A method for treating acrylonitrile wastewater

Abstract

The application provides a treatment method of acrylonitrile wastewater, and aims at the problems of high tar content in acrylonitrile wastewater, easy plugging in evaporation and difficult utilization of mother liquor, chemical impurity removal is carried out before the wastewater enters evaporation, granular activated carbon with a pore size of 10-50 nm is used as a selective impurity removal agent, by controlling the pore size range of the activated carbon (pore size less than 10 nm will excessively adsorb small molecular organic matters such as acrylonitrile, affecting the resource value of the subsequent mother liquor; pore size greater than 50 nm cannot effectively remove large molecular tar substances), selective removal of large molecular tar substances formed in the evaporation process is realized, and valuable small molecular organic matters are reserved, the technical problems of tar plugging and low evaporation efficiency in the treatment of acrylonitrile wastewater are effectively solved, and resource utilization of the mother liquor is realized.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of wastewater treatment, in particular to a treatment method of acrylonitrile wastewater. BACKGROUND

[0002] Acrylonitrile is an important organic chemical raw material, which is widely used in the production of ABS resin, acrylic fiber, carbon fiber, nitrile rubber and other products. However, the wastewater produced in the production process of acrylonitrile has the characteristics of complex pollutant composition, high chemical oxygen demand, high colority, high content of tar substances, etc., which is difficult to treat, has high investment and operation cost, and has industry technical barriers. Traditional treatment technologies mostly use single or combined pollutant removal methods, such as incineration method which can completely treat organic matter but has problems of high salt plugging, serious corrosion, high investment and operation cost, etc.; oxidation processes such as high-temperature wet oxidation, Fenton oxidation, electro-catalytic oxidation, etc. also have defects such as high investment, high operation cost, prominent safety hazards (such as high-temperature risk, large amount of slag, hydrogen release, etc.), etc., which are difficult to meet the needs of efficient, safe, economic and resourceful treatment. Therefore, it is urgent to develop a new type of acrylonitrile wastewater treatment process which is efficient, safe and reliable, and has high resource utilization degree, in order to overcome the shortcomings of the prior art and improve the treatment efficiency and economy. SUMMARY

[0003] The present application is aimed at the problems of high content of tar substances, high COD concentration and high colority in acrylonitrile wastewater, and proposes a full-process treatment method including chemical impurity removal, evaporation concentration, biochemical treatment, leaching treatment and reuse. The core of the method is to optimize the particle activated carbon with a pore size of 10-50 nm. By precisely controlling the pore size range of the activated carbon, the problem of excessive adsorption of small molecule organic matter caused by too small pore size and the problem of failure to effectively intercept tar macromolecules caused by too large pore size are avoided. The selective removal of macromolecular tar substances generated in the evaporation process is realized, and the valuable small molecule organic matter is retained, thereby effectively solving the problems of tar plugging and low evaporation efficiency, and realizing the resource utilization of the mother liquor. The technical scheme provided by the present application is as follows:

[0004] The present application provides a treatment method of acrylonitrile wastewater, which comprises the following steps:

[0005] (1) Chemical impurity removal: adding an impurity removal agent to the acrylonitrile wastewater, and separating the solid and liquid after reaction to obtain a filtrate; wherein the impurity removal agent comprises particle activated carbon with a pore size range of 10-50 nm;

[0006] (2) Evaporation concentration: evaporating and concentrating the filtrate to obtain coarse salt, fraction condensate and concentrated mother liquor, respectively;

[0007] (3) Biochemical treatment: performing biochemical treatment on the fraction condensate;

[0008] (4) leaching treatment: adding a reagent to the crude salt for leaching treatment, separating the salt from the organic substances attached to the surface of the salt, and obtaining a leaching solution;

[0009] (5) recycling: performing a rectification recovery treatment on the leaching solution, and recovering the reagent and a rectification residue, wherein the recovered reagent is returned to step (4) for recycling.

[0010] In some specific embodiments, in step (1), the impurity removal agent further comprises one or more of polyaluminum chloride, polyferric sulfate, and zinc sulfate, and the addition amount of the impurity removal agent is 0.5%-1.5% of the content of the acrylonitrile wastewater.

[0011] In some specific embodiments, the impurity removal agent is compounded from the granular activated carbon and any one flocculant selected from the polyaluminum chloride, the polyferric sulfate, and the zinc sulfate at a mass ratio of (3-5):1.

[0012] In some specific embodiments, in step (2), before the evaporation and concentration, the pH of the filtrate is adjusted to 3-5.

[0013] In some specific embodiments, in step (2), the evaporation and concentration is performed by multi-stage evaporation.

[0014] In some specific embodiments, the multi-stage evaporation is three-effect evaporation, and the control parameters are as follows: the steam pressure is greater than 0.5 MPa, the vacuum extraction pressure is 0.085-0.095 MPa, the temperature of the first-effect evaporation is 85-95 ℃, the temperature of the second-effect evaporation is 75-85 ℃, and the temperature of the third-effect evaporation is 60-70 ℃.

[0015] In some specific embodiments, in step (3), the biochemical treatment adopts a combined process of hydrolysis acidification, anoxic treatment, and aerobic treatment, wherein the hydrolysis acidification has a residence time of 1-2 d, a pH of 6-9, a dissolved oxygen of 0-0.2 mg / L, and a temperature of 20-40 ℃; the anoxic treatment has a residence time of 0.5-1.5 d, a dissolved oxygen of less than 0.5 mg / L, and a nitration liquid reflux ratio of 1-3; and the aerobic treatment has a residence time of 1-2 d, a dissolved oxygen of 2-4 mg / L, a pH of 7-8, and a temperature of 20-35 ℃.

