A process for treating ethylene caustic sludge wastewater

Abstract

The application discloses a process method for treating ethylene alkali residue wastewater, which comprises a wet oxidation section, a biochemical treatment section and a salt treatment section; the wet oxidation section comprises an adjusting tank, a heat exchange unit, a wet oxidation reactor, a cooler, an electrodialysis I and nanofiltration; the biochemical treatment section comprises an adjusting pool, primary biochemical treatment, secondary biochemical treatment and a recycled water pool in sequence; the salt treatment section comprises an electrodialysis II, a nitrate crystallizer, ozone catalytic oxidation and reverse osmosis; wherein a modified anion exchange membrane is used for the cathode membrane of the electrodialysis I and the electrodialysis II, which is crosslinked by polyvinyl alcohol, a positively charged amine compound and beta-cyclodextrin, and then modified by dopamine and copper sulfate. The application adopts a treatment process with homogeneous catalytic wet oxidation as the core, fully utilizes the characteristics of high catalytic activity and high treatment efficiency of the homogeneous catalytic wet oxidation, and greatly improves the treatment capacity of the wet oxidation.

Description

TECHNICAL FIELD

[0001] The present application relates to a treatment method of ethylene caustic residue wastewater, and belongs to the technical field of wastewater treatment. BACKGROUND

[0002] Ethylene waste lye is wastewater generated by alkali washing of cracking gas in the ethylene production process, and the pollutants are relatively complex, with high content of organic matter, sulfide and salt, and also containing malodorous gases such as mercaptan and sulfide. The most mainstream treatment method for ethylene caustic residue wastewater is wet oxidation method, which operates under high temperature (180-320℃) and high pressure (2.5-20 MPa), and uses gaseous oxygen as an oxidizing agent to oxidize and decompose organic matter in water into small molecular organic matter or inorganic matter. However, the traditional wet oxidation requires high temperature, pressure and relatively long residence time, has high operation cost per ton of water, has high requirements for equipment material, and also has high one-time investment.

[0003] In order to reduce the required temperature and pressure of the reaction and improve the treatment effect, catalytic wet air oxidation (CWAO) has become a research hotspot in recent years. CN201510274988.5 discloses a catalyst for catalytic wet oxidation of refractory organic wastewater, which is a "noble metal-transition metal-rare earth" composite catalyst, and the main component of the carrier FSC is alumina; CN201410340574.3 discloses a catalyst for catalytic wet oxidation treatment and a preparation method thereof, which uses a noble metal-non-noble metal nano-alloy as an active component and active carbon as a carrier; CN201510661575.2 discloses a heterogeneous wet oxidation catalyst, which includes a composite oxide carrier and a small amount of noble metal; and CN201310621017.4 discloses a preparation method of a catalyst carrier for catalytic wet oxidation, which uses active carbon as a core and amorphous silicon aluminum as a shell.

[0004] The above-mentioned patents all use heterogeneous catalytic wet oxidation, which has advantages in the separation and recovery of catalysts and metal loss, but may not be suitable for the existing wet oxidation process. The paper "Alkaline residue moderate wet oxidation + SBR treatment technology industrial application" (2011) discloses an alkaline residue moderate wet oxidation process of Fushun Petrochemical Research Institute, which has been popularized and applied in 28 refining enterprises and has strong representativeness. The wet oxidation reactor used in the process is a bubbling flow internal circulation reactor with an inner cylinder. If a heterogeneous catalyst is used in the reactor, it can be predicted that the gas-liquid circulation will be seriously affected, and even the reactor and pipeline will be blocked. If a fixed bed method is used, it will bring more gas resistance, which is more unfavorable for gas-liquid circulation, and the reaction rate will also be greatly reduced.

[0005] Homogeneous catalysis has higher catalytic efficiency than heterogeneous catalysis because of no internal and external diffusion effects and high dispersion, and the preparation of catalyst is much simpler than that of heterogeneous catalyst, but the biggest problem of homogeneous catalysis applied to wet oxidation is the loss of metal catalyst.

[0006] The COD concentration of ethylene waste lye is as high as tens of thousands mg / L, and a large part of it is false COD caused by sodium sulfide and sodium thiosulfate, and the purpose of wet oxidation treatment of waste lye is to convert sulfide and sodium thiosulfate into sodium sulfate, oxidize malodorous gases such as mercaptan and sulfide, and effectively remove organic matter, but the effluent of wet oxidation still has a certain COD and a large amount of salt, and the proper disposal of COD and salt is still a problem to be solved. SUMMARY

[0007] In view of the above problems, the present application provides a treatment method for ethylene lye residue wastewater, which realizes efficient treatment and zero discharge of ethylene lye residue wastewater by using homogeneous wet oxidation, improved electrodialysis, nanofiltration and other process combinations, and produces high-purity sodium sulfate, and solves the problem of catalyst loss in homogeneous catalytic process, and realizes the recycling of catalyst, and has the advantages of environmental protection and energy saving. In order to achieve the above technical purpose, the technical scheme adopted by the present application is as follows:

[0008] A process method for treating ethylene lye residue wastewater, comprising a wet oxidation section, a biochemical treatment section and a salt treatment section;

[0009] The wet oxidation section comprises a regulating tank, a heat exchange unit, a wet oxidation reactor, a cooler, electrodialysis I and nanofiltration; the ethylene lye residue wastewater first enters the regulating tank, is mixed with nanofiltration concentrated water and homogeneous catalyst, and is acidified for pH adjustment, and then is heated by the heat exchange unit and then enters the wet oxidation reactor; the effluent of the wet oxidation reactor enters the heat exchange unit for heat exchange and cooling, and then enters the electrodialysis I after being cooled by the cooler; the dilute liquid of the electrodialysis I enters the regulating tank of the biochemical treatment section, the anode concentrated liquid of the electrodialysis I enters the electrodialysis II of the salt treatment section, the cathode concentrated liquid of the electrodialysis I enters the nanofiltration, and the concentrated water of the nanofiltration enters the regulating tank, and the product water of the nanofiltration enters the electrodialysis II;

