Method and system for treating acrylonitrile ammonium sulfate wastewater

Abstract

The invention provides an acrylonitrile ammonium sulfate wastewater treatment method and system, and the treatment method comprises the following steps: 1, carrying out evaporative crystallization on acrylonitrile ammonium sulfate wastewater to obtain an evaporation condensate, a crystallized solid and an evaporation concentrated solution; step 2, mixing the evaporation concentrated solution with a reverse demulsifier; step 3, carrying out first oil-water separation on the mixed solution obtained in the step 2 under the action of gravity settling to obtain an oil phase and a water phase; 4, the water phase is subjected to secondary oil-water separation, the secondary oil-water separation mode is evaporation, after evaporation, residual mixed liquid is mixed with the acrylonitrile ammonium sulfate wastewater, and then evaporative crystallization is conducted circularly. According to the invention, the evaporation type second oil-water separator and the first oil-water separator are connected in series to carry out deep oil-water separation, so that residual small-particle-size emulsified oil and dissolved oil in a water phase are deeply removed, and the problem that an ammonium sulfate product is colored is fundamentally solved.

Description

Technical Field

[0001] The present invention belongs to the technical field of petrochemical industry, and particularly relates to a method and a system for treating acrylonitrile ammonium sulfate wastewater. Background Art

[0002] At present, domestic refineries all adopt the propylene ammoxidation process to produce acrylonitrile. During the production process, the unreacted ammonia gas discharged from the reactor enters the quench tower and is neutralized by sulfuric acid, thus generating a large amount of dilute ammonium sulfate solution. Production enterprises often use the evaporation crystallization method to treat the dilute ammonium sulfate solution. During the evaporation crystallization process, crystalline solids, evaporation condensate and evaporation concentrate are generated. The crystalline solid ammonium sulfate can be used as a fertilizer; the organic matter and ammonia nitrogen content in the evaporation condensate are relatively low, and can be recycled or discharged after treatment; the evaporation concentrate is of the O / W type, and complex components such as high-concentration polyacrylonitrile, aromatic compounds, and carbonyl compounds are dissolved in the water phase in the form of emulsified oil and dissolved oil. The particle size of the emulsified oil and dissolved oil droplets is generally less than 2 μm, and the particle size of the dissolved oil reaches below 0.1 μm, even reaching the nanometer level. It is difficult to achieve oil-water separation by conventional sewage treatment means.

[0003] At present, most refineries use gravity sedimentation (vertical oil removal tank) to treat the evaporation concentrate (oil-water separation). The oil phase is treated by incineration, and the water phase is recycled back to the evaporator. However, due to the poor separation effect of gravity sedimentation, the ammonium sulfate content in the oil phase is high. Taking a certain refinery as an example, the ammonium sulfate concentration in the concentrated liquid at the outlet of its evaporation crystallizer is as high as about 20%, resulting in problems such as increased pressure difference of the bag filter in the wastewater incineration unit, crystallization blockage, and frequent tripping of the incinerator. At the same time, there are also problems such as high oil content in the circulating water phase and colored crystalline ammonium sulfate products.

[0004] The acrylonitrile supporting ammonium sulfate unit of Daqing Petrochemical uses a polymer separator to separate oil and water from the ammonium sulfate concentrated liquid sent by the evaporation crystallizer. The separator is a gravity sedimentation tank specially designed and modified, with inclined partition plates and separation baffles inside. The inclined partition plates increase the separation power, and the separation baffles play the role of separation areas (feed area and sedimentation area). During separation, the heavy component ammonium sulfate solution enters the sedimentation chamber and is pumped to the evaporation crystallizer through the discharge port at the bottom of the sedimentation chamber to recover ammonium sulfate crystals. The light component polymer overflows from the overflow port at the high point of the separator, is diluted by water injection through the spray pipe on the upper part of the polymer separator, enters the polymer mixer, and a certain amount of dilution water is added in the mixer, and finally sent to the incinerator of the acrylonitrile unit for incineration (Yang Daming. Research on new equipment for solving polymer blockage in ammonium sulfate unit [J]. Refining and Chemical Industry, 2007(04):30 - 32 + 58.). This method has been specially designed from the internal structure of the oil-water separator and achieved a certain oil-water separation effect, but there is still a relatively serious phenomenon of mutual entrainment between the two phases, and it is difficult to fundamentally solve the problem of incomplete oil-water separation.

[0005] In addition to gravity sedimentation technology, enterprises and research and development units have also developed technologies such as extraction crystallization, extraction for oil removal, wet catalytic oxidation, membrane separation, and bioelectrochemistry for treating acrylonitrile ammonium sulfate wastewater.