[0016] In some specific embodiments, in step (4), the reagent used for the leaching treatment is methanol.

[0017] In some specific embodiments, in step (4), the leaching treatment is performed at room temperature, the leaching time is 10-30 min, and the mass ratio of the leaching reagent to the crude salt is (1-2):1.

[0018] In some specific embodiments, in step (5), the overhead temperature of the rectifying column in the rectification recovery treatment is 64-66 DEG C, the bottom temperature is > 70 DEG C, and the reflux ratio is 1-3.

[0019] With the technical scheme, the method for treating acrylonitrile wastewater has the following beneficial effects:

[0020] 1. The present application effectively removes tar and other impurities in wastewater through chemical impurity removal treatment, improving the evaporation efficiency of the subsequent evaporation concentration process, avoiding problems such as pipeline blockage and heat transfer efficiency reduction caused by tar accumulation in the evaporation process, and ensuring the stable operation of the evaporation system.

[0021] 2. The present application preferably uses granular activated carbon with a pore size of 10-50 nm as the impurity removal agent. By precisely controlling the pore size range of the activated carbon, the problem of excessive adsorption of small-molecule organic matter such as acrylonitrile by granular activated carbon with a small pore size, which reduces the organic matter content in the evaporation mother liquor, is avoided, and the problem of incomplete removal of large-molecule tar organic matter with a large pore size is also prevented, achieving selective removal of large-molecule tar organic matter while retaining small-molecule organic matter with recycling value, thereby improving the recycling value of the evaporation mother liquor and subsequent products.

[0022] 3. The present application realizes component separation and resource recovery through multi-stage evaporation concentration. After multi-stage evaporation treatment, crude salt, fraction condensate, and concentrated mother liquor are obtained. The concentrated mother liquor has a high organic matter content and has a certain product recycling value, which is beneficial to subsequent recycling and improves the comprehensive economic benefits of the wastewater treatment process.

[0023] 4. The crude salt obtained by evaporation concentration is treated by leaching with the addition of reagents, and the leaching liquid can be recycled after the reagents are recovered by rectification. The rectification residue has a high organic matter content, similar to the evaporation mother liquor, and also has high product value. This not only reduces the generation of solid waste, but also realizes effective separation and resource recovery of organic components and salt substances in waste liquid, reduces harmful substance emissions in the wastewater treatment process, achieves the goals of reduction, resource utilization, and harmlessness in wastewater treatment, and has good environmental and economic benefits. BRIEF DESCRIPTION OF DRAWINGS

[0024] In order to more clearly illustrate the technical solutions in the embodiments of the present application, the drawings needed in the embodiment description will be briefly introduced. Obviously, the drawings in the following description are only some embodiments of the present application, and other drawings can be obtained by those skilled in the art without creative labor.

[0025] Figure 1A process flow chart of a treatment method of acrylonitrile wastewater is provided for the embodiment of the present application. DETAILED DESCRIPTION

[0026] The technical solutions in the embodiments of the present application will be clearly and completely described with reference to the drawings in the embodiments of the present application. Obviously, the described embodiments are only part of the embodiments of the present application, rather than all the embodiments. Based on the embodiments in the present application, all other embodiments obtained by a person of ordinary skill in the art without creative work fall within the protection scope of the present application.

[0027] The term "one embodiment" or "an embodiment" as used herein means that a particular feature, structure, or characteristic described in connection with the embodiment can be included in at least one implementation of the present application. In the description of the present application, it should be understood that the terms "upper", "lower", "top", "bottom", etc. indicate the orientation or positional relationship shown in the drawings, and are only for the convenience of describing the present application and simplifying the description, and do not indicate or imply that the devices or elements referred to must have a particular orientation, be constructed and operated in a particular orientation, and therefore cannot be understood as a limitation on the present application. In addition, the terms "first", "second" are only for the purpose of description, and cannot be understood as indicating or implying relative importance or implicitly indicating the number of the technical features referred to. Therefore, the features limited by "first", "second" can be explicitly or implicitly included one or more of the features. Moreover, the terms "first", "second" and the like are used to distinguish similar objects, and do not necessarily describe a particular order or sequence. It should be understood that the data thus used can be interchanged under appropriate circumstances, so that the embodiments of the present application described herein can be implemented in an order other than that illustrated or described herein.

[0028] When a numerical range is disclosed herein, the range is considered continuous along the entire range and inclusive of the minimum and maximum values of the range, as well as every value between the minimum and maximum values. Further, when the range is for integers, every integer between the minimum and maximum values of the range is included. In addition, when multiple ranges are provided to describe a feature or characteristic, the ranges can be combined. In other words, unless otherwise indicated, all ranges disclosed herein are to be understood as including any and all sub-ranges subsumed therein. For example, a specified range of "1 to 10" should be considered to include any and all sub-ranges between (and including) the minimum value of 1 and the maximum value of 10. An exemplary sub-range of the range 1 to 10 includes, but is not limited to, 1 to 6.1, 3.5 to 7.8, 5.5 to 10, etc.

