A device and method for comprehensive utilization of high-salt acetonitrile wastewater

Abstract

This invention belongs to the field of industrial wastewater treatment technology, specifically relating to a comprehensive utilization device and method for high-salinity acetonitrile wastewater. It includes a pressure swing distillation system, a high-salinity wastewater treatment system, and a heat recovery system. The pressure swing distillation system includes a mixing tank, a first distillation column, and a second distillation column. The high-salinity wastewater treatment system includes a homogenization tank, a triple-effect evaporator, a NaCl electrolysis device, and a reverse osmosis device. The heat recovery system includes a flash tank. This invention effectively recovers acetonitrile from the wastewater, avoiding its contamination of the chlor-alkali ion exchange membrane in the NaCl electrolysis device, thus achieving resource recycling within the system. By rationally combining the pressure and temperature of the distillation device, this invention effectively avoids the problem of increased boiling point of wastewater caused by high salinity and high pressure. Simultaneously, the flash tank collects the condensate from the live steam generated in the distillation column, and the flash steam is used to heat the triple-effect evaporator, achieving comprehensive heat energy utilization.

Description

Technical Field

[0001] This invention belongs to the field of industrial wastewater resource utilization, specifically relating to a comprehensive utilization device and method for high-salt acetonitrile wastewater. Background Technology

[0002] Fine chemical production processes are lengthy, involving numerous organic chemical reactions, and resulting in the discharge of large quantities of wastewater containing organic solvents. Among these, acetonitrile in the wastewater is highly concentrated, toxic, and complex in composition. According to current national environmental protection requirements, acetonitrile wastewater must undergo specialized treatment processes for disposal, the cost of which is five times that of commercial acetonitrile. If acetonitrile and other components in the wastewater are separated and recycled, not only can environmental pollution be reduced, but unreacted acetonitrile can also be reused. Currently, the following are some treatment methods for acetonitrile-containing wastewater:

[0003] For high-concentration acetonitrile wastewater, the main methods involve single or combined processes centered on thermal methods to concentrate the acetonitrile to 99% or higher. Patent CN 109593059 A utilizes the pressure-dependent compositional variation of the acetonitrile-water azeotrope, employing pressure-swing distillation (both atmospheric and pressurized distillation). The final product is 99.6% high-purity acetonitrile at the bottom of the pressurized distillation column and 99.95% water at the bottom of the low-pressure distillation column. However, this method uses a single feed composition and still produces 500 ppm of low-concentration acetonitrile wastewater. Patent CN105968028A modifies the relative volatility of components by adding ethylene glycol extractant to an extractive distillation column. High-purity acetonitrile is obtained at the top of the column, and the aqueous ethylene glycol discharged from the bottom is purified in a dehydration column and returned to the extractive distillation column. This method requires an additional ethylene glycol dehydration column, increasing operating energy consumption. Patent CN101492391A employs a process combining extraction and distillation. Acetonitrile is extracted into the extract phase by adding dichloromethane as an extractant, and then the extract phase is fed into a distillation column to obtain high-purity acetonitrile, while the dichloromethane is returned to the extraction tank. This method generates wastewater containing both dichloromethane and acetonitrile during the purification process, leading to secondary pollution of the effluent. A process combining conventional distillation and dehydration utilizes conventional distillation to obtain an acetonitrile-water azeotrope, which is then dehydrated by freezing (patent CN 112812038 A) or liquid-phase membrane dehydration (patent CN114315641A) to obtain anhydrous acetonitrile. This type of method requires both high-temperature and low-temperature or special membrane equipment, resulting in higher operating costs.

