Method for treating waste liquid in electrochemical production of adiponitrile

Abstract

The application discloses a treatment method of waste liquid in electrochemical production of adiponitrile, which comprises the following steps: waste liquid and chloroform enter a chloroform azeotropic distillation tower, acrylonitrile, water and chloroform obtained from the top of the tower enter a chloroform recovery tower, high-purity chloroform and waste water are obtained by phase separation from the top of the tower, and acrylonitrile and chloroform are obtained from the bottom of the tower; chloroform recovery tower bottom liquid enters an acrylonitrile tower, chloroform and a small amount of light components are removed from the top of the tower, and acrylonitrile is obtained from the bottom of the tower; chloroform azeotropic distillation tower bottom liquid enters an adiponitrile light component removal tower, acrylonitrile, propionitrile, water and a small amount of adiponitrile are obtained from the top of the tower, and adiponitrile and heavy components are obtained from the bottom of the tower; adiponitrile light component removal tower top liquid enters a by-product propionitrile recovery tower, propionitrile is recovered from the top of the tower, and propylamine is produced under the action of a hydrogenation catalyst and an additive; tower bottom liquid enters an adiponitrile tower, high-purity adiponitrile is obtained from the top of the tower, and the total recovery rate of adiponitrile is high; and tower bottom liquid enters a hexanetristitane tower, hexanetristitane is obtained from the top of the tower. The method realizes effective recovery of waste liquid and reduces the production cost of adiponitrile.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of chemical waste liquid recovery, in particular to a method for recovering effective components from waste liquid in the production of adiponitrile by electrochemistry. BACKGROUND

[0002] Adiponitrile is a colorless transparent oily liquid, mainly used for the production of hexamethylenediamine, and for the preparation of polyamide (nylon 66 and nylon 6T, etc.) and HDI. The production capacity of adiponitrile is about 2 million tons / year, and only a few companies can produce it at present, and the production technology is in a highly monopolized state.

[0003] There are several production routes for adiponitrile at present. Butadiene direct cyanation method. It needs to go through three steps of cyanation, isomerization, and secondary cyanation, which is long in steps and complex in process, and needs to be matched with HCN device, which has high technical barriers. The main raw materials are butadiene, liquid ammonia and natural gas, and if there is a cheap source, the production cost will be lower.

[0004]

[0005] Butadiene direct cyanation method

[0006] Adipic acid catalytic ammoniation method. Adipic acid is used as raw material to obtain adiponitrile after high-temperature ammoniation and dehydration. Adipic acid will undergo a series of side reactions such as decarboxylation, dehydration and cyclization, and adiponitrile is also prone to isomerization, resulting in low quality of nylon salt. The process is complex, and needs to go through multiple steps such as dehydration, heavy component removal, vacuum distillation, etc., with more by-products of tar, large consumption of adipic acid and high production cost.

[0007]

[0008] Adipic acid catalytic ammoniation method

[0009] Acrylonitrile electrolysis dimerization method. Acrylonitrile is used as the main raw material, and the product is obtained by dimerization under electrolysis conditions. The reaction steps are short and the process is simple. The constraints are the cost of electrolysis and the source of acrylonitrile. Whether low-cost electricity and raw materials can be used becomes the key to the competition between this process and the butadiene route.

[0010]

[0011] Acrylonitrile electrolysis dimerization method

[0012] At present, the process of adiponitrile production by acrylonitrile electrolysis dimerization method does not have a reasonable solution to deal with the process waste liquid. With the increasing pressure of environmental protection, the accumulation of industrial waste liquid seriously restricts the production and development of enterprises. It is urgent to develop a simple and feasible process with less investment, which can realize the resourceization, reduction and regeneration of process waste liquid.

[0013] Generally, the main components of the waste liquid produced by acrylonitrile electrolytic dimerization method to produce adiponitrile are nitriles, a small amount of water, polymers and the like, and the composition is complex. Various azeotropes are formed between the components in the waste liquid, which increases the difficulty of waste liquid recovery, increases the production cost of the product, and increases the treatment cost of the waste liquid. SUMMARY

[0014] The present application provides a method for recycling effective components of waste liquid in electrochemical adiponitrile production, which efficiently recycles acrylonitrile as a raw material to the reactor, effectively reduces the unit consumption. The adiponitrile product in the waste liquid is recycled, the yield of the product is improved, the production cost is reduced, and the economic benefit is improved. The acrylonitrile is efficiently recycled, and a new type of hydrogenation catalyst is used to produce propylamine. The by-product hexanetristearate in the waste liquid is recycled.