[0029] Referring to Figure 1 The present application provides a treatment method of acrylonitrile wastewater, comprising the following steps:

[0030] (1) Chemical impurity removal: adding an impurity removal agent to the acrylonitrile wastewater, and after reaction, solid-liquid separation is performed to obtain a filtrate; wherein the impurity removal agent comprises granular activated carbon with a pore size range of 10-50 nm;

[0031] (2) Evaporation concentration: evaporating and concentrating the filtrate to obtain a crude salt, a fraction condensate and a concentrated mother liquor, respectively;

[0032] (3) Biochemical treatment: performing biochemical treatment on the fraction condensate;

[0033] (4) Leaching treatment: adding a reagent to the crude salt for leaching treatment, separating the salt from the organic substances attached to the surface of the salt, and obtaining a leaching solution;

[0034] (5) Reuse: performing rectification recovery treatment on the leaching solution to recover the reagent and a rectification residue liquid, respectively, wherein the recovered reagent is returned to step (4) for recycling.

[0035] Specifically, for high-concentration organic wastewater from an acrylonitrile production plant, the wastewater contains a high content of tar substances. However, the prior art does not perform targeted pretreatment on the tar substances, which leads to easy adhesion of the tar substances to the heat transfer surface of the evaporator in the subsequent evaporation and concentration process, resulting in equipment fouling, significant reduction of heat transfer efficiency, and even causing problems such as pipeline and heat exchanger blockage.Therefore, before entering the evaporation concentration process, the present application innovatively first uses a chemical impurity removal process to pretreat the wastewater, adds an impurity removal agent to the acrylonitrile wastewater, effectively removes tar substances, suspended solids and other macromolecular impurities in the wastewater through the synergistic effect of chemical reaction and physical adsorption, thereby improving the treatment efficiency and operation stability of subsequent evaporation concentration; wherein the impurity removal agent includes granular activated carbon, the pore size range of which is accurately controlled to be 10-50 nm (such as 15 nm, 25 nm, 35 nm, 45 nm, etc.), if the pore size is less than 10 nm, the activated carbon will preferentially adsorb small-molecule organic matters such as acrylonitrile and propylene, resulting in a decrease in the amount of organic matter that can be recovered in the evaporation mother liquor, and reducing the subsequent resource value; if the pore size is greater than 50 nm, it is difficult to effectively intercept tar macromolecular substances, and the problem of tar enrichment and pipeline blockage in the evaporation process cannot be solved; the granular activated carbon with a pore size range of 10-50 nm can effectively remove macromolecular tar impurities while retaining small-molecule organic matters with economic value in the fraction condensate, effectively preventing tar enrichment and blockage in the evaporation process, and ensuring long-term stable operation of the evaporation system; the filtrate after impurity removal is subjected to evaporation concentration, and water is evaporated under multi-stage evaporation conditions, and the soluble salts and high-concentration organic matters contained in the wastewater are gradually concentrated and precipitated, mainly obtaining three types of products: one is coarse salt mainly composed of inorganic salts and often with organic matters attached to the surface, the second is fraction condensate with low organic matter content, and the third is concentrated mother liquor with high organic matter content, wherein the coarse salt needs to be further treated, the fraction condensate has low organic matter content and is suitable for subsequent biochemical treatment, and the concentrated mother liquor has potential product recovery value due to the high concentration of organic matters; the fraction condensate then enters a biochemical treatment unit, and the metabolic action of microorganisms is used to degrade the easily biodegradable organic matters (such as alcohols, aldehydes, and part of organic acids) in the fraction condensate, effectively reducing pollution indicators such as COD and BOD, so that the effluent meets the discharge or reuse standards; for the organic matters attached to the surface of the coarse salt, a reagent leaching process is used to effectively separate the salt and the organic matters, and a leaching solution rich in high-concentration organic components is obtained; the leaching solution is then subjected to rectification treatment, and the reagent and organic residue are separated by taking advantage of the difference in boiling points of different components, on the one hand, the reagent is recovered and recycled to reduce the treatment cost, and on the other hand, a rectification residue with high organic matter content is obtained, which has an organic matter content equivalent to that of the concentrated mother liquor and has product or energy recovery value, realizing the high-value utilization of organic matter; the method solves the problems of tar blockage, low evaporation efficiency, difficult treatment of mother liquor and waste of resources in the traditional process through the integrated process route of "chemical impurity removal-evaporation concentration-biochemical treatment-leaching treatment-reuse", realizes the efficient removal of tar substances in wastewater, the separation and recycling of valuable substances, and has the advantages of high treatment efficiency, stable operation, high resource utilization degree, environmental friendliness, etc., and is suitable for the comprehensive treatment and green low-carbon cyclic utilization of high-concentration organic wastewater in the acrylonitrile and related chemical industries.

[0036] In some specific embodiments, in step (1), the impurity removal agent further comprises one or more of polyaluminum chloride, polyferric sulfate, zinc sulfate, and the addition amount of the impurity removal agent is 0.5%-1.5% of the content of the acrylonitrile wastewater. Specifically, the impurity removal agent is compounded by the granular activated carbon and one or more of polyaluminum chloride (PAC), polyferric sulfate (PFS), and zinc sulfate, wherein the pore size of the granular activated carbon is controlled to be 10-50 nm, which is used to efficiently remove tar macromolecular substances and suspended impurities in the wastewater through the synergistic effect of chemical adsorption and physical entrapment, and the auxiliary flocculants or adsorbents such as polyaluminum chloride, polyferric sulfate, and zinc sulfate can further enhance the coagulation, adsorption, and precipitation effect on fine suspended solids, colloids, and part of organic matters, and improve the overall impurity removal efficiency; the addition amount of the impurity removal agent is controlled to be 0.5%-1.5% (for example, 0.5%, 0.7%, 1.0%, 1.3%, 1.5%, etc.) of the total amount of the wastewater. If the addition amount is less than 0.5%, the tar substances and impurities in the wastewater cannot be removed sufficiently, which leads to tar enrichment, pipeline blockage, and heat transfer efficiency reduction in the evaporation and concentration process, and seriously affects the stable operation and treatment effect of the subsequent evaporation unit. If the addition amount is higher than 1.5%, although the initial impurity removal rate can be improved, a large amount of non-target substances will be adsorbed or flocculated and precipitated, which increases the burden of solid waste treatment, and the excess impurity removal agent will non-selectively adsorb acrylonitrile, propylene, and their polymers and other small-molecule organic matters with recycling value, thereby reducing the content of organic matters in the fraction condensate and concentrated mother liquor, and affecting the subsequent biochemical treatment effect and the productization and resource utilization value of the mother liquor. Therefore, by selecting the addition amount of 0.5%-1.5%, the economically valuable organic components in the wastewater can be maximally retained while ensuring the effective removal of tar substances and impurities and the efficient and stable operation of the evaporation system, and the treatment efficiency, system stability, and resource utilization efficiency are synergistically optimized.