[0004] For low-concentration acetonitrile wastewater, biological and physicochemical methods are mainly used to degrade the acetonitrile and achieve compliant discharge. Patent CN114214254A utilizes domesticated Rhodococcus rubrum to degrade acetonitrile. While this method can degrade acetonitrile into corresponding carboxylic acids and ammonia, and the carboxylic acids can be further oxidized to carbon dioxide and water, it also has the following drawbacks: aeration accelerates the stripping of acetonitrile from the wastewater, polluting the atmosphere; additionally, the increased ammonia nitrogen content in the effluent necessitates additional nitrification and denitrification processes, increasing operating costs; furthermore, if the salinity of the wastewater is high, it can inhibit microorganisms, reducing the effectiveness of biological treatment. Patent CN110803818A provides a method combining distillation and alkaline hydrolysis, reducing the acetonitrile content of low-concentration acetonitrile wastewater obtained from distillation to 5 ppm through alkaline hydrolysis. This method requires sodium hydroxide for alkaline hydrolysis, and the reaction time is long and the temperature is high, leaving trace amounts of acetonitrile in the effluent.

[0005] Therefore, none of the above methods can effectively treat acetonitrile wastewater with high salinity. Patent CN104817140A addresses the characteristics of perfluoroketone production wastewater, which contains acetonitrile and high salinity, by employing a two-step electrolytic oxidation process. First, acetonitrile is oxidized by low-pressure micro-current electrolysis, and then sodium hypochlorite is prepared by conventional current electrolysis of NaCl. This method degrades acetonitrile using expensive and energy-intensive electrolysis equipment, but it has strict requirements on the acetonitrile concentration in the wastewater, and the acetonitrile removal rate is greatly affected by salinity and pH, making it difficult to adapt to the fluctuating water quality characteristics of industrial production. Furthermore, the resulting sodium hypochlorite concentrate is low, and the byproducts and residual acetonitrile generated during prolonged electrolysis affect the purity of the sodium hypochlorite.

[0006] In summary, there is an urgent need for a method to achieve comprehensive utilization of acetonitrile and other components in wastewater while optimizing the energy consumption of the process. Summary of the Invention

[0007] To address the aforementioned technical problems, this invention provides a device and method for the comprehensive utilization of high-salt acetonitrile wastewater.

[0008] To achieve the above objectives, the present invention adopts the following technical solution:

[0009] A comprehensive utilization device for high-salt acetonitrile wastewater includes a pressure swing distillation system, a high-salt wastewater treatment system, and a heat recovery system.

[0010] The pressure swing distillation system includes a mixing tank, a first distillation column, and a second distillation column; the high-salt wastewater treatment system includes a homogenization tank, a triple-effect evaporator, a NaCl electrolysis unit, and a reverse osmosis unit; the heat recovery system includes a flash tank.

[0011] The outlet of the mixing tank is connected to the inlet of the first distillation column; the top outlet of the first distillation column is connected to the inlet of the second distillation column; the bottom outlet of the first distillation column is connected to the homogenizing tank; and the top outlet of the second distillation column is connected to the inlet of the mixing tank.

[0012] The outlet of the homogenizing tank is connected to the inlet of the triple-effect evaporator; the concentrated brine outlet of the triple-effect evaporator is connected to the NaCl electrolysis unit; the secondary steam condensate outlet of the triple-effect evaporator is connected to the reverse osmosis unit; the concentrated water outlet of the reverse osmosis unit is connected to the inlet of the blending tank; the desalinated water outlet of the reverse osmosis unit is connected to the inlet of the NaCl electrolysis unit; and the desalinated brine outlet of the NaCl electrolysis unit is connected to the inlet of the homogenizing tank.

[0013] Preferably, the feed inlet of the flash tank is connected to the reboiler live steam condensate outlet of the first distillation column and the reboiler live steam condensate outlet of the second distillation column, and the flash steam outlet of the flash tank is connected to the heater of the triple-effect evaporator.

[0014] Preferably, the high-salt wastewater treatment system further includes an alkaline absorption device, wherein the chlorine outlet and NaOH solution outlet of the NaCl electrolysis device and the freshwater outlet of the reverse osmosis device are all connected to the inlet of the alkaline absorption device.

[0015] Preferably, the first distillation column is a tray distillation column or a packed distillation column.

[0016] Preferably, the second distillation column is a tray distillation column or a packed distillation column.

[0017] This invention also provides a method for the comprehensive utilization of high-salt acetonitrile wastewater.