[0010] The biochemical treatment section comprises a regulating tank, a primary biochemical treatment, a secondary biochemical treatment and a recycled water tank in sequence;

[0011] The salt treatment section comprises electrodialysis II, nitrate crystallizer, ozone catalytic oxidation and reverse osmosis; the concentrated liquid of the electrodialysis II enters the nitrate crystallizer, and the dilute liquid of the electrodialysis II enters the ozone catalytic oxidation; the effluent of the ozone catalytic oxidation enters the reverse osmosis, the concentrated water of the reverse osmosis is returned to the electrodialysis II, and the product water of the reverse osmosis enters the secondary biochemical treatment unit of the biochemical treatment section; the product sodium sulfate is obtained from the nitrate crystallizer, and the remaining mother liquor is returned to the electrodialysis II or discharged as a mixed salt.

[0012] The electrodialysis I and the electrodialysis II are composed of anion exchange membranes and cation exchange membranes, wherein the anion exchange membranes are modified anion exchange membranes, and the cation exchange membranes are general cation exchange membranes.

[0013] The modified anion exchange membrane is prepared by the following steps:

[0014] In step a, polyvinyl alcohol is added to water to form a polyvinyl alcohol aqueous solution, and then a positively charged amine compound, β-cyclodextrin and a crosslinking agent are added to the solution, an inorganic acid is added to adjust the pH, and then the mixture is stirred and reacted to obtain a casting solution.

[0015] In step b, the casting solution obtained in step a is cast on a horizontal panel and dried to obtain a base membrane.

[0016] In step c, the base membrane obtained in step b is washed, alkalinized in a lye, and then soaked in water to obtain a polyvinyl alcohol anion exchange membrane.

[0017] In step d, dopamine is dissolved in a Tris-HCl buffer solution, and the pH is adjusted with hydrochloric acid to obtain a dopamine Tris buffer solution.

[0018] In step e, the anion exchange membrane obtained in step c is placed in the dopamine Tris buffer solution, and copper sulfate is added, and the mixture is stirred under the condition of air flow to obtain a modified anion exchange membrane.

[0019] Further, the positively charged amine compound is selected from one or more of 2,3-epoxypropyltrimethylammonium chloride, polyethyleneimine, polyepoxy chloropropane amine and quaternary ammonium chitosan, and preferably 2,3-epoxypropyltrimethylammonium chloride; the mass ratio of the positively charged amine compound to polyvinyl alcohol is 0.1:1 to 0.6:1.

[0020] Further, the mass ratio of the β-cyclodextrin to polyvinyl alcohol is 0.05:1 to 0.4:1.

[0021] Further, the crosslinking agent is selected from aldehyde or acid crosslinking agents, and preferably glutaraldehyde; the mass ratio of the crosslinking agent to polyvinyl alcohol is 0.01:1 to 0.1:1.

[0022] Further, the inorganic acid in step a is sulfuric acid, hydrochloric acid or nitric acid, and the pH of the solution is adjusted to 4 to 6.

[0023] Further, the mass fraction of the polyvinyl alcohol aqueous solution in step a is 5% to 15%, and the mixing reaction time of the polyvinyl alcohol aqueous solution with the positively charged amine compound, the β-cyclodextrin and the crosslinking agent is 4 to 16 hours.

[0024] Further, the polyvinyl alcohol aqueous solution is prepared by stirring the polyvinyl alcohol in water at 60 to 90°C until the polyvinyl alcohol is dissolved in water.

[0025] Further, the drying in step b is first drying at room temperature for 2-6 h, and then vacuum drying at 40-80℃ for 4-10 h.

[0026] Further, the washing in step c is washing with water until neutral.

[0027] Further, the alkali treatment uses 0.5-3 mol / L sodium hydroxide aqueous solution, and the alkali treatment time is 12-24 h.

[0028] Further, the soaking time in step c is 12-24 h.

[0029] Further, the concentration of Tris-HCl buffer in step d is 10-50 mmol / L.

[0030] Further, the mass concentration of dopamine in step d is 0.4-4 g / L, and the hydrochloric acid is used to adjust the pH to 8-9.

[0031] Further, the concentration of copper sulfate in step e is 1-20 mmol / L, and the stirring reaction time is 1-12 h. The copper sulfate can induce rapid polymerization of dopamine, and form a negative charged polydopamine electrolyte layer on the surface of the anion exchange membrane, thereby modifying the surface of the membrane.

[0032] Further, after obtaining the modified anion exchange membrane, it is stored in a sodium chloride solution. The mass concentration of the sodium chloride solution is 5-20 g / L.

[0033] The person skilled in the art should understand that the alkali residue wet oxidation effluent contains a small amount of negatively charged organic matter, dopamine has strong self-polymerization ability and adsorption capacity, and can increase the negative charge density of the membrane surface, therefore, the anion exchange membrane modified by polydopamine has a negative charge on the surface, has electrostatic repulsion to the negatively charged organic matter in water, and can inhibit the pollution of the organic matter to the anion exchange membrane. The person skilled in the art should also understand that the negative surface charge prevents the pollution of the organic matter through electrostatic effect, and also has an influence on the migration rate of inorganic anions, the more the ion charge number, the greater the influence, therefore, the sulfate ion is more affected than the chloride ion. The addition of β-cyclodextrin to the anion exchange membrane can give the membrane strong hydrophilicity and change the migration rate of anions, among which, the migration number of anions with low hydration degree such as bromide and nitrate relative to chloride is reduced, and the migration number of the sulfate ion with high hydration degree relative to chloride is increased. On the other hand, the hydrophilicity of the membrane is improved, the van der Waals force between the membrane and the organic matter solute is reduced, the attraction is reduced, and at the same time, the hydrophilic membrane and water molecules form a hydration layer due to hydrogen bonding, which can further hinder the adsorption of pollutants on the membrane surface. Therefore, after the anion exchange membrane of the application is modified by β-cyclodextrin and polydopamine, the anti-pollution ability of the membrane is greatly increased, and the selective permeability of the sulfate ion is increased.