[0037] In some specific embodiments, the impurity removal agent is compounded by granular activated carbon and any one flocculant selected from polyaluminum chloride, polyferric sulfate, zinc sulfate at a mass ratio of (3-5):1. Among them, the selected flocculant can promote the formation of flocculation aggregates of large molecular tar substances originally existing in a dispersed state in the wastewater through electric neutralization, bridging or net trapping, thereby increasing the particle size, improving the sedimentation or adsorption, and then facilitating the subsequent efficient removal by granular activated carbon through physical interception and surface adsorption, effectively avoiding the enrichment of tar substances in the evaporation and concentration process and causing pipeline blockage and heat transfer efficiency reduction; the impurity removal agent is compounded by granular activated carbon and the above flocculant at a mass ratio of (3-5):1 (such as 3:1, 3.5:1, 4:1, 4.5:1, 5:1, etc.). If the proportion of granular activated carbon is too small (i.e. insufficient granular activated carbon), the adsorption of tar aggregates formed after flocculation will not be complete, resulting in a high residual amount of tar substances in the wastewater, affecting the stable operation and treatment effect of the subsequent evaporation unit; if the proportion of granular activated carbon is too large (i.e. excessive granular activated carbon), it will non-selectively adsorb small molecular organic substances such as acrylonitrile, propylene and their polymers in the wastewater, reducing the content of organic components in the fraction condensate and concentrated mother liquor, thereby affecting the subsequent biochemical treatment effect and the productization and resource utilization value of the mother liquor; therefore, the mass ratio of (3-5):1 of granular activated carbon and flocculant can realize efficient removal of tar substances on the basis of the synergistic effect of the flocculation of large molecular tar substances by flocculants and the adsorption removal capacity of granular activated carbon, while minimizing non-selective adsorption of small molecular organic substances, ensuring the smooth progress of subsequent evaporation and concentration, biochemical treatment and mother liquor resource utilization.

[0038] In some specific embodiments, in step (2), the pH of the filtrate is adjusted to 3-5 before evaporation and concentration. By accurately controlling the pH of the filtrate in the range of 3-5, the pH of the fraction condensate generated in the subsequent evaporation and concentration process can be maintained at neutral, which can directly enter step (3) for biochemical treatment without additional adjustment, simplifying the process and reducing costs; if the pH is adjusted too low (less than 3), a large amount of H +The migration of water vapor into the distillate results in the distillate being acidic, and an alkali neutralization process needs to be added before entering the biochemical treatment, which not only increases the consumption of acid and alkali reagents and the operation steps, but also increases the overall treatment cost; if the pH is adjusted too high (more than 5), the ammonia nitrogen substances originally existing in ionic or combined state in the wastewater will be converted into free ammonia and transferred to the gas phase with the increase of pH, and enriched in the evaporation distillate, resulting in the increase of ammonia nitrogen concentration in the distillate, which not only needs to be readjusted in pH before biochemical treatment, but also reduces the biochemical treatment efficiency due to the inhibitory effect of high ammonia nitrogen on microbial activity, further increasing the operation risk and treatment difficulty; therefore, controlling the pH of the filtrate in the appropriate range of 3-5 can ensure efficient operation of the evaporation and concentration process while reducing the subsequent acid-base adjustment and ammonia nitrogen load impact.

[0039] In some specific embodiments, in step (2), multi-stage evaporation is used for evaporation and concentration. Through multi-stage evaporation, the evaporation intensity and separation efficiency are improved, the soluble salt substances in the wastewater are efficiently separated and crystallized, and the concentration of acrylonitrile, propylene and their polymers and other high-value organic substances in the mother liquor is gradually enriched and increased; by controlling the evaporation temperature, vacuum degree and material residence time of each stage, water is gradually evaporated in the multi-stage system, and salts reach the supersaturated state in the form of coarse salt due to solubility limitations, thereby maximizing the separation of salts and organic phases; at the same time, as water continues to evaporate, the originally low-concentration organic substances such as acrylonitrile, propylene and their polymers in the wastewater are concentrated in the mother liquor, forming a concentrated mother liquor with high organic content, providing a material basis for subsequent resource utilization (such as extracting organic components or energy recovery).

