Method for preparing dimethylamine hydrochloride by using ODPA production wastewater, and application

Abstract

This invention relates to the field of wastewater treatment technology, and more particularly to a method and application for preparing dimethylamine hydrochloride from ODPA production wastewater. The method specifically includes the following steps: ODPA production wastewater is fed into a distillation column and distilled under vacuum with increased temperature; the gas then enters a condenser; under illumination, the non-condensable gas is washed with an alkaline solution containing a catalyst, and then the gas is absorbed using hydrochloric acid absorbent to obtain an aqueous solution of dimethylamine hydrochloride. This method can effectively separate N,N-dimethylformamide and dimethylamine from ODPA production wastewater. After washing the dimethylamine with an alkaline solution and absorbing it with hydrochloric acid, the resulting dimethylamine hydrochloride can be used as an organic byproduct in the production of aminoethyl sulfide, thus realizing the resource utilization of dimethylamine hydrochloride.

Description

Technical Field

[0001] This invention relates to the field of wastewater treatment technology, specifically to a method and application for preparing dimethylamine hydrochloride using ODPA production wastewater. Background Technology

[0002] Polyimide products have wide applications in aerospace, motor winding, automotive, machinery, light industrial electrical appliances, precision machinery, and electronics industries. The large-scale application of polyimide in organic light-emitting semiconductors (smartphones) has led to an explosive increase in the demand for polyimide (PI), and ODPA (3,3',4,4'-diphenyl ether dianhydride) is a crucial monomer used in its manufacture. Therefore, the demand for these basic monomers, such as ODPA, has also increased year by year. Some problems that were easily solved or even ignored in the previous small-batch production of ODPA have become prominent in large-scale continuous production, especially environmental issues.

[0003] In existing technologies, the main synthesis method of ODPA involves using N,N-dimethylformamide (DMF) as a solvent and N-methyl-4-nitrophthalimide as a raw material. A condensation reaction yields oxobis-(N-methylphthalimide), which is then purified by hydrolysis and acidification, recrystallization, and dehydration to obtain ODPA. In this reaction, after coupling, water is added to the solvent to precipitate compound II, oxobis-(N-methylphthalimide). Producing 1 ton of ODPA generates 8-10 tons of ODPA wastewater. This wastewater contains approximately 70% N,N-dimethylformamide, 30% water, and dimethylamine. Water promotes the decomposition of N,N-dimethylformamide to produce dimethylamine. The dimethylamine gas carries N,N-dimethylformamide into the dimethylamine absorption system. When dimethylamine is absorbed using hydrochloric acid solution in the system, N,N-dimethylformamide is also absorbed, resulting in excessive N,N-dimethylformamide in the dimethylamine hydrochloride. This leads to excessive organic matter in the byproduct dimethylamine hydrochloride, which can only be treated as hazardous waste and cannot be recycled, resulting in resource waste.

[0004] Therefore, there is an urgent need to develop a method to recover dimethylamine hydrochloride, an organic byproduct that meets the standard requirements, from ODPA production wastewater, so as to realize the resource utilization of organic byproducts. Summary of the Invention

[0005] To address the above-mentioned technical problems, this invention provides a method and application for preparing dimethylamine hydrochloride from ODPA production wastewater. This method can recover dimethylamine hydrochloride, an organic byproduct that meets standard requirements, from ODPA production wastewater, realizing the resource utilization of organic byproducts and avoiding resource waste.

[0006] To solve the above-mentioned technical problems, the present invention adopts the following technical solution:

[0007] In a first aspect, the present invention provides a method for preparing dimethylamine hydrochloride using ODPA production wastewater, specifically including the following operations: feeding ODPA production wastewater into a distillation column, heating and distilling it under vacuum, and the gas entering a condenser; under light irradiation, washing the non-condensable gas with an alkaline solution containing a catalyst, and then absorbing the gas with hydrochloric acid absorbent to obtain an aqueous solution of dimethylamine hydrochloride.