[0018] Wastewater A from the production workshop, high-concentration acetonitrile wastewater F from the second distillation column, and concentrated water O from the reverse osmosis unit are mixed in a mixing tank and then distilled in the first distillation column. The acetonitrile-water azeotrope C produced at the top of the first distillation column enters the second distillation column, while the high-salt wastewater produced at the bottom of the first distillation column enters a homogenization tank. The high-concentration acetonitrile wastewater F produced at the top of the second distillation column is returned to the mixing tank for further distillation. The high-purity acetonitrile E obtained at the bottom of the second distillation column is recycled and reused in the production workshop.

[0019] High-salinity wastewater D is homogenized in a homogenizing tank to obtain homogenizing tank wastewater G, which is then concentrated in a triple-effect evaporator to obtain concentrated brine H and secondary steam condensate I, respectively.

[0020] Concentrated brine H enters the NaCl electrolysis unit, where it is electrolyzed to produce hydrogen gas N, chlorine gas K, and NaOH solution L; the resulting dilute brine J is returned to the homogenization tank for further concentration.

[0021] The secondary steam condensate I passes through the reverse osmosis unit, and the resulting concentrated water O is returned to the blending tank for further distillation to produce desalinated water P, which is then used in the NaCl electrolysis unit, the alkali absorption unit, and the production workshop for recycling.

[0022] Preferably, the high-salt acetonitrile wastewater A from the production workshop has an acetonitrile content of 10-25 wt% and a sodium chloride content of 14-18 wt%.

[0023] Preferably, the operating pressure of the first distillation column is 101~130 kPa, the top temperature is 77~86℃, and the bottom temperature is 110~114℃.

[0024] Preferably, the operating pressure of the second distillation column is 200~300 kPa, the top temperature is 97~111℃, and the bottom temperature is 105~121℃.

[0025] Preferably, the acetonitrile concentration of the high-concentration acetonitrile wastewater F produced at the top of the first distillation column is 81~82wt%; and the acetonitrile purity of the high-purity acetonitrile E obtained from the bottom of the second distillation column is 99.5~99.7%.

[0026] Preferably, the concentration of sodium chloride in the concentrated brine H obtained by the triple-effect evaporator is 22~30wt%.

[0027] Preferably, the condensate Q from the reboiler of the first distillation column and the condensate R from the reboiler of the second distillation column are collected in a closed system into a flash tank, and the flash steam S enters a triple-effect evaporator for heating.

[0028] More preferably, the operating pressure of the flash tank is 0.5~0.6 MPa.

[0029] Preferably, chlorine gas K, NaOH solution L, and partially demineralized water P are passed through an alkaline absorption device to produce sodium hypochlorite solution M.

[0030] Further preferably, the sodium hypochlorite solution concentration is 12~16wt%.

[0031] The present invention has the following beneficial effects:

[0032] (1) This invention can treat production wastewater with an acetonitrile content of 10~25wt% and a sodium chloride content of 14~18wt% into raw materials that meet the needs of workshop production, including obtaining 81~82% acetonitrile, 99.5~99.7% high-purity acetonitrile, 12~16wt% sodium hypochlorite solution and 0.01~0.02 MΩ·cm deionized water, etc. All indicators are flexible and controllable. At the same time, this method avoids the discharge of industrial wastewater into the environment, realizes the comprehensive utilization of wastewater resources, and is conducive to building a resource-saving and environmentally friendly society.

[0033] (2) This invention effectively recovers acetonitrile from wastewater, thus avoiding pollution of the chlor-alkali ion membrane in the NaCl electrolysis device; at the same time, it concentrates and refines sodium chloride that meets the technical standards for ion membrane caustic soda refining wet salt (QB / T 5270-2018), realizing resource recycling within the system, saving hazardous waste disposal costs, and reducing the raw material procurement cost for refined sodium chloride.

