A method for treating phenylacetonitrile product wastewater

Abstract

The application provides a treatment method for phenylacetonitrile product wastewater, and specifically comprises the following steps: firstly, a small amount of oxidizing agent is added to decompose cyanide in the wastewater into ammonium salt substances; then, a salen Cu (II) catalyst is added for electrolysis, so that the ammonium salt substances and residual cyanide in the wastewater are completely decomposed, and part of COD is decomposed; finally, the wastewater is evaporated in a three-effect evaporator, the evaporated water is treated in a biochemical system until reaching a discharge standard, the evaporated salt is used as an industrial by-product salt, and the last high-concentration mother liquor is concentrated and then incinerated as solid waste. The cyanide in the wastewater is treated by the method of oxidation followed by electrolysis, and a catalyst is added during electrolysis, so that the electrolysis efficiency is greatly enhanced, the comprehensive cost is greatly reduced, part of COD is decomposed, and the pressure of three-effect evaporation and biochemical treatment is reduced. The method is easy to operate in a large scale, and has wide application value.

Description

TECHNICAL FIELD

[0001] The present application relates to a treatment method of wastewater produced in cyanation reaction, in particular to a treatment method of wastewater produced in production of phenylacetonitrile products. BACKGROUND

[0002] The wastewater produced in the synthesis process of phenylacetonitrile products by using sodium cyanide as raw material and benzyl chloride as raw material has the following characteristics: high COD: 15000-40000 mg / L; high cyanide: 3000-5000 mg / L; high ammonia nitrogen: >1000 mg / L; high salt: sodium chloride mass fraction reaches 25%, close to saturated concentration; high pH: >10.5. If the wastewater produced in industrial production of phenylacetonitrile products is to be treated to reach the standard discharge, it needs to be treated to the following indexes: COD: <500 mg / L; cyanide: <1 mg / L; ammonia nitrogen: <30 mg / L; sodium chloride: <0.5%; pH: 7. From the above data, it can be seen that the indexes required to be reached by the wastewater treatment are very strict, and the wastewater produced in the production of phenylacetonitrile products is complex, so it is very difficult to treat such wastewater, which has become a big difficulty and research focus of environmental protection treatment.

[0003] In the prior art, for cyanide treatment, there are the following methods: (1) hypochlorite oxidation method, which uses hypochlorite to oxidize under weak alkaline conditions, and cyanate ions are oxidized into nitrogen, carbon dioxide and other gases, which is used for treating phenylacetonitrile production wastewater, and has the advantages of fast reaction and complete reaction, but has the disadvantages of high cost, and the odor of wastewater cannot be removed, and the unreacted hypochlorite will cause secondary pollution; (2) hydrogen peroxide oxidation method, which uses excess hydrogen peroxide to oxidize under the same weak alkaline conditions, and cyanate ions are also oxidized into nitrogen and carbon dioxide gas, which is used for treating phenylacetonitrile production wastewater, and has the advantages of removing odor, but has the disadvantages of adding excess hydrogen peroxide to meet the ammonia nitrogen standard, high treatment cost, and the excess hydrogen peroxide is easy to explode during three-effect evaporation, and is very dangerous if not handled properly; (3) high-pressure hydrolysis method, which uses high temperature and high pressure to make cyanate itself decompose into ammonium carbonate salt, which is used for treating phenylacetonitrile production wastewater, and has the advantages of not needing to add other chemicals, but has the disadvantages of high energy consumption leading to high cost, and special equipment is needed for high temperature and high pressure, and the high ammonia nitrogen also needs to be removed for further treatment; (4) electrolysis method, which uses electrochemical oxidation-reduction reaction to destroy cyanate in wastewater, which is used for treating phenylacetonitrile production wastewater, and has the advantages of not adding new toxic substances to wastewater and low treatment cost when treating high-concentration cyanide-containing wastewater, but has the disadvantages of large initial investment of equipment, low direct electrolysis efficiency due to high sodium chloride content in phenylacetonitrile production wastewater, long electrolysis time, and high energy consumption during operation due to the decrease of cyanate ion concentration, and the final treatment cost is higher than other methods; (5) biological chemical method, which uses specific bacteria to decompose cyanate into carbonate and nitrate in two stages, which is used for treating phenylacetonitrile production wastewater, and has the advantages of high efficiency of removing cyanate from wastewater, and non-toxic effluent, but has the disadvantages of poor adaptability, and can only treat low-concentration cyanide-containing wastewater with small fluctuation range of concentration; (6) acidification recovery method, which adjusts the pH value of cyanide-containing wastewater to be acidic by using acid, and cyanate is converted into hydrogen cyanide gas, and when inert gas is filled into the wastewater, the gas containing hydrogen cyanide contacts with sodium hydroxide solution, and the hydrogen cyanide is converted into sodium cyanide salt again and recovered for reuse, which is used for treating phenylacetonitrile production wastewater.The advantages of this method are low price of hydrochloric acid used for treatment, low treatment cost, and small influence of wastewater composition. The disadvantages are low safety factor, and once gas escapes from the equipment, the toxic hydrogen cyanide gas will cause instant fatal danger to the operator; (7) sulfur dioxide-air oxidation method, which is specifically: in a certain pH range, under the catalysis of copper salt, the cyanate in the cyanide-containing wastewater is oxidized by the cooperation of sulfur dioxide and air. According to the reaction mechanism, the sulfur dioxide gas is actually converted into sulfite, and the oxygen reacts with the copper salt to generate sulfate and active oxygen, which oxidizes the cyanate into ammonium carbonate salt. This method is used for treating phenylacetonitrile production wastewater. This method has the advantages of simple process, simple equipment, better treatment effect than hypochlorite oxidation method, low reagent cost, and low investment. The disadvantages are that the copper ions in the wastewater after treatment will exceed the standard, and the organic impurities and inorganic impurities in the wastewater and the pH value of the wastewater have a great influence on the catalysis of copper salt, so the application is greatly limited.