[0008] This method involves distilling ODPA production wastewater in a distillation column at a higher temperature, causing N,N-dimethylformamide and dimethylamine to volatilize along with the water, forming vapor. The vapor flows out from the top of the column and enters a condenser for cooling. N,N-dimethylformamide condenses, while dimethylamine in the vapor remains uncondensed, thus effectively separating N,N-dimethylformamide from dimethylamine in the vapor and obtaining a non-condensable gas with significantly reduced N,N-dimethylformamide levels. Under light irradiation, the non-condensable gas is scrubbed with an alkaline solution containing a catalyst, catalytically degrading the residual N,N-dimethylformamide in the gas into dimethylamine and formate. The formate is absorbed by the alkaline solution, while dimethylamine remains in the gas. The dimethylamine in the gas is then absorbed with hydrochloric acid absorbent to obtain an aqueous solution of dimethylamine hydrochloride. The dimethylamine hydrochloride in this aqueous solution can be used as an organic byproduct in the production of aminoethyl sulfide, realizing the resource utilization of dimethylamine hydrochloride.

[0009] This method solves the problem in existing technologies that dimethylamine hydrochloride generated during the recovery of ODPA production wastewater can only be treated as hazardous waste and cannot be recycled.

[0010] The gas scrubbing operation can be carried out in the treatment tower. First, the catalyst is dissolved in an alkaline solution, and then the alkaline solution containing the dissolved catalyst is rinsed from the top of the tower to scrub the gas, achieving the purpose of catalytic degradation of N,N-dimethylformyl in the gas. It should be noted that formate is absorbed by reacting with the alkali in the alkaline solution. When the pH of the alkaline solution is around 11, the solution reaches saturation for formate absorption. At this point, a fresh alkaline solution needs to be used for scrubbing to ensure absorption efficiency. After filtering and recovering the catalyst from the saturated alkaline solution, the solution can be used as a carbon source in the biological treatment tank, taking advantage of the good biodegradability of formate, for environmentally friendly biological treatment.

[0011] Preferably, the temperature of the vessel during the heating distillation is 105-110°C.

[0012] Preferably, the vacuum degree is -0.09 to -0.095 MPa, and the reflux ratio is 1:3-4.

[0013] Preferably, the refrigerant temperature in the condenser is 35-45°C.

[0014] In this embodiment of the invention, under a vacuum of -0.09 to -0.095 MPa, the boiling point of N,N-dimethylformamide is 72-90°C. With the aid of a refrigerant at 34-45°C, the N,N-dimethylformamide in the gas can be condensed, while dimethylamine will not condense and will continue to exist in the gas. This maximizes the separation of N,N-dimethylformamide and dimethylamine in the gas, preventing excessive levels of residual N,N-dimethylformamide in the dimethylamine gas. The refrigerant can be water or ethylene glycol, preferably water. Using water for condensation does not produce volatile organic compounds (VOCs), making it highly economical.

[0015] Preferably, the alkaline solution is a sodium hydroxide solution with a mass concentration of 15%-20% or a potassium hydroxide solution with a mass concentration of 15%-20%, and there is no limitation herein.

[0016] In this embodiment of the invention, when the mass concentration of the sodium hydroxide solution or potassium hydroxide solution is 15%-20%, the viscosity of the alkaline solution is low, resulting in a low viscosity of the alkaline mist, which is beneficial for the recycling of the alkaline solution. When the mass concentration of the alkaline solution is greater than 30%, the viscosity of the alkaline solution increases, resulting in a low viscosity of the alkaline mist, which is not beneficial for the recycling of the alkaline solution.

[0017] By washing the gas with an alkaline solution of the above concentration, the residual N,N-dimethylformamide in the gas can be converted into dimethylamine, thereby removing the residual N,N-dimethylformamide from the gas. This avoids the problem of dimethylamine gas carrying N,N-dimethylformamide into the dimethylamine absorption system, which would lead to excessive N,N-dimethylformamide levels in dimethylamine hydrochloride, a problem that can only be treated as hazardous waste.

[0018] Preferably, the catalyst is titanium trioxide, and the illumination is 210-230 nm, preferably 220 nm, as the catalytic degradation effect is best at 220 nm.

