Resource recycling method for nitrile-containing wastewater

Abstract

The invention relates to the field of water treatment, and discloses a nitrile-containing wastewater resource recovery method, which comprises: 1) carrying out two-phase counter-current extraction on nitrile-containing wastewater and styrene; 2) performing steam stripping on the raffinate to separate styrene; 3) evaporating and separating the raffinate to obtain a sulfate concentrated solution and an aqueous solution; 4) performing flash evaporation on the extract to remove salt, and performing rectification separation to obtain acrylonitrile and styrene solution 1; 5) rectifying the styrene solution 1 to separate a 2-phenyl-2-propanol solution and a styrene solution 2; and 6) condensing the styrene solution 2 and styrene and then recycling. According to the method, the nitrile-containing wastewater is subjected to resource recycling treatment by adopting an extraction, steam stripping and evaporation process for the first time, so that the treatment efficiency of the nitrile-containing wastewater can be remarkably improved, the consumption of acid and alkali is reduced, the generation of waste salt is reduced, the land occupation is reduced, and the concentration of organic nitriles and benzene series substances in the nitrile-containing wastewater is effectively reduced; and cyclic utilization of resources and zero discharge of wastewater are realized.

Description

Technical Field

[0001] This invention relates to the field of water treatment, and more particularly to a method for the resource recovery of nitrile-containing wastewater. Background Technology

[0002] Nitrile-containing wastewater refers to industrial wastewater containing nitrile substances, mainly originating from the production processes of the chemical, pharmaceutical, and synthetic resin industries. Nitriles are organic compounds containing the -CN functional group, exhibiting high toxicity and recalcitrant biodegradability. Therefore, the treatment of nitrile-containing wastewater has always been a challenge in the industry. Currently, reported pretreatment methods for nitrile-containing wastewater mainly include chemical treatment, physical treatment, and biological treatment. Given the complex composition of nitrile-containing production wastewater, it is difficult to meet discharge standards using a single treatment technology. Therefore, in practical applications, a combination of physical, chemical, and biochemical processes is commonly used. However, existing combined processes have many drawbacks, such as cumbersome and lengthy processes, high treatment costs, and the potential for environmental pollution from excessive chemical dosage.

[0003] Patent CN119912066A describes a method for treating wastewater with high nitrile content, which involves reacting excess Na2CO3 with -CN under alkaline conditions to generate ammonium carboxylate, followed by biochemical treatment. While this method converts nitrile into ammonium carboxylate with low biochemical toxicity, the introduction of large amounts of alkaline substances leads to secondary pollution and generates a large amount of alkaline wastewater. Therefore, further optimization is needed from both economic and environmental perspectives.

[0004] Patent CN119930017A utilizes sodium sulfite to convert acrylonitrile into sodium cyanoethyl sulfonate under alkaline conditions, which is then used for biochemical treatment. Similar to patent CN119912066A, this scheme also introduces secondary pollution, and the long chemical reaction time results in a large pretreatment device, limiting the efficiency of wastewater treatment.

[0005] Patent CN117069186A proposes a method of first performing azeotropic distillation on nitrile-containing wastewater, followed by high-temperature and high-pressure hydrolysis of the nitrile compounds. While this method can effectively reduce the nitrile content, the equipment investment is high and the energy consumption during industrial implementation is also high, requiring further optimization design.

[0006] Patent CN110066226B describes a process technology that uses benzene to extract acetonitrile in a decanter, thereby transferring most of the acetonitrile from the aqueous phase to the organic phase for subsequent distillation. This technology can effectively reduce the energy consumption of acetonitrile separation. However, the extraction effect using a decanter is limited, and the emulsion droplets containing the extractant in the raffinate phase still require further treatment to achieve optimal design of the material and energy system.

[0007] In summary, existing pretreatment methods for nitrile wastewater have some shortcomings, mainly in the following aspects: (1) high energy consumption and high chemical consumption, resulting in high treatment costs; (2) low removal efficiency for some recalcitrant organic compounds, such as acrylonitrile; (3) long reaction time and large treatment facilities are required, resulting in large land area and operating costs; (4) secondary pollution may be generated during the treatment process.

[0008] Therefore, there is a need to develop a more efficient, economical, and environmentally friendly wastewater treatment technology that can ensure the efficient removal of harmful organic matter from nitrile-containing wastewater while reducing energy consumption and chemical use. Summary of the Invention

[0009] To address the aforementioned technical problems, this invention provides a method for the resource recovery of nitrile-containing wastewater. This invention is the first to employ a combined process of extraction, stripping, and evaporation for the resource recovery of nitrile-containing wastewater. This method significantly improves the treatment efficiency of nitrile-containing wastewater, reduces acid and alkali consumption, decreases waste salt generation, reduces land occupation, and effectively reduces the concentration of organic nitriles and benzene compounds in the wastewater. Simultaneously, by recovering sulfates and water resources, it achieves resource recycling and zero wastewater discharge.

