Synthesis method of 2-cyanopyridine

Abstract

The invention discloses a synthesis method of 2-cyanopyridine, and belongs to the field of chemical engineering. According to the method, 2-picoline and ammonia are gasified, air is introduced, a catalyst is used for ammoxidation reaction, a combined three-stage spraying absorption tower is adopted, gas obtained after ammoxidation reaction is subjected to three-time absorption through a sulfuric acid solution, two-time extraction is conducted through benzene, washing and replacement are conducted through water, the absorption rate of the product 2-cyanopyridine is maximized, and the yield of the product 2-cyanopyridine is increased. The product yield reaches 90% or above; meanwhile, the absorption amount of the ammonia gas is greatly increased, so that the ammonia gas in the reaction gas is efficiently recovered, the content of the ammonia gas in the treated tail gas is lower than 50mg / m < 3 >, the discharged tail gas is clean, and the pollution to the atmosphere is reduced. And since the salt formed by the reaction of the sulfuric acid and the ammonia gas is relatively stable, the solution absorbed once can be continuously recycled, no sewage is discharged, and the cost is saved.

Description

Technical Field

[0001] The invention relates to a synthesis method of 2-cyanopyridine and belongs to the field of chemical industry. Background Art

[0002] 2-Cyanopyridine, also known as 2-pyridinecarbonitrile, is an organic compound with a molecular weight of 104.11, a melting point of 26-28°C, and a density of 1.081 g / mL. It is white to pale yellow crystals at low temperatures, insoluble in water, but soluble in strong polar organic solvents such as dimethyl sulfoxide. 2-Cyanopyridine has significant alkalinity and can react with acidic substances to form salts, such as sulfates and hydrochlorides. 2-Cyanopyridine is an important pharmaceutical and pesticide intermediate with low toxicity, low residues in soil and plants, and a short residual period. 2-Cyanopyridine can also be used to synthesize chromium picolinate, which has been applied to the aquaculture industry and has achieved relatively ideal application effects and economic benefits.

[0003] There are two main methods for producing 2-cyanopyridine. The first method is to introduce a cyano group at the 2nd position of pyridine: halogen, especially bromine or fluorine, is substituted in polar solvents such as dimethyl sulfoxide or dimethylformamide. Many of these cyanation processes use heavy metal reagents containing copper or nickel and polar reagents that are difficult to recover, producing toxic waste liquids; and this method has cumbersome steps and low product yield, which has defects in industrial production.

[0004] The second method is to use 2-methylpyridine to prepare through ammonia oxidation reaction: 2-methylpyridine is vaporized and mixed with ammonia and air, reacted under the action of a catalyst, and then the 2-cyanopyridine product obtained by absorption, extraction and distillation is absorbed; this method uses sulfuric acid for neutralization reaction and uses benzene for extraction. This method will produce volatile organic compounds (VOCs) during the reaction process, and the recovery effect of ammonia used in the reaction is also poor, so there is a certain environmental pollution problem.

[0005] Patent CN101602720A reports a method for synthesizing 2-cyanopyridine, wherein 2-methylpyridine is vaporized and mixed with ammonia and air, reacted in the presence of a catalyst, and then absorbed, extracted and distilled to obtain a 2-cyanopyridine product. The conversion rate of 2-methylpyridine is about 97%, and the yield of 2-cyanopyridine is about 84%, both of which are not ideal. Patent CN104356061A describes a method for efficiently absorbing 2-cyanopyridine, wherein high-pressure fine water mist is used as an absorbent to cool and absorb the mixed gas at a temperature of 200-230°C after the ammoxidation reaction and preliminary cooling, thereby inhibiting the hydrolysis of the product 2-cyanopyridine and improving the absorption efficiency of 2-cyanopyridine. However, the water absorption, extraction and separation effect is not good, and the water used in the high-pressure fine water mist is pure water, which is used once and not directly recycled, and will produce more waste water and waste.

[0006] In summary, the conventional method for preparing 2-cyanopyridine by ammoxidation reaction has the problems of poor ammonia recovery, low water absorption extraction and separation efficiency, low yield of product 2-cyanopyridine, waste water waste, VOCs waste gas pollution and environmental pollution. Summary of the invention

[0007] In order to solve the above technical problems, the present invention provides a method for efficiently absorbing 2-cyanopyridine. The present invention adopts a combined three-stage spray absorption tower, uses sulfuric acid solution to extract and absorb the ammonia-containing reaction gas, and finally uses water for washing and replacement. On the one hand, the present invention maximizes the absorption rate of 2-cyanopyridine through three absorptions, and the product yield reaches more than 90%; on the other hand, the present invention greatly increases the absorption amount of ammonia, so that the ammonia in the ammonia-containing reaction gas is efficiently recovered, and the VOC content of the tail gas after treatment is less than 50mg / m 3 , reducing pollution to the atmosphere; because the salt formed by the reaction of sulfuric acid and ammonia is relatively stable, the solution absorbed once can be recycled and no sewage is discharged, which not only saves costs but also solves the problem of waste water waste. The exhaust gas discharged after treatment is clean, which is beneficial to environmental protection.

[0008] The present invention provides a method for efficiently absorbing 2-cyanopyridine, which comprises the steps of:

[0009] (1) Primary absorption and extraction:

[0010] The reaction gas after the ammoxidation reaction is introduced from the top of the high-efficiency absorber, and the sulfuric acid solution is sprayed at the bottom of the high-efficiency absorber to make the reaction gas and the sulfuric acid solution fully contact, and the sulfuric acid solution absorbs the reaction gas in the first stage to obtain an absorption liquid, which is extracted with benzene to obtain a 2-cyanopyridine organic phase 1 and an ammonium sulfate mother liquor;

[0011] (2) Secondary absorption:

[0012] The remaining reaction gas and ammonium sulfate mother liquor in step (1) are introduced into the lower part of the absorption tower together, and gas-liquid separation is performed through the gas-liquid separator at the lower part of the absorption tower, and the ammonium sulfate mother liquor is retained at the bottom of the absorption tower. The reaction gas ascends from the lower part of the absorption tower into the packing layer in the middle part of the absorption tower, and the ammonium sulfate mother liquor collected from the bottom of the absorption tower is transported to the liquid distributor in the middle part of the absorption tower by the secondary circulating liquid absorption pump outside the absorption tower, and is sprayed, and the reaction gas is absorbed at the secondary level;

[0013] (3) Tertiary absorption:

[0014] After the secondary absorption in step (2), the reaction gas continues to ascend to the upper part of the absorption tower, is evenly distributed through the gas distributor at the upper part of the absorption tower, and is then washed by water spraying. The reaction gas is absorbed in the tertiary stage to obtain a washing liquid. The tail gas after the tertiary absorption is discharged from the chimney at the top of the absorption tower.

