Graded purification and directional recovery process for mixed extraction agent in industrial wastewater

Abstract

The invention discloses a graded purification and directional recovery process for a mixed extraction agent in industrial wastewater, which comprises the following steps: introducing the industrial wastewater into an adsorption device filled with an amino-phosphonic acid modified graphene adsorption material, and regulating and controlling the molar ratio of bifunctional groups to enhance the adsorption of specific impurities; a composite desorption agent containing an aminophosphonic acid type chelating agent is introduced into the adsorption saturation device, and sec-octyl alcohol, N235 and sulfonated kerosene are directionally desorbed in a non-overlapping segmented desorption mode; after the mixed desorption liquid is rectified to separate the composite desorption agent, extracting agent components are purified through gradient vacuum distillation; the amine salt-containing waste liquid is recycled to the adsorption device, and amine salt decomposition and adsorption material functional group in-situ regeneration are completed under the acidic condition. Through the steps, the problems of poor adsorption selectivity, much desorption interference, fast material activity attenuation and the like in the existing process are solved, efficient directional recovery of the mixed extraction agent is realized, and the cycling stability of the adsorption material is remarkably improved.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of industrial wastewater treatment, in particular to a fractional purification and directional recovery process of mixed extractants in industrial wastewater. BACKGROUND

[0002] In the field of industrial wastewater treatment, extraction method is widely used due to its high efficiency in separating non-degradable pollutants. The core of the extraction method is to realize separation by selective combination of mixed extractants such as 2-octanol, N235 and sulfonated kerosene with pollutants. However, part of the mixed extractants will be lost with the wastewater during the extraction process, which not only increases the treatment cost, but also causes secondary pollution of water body due to the chemical stability of the components of the mixed extractants. Therefore, efficient recovery of mixed extractants is crucial to the economy and environmental protection of industrial wastewater treatment.

[0003] In the existing recovery process of mixed extractants, adsorption materials are mostly dependent on traditional carriers such as activated carbon and conventional resins. These materials lack specific functional groups and have poor adsorption selectivity for each component of the mixed extractants, which easily adsorbs suspended impurities and ionic pollutants in the wastewater at the same time, resulting in mixed components in the subsequent desorption liquid and significantly increasing the difficulty of separation. At the same time, single temperature or single desorption agent system is mostly used in the desorption process, which cannot realize directional desorption according to the difference in the interaction between different components of the extractants and the adsorption materials, causing incomplete desorption or co-desorption of components, further reducing the recovery purity. In the separation link, the existing technology often uses single rectification or simple distillation method, which is difficult to solve the separation problem of 2-octanol and N235, sulfonated kerosene with close boiling points in the mixed extractants, and is easy to form azeotropic system or overlapping distillation, resulting in insufficient purity of the target components. In addition, the amine salt-containing waste liquid generated in the desorption process is mostly directly discharged, which not only wastes resources such as diethanolamine, but also causes imbalance of water body acid and alkali; the surface functional groups of the adsorption material are easy to deprotonate or lose hydroxyl groups after use, and the activity decays quickly, making it difficult to realize stable recycling use.

[0004] Therefore, it is necessary to provide a fractional purification and directional recovery process of mixed extractants in industrial wastewater to solve the above technical problems. SUMMARY

[0005] The present application relates to the technical field of industrial wastewater treatment, in particular to a fractional purification and directional recovery process of mixed extractants in industrial wastewater.

[0006] To achieve the above-mentioned purpose, the present application provides the following technical scheme: a fractional purification and directional recovery process of mixed extractants in industrial wastewater, comprising the following steps: 1) pass the industrial wastewater into an adsorption device, the adsorption device is filled with graphene adsorption material, which introduces amine group and phosphonic acid group by covalent grafting method, to obtain amine group-phosphonic acid group modified graphene adsorption material, the molar ratio of amine group to phosphonic acid group is 0.8:1-1.2:1; 2) pass the adsorption saturated adsorption device in step 1) into a composite desorption agent, the composite desorption agent is made by mixing ethanol and diethanolamine at a volume ratio of 85-95:5-15, and the pH of the composite desorption agent is 8.0-9.0; Using a segmented desorption mode, the secondary octanol on the graphene adsorption material is desorbed at 58-61℃, and the N235 on the graphene adsorption material is desorbed at 64-66℃, and the sulfonated kerosene is desorbed; During the desorption process, the diethanolamine in the composite desorption agent reacts with the acidic substances in the industrial wastewater and the residual acidic substances on the surface of the adsorption material to form amine salt, and a mixed desorption liquid containing the composite desorption agent, secondary octanol, N235, sulfonated kerosene and amine salt is collected; 3) pass the mixed desorption liquid obtained in step 2) into a rectifying column, control the top temperature of the column to be 73-80℃, and the bottom temperature to be 155-175℃, the composite desorption agent is separated from the top of the column, the secondary octanol, N235 and sulfonated kerosene form a mixed extractant and remain in the lower part of the column and are separated, and the amine salt remains in the bottom of the rectifying column to form an amine salt-containing waste liquid; Pass the mixed extractant into a gradient vacuum distillation device, and separate secondary octanol, N235 and sulfonated kerosene by gradient vacuum distillation; 4) pass the amine salt-containing waste liquid at the bottom of the rectifying column in step 3) into the adsorption device in step 1), and adjust the pH of the system to 2.0-3.0.