[0019] In this embodiment of the invention, the catalytic effect of titanium trioxide and the energy provided by nano-lighting can accelerate the rate at which alkaline solution promotes the decomposition of N,N-dimethylformamide into dimethylamine and formate.

[0020] Preferably, the mass ratio of the alkaline solution to the catalyst is 1:0.002-0.005. The amount of alkaline solution used is not specifically limited; it is only related to the amount of wastewater treated and has little effect on promoting the N,N-dimethylformyl reaction.

[0021] Preferably, the hydrochloric acid absorbent is a hydrochloric acid solution with a mass concentration of 20%-30%; when the pH of the hydrochloric acid absorbent is 3.5-4.5, a new hydrochloric acid absorbent is replaced.

[0022] In this embodiment of the invention, hydrochloric acid solution is used as the absorbent to absorb dimethylamine in the gas into an aqueous solution of dimethylamine hydrochloride. When the pH of the hydrochloric acid solution is 3.5-4.5, the hydrochloric acid solution reaches saturation in absorbing dimethylamine, and absorption stops. A new hydrochloric acid solution is then used as the absorbent.

[0023] Preferably, the above method for preparing dimethylamine hydrochloride further includes: distilling the aqueous solution of dimethylamine hydrochloride under reduced pressure, cooling, and centrifuging to obtain dimethylamine hydrochloride.

[0024] Preferably, the distillation is vacuum distillation; the vacuum degree of the vacuum distillation is -0.09 to -0.095 MPa, and the temperature is 65-85℃;

[0025] The temperature is then reduced to 25-35℃;

[0026] The centrifugation speed is 400-450 r / min, and the centrifugation time is 15-20 min. When the speed is lower or the centrifugation time is shorter, the obtained dimethylamine hydrochloride is more wet.

[0027] In this embodiment of the invention, the aqueous solution of dimethylamine hydrochloride is distilled to remove water, then cooled to precipitate crystals, and centrifuged to separate the mother liquor and dimethylamine hydrochloride. The mother liquor can be reused in the next batch of wastewater treatment processes, and the dimethylamine hydrochloride can be used as an organic byproduct to prepare aminoethyl sulfide, thus realizing the resource utilization of organic byproducts.

[0028] Secondly, the present invention also provides the application of the above-mentioned dimethylamine hydrochloride aqueous solution or dimethylamine hydrochloride in the preparation of aminoethyl thioether.

[0029] In this embodiment of the invention, dimethylamine hydrochloride aqueous solution or dimethylamine hydrochloride is used in the preparation of aminoethyl sulfide, thereby realizing the resource recycling of dimethylamine hydrochloride aqueous solution or dimethylamine hydrochloride. Detailed Implementation

[0030] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to specific embodiments. It should be understood that the specific embodiments described herein are merely illustrative of the invention and are not intended to limit the invention.

[0031] Example 1

[0032] 1500 kg of ODPA production wastewater containing crude N,N-dimethylformamide was collected. The concentration of N,N-dimethylformamide in the wastewater was determined to be 71.4%, the concentration of dimethylamine was 0.5%, and the remainder consisted of water and trace amounts of other impurities. This wastewater was then fed into a distillation column for heated distillation at 105°C. The vacuum was controlled at -0.092 MPa, and the reflux ratio was controlled at 1:3. The gas flowed out from the top of the column and entered a condenser using 35°C water as the coolant. N,N-dimethylformamide was recovered through condensation. The recovered N,N-dimethylformamide contained 41 ppm of dimethylamine and was ready for direct use.

[0033] During distillation, non-condensable gas is introduced into a deep treatment tower. A 220nm energy lamp is turned on inside the tower, and a 15% (w / w) sodium hydroxide solution containing 0.3% wt titanium trioxide is rinsed from the top of the tower for gas washing. The catalytic effect of titanium trioxide and the energy provided by the nano-light accelerate the degradation of residual N,N-dimethylformamide in the gas into dimethylamine and formate by the sodium hydroxide solution. Formate is absorbed by the sodium hydroxide solution, while dimethylamine remains in the gas. The washed gas is then treated with 35kg of a 20% (w / w) hydrochloric acid solution to absorb the dimethylamine (absorption is stopped when the pH of the hydrochloric acid solution reaches 4.2, and a new 20% (w / w) hydrochloric acid solution is used instead), yielding an aqueous solution of dimethylamine hydrochloride.