[0015] (4) Circulating spray washing reaction gas:

[0016] The washing liquid after water spray washing in step (3) flows back to the absorption tower by gravity, and is transported to the upper part of the absorption tower by the third-stage circulating liquid absorption pump to circulate and wash the reaction gas from the second-stage absorption; part of the washing liquid in the upper part of the absorption tower overflows to the middle of the absorption tower, dilutes the ammonium sulfate mother liquor in the middle of the absorption tower, and the diluted dilute ammonium sulfate mother liquor is circulated to the liquid distributor in the middle of the absorption tower to continue spraying the reaction gas from the first-stage absorption, and part of the dilute ammonium sulfate mother liquor in the middle of the absorption tower overflows to the bottom of the absorption tower;

[0017] (5) Secondary extraction and preparation of 2-cyanopyridine organic phase:

[0018] After the ammonium sulfate in the ammonium sulfate mother liquor at the bottom of the absorption tower reaches a certain mass concentration, it is extracted twice with benzene to obtain raffinate water and 2-cyanopyridine organic phase 2, and the 2-cyanopyridine organic phase 1 obtained in step (1) is combined, and benzene is recovered to obtain a 2-cyanopyridine organic phase;

[0019] (6) Preparation of ammonium sulfate by-product and 2-cyanopyridine product:

[0020] The raffinate water from the secondary extraction in step (5) is transported to an evaporative crystallizer, decolorized by activated carbon and subjected to triple-effect evaporation, the raffinate water is concentrated, cooled and crystallized to obtain ammonium sulfate by-product; the 2-cyanopyridine organic phase prepared in step (5) is continuously distilled to finally obtain a 2-cyanopyridine product.

[0021] In one embodiment of the present invention, the ammoxidation reaction in step (1) is as follows: 2-methylpyridine and ammonia are introduced into a fixed bed reactor containing a catalyst, and air is introduced so that the molar ratio of 2-methylpyridine, ammonia and air is 1: (50-60): (250-300), and an ammoxidation reaction is carried out to obtain a reaction gas.

[0022] In one embodiment of the present invention, the ammoxidation reaction temperature is 340-380°C; preferably, the reaction temperature is 360°C.

[0023] In one embodiment of the present invention, the catalyst is prepared by: 2 O 5 and magnesium oxide-zinc additives are added to water and stirred, oxalic acid and ammonium molybdate are added, the temperature is raised and stirred to obtain a viscous yellow solid; the solid is dried and calcined to obtain a catalyst for preparing 2-cyanopyridine by catalytic ammoxidation;

[0024] The preparation method of the magnesium oxide-zinc additive is as follows: Mg(NO 3 ) 2 6H 2 O、Zn(NO 3 ) 2 6H 2 O and water are stirred and mixed to obtain a mixture; ammonia water and ammonium bicarbonate are added, and the magnesium oxide-zinc additive is obtained through ultrasonication, filtration, drying and sieving.

[0025] In one embodiment of the present invention, Mg(NO 3 ) 2 6H 2 O、Zn(NO 3 ) 2 6H 2 The mass ratio of O, water, ammonia water and ammonium bicarbonate is (25-30):(20-55):(100-150):(2.0-5.0):(5.0-10).

[0026] In one embodiment of the present invention, titanium dioxide, V 2 O 5 The addition ratio of magnesium oxide-zinc additive, water, oxalic acid and ammonium molybdate is (180-220g):(25-35g):(3-7g):(950-1050mL):(2-3g):(1-3g).

[0027] In one embodiment of the present invention, the preparation method of the catalyst is:

[0028] Preparation of magnesium oxide-zinc additive: At room temperature 25°C, 28.3 g of Mg(NO 3 ) 2 6H 2 O and 23.3 g of Zn(NO 3 ) 2 6H 2O and 130g of water were stirred for 30min, then 3.4g of ammonia water and 8.5g of ammonium bicarbonate were added as precipitants, ultrasonicated at 70KHz for 55min, vacuum filtered, then dried at 106°C for 10h, and ball milled to obtain magnesium oxide-zinc additive (particle size 60-80μm);

[0029] At room temperature 25°C, 202.6 g of titanium dioxide and 30.2 g of vanadium oxide V 2 O 5 5.2 g of the above-mentioned magnesium oxide-zinc additive and 1000 mL of deionized water were added to a three-necked flask, stirred at 200 r / min for 2 h, and after stirring, 2.5 g of oxalic acid and 2.0 g of ammonium molybdate were added, the temperature was raised to 54 ° C and stirred at 230 r / min for 17 h to obtain a viscous yellow solid;

[0030] The obtained viscous yellow solid is dried at 60°C for 2 hours, and then extruded using an extruder to obtain a columnar embryo with a diameter of 4 to 5 mm; the obtained columnar embryo is dried at 100°C for 4 hours, calcined at 570°C in a muffle furnace for 16 hours, and after cooling, the catalyst can be prepared.

[0031] In one embodiment of the present invention, the reaction gas is introduced at a rate of 550 to 650 L / h in step (1); preferably, the introduction rate is 600 L / h.

[0032] In one embodiment of the present invention, the concentration of the sulfuric acid solution in step (1) is 50% to 80% (v / v).

[0033] In one embodiment of the present invention, the injection rate of the sulfuric acid solution in step (1) is 15 to 22 L / h; preferably, the injection rate of the sulfuric acid solution is 20 L / h.

[0034] In one embodiment of the present invention, the pH of the absorption liquid in step (1) is 8-9.

[0035] In one embodiment of the present invention, the mass concentration of ammonium sulfate in the ammonium sulfate mother liquor in step (1) is 10% to 14%.

[0036] In one embodiment of the present invention, the packing layer in step (2) uses ball ring packing.

[0037] In one embodiment of the present invention, the spraying amount of water in step (3) is 1 to 5 L / h; preferably, the spraying amount of water is 2 L / h.

[0038] In one embodiment of the present invention, the mass concentration of ammonium sulfate in the diluted ammonium sulfate mother liquor in step (4) is 7% to 10%.

[0039] In one embodiment of the present invention, after the mass concentration of ammonium sulfate in the ammonium sulfate mother liquor at the bottom of the absorption tower in step (5) reaches 21% to 25%, it is subjected to secondary extraction with benzene; preferably, the mass concentration reaches 22%.

[0040] The present invention also provides a method for synthesizing and efficiently absorbing 2-cyanopyridine, the specific steps of the method comprising:

[0041] (1) Synthesis of 2-cyanopyridine by ammoxidation reaction:

[0042] Passing 2-methylpyridine and ammonia into a fixed bed reactor containing a catalyst, passing air so that the molar ratio of 2-methylpyridine, ammonia and air is 1: (50-60): (250-300), performing an ammoxidation reaction, and obtaining a reaction gas containing 2-cyanopyridine;

[0043] The preparation method of the catalyst is: titanium dioxide, V 2 O 5 and magnesium oxide-zinc additives are added to water, stirred for the first time, oxalic acid and ammonium molybdate are added, the temperature is raised, and stirred for the second time to obtain a viscous yellow solid; the solid is dried for the first time, extruded to obtain a columnar embryo; dried for the second time, calcined, and cooled to prepare a catalyst for preparing 2-cyanopyridine by catalytic ammoxidation;

[0044] Among them, titanium dioxide, V 2 O 5 , magnesium oxide-zinc additive, water, oxalic acid, and ammonium molybdate are added in the following proportions: (180-220 g): (25-35 g): (3-7 g): (950-1050 mL): (2-3 g): (1-3 g);

[0045] The preparation method of the magnesium oxide-zinc additive is as follows: Mg(NO 3 ) 2 6H 2 O、Zn(NO 3 ) 2 6H 2 O and water are stirred and mixed to obtain a mixture; ammonia water and ammonium bicarbonate are added, and the mixture is subjected to ultrasonication, filtration, drying, and sieving to obtain a magnesium oxide-zinc additive;

[0046] Among them, Mg(NO 3 ) 2 6H 2 O、Zn(NO 3 ) 2 6H 2 The mass ratio of O, water, ammonia water and ammonium bicarbonate is (25-30): (20-55): (100-150): (2.0-5.0): (5.0-10);