[0034] Further, the acid is added to the adjusting tank to adjust the pH to 2-6; the acid is hydrochloric acid or sulfuric acid, preferably sulfuric acid.

[0035] Further, the heat exchange unit is composed of multiple heat exchangers, and the wet oxidation reactor effluent and the adjusting tank effluent are subjected to heat exchange, and after multiple heat exchanges, the temperature of the adjusting tank effluent is increased to 130-160℃, and the temperature of the wet oxidation reactor effluent is reduced to 50-75℃.

[0036] Further, the homogeneous catalyst is a transition metal catalyst selected from one or more of copper, iron, manganese, zinc and nickel, preferably a copper catalyst; the transition metal in the homogeneous catalyst exists in the form of a metal salt compound or a complex, and is dissolved in the liquid phase.

[0037] Further, the homogeneous catalyst is added according to a COD mass concentration to metal ion mass concentration ratio of 10000:1-30:1, and is appropriately supplemented according to the catalyst loss rate and the change in the concentration of the reaction liquid during normal operation.

[0038] Further, the wet oxidation reactor is a bubbling flow internal cylinder reactor, which uses gaseous oxygen (air) as oxidant to oxidize general organic matters in water into small molecular organic matters or inorganic matters under high temperature and high pressure conditions; those skilled in the art should understand that ethylene alkali residue wastewater is a typical difficult-to-treat wastewater, and the wet oxidation alone has strong removal capacity for sulfides in the wastewater but relatively weak removal capacity for organic matters, but under the condition of catalyst, oxygen under high temperature and high pressure is more likely to have free radical reaction, and the free radical strong oxidation greatly improves the decomposition conversion capacity and reaction rate of organic matters. On the other hand, the homogeneous catalyst itself has high activity and high selectivity, and is more rapid and effective in the treatment of special pollutants, and the problem of easy loss is solved through membrane technology.

[0039] Further, the reaction temperature of the wet oxidation reactor is 150-250 DEG C, the reaction pressure is 1-5 MPa, the liquid space velocity is 0.25-4 h -1 , and the gas-liquid volume ratio is 20:1-500:1.

[0040] Further, the cooling medium of the cooler is circulating water, which further cools the outlet water of the wet oxidation reactor, and the temperature is reduced to 30-50 DEG C, meeting the temperature requirement of the subsequent biochemical unit.

[0041] Further, the treatment time of the electrodialysis I and the electrodialysis II is 0.5-3 h, and the current density is 1-80 mA / cm 2 .

[0042] Further, the concentrated solution of the electrodialysis I is divided into anode concentrated solution and cathode concentrated solution, the anode concentrated solution mainly contains anions such as sulfate ions and chloride ions, and the cathode concentrated solution mainly contains cations such as sodium, potassium, copper and iron.

[0043] Further, the nanofiltration water production rate is 50%-75%, which has good interception effect on high-valence cations, so as to realize the separation of monovalent ions such as sodium and potassium from high-valence metal ions such as copper, iron and zinc, and realize the recycling of metal catalysts.

[0044] Further, the adjusting tank adjusts the pH value to 6-9 by adding alkali, and the alkali is one of sodium hydroxide, calcium hydroxide and potassium hydroxide.

[0045] Further, the primary biochemical process adopts pure aerobic process, and one of BAF, MBR, contact oxidation tank and MBBR is selected, ordinary biological bacteria are used for sludge, and the residence time is 12-72 h.

[0046] Further, the secondary biochemical process adopts the anoxic and aerobic process, selects one of A / O or SBR, and the sludge adopts common biological bacteria, and the residence time is 6-36h.

[0047] Further, in the ozone catalytic oxidation, the ozone dosage is 0.1-2 times of the required oxidant dosage calculated according to the COD value of the wastewater, the reaction time is 10-120 minutes, and the catalyst is a conventional solid-supported metal catalyst.

[0048] Further, the operating pressure of the reverse osmosis is 1.0-3.0 Mpa, and the water production rate is 50%-80%.

[0049] Further, the operation temperature of the nitrate crystallizer is controlled at 40-110℃, the purity of the sodium sulfate product of the nitrate crystallizer is greater than 99%, further, the mother liquor generated by the nitrate crystallizer is refluxed to the electrodialysis I for recycling treatment, when the sodium chloride concentration in the mother liquor is increased to 250-350g / L after multiple recycling, the mother liquor is completely discharged in the form of mixed salt.

[0050] Compared with the prior art, the present application has the following advantages:

[0051] (1) According to the characteristics of high COD, high salt content, high toxicity and difficult degradation of the ethylene alkali residue wastewater, the present application adopts a treatment process with homogeneous catalytic wet oxidation as the core, fully utilizes the characteristics of high catalytic activity and high treatment efficiency of the homogeneous catalytic wet oxidation, and greatly improves the treatment capacity of the wet oxidation.

[0052] (2) The present application solves the problem of catalyst loss in the homogeneous catalytic wet oxidation by combining the wet oxidation with the electrodialysis and nanofiltration membrane technology, and realizes the recycling use of the catalyst.

[0053] (3) In the wet oxidation section, the modified anion exchange membrane and the improved electrodialysis of the present application can effectively realize the separation of salt and organic matter in the ethylene alkali residue wet oxidation effluent, solve the problem of difficult treatment of the organic matter in the oil refining alkali residue wet oxidation effluent, reduce the treatment pressure of the wet oxidation unit, and are conducive to alleviating the relatively harsh treatment conditions of the wet oxidation; the separated solution containing organic matter can reach the reuse condition by simple biochemical treatment due to the low salt content; the modified electrodialysis has the characteristics of strong anti-pollution ability and high ion exchange rate, and has high application value.

