Method for treating polychlorinated nitrobenzene-containing wastewater by adopting calcium hydroxide alkaline hydrolysis

Abstract

The invention discloses a method for treating polychlorinated nitrobenzene-containing wastewater by adopting calcium hydroxide alkaline hydrolysis. The method comprises the following steps: firstly, adding calcium hydroxide into wastewater containing polychlorinated nitrobenzene, carrying out hydrolysis reaction under stirring and temperature control conditions, carrying out nucleophilic substitution on activated chlorine substitution sites and nitro substitution sites in polychlorinated nitrobenzene molecules by utilizing hydroxyl ions to generate phenolic substances such as trinitrodichlorophenol and the like, and separating the phenolic substances to obtain the polychlorinated nitrobenzene-containing wastewater. Performing ultrasonic treatment on the first treatment liquid until the solution turns yellow and the chromaticity is not increased any more to obtain a first treatment liquid, and performing ultrasonic treatment, washing and filtering on the first treatment liquid to remove precipitated solids to obtain the treatment liquid. According to the method disclosed by the invention, the primary attenuation of the polychlorinated nitrobenzene-containing wastewater is realized, and the treatability of the wastewater is improved.

Description

Technical Field

[0001] This invention belongs to the field of polychlorinated nitrobenzene wastewater treatment technology, specifically relating to a method for treating polychlorinated nitrobenzene wastewater by alkaline hydrolysis with calcium hydroxide. Background Technology

[0002] 1,3,5-Triamino-2,4,6-trinitrobenzene (TATB) is an important insensitive high-energy explosive. Compared with traditional explosives such as 2,4,6-trinitrotoluene (TNT), cyclotrimethylenetrinitramine (RDX), and cyclotetramethylenetetranitramine (HMX), it has the characteristics of low sensitivity, good thermal stability, and excellent overall performance. The production of TATB generates a certain amount of acidic wastewater, which typically contains polychlorinated nitrobenzenes (PCBs) such as trinitrotrichlorobenzene (TCTNB). PCBs are highly toxic and environmentally hazardous, easily causing adverse effects on the ecological environment and biological health; therefore, the treatment of its wastewater requires high levels of safety.

[0003] Existing technologies for treating polychlorinated nitrobenzene (PCB) wastewater mainly include biological and physicochemical methods, such as biodegradation, bioelectrochemical processes, advanced oxidation, reduction-oxidation coupling, and photoelectrocatalysis. However, typical chloronitrobenzene aromatic compounds have stable molecular structures and poor biodegradability, making them difficult to effectively degrade using conventional biological methods. Furthermore, the chlorine and nitro groups in their molecules have strong electron-withdrawing effects, leading to high reagent consumption and treatment costs when using advanced oxidation methods to achieve deep degradation or complete mineralization. Existing technologies also generally suffer from complex processes, high operating costs, and the potential for secondary pollution. Summary of the Invention

[0004] To address the problems of high cost, harmful byproducts, and secondary pollution associated with existing methods for treating wastewater containing polychlorinated nitrobenzene (PCBs), this invention provides a method for treating PCB-containing wastewater using alkaline hydrolysis with calcium hydroxide. This method utilizes calcium hydroxide to provide hydroxide ions in the system, promoting the gradual hydrolysis of PCBs to generate phenolic substances such as trinitrodichlorophenol, thereby reducing their toxicity and improving the feasibility of subsequent wastewater treatment.

[0005] The technical solution of the present invention is as follows:

[0006] A method for treating wastewater containing polychlorinated nitrobenzene using alkaline hydrolysis of calcium hydroxide includes the following steps:

[0007] (1) Add calcium hydroxide to the wastewater containing polychlorinated nitrobenzene and carry out hydrolysis reaction under stirring and temperature control. Use hydroxide ions to nucleophilically replace the activated chlorine substitution sites and nitro substitution sites in the polychlorinated nitrobenzene molecule to generate phenolic substances such as trinitrodichlorophenol until the solution turns yellow and the color no longer increases, and the first treatment solution is obtained.

[0008] (2) The first treatment liquid is subjected to ultrasonication, washing and filtration to remove the precipitated solids and obtain the treatment liquid.

[0009] Furthermore, in step (1), polychlorinated nitrobenzenes include, but are not limited to, TCTNB.

[0010] Furthermore, in step (1), the mass fraction of calcium hydroxide is 97%, and the amount of calcium hydroxide added is until the pH of the wastewater is 11.

[0011] Furthermore, in step (1), the stirring method is magnetic stirring, and the stirring speed is 300 r / min.

[0012] Further, in step (1), the temperature control process is as follows: first, the initial temperature is controlled at 25 ℃~28 ℃, then the temperature is increased to 60 ℃ at a heating rate of 1~3 ℃ / min, and the constant temperature reaction is maintained at 60 ℃.