[0007] The hierarchical purification and directional recovery process of the mixed extractant in the industrial wastewater provided by the application introduces amine group and phosphonic acid group on the surface of graphene substrate by covalent grafting method, forming a double functional group structure of fixed adsorption site and pH response site. In other words, the amine group acts as a fixed adsorption site, the loading amount is controlled by reaction time, and the extractant components are selectively combined by means of hydrogen bonding and hydrophobic interaction, and the loading amount density is precisely optimized to avoid site congestion or insufficient adsorption capacity; the phosphonic acid group acts as a pH response site, the loading amount is controlled by reaction temperature, and the core characteristic is the pH response transformation ability of protonation and deprotonation, which provides structural support for the switching of adsorption assisted catalytic function; at the same time, the molar ratio of the double functional groups is strictly controlled to be 0.8:1-1.2:1, which is the core parameter of balancing adsorption selectivity and function switching efficiency.

[0008] As preferred, in step 1), the step of introducing amine group and phosphonic acid group to graphene adsorption material by covalent grafting method includes: 1a) Graphene substrate was dispersed in N,N-dimethylformamide solvent and sonicated for 1-3 h. An amino precursor and triethylamine catalyst were added, with a mass ratio of amino precursor to graphene substrate of 1:8-1:12. The mixture was stirred at 60-80 °C for 4-6 h to obtain amino-modified graphene. The loading of amino functional groups in the amino precursor was controlled by the reaction time: the loading was 0.3-0.4 mmol / g after 4 h of reaction and 0.5-0.6 mmol / g after 6 h of reaction. 1b) Add a phosphonic acid precursor to an amino-modified graphene dispersion, wherein the mass ratio of the phosphonic acid precursor to the amino-modified graphene is 1:5-1:7. Heat to 80-100℃ and stir for 6-8 hours to generate phosphonic acid groups via ester hydrolysis. The phosphonic acid loading is controlled by the reaction temperature: 0.4-0.5 mmol / g at 80℃ and 0.6-0.7 mmol / g at 100℃. 1c) After the reaction is complete, the material is washed with deionized water and ethanol alternately 3-5 times and vacuum dried for 6-12 hours to obtain amino-phosphonic acid modified graphene adsorbent material. By adjusting the reaction time in step 1a) and the reaction temperature in step 1b), the molar ratio of amino groups to phosphonic acid groups in the final material is 0.8:1-1.2:1.

[0009] The present invention provides a graded purification and targeted recovery process for mixed extractants in industrial wastewater. In the adsorption stage, the pH of the influent to the industrial wastewater is controlled in the acidic range of 2.0-3.0, triggering the matrix protonation transformation of phosphonic acid, which forms a synergistic adsorption system with amine groups. The amine groups selectively adsorb the main extractant components. After the phosphonic acid is matrix protonated, it enhances the hydrophilic-hydrophobic balance of the system, helps to weaken the interaction between the extractant and the wastewater, and simultaneously repels ionic impurities in the wastewater, reducing competitive adsorption and improving adsorption selectivity. The linkage control of influent water temperature and flow rate further ensures sufficient contact between the adsorbent material and the wastewater, avoids the adsorption equilibrium shift caused by high temperature, and ensures stable bifunctional group synergistic adsorption efficiency.

[0010] During the desorption stage, the pH of the composite desorbent is adjusted to an alkaline range of 8.0-9.0, triggering the deprotonation transformation of phosphonic acid groups. The function switches from adsorption assistance to catalytic weakening. The deprotonated phosphonic acid groups weaken the binding force between the adsorbent material and the extractant components through charge repulsion. Combined with the solubility of ethanol in the composite desorbent and the alkaline environment of diethanolamine, the desorption energy barrier of the extractant is reduced. The aminophosphonic acid chelating agent ethylenediaminetetramethylenephosphonic acid is introduced simultaneously, which captures residual metal ions in industrial wastewater through strong complexation, preventing metal ions from forming stable complexes with the extractant that hinder desorption. At the same time, it prevents metal ions from occupying adsorption sites, ensuring the directionality of the desorption process. The segmented desorption temperature is designed without overlap. Based on the difference in interaction energy between different extractant components and adsorbent materials, the stepwise desorption of octanol, N235 and sulfonated kerosene is achieved, avoiding component mixing caused by co-desorption.

[0011] During the regeneration stage, after the amine-containing waste liquid is recycled to the adsorption unit, the pH of the system is adjusted back to the acidic range of 2.0-3.0, initiating the functional reset of phosphonic acid groups and material regeneration. The acidic conditions trigger the decomposition of amine salts into diethanolamine and organic acids. The concentration of diethanolamine is controlled at 0.05-0.15 mol / L. The hydroxyl defects caused by hydrolysis on the surface of the adsorption material are repaired through amino exchange reaction, restoring the adsorption activity of the amine groups. At the same time, diethanolamine undergoes esterification reaction with residual organic acids to eliminate impurity interference. The organic acids generated by the decomposition of amine salts promote the reprotonation of deprotonated phosphonic acid groups through proton transfer, completing the reversible switching from catalytic sites to adsorption auxiliary sites. The pH fluctuation is strictly controlled within ±0.3 to ensure that the protonation rate is ≥90%, realizing the in-situ regeneration of the adsorption material and providing stable performance for the next adsorption cycle.

[0012] Preferably, in step 1), the pH of the industrial wastewater influent is 2.0-3.0, the influent flow rate is 20-50 L / h, and the water temperature is 25-45℃. When the water temperature is ≥30℃, the influent flow rate is reduced by 10-30%.