[0006] CN110330035A discloses a method for recovering ammonium sulfate from the evaporation concentrate of acrylonitrile ammonium sulfate solution by using multi-stage extraction crystallization technology. The extractant is one or a mixture of monohydric alcohols and dihydric alcohols with a carbon number ≤ 4. After the extractant is mixed with the concentrate, the polarity of the solution is reduced, thereby reducing the solubility of ammonium sulfate in the solution and promoting the crystallization of ammonium sulfate. At the same time, the dissolution ability of the solution system for polymers is significantly improved, and the adsorption of polymers by crystals during the ammonium sulfate crystallization process is reduced. After the ammonium sulfate is crystallized and separated, the extractant is used to wash the polymers adsorbed and wrapped on the crystal surface, realizing the efficient separation of ammonium sulfate and polymers. This method solves the problems of blockage in the incineration unit and colored ammonium sulfate products from the perspective of extraction crystallization. However, an additional distillation section is required for subsequent separation of the extractant, which significantly increases equipment investment and energy consumption.

[0007] CN111423433A discloses a preparation method of an extractant and its application in treating ammonium sulfate wastewater. The extractant includes fatty amines and aromatic amines. The structure of the fatty amine is The structure of the aromatic amine is This mixed extractant has good selective solubility for the heavy components and polymers in the ammonium sulfate solution, can extract the heavy components and polymers from the ammonium sulfate solution into the organic phase, realize the efficient separation of ammonium sulfate solution and heavy component waste oil, and significantly improve the quality of ammonium sulfate products. However, this method also has the problem of extractant distillation separation, which greatly increases the process cost and has poor economy.

[0008] CN104108779A discloses a wet catalytic oxidation technology for treating ammonium sulfate wastewater. Using the ammonium sulfate wastewater generated in the acrylonitrile production process as raw material, a multiphase catalyst and a fixed-bed reactor are used. The wastewater, carrier gas, and catalyst are fully contacted and reacted in the reactor. The reaction temperature is 200 - 300 °C, the reaction pressure is 5 - 10 MPa, and the residence time is 10 - 120 min. The catalyst uses a noble metal catalyst supported on zirconia or alumina ceramic foam plates. After treatment, the COD of the wastewater is reduced by 90.8%. The wet catalytic oxidation technology has the advantages of high treatment efficiency and less secondary pollution, but it needs to be carried out under high temperature and high pressure conditions, with high energy consumption, and will produce organic acid intermediate products, causing corrosion to equipment. At the same time, there are also problems such as high costs for catalyst preparation, regeneration, and heavy metal ion pollution of the catalyst.

[0009] CN105366754A discloses a technology for treating ammonium sulfate wastewater using a multi-stage membrane contactor. The membrane materials are hydrophobic polypropylene, polyvinylidene fluoride, and polytetrafluoroethylene, and the morphology is hollow fiber membrane and flat membrane. After treatment, the ammonia nitrogen removal rate of the wastewater reaches 98.7%, and at the same time, a high-concentration ammonium sulfate solution is obtained. The solution is further evaporated, concentrated, and crystallized to obtain an industrial-grade ammonium sulfate product.

[0010] The membrane filtration technology is mainly used to remove free ammonia and floating oil. Treating acrylonitrile ammonium sulfate wastewater rich in high-viscosity polymer-contaminated oil will quickly clog the membrane pores and force the device to stop. Therefore, this technology is only limited to treating low-viscosity dilute solutions.

[0011] CN105645586A discloses a continuous flow three-stage bioelectricity generation and desalination technology for treating ammonium sulfate refining wastewater. The bioelectric desalination device consists of an anode chamber, a cathode chamber, a cation exchange membrane, an anion exchange membrane, an aeration device, and a facultative chamber, etc. After the cultivation stage, the acclimation stage, and continuous operation, the aeration device is started. The ammonium sulfate wastewater is treated in turn through the anode chamber - facultative chamber - cathode chamber - desalination chamber. A stable current output is obtained during the treatment process, and the ammonium sulfate removal rate reaches more than 80%, realizing three functions of pollutant degradation, electricity generation, and desalination. This method uses microorganisms to degrade organic matter, converts chemical energy into electrical energy, realizes the resource recycling of organic waste, and provides new ideas and development directions for chemical wastewater treatment. However, the cultivation of biological flora is difficult and costly, and it is difficult to achieve efficient degradation of complex polymers in acrylonitrile ammonium sulfate wastewater.

[0012] CN104986889A discloses a combined process for treating fracturing and drilling wastewater, specifically separation - filtration - aeration - coagulation sedimentation - adsorption filtration. In the first separation process, the gravity sedimentation method is used to separate the oil-water two phases, and it is mentioned that the oil-water separation effect can be enhanced by adding a reverse demulsifier. This separation process only plays a pretreatment role, and the water can meet the standard when the oil content is ≤580mg / L. The wastewater purification is mainly completed by the subsequent processes. This technology uses a large number of chemicals and has a complex process flow, and is not suitable for treating acrylonitrile ammonium sulfate wastewater.