[0010] The specific technical solution of the present invention includes: a method for resource recovery of nitrile-containing wastewater, comprising the following steps: 1) Nitrile-containing wastewater and styrene extractant enter from the top and bottom of the extraction tower, respectively, for two-phase countercurrent extraction.

[0011] 2)1) The obtained raffinate enters the stripping tower, where styrene is separated by steam stripping.

[0012] 3)2) The obtained raffinate enters the multi-effect evaporation system, and after evaporation and separation, sulfate (e.g., potassium sulfate) concentrate and aqueous solution are obtained.

[0013] 4)1) The obtained extract was desalted by flash evaporation and then separated into acrylonitrile and styrene solution 1 by first distillation.

[0014] 5) After a second distillation, styrene solution 1 was separated into 2-phenyl-2-propanol solution and styrene solution 2.

[0015] 6) The styrene obtained from styrene solution 2 and 2) is recycled after condensation.

[0016] In the above steps, the nitrile-containing wastewater and the extractant first enter the extraction tower for two-phase countercurrent extraction. The extract stream is obtained at the top of the tower, and the raffinate enters the stripping tower to separate the extractant by steam stripping. The remaining wastewater is treated with a multi-effect evaporation system to recover salts. The extract stream is then desalted in a flash tank and passed through the first and second distillation towers to obtain organic products. The extractant is recovered and recycled after condensation.

[0017] This invention is the first to employ a combined process of extraction, stripping, and evaporation for the resource recovery and treatment of nitrile-containing wastewater. This method not only effectively removes harmful nitrile substances from the wastewater but also recovers valuable raw materials such as acrylonitrile and styrene, achieving zero wastewater discharge and resource recycling. This invention solves the problems of large footprint, high cost, inability to recover water resources, and difficulty in separating acrylonitrile found in traditional pretreatment methods. Furthermore, it achieves the effective recovery and utilization of potassium sulfate and sodium, reducing the raw material consumption of the original system.

[0018] Further, in 1), the main pollutants of the nitrile-containing wastewater are acrylonitrile, other harmful nitriles, and benzene series substances, wherein the acrylonitrile content is 50-1000 ppm, the chemical oxygen demand (COD) is 1000-5000 ppm, and the sulfate content is 4000-6000 ppm; the wastewater temperature is room temperature, and the pressure is normal pressure.

[0019] Further, in 1), the extraction is carried out using a two-phase countercurrent extraction tower, the volumetric flow ratio of the extractant to the acrylonitrile-containing wastewater is 0.2-5:1, and the operating pressure of the extraction tower is 1-5 bar.

[0020] Furthermore, in 1), the content of benzene series substances and organic nitrile substances (such as 2-phenyl-2-propanol / acrylonitrile) in the raffinate after extraction is less than 1 ppm.

[0021] Furthermore, in section 1), this invention discovered that because nitrile-containing wastewater typically contains surfactants (sodium rosinate, sodium oleate) and inorganic salts (potassium sulfate, sodium sulfate), organic compounds such as acrylonitrile are easily emulsified. Therefore, this invention adds a pulsed electric field demulsification unit before the wastewater enters the extraction tower. By utilizing the polarization of polar oil droplets under an alternating electric field, the opposite poles attract, collide, and coalesce, thereby effectively increasing the mass transfer rate of solute diffusion from the aqueous phase to the organic phase within the extraction tower.

[0022] Furthermore, the pulsed electric field demulsification unit is composed of an interleaved parallel electrode plate group with an electrode spacing of 50-100mm, arranged perpendicular to the wastewater flow direction; it includes a high-voltage pulse power supply with a frequency of 10-50kHz and a peak voltage of 15-22kV; the processing capacity of the pulsed electric field demulsification unit is matched with a flow rate of 150-250ton / h, and the wastewater residence time in the electric field zone is ≤30s.

[0023] Further, in 1), the styrene extractant contains 0.5-2 wt% of a hydrophobic ionic liquid [P66614][NTf2].

[0024] To further prevent styrene from emulsifying when in contact with surfactants and inorganic salts, a hydrophobic ionic liquid [P66614][NTf2] can be added to styrene. This can suppress salt ion interference through electrostatic shielding and simultaneously enhance the partition coefficient of acrylonitrile.

[0025] Furthermore, in 2), the stripping tower used for stripping is equipped with a top total condenser but no bottom reboiler, and the operating pressure is atmospheric pressure.