[0034] (3) By rationally combining the operating pressure and temperature parameters of the distillation unit, the present invention effectively avoids the problem of increased boiling point of wastewater caused by high salt content and high pressure. At the same time, by using the flash tank to collect the condensate of the live steam generated by the distillation tower, the flash steam is used to heat the triple-effect evaporation unit, thereby reducing the demand for high-grade heat energy by 1.9% to 2.5% and realizing comprehensive utilization of heat energy. Attached Figure Description

[0035] Figure 1 This invention relates to a system for the comprehensive utilization of high-salt acetonitrile wastewater in the fine chemical production process.

[0036] Figure labels: 1-Blending tank, 2-First distillation column, 3-Second distillation column, 4-Homogenizing tank, 5-Flash tank, 6-Triple-effect evaporator, 7-NaCl electrolysis unit, 8-Alkali absorption unit; 9-Reverse osmosis unit.

[0037] A. Wastewater from the production workshop; B. Wastewater from the mixing tank; C. Acetonitrile-water azeotrope; D. High-salinity wastewater; E. High-purity acetonitrile; F. High-concentration acetonitrile wastewater; G. Wastewater from the homogenization tank; H. Concentrated brine; I. Secondary steam condensate; J. Dilute brine; K. Chlorine; L. NaOH solution; M. Sodium hypochlorite solution; N. Hydrogen; O. Concentrated water; P. Demineralized water; Q. First live steam condensate; R. Second live steam condensate; S. Flash steam. Detailed Implementation

[0038] The present invention will now be described in detail through specific embodiments. The distillation column, flash tank, triple-effect evaporator, NaCl electrolysis device, alkali absorption device, and reverse osmosis device used in the present invention are all commonly used equipment in the field, and are sufficient to fulfill their functions in the present invention.

[0039] Example 1

[0040] like Figure 1 As shown, the present invention provides a system for the comprehensive utilization of high-salt acetonitrile wastewater, including a pressure swing distillation system, a high-salt wastewater treatment system, and a heat recovery system.

[0041] The pressure swing distillation system includes a mixing tank 1, a first distillation column 2, and a second distillation column 3. The outlet of the mixing tank 1 (mixing tank wastewater B) is connected to the inlet of the first distillation column 2. The top outlet of the first distillation column 2 (acetonitrile-water azeotrope C) is connected to the inlet of the second distillation column 3. The bottom outlet of the first distillation column 2 (high salinity wastewater D) is connected to the homogenization tank 4 of the high salinity wastewater treatment system. The top outlet of the second distillation column 3 (high concentration acetonitrile wastewater F) is connected to the mixing tank 1. High-purity acetonitrile E is obtained from the bottom of the second distillation column 3.

[0042] The high-salinity wastewater treatment system includes a homogenization tank 4, a triple-effect evaporator 6, a NaCl electrolysis unit 7, an alkaline absorption unit 8, and a reverse osmosis unit 9. The outlet of the homogenization tank 4 (wastewater G) is connected to the inlet of the triple-effect evaporator 6; the concentrated brine outlet (concentrated brine H) of the triple-effect evaporator 6 is connected to the NaCl electrolysis unit 7; the secondary steam condensate outlet (secondary steam condensate I) of the triple-effect evaporator 6 is connected to the reverse osmosis unit 9; and the desalinated brine outlet (desalinated brine J) of the NaCl electrolysis unit 7 is connected to... The homogenizing tank 4 is connected to the feed inlet; the chlorine outlet (chlorine K) and NaOH solution outlet (NaOH solution L) of the NaCl electrolysis unit 7 are connected to the inlet of the alkali absorption unit 8. The NaOH solution L and chlorine K are absorbed by the alkali absorption unit 8 to obtain sodium hypochlorite solution M. The NaCl electrolysis unit 7 also produces hydrogen N. The concentrated water O produced by the reverse osmosis unit 9 is connected to the feed inlet of the mixing tank 1 through the concentrated water outlet. At the same time, demineralized water P is produced and used for recycling in the NaCl electrolysis unit 7, the alkali absorption unit 8, and the production workshop.

[0043] The heat recovery system includes a flash tank 5. The inlet of the flash tank 5 is connected to the reboiler live steam condensate outlet (first live steam condensate Q) of the first distillation column 2 and the reboiler live steam condensate outlet (second live steam condensate R) of the second distillation column 3. The flash steam outlet (flash steam S) of the flash tank 5 is connected to the heater of the triple-effect evaporator 6.