[0040] In some specific embodiments, the multi-stage evaporation is a three-effect evaporation, and the control parameters are as follows: the steam pressure is greater than 0.5 MPa, the vacuumizing pressure is 0.085-0.095 MPa, the temperature of the first-effect evaporation is 85-95 ℃, the temperature of the second-effect evaporation is 75-85 ℃, and the temperature of the third-effect evaporation is 60-70 ℃. Specifically, the steam pressure needs to be greater than 0.5 MPa, if the pressure is too low, the heating capacity is insufficient, resulting in a decrease in the amount of feed per unit time, affecting the overall processing efficiency and system capacity; the condenser vacuumizing pressure is controlled in the range of 0.085-0.095 MPa, if the vacuum degree is too low (less than 0.085 MPa), the evaporation temperature in the system will rise, the liquid level will abnormally rise, which may cause the risk of overflow of the evaporator, affecting the safe operation; the temperatures of the first-effect, second-effect and third-effect evaporation are controlled at 85-95 ℃, 75-85 ℃ and 60-70 ℃, respectively, which meets the process requirements of the multi-stage evaporation with step-by-step temperature reduction, which can not only ensure efficient evaporation of water, but also avoid decomposition of organic matter, rapid crystallization of salts due to oversaturation or fouling and plugging of the inner wall of the evaporator caused by too high temperature, thereby ensuring long-term stable operation of the system; if the temperature of each stage of evaporation is too low, the heat transfer driving force is insufficient, the evaporation rate decreases, and the processing efficiency decreases; through the precise control of the above parameters, the acrylonitrile wastewater is finally concentrated to less than 1 / 10 of the original volume (i.e. the concentration multiple of the mother liquor is ≥10 times), the concentration of organic matter such as acrylonitrile, propylene and its polymers in the mother liquor is increased, and the concentrated mother liquor has high product recovery value or resource utilization potential, realizing efficient separation of water, effective precipitation of salts and efficient enrichment of target organic matter.

[0041] In some specific embodiments, in step (3), the biochemical treatment adopts a combined process of hydrolysis acidification, anoxic and aerobic treatment, wherein the hydrolysis acidification has a residence time of 1-2 d, a pH of 6-9, a dissolved oxygen of 0-0.2 mg / L and a temperature of 20-40 ℃; the anoxic treatment has a residence time of 0.5-1.5 d, a dissolved oxygen of less than 0.5 mg / L and a nitration liquid reflux ratio of 1-3; and the aerobic treatment has a residence time of 1-2 d, a dissolved oxygen of 2-4 mg / L, a pH of 7-8 and a temperature of 20-35 ℃.

[0042] Specifically, in step (3), biochemical treatment adopts a combined process of hydrolysis acidification, anoxic and aerobic for treating the fraction condensate produced after multi-stage evaporation concentration. The fraction condensate is characterized by a COD (Chemical Oxygen Demand) to ammonia nitrogen content ratio greater than 10:1 (i.e. carbon to nitrogen ratio > 10:1) due to the imbalance between organic matter and ammonia nitrogen after evaporation of the original wastewater, and needs to be treated by the combined process to achieve macromolecular organic matter chain breaking, ammonia nitrogen denitrification and COD deep removal, so that the effluent finally meets the receiving standard of the park wastewater treatment plant. The residence time of the hydrolysis acidification section is controlled at 1-2 days, the pH range is 6-9, the dissolved oxygen is maintained at 0-0.2 mg / L (preferably 0 mg / L), and the temperature is 20-40℃. In this stage, the large molecular refractory organic matter in the condensate is broken and hydrolyzed into small molecular easily biodegradable organic matter by the fermentation of anaerobic microorganisms, providing high-quality substrate for the microorganisms in the subsequent aerobic section and improving the overall organic matter removal efficiency. The pH control at 6-9 can maintain the appropriate enzyme activity environment for the hydrolysis bacterial flora, the dissolved oxygen maintained at 0-0.2 mg / L ensures strict anaerobic conditions, and the temperature of 20-40℃ is the optimal growth range for most hydrolysis microorganisms. The residence time of the anoxic section is 0.5-1.5 days (typical value is 1 day), and the dissolved oxygen is strictly controlled at less than 0.5 mg / L, and the nitrification liquid reflux ratio is 1-3. Its main function is to use organic matter as carbon source by denitrifying bacteria to reduce nitrate nitrogen (NO3 - / NO2 - ) from the aerobic section or remaining in the system to nitrogen (N2) for removal, thereby reducing the total nitrogen content. The dissolved oxygen less than 0.5 mg / L ensures anoxic environment, and the appropriate reflux ratio can provide sufficient nitrate nitrogen and optimize carbon source utilization efficiency. The residence time of the aerobic section is 1-2 days, the dissolved oxygen is controlled at 2-4 mg / L, the pH is 7-8, and the temperature is 20-35℃. In this stage, the remaining small molecular organic matter is completely oxidized and decomposed by the metabolic activity of aerobic microorganisms to reduce COD, and ammonia nitrogen is simultaneously nitrified to nitrate nitrogen to create conditions for subsequent anoxic denitrification. The dissolved oxygen of 2-4 mg / L is the optimal metabolic condition for aerobic bacterial flora, the pH of 7-8 is the optimal range for nitrification and COD degradation bacteria, and the temperature of 20-35℃ ensures microbial activity and treatment efficiency. Through the cooperation of hydrolysis acidification, anoxic and aerobic three stages, the combined process realizes the step-by-step conversion of macromolecular organic matter → small molecular organic matter → COD degradation, ammonia nitrogen → nitrate nitrogen → nitrogen, and finally effectively removes the main pollutants in the condensate to ensure that the effluent meets the receiving standard of the park wastewater treatment plant.