[0034] An aqueous solution of dimethylamine hydrochloride was passed into a vacuum distillation reactor for vacuum distillation. The water was evaporated under a vacuum of -0.090 MPa and a reactor temperature of 80°C. The solution was then cooled to 30°C for crystallization. After crystallization, the solution was centrifuged at high speed at 450 r / min for 20 min to obtain a dimethylamine hydrochloride mother liquor and 10.1 kg of dimethylamine hydrochloride.

[0035] Example 2

[0036] 1500 kg of ODPA production wastewater containing crude N,N-dimethylformamide was collected. The concentration of N,N-dimethylformamide in the wastewater was determined to be 70.19%, the concentration of dimethylamine was 0.51%, and the remainder consisted of water and trace amounts of other impurities. This wastewater was then fed into a distillation column for heated distillation at 108°C. The vacuum was controlled at -0.090 MPa, and the reflux ratio was controlled at 1:3.5. The gas exited from the top of the column and entered a condenser using 40°C water as the coolant. The recovered N,N-dimethylformamide contained 42 ppm of dimethylamine and was ready for direct use.

[0037] During distillation, non-condensable gas is introduced into a deep treatment tower. A 220 nm energy lamp is turned on inside the tower, and a 15% potassium hydroxide solution containing 0.5% wt titanium trioxide is rinsed from the top of the tower for gas washing. The catalytic effect of titanium trioxide and the energy provided by the nano-light accelerate the degradation of residual N,N-dimethylformamide in the gas into dimethylamine and formate by the potassium hydroxide solution. The formate is absorbed by the potassium hydroxide solution, while the dimethylamine remains in the gas. The washed gas is then treated with 28 kg of 25% hydrochloric acid absorbent to absorb the dimethylamine (absorption is stopped when the pH of the hydrochloric acid solution reaches 3.8, and a new 25% hydrochloric acid absorbent is used), yielding an aqueous solution of dimethylamine hydrochloride.

[0038] An aqueous solution of dimethylamine hydrochloride was passed into a vacuum distillation reactor for vacuum distillation. The water was evaporated under a vacuum of -0.095 MPa and a reactor temperature of 75°C. The solution was then cooled to 25°C for crystallization. After crystallization, the solution was centrifuged at high speed at 430 r / min for 20 min to obtain a dimethylamine hydrochloride mother liquor and 10.3 kg of dimethylamine hydrochloride.

[0039] Example 3

[0040] 1500 kg of ODPA production wastewater containing crude N,N-dimethylformamide was taken. The concentration of N,N-dimethylformamide in the wastewater was determined to be 70.19%, and the concentration of dimethylamine was 0.51%, with the remainder being water and trace amounts of other impurities. This wastewater was then fed into a distillation column for heated distillation at 110°C, with a vacuum controlled at -0.095 MPa and a reflux ratio of 1:4. The gas flowed out from the top of the column and entered a condenser using 45°C water as the coolant. The recovered N,N-dimethylformamide contained 40 ppm of dimethylamine and was ready for direct use.

[0041] During distillation, non-condensable gas is introduced into a deep treatment tower. A 220 nm energy lamp is turned on inside the tower, and a 15% (w / w) sodium hydroxide solution containing 0.3% wt titanium trioxide is rinsed from the top of the tower for gas washing. The catalytic effect of titanium trioxide and the energy provided by the nano-light accelerate the degradation of residual N,N-dimethylformyl in the gas into dimethylamine and formate by the sodium hydroxide solution. The formate is absorbed by the sodium hydroxide solution, while the dimethylamine remains in the gas. The washed gas is then treated with 28 kg of 30% (w / w) hydrochloric acid absorbent to absorb the dimethylamine (absorption is stopped when the pH of the hydrochloric acid solution reaches 4.5, and a new 30% (w / w) hydrochloric acid absorbent is used), yielding an aqueous solution of dimethylamine hydrochloride.