[0013] Furthermore, in step (2), the vibration frequency of the ultrasonic treatment is 50~200kHz, preferably 80kHz; the vibration frequency gradient is 0~30kHz / min.

[0014] Further, in step (2), the filtration method is as follows: a 0.22 μm organic phase filter membrane is used, and vacuum sand core filtration device is used for filtration.

[0015] Compared with the prior art, the present invention has the following beneficial effects:

[0016] (1) The present invention uses calcium hydroxide to perform alkaline hydrolysis treatment on acidic wastewater containing polychlorinated nitrobenzene, which not only achieves the initial neutralization of the wastewater, but also improves its acidic conditions that are not suitable for biochemical treatment.

[0017] (2) Compared with strong bases such as sodium hydroxide and potassium hydroxide, calcium hydroxide is more reactive, and the calcium sulfate generated can be recycled after treatment, reducing costs while restoring the system to neutrality.

[0018] (3) Compared with weak bases such as ammonia, calcium hydroxide can more stably provide the OH- required for alkaline hydrolysis. - It can more effectively promote the nucleophilic substitution of activated chlorine substitution sites and nitro substitution sites in polychlorinated nitrobenzene molecules to generate phenolic products, and has the advantages of no ammonia volatilization, easy solid-liquid separation and low cost for engineering applications.

[0019] (4) This invention utilizes OH in the solution - Nucleophilic substitution reactions of polychlorinated nitrobenzenes produce less toxic products such as chloronitrobenzene, which not only reduces the ecotoxicity of wastewater but also improves its biodegradability, creating favorable conditions for subsequent advanced treatment. Attached Figure Description

[0020] Figure 1 A simplified hydrolysis pathway of calcium hydroxide in TCTNB and its formation energy diagram;

[0021] Figure 2 Transition state and free energy diagram of the alkaline hydrolysis reaction of TCTNB calcium hydroxide;

[0022] Figure 3 This is a diagram of the first step of the hydroxyl substitution and dechlorination reaction in TCTNB.

[0023] Figure 4 This is a diagram of the first step of the hydroxyl group substitution and denitration reaction process in TCTNB;

[0024] Figure 5 Hershfield charge heatmap of the alkaline hydrolysis products of TCTNB calcium hydroxide;

[0025] Figure 6 This is a comparison chart of the acute toxicity of calcium hydroxide before and after alkaline hydrolysis. Detailed Implementation

[0026] To further understand the present invention, the technical solutions of the present invention will be described in detail below with reference to specific embodiments and accompanying drawings. However, it should be understood that these descriptions are only for further illustrating the features and advantages of the present invention, and not for limiting the scope of protection of the present invention.

[0027] Example 1

[0028] This embodiment provides a method for treating TCTNB-containing wastewater using calcium hydroxide hydrolysis. Using TCTNB as a typical representative of polychlorinated nitrobenzene compounds, 100 mg of TCTNB is accurately weighed using a 0.01% balance, dissolved in methanol or acetonitrile, and diluted to 100 mL to prepare a TCTNB stock solution with a mass concentration of 1 g / L. The stock solution is then diluted with deionized water to prepare a TCTNB working solution with a mass concentration of 100 mg / L. 100 mL of the TCTNB working solution is placed in a beaker, and 97% pure calcium hydroxide solid is added. The pH of the system is adjusted to 11, and the reaction temperature is controlled at 60 °C for hydrolysis until the solution turns yellow and the color no longer deepens, yielding the first treated solution. The first treatment solution was subjected to ultrasonic treatment at a frequency of 80 kHz for 5 min. Subsequently, a vacuum sand core filtration device was used in conjunction with an organic phase filter membrane with a pore size of 0.22 μm to remove the solid substances precipitated during the reaction, resulting in a calcium hydroxide hydrolysis treatment solution.

[0029] The concentration of TCTNB in ​​the first treatment solution was determined by liquid chromatography. The results showed that the concentration of TCTNB after treatment was less than 10 mg / L.

[0030] The above results show that, under the conditions of pH 11 and reaction temperature of 60 ℃, calcium hydroxide can effectively promote the hydrolysis and transformation of TCTNB, significantly reducing the concentration of TCTNB in ​​wastewater. This indicates that the method has a good preliminary detoxification effect on TCTNB-containing wastewater.

[0031] To further elucidate the hydrolysis mechanism of calcium hydroxide on TCTNB, density functional theory was used to conduct thermodynamic and kinetic analyses of the TCTNB hydrolysis process, and possible reaction sites and products were identified.