[0054] (4) In the salt treatment section, the modified anion exchange membrane and the improved electrodialysis not only realize the concentration of salt, but also retain most of the organic matter in the desalination liquid, thereby reducing the organic matter content in the subsequent salt crystallization, greatly increasing the product purity, and finally realizing zero discharge.

[0055] Other features and advantages of the present application will be described in detail in the following specific embodiments. Attached Figure Description

[0056] Figure 1 Flowchart of the treatment process for ethylene alkali residue wastewater in Example 1. Detailed Implementation

[0057] The present invention will be further described in detail below with reference to specific embodiments. These embodiments are implemented based on the technical solution of the present invention, providing detailed implementation methods and specific operating procedures. However, the scope of protection of the present invention is not limited to the following embodiments.

[0058] Example 1

[0059] The process method of this invention is used to treat ethylene alkali residue wastewater.

[0060] The process flow diagram for treating ethylene alkali residue wastewater is as follows: Figure 1 As shown: Ethylene alkali residue wastewater first enters the equalization tank, where it is mixed with nanofiltration concentrate and homogeneous catalyst, and acid is added for pH adjustment. Then it enters the heat exchange unit, where a heat exchanger exchanges heat between the effluent from the wet oxidation reactor and the equalization tank. Afterward, it enters the wet oxidation reactor. The effluent from the wet oxidation reactor enters the heat exchange unit for cooling, and then, after being cooled by a cooler, enters electrodialysis I. The desalinated water from electrodialysis I undergoes equalization, primary biological treatment, and secondary biological treatment before entering the reclaimed water tank. The anion exchange solution from electrodialysis I... The concentrated solution enters the nanofiltration unit, the nanofiltration concentrate enters the regulating tank, and the nanofiltration permeate is mixed with the anolyte concentrate from electrodialysis I before entering electrodialysis II in the salt treatment section. The concentrate from electrodialysis II enters the nitrification crystallizer, and the desalinated solution from electrodialysis II enters the ozone catalytic oxidation unit. The effluent from the ozone catalytic oxidation unit enters the reverse osmosis unit, the reverse osmosis concentrate is returned to electrodialysis II, and the reverse osmosis permeate enters the secondary biological unit of the biological treatment section. The nitrification crystallizer produces sodium sulfate, and the remaining mother liquor is returned to electrodialysis II. When the chloride concentration in the mother liquor is high, it is discharged as miscellaneous salts.

[0061] The wastewater from a certain ethylene alkali residue has the following characteristics: COD 18250 mg / L, chloride ion 1605 mg / L, sulfate ion 6500 mg / L, total salt content 19550 mg / L, sulfide 2100 mg / L, ammonia nitrogen 33 mg / L, total nitrogen 250 mg / L, pH 12.1, and influent flow rate 20 t / h.

[0062] In this embodiment, both electrodialysis I and electrodialysis II are modified electrodialysis methods. The anion exchange membrane is a modified anion exchange membrane with strong antifouling ability and high ion permeability, and the cation exchange membrane is a general-purpose cation exchange membrane (Hefei Capgemini Polymer Co., Ltd., China, model CJ-MC-3).

[0063] The modified anion exchange membrane described above was prepared by the following method:

[0064] Step a: polyvinyl alcohol was added to deionized water to form a 10% by mass aqueous solution, which was stirred at 80°C until dissolved, then 2,3-epoxypropyltrimethylammonium chloride, β-cyclodextrin, and glutaraldehyde were added to the water, the mass ratio of 2,3-epoxypropyltrimethylammonium chloride to polyvinyl alcohol was 0.5:1, the mass ratio of β-cyclodextrin to polyvinyl alcohol was 0.25:1, and the mass ratio of glutaraldehyde to polyvinyl alcohol was 0.05:1, hydrochloric acid was used to adjust the pH to 5, and the reaction was carried out for 9 hours to obtain a viscous liquid, which was the casting solution;

[0065] Step b: the casting solution was cast on a horizontal glass plate and dried at room temperature for 3 hours, then the formed membrane was further dried at 60°C under vacuum for 6 hours to obtain the base membrane;

[0066] Step c: the base membrane obtained in step b was washed with deionized water until neutral, then alkalinized in a 1 mol / L sodium hydroxide aqueous solution for 16 hours, and then soaked in deionized water for 16 hours to obtain a polyvinyl alcohol anion exchange membrane;

[0067] Step d: dopamine was dissolved in a 20 mmol / L Tris-HCl buffer solution, and hydrochloric acid was used to adjust the pH to 8.5 to obtain a dopamine Tris buffer solution, and the mass concentration of dopamine in the buffer solution was 0.8 g / L;

[0068] Step e: the polyvinyl alcohol anion exchange membrane to be modified was placed in the dopamine Tris buffer solution, and 4 mmol / L copper sulfate was added, and the reaction was stirred for 5 hours while maintaining air flow, wherein the copper sulfate can induce rapid polymerization of dopamine to form a negatively charged polydopamine electrolyte layer on the surface of the anion exchange membrane, and the modified anion exchange membrane was obtained after the reaction;

[0069] Step f: the modified anion exchange membrane was taken out and placed in a 10 g / L sodium chloride solution for use.

[0070] The specific operation parameters for treating ethylene alkali residue wastewater are as follows:

[0071] The above-mentioned ethylene alkali residue wastewater 20 t / / h first enters the adjusting tank, is mixed with nanofiltration concentrated water and homogeneous catalyst, and sulfuric acid is added to adjust the pH to 5, the homogeneous catalyst is copper catalyst, specifically copper sulfate, the concentration of copper metal ions in the mixed liquid is about 90 mg / L; the water from the adjusting tank is heated to a temperature of 150°C, then enters the wet oxidation reactor, the reaction temperature of the wet oxidation reactor is 185°C, the pressure is 3 MPa, the liquid space velocity is 1 h -1, gas-liquid volume ratio of 90:1; wet oxidation effluent is cooled to 65°C by heat exchange unit, then cooled to 45°C by cooler and enters the conditioning tank, at this time the wastewater COD is 1013 mg / L, total salt content is 26557 mg / L, sulfide is 0.2 mg / L, total nitrogen is 55 mg / L, sulfide removal rate is greater than 99%, COD removal rate is 93.8%, total nitrogen removal rate is 77.4%, effluent enters electrodialysis I.