[0047] (2) Primary absorption and extraction:

[0048] The reaction gas obtained in step (1) is introduced from the top of the high-efficiency absorber, and sulfuric acid solution is sprayed at the bottom of the high-efficiency absorber to make the reaction gas and sulfuric acid solution fully contact, and the sulfuric acid solution absorbs the reaction gas in the first stage to obtain an absorption liquid, which is extracted with benzene to obtain a 2-cyanopyridine organic phase and an ammonium sulfate mother liquor;

[0049] (3) Secondary absorption:

[0050] The remaining reaction gas and ammonium sulfate mother liquor in step (2) are introduced into the lower part of the absorption tower together, and gas-liquid separation is performed through the gas-liquid separator at the lower part of the absorption tower. The ammonium sulfate mother liquor remains at the bottom of the absorption tower. The reaction gas ascends from the lower part of the absorption tower into the packing layer in the middle of the absorption tower. The ammonium sulfate mother liquor collected from the bottom of the absorption tower is transported to the liquid distributor in the middle of the absorption tower by a secondary circulating liquid absorption pump outside the absorption tower, and is sprayed to absorb the reaction gas at the secondary level;

[0051] (4) Tertiary absorption:

[0052] After the secondary absorption in step (3), the reaction gas continues to ascend to the upper part of the absorption tower, is evenly distributed through the gas distributor at the upper part of the absorption tower, and is then washed by water spraying. The reaction gas is absorbed in the tertiary stage to obtain a washing liquid. The tail gas after the tertiary absorption is discharged from the chimney at the top of the absorption tower.

[0053] (5) Circulating spray washing reaction gas:

[0054] The washing liquid after water spray washing in step (4) flows back to the absorption tower by gravity, and is transported to the upper part of the absorption tower by the three-stage circulating liquid absorption pump to circulate and wash the reaction gas after the secondary absorption; part of the washing liquid in the upper part of the absorption tower overflows to the middle of the absorption tower, dilutes the ammonium sulfate mother liquor in the middle of the absorption tower, and the diluted dilute ammonium sulfate mother liquor is circulated to the liquid distributor in the middle of the absorption tower to continue spraying the reaction gas from the primary absorption, and part of the dilute ammonium sulfate mother liquor in the middle of the absorption tower overflows to the bottom of the absorption tower;

[0055] (6) Secondary extraction and preparation of 2-cyanopyridine organic phase:

[0056] After the ammonium sulfate in the ammonium sulfate mother liquor at the bottom of the absorption tower reaches a certain mass concentration, it is extracted twice with benzene to obtain raffinate water and 2-cyanopyridine organic phase 2, and the 2-cyanopyridine organic phase 1 obtained in step (2) is combined, and benzene is recovered to obtain a 2-cyanopyridine organic phase;

[0057] (7) Preparation of ammonium sulfate by-product and 2-cyanopyridine product:

[0058] The raffinate water from the secondary extraction in step (6) is transported to an evaporative crystallizer, decolorized with activated carbon and subjected to triple-effect evaporation, the raffinate water is concentrated, cooled and crystallized to obtain an ammonium sulfate by-product; the 2-cyanopyridine organic phase prepared in step (6) is continuously distilled to finally obtain a 2-cyanopyridine product.

[0059] In one embodiment of the present invention, the reaction conditions in step (1) are 340-380°C.

[0060] In one embodiment of the present invention, the preparation method of the catalyst in step (1) is: titanium dioxide, V 2 O 5 and magnesium oxide-zinc additives are added to water, stirred for the first time, oxalic acid and ammonium molybdate are added, the temperature is raised, stirred for the second time, and a viscous yellow solid is obtained; the solid is dried for the first time, extruded to obtain a columnar embryo; dried for the second time, calcined, and cooled to obtain a catalyst;

[0061] The preparation method of the magnesium oxide-zinc additive is as follows: Mg(NO 3 ) 2 6H 2 O、Zn(NO 3 ) 2 6H 2 O and water are stirred and mixed to obtain a mixture; ammonia water and ammonium bicarbonate are added, and the mixture is subjected to ultrasonication, filtration, drying and sieving to obtain a magnesium oxide-zinc additive.

[0062] In one embodiment of the present invention, Mg(NO 3 ) 2 6H 2 O、Zn(NO 3 ) 2 6H 2 The mass ratio of O, water, ammonia water and ammonium bicarbonate is (25-30):(20-55):(100-150):(2.0-5.0):(5.0-10).

[0063] In one embodiment of the present invention, the ultrasonic condition is 65-75KHz for 50-60min.

[0064] In one embodiment of the present invention, the drying condition is drying at 100-110° C. for 9-10 hours.

[0065] In one embodiment of the present invention, the particle size of the magnesium oxide-zinc additive is 60 to 80 μm.

[0066] In one embodiment of the present invention, the specific surface area of ​​the magnesium oxide-zinc additive is 360 to 390 m 2 / g, the porosity is 45% to 65%, and the loaded lattice oxygen content is 8% to 10%.

[0067] In one embodiment of the present invention, titanium dioxide, V 2 O 5 The addition ratio of magnesium oxide-zinc additive, water, oxalic acid and ammonium molybdate is (180-220g):(25-35g):(3-7g):(950-1050mL):(2-3g):(1-3g).

[0068] In one embodiment of the present invention, the heating temperature is 50-60°C.

[0069] In one embodiment of the present invention, the first stirring condition is stirring at 190-210 r / min for 1-3 hours.

[0070] In one embodiment of the present invention, the second stirring condition is stirring at 200-250 r / min for 15-18 hours.

[0071] In one embodiment of the present invention, the first drying condition is 50-60° C. for 1-3 hours.

[0072] In one embodiment of the present invention, the second drying is performed at 100-110° C. for 2-6 hours.

[0073] In one embodiment of the present invention, the diameter of the columnar embryo is 4 to 5 mm.

[0074] In one embodiment of the present invention, the calcination condition is calcination at 500-600° C. for 15-18 hours.

[0075] In one embodiment of the present invention, the components and mass contents of the catalyst for catalytic ammoxidation to prepare 2-cyanopyridine are as follows: V: Mo: Mg: Zn: TiO 2 =(11-14%):(0.8-1.0%):(0.9-1.2%):(0.9-1.2%):(80%-85%).

[0076] In one embodiment of the present invention, the reaction gas is introduced at a rate of 550 to 650 L / h in step (2); preferably, the introduction rate is 600 L / h.

[0077] In one embodiment of the present invention, the concentration of the sulfuric acid solution in step (2) is 50% to 80% (v / v).

[0078] In one embodiment of the present invention, the injection rate of the sulfuric acid solution in step (2) is 15 to 22 L / h; preferably, the injection rate of the sulfuric acid solution is 20 L / h.

[0079] In one embodiment of the present invention, the pH of the absorption liquid in step (2) is 8-9.

[0080] In one embodiment of the present invention, the mass concentration of ammonium sulfate in the ammonium sulfate mother liquor in step (2) is 10% to 14%.

[0081] In one embodiment of the present invention, the packing layer in step (3) uses ball ring packing.

[0082] In one embodiment of the present invention, the spraying amount of water in step (4) is 1 to 5 L / h; preferably, the spraying amount of water is 2 L / h.

[0083] In one embodiment of the present invention, the mass concentration of ammonium sulfate in the diluted ammonium sulfate mother liquor in step (5) is 7% to 10%.