[0044] Example 2

[0045] A method for the resource utilization of high-salt acetonitrile wastewater, using the apparatus described in Example 1, involves the following steps: wastewater A (acetonitrile content of 25 wt% and sodium chloride content of 18 wt%) from the production workshop enters the mixing tank 1 at a rate of 1000 kg / h, and the mixed wastewater B (acetonitrile content of 41.38 wt% and sodium chloride content of 8.44 wt%) enters the first distillation column 2 at a rate of 2267 kg / h for distillation.

[0046] The first distillation column 2 is a tray distillation column with an operating pressure of 101 kPa, a top temperature of 77℃, a bottom temperature of 110℃, and requires 271 kg / h of live steam at 0.8 MPa. The acetonitrile-water azeotrope C (acetonitrile content of 82 wt%) produced at the top of the first distillation column 2 enters the second distillation column 3 at a rate of 1138 kg / h. The high-salt wastewater D (acetonitrile content of 0.42 wt%, sodium chloride content of 16.96 wt%, and a yield of 1129 kg / h) produced at the bottom of the first distillation column 2 enters the homogenization tank 4 of the high-salt wastewater treatment system.

[0047] The second distillation column 3 is a tray distillation column, operating at a pressure of 300 kPa, with a top temperature of 111℃ and a bottom temperature of 121℃, requiring 124 kg / h of live steam at 0.8 MPa. The high-concentration acetonitrile wastewater F (acetonitrile content 77wt%, yield 888 kg / h) produced from the top of the second distillation column 3 is returned to the blending tank 1 for further distillation. The high-purity acetonitrile E (250 kg / h) obtained from the bottom of the second distillation column 3 has a purity of 99.7% and is directly recycled in the production workshop.

[0048] After homogenization treatment in homogenizer 4, high-salinity wastewater D is followed by wastewater G (acetonitrile content 0.22 wt%, sodium chloride content 17.46 wt%), which enters triple-effect evaporator 6 at a rate of 2179 kg / h. This produces concentrated brine H (sodium chloride concentration 30 wt%, yield 1230 kg / h) and secondary steam condensate I (acetonitrile content 0.49 wt%, sodium chloride content 1.20 wt%, yield 949 kg / h). Triple-effect evaporator 6 requires 7.69 kg / h of 0.6 MPa steam, which is generated by flash tank 5. Flash tank 5 collects first live steam condensate Q and second live steam condensate R through a closed system (controlled pressure 0.6 MPa), producing 7.82 kg / h of 0.6 MPa flash steam S, with a surplus of 0.13 kg / h.

[0049] The secondary steam condensate I is processed by reverse osmosis unit 9 to produce demineralized water P (0.02 MΩ·cm, yield 570 kg / h), which is used in NaCl electrolysis unit 7, alkali absorption unit 8 and directly reused in the production workshop. The resulting concentrated water O (acetonitrile content 1.23wt%, sodium chloride content 3.00wt%, yield 379 kg / h) is returned to blending tank 1 for further distillation.

[0050] Concentrated brine H and partially demineralized brine P (287 kg / h) enter the NaCl electrolysis unit 7, where electrolysis produces hydrogen gas N, chlorine gas K, and NaOH solution L. The resulting dilute brine J (sodium chloride concentration of 18 wt%, yield of 1050 kg / h) is returned to the homogenization tank 4 for further concentration.

[0051] Chlorine gas K, NaOH solution L, and partially demineralized water P (149 kg / h) are processed by alkaline absorption device 8 to produce sodium hypochlorite solution M with a concentration of 16%, which is directly recycled in the production workshop.

[0052] Example 3

[0053] A method for the resource utilization of high-salt acetonitrile wastewater, using the apparatus described in Example 1, involves the following: wastewater A (acetonitrile content 10 wt%, sodium chloride content 14 wt%) from the production workshop enters the mixing tank 1 at a rate of 1000 kg / h, and the mixed wastewater B (acetonitrile content 34.43 wt%, sodium chloride content 6.55 wt%) enters the first distillation column 2 at a rate of 2436 kg / h for distillation.