[0015] The present application aims to provide a method for efficiently recycling effective components of waste liquid in electrochemical adiponitrile production, which realizes the recycling of acrylonitrile, propylamine, adiponitrile and hexanetristearate.

[0016] To achieve the above-mentioned purpose, the scheme of the present application includes the following steps:

[0017] A method for treating waste liquid in electrochemical adiponitrile production, comprising the following steps:

[0018] (1) mixing the waste liquid in electrochemical adiponitrile production with a certain proportion of chloroform, and then entering the chloroform azeotropic distillation tower for azeotropic distillation;

[0019] (2) the liquid taken out from the top of the chloroform azeotropic distillation tower enters the chloroform recovery tower, and the mixture of chloroform and water obtained from the top is separated into oil and water at the top, the oil phase is recycled to the chloroform azeotropic distillation tower, and the water phase is organic waste water;

[0020] (3) the liquid taken out from the bottom of the chloroform recovery tower enters the acrylonitrile tower for pressurized distillation, the organic waste liquid is obtained from the top, and high-purity 95-99wt% acrylonitrile is obtained from the bottom;

[0021] (4) the liquid taken out from the bottom of the chloroform azeotropic distillation tower enters the adiponitrile light component removal tower, the light components obtained from the top enter the by-product propylamine recovery tower, and the liquid taken out from the bottom enters the adiponitrile tower;

[0022] (5) the by-product propylamine recovery tower is subjected to vacuum distillation, propylamine is recycled from the top, and propylamine is produced under the action of hydrogenation catalyst and adjuvant, and the reaction liquid obtained by hydrogenation reaction enters the distillation tower for further removal of light components and purification, and high-purity propylamine is obtained from the top;

[0023] (6) the adiponitrile tower is subjected to vacuum distillation, and adiponitrile is obtained from the top;

[0024] (7) the liquid taken out from the bottom of the adiponitrile tower enters the hexanetristearate tower, hexanetristearate is obtained from the top, and the heavy component pot residue is obtained from the bottom.

[0025] The waste liquid comprises acrylonitrile 15-16.5 wt%, propionitrile 1-1.8 wt%, adiponitrile 65-70 wt%, methylglutaronitrile 0.1-1 wt%, water 5-7 wt%, hexanetritrile 5-6 wt%, 3-hydroxypropionitrile 0.1-0.5 wt%, and acrylonitrile polymer 2-3 wt%.

[0026] In the step (1), the mass ratio of the chloroform as the entrainer to the waste liquid in the chloroform azeotropic rectification tower is 0.5:1-0.9:1, preferably 0.6:1-0.85:1, and more preferably 0.65:1-0.8:1.

[0027] In the step (1), the chloroform azeotropic rectification tower has 22-28 trays, preferably 23-27 trays, and more preferably 24-26 trays.

[0028] In the step (1), the chloroform azeotropic rectification tower is fed at the lower part of the tower. The operating pressure is 0.5-0.9 bar, preferably 0.6-0.88 bar, and more preferably 0.7-0.85 bar. The temperature at the tower bottom is 210-230℃, and the temperature at the tower top is 45-50℃.

[0029] In the step (2), the chloroform recovery tower has 20-30 trays, preferably 22-28 trays, and more preferably 24-26 trays.

[0030] In the step (2), the chloroform recovery tower is fed at the lower part of the tower. The operating pressure is 0.5-0.9 bar, preferably 0.6-0.88 bar, and more preferably 0.7-0.85 bar. The temperature at the tower bottom is 65-75℃, and the temperature at the tower top is 40-45℃. The liquid at the tower top is separated into oil and water, and the phase separation temperature is 25-35℃, and the phase separation pressure is 1 bar.

[0031] In the step (3), the acrylonitrile tower has 45-52 trays, preferably 46-51 trays, and more preferably 48-50 trays.

[0032] In the step (3), the acrylonitrile tower is fed at the upper part of the tower. The operating pressure is 1.5-3 bar, preferably 1.6-2.8 bar, and more preferably 1.8-2.4 bar. The temperature at the tower bottom is 90-105℃, and the temperature at the tower top is 85-95℃.