[0072] electrodialysis I treatment time is 1.2h, current density is 30mA / cm 2 , after treatment, the dilution liquid in electrodialysis I has COD concentration of 1538 mg / L, total salt content of 4386 mg / L, dilution liquid flow accounts for 60% of the water flow of electrodialysis I; anode concentrate has COD concentration of 398 mg / L, total salt content of 75196 mg / L, anode concentrate accounts for 21% of the water flow of electrodialysis I; cathode concentrate has COD concentration of 35 mg / L, total salt content of 42810 mg / L, cathode concentrate accounts for 19% of the water flow of electrodialysis I; the total sulfate ion selective permeability of electrodialysis I is 89.3%, the chloride ion selective permeability is 91.8%, and the organic matter interception rate is 91.1%; the cathode concentrate of electrodialysis I enters nanofiltration treatment, nanofiltration water production rate is 65%, copper catalyst interception rate is 94%, copper catalyst is returned to the conditioning tank with nanofiltration concentrated water for recycling, and the total loss rate of catalyst is 14.1%, and the catalyst in the conditioning tank is supplemented at 12.7 mg / L.

[0073] electrodialysis I dilution liquid enters the conditioning tank, sodium hydroxide is added to adjust the pH to 7, the total salt content becomes 4489 mg / L, the primary biochemical adopts contact oxidation tank, the sludge adopts ordinary biological bacteria, the residence time is 32h, the effluent COD is reduced to 460 mg / L; the primary biochemical effluent enters the secondary biochemical, and the reverse osmosis water also enters the secondary biochemical, the secondary biochemical adopts A / O process, the sludge adopts ordinary biological bacteria, the residence time is 20h, the effluent COD is 48 mg / L, the total salt content is 3255 mg / L, and it enters the reuse water tank.

[0074] electrodialysis II treatment time is 1h, current density is 30mA / cm 2COD concentration of the concentrated solution in the post-treatment electrodialysis II is 36 mg / L, total salt content is 200345 mg / L, water volume of the concentrated solution accounts for 26% of the total water volume, COD concentration of the diluting solution is 245 mg / L, total salt content is 17520 mg / L, water volume of the diluting solution accounts for 74% of the total water volume; the diluting solution of the electrodialysis II enters ozone catalytic oxidation, ozone dosage concentration is 100 mg / L, reaction time is 30 min, and the effluent COD is as low as 98 mg / L, which enters reverse osmosis; the water production rate of the reverse osmosis is 64%, the salt content of the produced water is less than 2000 mg / L, which enters secondary biochemical treatment and is used for diluting salt in the secondary biochemical treatment, and the concentrated water is returned to the electrodialysis II for reprocessing; the concentrated solution of the electrodialysis II enters a nitrate crystallizer, the temperature of the nitrate crystallizer is controlled at 88 ℃, and the crystallization obtains product sodium sulfate with a purity of 99.7%, and the remaining mother liquor returns to the electrodialysis I for secondary processing, sodium chloride in the mother liquor is still in a dissolved state, which does not affect the purity of the sodium sulfate product, and when the concentration of sodium chloride in the mother liquor rises to 320 g / L after multiple cycles, the sodium chloride is discharged in the form of a mixed salt.

[0075] It can be known from the embodiment that the process method of the application realizes efficient operation of homogeneous catalytic wet oxidation, and in view of the problems of high COD, high toxicity and difficult degradation of ethylene lye waste water, the COD removal rate of the wet oxidation unit in the embodiment is as high as 93.8%, the total nitrogen removal rate is 77.4%, and the sulfide removal rate is greater than 99%, so that the ethylene lye waste water is finally zero discharged, and high-purity sodium sulfate is prepared. At the same time, the modified electrodialysis plays an important role in the embodiment, which solves the problem of loss of homogeneous catalyst in combination with nanofiltration technology.

[0076] Example 2

[0077] By using Figure 1 the process shown in the figure to treat certain ethylene lye waste water

[0078] A certain ethylene lye waste water, and the water quality is as follows: COD 27500 mg / L, chloride ion 2025 mg / L, sulfate ion 8500 mg / L, total salt content is 25120 mg / L, sulfide 3000 mg / L, ammonia nitrogen 45 mg / L, total nitrogen 400 mg / L, pH 12.4, and the water inflow is 20 t / h.

[0079] The process route and implementation steps of the ethylene alkali residue wastewater in this example are the same as those in Example 1. The electrodialysis I and the electrodialysis II in the process route are both modified electrodialysis, wherein the anion exchange membrane is a modified anion exchange membrane, and the cation exchange membrane is a general cation exchange membrane (Hefei Kaijie Polymer Co., Ltd., China, model CJ-MC-3). In the preparation process of the modified anion exchange membrane, in addition to the positive electric amine compound in step a being polyethyleneimine, the mass ratio of polyethyleneimine to polyvinyl alcohol being 0.5:1, the mass ratio of β-cyclodextrin to polyvinyl alcohol being 0.3:1, the mass ratio of glutaraldehyde to polyvinyl alcohol being 0.06:1, and the reaction time of step a being 10 h, the others are the same as in Example 1.