[0013] Therefore, further research on the treatment of acrylonitrile ammonium sulfate wastewater is still needed in this field. Summary of the Invention

[0014] The main purpose of the present invention is to provide a method and system for treating acrylonitrile ammonium sulfate wastewater to solve the problem of difficult oil-water separation of acrylonitrile ammonium sulfate wastewater.

[0015] To achieve the above purpose, the present invention provides a method for treating acrylonitrile ammonium sulfate wastewater, including the following steps:

[0016] Step 1, evaporate and crystallize the acrylonitrile ammonium sulfate wastewater to obtain evaporation condensate, crystalline solid, and evaporation concentrate;

[0017] Step 2: Mix the evaporation concentrate with an inverse demulsifier.

[0018] Step 3: Perform the first oil-water separation on the mixture obtained in Step 2 under the action of gravity sedimentation to obtain an oil phase and a water phase.

[0019] Step 4: Perform a second oil-water separation on the water phase. The method of the second oil-water separation is evaporation. After evaporation, the remaining mixture is mixed with the acrylonitrile ammonium sulfate wastewater and then cycled for the evaporation crystallization.

[0020] In the method for treating acrylonitrile ammonium sulfate wastewater of the present invention, the ratio of the flow rate of the evaporation condensate to the flow rate of the acrylonitrile ammonium sulfate wastewater is 1:(1 - 5); the ratio of the flow rate of the evaporation concentrate to the flow rate of the acrylonitrile ammonium sulfate wastewater is 1:(1 - 3).

[0021] In the method for treating acrylonitrile ammonium sulfate wastewater of the present invention, the first oil-water separation is carried out in a horizontal separation tank, and the ratio of the height to the length of the horizontal separation tank is 1:(2 - 10).

[0022] In the method for treating acrylonitrile ammonium sulfate wastewater of the present invention, the ratio of the flow rate of the acrylonitrile ammonium sulfate wastewater to the flow rate of the oil phase is (1 - 5):1; the ratio of the flow rate of the water phase to the flow rate of the oil phase is (1 - 5):1.

[0023] In the method for treating acrylonitrile ammonium sulfate wastewater of the present invention, the evaporation obtains an oil-containing water phase and a remaining mixture. The oil-containing water phase is mixed with the evaporation concentrate and the inverse demulsifier, and the ratio of the flow rate of the oil-containing water phase to the flow rate of the water phase is 1:(3 - 10).

[0024] In the method for treating acrylonitrile ammonium sulfate wastewater of the present invention, the preparation method of the inverse demulsifier includes:

[0025] Step a: Perform a ring-opening polymerization reaction on azodinitrile and propylene oxide to obtain an azo polyether oil head.

[0026] Step b: Copolymerize the azo polyether oil head, ethylene oxide, and propylene oxide to obtain a block azo polyether.

[0027] Step c: Perform a cross-linking reaction on the block azo polyether under the action of a cross-linking agent to obtain a cross-linked polyether.

[0028] Step d: React the cross-linked polyether and quaternary ammonium salt under heating to obtain an oil-soluble inverse demulsifier.

[0029] The treatment method of acrylonitrile ammonium sulfate wastewater according to the present invention, wherein, the azo dinitrile is one of azobisisobutyronitrile, azobisisovaleronitrile, and azobisisoheptonitrile; the reaction of the azo dinitrile and propylene oxide is carried out under the action of a ring-opening polymerization catalyst and in an oil-soluble solvent, and the ring-opening polymerization catalyst is one of sodium hydroxide, potassium hydroxide, calcium hydroxide, and magnesium hydroxide; the oil-soluble solvent is one of acetone, methyl ethyl ketone, methyl isobutyl ketone, and tetrahydrofuranone.

[0030] The treatment method of acrylonitrile ammonium sulfate wastewater according to the present invention, wherein, the mass ratio of the azo dinitrile to propylene oxide is 2:1 - 8:1, and the dosage of the ring-opening polymerization catalyst is 0.05 - 0.3% of the total mass of the azo dinitrile and propylene oxide; the reaction temperature of the azo dinitrile and propylene oxide is 100 - 120 °C, and the reaction time is 1 - 3 h.

[0031] The treatment method of acrylonitrile ammonium sulfate wastewater according to the present invention, wherein, the reaction of the azo polyether oil head, ethylene oxide, and propylene oxide is carried out under the action of a ring-opening polymerization catalyst, the ring-opening polymerization catalyst is one of sodium hydroxide, potassium hydroxide, calcium hydroxide, and magnesium hydroxide, and the dosage of the ring-opening polymerization catalyst is 0.05 - 0.3% of the total mass of the azo polyether oil head, ethylene oxide, and propylene oxide.