[0084] In one embodiment of the present invention, after the mass concentration of ammonium sulfate in the ammonium sulfate mother liquor at the bottom of the absorption tower in step (6) reaches 21% to 25%, it is subjected to secondary extraction with benzene; preferably, the mass concentration reaches 22%.

[0085] Beneficial Effects

[0086] (1) The present invention replaces the complicated three-stage absorption tower by performing three absorption treatments on the reaction gas, efficiently absorbs 2-cyanopyridine in the reaction gas, and improves the equipment utilization rate; the absorption rate of 2-cyanopyridine is maximized to 99.5%, and the product yield reaches more than 90%.

[0087] (2) After the three-stage absorption treatment of the present invention, the tail gas ammonia is absorbed by sulfuric acid to generate ammonium sulfate, and the tail gas VOC content is reduced from 70 mg / m 3 Reduce to 50 mg / m 3 At the same time, when the ammonium sulfate concentration at the bottom of the absorption tower reaches a certain value, after extraction, the residual water is transported to the evaporation tower to recover the by-product ammonium sulfate, which is not only not easy to cause secondary pollution, but also can reuse the by-product. BRIEF DESCRIPTION OF THE DRAWINGS

[0088] Figure 1 It is a device diagram of the 2-cyanopyridine absorption method of the present invention.

[0089] Figure 2The absorption tower device diagram of the present invention is shown in FIG. 1 is the reaction gas inlet; 2 is the gas-liquid separator; 3 is the filler; 4 is the liquid distributor 2; 5 is the circulating ammonium sulfate mother liquor inlet; 6 is the gas distributor 3; 7 is the water circulation inlet; and 8 is the tail gas outlet. DETAILED DESCRIPTION

[0090] The preferred embodiments of the present invention are described below. It should be understood that the embodiments are for better explaining the present invention and are not used to limit the present invention.

[0091] The test methods involved in the following embodiments are as follows:

[0092] The yield of 2-cyanopyridine product refers to the ratio of the final product mass to the theoretically generated product mass;

[0093] The absorption rate of 2-cyanopyridine refers to the ratio of the amount of 2-cyanopyridine absorbed by the reaction gas after three-stage absorption to the original content;

[0094] Use a VOC detector to detect the VOC content in exhaust gas.

[0095] The raw materials involved in the following embodiments are:

[0096] Ball ring packing was purchased from Lantaixing Environmental Protection Materials Co., Ltd.;

[0097] 2-Methylpyridine was purchased from Hebi Saike Chemical Co., Ltd.

[0098] The absorption tower involved in the following embodiments is divided into a lower part, a middle part, and an upper part; the lower part contains a gas-liquid separator to separate gas and liquid; the middle part contains a packing layer and a liquid distributor, which is sprayed through the liquid distributor for secondary absorption; the upper part contains a gas distributor, which sprays water for tertiary absorption; at the same time, the absorption tower contains a secondary circulating liquid absorption pump and a tertiary circulating liquid absorption pump outside the absorption tower, and the secondary circulating liquid absorption pump transports the ammonium sulfate mother liquor to the liquid distributor in the middle of the absorption tower for spraying for secondary absorption; the tertiary circulating liquid absorption pump transports the washing liquid after water spray washing to the upper part of the absorption tower for spraying for tertiary absorption; in addition, part of the washing liquid in the upper part of the absorption tower overflows to the middle part of the absorption tower to dilute the ammonium sulfate mother liquor in the middle part of the absorption tower; part of the dilute ammonium sulfate mother liquor in the middle part of the absorption tower overflows to the lower part of the absorption tower.

[0099] Example 1: Preparation method of catalyst for ammoxidation of 2-cyanopyridine and ammoxidation reaction

[0100] (1) Preparation of magnesium oxide-zinc additive:

[0101] At room temperature 25°C, 28.3 g of Mg(NO 3 ) 2 6H 2 O and 23.3 g of Zn(NO3 ) 2 6H 2 O and 130g of water were stirred for 30min, then 3.4g of ammonia water and 8.5g of ammonium bicarbonate were added as precipitants, ultrasonicated at 70KHz for 55min, vacuum filtered, then dried at 106°C for 10h, and ball milled to obtain magnesium oxide-zinc additive (particle size 60-80μm);

[0102] The specific surface area of ​​the prepared magnesium oxide-zinc additive is 375m 2 / g, porosity of 50.7%, and supported lattice oxygen content of 8.9%;

[0103] (2) Preparation of crude catalyst:

[0104] At room temperature 25°C, 202.6 g of titanium dioxide and 30.2 g of vanadium oxide V 2 O 5 5.2 g of magnesium oxide-zinc additive and 1000 mL of deionized water were added to a three-necked flask and stirred at 200 r / min for 2 h. After stirring, 2.5 g of oxalic acid and 2.0 g of ammonium molybdate were added, the temperature was raised to 54 ° C and stirred at 230 r / min for 17 h to obtain a viscous yellow solid.

[0105] (3) Drying extrusion:

[0106] The viscous yellow solid obtained in step (2) is dried at 60° C. for 2 h, and then extruded using an extruder to obtain a columnar embryo with a diameter of 4 to 5 mm;

[0107] (4) Preparation of finished catalyst:

[0108] The columnar embryo obtained in step (3) is dried at 100° C. for 4 h, calcined in a muffle furnace at 570° C. for 16 h, and cooled to obtain a catalyst for preparing 2-cyanopyridine by catalytic oxidation of ammonia.

[0109] The V, Mo, Mg, Zn, TiO in the catalyst for preparing 2-cyanopyridine by high-efficiency catalytic ammoxidation prepared in Example 5 2 The mass content of the components is: V:Mo:Mg:Zn:TiO 2 =12.5%:0.88%:1.02%:1.08%:83.5%.

[0110] (5) Preparation of 2-cyanopyridine by ammoxidation reaction:

[0111] In a tubular fixed-bed reactor, 2-methylpyridine, ammonia and air were mixed at a ratio of 1:60:300 (molar ratio) at 210°C, and the feed rate of 2-methylpyridine was 21 g / h. 541 g of the prepared catalyst was loaded, and an ammoxidation reaction was carried out at 335°C. The reaction was stabilized for 2 hours before detection.

[0112] Test results:

[0113] The yield of 2-cyanopyridine was 91.92%, the conversion rate of 2-methylpyridine was 99.90%, the reaction selectivity was 92.01%, the content of by-product 2-nicotinamide was 2.92%, and the content of pyridine was 2.01%.