[0032] The thermodynamic feasibility of a reaction is evaluated by calculating the reaction formation energy ΔE. The calculation formula is as follows:

[0033] ΔE = E 产物 -E 反应物 (1),

[0034] Where ΔE represents the reaction formation energy, E 产物 E represents the total energy of the products. 反应物 This represents the total energy of the reactants. The more negative ΔE is, the more thermodynamically favorable the formation of the corresponding product.

[0035] Five possible substitution products were calculated. Among them, 1N(OH) represents the substitution of a NO2 group in the TCTNB molecule by an OH group, with a ΔE of -6.77 kcal / mol, indicating that this substitution process is thermodynamically feasible. Further analysis shows that OH... - It can gradually replace the Cl or NO2 groups in the TCTNB molecule and form a more stable product, thereby promoting Cl... - and NO2 - The continuous release of these substances. Although all of the above-mentioned substitution products are thermodynamically possible, the dominant reaction pathway still needs further analysis in conjunction with the transition state energy barrier.

[0036] Further calculations were performed on the transition state structures of possible reaction pathways. The results show that the attack mechanisms of each substitution reaction are basically similar, all exhibiting an OH transition state. - Attacking electron-deficient carbon sites from the side of the benzene ring causes the C-Cl or C-NO2 bond to gradually elongate until the leaving group detaches. Calculations show that the activation barrier for a single Cl substitution reaction is 70.69 kcal / mol, and the activation barrier for a single NO2 substitution reaction is 103.88 kcal / mol. Therefore, OH... - The energy barrier required to replace the Cl group is significantly lower than that required to replace the NO2 group, indicating that the Cl substitution pathway is kinetically more dominant.

[0037] Based on Hirshfeld charge analysis, the carbon atom corresponding to the Cl substitution site has higher electrophilicity, which is more favorable for OH. - Nucleophilic attack occurs. Based on the combined results of formation energy analysis, transition state energy barrier analysis, and electrophilicity analysis, TCTNB can undergo nucleophilic aromatic substitution hydrolysis under alkaline conditions, and the Cl group is preferentially attacked by OH groups before the NO2 group. - The substitution process generates phenolic products such as trinitrodichlorophenol, achieving the initial detoxification transformation of TCTNB.

[0038] In summary, this invention utilizes calcium hydroxide for alkaline hydrolysis treatment of process wastewater containing polychlorinated nitrobenzenes (PCBs). This effectively adjusts the wastewater's pH, hydrolyzes pollutants, reduces ecotoxicity, and significantly improves the wastewater's biodegradability. This method overcomes the drawbacks of traditional treatment processes, such as high cost, the generation of harmful byproducts, and secondary pollution. The dosage of calcium hydroxide and the reaction temperature can be flexibly adjusted according to actual engineering conditions, demonstrating good engineering adaptability and application potential. It is suitable for the pretreatment of wastewater containing PCBs.

Claims

1. A method for treating wastewater containing polychlorinated nitrobenzene using alkaline hydrolysis of calcium hydroxide, characterized in that, Includes the following steps: (1) Add calcium hydroxide to the wastewater containing polychlorinated nitrobenzene and carry out hydrolysis reaction under stirring and temperature control. Use hydroxide ions to nucleophilically replace the activated chlorine substitution sites and nitro substitution sites in the polychlorinated nitrobenzene molecule to generate phenolic substances such as trinitrodichlorophenol until the solution turns yellow and the color no longer increases, and the first treatment solution is obtained. (2) The first treatment liquid is subjected to ultrasonication, washing and filtration to remove the precipitated solids and obtain the treatment liquid.

2. The method according to claim 1, characterized in that, In step (1), the polychlorinated nitrobenzene is TCTNB.

3. The method according to claim 1, characterized in that, In step (1), the mass fraction of calcium hydroxide is 97%, and the amount of calcium hydroxide added is until the pH of the wastewater is 11.

4. The method according to claim 1, characterized in that, In step (1), the stirring method is magnetic stirring, and the stirring speed is 300 r / min.

5. The method according to claim 1, characterized in that, In step (1), the temperature control process is as follows: first, the initial temperature is controlled at 25 ℃~28 ℃, then the temperature is increased to 60 ℃ at a heating rate of 1~3 ℃ / min, and the constant temperature reaction is maintained at 60 ℃.

6. The method according to claim 1, characterized in that, In step (2), the vibration frequency of the ultrasonic treatment is 50~200kHz, and the vibration frequency gradient is 0~30 kHz / min.

7. The method according to claim 1, characterized in that, In step (2), the vibration frequency of the ultrasonic treatment is 80 kHz.

8. The method according to claim 1, characterized in that, In step (2), the filtration method is as follows: a 0.22 μm organic phase filter membrane is used, and vacuum sand core filtration device is used for filtration.

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