[0042] An aqueous solution of dimethylamine hydrochloride was passed into a vacuum distillation reactor for vacuum distillation. The water was evaporated under a vacuum of -0.092 MPa and a reactor temperature of 65°C. The solution was then cooled to 25°C for crystallization. After crystallization, the solution was centrifuged at high speed at 400 r / min for 20 min to obtain a dimethylamine hydrochloride mother liquor and 10.4 kg of dimethylamine hydrochloride.

[0043] Comparative Example 1

[0044] 1500 kg of ODPA production wastewater containing crude N,N-dimethylformamide was collected. The concentration of N,N-dimethylformamide in the wastewater was determined to be 71.4%, and the concentration of dimethylamine was 0.5%, with the remainder being water and trace amounts of other impurities. This wastewater was then fed into a distillation column for heated distillation at 110°C, with a vacuum controlled at -0.095 MPa and a reflux ratio of 1:3.5. The gas exited from the top of the column and entered a condenser using 7°C water as the coolant. N,N-dimethylformamide was recovered through condensation. However, the recovered N,N-dimethylformamide contained 0.12% dimethylamine, exceeding the standard and failing to meet the alkalinity requirements for industrial DMF, thus rendering it unsuitable for direct use.

[0045] During the distillation process, the non-condensable gas is introduced into the deep treatment tower, and 5 kg of 20% hydrochloric acid absorbent solution is used (when the pH of the hydrochloric acid solution is 4.0, absorption is stopped and replaced with a new 20% hydrochloric acid absorbent solution) to obtain dimethylamine hydrochloride aqueous solution.

[0046] An aqueous solution of dimethylamine hydrochloride was passed into a vacuum distillation reactor for vacuum distillation. The water was evaporated under a vacuum of -0.095 MPa and a reactor temperature of 75°C. The solution was then cooled to 25°C for crystallization. After crystallization, the solution was centrifuged at high speed at 430 r / min for 20 min to obtain a dimethylamine hydrochloride mother liquor and 10.1 kg of dimethylamine hydrochloride.

[0047] Comparative Example 2

[0048] 1500 kg of ODPA production wastewater containing crude N,N-dimethylformamide was collected. The concentration of N,N-dimethylformamide in the wastewater was determined to be 71.4%, the concentration of dimethylamine was 0.5%, and the remainder consisted of water and trace amounts of other impurities. This wastewater was then fed into a distillation column for heated distillation at 110°C. The vacuum was controlled at -0.095 MPa, and the reflux ratio was controlled at 1:3.5. The gas flowed out from the top of the column and entered a condenser using 35°C water as the coolant. N,N-dimethylformamide was recovered through condensation. The recovered N,N-dimethylformamide contained 43 ppm of dimethylamine and was ready for direct use.

[0049] During the distillation process, the non-condensable gas is introduced into the deep treatment tower, and 35 kg of 20% hydrochloric acid absorbent solution is used (when the pH of the hydrochloric acid solution is 4.2, absorption is stopped and replaced with a new 20% hydrochloric acid absorbent solution) to obtain dimethylamine hydrochloride aqueous solution.

[0050] An aqueous solution of dimethylamine hydrochloride was passed into a vacuum distillation reactor for vacuum distillation. The water was evaporated under a vacuum of -0.095 MPa and a reactor temperature of 75°C. The solution was then cooled to 25°C for crystallization. After crystallization, the solution was centrifuged at high speed at 430 r / min for 20 min to obtain a dimethylamine hydrochloride mother liquor and 10.2 kg of dimethylamine hydrochloride.

[0051] Comparative Example 3

[0052] 1500 kg of ODPA production wastewater containing crude N,N-dimethylformamide was collected. The concentration of N,N-dimethylformamide in the wastewater was determined to be 71.4%, the water concentration to be 28.1%, and the dimethylamine concentration to be 0.5%. This wastewater was then fed into a distillation column for heated distillation at 110°C. The vacuum was controlled at -0.092 MPa, and the reflux ratio was controlled at 1:3.5. The gas exited from the top of the column and entered a condenser using 35°C water as the coolant. N,N-dimethylformamide was recovered, with a dimethylamine content of 42.5 ppm, which is suitable for direct use.