[0114] Example 2: A method for absorbing 2-cyanopyridine

[0115] Specific steps are as follows Figure 1 and Figure 2 As shown:

[0116] (1) Ammoxidation reaction:

[0117] 2-Methylpyridine (feed rate of 20 g / h) and liquid ammonia are introduced into a fixed bed reactor containing 550 g of the catalyst obtained in Example 1, the horizontal bed gasification temperature is 220° C., air is introduced, and the molar ratio of air: ammonia: 2-methylpyridine is 250:50:1; the vertical bed reaction temperature is 360° C., and a reaction gas (95% air, 1% 2-cyanopyridine, 1.8% ammonia, 0.2% pyridine, 0.2% nicotinamide, etc.) is obtained;

[0118] (2) Primary absorption and primary extraction:

[0119] The reaction gas after the reaction in step (1) is introduced from the top of the high-efficiency absorber at a rate of 600 L / h, and a 50% (v / v) sulfuric acid solution is sprayed at a rate of 20 L / h at the bottom of the high-efficiency absorber to fully contact the reaction gas and the sulfuric acid solution. After the sulfuric acid solution absorbs ammonia and 2-cyanopyridine in the reaction gas in the first stage, the pH of the absorption liquid is controlled at 8 to 9, and the 2-cyanopyridine organic phase 1 is obtained by extraction with benzene, and raffinate water (the ammonium sulfate mother liquor obtained after benzene extraction is a mixed solution of ammonium sulfate, sulfuric acid, 2-cyanopyridine, etc., and the mass concentration of ammonium sulfate is 12%);

[0120] (3) Secondary absorption:

[0121] The remaining reaction gas in step (2) and the ammonium sulfate mother liquor (raffinate water, ammonium sulfate mass concentration of about 12%) obtained after benzene extraction are introduced into the lower part of the absorption tower together, and gas-liquid separation is performed through the gas-liquid separator at the lower part of the absorption tower. The ammonium sulfate mother liquor remains at the bottom of the absorption tower, and the reaction gas ascends from the lower part of the absorption tower into the packing layer (using ball ring packing) in the middle part of the absorption tower. The ammonium sulfate mother liquor with an ammonium sulfate mass concentration of 12% collected from the gas-liquid separator at the bottom of the absorption tower is transported to the liquid distributor 2 in the upper part of the absorption tower by a secondary circulating liquid absorption pump outside the absorption tower, and is sprayed, and the reaction gas is absorbed at the secondary level;

[0122] (4) Tertiary absorption:

[0123] After the secondary absorption in step (3), the reaction gas continues to ascend to the upper part of the absorption tower, and after being evenly distributed by the gas distributor 3 at the upper part of the absorption tower, it is sprayed and washed with process water at a rate of 2L / h, and the reaction gas is absorbed in the tertiary stage to obtain a washing liquid; the tail gas after the tertiary absorption is discharged from the chimney at the top of the absorption tower;

[0124] (5) Circulating spray washing reaction gas:

[0125] The washing liquid after the process water spray washing in step (4) flows back to the absorption tower by gravity, and is transported to the upper part of the absorption tower by the three-stage circulating liquid absorption pump to circulate and wash the reaction gas from the secondary absorption; part of the washing liquid at the upper part of the absorption tower overflows to the middle of the absorption tower, dilutes the ammonium sulfate mother liquor in the middle of the absorption tower, and the diluted dilute ammonium sulfate mother liquor (ammonium sulfate mass concentration is 8%) is circulated to the liquid distributor 2 in the middle of the absorption tower, and the reaction gas from the primary absorption is continuously sprayed, and part of the dilute ammonium sulfate mother liquor in the middle of the absorption tower overflows to the bottom of the absorption tower;

[0126] (6) Secondary extraction and preparation of 2-cyanopyridine organic phase:

[0127] After the mass concentration of ammonium sulfate in the ammonium sulfate mother liquor at the bottom of the absorption tower reaches 22%, it is extracted twice with benzene to obtain raffinate water and 2-cyanopyridine organic phase 2, and the 2-cyanopyridine organic phase 1 obtained in step (2) is combined, benzene is recovered, and then a 2-cyanopyridine organic phase is obtained;

[0128] (7) Preparation of ammonium sulfate by-product and 2-cyanopyridine product:

[0129] The raffinate water from the secondary extraction in step (6) is transported to an evaporative crystallizer, decolorized with activated carbon and subjected to triple-effect evaporation, the raffinate water is concentrated, cooled and crystallized to obtain an ammonium sulfate by-product; the 2-cyanopyridine organic phase prepared in step (6) is continuously distilled to finally obtain a 2-cyanopyridine product.

[0130] The results showed that the VOC content of the exhaust gas discharged in step (4) was 49.2 mg / m 3The absorption rate of 2-cyanopyridine is 99.3%, and the yield of 2-cyanopyridine product in step (7) is 90.5%.

[0131] Example 3: A method for absorbing 2-cyanopyridine

[0132] The specific implementation method is the same as that of Example 2, except that the concentration of the sulfuric acid solution in step (2) is adjusted from 50% (v / v) to 60% (v / v); at the same time, step (6) is adjusted as follows:

[0133] (6) Secondary extraction and preparation of 2-cyanopyridine organic phase:

[0134] After the mass concentration of ammonium sulfate in the ammonium sulfate mother liquor at the bottom of the absorption tower reaches 25%, it is extracted twice with benzene to obtain raffinate water and 2-cyanopyridine organic phase 2, combined with the 2-cyanopyridine organic phase 1 obtained in step (2), benzene is recovered, and then a 2-cyanopyridine organic phase is obtained;

[0135] The remaining steps were the same as in Example 2. The results showed that the yield of 2-cyanopyridine was 89.1%, and the absorption rate of 2-cyanopyridine was 96.1%. The VOC content of the tail gas discharged in step (4) was 65.5 mg / m 3 .

[0136] Example 4: A method for absorbing 2-cyanopyridine

[0137] The specific implementation is the same as that of Example 2, except that the concentration of the sulfuric acid solution in step (1) is adjusted to 65% (v / v), 70% (v / v) or 80% (v / v).

[0138] The remaining steps are the same as in Example 2, and the results are as follows:

[0139] When the concentration of sulfuric acid solution is 65% (v / v), the yield of 2-cyanopyridine product is 91.4%, and the absorption rate of 2-cyanopyridine is 98.5%; the VOC content of the tail gas discharged in step (4) is 55.7 mg / m 3 ;

[0140] When the concentration of sulfuric acid solution is 70% (v / v), the yield of 2-cyanopyridine product is 90.9%, and the absorption rate of 2-cyanopyridine is 97.2%; the VOC content of the tail gas discharged in step (4) is 58.8 mg / m 3 ;

[0141] When the concentration of sulfuric acid solution is 80% (v / v), the yield of 2-cyanopyridine product is 89.5%, and the absorption rate of 2-cyanopyridine is 96.5%; the VOC content of the tail gas discharged in step (4) is 62.3 mg / m 3 .

[0142] Example 5: A method for absorbing 2-cyanopyridine

[0143] The specific implementation method is the same as that of Example 2, except that the mass concentration of ammonium sulfate in the ammonium sulfate mother liquor (raffinate water) obtained after benzene extraction in step (2) and step (3) is adjusted to 10% or 11%.

[0144] The remaining steps are the same as in Example 2, and the results are as follows:

[0145] When the ammonium sulfate mass concentration in the ammonium sulfate mother liquor (raffinate water) obtained after benzene extraction in step (2) and step (3) is 10%, the yield of 2-cyanopyridine product is 88.4%, and the absorption rate of 2-cyanopyridine is 95.4%; the VOC content of the tail gas discharged in step (4) is 63.5 mg / m 3 ;

[0146] When the ammonium sulfate mass concentration in the ammonium sulfate mother liquor (raffinate water) obtained after benzene extraction in step (2) and step (3) is 11%, the yield of 2-cyanopyridine product is 90.2%, and the absorption rate of 2-cyanopyridine is 96.9%; the VOC content of the tail gas discharged in step (4) is 59.2 mg / m 3 .

[0147] Example 6: A method for absorbing 2-cyanopyridine

[0148] The specific implementation method is the same as that of Example 2, except that the mass concentration of ammonium sulfate in the diluted ammonium sulfate mother liquor after adjustment in step (5) is 9% or 10%.