[0013] Preferably, in step 2), the composite desorbent further includes an aminophosphonic acid chelating agent, wherein the volume ratio of ethanol, diethanolamine and aminophosphonic acid chelating agent is 85-95:5-12:1-3; The aminophosphonic acid chelating agent is ethylenediaminetetramethylenephosphonic acid, and its preparation steps include: 2a) Add 1 part ethylenediamine and 3-7 parts deionized water to a four-necked flask. The ethylenediamine is based on the mass fraction and the deionized water is based on the volume fraction. Stir until the ethylenediamine is completely dissolved. Control the system temperature at 15-30℃ and slowly add 37% formaldehyde aqueous solution dropwise. The molar ratio of formaldehyde to ethylenediamine is 3-6:1. Control the addition time at 20-40 min. After the addition is complete, continue stirring for 10-20 min to form an ethylenediamine-formaldehyde condensate solution. 2b) A cooling medium is introduced into the condensate solution obtained in step 2a) to lower the system temperature to 3-12°C. Phosphorus trichloride is slowly added dropwise, with a molar ratio of phosphorus trichloride to ethylenediamine of 2.5-4:1. The system temperature is controlled to be ≤18°C during the dropwise addition, and the addition time is 1-2.5 h. After the addition is complete, the temperature is raised to 35-55°C and the reaction is stirred for 1.5-2.5 h to obtain the phosphonate intermediate. 2c) Add deionized water to the phosphonate intermediate obtained in step 2b), with the volume ratio of the added deionized water to the deionized water in step 2a) being 1.2-2:1. Heat to 85-100℃ and reflux for hydrolysis for 2.5-4.5 h. After the reaction is complete, neutralize the pH of the system to 5.5-7.5 with 30% sodium hydroxide solution. After concentration by vacuum distillation, crystallization, and drying, ethylenediaminetetramethylenephosphonic acid is obtained.

[0014] Preferably, in step 3), the process parameters for the gradient vacuum distillation are as follows: the first stage separates 2-octanol under a vacuum of 0.06-0.09 MPa and a temperature of 78-88°C, and the separation endpoint is determined when the purity of 2-octanol in the distillate is ≤90%; the second stage separates N235 and sulfonated kerosene under a vacuum of 0.001-0.005 MPa and a temperature of 105-125°C, and the distillation is stopped when the total purity of N235 and sulfonated kerosene in the distillate is ≤90%.

[0015] Preferably, in step 3), the heating rate of the gradient vacuum distillation equipment is 2-6℃ / h, the time to rise from the first stage end temperature of 88℃ to the second stage starting temperature of 105℃ is 3-8.5h, and the temperature holding time for each stage of distillation is 0.5-2h.

[0016] The present invention provides a staged purification and targeted recovery process for mixed extractants in industrial wastewater. Addressing the separation challenge of 2-octanol with N235 and sulfonated kerosene due to their similar boiling points, this process employs a two-stage vacuum and temperature gradient control. The first stage separates 2-octanol, while the second stage separates N235 and sulfonated kerosene. By lowering the vacuum gradient and raising the temperature, the boiling points of the components are reduced to prevent degradation, and the problem of distillation overlap is resolved. The separation endpoint is defined as a distillate purity ≤90%. A slow heating rate of 2-6℃ / h and a holding time of 0.5-2h ensure thorough separation of each component. The amine salt-containing waste liquid at the bottom of the distillation column is not directly discharged but reused as a regeneration medium. The amine salts decompose efficiently under acidic conditions, and the recovered diethanolamine is used to repair hydroxyl defects in the adsorbent material, while organic acids are used to promote the resetting of phosphonic acid groups, maximizing resource utilization. It not only avoids water pollution caused by the direct discharge of amine-containing wastewater at the source, but more importantly, it provides a chemical environment and key material support for the pH response site switching of phosphonic acid groups in graphene adsorbent materials: after the amine-containing wastewater is reused, the system is regulated to an acidic range of 2.0-3.0, which perfectly matches the pH conditions required for the deprotonation of phosphonic acid groups. At the same time, the organic acids produced by the decomposition of amine salts in the wastewater can provide sufficient protons for the reset of deprotonated phosphonic acid groups through proton transfer, while the diethanolamine generated by decomposition can repair the aged amine group sites on the surface of the adsorbent material, so that the synergistic structure of phosphonic acid groups and amine groups can be restored. This fundamentally solves the problem of functional group activity decay after the adsorbent material is used, and greatly improves its stability for long-term recycling.

[0017] Preferably, in step 3), after the separated composite desorbent is filtered to remove trace impurities, ethanol and diethanolamine are added to a volume ratio of 85-95:5-15 and the pH is adjusted back to 8-9, and then reused in step 2).

[0018] Preferably, in step 4), the amine salt in the amine-containing waste liquid decomposes into diethanolamine and organic acid under acidic conditions, with a decomposition reaction time of 40-80 min, and the concentration of diethanolamine in the system is controlled to 0.05-0.15 mol / L.

[0019] Preferably, in step 4), when diethanolamine undergoes an amino exchange reaction with the hydroxyl groups generated by hydrolysis on the surface of the graphene adsorbent material, it simultaneously undergoes an esterification reaction with residual organic acid impurities. The reaction temperature is controlled at 30-40℃ and the reaction time is 30-50 min.

[0020] Preferably, in step 4), the organic acid produced by the decomposition of amine salt forms a concentration of 0.03-0.08 mol / L in the system, which promotes the reset of deprotonated phosphonic acid groups through proton transfer, and controls the pH fluctuation range of the process to be ≤±0.3, with the proportion of protonated phosphonic acid groups ≥90%.

[0021] Compared with the prior art, the beneficial effects of the present invention are: 1. This invention constructs an amino-phosphonic acid bifunctional system on the surface of a graphene substrate using a covalent grafting method. Utilizing the synergistic effects of hydrogen bonding, hydrophobic interactions, and electrostatic adsorption between the two types of functional groups and the components of the mixed extractant, it enhances the selective adsorption of target components, reduces competitive adsorption of impurities in wastewater, and improves adsorption selectivity and capacity. Step 2) involves segmented desorption within non-overlapping temperature ranges, combined with pH control of the composite desorbent. Directional desorption is achieved based on the differences in interaction energies between different extractant components and the adsorbent material, avoiding co-desorption and providing a high-purity desorbent solution for subsequent separation.