[0004] In the prior art, for the COD in the wastewater, there are the following treatment methods: (1) precipitation method, using flocculants such as PAC and PAM to flocculate the organic matter in the wastewater into precipitate and remove it by filtration. The advantages of this method are fast removal, and the disadvantages are low removal rate for high COD and high treatment cost; (2) strong oxidation method, using strong oxidizing agent to oxidize and decompose the organic matter in the wastewater into carbon dioxide and water. This method is high in cost and only suitable for treating low-concentration COD; (3) distillation method, using distillation and concentration method to evaporate water, and high COD remains in the bottom as solid waste for incineration. This method is suitable for high COD and low proportion of low-boiling-point organic matter in wastewater.

[0005] In the prior art, for high ammonia nitrogen in wastewater, there are the following treatment methods: (1) electrolysis method, using electrolysis method to decompose ammonia nitrogen into nitrogen gas. The advantages of this method are high removal rate and basically no secondary pollution; (2) strong oxidation method, using strong oxidizing agent to decompose ammonia nitrogen into nitrogen gas. This method is only suitable for treating low ammonia nitrogen, and the treatment cost is too high for high ammonia nitrogen, and the secondary pollution is large; (3) ion membrane method, using ion membrane to separate ammonia nitrogen from wastewater. The application of this method is limited by salt content, pH value, COD and other factors in the wastewater, and it can only treat pure ammonia nitrogen wastewater.

[0006] In the prior art, for high content sodium chloride in wastewater, there are the following treatment methods: (1) distillation method, using the method of distillation to concentrate the wastewater, and the sodium chloride is precipitated and centrifuged into industrial by-product salt for treatment, which needs to use special equipment such as three-effect equipment, otherwise the cost is too high; (2) ion membrane method, which is limited by factors such as COD and pH, and is suitable for treating low-concentration sodium chloride; (3) electrodialysis method, which separates sodium chloride in wastewater by using electrodialysis method, which needs special dialysis equipment, and the investment is large, and this method needs to be combined with distillation method, and is not suitable for the case of almost saturated sodium chloride.