[0149] The remaining steps are the same as in Example 2, and the results are as follows:

[0150] When the diluted ammonium sulfate mother liquor in step (5) is 9%, the yield of 2-cyanopyridine product is 90.5%, and the absorption rate of 2-cyanopyridine is 97.1%; the VOC content of the tail gas discharged in step (4) is 57.2 mg / m 3 ;

[0151] When the diluted ammonium sulfate mother liquor in step (5) is 10%, the yield of 2-cyanopyridine product is 89.1%, and the absorption rate of 2-cyanopyridine is 96.2%; the VOC content of the tail gas discharged in step (4) is 62.7 mg / m 3 .

[0152] Example 7: A method for absorbing 2-cyanopyridine

[0153] The specific implementation method is the same as Example 2, except that the mass concentration of ammonium sulfate in the ammonium sulfate mother liquor in step (6) is adjusted to: 23%, 24%, 25%.

[0154] The remaining steps are the same as in Example 2, and the results are as follows:

[0155] When the mass concentration of the ammonium sulfate mother liquor in step (6) reaches 23%, the yield of 2-cyanopyridine product is 91.5%, and the absorption rate of 2-cyanopyridine is 98.6%; the VOC content of the tail gas discharged in step (4) is 55.9 mg / m 3 ;

[0156] When the mass concentration of the ammonium sulfate mother liquor in step (6) reaches 24%, the yield of 2-cyanopyridine product is 90.9%, and the absorption rate of 2-cyanopyridine is 97.3%; the VOC content of the tail gas discharged in step (4) is 58.9 mg / m 3 ;

[0157] When the mass concentration of the ammonium sulfate mother liquor in step (6) reaches 25%, the yield of 2-cyanopyridine product is 90.2%, and the absorption rate of 2-cyanopyridine is 96.8%; the VOC content of the tail gas discharged in step (4) is 59.3 mg / m 3 .

[0158] Example 8: A method for absorbing 2-cyanopyridine

[0159] The specific implementation method is the same as Example 2, except that the concentration of the sulfuric acid solution in step (2) is adjusted from 50% (v / v) to 80% (v / v); at the same time, the mass concentration of ammonium sulfate in the ammonium sulfate mother liquor at the bottom of the absorption tower in step (6) is adjusted to 25%; at the same time, the mass concentration of ammonium sulfate in the ammonium sulfate mother liquor (raffinate water) obtained after benzene extraction in steps (2) and (3) is adjusted to 10%; at the same time, the mass concentration of ammonium sulfate in the diluted ammonium sulfate mother liquor in step (5) is adjusted to 10%.

[0160] The remaining steps were the same as in Example 2. The results showed that the yield of 2-cyanopyridine product was 87.2%, and the VOC content of the tail gas discharged in step (4) was 68.8 mg / m 3 , the absorption rate of 2-cyanopyridine is 94.2%.

[0161] Comparative Example 1: Preparation of Catalyst

[0162] The specific implementation method is the same as Example 1, except that magnesium oxide-zinc additive is not used, that is, step (1) is deleted and step (2) is adjusted to:

[0163] At room temperature 25°C, 202.6g of titanium dioxide, 30.2g of V 2 O 51000 mL of deionized water were added to a three-necked flask and stirred at 200 r / min for 2 h. After stirring, 2.5 g of oxalic acid and 2.0 g of ammonium molybdate were added. The temperature was raised to 54°C and stirred at 230 r / min for 17 h to obtain a viscous yellow solid.

[0164] The other conditions were the same as those in Example 1, and a catalyst for catalytic ammoxidation to prepare 2-cyanopyridine was prepared.

[0165] The V, Mo, and TiO in the catalyst for catalytic ammoxidation to prepare 2-cyanopyridine prepared in this comparative example 2 The mass content of the components is V:Mo:TiO 2 =12.7%:0.87%:85.4%.

[0166] Comparative Example 2: Preparation of Catalyst

[0167] The specific implementation method is the same as that of Example 1, except that the magnesium oxide-zinc additive in the adjustment step (1) is a single magnesium oxide additive, that is, the adjustment step (1) is:

[0168] (1) Preparation of single magnesium oxide additive:

[0169] At room temperature of 25°C, 32.8 g of magnesium chloride was dissolved in 200 mL of water, and 27.6 g of sodium hydroxide was added to precipitate magnesium hydroxide. The precipitate was vacuum filtered, dried at 100°C for 4 h, and calcined at 400°C for 10 h to obtain a magnesium oxide additive.

[0170] The specific surface area of ​​the single magnesium oxide additive prepared in this comparative example is 220 m 2 / g, the porosity is 34.2%, and the supported lattice oxygen content is 5.2%.

[0171] The other conditions were the same as those in Example 1, and a catalyst for catalytic ammoxidation to prepare 2-cyanopyridine was prepared.

[0172] The V, Mo, Mg, and TiO in the catalyst for catalytic ammoxidation to prepare 2-cyanopyridine prepared in this comparative example are 2 The mass content of the components is V:Mo:Mg:TiO 2 =12.5%:0.86%:2.1%:83.5%.

[0173] Comparative Example 3: Preparation of Catalyst

[0174] Compared with Example 1, the magnesium oxide-zinc additive was changed to a single zinc oxide additive, and the rest was the same as Example 1:

[0175] The specific implementation method is the same as that of Example 1, except that the magnesium oxide-zinc additive in the adjustment step (1) is a single zinc oxide additive, that is, the adjustment step (1) is:

[0176] (1) Preparation of zinc oxide additive:

[0177] At room temperature of 25°C, 28.9 g of zinc chloride was dissolved in 200 mL of water, and 18.2 g of sodium hydroxide was added to precipitate zinc hydroxide. The precipitate was vacuum filtered, dried at 100°C for 4 h, and calcined at 400°C for 10 h to obtain a zinc oxide additive.

[0178] The specific surface area of ​​the single zinc oxide additive prepared in this comparative example is 208m 2 / g, the porosity is 30.2%, and the supported lattice oxygen content is 3.4%.

[0179] The other conditions were the same as those in Example 1, and a catalyst for catalytic ammoxidation to prepare 2-cyanopyridine was prepared.

[0180] The V, Mo, Mg, and TiO in the catalyst for catalytic ammoxidation to prepare 2-cyanopyridine prepared in this comparative example are 2 The mass content of the components is V:Mo:Mg:TiO 2 =12.5%:0.85%:2.1%:83.5%.

[0181] Comparative Example 4: Preparation of Catalyst

[0182] The specific implementation method is the same as that of Example 1, except that the preparation of the auxiliary agent in step (1) is adjusted to use Ni(NO 3 ) 2 6H 2 O and Cu(NO 3 ) 2 ·H 2 O prepares the catalyst promoter, that is, adjusts step (1) to:

[0183] (1) Preparation of nickel oxide-copper additive:

[0184] At room temperature 25°C, 32.1 g of Ni(NO 3 ) 2 6H 2 O and 22.8 g of Cu(NO 3 ) 2 ·H 2 O and 140g of water were stirred for 30 minutes, and then 3.4g of ammonia water and 8.5g of ammonium bicarbonate were added as precipitants, and ultrasonic treatment was performed at 70KHz for 55 minutes to precipitate the mixture, and the precipitate was obtained by centrifugation. Then, the precipitate was dried at 106°C for 10 hours, and the nickel oxide-copper additive was obtained by ball milling and sieving;

[0185] The specific surface area of ​​the nickel oxide-copper additive prepared in this comparative example is 345m 2 / g, the porosity is 38.4%, and the supported lattice oxygen content is 5.2%.

[0186] The other conditions were the same as those in Example 1, and a catalyst for catalytic ammoxidation to prepare 2-cyanopyridine was prepared.

