slowly dripped into solution II and heated to 80°C and refluxed for 2 h to obtain solution III;

[0105] (5) Solution III was cooled, concentrated sulfuric acid was added dropwise until pH = 1, and after evaporation and concentration, anhydrous ethanol was added, and by-products were removed by filtration. The filtrate was evaporated and concentrated, cooled, and crystals were precipitated. 1-(2-dimethylaminoethyl)-5-mercapto-tetrazole was obtained by filtration and drying. The purity was 99.5% and the yield was 84.4%.

[0106] The concentration of nitrogen oxides in the treated tail gas of Examples 1-7 is all 50 mg / m 3 the following.

[0107] Comparative Example 1

[0108] The six-stage alkaline solution absorption treatment of nitromethane production tail gas was used as a comparison. The nitromethane tail gas was purified by passing through two-stage pH=10 sodium hydroxide, two-stage pH=11 sodium hydroxide, and two-stage pH=12 sodium hydroxide aqueous solution absorption devices at a flow rate of 0.1L / min. The nitrogen oxide concentration in the treated tail gas was measured to be 433.2mg / m 3 (GB16297-1996 Air Pollutant Comprehensive Emission Standard, emission concentration limit 240mg / m 3 ).

[0109] Comparative Example 2

[0110] The same as Example 1, except that the nitromethane tail gas is introduced into the absorption tower at a flow rate of 5 L / min. The gas flow rate is too fast and cannot be completely absorbed, escaping to the external environment, which easily leads to excessively high concentrations of nitrogen oxide emissions.

[0111] Comparative Example 3

[0112] The same as Example 1, except that the nitromethane tail gas is introduced into the absorption tower at a flow rate of 0.05 L / min. The gas flow rate is too slow, and the absorption time is excessively prolonged, which cannot meet the actual production demand for tail gas treatment.

[0113] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, etc. made within the spirit and principle of the present invention should be included in the protection scope of the present invention.

[0114] The aforementioned embodiments and methods described in the present invention may be varied based on the ability, experience and preference of those skilled in the art.

[0115] In the present invention, merely listing the steps of the method in a certain order does not constitute any limitation on the order of the method steps.

Claims

1. A method for recycling nitromethane tail gas, comprising the following steps: (1) first dissolving the isothiocyanate in solvent I, then passing nitromethane tail gas into the solvent I for absorption, thereby obtaining solution I; or first passing nitromethane tail gas into solvent I for absorption, then adding the isothiocyanate, thereby obtaining solution I; (2) dissolving hydrazine hydrate and a base in solvent II to obtain solution II; (3) Mixing solution I and solution II, heating and refluxing to obtain solution III; (4) Adding acid to solution III; (5) separating and purifying the product after the reaction in step (4); The solvent I in step (1) is selected from methanol or ethanol; The solvent II in step (2) is selected from methanol or ethanol; In step (1), the flow rate of nitromethane tail gas into solvent I is 0.1-1.0 L / min; The base in step (2) is sodium hydroxide or potassium hydroxide; The acid in step (4) is concentrated hydrochloric acid or concentrated sulfuric acid; The isothiocyanate is methyl isothiocyanate, ethyl isothiocyanate, phenyl isothiocyanate, hydroxymethyl isothiocyanate or hydroxyethyl isothiocyanate; The nitromethane tail gas is nitromethane tail gas containing methyl nitrite.

2. The method according to claim 1, characterized in that The absorption process of nitromethane tail gas in step (1) is carried out under pressurized conditions.

3. The method according to claim 1, characterized in that The solvent I in step (1) is ethanol; The solvent II in step (2) is ethanol.

4. The method according to any one of claims 1 to 3, characterized in that: The nitromethane tail gas is the tail gas produced by the reaction of dimethyl sulfate and nitrite to produce nitromethane.

5. Application of the method according to any one of claims 1 to 4 in the treatment of nitromethane tail gas.

Images