[0080] The specific operation parameters for treating the ethylene alkali residue wastewater are as follows:

[0081] The above-mentioned ethylene alkali residue wastewater 20 t / h first enters the adjustment tank, is mixed with the nanofiltration concentrated water and the homogeneous catalyst in the adjustment tank, and sulfuric acid is added to adjust the pH to 5. The homogeneous catalyst is a copper catalyst, specifically copper sulfate. After mixing, the concentration of copper metal ions in the liquid is about 120 mg / L; the wastewater temperature is raised to 150°C after heat exchange of the adjustment tank effluent, and then the wastewater enters the wet oxidation reactor. The reaction temperature of the wet oxidation reactor is 190°C, the pressure is 3 MPa, the liquid space velocity is 1 h -1 , and the gas-liquid volume ratio is 100:1; the wet oxidation effluent is cooled to 65°C by a heat exchange unit, and then cooled to 45°C by a cooler before entering the adjustment tank. At this time, the wastewater COD is 1155 mg / L, the total salt content is 33540 mg / L, the sulfide is 0.3 mg / L, the total nitrogen is 67 mg / L, the sulfide removal rate is greater than 99%, the COD removal rate is 94.5%, and the total nitrogen removal rate is 79.2%. The effluent enters the electrodialysis I.

[0082] The treatment time of the electrodialysis I is 1.3 h, the current density is 35 mA / cm 2 , and the COD concentration of the dilute liquid in the electrodialysis I after treatment is 2003 mg / L, the total salt content is 4870 mg / L, the dilute liquid flow accounts for 52% of the water flow of the electrodialysis I; the COD concentration of the anode concentrated liquid is 407 mg / L, the total salt content is 81120 mg / L, the anode concentrated liquid accounts for 25% of the water flow of the electrodialysis I; the COD concentration of the cathode concentrated liquid is 50 mg / L, the total salt content is 46639 mg / L, and the cathode concentrated liquid accounts for 23% of the water flow of the electrodialysis I; the total sulfate ion selective permeation rate of the electrodialysis I is 91.6%, the chloride ion selective permeation rate is 93.8%, and the organic matter interception rate is 90.2%; the cathode concentrated liquid of the electrodialysis I enters the nanofiltration treatment, the nanofiltration water production rate is 60%, the copper catalyst interception rate is 93%, the copper catalyst is returned to the adjustment tank with the nanofiltration concentrated water for recycling, the total catalyst loss rate is 12.8%, and the adjustment tank catalyst is supplemented at 15.3 mg / L.

[0083] The dilute solution of the electrodialysis I enters a regulating tank, sodium hydroxide is added to adjust the pH to 7, the total salt content becomes 4980 mg / L, the first-stage biochemical treatment adopts a contact oxidation tank, ordinary biological bacteria are used for sludge, and the residence time is 36 h, the effluent COD is reduced to 580 mg / L; the effluent of the first-stage biochemical treatment enters the second-stage biochemical treatment, the reverse osmosis water also enters the second-stage biochemical treatment, the second-stage biochemical treatment adopts an SBR process, ordinary biological bacteria are used for sludge, and the residence time is 20 h, the effluent COD is 55 mg / L, the total salt content is 3320 mg / L, and the effluent enters a reuse water tank.

[0084] The treatment time of the electrodialysis II is 1 h, and the current density is 35 mA / cm 2 After treatment, the COD concentration of the concentrated solution in the electrodialysis II is 38 mg / L, the total salt content is 196840 mg / L, the concentrated water accounts for 30% of the total water, the COD concentration of the dilute solution is 233 mg / L, the total salt content is 15530 mg / L, and the dilute water accounts for 70% of the total water; the dilute solution of the electrodialysis II enters ozone catalytic oxidation, the ozone adding concentration is 110 mg / L, the reaction time is 30 min, the effluent COD is as low as 85 mg / L, and the effluent enters reverse osmosis; the reverse osmosis water production rate is 66%, the salt content of the produced water is less than 1800 mg / L, the produced water enters the second-stage biochemical treatment and is used for diluting the salt in the second-stage biochemical treatment, the concentrated water is returned to the electrodialysis II for re-treatment; the concentrated solution of the electrodialysis II enters a nitrate crystallizer, the temperature of the nitrate crystallizer is controlled at 92℃, the crystallization product is sodium sulfate with a purity of 99.6%, the remaining mother liquor is returned to the electrodialysis I for secondary treatment, the sodium chloride in the mother liquor is still in a dissolved state, and does not affect the purity of the sodium sulfate product; when the sodium chloride concentration in the mother liquor is increased to 300 g / L after multiple cycles, the sodium chloride is discharged in the form of a mixed salt.

[0085] It can be known from the embodiment that the process method of the application can treat ethylene alkali residue wastewater with a higher concentration, finally realizes zero discharge of ethylene alkali residue wastewater, and prepares high-purity sodium sulfate.

[0086] Example 3

[0087] The water quality of the treated ethylene alkali residue wastewater is the same as that of example 1, the process route, implementation steps and reaction parameters are also the same as those of example 1, only the type of the catalyst is different, an iron salt catalyst is used, and the treatment effect of the wet oxidation unit is shown in Table 1.

[0088] Example 4

[0089] The water quality of the treated ethylene alkali residue wastewater is the same as that of example 1, the process route, implementation steps and reaction parameters are also the same as those of example 1, only the type of the catalyst is different, a nickel salt catalyst is used, and the treatment effect of the wet oxidation unit is shown in Table 1.

[0090] Example 5

[0091] The water quality of the ethylene caustic sludge wastewater treated is the same as that of Example 1, the process route, implementation steps, and reaction parameters are also the same as those of Example 1, and only the type of catalyst is different, a zinc salt catalyst is used, and the treatment effect of the wet oxidation unit is shown in Table 1.

[0092] Comparative Example 1

[0093] The water quality of the ethylene caustic sludge wastewater treated is the same as that of Example 1, the process route, implementation steps, and reaction parameters are also the same as those of Example 1, and only the type of catalyst is different, a zinc salt catalyst is used, and the treatment effect of the wet oxidation unit is shown in Table 1.