[0026] Further, in 2), the temperature of the water vapor is 100-250℃, and the vapor phase fraction is 0.8-1.

[0027] Furthermore, in step 2), the styrene content in the raffinate is less than 1 ppm.

[0028] Furthermore, in 2), the stripping tower adopts a stepped temperature distribution tray, and the tower body is divided into three temperature control zones: 95-105℃ at the top, 115-125℃ in the middle, and 145-155℃ at the bottom. Each zone is equipped with an independent steam coil and temperature sensor.

[0029] To mitigate the risk of styrene thermal polymerization, stripping towers can employ stepped temperature distribution trays to reduce residence time in the high-temperature zone.

[0030] Furthermore, in 3), the multi-effect evaporation system used for evaporation consists of at least four flash tanks connected in series, and the operating pressure of the flash tanks decreases step by step, ranging from 0.1 to 0.25 bar.

[0031] Furthermore, in 3), the sulfate concentrate contains 10% to saturate sulfate by mass, or is further completely crystallized into sulfate crystals.

[0032] Furthermore, in step 3), the raffinate is treated with a sodium ion sieve adsorption tower before evaporation to selectively remove sodium ions.

[0033] Furthermore, the sodium ion sieve adsorption tower is filled with zirconium-based sodium sieve / acid-modified molecular sieve Zr-MOFs, and adopts a dual-tower parallel design with a height-to-diameter ratio of 3-5:1. It is equipped with a water distributor and a backwash distributor.

[0034] To reduce the impact of sodium ions on the purity of potassium sulfate, a sodium ion sieve adsorption tower can be added before the multi-effect evaporation system to selectively adsorb sodium ions. + (Na + / K + Separation factor > 120), Na + The recovery rate is higher than 99%.

[0035] Furthermore, in 4), the flash evaporation uses a flash tank with an operating pressure of 0.1-2 bar and an operating temperature of 50-150°C, and the salt obtained by crystallization is solid.

[0036] Furthermore, in 4), the first distillation column used in the first distillation is a packed column with an operating pressure of 0.5-1.5 bar and an acrylonitrile removal rate of more than 99% in the feed.

[0037] Further, in 5), the second distillation column used in the second distillation is a packed column with an operating pressure of 0.25-1.5 bar. The removal rate of 2-phenyl-2-propanol contained in the feed is greater than 99%, and it is distilled off from the bottom of the column.

[0038] Furthermore, in step 5), after the second distillation of the nitrile-containing wastewater, the total content of nitrile substances and benzene series substances is less than 1 ppm, and the sulfate recovery rate reaches 99.9%.

[0039] Compared with the prior art, the beneficial effects of the present invention are: (1) This invention is the first to employ a combined process of "extraction + stripping + evaporation" for the resource recovery and treatment of nitrile-containing wastewater. This not only effectively removes harmful nitrile substances from the wastewater but also recovers valuable raw materials such as acrylonitrile and styrene, achieving zero wastewater discharge and resource recycling. This invention solves the problems of large footprint, high cost, inability to recover water resources, and difficulty in separating acrylonitrile found in traditional pretreatment methods. Furthermore, it achieves effective recovery and utilization of potassium sulfate and sodium, reducing the raw material consumption of the original system.

[0040] (2) To avoid emulsification of acrylonitrile and other organic substances by surfactants and inorganic salts in nitrile-containing wastewater, this invention adds a pulsed electric field demulsification unit to improve the mass transfer rate of solute diffusion from the aqueous phase to the organic phase in the extraction tower. Additionally, a hydrophobic ionic liquid [P66614][NTf2] can be added to styrene to suppress salt ion interference through electrostatic shielding, while simultaneously enhancing the partition coefficient for acrylonitrile.

[0041] (3) In order to suppress the risk of styrene thermal polymerization, the stripping tower of the present invention adopts a stepped temperature distribution tray to reduce the residence time in the high temperature zone.

[0042] (4) To reduce the impact of sodium ions on the purity of potassium sulfate, this invention adds a sodium ion sieve adsorption tower before the multi-effect evaporation system to selectively adsorb sodium ions. + . Detailed Implementation

[0043] The present invention will be further described below with reference to embodiments.

[0044] General Implementation Examples A method for resource recovery of nitrile-containing wastewater includes the following steps: 1) Nitrile-containing wastewater and styrene extractant enter from the top and bottom of the extraction tower, respectively, for two-phase countercurrent extraction.

[0045] In some specific implementation cases, the main pollutants in the nitrile-containing wastewater are acrylonitrile, other nitriles, and benzene series substances, with acrylonitrile content of 50-1000 ppm, COD of 1000-5000 ppm, and sulfate content of 4000-6000 ppm; the wastewater temperature is ambient temperature, and the pressure is atmospheric pressure.