[0043] In some specific embodiments, in step (4), the leaching treatment uses methanol as the agent, which is selected based on the characteristics of the small amount of organic matter (mainly acrylonitrile, propylene and their polymers, and other high-boiling organic matter similar to the components of the mother liquor) attached to the surface of the crude salt after evaporation and concentration, which has good solubility. As a polar organic solvent, methanol can form a uniform and mutually soluble system with these organic matters, effectively washing off the organic matter attached to the surface of the salt particles, while methanol has almost no solubility for salt substances (such as inorganic salt crystals), which will not cause salt loss or introduce impurities, ensuring efficient separation of salt and organic matter; in step (5), the used leaching liquid is treated by rectification process, which can effectively separate methanol and organic matter by taking advantage of the significant difference in boiling point between methanol and organic matter (the boiling point of methanol is about 64.7℃, while the boiling point of organic matter such as acrylonitrile is generally higher): low-boiling-point methanol is evaporated and condensed for recovery, and after purification, it can be recycled to step (4) as a leaching agent, greatly reducing the consumption of the agent and the processing cost; while the high-boiling distillation residue (i.e. organic matter concentrated phase) is rich in acrylonitrile, propylene and their polymers and other high-value components washed off from the surface of the crude salt, which has a content of organic matter similar to that of the concentrated mother liquor, and has similar potential for productization or energy utilization as the mother liquor, thereby realizing efficient recovery and resource utilization of the solvent and valuable organic components in the leaching liquid.

[0044] In some specific embodiments, in step (4), the leaching treatment is carried out at room temperature, the leaching time is 10-30 min, and the mass ratio of leaching agent to crude salt is (1-2):1. Specifically, when the leaching treatment is carried out at room temperature, the mass ratio of leaching agent to crude salt is preferably (1-2):1; when the mass ratio is less than 1:1, the amount of leaching agent is insufficient, which makes it difficult to effectively remove the organic matter on the surface of the crude salt, affecting the leaching effect; when the mass ratio is greater than 2:1, although it helps to improve the impurity removal efficiency, it will lead to excessive use of leaching agent, increasing the load and cost of subsequent recovery and processing procedures, which is less economical. Therefore, controlling the mass ratio of leaching agent to crude salt within the range of (1-2):1 can ensure the leaching effect while taking into account the economy and rationality of the process.

[0045] In some specific embodiments, in step (5), the overhead temperature of the rectification column in the rectification recovery treatment is 64-66℃, the column bottom temperature is >70℃, and the reflux ratio is 1-3. Among them, the reflux ratio is a key parameter affecting the recovery efficiency and operating cost of methanol. When the reflux ratio is less than 1, the gas-liquid mass transfer and reflux in the rectification column are insufficient, leading to incomplete recovery of methanol and reducing the recovery rate; when the reflux ratio is greater than 3, although it helps to improve the separation effect, it will increase the heat load of the reboiler and the load of the condenser, leading to increased energy consumption and processing cost; therefore, controlling the reflux ratio within the range of 1-3 can ensure efficient recovery of methanol while taking into account the stability and economy of the process.

[0046] The following detailed description of examples of the present application is exemplary only and is intended to be illustrative of the present application, and is not to be understood as limiting the present application. Among them, the wastewater is taken from the acrylonitrile wastewater of a production workshop of an acrylonitrile chemical plant in Jilin, and the water quality is as follows: COD = 86765 mg / L, pH = 5, ammonia nitrogen = 58048 mg / L.

[0047] Example 1

[0048] A treatment method of acrylonitrile wastewater, the specific treatment steps are as follows:

[0049] (1) Chemical impurity removal: take 500 mL of wastewater sample from the acrylonitrile production workshop, add 5 g of impurity removal agent, which is compounded by granular activated carbon and polyaluminum chloride (PAC) at a mass ratio of 4:1, wherein the average pore size of the granular activated carbon is 35 nm; After mixing the wastewater and the impurity removal agent, stir for 30 min to remove the tar and macromolecular organic matter, and then perform suction filtration separation to obtain a filtrate;

[0050] (2) Evaporation concentration: adjust the pH value of the filtrate obtained in step (1) to 4, and then put it into the evaporation system for multi-stage evaporation concentration treatment, using three-effect evaporation process, the specific control parameters are: steam pressure is 0.8 MPa, vacuum pressure is 0.095 MPa, one-effect evaporation temperature is 90 ℃, two-effect evaporation temperature is 80 ℃, and three-effect evaporation temperature is 70 ℃; Obtain crude salt, distillate condensate and concentrated mother liquor;

[0051] (3) Biochemical treatment: take the distillate condensate obtained in step (2) for biochemical treatment, using the combination process of hydrolysis acidification + anoxic + aerobic, the specific parameters are:

[0052] Hydrolysis acidification section: residence time 2 d, pH = 8, dissolved oxygen 0 mg / L, temperature 28 ℃;

[0053] Anoxic section: residence time 1 d, dissolved oxygen 0.3 mg / L, nitration liquid reflux ratio 2;

[0054] Aerobic section: residence time 2 d, dissolved oxygen 3 mg / L, pH = 8, temperature 30 ℃;

[0055] (4) Leaching treatment: put the crude salt separated in step (2) into a small beaker, add methanol, soak at room temperature for 30 min, and then perform filtration separation to obtain leaching liquid and pure salt solid;

[0056] (5) Rectification recovery: the leaching solution obtained in step (4) is subjected to rectification recovery treatment, wherein the rectification column top temperature is 65℃, the column bottom temperature is 75℃, the reflux ratio is 2.5, and the reagent and the rectification residue are recovered respectively, and the recovered reagent is returned to step (4) for recycling.