[0033] In the step (4), the adiponitrile light-removing tower has 40-52 trays, preferably 41-51 trays, and more preferably 43-50 trays.

[0034] In the present application, in step (4), the adiponitrile light-removing column is fed at the middle part. The operating pressure is 0.05-0.2 bar, preferably 0.1-0.18 bar, more preferably 0.15-0.17 bar; the column bottom temperature is 210-225℃, and the column top temperature is 40-55℃.

[0035] In the present application, in step (5), the by-product propionitrile recovery column has 22-30 trays, preferably 23-29 trays, more preferably 24-28 trays.

[0036] In the present application, in step (5), the by-product propionitrile recovery column is fed at the lower part. The operating pressure is 0.5-0.95 bar, preferably 0.55-0.9 bar, more preferably 0.6-0.85 bar; the column bottom temperature is 240-265℃, and the column top temperature is 75-88℃.

[0037] In the present application, in step (5), the hydrogenation catalyst is β-Al2O3-supported Ni-C O , and the catalyst dosage is 1-5 wt% of the propionitrile feed.

[0038] In the present application, in the hydrogenation catalyst, the molar ratio of nickel to cobalt is 3:1-1.1:1, preferably 2.8:1-1.3:1, more preferably 2.5:1-1.8:1, and the metal loading in the catalyst is 25-66 wt% of the total mass of the catalyst, preferably 33-60 wt%, more preferably 38-55 wt%.

[0039] In the present application, in step (5), the adjuvant is furfural dimethyl acetal, and the dosage is 0.4-1.2 wt% of the propionitrile feed.

[0040] In the present application, in step (5), the hydrogenation operating temperature is 150-180℃, the operating pressure is 10-15 bar, and the hydrogenation reaction feed space velocity is 18-20 h -1 .

[0041] As a preferred scheme, in step (5) of the present application, the reaction product is subjected to vacuum rectification to obtain propylamine with a purity of 97.5-99 wt%. The rectification column has 22-25 trays, and is fed at the middle part. The operating pressure is 0.85-0.95 bar. High-purity propylamine is obtained at the column top, and the column bottom is heavy component waste liquid.

[0042] In step (5) of the present application, the propionitrile obtained at the column top has a water content of <3 wt%, a propionitrile content of >90 wt%, an acrylonitrile content of >5 wt%, and a total propionitrile recovery rate of >98 wt%.

[0043] In step (5) of the present application, the reaction product obtained by hydrogenation of propionitrile is subjected to vacuum rectification to obtain high-purity 98-99wt% propylamine.

[0044] In step (6) of the present application, the hexanedinitrile column has 35-46 plates, preferably 36-45 plates, and more preferably 38-43 plates; the feed is introduced into the lower part of the column. The operating pressure is 0.02-0.2bar, preferably 0.03-0.18bar, and more preferably 0.04-0.15bar; the column bottom temperature is 300-350℃, and the column top temperature is 180-200℃.

[0045] In step (6) of the present application, the purity of the obtained hexanedinitrile is 98-99.9wt%, and the total recovery rate is >95wt%.

[0046] In step (7) of the present application, the hexanetritrile column has 10-20 plates, preferably 12-18 plates, and more preferably 14-18 plates; the feed is introduced into the middle part of the column. The operating pressure is 0.01-0.2bar, preferably 0.03-0.18bar, and more preferably 0.04-0.15bar; the column bottom temperature is 550-580℃, and the column top temperature is 280-310℃.

[0047] In step (7) of the present application, the purity of the obtained hexanetritrile is >98wt%, and the total recovery rate of hexanetritrile is >99wt%.

[0048] The present application has the following positive effects:

[0049] (1) The organic waste liquid in the production of electrochemical hexanedinitrile contains a large amount of nitriles, a small amount of water, and polymers, and has complex components. If it is directly treated as waste liquid, not only the treatment cost of the three wastes is increased, but also resources are wasted. Therefore, it is of great significance to recover and utilize propylene nitrile, propionitrile, hexanedinitrile, and hexanetritrile in the organic waste liquid.