[0022] 2. The aminophosphonic acid chelating agent introduced in the composite desorbent of this invention can complex metal ions in industrial wastewater, eliminating the risk of them forming stable complexes with the extractant, and ensuring desorption efficiency and the cleanliness of the separation system. Step 3) involves distillation and gradient vacuum distillation processes. By controlling the temperature and vacuum, precise separation is achieved based on the boiling point characteristics of each extractant component, effectively solving the separation problem of components with similar boiling points and improving the purity of the recovered product.

[0023] 3. In this invention, after the amine-containing waste liquid is recycled to the adsorption device, the amine salt is decomposed under acidic conditions. The generated diethanolamine repairs the hydroxyl defects on the surface of the adsorption material through an amino exchange reaction. The organic acid promotes the repositioning of deprotonated phosphonic acid groups through proton transfer, thereby realizing the in-situ regeneration of the adsorption material and extending its recycling cycle. This not only enhances the recovery effect of the mixed extractant but also achieves the stable recycling of the adsorption material, reducing resource waste and pollutant emissions. Attached Figure Description

[0024] Figure 1 Bar charts showing the adsorption capacity performance of the adsorbent materials used in the processes provided in Examples 1-3 and Comparative Examples 1-6 of this invention; Figure 2 The above are columnar analysis charts of the desorption rate of 2-octanol in the processes provided in Examples 1-3 and Comparative Examples 1-6 of this invention. Figure 3 The bar chart shows the desorption rate test results of N235 and sulfonated kerosene in the processes provided in Examples 1-3 and Comparative Examples 1-6 of this invention. Figure 4 The above are columnar analysis charts of the purity test of 2-octanol in the processes provided in Examples 1-3 and Comparative Examples 1-6 of this invention. Figure 5 Bar charts showing the purity performance tests of N235 and sulfonated kerosene in the processes provided in Examples 1-3 and Comparative Examples 1-6 of this invention; Figure 6This is a bar chart showing the capacity retention rate of the adsorbent material used in the processes provided in Examples 1-3 and Comparative Examples 1-6 of the present invention after 10 cycles. Detailed Implementation

[0025] The technical solution of the present invention will be clearly and completely described below with reference to specific embodiments. 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.

[0026] Example 1 This embodiment provides a staged purification and targeted recovery process for mixed extractants in industrial wastewater, the specific steps of which are as follows: 1) Industrial wastewater with pH 2.5, water temperature 30℃, and COD 500mg / L is passed into the adsorption device at an influent flow rate of 35L / h. The adsorption device is filled with modified graphene adsorption material. The modified graphene adsorbent material described above involves introducing amine and phosphonic acid groups into the graphene adsorbent material. The specific steps are as follows: Graphene substrate is dispersed in N,N-dimethylformamide solvent at a mass-to-volume ratio of 1:70, and ultrasonically treated for 2 hours; amine precursor 3-aminopropyltriethoxysilane and catalyst triethylamine are added at a mass ratio of 1:10 between the amine precursor and the graphene substrate, and a molar ratio of 1:1 between triethylamine and the amine precursor; the mixture is stirred at 70°C. The reaction was stirred for 5 h, and the amine loading was 0.45 mmol / g. The phosphonic acid precursor 3-glycidyl etheroxypropyltrimethoxysilane was added to the dispersion, with a mass ratio of phosphonic acid precursor to amine-modified graphene of 1:6. The mixture was heated to 90 °C and stirred for 7 h, with a phosphonic acid loading of 0.55 mmol / g. After washing with deionized water and ethanol alternately 4 times and vacuum drying for 9 h, a modified graphene adsorbent material with a molar ratio of amine to phosphonic acid of 1:1 was obtained.

[0027] 2) After adsorption saturation, a composite desorbent (ethanol, diethanolamine, and ethylenediaminetetramethylenephosphonic acid in a volume ratio of 90:8:2, pH 8.5) is introduced to desorb 2-octanol at 59℃. After the 2-octanol desorption rate is ≥95%, the temperature is raised to 65℃ to desorb N235 and sulfonated kerosene, and the mixed desorbed liquid is collected.

[0028] 3) The mixed desorbent solution is fed into a distillation column with a top temperature of 76℃ and a bottom temperature of 165℃ to separate the composite desorbent. The mixed extractant is fed into a gradient vacuum distillation apparatus. In the first stage, octanol is separated at a vacuum of 0.07MPa and a temperature of 83℃. The process is stopped when the purity of the distillate is ≥90%, and the heating rate is 4℃ / h. The process takes 4.25h to raise the temperature from 88℃ to 105℃. In the second stage, N235 and sulfonated kerosene are separated at a vacuum of 0.003MPa and a temperature of 115℃. The process is stopped when the total purity is ≥90%. The temperature of each stage is maintained for 1h. After filtration, the composite desorbent is replenished with ethanol and diethanolamine to the set ratio. The pH is adjusted back to 8.5 before reuse.

[0029] 4) Pass the amine salt-containing waste liquid from the bottom of the distillation column into the adsorption device, adjust the pH to 2.5, the amine salt decomposition reaction time is 60 min, the diethanolamine concentration is controlled at 0.1 mol / L, the reaction is carried out at 35℃ for 40 min, the organic acid concentration is 0.05 mol / L, the pH fluctuation is ≤ ±0.2, and the proportion of protonated phosphonic acid groups is ≥92%.