[0046] In some specific implementation cases, the extraction adopts a two-phase countercurrent extraction tower, the volume flow ratio of extractant to nitrile wastewater is 0.2-5:1, and the operating pressure of the extraction tower is 1-5 bar.

[0047] In some specific implementation cases, the content of benzene series substances and organic nitriles (such as 2-phenyl-2-propanol / acrylonitrile) in the raffinate after extraction is less than 1 ppm.

[0048] In some specific implementation cases, when the nitrile wastewater also contains surfactants (sodium rosinate, sodium oleate, etc.), the nitrile wastewater is demulsified by a pulsed electric field unit before two-phase countercurrent extraction. Furthermore, the styrene extractant contains 0.5-2 wt% of a hydrophobic ionic liquid [P66614][NTf2].

[0049] In some more specific implementation cases, the pulsed electric field demulsification unit is composed of an interleaved parallel electrode plate group with an electrode spacing of 50-100mm, arranged perpendicular to the wastewater flow direction; it includes a high-voltage pulse power supply with a frequency of 10-50kHz and a peak voltage of 15-22kV; the processing capacity of the pulsed electric field demulsification unit is matched with a flow rate of 150-250ton / h, and the wastewater residence time in the electric field zone is ≤30s.

[0050] 2)1) The obtained raffinate enters the stripping tower, where styrene is separated by steam stripping.

[0051] In some specific implementation cases, the stripping tower used in the stripping process is equipped with a total condenser at the top of the tower but no reboiler at the bottom, and the operating pressure is atmospheric pressure.

[0052] In some specific implementation cases, the temperature of the water vapor is 100-250℃ and the vapor phase fraction is 0.8-1.

[0053] In some specific implementation cases, the styrene content in the raffinate is less than 1 ppm.

[0054] In some specific implementation cases, the stripping tower adopts a stepped temperature distribution tray, and the tower body is divided into three temperature control zones: 95-105℃ at the top, 115-125℃ in the middle, and 145-155℃ at the bottom. Each zone is equipped with an independent steam coil and temperature sensor.

[0055] 3)2) The obtained raffinate enters the multi-effect evaporation system, and after evaporation and separation, sulfate concentrate and aqueous solution are obtained.

[0056] In some specific implementation cases, the multi-effect evaporation system used for evaporation consists of at least four flash tanks connected in series, and the operating pressure of the flash tanks decreases step by step, ranging from 0.1 to 0.25 bar.

[0057] In some specific implementation cases, the sulfate concentrate contains 10% sulfate by mass to saturation, or further crystallizes completely into sulfate crystals.

[0058] 4)1) The obtained extract was desalted by flash evaporation and then separated into acrylonitrile and styrene solution 1 by first distillation.

[0059] In some specific implementation cases, the flash evaporation uses a flash tank with an operating pressure of 0.1-2 bar and an operating temperature of 50-150°C, and the salt obtained by crystallization is solid.

[0060] In some preferred embodiments, the raffinate is treated with a sodium ion sieve adsorption tower before evaporation to selectively remove sodium ions.

[0061] In some more specific implementation cases, the sodium ion sieve adsorption tower is filled with zirconium-based sodium sieve / acid-modified molecular sieve Zr-MOFs, and adopts a dual-tower parallel design with a height-to-diameter ratio of 3-5:1. It is equipped with a water distributor and a backwash distributor.

[0062] In some specific implementation cases, the first distillation column used in the first distillation is a packed column with an operating pressure of 0.5-1.5 bar and an acrylonitrile removal rate of more than 99% in the feed.

[0063] 5) After a second distillation, styrene solution 1 was separated into 2-phenyl-2-propanol solution and styrene solution 2.

[0064] In some specific implementation cases, the second distillation column used in the second distillation is a packed column with an operating pressure of 0.25-1.5 bar. The removal rate of 2-phenyl-2-propanol in the feed is greater than 99%, and it is distilled off from the bottom of the column.

[0065] In some specific implementation cases, after the second distillation of the nitrile-containing wastewater, the total content of nitrile and benzene series substances is less than 1 ppm, and the sulfate recovery rate reaches 99.9%.

[0066] 6) The styrene obtained from styrene solution 2 and 2) is recycled after condensation.

[0067] Specific embodiments and comparative examples Example 1 A method for resource recovery of nitrile-containing wastewater includes the following steps: 1) Nitrile-containing wastewater and styrene extractant enter the extraction tower from the top and bottom, respectively, for two-phase countercurrent extraction. The main components of the nitrile-containing wastewater are shown in Table 1. The wastewater flow rate is 200 tons / h, the styrene extractant flow rate is 75 tons / h, the wastewater temperature is ambient, and the pressure is atmospheric pressure. A two-phase countercurrent extraction tower is used, a rotary table tower with a diameter of 5.5 m and a height of 15 m. The volumetric flow rate ratio of extractant to nitrile-containing wastewater is 0.38:1, and the operating pressure of the extraction tower is 3.0 bar.

