Alkali precipitation desalting method suitable for amine steaming wastewater

Abstract

The alkali precipitation desalting method comprises the following steps: S1, taking the distilled amine wastewater, slowly adding a certain amount of caustic soda flakes into the distilled amine wastewater, stirring and dissolving in a water bath at 50 DEG C, then cooling to 25 DEG C, and standing for 30 minutes; s2, the solution obtained after standing is further subjected to centrifugal separation and precipitation, upper-layer alkali liquor and precipitates are obtained, and the upper-layer alkali liquor can be circularly used for neutralization reaction liquid to serve as an alkaline raw material for producing tetramethylethylenediamine; and S3, washing the precipitate with deionized water, pouring the washed precipitate into a Buchner funnel, carrying out suction filtration, and carrying out vacuum drying treatment on a filter cake to obtain a pure sodium salt product. Compared with a traditional desalting method, the alkali precipitation desalting method for the amine steaming wastewater has the advantages that the cost is saved, steam distillation is avoided, the upper-layer alkali liquor can still be used as alkali to neutralize reaction liquid before amine steaming, the replacement desalting efficiency is high, the recycled salt can be recycled, the production cost is reduced, environmental protection and economical efficiency are both considered, and the alkali precipitation desalting method is suitable for industrial popularization and application.

Description

Technical Field

[0001] This invention relates to the field of applied chemistry, and in particular to an alkaline precipitation desalination method suitable for amine-containing wastewater. Background Technology

[0002] Tetramethylethylenediamine (TMD) is an important chemical raw material widely used in the synthesis of pharmaceuticals, agrochemicals, and other industrial products. Its production process often generates wastewater containing high levels of salt, commonly known as "amine distillation wastewater." This wastewater is produced after the reaction solution is distilled with alkali, and its salt content can reach approximately 25% by mass. This characteristic makes its treatment quite challenging. Due to the excessively high salt concentration, traditional biological treatment methods are difficult to apply directly to amine distillation wastewater. Therefore, pretreatment with desalination measures is necessary to ensure the wastewater meets the standards for subsequent treatment or discharge.

[0003] Currently, there are two main desalination technologies commonly used in industry: vacuum dehydration and multi-effect evaporation. However, both methods have revealed significant drawbacks during application, preventing them from achieving ideal treatment results and incurring high operating costs, thus limiting their widespread use. Vacuum dehydration is a technology that utilizes reduced system pressure to lower the boiling point of water and promote evaporation. While this method seems simple in operation, it has several significant drawbacks: First, vacuum dehydration requires very precise control of parameters such as heating temperature and system pressure. Improper control can lead to low or unstable evaporation efficiency, or even incomplete evaporation or failure to remove salt. Second, impurities in the water (such as suspended solids and trace metals) can interfere with the crystallization process, reducing desalination efficiency. These impurities not only affect the stability of the desalination process but can also accumulate in the equipment, causing scaling or blockage, further reducing equipment lifespan and system operating efficiency. In addition, the desalination effect of vacuum dehydration is often not ideal and it is difficult to meet the standards for discharge or reuse. This means that the wastewater still needs to be sent to other treatment facilities after treatment, which increases the overall cost.

[0004] Multi-effect evaporation desalination is a technology that desalinates wastewater through a multi-stage evaporation process. This method uses multiple evaporation units connected in series, utilizing the steam generated in the first stage of evaporation to provide a heat source for the second stage, thereby reducing energy consumption and improving evaporation efficiency. While this method is theoretically energy-efficient, several problems exist in practical applications. Due to the series operation of multiple evaporation units, the temperature difference loss in the system increases progressively, leading to energy waste. Furthermore, as the number of effects increases, energy loss multiplies, further increasing operating costs. Secondly, the complex structure of multi-effect evaporation systems results in high equipment investment costs. In addition, although multi-effect evaporation can reduce steam consumption to some extent, the evaporated wastewater still needs to be sent to a waste gas treatment plant for secondary treatment. This not only increases wastewater treatment costs but also exacerbates the burden of waste gas and wastewater emissions. Therefore, the overall comprehensive cost remains high, and the method has a significant environmental burden, making it difficult to meet increasingly stringent environmental protection requirements. In summary, both vacuum dehydration and desalination and multi-effect evaporation desalination have their drawbacks in practical applications, particularly in the treatment of high-salinity wastewater, where they face problems such as high costs and unstable results. Especially in industrial-scale applications, the high investment and complex operating procedures required by these methods significantly reduce their economic and technical feasibility.