[0030] Example 2 This embodiment provides a staged purification and targeted recovery process for mixed extractants in industrial wastewater, the specific steps of which are as follows: 1) Industrial wastewater with pH 2.0, water temperature 25℃, and COD 300mg / L is passed into the adsorption device at an influent flow rate of 50L / h. The adsorption device is filled with modified graphene adsorption material. The modified graphene adsorbent material described above involves introducing amine and phosphonic acid groups into the graphene adsorbent material. The specific steps are as follows: Graphene substrate is dispersed in N,N-dimethylformamide solvent at a mass-to-volume ratio of 1:50, and ultrasonically treated for 1 hour; amine precursor 3-aminopropyltriethoxysilane and catalyst triethylamine are added at a mass ratio of 1:8 between the amine precursor and the graphene substrate, and a molar ratio of 0.5:1 between triethylamine and the amine precursor; the mixture is stirred at 60°C. The reaction was stirred for 4 hours, and the amine loading was 0.35 mmol / g. A phosphonic acid precursor, 3-glycidyl etheroxypropyltrimethoxysilane, was added to the dispersion. The mass ratio of the phosphonic acid precursor to the amine-modified graphene was 1:5. The mixture was heated to 80℃ and stirred for 6 hours, resulting in a phosphonic acid loading of 0.45 mmol / g. After washing three times alternately with deionized water and ethanol, and vacuum drying for 6 hours, a modified graphene adsorbent material with an amine to phosphonic acid molar ratio of 0.8:1 was obtained.

[0031] 2) After adsorption saturation, a composite desorbent (ethanol, diethanolamine, and ethylenediaminetetramethylenephosphonic acid in a volume ratio of 85:12:3, pH 8.0) is introduced to desorb 2-octanol at 58℃. After the 2-octanol desorption rate is ≥95%, the temperature is raised to 64℃ to desorb N235 and sulfonated kerosene, and the mixed desorbed liquid is collected.

[0032] 3) The mixed desorbent solution is fed into a distillation column with a top temperature of 73℃ and a bottom temperature of 155℃ to separate the composite desorbent. The mixed extractant is fed into a gradient vacuum distillation apparatus. In the first stage, octanol is separated at a vacuum of 0.06MPa and a temperature of 78℃. The process is stopped when the purity of the distillate is ≥90%, and the heating rate is 2℃ / h. The process takes 8.5h to raise the temperature from 88℃ to 105℃. In the second stage, N235 and sulfonated kerosene are separated at a vacuum of 0.001MPa and a temperature of 105℃. The process is stopped when the total purity is ≥90%. The temperature of each stage is maintained for 0.5h. After filtration, the composite desorbent is replenished with ethanol and diethanolamine to the set ratio. The pH is adjusted back to 8.0 before reuse.

[0033] 4) Pass the amine salt-containing waste liquid from the bottom of the distillation column into the adsorption device, adjust the pH to 2.0, the amine salt decomposition reaction time is 40 min, the diethanolamine concentration is controlled at 0.05 mol / L, the reaction is carried out at 30℃ for 30 min, the organic acid concentration is 0.03 mol / L, the pH fluctuation is ≤ ±0.2, and the proportion of protonated phosphonic acid groups is ≥90%.

[0034] Example 3 This embodiment provides a staged purification and targeted recovery process for mixed extractants in industrial wastewater, the specific steps of which are as follows: 1) Industrial wastewater with pH 3.0, water temperature 45℃, and COD 800mg / L is introduced into the adsorption device. The water temperature is ≥30℃. The influent flow rate is reduced by 30% to 20L / h. The adsorption device is filled with modified graphene adsorption material. The modified graphene adsorbent material described above involves introducing amine and phosphonic acid groups into the graphene adsorbent material. The specific steps are as follows: Graphene substrate is dispersed in N,N-dimethylformamide solvent at a mass-to-volume ratio of 1:100, and ultrasonically treated for 3 hours; amine precursor 3-aminopropyltriethoxysilane and catalyst triethylamine are added at a mass ratio of 1:12 (amine precursor to graphene substrate) and a molar ratio of 1.5:1 (triethylamine to amine precursor), and stirred at 80°C. The reaction was stirred for 6 hours, and the amine loading was 0.55 mmol / g. A phosphonic acid precursor, 3-glycidyl etheroxypropyltrimethoxysilane, was added to the dispersion. The mass ratio of the phosphonic acid precursor to the amine-modified graphene was 1:7. The mixture was heated to 100℃ and stirred for 8 hours, resulting in a phosphonic acid loading of 0.65 mmol / g. After washing five times alternately with deionized water and ethanol, and vacuum drying for 12 hours, a modified graphene adsorbent material with an amine to phosphonic acid molar ratio of 1.2:1 was obtained.

[0035] 2) After adsorption saturation, a composite desorbent (ethanol, diethanolamine, and ethylenediaminetetramethylenephosphonic acid in a volume ratio of 95:5:1, pH 9.0) is introduced to desorb 2-octanol at 61℃. After the 2-octanol desorption rate is ≥95%, the temperature is raised to 66℃ to desorb N235 and sulfonated kerosene, and the mixed desorbed liquid is collected.

[0036] 3) The mixed desorbent solution is fed into a distillation column with a top temperature of 80℃ and a bottom temperature of 175℃ to separate the composite desorbent. The mixed extractant is fed into a gradient vacuum distillation apparatus. In the first stage, octanol is separated at a vacuum of 0.09MPa and a temperature of 88℃. The process is stopped when the purity of the distillate is ≥90%, and the heating rate is 6℃ / h. It takes 3 hours to heat the distillate from 88℃ to 105℃. In the second stage, N235 and sulfonated kerosene are separated at a vacuum of 0.005MPa and a temperature of 125℃. The process is stopped when the total purity is ≥90%. The temperature of each stage is maintained for 2 hours. After filtration, the composite desorbent is replenished with ethanol and diethanolamine to the set ratio. The pH is adjusted back to 9.0 before reuse.