[0053] During distillation, non-condensable gas is introduced into a deep treatment tower. Inside the tower, a 220nm energy lamp is turned on, and water containing 0.3% wt titanium trioxide is rinsed from the top of the tower to wash the gas. The catalytic effect of titanium trioxide and the energy provided by the nano-lighting accelerate the catalytic degradation of residual N,N-dimethylformamide in the gas into dimethylamine and formate. The formate is absorbed by the water, while the dimethylamine remains in the gas. The gas after washing is then treated with 35kg of 20% hydrochloric acid absorbent to absorb the dimethylamine. When the pH of the hydrochloric acid solution reaches 4.2, absorption is stopped, yielding an aqueous solution of dimethylamine hydrochloride.

[0054] An aqueous solution of dimethylamine hydrochloride was passed into a vacuum distillation reactor for vacuum distillation. The water was evaporated under a vacuum of -0.095 MPa and a reactor temperature of 75°C. The temperature was then lowered to 25°C. The reactor was then centrifuged at high speed at 430 r / min for 20 min to obtain a dimethylamine hydrochloride mother liquor and 10.2 kg of dimethylamine hydrochloride.

[0055] Verification Example 1

[0056] The quality standard for the content of dimethylamine in N,N-dimethylformamide is ≤0.01%.

[0057] The quality standards for dimethylamine hydrochloride of the enterprise are shown in Table 1.

[0058] Table 1. Quality Standards for Dimethylamine Hydrochloride from Enterprises

[0059] project index Dimethylamine hydrochloride content (%) Mass concentration ≥98.0 pH value 3.5-5.0 Moisture % mass concentration ≤2.0 DMF residual value ≤50ppm

[0060] The dimethylamine hydrochloride obtained in Examples 1-3 and Comparative Examples 1-3 was tested. The content of dimethylamine hydrochloride was determined by titration, moisture content by Karl Fischer method, acidity by pH meter, and DMF residue by gas chromatography-mass spectrometry. The test results are shown in Table 2.

[0061] Table 2 shows the detection results of dimethylamine hydrochloride in Examples 1-3 and Comparative Examples 1-3.

[0062]

[0063] As can be seen from Tables 1 and 2, the dimethylamine hydrochloride obtained in Examples 1-3 meets the company's dimethylamine hydrochloride quality standard, while the dimethylamine hydrochloride obtained in Comparative Examples 1-3 does not meet the company's dimethylamine hydrochloride quality standard, and the DMF residue is much greater than 50 ppm in the quality standard.

[0064] In Comparative Example 1, using 7°C water as the refrigerant, the dimethylamine content in the recovered N,N-dimethylformamide was 0.12% by mass, far exceeding the company's quality standard requirement of ≤0.01% by mass for dimethylamine content in N,N-dimethylformamide. This excessive dimethylamine content does not meet the alkalinity requirements for industrial DMF and is therefore unsuitable for direct use. This demonstrates that using 7°C water as the refrigerant cannot effectively separate N,N-dimethylformamide from dimethylamine in the gas. Dimethylamine will enter the recovered N,N-dimethylformamide, leading to excessive dimethylamine content.

[0065] Compared with Examples 1-3, Comparative Example 2 did not use alkaline gas washing, but directly used hydrochloric acid solution to absorb the gas. The resulting dimethylamine hydrochloride had a DMF residue concentration of 0.92%, which far exceeded the requirement of ≤50ppm for DMF residue in the company's dimethylamine hydrochloride quality standard.

[0066] Compared with Examples 1-3, Comparative Example 3 replaced the alkaline solution with water, and the resulting dimethylamine hydrochloride had a DMF residue concentration of 0.12% by mass, which far exceeded the requirement of ≤50ppm for DMF residue in the company's dimethylamine hydrochloride quality standard.

[0067] As can be seen, the present invention, using water at 35-45℃ as a coolant, can effectively separate N,N-dimethylformamide and dimethylamine from ODPA production wastewater. The dimethylamine content in the obtained N,N-dimethylformamide meets the standard requirements and the alkalinity requirements for industrial DMF, and can be used directly. The alkaline solution helps to convert residual N,N-dimethylformamide in the gas to dimethylamine to the maximum extent. The dimethylamine hydrochloride obtained by absorbing dimethylamine with hydrochloric acid has high purity, with residual DMF ≤50ppm, meeting the enterprise's dimethylamine hydrochloride quality standard requirements.