[0068] Table 1: Main Components of Nitrile-Containing Wastewater Element content illustrate Acrylonitrile 150ppm Acrylonitrile 15ton / h styrene 30ppm 45 tons / hour of styrene 2-Phenylon 200ppm Introduced by initiator <![CDATA[K + Ions 4000ppm / <![CDATA[Na + Ions 300ppm Other additives brought in S content 5000ppm It exists in the form of sulfate. Rosin salts 300ppm surfactants COD 4000ppm / 2) The raffinate obtained in 1) enters a stripping tower, where styrene is separated by steam stripping. The stripping tower is equipped with a total condenser at the top but no reboiler at the bottom, and uses a stepped temperature distribution tray. The tower body is divided into three temperature control zones: 95°C at the top, 115°C in the middle, and 145°C at the bottom. Each zone is equipped with an independent steam coil and temperature sensor, and the operating pressure is atmospheric pressure. The steam temperature is 105°C, and the vapor fraction is 1.0. After extraction and stripping, the acrylonitrile and other harmful nitriles and benzene series substances in the nitrile-containing wastewater are less than 1.0 ppm.

[0069] 3) The raffinate obtained in step 2) enters a multi-effect evaporation system, where it is evaporated and separated to obtain potassium sulfate concentrate and aqueous solution. The multi-effect evaporation system consists of four flash tanks connected in series, with absolute pressures of 1.0 bar, 0.78 bar, 0.56 bar, and 0.44 bar for the first to fourth evaporators, respectively. The first evaporator is heated by a 64000 kg / h, 4 MPa steam phase change heating system. After four-effect evaporation, the potassium sulfate concentrate reaches a mass concentration of 11%.

[0070] 4) The obtained extract was selectively treated with a sodium ion sieve adsorption tower to remove sodium ions before evaporation, and then desalted in a flash tank. After a first distillation, acrylonitrile and styrene solution 1 was obtained. The flash tank used for flash evaporation operated at a pressure of 0.10 bar and a temperature of 80°C, and the salt obtained by crystallization was solid. The sodium ion sieve adsorption tower was filled with zirconium-based sodium sieve / acid-modified molecular sieve Zr-MOFs and adopted a dual-tower parallel design with a height-to-diameter ratio of 4:1. It was equipped with a water distributor and a backwash distributor. The first distillation tower was a packed tower with an operating pressure of 0.5 bar and an acrylonitrile removal rate of more than 99% in the feed.

[0071] 5) Styrene solution 1 was subjected to a second distillation to separate 2-phenyl-2-propanol solution and styrene solution 2. The second distillation column was a packed column with an operating pressure of 0.25 bar. The removal rate of 2-phenyl-2-propanol in the feed was greater than 99%, and it was distilled off from the bottom of the column. After treatment by the first and second distillation columns, the recovery rate of nitrile and benzene series compounds reached 99.9% or higher, and the purity of the recycled styrene extractant reached 95.00%, with almost no harmful organic matter accumulating in the recycling system.

[0072] 6) The styrene obtained from styrene solution 2 and 2) is recycled after condensation.

[0073] Example 2 A method for resource recovery of nitrile-containing wastewater differs from Example 1 only in that the nitrile-containing wastewater undergoes demulsification treatment by a pulsed electric field unit before two-phase countercurrent extraction in step 1). Specifically, it includes the following steps: 1) Nitrile-containing wastewater is pre-demulsified by a pulsed electric field unit. After demulsification, it and styrene extractant enter the extraction tower from the top and bottom respectively for two-phase countercurrent extraction. The main components of the nitrile-containing wastewater are shown in Table 1. The wastewater flow rate is 200 tons / h, the styrene extractant flow rate is 75 tons / h, the wastewater temperature is ambient, and the pressure is atmospheric. The pulsed electric field demulsification unit consists of staggered parallel electrode plates with a 100mm electrode spacing, arranged perpendicular to the wastewater flow direction. It includes a high-voltage pulse power supply with a frequency of 50kHz and a peak voltage of 22kV. The processing capacity of the pulsed electric field demulsification unit is matched to a flow rate of 150-250 tons / h, and the residence time of wastewater in the electric field zone is ≤30s. The extraction tower adopts a two-phase countercurrent extraction tower, a rotary tower with a diameter of 5.0m and a height of 12m. The volumetric flow rate ratio of extractant to nitrile-containing wastewater is 0.38:1, and the operating pressure of the extraction tower is 3.0 bar.