[0054] The first distillation column 2 is a tray distillation column with an operating pressure of 130 kPa, a top temperature of 86℃, a bottom temperature of 114℃, and requires 352 kg / h of live steam at 0.8 MPa. The acetonitrile-water azeotrope C (acetonitrile content of 81 wt%) produced at the top of the first distillation column 2 enters the second distillation column 3 at a rate of 1030 kg / h. The high-salt wastewater D (acetonitrile content of 0.30 wt%, sodium chloride content of 11.35 wt%, and a yield of 1406 kg / h) produced at the bottom of the first distillation column 2 enters the homogenization tank 4 of the high-salt wastewater treatment system.

[0055] The second distillation column 3 is a tray distillation column, operating at a pressure of 200 kPa, with a top temperature of 97℃ and a bottom temperature of 105℃, requiring 48 kg / h of live steam at 0.8 MPa. The high-concentration acetonitrile wastewater F (acetonitrile content 79 wt%, yield 930 kg / h) produced at the top of the second distillation column 3 is returned to the blending tank 1 for further distillation. The high-purity acetonitrile E (100 kg / h) obtained from the bottom of the second distillation column 3 has a purity of 99.5% and is directly recycled in the production workshop.

[0056] After homogenization treatment in homogenizer 4, high-salinity wastewater D is followed by wastewater G (acetonitrile content 0.10 wt%, sodium chloride content 15.74 wt%), which enters triple-effect evaporator 6 at a rate of 4136 kg / h. This produces concentrated brine H (sodium chloride concentration 22 wt%, yield 2870 kg / h) and secondary steam condensate I (acetonitrile content 0.33 wt%, sodium chloride content 1.54 wt%, yield 1266 kg / h). Triple-effect evaporator 6 requires 10.17 kg / h of 0.5 MPa steam, which is generated by flash tank 5. Flash tank 5 collects first live steam condensate Q and second live steam condensate R through a closed system (controlled pressure 0.5 MPa), producing 12.35 kg / h of 0.5 MPa flash steam S, with a surplus of 2.18 kg / h.

[0057] The secondary steam condensate I is processed by reverse osmosis unit 9 to produce demineralized water P (0.01 MΩ·cm, output 760 kg / h), which is used in NaCl electrolysis unit 7, alkali absorption unit 8 and directly reused in the production workshop. The resulting concentrated water O (acetonitrile content 0.83wt%, sodium chloride content 3.85wt%, output 506 kg / h) is returned to blending tank 1 for further distillation.

[0058] Concentrated brine H and partially demineralized brine P (223 kg / h) enter the NaCl electrolysis unit 7, where electrolysis produces hydrogen gas N, chlorine gas K, and NaOH solution L. The resulting dilute brine J (sodium chloride concentration of 18 wt%, yield of 2730 kg / h) is returned to the homogenization tank 4 for further concentration.

[0059] Chlorine gas K, NaOH solution L, and partially demineralized water P (160 kg / h) are processed by alkaline absorption device 8 to produce sodium hypochlorite solution M with a concentration of 12%, which is directly recycled in the production workshop.

[0060] Comparative Example 1

[0061] A method for the resource utilization of high-salt acetonitrile wastewater, using the apparatus described in Example 1, involves the following steps: wastewater A (acetonitrile content 35 wt%, sodium chloride content 10 wt%) from the production workshop enters the mixing tank 1 at a rate of 1000 kg / h, and the mixed wastewater B (acetonitrile content 50.35 wt%, sodium chloride content 4.08 wt%) enters the first distillation column 2 at a rate of 2609 kg / h for distillation.