[0094] Table 1

[0095]

[0096] Comparative Example 2

[0097] The water quality of the ethylene caustic sludge wastewater treated in Comparative Example 2 is the same as that of Example 1, and the process route and implementation steps are also the same as those of Example 1, and the difference is that the anion and cation exchange membranes of the electrodialysis I are general type membranes and are not modified, the anion exchange membrane is a product of Japan Asahi Glass Company (SELEMION AMV), and the cation exchange membrane is a product of China Hefei Kaitai Polymer Co., Ltd. (model CJ-MC-3).

[0098] Specifically, as in Example 1, the wastewater is adjusted by the adjusting tank and then enters the wet oxidation reactor, and the effluent is cooled by the cooler and then enters the ordinary electrodialysis I, at this time, the wastewater COD is 1013 mg / L, and the total salt content is 26557 mg / L; the treatment time of the ordinary electrodialysis I is 1.2 h, the current density is 30 mA / cm 2, the COD concentration of the dilute liquid of the electrodialysis I is 1296 mg / L, the total salt content is 8631 mg / L, the dilute liquid flow accounts for 60% of the water flow of the electrodialysis I; the COD concentration of the anode concentrated liquid is 1075 mg / L, the total salt content is 68196 mg / L, the anode concentrated liquid accounts for 21% of the water flow of the electrodialysis I; the COD concentration of the cathode concentrated liquid is 51 mg / L, the total salt content is 37141 mg / L, the cathode concentrated liquid accounts for 19% of the water flow of the electrodialysis I; the total sulfate ion selective permeation rate of the electrodialysis I is 79.3%, the chloride ion selective permeation rate is 81.8%, which is obviously decreased compared with Example 1, and the membrane flux is obviously decreased, which may be related to the membrane blockage. In addition, the organic matter retention rate is reduced to 76.8%, which indicates that a large amount of negatively charged organic matter passes through the anion membrane, increasing the possibility of membrane blockage. The dilute liquid of the electrodialysis I enters the adjusting tank, sodium hydroxide is added to adjust the pH to 7, the total salt content becomes 8785 mg / L, the primary biochemical treatment adopts the contact oxidation tank, the sludge adopts the ordinary biological strain, the residence time is 32 h, the effluent COD is reduced to 865 mg / L; the primary biochemical effluent enters the secondary biochemical treatment, and the reverse osmosis water also enters the secondary biochemical treatment, the secondary biochemical treatment adopts the A / O process, the sludge adopts the ordinary biological strain, the residence time is 16 h, the effluent COD is 655 mg / L, and the total salt content is 7356 mg / L, which cannot be reused and still needs further treatment. The reason is that the high salt concentration leads to the poor treatment efficiency of the primary biochemical treatment and the secondary biochemical treatment.

[0099] From the present comparative example, it can be seen that the electrodialysis I adopts the unmodified anion and cation exchange membranes, which cannot effectively separate the organic matter and the salt, thereby leading to the high salt content of the biochemical unit, and the wastewater cannot be treated for reuse.

[0100] Comparative Example 3

[0101] The ethylene alkali residue wastewater in Comparative Example 3 is treated in the same way as in Example 1, the process route and the implementation steps are also the same as in Example 1, the electrodialysis I is modified in the same way as in Example 1, and the difference is that the anion and cation exchange membranes of the electrodialysis II are general type membranes and are not modified, the anion exchange membrane adopts the product (SELEMION AMV) of Japan Asahi Glass Company, and the cation exchange membrane adopts the product (model CJ-MC-3) of China Hefei Kaijie Polymer Co., Ltd.

[0102] Specifically: same as example 1, after the wastewater is treated by wet oxidation and electrodialysis I, the COD concentration of the anode concentrated solution is 398 mg / L, the total salt content is 75196 mg / L, the anode concentrated solution accounts for 21% of the water flow of the electrodialysis I, the COD concentration of the cathode concentrated solution is 35 mg / L, the total salt content is 42810 mg / L, the cathode concentrated solution accounts for 19% of the water flow of the electrodialysis I, the cathode concentrated solution is treated by nanofiltration, and the produced water is mixed with the anode concentrated solution and then enters the electrodialysis II; the treatment time of the electrodialysis II is 1 h, and the current density is 30 mA / cm 2 , the COD concentration of the concentrated solution in the electrodialysis I after treatment is 135 mg / L, the total salt content is 148230 mg / L, the concentrated water accounts for 26% of the total water flow, the COD concentration of the dilute solution is 211 mg / L, the total salt content is 35830 mg / L, and the dilute solution accounts for 74% of the total water flow; the dilute solution of the electrodialysis II enters ozone catalytic oxidation, the ozone addition concentration is 100 mg / L, the reaction time is 30 min, the COD of the effluent is as low as 83 mg / L, and the effluent enters the reverse osmosis; the water production rate of the reverse osmosis is 64%, and the salt content of the produced water is 4019 mg / L, which is relatively high, and cannot play a good role in diluting the salt, so that after being mixed into the secondary biochemical unit, the salt content of the effluent is as high as 4155 mg / L, the COD is 73 mg / L, and the effluent cannot meet the reuse index; the salt content of the concentrated solution of the electrodialysis II is relatively low, which affects the crystallization efficiency of the nitrate crystallizer, and the COD slightly increases, and finally the purity of the product sodium sulfate is 98.9%.

[0103] It can be known from the present comparative example that the electrodialysis II uses unmodified anion and cation exchange membranes, and the separation ability of the organic matter and the salt is poor, the anion exchange membrane is easily polluted by the organic matter, the salt content of the dilute solution of the electrodialysis II is high, the biochemical unit cannot play a good dilution role, and the effluent of the biochemical treatment section cannot meet the reuse requirement. At the same time, the organic matter content of the concentrated solution of the electrodialysis II is high and the salt content is low, which leads to the decrease of the freezing crystallization efficiency of the salt treatment section, and the purity of the prepared sodium sulfate decreases.