[0005] Therefore, there is an urgent need to provide an alkaline precipitation desalination method suitable for amine distillation wastewater, which can avoid steam distillation, save costs, and be a highly efficient and economical desalination method. At the same time, the alkaline solution can be recycled and the recovered salt can also be reused. Summary of the Invention

[0006] The purpose of this invention is to provide an alkaline precipitation desalination method suitable for amine distillation wastewater, in order to solve the problems mentioned in the background art, such as the high cost and complex operation of steam distillation, thereby saving costs and recycling the alkaline solution.

[0007] To achieve the above objectives, the present invention provides the following technical solution: An alkaline precipitation desalination method suitable for amine-containing wastewater includes the following steps: S1. Take 200~250g of amine-distilled wastewater into a 500mL beaker, slowly add caustic soda flakes, stir and dissolve in a 50℃ water bath, then cool to 25℃ and let stand for 30min.

[0008] S2. Centrifuge the solution after it has been allowed to stand to separate the precipitate, and obtain the upper alkaline solution and the precipitate. The upper alkaline solution can be recycled for use as a neutralization reaction solution and as an alkaline raw material for the production of tetramethylethylenediamine.

[0009] S3. After washing the precipitate with deionized water, pour it into a Buchner funnel for filtration. The filter cake is then vacuum dried to obtain a pure sodium salt product.

[0010] As a preferred embodiment of the present invention, the amount of caustic soda added is 50-75g.

[0011] As a preferred embodiment of the present invention, the stirring time is 30-40 minutes.

[0012] As a preferred embodiment of the present invention, the centrifugation speed is 3000~3500 rpm and the time is 10~15 minutes.

[0013] As a preferred embodiment of the present invention, the precipitate is washed with deionized water 2-3 times, with each wash using 50ml of water.

[0014] As a preferred embodiment of the present invention, the filtration time is 30-40 minutes.

[0015] As a preferred embodiment of the present invention, the drying temperature is 80~100℃ and the drying time is 3~4 hours.

[0016] Compared with the prior art, the beneficial effects of the present invention are: 1. This invention utilizes caustic soda flakes to treat salts in amine distillation wastewater. Through low-temperature dissolution and efficient separation, it achieves excellent desalination, effectively separating salts from the wastewater. This avoids the energy consumption of high-temperature steam distillation and eliminates the need for complex operating procedures. This process is not only highly efficient and energy-saving, but also has relatively low equipment costs. Furthermore, it is simple to operate, energy-saving, and environmentally friendly, while maintaining high salt separation efficiency. Low-temperature treatment reduces energy loss and environmental burden, while improving the purity of the separated salts. This process reduces equipment investment and operating costs, providing a new and more sustainable solution for amine distillation wastewater treatment. In addition, this process meets modern environmental protection requirements. Through efficient salt separation, the wastewater treatment process not only reduces energy consumption but also reduces emissions of waste gas and wastewater. This method has strong industrial application potential, especially in the production of tetramethylethylenediamine, providing enterprises with a more economical and environmentally friendly wastewater treatment method and promoting the sustainable development of this industry.

[0017] 2. The alkaline filtrate produced in this invention contains unreacted alkali, which can be directly reused in the neutralization reaction, reducing the amount of fresh caustic soda flakes used. This significantly reduces caustic soda consumption and raw material costs, resulting in substantial economic benefits. Furthermore, the recycled alkaline water, after centrifugal separation, effectively removes impurities, ensuring a low impurity concentration during reuse. This treatment step greatly reduces pH fluctuations, facilitating more precise control of reaction conditions and thus improving the yield and purity of tetramethylethylenediamine. Additionally, no further treatment is required for reuse, simplifying the process and avoiding production interruptions due to alkali replacement. Traditional alkali replacement often requires shutdown for cleaning and refilling with new alkali, impacting production progress and increasing labor and maintenance costs. The alkali reuse technology of this invention enables continuous operation, maximizing overall production efficiency. The recycling of alkali significantly reduces wastewater discharge, alleviating the burden of wastewater treatment. By reducing wastewater generation, it not only saves on wastewater treatment costs but also reduces environmental pollution. This closed-loop system aligns with the principles of green chemistry, helping companies move towards carbon neutrality. While achieving resource conservation and waste reduction, it promotes the formation of sustainable production models, demonstrating the dual advantages of economic and environmental benefits.