[0187] The catalyst prepared in this comparative example for catalytic ammoxidation to prepare 2-cyanopyridine contains V, Mo, Ni, Cu, TiO 2 The mass content of the components is V:Mo:Ni:Cu:TiO 2 =12.5%:0.83%:1.1.07%:1.03%:83.5%.

[0188] Comparative Example 5: Preparation of Catalyst

[0189] Compared with Example 1, the preparation method of the magnesium oxide-zinc additive was changed, and the rest was consistent with Example 1:

[0190] The specific implementation method is the same as that of Example 1, except that the Mg(NO 3 ) 2 6H 2 O is other magnesium compounds MgSO 4 ; Adjust Zn(NO 3 ) 2 6H 2 O is other zinc compounds ZnSO 4 ·4H 2 O; that is, adjust step (1) to:

[0191] (1) Preparation of magnesium oxide-zinc additive:

[0192] At room temperature (25°C), 25.8 g of MgSO 4 and 29.6 g of ZnSO 4 ·4H 2 O and 130g of water were stirred for 30min to mix, then 3.4g of ammonia water and 8.5g of ammonium bicarbonate precipitant were added, ultrasonicated at 70KHz for 55min, vacuum filtered, then dried at 106°C for 10h, ball milled and sieved to obtain magnesium oxide-zinc additive;

[0193] The specific surface area of ​​the magnesium oxide-zinc additive prepared in this comparative example is 326 m 2 / g, the porosity is 35.3%, and the supported lattice oxygen content is 4.6%.

[0194] The other conditions were the same as those in Example 1, and a catalyst for catalytic ammoxidation to prepare 2-cyanopyridine was prepared.

[0195] The catalyst prepared in this comparative example for catalytic ammoxidation to prepare 2-cyanopyridine contains V, Mo, Mg, Zn, TiO 2 The mass content of the components is V:Mo:Mg:Zn:TiO 2 =12.5%:0.82%:1.42%:0.68%:83.5%.

[0196] Comparative Example 6: Preparation of Catalyst

[0197] The specific implementation method is the same as that of Example 1, except that the preparation of the crude catalyst in step (2) is adjusted to use V 2 O 3 Replace V 2 O 5 Prepare the crude catalyst, i.e. adjust step (2) to:

[0198] (2) Preparation of crude catalyst:

[0199] At room temperature 25°C, 202.6g of titanium dioxide, 30.2g of V 2 O 3 5.2 g of magnesium oxide-zinc additive and 1000 mL of deionized water were added to a three-necked flask and stirred for 2 h. After stirring, 2.5 g of oxalic acid and 2.0 g of ammonium molybdate were added. The temperature was raised to 54 ° C and stirred for 17 h to obtain a viscous yellow solid.

[0200] The catalyst prepared in this comparative example for catalytic ammoxidation to prepare 2-cyanopyridine contains V, Mo, Mg, Zn, TiO 2 The mass content of the components is V:Mo:Mg:Zn:TiO 2 =12.1%:0.83%:1.03%:1.10%:83.5%.

[0201] The catalyst obtained in Comparative Examples 1-6 is used for an ammoxidation reaction to prepare 2-cyanopyridine, which specifically comprises the following steps:

[0202] In a tubular fixed-bed reactor, 2-methylpyridine, ammonia and air were mixed at a molar ratio of 1:60:300 at 210°C, and the 2-methylpyridine feed rate was 21 g / h; 541 g of the catalyst prepared in the above comparative examples 1 to 6 were respectively filled, and ammoxidation reaction was carried out at 335°C. The reaction was stabilized for 2 hours before detection.

[0203] The yield of 2-cyanopyridine, the conversion rate of 2-methylpyridine, the reaction selectivity, the content of by-product 2-nicotinamide, and the content of pyridine are shown in Table 1.

[0204] Table 1

[0205] Comparative Example 2-Cyanopyridine yield% 2-Methylpyridine conversion rate % 2-Niacinamide content% Pyridine content% Reaction selectivity% 1 52.83 84.32 30.42 23.78 62.65 2 63.27 90.42 13.66 11.28 69.97 3 72.62 90.84 10.82 5.62 79.94 4 77.46 94.21 14.22 8.36 82.22 5 84.17 98.36 8.67 5.43 85.57 6 68.28 93.22 16.73 9.74 73.25

[0206] Although the present invention has been disclosed as above in the form of a preferred embodiment, it is not intended to limit the present invention. Anyone familiar with this technology can make various changes and modifications without departing from the spirit and scope of the present invention. Therefore, the scope of protection of the present invention should be based on the definition of the claims.

Claims

1. A method for efficiently absorbing 2-cyanopyridine, characterized in that: The steps include: (1) Primary absorption and extraction: The reaction gas after the ammoxidation reaction is introduced from the top of the high-efficiency absorber, and the sulfuric acid solution is sprayed at the bottom of the high-efficiency absorber to make the reaction gas and the sulfuric acid solution fully contact, and the sulfuric acid solution absorbs the reaction gas in the first stage to obtain an absorption liquid, which is extracted with benzene to obtain a 2-cyanopyridine organic phase 1 and an ammonium sulfate mother liquor; (2) Secondary absorption: The remaining reaction gas and ammonium sulfate mother liquor in step (1) are introduced into the lower part of the absorption tower together, and gas-liquid separation is performed through the gas-liquid separator at the lower part of the absorption tower, and the ammonium sulfate mother liquor is retained at the bottom of the absorption tower. The reaction gas ascends from the lower part of the absorption tower into the packing layer in the middle part of the absorption tower, and the ammonium sulfate mother liquor collected from the bottom of the absorption tower is transported to the liquid distributor in the middle part of the absorption tower by the secondary circulating liquid absorption pump outside the absorption tower, and is sprayed, and the reaction gas is absorbed at the secondary level; (3) Tertiary absorption: After the secondary absorption in step (2), the reaction gas continues to ascend to the upper part of the absorption tower, is evenly distributed through the gas distributor at the upper part of the absorption tower, and is then washed by water spraying. The reaction gas is absorbed in the tertiary stage to obtain a washing liquid. The tail gas after the tertiary absorption is discharged from the chimney at the top of the absorption tower. (4) Circulating spray washing reaction gas: The washing liquid after water spray washing in step (3) flows back to the absorption tower by gravity, and is transported to the upper part of the absorption tower by the third-stage circulating liquid absorption pump to circulate and wash the reaction gas from the second-stage absorption; part of the washing liquid in the upper part of the absorption tower overflows to the middle of the absorption tower, dilutes the ammonium sulfate mother liquor in the middle of the absorption tower, and the diluted dilute ammonium sulfate mother liquor is circulated to the liquid distributor in the middle of the absorption tower to continue spraying the reaction gas from the first-stage absorption, and part of the dilute ammonium sulfate mother liquor in the middle of the absorption tower overflows to the bottom of the absorption tower; (5) Secondary extraction and preparation of 2-cyanopyridine organic phase: After the ammonium sulfate in the ammonium sulfate mother liquor at the bottom of the absorption tower reaches a certain mass concentration, it is extracted twice with benzene to obtain raffinate water and 2-cyanopyridine organic phase 2, and the 2-cyanopyridine organic phase 1 obtained in step (1) is combined, and benzene is recovered to obtain a 2-cyanopyridine organic phase; (6) Preparation of ammonium sulfate by-product and 2-cyanopyridine product: The raffinate water from the secondary extraction in step (5) is transported to an evaporative crystallizer, decolorized by activated carbon and subjected to triple-effect evaporation, the raffinate water is concentrated, cooled and crystallized to obtain ammonium sulfate by-product; the 2-cyanopyridine organic phase prepared in step (5) is continuously distilled to finally obtain a 2-cyanopyridine product.