[0050] (2) The organic components in the organic waste liquid are complex and azeotropic. Through azeotropic rectification, vacuum and pressure rectification, and oil-water phase separation, effective recovery of propylene nitrile, propionitrile, hexanedinitrile, and hexanetritrile is achieved, the production cost is effectively reduced, the amount of three wastes is reduced, and the pollution to the environment is reduced.

[0051] (3) The assistant guaiacol dimethyl acetal, due to its special structure, can activate the substrate propionitrile, making it more easily hydrogenated, and can also shorten the distance between the substrate propionitrile and the activated hydrogen on the catalyst, so that the reaction is more likely to occur and the reaction effect is better.

[0052] (3) The entire process has high automation degree, which is conducive to the realization of industrialized continuous production. BRIEF DESCRIPTION OF DRAWINGS

[0053] Figure 1 A flow diagram for efficient recovery of effective components of waste liquid in electrochemical production of adiponitrile in the present application.

[0054] C001 chloroform azeotrope distillation column, C002 chloroform recovery column, D001 chloroform oil-water phase separation tank, C003 acrylonitrile column, C004 adiponitrile light-removing column, C005 by-product propionitrile recovery column, C006 adiponitrile column, C007 hexanetristriazine column. DETAILED DESCRIPTION

[0055] The following examples are not intended to limit the scope of the present application, and modifications or equivalent replacements to the present application, if not departing from the spirit and scope of the present application, should be covered in the protection scope of the claims of the present application.

[0056] The chloroform used is ≥99.8wt% from Merck, the β-alumina raw material for hydrogenation catalyst is from Zibo Honghe Chemical Co., Ltd., 98% pure nickel nitrate is from Aladdin, and 99% pure cobalt nitrate is from Aladdin. Anhydrous grass is purchased from Hubei Julongtang Pharmaceutical Chemical Co., Ltd. The recovery rates of acrylonitrile, propylene, adiponitrile, and hexanetristriazine are calculated by analyzing the liquid chromatograph equipped with an ultraviolet detector. The liquid chromatograph is Agilent 1200 series, equipped with a C18 liquid chromatograph column, the column temperature is set to 40℃, acetonitrile and 0.05mol / L NaH2PO4 solution are used as the mobile phase, the flow rate is 1.0mL / min, the ultraviolet detector is detected at 360nm wavelength, and the external standard method is used for quantitative determination. Before sampling, the sample is appropriately diluted with ultrapure water, and then derivatized with an excess of dinitrofluorobenzene solution before sampling and analysis.

[0057] Preparation of catalyst:

[0058] (1) 18g Ni(NO3)2, 8.96g Co(NO3)2 were added to 100ml of deionized water, and stirred until completely dissolved.

[0059] (2) In a round-bottom flask, 53.92g of β-Al2O3 carrier was added, and the solution of step 1 was introduced for soaking. After the carrier was taken out, it was drained to remove excess solution, and then dried at 12KPa(A), 175℃;

[0060] (3) The carrier impregnation obtained in step (2) was added to a round-bottom flask, and then 20wt% oxalic acid solution was added for soaking for 2.5h. After the carrier was taken out, it was drained to remove excess solution, and then dried at 12KPa(A), 175℃;

[0061] (4) The carrier impregnation obtained in step (3) is added to a muffle furnace for calcination. First, it is calcined at 265°C for 1 hour, then the temperature is raised to 410°C within 0.5 hours and calcined for another 3 hours. Finally, it is reduced with hydrogen for 4 hours to obtain the β-Al2O3 supported nickel and cobalt catalyst for the oxidation reaction.

[0062] Example 1

[0063] Reference Figure 1 As shown, the present invention adopts Figure 1 The waste liquid treatment system shown uses 880g of waste liquid from the electrochemical adiponitrile production process, which includes 15.95wt% acrylonitrile, 1.42wt% propionitrile, 67.37wt% adiponitrile, 0.7wt% methylglutaronitrile, 6.1wt% water, 5.55wt% hexanetrionitrile, 0.3wt% 3-hydroxypropionitrile, and 2.61wt% acrylonitrile polymer. 615g of chloroform is used as the azeotropic agent. After mixing with the waste liquid, the chloroform is fed into a chloroform azeotropic distillation column for azeotropic distillation. The azeotropic distillation column has 25 trays, with the feed tray being the 20th tray. The operating pressure is 0.8 bar absolute; the overall pressure drop is 2 kPa; the bottom temperature is 225℃; and the top temperature is 48℃.