[0057] Example 2

[0058] Reference Example 1 acrylonitrile wastewater treatment method, the difference is that the impurity removing agent does not add polyaluminum chloride (i.e. the impurity removing agent only contains granular activated carbon).

[0059] Example 3

[0060] Reference Example 1 acrylonitrile wastewater treatment method, the difference is that the addition amount of the impurity removing agent is 0.5 g (i.e. the addition amount is 0.1% of the content of acrylonitrile wastewater).

[0061] Example 4

[0062] Reference Example 1 acrylonitrile wastewater treatment method, the difference is that the granular activated carbon and polyaluminum chloride are compounded in a mass ratio of 1:1.

[0063] Example 5

[0064] Reference Example 1 acrylonitrile wastewater treatment method, the difference is that after the filtrate in step (1) is obtained, it is directly sent to three-effect evaporation without adjusting the pH with acid.

[0065] Example 6

[0066] Reference Example 1 acrylonitrile wastewater treatment method, the difference is that single-effect evaporator is used for evaporation concentration, atmospheric pressure, evaporation temperature 105 ℃, no multi-stage.

[0067] Example 7

[0068] Reference Example 1 acrylonitrile wastewater treatment method, the difference is that in step (2), three-effect evaporation is used for evaporation concentration, and the parameters are changed to: one-effect evaporation temperature 110 ℃, two-effect evaporation temperature 95 ℃, three-effect evaporation temperature 80 ℃, steam pressure 0.4 MPa, and vacuum degree 0.080 MPa.

[0069] Example 8

[0070] Reference Example 1 acrylonitrile wastewater treatment method, the difference is that the pH of hydrolysis acidification in biochemical treatment is 5.

[0071] Example 9

[0072] Reference Example 1 acrylonitrile wastewater treatment method, the difference is that the dissolved oxygen in the aerobic section of biochemical treatment is controlled at 6 mg / L.

[0073] Example 10

[0074] The acrylonitrile wastewater treatment method of Reference Example 1 was used, except that the leaching treatment used ethanol as the reagent instead of methanol.

[0075] Comparative Example 1

[0076] The acrylonitrile wastewater treatment method of Reference Example 1 was used, except that the acrylonitrile wastewater was not subjected to any chemical impurity removal and was directly pumped into the triple-effect evaporator for evaporation and concentration.

[0077] Comparative Example 2

[0078] The acrylonitrile wastewater treatment method of Reference Example 1 was used, except that the impurity removal agent of step (1) was granular activated carbon, but the average pore size was 80 nm.

[0079] Comparative Example 3

[0080] The acrylonitrile wastewater treatment method of Reference Example 1 was used, except that the impurity removal agent of step (1) was granular activated carbon, but the average pore size was 5 nm.

[0081] Comparative Example 4

[0082] The acrylonitrile wastewater treatment method of Reference Example 1 was used, except that no granular activated carbon was added to the impurity removal agent, and only a polyaluminum chloride flocculant was used.

[0083] Test Example

[0084] The typical products generated in each step of the acrylonitrile wastewater treatment method in Examples 1-10 and Comparative Examples 1-4, including the filtrate obtained in the chemical impurity removal step, the fraction condensate generated in the evaporation and concentration step, the concentrated mother liquor and crude salt, the final effluent of the biochemical treatment step, the leaching solution obtained in the leaching treatment step, and the reagent recovered in the rectification recovery step and the rectification residue, were tested and analyzed: the chemical impurity removal effect was evaluated by measuring the COD (dichromate method) and ammonia nitrogen (Nessler's reagent colorimetric method or salicylic acid spectrophotometric method) of the original acrylonitrile wastewater and the filtrate, assessing the adsorption removal efficiency of the activated carbon-flocculant compounded impurity removal agent for tar and macromolecular organic matter, and comprehensively judging by the clarity of the solid-liquid separation after filtration (the characterization results are shown in Table 1); the evaporation and concentration product characteristics were analyzed by detecting the COD (dichromate method), pH (glass electrode method) and ammonia nitrogen (Nessler's reagent method or salicylic acid method) of the fraction condensate, observing the appearance and composition characteristics of the concentrated mother liquor and the appearance of the crude salt (the characterization results are shown in Table 2); the biochemical treatment performance was verified by measuring the COD (dichromate method), ammonia nitrogen (Nessler's reagent method) and pH (glass electrode method) of the final effluent after biochemical treatment of the fraction condensate (the characterization results are shown in Table 3); the leaching treatment effect was evaluated by investigating the organic matter content (such as COD or specific organic matter concentration) in the leaching solution obtained by filtering the crude salt soaked with reagent for 30 min and the purity of the salt solid (visual observation or COD measurement after dissolution), and the desorption capacity of the reagent for the organic matter attached to the surface of the salt (the related data are integrated in Table 4); the rectification recovery efficiency was verified by measuring the purity of the reagent (such as the reagent content analyzed by gas chromatography GC) after rectification recovery of the leaching solution and the properties of the rectification residue (including COD and component composition), verifying the recycling efficiency of the reagent in the rectification system and the feasibility of the disposal of the residue, so as to ensure the closed-loop operation and resource level of the process (the characterization results are also shown in Table 4).