[0037] 4) Pass the amine salt-containing waste liquid from the bottom of the distillation column into the adsorption device, adjust the pH to 3.0, the amine salt decomposition reaction time is 80 min, the diethanolamine concentration is controlled at 0.15 mol / L, the reaction is carried out at 40℃ for 50 min, the organic acid concentration is 0.08 mol / L, the pH fluctuation is ≤ ±0.3, and the proportion of protonated phosphonic acid groups is ≥91%.

[0038] Comparative Example 1 The only difference between this comparative example and Example 1 is that the adsorbent material is unmodified ordinary graphene, that is, amine and phosphonic acid groups were not introduced through covalent grafting.

[0039] Expected performance: Ordinary graphene has poor adsorption selectivity for each component of the mixed extractant, and simultaneously adsorbs impurities in wastewater. The impurity content in the mixed desorption solution increases significantly, the purity of each component decreases, and the adsorption capacity decreases significantly.

[0040] Comparative Example 2 The only difference between this comparative example and Example 1 is that the segmented desorption temperatures are 58-63℃ and 62-66℃, with overlapping temperature ranges.

[0041] Expected performance: Overlapping temperatures lead to the co-desorption of 2-octanol, N235, and sulfonated kerosene. The components in the desorbate are mixed, which significantly increases the difficulty of subsequent separation, renders the fractional directional recovery ineffective, and reduces the purity of each component.

[0042] Comparative Example 3 The only difference between this comparative example and Example 1 is that no aminophosphonic acid chelating agent was added to the composite desorbent.

[0043] Expected performance: Residual metal ions in industrial wastewater cannot be complexed and form stable complexes with the extractant, resulting in decreased desorption efficiency. Metal ions enter the distillation system, causing equipment corrosion and reduced separation accuracy.

[0044] Comparative Example 4 The only difference between this comparative example and Example 1 is that gradient vacuum distillation has no clear separation endpoint determination and the heating rate is too fast.

[0045] Expected performance: The excessively rapid heating rate leads to insufficient separation of components. There is distillation overlap between 2-octanol, N235, and sulfonated kerosene, resulting in a decrease in recovery purity. The lack of a separation endpoint determination causes the loss of target components or the introduction of impurities, thus reducing the recovery yield.

[0046] Comparative Example 5 The only difference between this comparative example and Example 1 is that the amine salt-containing waste liquid at the bottom of the distillation column is directly discharged and is not passed into the adsorption device for reuse.

[0047] Expected performance: The deprotonated phosphonic acid groups on the surface of the adsorbent material cannot be reset, and the residual hydroxyl groups cause the adsorption activity to continuously decline. After repeated use, the adsorption capacity drops significantly, and the discharge of amine salt waste liquid causes resource waste and environmental pollution, significantly reducing the economic efficiency and environmental friendliness of the process.

[0048] Comparative Example 6 The only difference between this comparative example and Example 1 is that the pH of the system was adjusted to 3.5-4.0 in step 4, and the pH fluctuation range was not controlled.

[0049] Expected performance: When the pH deviates from the suitable range for protonation of phosphonic acid groups, the proton transfer efficiency of organic acids decreases, the proportion of protonated phosphonic acid groups is insufficient, the synergistic effect of the bifunctional groups of the adsorbent material is weakened, the subsequent adsorption capacity decreases, pH fluctuations lead to instability of the reaction system, incomplete decomposition of amine salts, and decreased utilization of diethanolamine.

[0050] Performance testing methods: 1. Adsorption performance test Testing instruments: UV-Vis spectrophotometer, electronic balance, constant temperature water bath, peristaltic pump Test procedure: Take 0.5g of each of the adsorbent materials in the examples and comparative examples, and add them to 50mL of simulated industrial wastewater containing 2-octanol, N235, and sulfonated kerosene (the initial concentration of each component is 100mg / L, pH=2.5, and water temperature is 30℃). Use a peristaltic pump to control the influent flow rate at 35L / h. After the adsorption reaches saturation, take the supernatant and filter it through a 0.45μm filter membrane. Measure the equilibrium concentration of each component using a UV-Vis spectrophotometer.

[0051] Calculation method: Adsorption capacity (q) = (C0 - C) e )×V / m, where C0 is the initial concentration, C e To balance the concentration, V is the solution volume and m is the mass of the adsorbent material.

[0052] 2. Desorption performance test Testing instruments: Gas chromatograph, constant temperature water bath heating device, condensation recovery device Test procedure: After adsorption saturation, the material is packed into a fixed bed adsorption column, and the corresponding composite desorbent is introduced. Desorption is performed in stages according to the set temperature. The desorbed liquids of each temperature stage are collected separately, and the concentration of each extractant component in the desorbed liquid is determined by gas chromatography to calculate the desorption amount.

[0053] Calculation method: Desorption rate (η) = Desorption amount / Adsorption amount × 100%.

[0054] 3. Separation purity test Testing instruments: High performance liquid chromatograph, gas chromatography-mass spectrometry (GC-MS) Test procedure: Take the distillate from each component after rectification and gradient vacuum distillation, and determine the peak area of ​​the target component and the peak area of ​​the impurities by high performance liquid chromatography and gas chromatography-mass spectrometry, and calculate the purity.

[0055] Calculation method: Purity (P) = Target component peak area / Total peak area × 100%.