[0074] 2) The raffinate obtained in 1) enters a stripping tower, where styrene is separated by steam stripping. The stripping tower is equipped with a total condenser at the top but no reboiler at the bottom, and uses a stepped temperature distribution tray. The tower body is divided into three temperature control zones: 95°C at the top, 115°C in the middle, and 145°C at the bottom. Each zone is equipped with an independent steam coil and temperature sensor, and the operating pressure is atmospheric pressure. The steam temperature is 105°C, and the vapor fraction is 1.0. After extraction and stripping, the acrylonitrile and other harmful nitriles and benzene series substances in the nitrile-containing wastewater are less than 1.0 ppm.

[0075] 3) The raffinate obtained in step 2) enters a multi-effect evaporation system, where it is evaporated and separated to obtain potassium sulfate concentrate and aqueous solution. The multi-effect evaporation system consists of four flash tanks connected in series, with absolute pressures of 1.0 bar, 0.78 bar, 0.56 bar, and 0.44 bar for the first to fourth evaporators, respectively. The first evaporator is heated by a 64000 kg / h, 4 MPa steam phase change heating system. After four-effect evaporation, the potassium sulfate concentrate reaches a mass concentration of 11%.

[0076] 4) The obtained extract was selectively treated with a sodium ion sieve adsorption tower to remove sodium ions before evaporation, and then desalted in a flash tank. After a first distillation, acrylonitrile and styrene solution 1 was obtained. The flash tank used for flash evaporation operated at a pressure of 0.10 bar and a temperature of 80°C, and the salt obtained by crystallization was solid. The sodium ion sieve adsorption tower was filled with zirconium-based sodium sieve / acid-modified molecular sieve Zr-MOFs and adopted a dual-tower parallel design with a height-to-diameter ratio of 4:1. It was equipped with a water distributor and a backwash distributor. The first distillation tower was a packed tower with an operating pressure of 0.5 bar and an acrylonitrile removal rate of more than 99% in the feed.

[0077] 5) Styrene solution 1 was subjected to a second distillation to separate 2-phenyl-2-propanol solution and styrene solution 2. The second distillation column was a packed column with an operating pressure of 0.25 bar. The removal rate of 2-phenyl-2-propanol in the feed was greater than 99%, and it was distilled off from the bottom of the column. After treatment by the first and second distillation columns, the recovery rate of nitrile and benzene series compounds reached 99.9% or higher, and the purity of the recycled styrene extractant reached 98.00%, with almost no harmful organic matter accumulating in the recycling system.

[0078] 6) The styrene obtained from styrene solution 2 and 2) is recycled after condensation.

[0079] Example 3 A method for resource recovery of nitrile-containing wastewater differs from Example 1 only in that: the nitrile-containing wastewater undergoes demulsification treatment by a pulsed electric field unit before two-phase countercurrent extraction in step 1), and the extractant contains a hydrophobic ionic liquid [P66614][NTf2]. Specifically, it includes the following steps: 1) Nitrile-containing wastewater is pre-demulsified by a pulsed electric field unit. After demulsification, it is then introduced into the extraction tower from the top and bottom respectively with styrene extractant (containing 2.0 wt% hydrophobic ionic liquid [P66614][NTf2]) for two-phase countercurrent extraction. The main components of the nitrile-containing wastewater are shown in Table 1. The wastewater flow rate is 200 ton / h, the styrene extractant flow rate is 75 ton / h, the wastewater temperature is ambient, and the pressure is atmospheric. The pulsed electric field demulsification unit consists of staggered parallel electrode plates with an electrode spacing of 100 mm, arranged perpendicular to the wastewater flow direction. It includes a high-voltage pulsed power supply with a frequency of 50 kHz and a peak voltage of 22 kV. The processing capacity of the pulsed electric field demulsification unit is matched to a flow rate of 150-250 ton / h, and the residence time of the wastewater in the electric field zone is ≤30 s. The extraction tower adopts a two-phase countercurrent extraction tower, and the tower type is selected as a rotary table tower with a tower diameter of 4.5m and a tower height of 9.0m. The volumetric flow rate ratio of extractant to acrylonitrile-containing wastewater is 0.38:1, and the operating pressure of the extraction tower is 3.0 bar.

[0080] 2) The raffinate obtained in 1) enters a stripping tower, where styrene is separated by steam stripping. The stripping tower is equipped with a total condenser at the top but no reboiler at the bottom, and uses a stepped temperature distribution tray. The tower body is divided into three temperature control zones: 95°C at the top, 115°C in the middle, and 145°C at the bottom. Each zone is equipped with an independent steam coil and temperature sensor, and the operating pressure is atmospheric pressure. The steam temperature is 105°C, and the vapor fraction is 1.0. After extraction and stripping, the acrylonitrile and other harmful nitriles and benzene series substances in the nitrile-containing wastewater are less than 1.0 ppm.