2. The method according to claim 1, characterized in that The ammoxidation reaction in step (1) is as follows: 2-methylpyridine and ammonia are introduced into a fixed bed reactor containing a catalyst, and air is introduced so that the molar ratio of 2-methylpyridine, ammonia and air is 1: (50-60): (250-300), and an ammoxidation reaction is performed to obtain a reaction gas; The preparation method of the catalyst comprises the following steps: adding titanium dioxide, V2O5 and magnesium oxide-zinc additive into water and stirring, adding oxalic acid and ammonium molybdate, heating and stirring to obtain a viscous yellow solid; drying and calcining the solid to obtain a catalyst for preparing 2-cyanopyridine by catalytic ammoxidation; The preparation method of the magnesium oxide-zinc auxiliary agent comprises the following steps: stirring and mixing Mg(NO3)2·6H2O, Zn(NO3)2 6H2O and water to obtain a mixture; adding ammonia water and ammonium bicarbonate, and obtaining the magnesium oxide-zinc auxiliary agent through ultrasonication, filtration, drying and sieving.

3. The method according to claim 1 or 2, characterized in that: In step (1), the reaction gas is introduced at a rate of 550 to 650 L / h; preferably, the introduction rate is 600 L / h.

4. The method according to any one of claims 1 to 3, characterized in that: The concentration of the sulfuric acid solution in step (1) is 50% to 80% (v / v).

5. The method according to any one of claims 1 to 4, characterized in that: The injection rate of the sulfuric acid solution in step (1) is 15 to 22 L / h; preferably, the injection rate of the sulfuric acid solution is 20 L / h.

6. The method according to any one of claims 1 to 5, characterized in that: The mass concentration of ammonium sulfate in the ammonium sulfate mother liquor in step (1) is 10% to 14%.

7. The method according to any one of claims 1 to 6, characterized in that: In step (3), the water spraying rate is 1 to 5 L / h; preferably, the water spraying rate is 2 L / h.

8. The method according to any one of claims 1 to 7, characterized in that: The mass concentration of ammonium sulfate in the diluted ammonium sulfate mother liquor in step (4) is 7% to 10%.

9. The method according to any one of claims 1 to 8, characterized in that: After the mass concentration of ammonium sulfate in the ammonium sulfate mother liquor at the bottom of the absorption tower in step (5) reaches 21% to 25%, it is subjected to secondary extraction with benzene; preferably, the mass concentration reaches 22%.

10. A method for synthesizing and efficiently absorbing 2-cyanopyridine, characterized in that: The specific steps of the method include: (1) Synthesis of 2-cyanopyridine by ammoxidation reaction: Passing 2-methylpyridine and ammonia into a fixed bed reactor containing a catalyst, passing air so that the molar ratio of 2-methylpyridine, ammonia and air is 1: (50-60): (250-300), performing an ammoxidation reaction, and obtaining a reaction gas containing 2-cyanopyridine; The preparation method of the catalyst comprises the following steps: adding titanium dioxide, V2O5 and magnesium oxide-zinc additive into water, stirring for the first time, adding oxalic acid and ammonium molybdate, heating, stirring for the second time, and obtaining a viscous yellow solid; drying the solid for the first time, extruding strips, and obtaining a columnar embryo; performing a second drying, calcining, and cooling to obtain a catalyst for preparing 2-cyanopyridine by catalytic ammoxidation; Among them, the addition ratio of titanium dioxide, V2O5, magnesium oxide-zinc additive, water, oxalic acid, and ammonium molybdate is (180-220g):(25-35g):(3-7g):(950-1050mL):(2-3g):(1-3g); The preparation method of the magnesium oxide-zinc auxiliary agent is as follows: Mg(NO3)2·6H2O, Zn(NO3)2 6H2O and water are stirred and mixed to obtain a mixture; ammonia water and ammonium bicarbonate are added, and the mixture is subjected to ultrasonication, filtration, drying and sieving to obtain the magnesium oxide-zinc auxiliary agent; Wherein, the mass ratio of Mg(NO3)2·6H2O, Zn(NO3)2·6H2O, water, aqueous ammonia, and ammonium bicarbonate is (25-30):(20-55):(100-150):(2.0-5.0):(5.0-10); (2) Primary absorption and extraction: The reaction gas obtained in step (1) is introduced from the top of the high-efficiency absorber, and sulfuric acid solution is sprayed at the bottom of the high-efficiency absorber to make the reaction gas and sulfuric acid solution fully contact, and the sulfuric acid solution absorbs the reaction gas in the first stage to obtain an absorption liquid, which is extracted with benzene to obtain a 2-cyanopyridine organic phase and an ammonium sulfate mother liquor; (3) Secondary absorption: The remaining reaction gas and ammonium sulfate mother liquor in step (2) are introduced into the lower part of the absorption tower together, and gas-liquid separation is performed through the gas-liquid separator at the lower part of the absorption tower. The ammonium sulfate mother liquor remains at the bottom of the absorption tower. The reaction gas ascends from the lower part of the absorption tower into the packing layer in the middle of the absorption tower. The ammonium sulfate mother liquor collected from the bottom of the absorption tower is transported to the liquid distributor in the middle of the absorption tower by a secondary circulating liquid absorption pump outside the absorption tower, and is sprayed to absorb the reaction gas at the secondary level; (4) Tertiary absorption: After the secondary absorption in step (3), the reaction gas continues to ascend to the upper part of the absorption tower, is evenly distributed through the gas distributor at the upper part of the absorption tower, and is then washed by water spraying. The reaction gas is absorbed in the tertiary stage to obtain a washing liquid. The tail gas after the tertiary absorption is discharged from the chimney at the top of the absorption tower. (5) Circulating spray washing reaction gas: The washing liquid after water spray washing in step (4) flows back to the absorption tower by gravity, and is transported to the upper part of the absorption tower by the three-stage circulating liquid absorption pump to circulate and wash the reaction gas after the secondary absorption; part of the washing liquid in the upper part of the absorption tower overflows to the middle of the absorption tower, dilutes the ammonium sulfate mother liquor in the middle of the absorption tower, and the diluted dilute ammonium sulfate mother liquor is circulated to the liquid distributor in the middle of the absorption tower to continue spraying the reaction gas from the primary absorption, and part of the dilute ammonium sulfate mother liquor in the middle of the absorption tower overflows to the bottom of the absorption tower; (6) Secondary extraction and preparation of 2-cyanopyridine organic phase: After the ammonium sulfate in the ammonium sulfate mother liquor at the bottom of the absorption tower reaches a certain mass concentration, it is extracted twice with benzene to obtain raffinate water and 2-cyanopyridine organic phase 2, and the 2-cyanopyridine organic phase 1 obtained in step (2) is combined, and benzene is recovered to obtain a 2-cyanopyridine organic phase; (7) Preparation of ammonium sulfate by-product and 2-cyanopyridine product: The raffinate water from the secondary extraction in step (6) is transported to an evaporative crystallizer, decolorized with activated carbon and subjected to triple-effect evaporation, the raffinate water is concentrated, cooled and crystallized to obtain an ammonium sulfate by-product; the 2-cyanopyridine organic phase prepared in step (6) is continuously distilled to finally obtain a 2-cyanopyridine product.

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