[0018] 3. This invention achieves efficient recovery of sodium salt through caustic soda replacement, avoiding the discharge of waste salt. Traditional methods such as multi-effect evaporation require outsourcing the treatment of waste salt, generating more than 200 tons of hazardous waste annually. The caustic soda method achieves zero discharge of waste salt and avoids steam consumption, which can significantly reduce carbon dioxide emissions. Trace organic matter in the recovered salt is removed by water washing, ensuring that the product quality is not affected during reuse. This invention achieves desalination and salt utilization at low cost and low energy consumption. Attached Figure Description

[0019] Figure 1 This is a flowchart illustrating the alkaline precipitation desalination process for amine-containing wastewater, applicable to the present invention. Detailed Implementation

[0020] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0021] Amine vaporization wastewater is characterized by high salinity. This wastewater cannot be directly treated in the biological treatment tank and needs to be desalinated first. This is because excessive salinity will directly pollute the water body, and desalination is necessary to reduce it to the discharge standard to meet environmental protection requirements. Secondly, the recovered sodium salt can be recycled, effectively reducing production costs. At the same time, the high-salt environment can easily corrode the treatment equipment and inhibit the activity of microorganisms in the biological treatment system, ensuring stable operation of the process. These factors together constitute the core driving force of desalination treatment, taking into account both environmental governance and efficient resource utilization.

[0022] Sodium hydroxide flakes, also known as caustic soda, are white, flaky solids. In wastewater treatment, their solid form facilitates accurate measurement, avoiding dosing errors caused by concentration fluctuations in liquid caustic soda. Furthermore, the storage and transportation costs of sodium hydroxide flakes are low. Using sodium hydroxide flakes to treat salts in amine distillation wastewater results in highly efficient salt separation, high product purity, and eliminates the need for high-temperature steam distillation; low-temperature dissolution is sufficient. This method is highly efficient and energy-saving, requires fewer operating steps, and has low equipment costs, balancing environmental protection and economics, making it suitable for industrial-scale application.

[0023] Using caustic soda flakes to treat salts in amine distillation wastewater achieves excellent desalination through low-temperature dissolution and efficient separation, effectively separating salts from the wastewater while avoiding the energy consumption of high-temperature steam distillation and eliminating the need for complex operating procedures. This makes the process not only highly efficient and energy-saving, but also relatively low in equipment cost, simple to operate, energy-saving and environmentally friendly, and with high salt separation efficiency. Low-temperature treatment reduces energy loss and environmental burden while improving the purity of the separated salts. This process reduces equipment investment and operating costs, providing a new and more sustainable solution for amine distillation wastewater treatment. Furthermore, this process meets modern environmental protection requirements. Through efficient salt separation, the wastewater treatment process not only reduces energy consumption but also reduces emissions of waste gas and wastewater, making this method highly promising for industrial applications, especially in the production of tetramethylethylenediamine, where it can provide enterprises with a more economical and environmentally friendly wastewater treatment method, promoting the sustainable development of this industry.

[0024] The alkali solution produced when using caustic soda flakes to treat amine-removing wastewater contains unreacted alkali, which can be directly recycled for neutralization reactions, reducing the amount of fresh caustic soda flakes used. This method not only significantly reduces caustic soda consumption but also lowers raw material costs, resulting in substantial economic benefits. Furthermore, the recycled alkali water, after centrifugal separation, effectively removes impurities, ensuring that the alkali solution maintains a low impurity concentration during reuse.