[0062] The first distillation column 2 is a tray distillation column with an operating pressure of 101 kPa, a top temperature of 77℃, a bottom temperature of 110℃, and requires 267 kg / h of live steam at 0.8 MPa. The acetonitrile-water azeotrope C (acetonitrile content of 82 wt%) produced at the top of the first distillation column 2 enters the second distillation column 3 at a rate of 1594 kg / h. The high-salt wastewater D (acetonitrile content of 0.65 wt%, sodium chloride content of 10.48 wt%, and a yield of 1015 kg / h) produced at the bottom of the first distillation column 2 enters the homogenization tank 4 of the high-salt wastewater treatment system.

[0063] The second distillation column 3 is a tray distillation column, operating at a pressure of 300 kPa, with a top temperature of 111℃ and a bottom temperature of 121℃, requiring 174 kg / h of live steam at 0.8 MPa. The high-concentration acetonitrile wastewater F (acetonitrile content 77wt%, yield 1243 kg / h) produced from the top of the second distillation column 3 is returned to the blending tank 1 for further distillation. The high-purity acetonitrile E (351 kg / h) obtained from the bottom of the second distillation column 3 has a purity of 99.7% and is directly recycled in the production workshop.

[0064] After homogenization treatment in homogenizer 4, high-salinity wastewater D is followed by wastewater G (acetonitrile content 0.41 wt%, sodium chloride content 13.22 wt%), which enters triple-effect evaporator 6 at a rate of 1598 kg / h. This produces concentrated brine H (sodium chloride concentration 30 wt%, yield 683 kg / h) and secondary steam condensate I (acetonitrile content 0.72 wt%, sodium chloride content 0.69 wt%, yield 915 kg / h). Triple-effect evaporator 6 requires 7.42 kg / h of 0.6 MPa steam, which is generated by flash tank 5. Flash tank 5 collects first live steam condensate Q and second live steam condensate R through a closed system (controlled pressure 0.6 MPa), producing 8.73 kg / h of 0.6 MPa flash steam S, with a surplus of 1.31 kg / h.

[0065] The secondary steam condensate I is processed by reverse osmosis unit 9 to produce demineralized water P (0.02 MΩ·cm, yield 549 kg / h), which is used in NaCl electrolysis unit 7, alkali absorption unit 8 and directly reused in the production workshop. The resulting concentrated water O (acetonitrile content 1.79wt%, sodium chloride content 1.73wt%, yield 366 kg / h) is returned to blending tank 1 for further distillation.

[0066] Concentrated brine H and partially demineralized brine P (160 kg / h) enter the NaCl electrolysis unit 7, where electrolysis produces hydrogen gas N, chlorine gas K, and NaOH solution L. The resulting dilute brine J (sodium chloride concentration of 18 wt%, yield of 583 kg / h) is returned to the homogenization tank 4 for further concentration.

[0067] Chlorine gas K, NaOH solution L, and a portion of demineralized water P (83 kg / h) are processed by alkaline absorption device 8 to produce sodium hypochlorite solution M with a concentration of 16%, which is directly recycled in the production workshop.

[0068] Compared to Example 2, the processing cost increased by 12%.