[0007] The above methods are not suitable for the treatment of phenylacetonitrile production wastewater, therefore, it is of great significance to develop a new process suitable for phenylacetonitrile production wastewater and taking into account safety, environmental protection and low cost. SUMMARY

[0008] The purpose of the present application is to provide a method suitable for phenylacetonitrile production wastewater and taking into account safety, environmental protection and low cost. The specific technical scheme is as follows:

[0009] A phenylacetonitrile production wastewater treatment method, comprising an oxidation step, an electrolysis step and a post-treatment step, the oxidation step is specifically: adding an oxidizing agent to the wastewater to obtain a first mixed solution; the electrolysis step is specifically: adding a catalyst to the first mixed solution for electrolysis to obtain a second mixed solution; the post-treatment step is specifically: filtering and evaporating the second mixed solution.

[0010] In the above technical scheme, preferably, the amount of oxidizing agent in the oxidation step is 3.5-4.5% of the mass of wastewater; the amount of catalyst in the electrolysis step is 0.01-0.04% of the mass of wastewater, the current density is 1000-1500 A / m2, and the electrolysis temperature is 50-70℃.

[0011] In the above technical scheme, preferably, the oxidizing agent is at least one of hydrogen peroxide with a mass fraction of 27.5%, sodium hypochlorite with a mass fraction of 10% and sodium chlorate with a mass fraction of 10%; the catalyst is at least one of salen Cu(II) catalyst, salen Co(II) catalyst and salen(Mn(II) catalyst; a diaphragmless electrolytic cell is used during electrolysis.

[0012] In the above technical scheme, preferably, the oxidation step is specifically: the oxidizing agent is added dropwise to the wastewater under stirring, the dropwise adding time is 0.5-1.5 hours, after the dropwise adding is completed, the stirring is continued for 1.8-2.5 hours, and the stirring rate is 800-1200 r / min.

[0013] Preferably in the above technical solution, the electrolysis step is specifically: transferring the first mixed solution into a diaphragmless electrolytic cell, adding a catalyst, turning on the power supply, adjusting the current density, heating the electrolytic cell, the heating rate is 2-5 ℃ / min, and electrolyzing for 1.0-6.0 hours.

[0014] Preferably in the above technical solution, the evaporation is performed in a three-effect evaporator, and the pH value is adjusted to 8-8.5 before the evaporation.

[0015] The wastewater treatment method of the application is specifically: first, a small amount of oxidant is added to decompose the cyanide in the wastewater into ammonium salt substances, then a salen Cu(II) catalyst is added for electrolysis, the ammonium salt substances and residual cyanide in the wastewater are completely decomposed, and part of COD is decomposed, finally, the wastewater is fed into a three-effect evaporator for evaporation, the evaporated water is fed into a biochemical system for treatment to reach the discharge standard, the evaporated salt is used as an industrial by-product salt, and the last high-concentration mother liquor is concentrated and then used as solid waste for incineration treatment, and the effect is:

[0016] 1. The method can be applied to the treatment of wastewater produced in the production of phenylacetonitrile products. Before the wastewater treatment: COD=15500 mg / L, cyanide=4000 mg / L, ammonia nitrogen=1050 mg / L, and pH=11.2; after the wastewater treatment, the evaporated water has the following detection results: COD=1858 mg / L, ammonia nitrogen=80 mg / L, and pH=7-8, and the evaporated water is fed into a biochemical system for treatment to reach the discharge standard (i.e. COD<500 mg / L, cyanide<1 mg / L, ammonia nitrogen<30 mg / L, sodium chloride<0.5%, and pH: 7); the evaporated salt after the wastewater treatment has the following detection results: cyanide=2.5 mg / L, and ammonia nitrogen=150 mg / L, which meets the by-product industrial salt standard.

[0017] 2. Unique treatment process. The present invention adopts a first oxidation and then electrolysis process to treat cyanide-containing wastewater. A small amount of oxidant (hydrogen peroxide) is first used to break the cyanide, and then a short period of electrolysis is performed to break the remaining cyanide and decompose a large amount of ammonia nitrogen. To improve the efficiency of electrolysis, a catalyst (salen Cu (II) catalyst) is added to improve the efficiency of electrolysis, thereby greatly improving the efficiency of breaking the cyanide and ammonia nitrogen. Sodium chloride is a strong electrolyte. Sodium chloride is conducive to electrolysis efficiency during electrolysis. Optimum sodium chloride mass fraction is between 8-10% during electrolysis. The sodium chloride mass fraction of benzyl cyanide product production wastewater reaches 25%, which is close to saturation concentration. After the sodium chloride mass fraction exceeds 10%, the electrolysis efficiency reduces along with the raising of sodium chloride content. Salen catalyst is a compound combined with an organic ligand and a metal ion, and is non-water-soluble. However, it can greatly enhance electrolysis efficiency when added to water for electrolysis. Therefore, the processing step of oxidizing and then electrolyzing the benzyl cyanide production wastewater is very effective in the present invention, greatly reducing costs. Specifically, compared with the prior art, the cost of the present invention is between 150-200 yuan for processing 1 cubic meter of water, while the prior art is lowest and also requires 500-600 yuan, which is down to about 30%.