[0081] 3) The raffinate obtained in step 2) enters a multi-effect evaporation system, where it is evaporated and separated to obtain potassium sulfate concentrate and aqueous solution. The multi-effect evaporation system consists of four flash tanks connected in series, with absolute pressures of 1.0 bar, 0.78 bar, 0.56 bar, and 0.44 bar for the first to fourth evaporators, respectively. The first evaporator is heated by a 64000 kg / h, 4 MPa steam phase change heating system. After four-effect evaporation, the potassium sulfate concentrate reaches a mass concentration of 11%.

[0082] 4) The extract obtained in step 3) was treated with a sodium ion sieve adsorption tower to selectively remove sodium ions before evaporation, and then desalted in a flash evaporator. After a first distillation, acrylonitrile and styrene solution 1 was obtained. The flash evaporator operated at a pressure of 0.10 bar and a temperature of 80°C, and the resulting salt was solid. The sodium ion sieve adsorption tower was filled with zirconium-based sodium sieves / acid-modified molecular sieves (Zr-MOFs) and employed a parallel dual-tower design with a height-to-diameter ratio of 4:1. It was equipped with a water distributor and a backwash distributor. The first distillation tower was a packed tower, operating at a pressure of 0.5 bar, with an acrylonitrile removal rate of over 99% in the feed.

[0083] 5) Styrene solution 1 was subjected to a second distillation to separate 2-phenyl-2-propanol solution and styrene solution 2. The second distillation column was a packed column with an operating pressure of 0.25 bar. The removal rate of 2-phenyl-2-propanol in the feed was greater than 99%, and it was distilled off from the bottom of the column. After treatment by the first and second distillation columns, the recovery rate of nitrile and benzene series compounds reached 99.9% or higher, and the purity of the recycled styrene extractant reached 99.99%, with almost no harmful organic matter accumulating in the recycling system.

[0084] 6) The styrene obtained from styrene solution 2 and 2) is recycled after condensation.

[0085] Comparative Example 1 The conventional process for treating acrylonitrile-containing wastewater has the main components shown in Table 1. The treatment capacity is 200 tons / hour. The process involves adjusting the pH of the wastewater to 1.0 by adding sulfuric acid in a 10,000 m3 pretreatment tank. The average retention time of the wastewater is 50 hours. Acrylonitrile hydrolyzes into organic compounds with low biological toxicity, such as acrylic acid, in a strongly acidic environment. After adjusting the pH by adding alkali, the wastewater undergoes anaerobic-aerobic treatment to meet discharge standards.

[0086] Compared with Examples 1-3, the disadvantages of Comparative Example 1 are: on the one hand, it consumes a large amount of acid and alkali, generating a large amount of waste salt; on the other hand, because the pretreatment tank has a large volume (200 tons / h of wastewater, requiring 10,000 m³), ​​it is also less efficient. 3 The pretreatment tank is required, and the subsequent anaerobic-aerobic process occupies a large area, wasting a significant amount of land. Table 2 shows the separation effect and device footprint of Examples 1-3 and Comparative Example 1. Compared with Comparative Example 1, the device footprint is reduced by two orders of magnitude under the same acrylonitrile-containing wastewater treatment capacity.

[0087] Table 2: Separation effect of extraction towers and estimated equipment footprint for Examples 1-3 and Comparative Example 1 Case styrene purity <![CDATA[Volume of extraction column / m 3 > <![CDATA[Device floor area estimation / m 2 > Example 1 95.00％ 356 47 Example 2 98.00％ 236 43 Example 3 99.99％ 143 39 Comparative Example 1 / / ＞1000 Furthermore, a comparison of the data in Table 2 shows that the styrene purity of Examples 1-3 increases sequentially, with Example 3 showing the best results. This is because Example 2 further added a pulsed electric field unit for pre-demulsification treatment based on Example 1, while Example 3 added 2.0 wt% of a hydrophobic ionic liquid [P66614][NTf2] to the styrene extractant based on Example 2.

[0088] Unless otherwise specified, the raw materials and equipment used in this invention are all commonly used in the field; unless otherwise specified, the methods used in this invention are all conventional methods in the field.

[0089] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention in any way. Any simple modifications, alterations, and equivalent transformations made to the above embodiments based on the technical essence of the present invention shall still fall within the protection scope of the present invention.