[0064] The overhead product from the chloroform azeotropic distillation column enters the chloroform recovery column for azeotropic agent recovery. The chloroform recovery column has 25 trays, with the feed tray being the 20th tray. The operating pressure is 0.8 bar absolute; the overall pressure drop is 2 kPa; the bottom temperature is 69°C; and the top temperature is 42°C. The overhead product undergoes oil-water phase separation at a temperature of 25°C and a pressure of 1 bar absolute.

[0065] The effluent from the chloroform recovery tower enters the acrylonitrile tower, which has 50 trays, with the feed tray being the 5th tray. The operating pressure is 2 bar absolute; the overall pressure drop is 2 kPa; the bottom temperature is 100°C; and the top temperature is 92°C. Organic waste liquid is obtained at the top of the tower, and high-purity (99 wt%) acrylonitrile is recovered from the bottom.

[0066] The bottom product of the chloroform azeotropic distillation column enters the adiponitrile removal column, which has 45 trays, with the feed tray being the 25th tray. The operating pressure is absolute 0.1 bar; the overall pressure drop is 1 kPa; the bottom temperature is 214°C; and the top temperature is 49°C.

[0067] The overhead liquid from the adiponitrile removal tower enters the by-product propionitrile recovery tower, which has 25 trays, with the feed tray being the 20th tray. The operating pressure is absolute 0.8 bar; the overall pressure drop is 1 kPa; the reboiler temperature is 257°C; and the top temperature is 83°C. The reboiler yields a mixture of acrylonitrile and propionitrile with a water content of 2.1 wt%, which is used as a hydrogenation feedstock, with β-Al₂O₃ supporting Ni-C. OThe hydrogenation catalyst was used at 2 wt% of the feedstock, and the auxiliary agent cinnamaldehyde dimethyl acetal was used at 0.5 wt% of the feedstock. The hydrogenation operation temperature was 160℃ and the operating pressure was 11 bar. Propanonitrile was hydrogenated, with a conversion rate of 95 wt% and a selectivity of 96 wt%. The reaction product was purified by vacuum distillation to obtain 98 wt% propylamine.

[0068] The bottom liquid from the adiponitrile removal column enters the adiponitrile column, yielding high-purity adiponitrile (99.99 wt%) at the top, with an adiponitrile recovery rate of 96 wt%. The column has 40 trays, with the feed tray being the 35th tray. The column operating pressure is absolute 0.05 bar, and the overall pressure drop is 2 kPa. The bottom temperature is 310°C, and the top temperature is 185°C.

[0069] The adiponitrile column bottom liquid enters the hexanetrionitrile column, yielding 98.7 wt% hexanetrionitrile at the top, with a hexanetrionitrile recovery rate of 99.6 wt%. Heavy component residue is obtained from the bottom. The column has 15 trays, with the feed tray being the 7th tray. The column operating pressure is absolute 0.05 bar, and the overall pressure drop is 1 kPa. The bottom temperature is 550°C, and the top temperature is 295°C.

[0070] Example 2

[0071] Reference Figure 1 As shown, the present invention adopts Figure 1 The waste liquid treatment system shown uses 1600g of waste liquid from the electrochemical adiponitrile production process, which includes 16.5wt% acrylonitrile, 1.8wt% propionitrile, 67.5wt% adiponitrile, 0.1wt% methylglutaronitrile, 6.3wt% water, 5.02wt% hexanetrionitrile, 0.45wt% 3-hydroxypropionitrile, and 2.33wt% acrylonitrile polymer. 800g of chloroform is used as the azeotropic agent. After mixing with the waste liquid, the chloroform is fed into a chloroform azeotropic distillation column for azeotropic distillation. The azeotropic distillation column has 28 trays, with the feed tray being the 24th tray. The operating pressure is absolute 0.9 bar; the overall pressure drop is 2 kPa; the bottom temperature is 229℃; and the top temperature is 48℃.

[0072] The overhead product from the chloroform azeotropic distillation column enters the chloroform recovery column for azeotropic agent recovery. The chloroform recovery column has 28 trays, with the feed tray being the 25th tray. The operating pressure is 0.85 bar absolute; the overall pressure drop is 2 kPa; the bottom temperature is 75°C; and the top temperature is 45°C. The overhead product undergoes oil-water phase separation at a temperature of 30°C and a pressure of 1 bar absolute.