[0025] This processing step significantly reduces pH fluctuations, allowing for more precise control of reaction conditions and thus improving the yield and purity of tetramethylethylenediamine. Furthermore, the alkali solution requires no additional treatment upon reuse, simplifying the process and avoiding production interruptions caused by alkali solution replacement. Traditional alkali solution replacement often requires shutdown for cleaning and refilling with new alkali solution, which not only affects production schedules but also increases labor and maintenance costs. The alkali solution reuse technology of this invention enables continuous operation, maximizing overall production efficiency. The recycling of alkali solution significantly reduces wastewater discharge, alleviating the burden of wastewater treatment. By reducing wastewater generation, it not only saves on wastewater treatment costs but also reduces environmental pollution. This closed-loop recycling system aligns with the principles of green chemistry, helping enterprises move towards carbon neutrality. While achieving resource conservation and waste reduction, it promotes the formation of sustainable production models, demonstrating the dual advantages of economic and environmental benefits.

[0026] Sodium salt replacement achieves efficient recovery of sodium salt and avoids the discharge of waste salt. Traditional methods such as multi-effect evaporation require outsourcing the treatment of waste salt, generating more than 200 tons of hazardous waste salt annually. The sodium salt replacement method achieves zero discharge of waste salt and avoids steam consumption, which can significantly reduce carbon dioxide emissions. Trace organic matter in the recovered salt is removed by water washing, ensuring that the product quality is not affected during reuse. This method achieves desalination and salt utilization at low cost and low energy consumption.

[0027] like Figure 1 As shown, an alkaline precipitation desalination method suitable for amine-distilled wastewater includes the following steps: S1. Take 200-250g of amine-distilled wastewater into a 500mL beaker, slowly add caustic soda flakes, stir and dissolve in a 50℃ water bath, then cool to 25℃ and let stand for 30min. S2. Further centrifuge the solution after standing to separate the precipitate, obtaining the upper alkaline solution and precipitate. The upper alkaline solution can be recycled for neutralization reaction and used as an alkaline raw material for the production of tetramethylethylenediamine. S3. Wash the precipitate with deionized water and pour it into a Buchner funnel for suction filtration. The filter cake is vacuum dried to obtain a pure sodium salt product.

[0028] All raw materials used in this invention are commercially available.

[0029] Example 1

[0030] S1. Take 200g of amine-distilled wastewater with an alkali concentration of 10.5% and a salt concentration of 23%, pour it into a 500mL beaker, slowly add 50g of caustic soda flakes, stir in a 50℃ water bath for 30 minutes to dissolve, then cool to 25℃ and let stand for 30 minutes.

[0031] S2. The solution after standing is further centrifuged to separate the precipitate, and the upper alkaline solution and precipitate are obtained. The centrifugation speed is 3000 rpm and the time is 10 minutes. The upper alkaline solution is 198g and the alkalinity is 35.6%.

[0032] S3. Wash the precipitate twice with deionized water, using 50ml each time. After washing, pour the precipitate into a Buchner funnel for filtration for 30 minutes, yielding a total of 52g of wet salt. Vacuum dry the filter cake at 80℃ for 3 hours to obtain a pure sodium salt product weighing 48.8g with a moisture content of 6%.

[0033] Example 2

[0034] S1. Take 250g of amine-distilled wastewater with an alkali concentration of 11% and a salt concentration of 24%, pour it into a 500mL beaker, slowly add 75g of caustic soda flakes, stir in a 50℃ water bath for 30 minutes to dissolve, then cool to 25℃ and let stand for 30 minutes.

[0035] S2. The solution after standing is further centrifuged to separate the precipitate, and the upper alkaline solution and precipitate are obtained. The centrifugation speed is 3500 rpm and the time is 15 minutes. The upper alkaline solution is 263g and the alkalinity is 38.2%.

[0036] S3. Wash the precipitate three times with 50ml of deionized water each time. After washing, pour the precipitate into a Buchner funnel for filtration for 40 minutes, yielding a total of 62g of wet salt. Vacuum dry the filter cake at 100℃ for 4 hours to obtain 57.6g of pure sodium salt product with a moisture content of 7%.

[0037] Comparative Example 1: S1. Take 200g of amine-distilled wastewater with an alkali concentration of 10.5% and a salt concentration of 23%, pour it into a 500mL beaker, slowly add 50g of sodium nitrate, stir in a 50℃ water bath for 30 minutes to dissolve, then cool to 25℃ and let stand for 30 minutes.