[0085] Table 1 Chemical impurity removal effect

[0086]

[0087] Table 2 Evaporation and concentration product characteristics

[0088]

[0089] Table 3 Biochemical treatment performance (final effluent)

[0090]

[0091] Table 4 Rectification recovery efficiency

[0092]

[0093] From the test data of Examples 1-10 and Comparative Examples 1-4, in the whole process of salt-containing wastewater treatment, the parameters of each process step of Example 1 synergistically achieve the optimum: the chemical impurity removal uses an impurity removal agent compounded from granular activated carbon and polyaluminum chloride (PAC) at a mass ratio of 4:1, the removal effect of tar and macromolecular organic matter is the best, the COD removal rate is 17.2%, and the filtrate clarity is significantly improved (SS < 150), which is much better than Example 2 without adding PAC, Comparative Examples 2-3 with unsuitable activated carbon pore size, and Comparative Example 4 using only PAC, and avoids the problems of evaporation system blockage, high COD of distillate condensate (6320 mg / L), and tar entrainment in coarse salt caused by direct evaporation without chemical impurity removal in Comparative Example 1, and the obtained distillate condensate has a lower COD (4000 mg / L), moderate ammonia nitrogen (375 mg / L), and good appearance of coarse salt; in the evaporation and concentration link, single-effect atmospheric evaporation (Example 6) and high-temperature three-effect evaporation (Example 7) do not show obvious advantages and may increase energy consumption; the biochemical treatment uses the combined process of "hydrolysis acidification + anoxic + aerobic", the final effluent COD is as low as 289 mg / L, the COD removal rate is 99.7%, the ammonia nitrogen is reduced to 14 mg / L, and the removal rate is 99.9%, which is significantly better than the treatment effect under conditions such as abnormal pH (Example 8) or high dissolved oxygen (Example 9); in the leaching treatment, using methanol as the leaching agent and soaking at room temperature for 30 min can effectively remove the organic matter on the surface of the coarse salt, and obtain salt solids with a purity of 99.0%, which is better than using ethanol (Example 10) or indirectly affected by the non-optimized impurity removal (Comparative Example 1); in the rectification recovery link, under the optimized conditions of distillation column overhead temperature 65℃, column bottom temperature 75℃, and reflux ratio 2.5, efficient recovery of leaching reagent is achieved (purity 98.0%, recovery rate 98.0%). Therefore, Example 1 exhibits the best pollutant removal efficiency, system operation stability, and resource utilization performance, and has significant technical advancement and economic rationality compared to each comparative example and parameter deviated example.

[0094] The preferred embodiments of the application are described in detail above, but the application is not limited thereto. Within the technical concept of the application, various simple modifications can be made to the technical solutions of the application, including the combination of various technical features in any other suitable manner, and these simple modifications and combinations should also be considered as disclosed by the application and fall within the protection scope of the application.

Claims

1. A method for treating acrylonitrile wastewater, characterized by, The method comprises the following steps: (1) Chemical impurity removal: adding an impurity removal agent to acrylonitrile wastewater, and separating solid and liquid after reaction to obtain a filtrate; wherein the impurity removal agent comprises granular activated carbon with a pore size range of 10-50 nm; (2) Evaporation concentration: evaporating and concentrating the filtrate to obtain crude salt, fraction condensate and concentrated mother liquor, respectively; (3) Biochemical treatment: performing biochemical treatment on the fraction condensate; (4) Leaching treatment: adding a leaching agent methanol to the crude salt for leaching treatment under normal temperature conditions for 10-30 min, the mass ratio of leaching agent to crude salt being (1-2):1, separating salt and organic substances attached to the surface of the salt to obtain a leaching solution; (5) Recycling: performing rectification recovery treatment on the leaching solution to recover the leaching agent and rectification residue, wherein the recovered leaching agent is returned to step (4) for recycling.

2. The method for treating acrylonitrile wastewater according to claim 1, characterized by, In step (1), the impurity removal agent further comprises one or more of polyaluminum chloride, polyferric sulfate and zinc sulfate.

3. The method for treating acrylonitrile wastewater according to claim 2, characterized by, The impurity removal agent is compounded from the granular activated carbon and any flocculant selected from the polyaluminum chloride, polyferric sulfate and zinc sulfate at a mass ratio of (3-5):

1.

4. The method for treating acrylonitrile wastewater according to claim 1, characterized by, In step (2), the pH of the filtrate is adjusted to 3-5 before evaporation concentration.

5. The method for treating acrylonitrile wastewater according to claim 1, characterized by, In step (2), multi-stage evaporation is used for evaporation concentration.

6. The method for treating acrylonitrile wastewater according to claim 5, characterized by, The multi-stage evaporation is three-effect evaporation, and the control parameters are as follows: steam pressure is greater than 0.5 MPa, vacuum extraction pressure is 0.085-0.095 MPa, one-effect evaporation temperature is 85-95 ℃, two-effect evaporation temperature is 75-85 ℃, and three-effect evaporation temperature is 60-70 ℃.

7. The method for treating acrylonitrile wastewater according to claim 1, characterized by, In step (3), the biochemical treatment adopts a combined process of hydrolysis acidification, anoxic and aerobic processes, wherein the hydrolysis acidification has a residence time of 1-2 d, a pH of 6-9, a dissolved oxygen of 0-0.2 mg / L and a temperature of 20-40 ℃; the anoxic process has a residence time of 0.5-1.5 d, a dissolved oxygen of less than 0.5 mg / L and a nitration liquid reflux ratio of 1-3; and the aerobic process has a residence time of 1-2 d, a dissolved oxygen of 2-4 mg / L, a pH of 7-8 and a temperature of 20-35 ℃.

8. The method for treating acrylonitrile wastewater according to claim 1, characterized by, In step (5), the rectification column in the rectification recovery treatment has a top temperature of 64-66 ℃, a bottom temperature of >70 ℃ and a reflux ratio of 1-3.

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