[0073] The effluent from the chloroform recovery tower enters the acrylonitrile tower, which has 45 trays, with the feed tray being the 10th tray. The operating pressure is 2.5 bar absolute; the overall pressure drop is 2 kPa; the bottom temperature is 105°C; and the top temperature is 95°C. Organic waste liquid is obtained at the top of the tower, and high-purity (98.9 wt%) acrylonitrile is recovered from the bottom.

[0074] The chloroform co-boiling rectification column tower pot effluent enters the adiponitrile light-removing column, which has 52 plates, and the feed plate is the 28th plate. The operating pressure is 0.15 bar; the whole column pressure drop is 1 KPa, the tower pot temperature is 225℃, and the tower top temperature is 55℃.

[0075] The adiponitrile light-removing column tower top liquid enters the by-product propionitrile recovery column, which has 28 plates, and the feed plate is the 22nd plate. The operating pressure is 0.88 bar; the whole column pressure drop is 1 KPa, the tower pot temperature is 262℃, and the tower top temperature is 88℃. The tower pot obtains a propylene cyanide, propionitrile mixed liquid with a water content of 2.5wt%, which is used as a hydrogenation raw material. The amount of β-Al2O3 supported Ni-CO used as a hydrogenation catalyst is 2.5wt% of the raw material feed amount, the amount of assistant, guaiacol dimethyl acetal, is 0.4wt% of the raw material feed amount, the hydrogenation operating temperature is 175℃, the operating pressure is 12 bar, propionitrile is hydrogenated, the conversion rate is 90wt%, the selectivity is 86wt%, and the reaction product is subjected to vacuum rectification to obtain pure propylamine with a purity of 85wt%.

[0076] The adiponitrile light-removing column tower pot liquid enters the adiponitrile column, and high-purity 99.94wt% adiponitrile is obtained at the tower top, and the adiponitrile recovery rate is 95.8wt%. The column has 45 plates, the feed plate is the 38th plate, the column operating pressure is 0.15 bar, and the whole column pressure drop is 2 KPa. The tower pot temperature is 342℃, and the tower top temperature is 198℃.

[0077] The adiponitrile column tower pot liquid enters the hexanetristitile column, and 98.5wt% hexanetristitile is obtained at the tower top, and the hexanetristitile recovery rate is 99wt%. The tower pot obtains heavy component pot residue. The column has 18 plates, the feed plate is the 9th plate, the column operating pressure is 0.08 bar, and the whole column pressure drop is 1 KPa. The tower pot temperature is 555℃, and the tower top temperature is 290℃.

[0078] Comparative Example 1

[0079] Except that the amount of assistant used is 0.5wt% of the raw material feed amount, which is methylal, the rest of the conditions are the same as in Example 1. Propionitrile is hydrogenated, the conversion rate is 70wt%, the selectivity is 86wt%, and the reaction product is subjected to vacuum rectification to obtain pure propylamine with a purity of 84wt%.

Claims

1. A method for treating waste liquid in the electrochemical adiponitrile production process, comprising the following steps: (1) The waste liquid from the electrochemical adiponitrile production is mixed with a certain proportion of chloroform and then fed into a chloroform azeotropic distillation column for azeotropic distillation. (2) The liquid collected from the top of the chloroform azeotropic distillation column enters the chloroform recovery column. The chloroform and water mixture obtained at the top of the column is subjected to oil-water separation at the top of the column. The oil phase is recycled to the chloroform azeotropic distillation column, and the water phase is organic wastewater. (3) The liquid collected from the bottom of the chloroform recovery tower enters the acrylonitrile tower for pressurized distillation. Organic waste liquid is obtained at the top of the tower, and high-purity acrylonitrile of 95-99 wt% is obtained at the bottom of the tower. (4) The bottom product of the chloroform azeotropic distillation column enters the adiponitrile removal column, the light component obtained at the top of the column enters the by-product propionitrile recovery column, and the bottom product enters the adiponitrile column. (5) The by-product propionitrile recovery tower is subjected to vacuum distillation. Propionitrile is recovered at the top of the tower and produced as propylamine under the action of hydrogenation catalyst and additives. The reaction liquid obtained from the hydrogenation reaction enters the distillation tower for further purification to remove light components. High-purity propylamine is obtained at the top of the tower. (6) Adiponitrile column vacuum distillation, adiponitrile is obtained at the top of the column; (7) The bottom product of the adiponitrile tower enters the hexanetrionitrile tower, and hexanetrionitrile is obtained at the top of the tower, while the bottom product is the residue of the heavy component. The waste liquid includes 15-16.5 wt% acrylonitrile, 1-1.8 wt% propionitrile, 65-70 wt% adiponitrile, 0.1-1 wt% methylglutaronitrile, 5-7 wt% water, 5-6 wt% hexanetrionitrile, 0.1-0.5 wt% 3-hydroxypropionitrile, and 2-3 wt% acrylonitrile polymer. The hydrogenation catalyst is β-Al₂O₃ supported on Ni-Co; The additive is cinnamaldehyde dimethyl acetal.