[0038] S2. The solution after standing is further centrifuged to separate the precipitate, and the upper alkaline solution and precipitate are obtained. The centrifugation speed is 3000 rpm and the time is 10 minutes. The upper alkaline solution is 199g and the alkalinity is 10.5%.

[0039] S3. Wash the precipitate twice with deionized water, using 50ml each time. After washing, pour the precipitate into a Buchner funnel for filtration for 30 minutes, yielding a total of 27g of wet salt. Vacuum dry the filter cake at 80℃ for 3 hours to obtain 24.5g of pure sodium salt product with a moisture content of 9%.

[0040] Experimental results showed that salting out was observed in Examples 1, 2, and Comparative Example 1, but the sodium salt replacement efficiency differed significantly. Examples 1 and 2, by adding caustic soda flakes, yielded significantly higher salt content than Comparative Example 1 using sodium nitrate. Furthermore, the recovered sodium salt, after passing purity testing, could be recycled, effectively reducing production costs. Further analysis revealed that after adjusting the aqueous alkaline solution in Examples 1 and 2 with caustic soda flakes, the alkali content increased to 25.1% and 27.2%, respectively, significantly increasing the alkali concentration in the waste liquid. This allowed for direct recycling of the neutralization reaction solution as an alkaline raw material for the production of tetramethylethylenediamine, achieving a closed-loop resource system of "salting out - alkali recovery." In contrast, although the sodium nitrate system could also replace salt, the amount of salt precipitated per unit volume was lower, and the alkali content in the filtrate after replacement did not change significantly, failing to meet the requirements of the neutralization reaction. Additional fresh alkali solution was still needed, and the resulting nitrate-containing waste liquid required specialized treatment, resulting in higher overall costs. Therefore, through the synergistic effect of "alkali enhancement-salt enrichment", the caustic soda flake system demonstrates superior performance in terms of improving resource utilization, reducing waste generation and lowering production costs, providing a more efficient and environmentally friendly technical solution for industrial production.

[0041] The alkaline precipitation desalination method of the present invention for amine distillation wastewater is more cost-effective than traditional desalination methods, avoids the use of steam distillation, and the upper alkaline water can still be used for neutralization of the reaction solution. It has high displacement desalination efficiency, the recovered salt can be recycled, reduces production costs, and takes into account both environmental protection and economy, making it suitable for industrial promotion and use.

[0042] The above are merely specific embodiments of the present invention, but the technical features of the present invention are not limited thereto. Any simple changes, equivalent substitutions, or modifications made based on the present invention to solve essentially the same technical problems and achieve essentially the same technical effects are all covered within the protection scope of the present invention.

Claims

1. A method for alkaline precipitation desalination of amine-containing wastewater, characterized in that, Includes the following steps: S1. Take 200~250g of amine-distilled wastewater into a 500mL beaker, slowly add caustic soda flakes, stir and dissolve in a 50℃ water bath, then cool to 25℃ and let stand for 30min. S2. Centrifuge the solution after it has been allowed to stand to separate the precipitate, and obtain the upper alkaline solution and the precipitate. The upper alkaline solution can be recycled for use as a neutralization reaction solution and as an alkaline raw material for the production of tetramethylethylenediamine. S3. After washing the precipitate with deionized water, pour it into a Buchner funnel for filtration. The filter cake is then vacuum dried to obtain a pure sodium salt product.

2. The alkaline precipitation desalination method for amine-containing wastewater according to claim 1, characterized in that, The amount of caustic soda added is 50-75g.

3. The alkaline precipitation desalination method for amine-containing wastewater according to claim 1, characterized in that, The stirring time is 30-40 minutes.

4. The alkaline precipitation desalination method for amine-containing wastewater according to claim 1, characterized in that, The centrifugation speed is 3000~3500 rpm, and the time is 10~15 minutes.

5. The alkaline precipitation desalination method for amine-containing wastewater according to claim 1, characterized in that, The precipitate was washed with deionized water 2-3 times, with 50ml of water used each time.

6. The alkaline precipitation desalination method for amine-containing wastewater according to claim 1, characterized in that, The filtration time is 30-40 minutes.

7. The alkaline precipitation desalination method for amine-containing wastewater according to claim 1, characterized in that, The drying temperature is 80~100℃, and the time is 3~4 hours.

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