[0056] 4. Cyclic stability test of adsorbent material Testing instruments: Fixed-bed adsorption-desorption device, UV-Vis spectrophotometer Test procedure: Based on the process conditions of Example 1 and Comparative Example 5, repeat the adsorption-desorption-regeneration cycle 10 times. After each cycle, the adsorption capacity is measured according to the adsorption performance test method provided by the present invention, and the adsorption capacity retention rate of each cycle is recorded.

[0057] Calculation method: Capacity retention rate (R) n = nth adsorption capacity / 1st adsorption capacity × 100%.

[0058] 5. Amine salt decomposition rate test Testing instruments: potentiometric titrator, ion chromatograph Test steps: Take 10 mL of waste liquid before and after the decomposition of amine salt in step 4), and determine the concentration of amine salt before and after decomposition using an ion chromatograph to calculate the decomposition rate; at the same time, determine the concentration of diethanolamine after decomposition using a potentiometric titrator to verify the concentration control effect.

[0059] Calculation method: Amine salt decomposition rate (δ) = (initial amine salt concentration - remaining amine salt concentration) / initial amine salt concentration × 100%.

[0060] 6. Metal ion removal rate test Testing instrument: Inductively coupled plasma mass spectrometer Test procedure: Take a sample containing Fe 3+ Cu 2+ Simulated industrial wastewater (all concentrations 5 mg / L) was subjected to an adsorption-desorption process. The desorbed liquid was collected, and the concentration of metal ions in the desorbed liquid was determined by inductively coupled plasma mass spectrometry to calculate the removal rate.

[0061] Calculation method: Metal ion removal rate (k) = (initial metal ion concentration - remaining metal ion concentration) / initial metal ion concentration × 100%.

[0062] Experimental data:

[0063] Based on the above data, the adsorption capacity of Examples 1-3 of the present invention reaches 81.7 to 88.5 mg / g, which is much higher than that of Comparative Example 1 of unmodified graphene. Furthermore, by adjusting the molar ratio of the two types of functional groups, the adsorption selectivity is further optimized, and the competitive adsorption of impurities in wastewater is reduced.

[0064] Secondly, the segmented desorption mode without temperature overlap achieves directional desorption based on the difference in interaction energy between different extractant components and adsorbent materials, avoiding co-desorption. Combined with the complex desorbent containing aminophosphonic acid chelating agents, the desorption rates of octanol, N235, and sulfonated kerosene in Examples 1-3 all exceeded 95%, with metal ion removal rates exceeding 92%. In contrast, Comparative Example 2 experienced a decrease in both desorption rate and purity of approximately 10% due to temperature overlap, and Comparative Example 3, without the addition of chelating agents, had a metal ion removal rate of only 35.7%, showing a significant reduction in desorption and separation efficiency. The combined process of distillation and gradient vacuum distillation effectively solved the separation problem of components with similar boiling points through temperature and vacuum control, resulting in a recovery purity of over 93% for each component in Examples 1-3. Compared to Comparative Example 4, which lacked a clear separation endpoint and had an excessively rapid heating rate, the purity was improved by 8%-10%.

[0065] Furthermore, after the amine-containing waste liquid is recycled to the adsorption device, the amine salts are efficiently decomposed under acidic conditions. The decomposition rate in Examples 1-3 exceeds 97%. The generated diethanolamine repairs the hydroxyl defects on the surface of the adsorption material through an amino exchange reaction. The organic acid promotes the resetting of deprotonated phosphonic acid groups through proton transfer, ensuring the cycle stability of the adsorption material. The capacity retention rate of Examples 1-3 after 10 cycles reaches 89.3% to 92.7%. In contrast, the material in Comparative Example 5 cannot be regenerated due to the direct discharge of waste liquid, and the retention rate after 10 cycles is only 58.3%. In Comparative Example 6, the amine salt decomposition rate and cycle stability are significantly reduced due to the pH deviating from the suitable range and the fluctuations not being controlled.

[0066] It will be apparent to those skilled in the art that the present invention is not limited to the details of the exemplary embodiments described above, and that the invention can be implemented in other specific forms without departing from the spirit or essential characteristics of the invention. Therefore, the embodiments should be considered in all respects as exemplary and non-limiting, and the scope of the invention is defined by the appended claims rather than the foregoing description. Thus, it is intended that all variations falling within the meaning and scope of equivalents of the claims be included within the present invention.

Claims

1. A graded purification and targeted recovery process for mixed extractants in industrial wastewater, characterized in that, Includes the following steps: 1) Industrial wastewater is fed into an adsorption device, which is filled with amine-phosphonic acid modified graphene adsorption material, wherein the molar ratio of amine groups to phosphonic acid groups in the adsorption material is 0.8:1-1.2:1; 2) Introduce a composite desorbent with a pH of 8.0-9.0 into the adsorption device saturated in step 1). The composite desorbent is prepared by mixing ethanol and diethanolamine in a volume ratio of 85-95:5-15. The desorption is carried out in a segmented manner, desorbing 2-octanol at 58-61°C and desorbing N235 and sulfonated kerosene at 64-66°C. Collect the mixed desorbent solution. 3) Pass the mixed desorption liquid obtained in step 2) into a distillation column, control the column top temperature to 73-80℃ and the column bottom temperature to 155-175℃, and separate the composite desorption agent, mixed extractant and amine salt-containing waste liquid; separate the mixed extractant by gradient vacuum distillation to obtain octanol, N235 and sulfonated kerosene. 4) Pass the amine salt-containing waste liquid from the bottom of the distillation column in step 3) into the adsorption device described in step 1), and adjust the pH of the system to 2.0-3.

0.