Claims

1. A method for the comprehensive utilization of high-salt acetonitrile wastewater, characterized in that, The equipment used includes a pressure swing distillation system, a high-salinity wastewater treatment system, and a heat recovery system; The pressure swing distillation system includes a mixing tank (1), a first distillation column (2), and a second distillation column (3); the high-salt wastewater treatment system includes a homogenization tank (4), a triple-effect evaporator (6), a NaCl electrolysis unit (7), and a reverse osmosis unit (9); the heat recovery system includes a flash tank (5). The outlet of the mixing tank (1) is connected to the inlet of the first distillation column (2), the top outlet of the first distillation column (2) is connected to the inlet of the second distillation column (3), the bottom outlet of the first distillation column (2) is connected to the homogenizing tank (4); the top outlet of the second distillation column (3) is connected to the inlet of the mixing tank (1). The outlet of the homogenizing tank (4) is connected to the inlet of the triple-effect evaporator (6), the concentrated brine outlet of the triple-effect evaporator (6) is connected to the NaCl electrolysis device (7), the secondary steam condensate outlet of the triple-effect evaporator (6) is connected to the reverse osmosis device (9), the concentrated water outlet of the reverse osmosis device (9) is connected to the inlet of the mixing tank (1), the fresh water outlet of the reverse osmosis device (9) is connected to the inlet of the NaCl electrolysis device (7), and the brine outlet of the NaCl electrolysis device (7) is connected to the inlet of the homogenizing tank (4). Wastewater A from the production workshop, high-concentration acetonitrile wastewater F from the second distillation column (3), and concentrated water O from the reverse osmosis unit (9) are mixed in the mixing tank (1) and then enter the first distillation column (2) for distillation. The acetonitrile-water azeotrope C produced at the top of the first distillation column (2) enters the second distillation column (3). The high-salt wastewater D produced at the bottom of the first distillation column (2) enters the homogenization tank (4). The high-concentration acetonitrile wastewater F produced at the top of the second distillation column (3) is returned to the mixing tank (1) for distillation again. The high-purity acetonitrile E obtained at the bottom of the second distillation column (3) is recycled and reused in the production workshop. High-salt wastewater D is homogenized in a homogenizing tank (4) to obtain homogenizing tank wastewater G, which is then concentrated in a triple-effect evaporator (6) to obtain concentrated brine H and secondary steam condensate I, respectively. Concentrated brine H enters the NaCl electrolysis device (7), where it is electrolyzed to produce hydrogen gas N, chlorine gas K, and NaOH solution L; the resulting dilute brine J is returned to the homogenization tank (4) for further concentration. The secondary steam condensate I passes through the reverse osmosis unit (9), and the resulting concentrated water O is returned to the mixing tank (1) for further distillation to produce desalinated water P, which is used in the NaCl electrolysis unit (7), the alkali absorption unit (8), and the production workshop for recycling. The acetonitrile content in wastewater A from the production workshop is 10~25wt%, and the sodium chloride content is 14~18wt%. The first distillation column (2) operates at a pressure of 101~130 kPa, a top temperature of 77~86℃, and a bottom temperature of 110~114℃; the second distillation column (3) operates at a pressure of 200~300 kPa, a top temperature of 97~111℃, and a bottom temperature of 105~121℃.

2. The method for comprehensive utilization of high-salinity acetonitrile wastewater according to claim 1, characterized in that, The high-concentration acetonitrile wastewater F produced at the top of the first distillation column (2) has an acetonitrile concentration of 81~82wt%; the high-purity acetonitrile E obtained from the bottom of the second distillation column (3) has an acetonitrile purity of 99.5~99.7wt%; and the concentrated brine H obtained from the triple-effect evaporator (6) has a sodium chloride concentration of 22~30wt%.

3. The method for comprehensive utilization of high-salinity acetonitrile wastewater according to claim 1, characterized in that, The condensate Q from the reboiler of the first distillation column (2) and the condensate R from the reboiler of the second distillation column (3) are collected in a closed system and sent to a flash tank (5). The flash steam S enters a triple-effect evaporator (6) for heating.

4. The method for comprehensive utilization of high-salinity acetonitrile wastewater according to claim 3, characterized in that, The operating pressure of the flash tank (5) is 0.5~0.6 MPa.

5. The method for comprehensive utilization of high-salinity acetonitrile wastewater according to claim 1, characterized in that, The feed inlet of the flash tank (5) is connected to the reboiler steam condensate outlet of the first distillation column (2) and the reboiler steam condensate outlet of the second distillation column (3), respectively. The flash steam outlet of the flash tank (5) is connected to the heater of the triple-effect evaporator (6).

6. The method for comprehensive utilization of high-salinity acetonitrile wastewater according to claim 1, characterized in that, The high-salt wastewater treatment system described in the device also includes an alkaline absorption device (8), and the chlorine outlet and NaOH solution outlet of the NaCl electrolysis device (7) and the fresh water outlet of the reverse osmosis device (9) are all connected to the inlet of the alkaline absorption device (8).

7. The method for comprehensive utilization of high-salinity acetonitrile wastewater according to claim 1, characterized in that, The first distillation column (2) of the apparatus is a tray distillation column or a packed distillation column; the second distillation column (3) is a tray distillation column or a packed distillation column.

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