Claims

1. A process for treating ethylene caustic sludge wastewater, comprising a wet oxidation section, a biochemical treatment section and a salt treatment section; The wet oxidation section comprises a conditioning tank, a heat exchange unit, a wet oxidation reactor, a cooler, an electrodialysis I and a nanofiltration; the ethylene caustic sludge wastewater first enters the conditioning tank, is mixed with nanofiltration concentrated water and a homogeneous catalyst, and is acidified to adjust the pH, then is heated by the heat exchange unit and enters the wet oxidation reactor; the water from the wet oxidation reactor enters the heat exchange unit to be cooled, then enters the cooler, and then enters the electrodialysis I; the dilute liquid from the electrodialysis I enters the conditioning tank of the biochemical treatment section, the anode concentrated liquid from the electrodialysis I enters the electrodialysis II of the salt treatment section, the cathode concentrated liquid from the electrodialysis I enters the nanofiltration, the concentrated water from the nanofiltration enters the conditioning tank, and the product water from the nanofiltration enters the electrodialysis II; The biochemical treatment section comprises a conditioning tank, a primary biochemical treatment, a secondary biochemical treatment and a reuse water tank in sequence; The salt treatment section comprises electrodialysis II, nitrate crystallizer, ozone catalytic oxidation and reverse osmosis; the concentrated solution of the electrodialysis II enters the nitrate crystallizer, the dilute solution of the electrodialysis II enters the ozone catalytic oxidation; the effluent of the ozone catalytic oxidation enters the reverse osmosis, the concentrated water of the reverse osmosis is sent back to the electrodialysis II, and the produced water of the reverse osmosis enters the secondary biochemical unit of the biochemical treatment section; The product sodium sulfate is obtained from the nitrate crystallizer, and the remaining mother liquor is returned to the electrodialysis II or is discharged as a mixed salt; The electrodialysis I and the electrodialysis II are composed of anion exchange membranes and cation exchange membranes, wherein the anion exchange membranes are modified anion exchange membranes, and the cation exchange membranes are general cation exchange membranes; the modified anion exchange membranes are prepared by the following steps: Step a: polyvinyl alcohol is added to water to prepare a polyvinyl alcohol aqueous solution, then a positively charged amine compound, β-cyclodextrin and a crosslinking agent are added to the solution, an inorganic acid is added to adjust the pH, and then the mixture is stirred and reacted to obtain a casting solution; Step b: the casting solution obtained in step a is cast on a horizontal panel and dried to obtain a base membrane; Step c: the base membrane obtained in step b is washed, alkalinized in a lye, and then soaked in water to obtain a polyvinyl alcohol anion exchange membrane; Step d: dopamine is dissolved in a Tris-HCl buffer solution, and the pH is adjusted by hydrochloric acid to obtain a dopamine Tris buffer solution; Step e: the anion exchange membrane obtained in step c is placed in the dopamine Tris buffer solution, copper sulfate is added, and the mixture is stirred under the condition of air flow to obtain a modified anion exchange membrane.

2. The process of claim 1, wherein, The positively charged amine compound is selected from one or more of 2,3-epoxypropyltrimethylammonium chloride, polyethyleneimine, polyepoxy chloropropane amine and quaternized chitosan, and the mass ratio of the positively charged amine compound to polyvinyl alcohol is 0.1:1-0.6:

1.

3. The process of claim 1, wherein, The mass ratio of the β-cyclodextrin to polyvinyl alcohol is 0.05:1-0.4:

1.

4. The process of claim 1, wherein, The crosslinking agent is glutaraldehyde, and the mass ratio of the crosslinking agent to polyvinyl alcohol is 0.01:1-0.1:

1.

5. The process of claim 1, wherein, In step a, the pH of the solution is adjusted to 4-6, the mass fraction of the polyvinyl alcohol aqueous solution is 5%-15%, and the mixing and reaction time of the positively charged amine compound, the β-cyclodextrin and the crosslinking agent is 4-16 h.

6. The process of claim 1, wherein, The alkalinization is performed by using a 0.5-3 mol / L sodium hydroxide aqueous solution, and the alkalinization time is 12-24 h.

7. The process of claim 1, wherein, In step d, the mass concentration of dopamine is 0.4-4 g / L, and the pH range adjusted by hydrochloric acid is 8-9.

8. The process of claim 1, wherein, In the conditioning tank, the pH is adjusted to 2-6 by adding acid.

9. The process of claim 1, wherein, The heat exchange unit is composed of multiple heat exchangers, and the wet oxidation reactor outlet water and the adjusting tank outlet water are subjected to heat exchange, and after multiple heat exchange, the temperature of the adjusting tank outlet water is increased to 130-160 DEG C, and the temperature of the wet oxidation reactor outlet water is decreased to 50-75 DEG C.

10. The process of claim 1, wherein, The homogeneous catalyst is selected from one or more of copper, iron, manganese, zinc and nickel, and exists in the form of a metal salt compound or a complex and is dissolved in a liquid phase.

11. The process of claim 1, wherein, The wet oxidation reactor has a reaction temperature of 150-250 DEG C, a reaction pressure of 1-5 MPa, a liquid space velocity of 0.25-4 h -1 -1, and a gas-liquid volume ratio of 20:1-500:

1.

12. The process of claim 1, wherein, The treatment time of the electrodialysis I and the electrodialysis II is 0.5-3h, and the current density is 1-80mA / cm 2 .

13. The process of claim 1, wherein, The primary biochemical treatment adopts a pure aerobic process, and is selected from one of a BAF, MBR, contact oxidation tank and MBBR aerobic process; and the secondary biochemical treatment adopts an anoxic-aerobic process, and is selected from one of A / O or SBR.

14. The process of claim 1, wherein, The reverse osmosis operating pressure is 1.0-3.0 Mpa, and the water production rate is 50%-80%.

15. The process of claim 1, wherein, The nitrate crystallizer operating temperature is controlled at 40-110 DEG C.

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