[0018] 3. Easy to operate on a large scale. The present invention is not limited by organic and inorganic impurities in wastewater, is a method that is easy to use in large-scale production, and has wide application value.

[0019] In addition to the above-described objects, features and advantages, the present invention has other objects, features and advantages. The present invention will be further described in detail with reference to the following embodiments. DETAILED DESCRIPTION

[0020] The solutions of the present invention are described in detail below with reference to the embodiments. However, the present invention can be implemented in many different ways as defined and covered by the claims.

[0021] Example 1:

[0022] The test results of wastewater from the production process of 10,000 kg of benzyl cyanide are as follows: COD = 15,500 mg / L, cyanide = 4,000 mg / L, ammonia nitrogen = 1,050 mg / L, and pH = 11.2.

[0023] 420 kg of 27.5% hydrogen peroxide was slowly added dropwise to the wastewater over 1.2 hours. After the addition was complete, the mixture was stirred for 2 hours to obtain a first mixed solution. The test results showed: COD = 15500 mg / L, cyanide = 76 mg / L, ammonia nitrogen = 3018 mg / L, and pH = 10.1.

[0024] The first mixed solution was pumped into a non-diaphragm electrolytic cell, 1 kg of salen Cu (II) catalyst was added, the power was turned on, and the current density was adjusted to about 1200 A / m2 , electrolysis is carried out, and the temperature of the wastewater will slowly rise to 60-65°C. After 2 hours of electrolysis, sampling test results are: COD = 9860 mg / L, cyanide = 0.54 mg / L, ammonia nitrogen = 130 mg / L, pH value 8.7, and electrolysis is stopped to obtain the second mixed solution.

[0025] The second mixed liquid is filtered to recover the salen Cu(II) catalyst. The filtrate is pumped to a triple-effect evaporator raw water tank, where the pH is adjusted to 8-8.5. The filtrate is then pumped into a triple-effect evaporator for evaporation. The evaporated water is tested for COD of 1858 mg / L, ammonia nitrogen of 80 mg / L, and pH of 7.3. The evaporated water is then treated in a biochemical system until it meets acceptable discharge standards. The evaporated salt is tested for cyanide of 2.5 mg / L and ammonia nitrogen of 150 mg / L, meeting the standards for by-product industrial salt. The highly concentrated mother liquor is then concentrated and incinerated as solid waste (referring to the procedures of the prior art).

[0026] The technical solution of this embodiment is adopted, and the effects are shown in Table 2.

[0027] Example 2-Example 5

[0028] Similarly, the wastewater from the production process of 10,000 kg of benzyl cyanide has the following test results: COD = 15,500 mg / L, cyanide = 4,000 mg / L, ammonia nitrogen = 1,050 mg / L, and pH = 11.2.

[0029] The differences between Example 2 to Example 5 and Example 1 are shown in Table 1:

[0030] Table 1 Parameter comparison table of Examples 1-5

[0031] Case / parameters Oxidizing agent Catalyst Current density Electrolysis time Example 1 420 kg 27.5% hydrogen peroxide 1 kg salen Cu(II) 1200 A / m 2 ]] 2h Example 2 380 kg 10% sodium hypochlorite 1 kg salen Cu(II) 1150 A / m 2 ]] 1.5h Example 3 350 kg 10% sodium hypochlorite 1 kg salen Cu(II) 1250 A / m 2 ]] 2h Example 4 420 kg 27.5% hydrogen peroxide 1 kg salen Co(II) 1200 A / m 2 ]] 1.5h Example 5 380 kg 10% sodium hypochlorite 1 kg salen Mn(II) 1220 A / m 2 ]] 2h

[0032] The wastewater treatment was carried out using the technical solutions of Examples 2 to 5, and the results are shown in Table 2:

[0033] Table 2 Comparison of wastewater treatment effects of Examples 1-5

[0034]

[0035] Comparative Example:

[0036] The test results of wastewater from the production process of 10,000 kg of benzyl cyanide are as follows: COD = 15,500 mg / L, cyanide = 4,000 mg / L, ammonia = 1,050 mg / L, and pH = 11.2.