[0068] In summary, the method provided by this invention can effectively separate N,N-dimethylformamide and dimethylamine from ODPA production wastewater, and the obtained N,N-dimethylformamide and dimethylamine products both meet quality standards. This method separates N,N-dimethylformamide and dimethylamine hydrochloride from the gas through heated distillation and cooling with a condensing gas refrigerant. The N,N-dimethylformamide recovered by condensation can be used directly. Further gas washing with an alkaline solution and absorption with hydrochloric acid yields dimethylamine hydrochloride, which, as an organic byproduct, can be used in the preparation of aminoethyl sulfide, thus realizing the resource utilization of dimethylamine hydrochloride and N,N-dimethylformamide. This method also has the advantages of low energy consumption, low processing cost, and being environmentally friendly and safe.

[0069] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions or improvements made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for preparing dimethylamine hydrochloride using ODPA production wastewater, characterized in that, Specifically, the operation includes the following steps: ODPA production wastewater is fed into a distillation column and heated under vacuum for distillation, causing N,N-dimethylformamide and dimethylamine to volatilize together with the water, forming vapor. The gas flows out from the top of the column and enters a condenser for cooling. N,N-dimethylformamide condenses while dimethylamine in the gas does not condense, thus effectively separating N,N-dimethylformamide and dimethylamine in the gas and obtaining non-condensable gas with a significantly reduced N,N-dimethylformamide content. Under light irradiation, the non-condensable gas is washed with an alkaline solution containing a catalyst to catalytically degrade the N,N-dimethylformamide remaining in the gas into dimethylamine and formate. The formate is absorbed by the alkaline solution, while the dimethylamine remains in the gas. Then, the dimethylamine in the gas is absorbed by hydrochloric acid absorbent to obtain an aqueous solution of dimethylamine hydrochloride. The catalyst is titanium trioxide, and the illumination is 210-230nm light.

2. The method for preparing dimethylamine hydrochloride using ODPA production wastewater according to claim 1, characterized in that, The temperature of the vessel during the heating distillation is 105-110°C.

3. The method for preparing dimethylamine hydrochloride using ODPA production wastewater according to claim 1, characterized in that, The vacuum degree is -0.09 to -0.095 MPa, and the reflux ratio is 1:3-4.

4. The method for preparing dimethylamine hydrochloride using ODPA production wastewater according to claim 3, characterized in that, The refrigerant temperature in the condenser is 35-45°C.

5. The method for preparing dimethylamine hydrochloride using ODPA production wastewater according to claim 1, characterized in that, The alkaline solution is a sodium hydroxide solution with a mass concentration of 15%-20% or a potassium hydroxide solution with a mass concentration of 15%-20%.

6. The method for preparing dimethylamine hydrochloride using ODPA production wastewater according to claim 1, characterized in that, The mass ratio of the alkaline solution to the catalyst is 1:0.002-0.

005.

7. The method for preparing dimethylamine hydrochloride using ODPA production wastewater according to claim 1, characterized in that, The hydrochloric acid absorbent is a hydrochloric acid solution with a mass concentration of 20%-30%; when the pH of the hydrochloric acid absorbent is 3.5-4.5, it should be replaced with a new hydrochloric acid absorbent.

8. The method for preparing dimethylamine hydrochloride using ODPA production wastewater according to claim 1, characterized in that, Also includes: The dimethylamine hydrochloride aqueous solution is distilled, cooled, and centrifuged to obtain dimethylamine hydrochloride.

9. The method for preparing dimethylamine hydrochloride using ODPA production wastewater according to claim 8, characterized in that, The distillation is vacuum distillation; the vacuum degree of the vacuum distillation is -0.09 to -0.095 MPa, and the temperature is 65-85°C; and / or The temperature is reduced to 25-35°C; and / or The centrifugation speed is 400-450 r / min, and the centrifugation time is 15-20 min.

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