2. The method according to claim 1, characterized in that, In step (1), the mass ratio of the azeotropic agent chloroform to the waste liquid in the chloroform azeotropic distillation column is 0.5:1-0.9:

1.

3. The method according to claim 2, characterized in that, The mass ratio of the azeotropic agent chloroform to the waste liquid is 0.6:1-0.85:

1.

4. The method according to claim 2, characterized in that, The mass ratio of the azeotropic agent chloroform to the waste liquid is 0.65:1-0.8:

1.

5. The method according to claim 1, characterized in that, In step (1), the chloroform azeotropic distillation column operates at an absolute pressure of 0.5-0.9 bar; the bottom temperature is 210-230℃; and the top temperature is 45-50℃.

6. The method according to claim 5, characterized in that, The operating pressure is absolute pressure of 0.6-0.88 bar.

7. The method according to claim 5, characterized in that, The operating pressure is absolute pressure 0.7-0.85 bar.

8. The method according to claim 1, characterized in that, In step (3), the acrylonitrile tower operates at an absolute pressure of 1.5-3 bar; the bottom temperature is 90-105℃; and the top temperature is 85-95℃.

9. The method according to claim 8, characterized in that, The operating pressure is absolute pressure 1.6-2.8 bar.

10. The method according to claim 8, characterized in that, The operating pressure is absolute pressure 1.8-2.4 bar.

11. The method according to claim 1, characterized in that, In step (4), the adiponitrile removal tower operates at an absolute pressure of 0.05-0.2 bar; the bottom temperature is 210-225℃; and the top temperature is 40-55℃.

12. The method according to claim 11, characterized in that, The operating pressure is absolute pressure of 0.1-0.18 bar.

13. The method according to claim 11, characterized in that, The operating pressure is absolute pressure of 0.15-0.17 bar.

14. The method according to claim 1, characterized in that, In step (5), the by-product propionitrile recovery tower operates at a pressure of 0.5-0.95 bar; the bottom temperature is 240-265℃, and the top temperature is 75-88℃.

15. The method according to claim 14, characterized in that, The operating pressure is 0.55-0.9 bar.

16. The method according to claim 14, characterized in that, The operating pressure is 0.6-0.85 bar.

17. The method according to claim 1, characterized in that, In step (5), the amount of hydrogenation catalyst used accounts for 1-5 wt% of the propionitrile feed.

18. The method according to claim 1, characterized in that, In the hydrogenation catalyst, the molar ratio of nickel to cobalt is 3:1 to 1.1:1, and the metal loading in the catalyst is 25-66 wt% of the total catalyst mass.

19. The method according to claim 18, characterized in that, In the hydrogenation catalyst, the molar ratio of nickel to cobalt is 2.8:1-1.3:1, and the metal loading in the catalyst is 33-60 wt% of the total catalyst mass.

20. The method according to claim 18, characterized in that, In the hydrogenation catalyst, the molar ratio of nickel to cobalt is 2.5:1-1.8:1, and the metal loading in the catalyst is 38-55 wt% of the total catalyst mass.

21. The method according to claim 1, characterized in that, In step (5), the amount of the auxiliary agent is 0.4-1.2 wt% of the propionitrile feed; in step (5), the hydrogenation operation temperature is 150-180℃, the operation pressure is 10-15 bar, and the hydrogenation reaction feed space velocity is 18-20 h⁻¹. -1 .

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