[0037] The first mixed solution was pumped into a non-diaphragm electrolytic cell, 1 kg of salen Cu (II) catalyst was added, the power was turned on, and the current density was adjusted to about 1200 A / m 2, electrolysis is carried out, and the temperature of the wastewater is slowly increased to 60-65 DEG C. After 6 hours of electrolysis, the sample detection results are: COD = 18900 mg / L, cyanide = 254 mg / L, and ammonia nitrogen = 158 mg / L. The electrolysis is stopped, and the electrolysis mixture is obtained.

[0038] 420 kg of 27.5% mass fraction hydrogen peroxide is slowly added to the wastewater, and the addition is completed in 1.2 hours. After 2 hours of stirring, the oxidation mixture is obtained, and the detection results are: COD = 18670 mg / L, cyanide = 86 mg / L, ammonia = 318 mg / L, and pH = 9.8. Because the cyanide is not completely decomposed, the water cannot meet the standard for entering the three-effect evaporator.

[0039] The present comparative example uses a process of first electrolysis and then oxidation treatment. Because the sodium chloride concentration is as high as 25% or more, the electrolysis is equivalent to short circuit, the current efficiency is very low, and the electrolysis has very low decomposition efficiency for high cyanide. After 6 hours of electrolysis and then addition of the oxidizing agent, the water still cannot meet the standard for entering the three-effect evaporator. Because the electrolysis time is long, the power consumption is high, and the cost is high.

[0040] The above only describes preferred embodiments of the present application and is not used to limit the present application. For those skilled in the art, the present application can have various modifications and changes. Any modification, equivalent replacement, improvement, etc. within the spirit and principle of the present application shall be included in the protection scope of the present application.

Claims

1. A method for treating wastewater from the production of benzyl cyanide products, characterized in that: The method comprises an oxidation step, an electrolysis step and a post-processing step. The oxidation step specifically comprises: adding an oxidant to wastewater to obtain a first mixed solution; the electrolysis step specifically comprises: adding a catalyst to the first mixed solution for electrolysis to obtain a second mixed solution; and the post-processing step specifically comprises: filtering and evaporating the second mixed solution. The amount of oxidant used in the oxidation step is 3.5-4.5% of the wastewater mass; the amount of catalyst used in the electrolysis step is 0.01-0.04% of the wastewater mass, and the current density is 1000-1500A / m 2 , the electrolysis temperature is 50℃~70℃; The oxidant is at least one of 27.5% by mass of hydrogen peroxide, 10% by mass of sodium hypochlorite, and 10% by mass of sodium chlorate; the catalyst is at least one of a salen Cu(II) catalyst, a salen Co(II) catalyst, and a salen Mn(II) catalyst; and a diaphragmless electrolytic cell is used during electrolysis. The oxidation step is specifically as follows: adding the oxidant dropwise to the wastewater under stirring conditions for 0.5-1.5 hours, and after the addition is completed, continuing to stir for 1.8-2.5 hours at a stirring rate of 800-1200 r / min; The electrolysis step specifically comprises: transferring the first mixed solution to a non-diaphragm electrolytic cell, adding a catalyst, turning on the power supply, adjusting the current density, heating the electrolytic cell at a heating rate of 2°C-5°C / min, and electrolyzing for 1.0-2.0 hours; The wastewater has the following characteristics: COD = 15500 mg / L, cyanide = 4000 mg / L, ammonia nitrogen = 1050 mg / L, pH = 11.

2.

2. The method for treating wastewater from the production of benzyl cyanide products according to claim 1, wherein: The evaporation was carried out in a triple-effect evaporator, and the pH value was adjusted to 8-8.5 before evaporation.

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