Claims

1. A method for resource recovery of nitrile-containing wastewater, characterized in that... include: 1) A two-phase countercurrent extraction was performed on the acrylonitrile-containing wastewater and styrene extractant; 2) The raffinate obtained in 1) was stripped with steam to separate styrene; 3) The raffinate obtained in step 2) was evaporated and separated to obtain a sulfate concentrate and an aqueous solution; 4) 1) The obtained extract was flash-distilled to remove salt, and after a first distillation, a solution of acrylonitrile and styrene was obtained. 5) After a second distillation, styrene solution 1 was separated into 2-phenyl-2-propanol solution and styrene solution 2; 6) The styrene obtained from styrene solution 2 and 2) is recycled after condensation.

2. The method for resource recovery of nitrile-containing wastewater according to claim 1, characterized in that: In 1), the main pollutants in the nitrile-containing wastewater are acrylonitrile, other harmful nitriles, and benzene series substances, wherein the acrylonitrile content is 50-1000 ppm, the chemical oxygen demand is 1000-5000 ppm, and the sulfate content is 4000-6000 ppm; the wastewater temperature is ambient temperature, and the pressure is atmospheric pressure.

3. The method for resource recovery of nitrile-containing wastewater according to claim 1 or 2, characterized in that: 1) In, The extraction is performed using a two-phase countercurrent extraction tower, with a volumetric flow rate ratio of extractant to acrylonitrile-containing wastewater of 0.2-5:1, and an operating pressure of 1-5 bar. The content of benzene series substances and organic nitriles in the raffinate after extraction is less than 1 ppm.

4. The method for resource recovery of nitrile-containing wastewater according to claim 1 or 2, characterized in that: 1) In, The nitrile-containing wastewater also contains surfactants; The acrylonitrile-containing wastewater is demulsified by a pulsed electric field unit before two-phase countercurrent extraction; The pulsed electric field demulsification unit consists of an alternating parallel electrode plate group with an electrode spacing of 50-100mm, arranged perpendicular to the wastewater flow direction; it includes a high-voltage pulse power supply with a frequency of 10-50kHz and a peak voltage of 15-22kV; the processing capacity of the pulsed electric field demulsification unit is matched with a flow rate of 150-250ton / h, and the wastewater residence time in the electric field zone is ≤30s. The styrene extractant contains 0.5-2 wt% of a hydrophobic ionic liquid [P66614][NTf2].

5. The method for resource recovery of nitrile-containing wastewater according to claim 1, characterized in that: 2) In, The stripping tower used in the stripping process is equipped with a total condenser at the top of the tower but no reboiler at the bottom, and the operating pressure is atmospheric pressure. The temperature of the water vapor is 100-250℃, and the vapor phase fraction is 0.8-1. The styrene content in the raffinate is less than 1 ppm.

6. The method for resource recovery of nitrile-containing wastewater according to claim 5, characterized in that: In section 2), the stripping tower adopts a stepped temperature distribution tray, and the tower body is divided into three temperature control zones: 95-105℃ at the top, 115-125℃ in the middle, and 145-155℃ at the bottom. Each zone is equipped with an independent steam coil and temperature sensor.

7. The method for resource recovery of nitrile-containing wastewater according to claim 1, characterized in that: 3) In, The multi-effect evaporation system used in the evaporation consists of at least four flash tanks connected in series, and the operating pressure of the flash tanks decreases step by step, ranging from 0.1 to 0.25 bar. The sulfate concentrate contains 10% sulfate by mass until saturation, or further crystallizes completely into sulfate crystals.

8. The method for resource recovery of nitrile-containing wastewater according to claim 1 or 7, characterized in that: 3) In, The raffinate is treated with a sodium ion sieve adsorption tower before evaporation to selectively remove sodium ions; The sodium ion sieve adsorption tower is filled with zirconium-based phosphate molecular sieves and adopts a dual-tower parallel design with a height-to-diameter ratio of 3-5:

1. It is equipped with a water distributor and a backwash distributor.

9. The method for resource recovery of nitrile-containing wastewater according to claim 1, characterized in that: 4) In, The flash evaporation process uses a flash tank with an operating pressure of 0.1-2 bar and an operating temperature of 50-150°C, and the resulting salt is a solid. The first distillation uses a packed column with an operating pressure of 0.5-1.5 bar and an acrylonitrile removal rate of more than 99% in the feed.

10. The method for resource recovery of nitrile-containing wastewater according to claim 1, characterized in that: 5) The second distillation uses a packed column with an operating pressure of 0.25-1.5 bar. The removal rate of 2-phenyl-2-propanol in the feed is greater than 99%, and it is distilled off from the bottom of the column. After a second distillation, the total content of nitrile and benzene compounds in the nitrile-containing wastewater is less than 1 ppm, and the sulfate recovery rate reaches 99.9%.