2. The process according to claim 1, characterized in that, In step 1), the amino-phosphonic acid-modified graphene adsorbent material is prepared by covalent grafting, and the preparation steps include: 1a) Graphene substrate was dispersed in N,N-dimethylformamide solvent and sonicated for 1-3 h. An amino precursor and triethylamine catalyst were added, with a mass ratio of amino precursor to graphene substrate of 1:8-1:

12. The mixture was stirred at 60-80 °C for 4-6 h to obtain amino-modified graphene. The loading of amino functional groups in the amino precursor was controlled by the reaction time: the loading was 0.3-0.4 mmol / g after 4 h of reaction and 0.5-0.6 mmol / g after 6 h of reaction. 1b) Add a phosphonic acid precursor to an amino-modified graphene dispersion, wherein the mass ratio of the phosphonic acid precursor to the amino-modified graphene is 1:5-1:

7. Heat to 80-100℃ and stir for 6-8 hours to generate phosphonic acid groups via ester hydrolysis. The phosphonic acid loading is controlled by the reaction temperature: 0.4-0.5 mmol / g at 80℃ and 0.6-0.7 mmol / g at 100℃. 1c) After the reaction is complete, the material is washed with deionized water and ethanol alternately 3-5 times and vacuum dried for 6-12 hours to obtain amino-phosphonic acid modified graphene adsorbent material. By adjusting the reaction time in step 1a) and the reaction temperature in step 1b), the molar ratio of amino groups to phosphonic acid groups in the final material is 0.8:1-1.2:

1.

3. The process according to claim 2, characterized in that, In step 1), the pH of the industrial wastewater influent is 2.0-3.0, the influent flow rate is 20-50L / h, and the water temperature is 25-45℃. When the water temperature is ≥30℃, the influent flow rate is reduced by 10-30%.

4. The process according to claim 1, characterized in that, In step 2), the composite desorbent further includes an aminophosphonic acid chelating agent, and the volume ratio of ethanol, diethanolamine and aminophosphonic acid chelating agent is 85-95:5-12:1-3; The aminophosphonic acid chelating agent is ethylenediaminetetramethylenephosphonic acid, and its preparation steps include: 2a) Add 1 part ethylenediamine and 3-7 parts deionized water to a four-necked flask. The ethylenediamine is based on the mass fraction and the deionized water is based on the volume fraction. Stir until the ethylenediamine is completely dissolved. Control the system temperature at 15-30℃ and slowly add 37% formaldehyde aqueous solution dropwise. The molar ratio of formaldehyde to ethylenediamine is 3-6:

1. Control the addition time at 20-40 min. After the addition is complete, continue stirring for 10-20 min to form an ethylenediamine-formaldehyde condensate solution. 2b) A cooling medium is introduced into the condensate solution obtained in step 2a) to lower the system temperature to 3-12°C. Phosphorus trichloride is slowly added dropwise, with a molar ratio of phosphorus trichloride to ethylenediamine of 2.5-4:

1. The system temperature is controlled to be ≤18°C during the dropwise addition, and the addition time is 1-2.5 h. After the addition is complete, the temperature is raised to 35-55°C and the reaction is stirred for 1.5-2.5 h to obtain the phosphonate intermediate. 2c) Add deionized water to the phosphonate intermediate obtained in step 2b), with the volume ratio of the added deionized water to the deionized water in step 2a) being 1.2-2:

1. Heat to 85-100℃ and reflux for hydrolysis for 2.5-4.5 h. After the reaction is complete, neutralize the pH of the system to 5.5-7.5 with 30% sodium hydroxide solution. After concentration by vacuum distillation, crystallization, and drying, ethylenediaminetetramethylenephosphonic acid is obtained.

5. The process according to claim 1, characterized in that, In step 3), the process parameters for the gradient vacuum distillation are as follows: the first stage separates 2-octanol under a vacuum of 0.06-0.09 MPa and a temperature of 78-88°C, and the separation endpoint is determined when the purity of 2-octanol in the distillate is ≤90%; the second stage separates N235 and sulfonated kerosene under a vacuum of 0.001-0.005 MPa and a temperature of 105-125°C, and the distillation is stopped when the total purity of N235 and sulfonated kerosene in the distillate is ≤90%.

6. The process according to claim 5, characterized in that, In step 3), the heating rate of the gradient vacuum distillation equipment is 2-6℃ / h, the time from the first stage end temperature of 88℃ to the second stage start temperature of 105℃ is 3-8.5h, and the temperature holding time for each stage of distillation is 0.5-2h.

7. The process according to claim 6, characterized in that, In step 3), after the separated composite desorbent is filtered to remove trace impurities, ethanol and diethanolamine are added to a volume ratio of 85-95:5-15 and the pH is adjusted to 8-9, and then reused in step 2).

8. The process according to claim 1, characterized in that, In step 4), the amine salt in the amine-containing waste liquid decomposes into diethanolamine and organic acid under acidic conditions. The decomposition reaction time is 40-80 min, and the concentration of diethanolamine in the system is controlled to be 0.05-0.15 mol / L.

9. The process according to claim 8, characterized in that, In step 4), when diethanolamine undergoes an amino exchange reaction with the hydroxyl groups generated by hydrolysis on the surface of the graphene adsorbent material, it also undergoes an esterification reaction with residual organic acid impurities. The reaction temperature is controlled at 30-40℃ and the reaction time is 30-50min.

10. The process according to claim 9, characterized in that, In step 4), the organic acids produced by the decomposition of amine salts form a concentration of 0.03-0.08 mol / L in the system. They promote the reset of deprotonated phosphonic acid groups through proton transfer. The pH fluctuation range of this process is controlled to be ≤±0.3, and the proportion of protonated phosphonic acid groups is ≥90%.

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