[0032] The treatment method of acrylonitrile ammonium sulfate wastewater according to the present invention, wherein, the reaction temperature of the azo polyether oil head, ethylene oxide, and propylene oxide is 110 - 120 °C, the mass ratio of the azo polyether oil head to ethylene oxide is 1:2 - 1:5, and the mass ratio of the azo polyether oil head to propylene oxide is 1:8 - 1:12.

[0033] The treatment method of acrylonitrile ammonium sulfate wastewater according to the present invention, wherein, the cross-linking agent is epichlorohydrin, and the mass ratio of the block azo polyether to the cross-linking agent is 500:1 - 600:1.

[0034] The treatment method of acrylonitrile ammonium sulfate wastewater according to the present invention, wherein, the temperature of the cross-linking reaction is 60 - 80 °C, and the time is 1 - 3 h.

[0035] The treatment method of acrylonitrile ammonium sulfate wastewater according to the present invention, wherein, the quaternary ammonium salt is one of dodecyl trimethyl ammonium chloride, tetradecyl trimethyl ammonium bromide, and hexadecyl trimethyl ammonium chloride, and the dosage of the quaternary ammonium salt is 20 - 30% of the mass of the cross-linked polyether.

[0036] The treatment method of acrylonitrile ammonium sulfate wastewater according to the present invention, wherein, the temperature of heating in step d is 80 - 95 °C, and the reaction time is 3 - 5 h; the reaction mixture of the cross-linked polyether and the quaternary ammonium salt is subjected to oil-water separation, and the obtained oil phase is distilled to obtain an oil-soluble reverse demulsifier.

[0037] To achieve the above object, the present invention also provides a treatment system for acrylonitrile ammonium sulfate wastewater, comprising:

[0038] An evaporation crystallizer for evaporating and crystallizing acrylonitrile ammonium sulfate wastewater to obtain evaporation condensate, crystalline solid and evaporation concentrate;

[0039] A static mixer connected to the evaporation crystallizer for mixing the evaporation concentrate with an inverse demulsifier;

[0040] A first oil-water separator connected to the static mixer for performing the first oil-water separation on the mixed liquid of the static mixer under the action of gravity sedimentation to obtain an oil phase and a water phase;

[0041] A second oil-water separator, which is an evaporator, connected to the first oil-water separator and the evaporation crystallizer respectively for evaporating the water phase, and circulating the remaining mixed liquid after evaporation back to the evaporation crystallizer for evaporation and crystallization.

[0042] In the treatment system for acrylonitrile ammonium sulfate wastewater of the present invention, the inverse demulsifier is prepared by the following steps:

[0043] Step a, subjecting azodinitrile to ring-opening polymerization reaction with propylene oxide to obtain an azo polyether oil head;

[0044] Step b, copolymerizing the azo polyether oil head, ethylene oxide and propylene oxide to obtain a block azo polyether;

[0045] Step c, subjecting the block azo polyether to crosslinking reaction under the action of a crosslinking agent to obtain a crosslinked polyether;

[0046] Step d, reacting the crosslinked polyether with a quaternary ammonium salt under heating to obtain an oil-soluble inverse demulsifier.

[0047] Advantages of the present invention:

[0048] The present invention adopts a series connection of an evaporation-type second oil-water separator and a first oil-water separator for deep oil-water separation, deeply removing the micro-sized emulsified oil and dissolved oil remaining in the water phase, and fundamentally solving the problem of colored ammonium sulfate products.

[0049] The oil-soluble inverse demulsifier provided by the present invention has the characteristics of good oil-water stratification effect of non-ionic polyether and fast oil removal rate of polyquaternary ammonium salt, can quickly break the double electric layer balance at the oil-water interface, promote the coalescence of oil droplets, achieve efficient and deep demulsification, and significantly improve the oil-water separation effect.

[0050] The reverse demulsifier provided by the present invention has good oil solubility and better solubility in the upper oil phase of acrylonitrile ammonium sulfate wastewater. When used to treat ammonium sulfate wastewater, it dissolves in the oil phase, enters the incinerator with the oil phase, and does not pollute the water phase, ensuring the quality of ammonium sulfate products while achieving efficient demulsification and oil removal. BRIEF DESCRIPTION OF THE DRAWINGS

[0051] Figure 1 It is a schematic diagram of an acrylonitrile ammonium sulfate wastewater treatment system in an embodiment of the present invention.

[0052] Figure 2 It is a schematic diagram of an acrylonitrile ammonium sulfate wastewater treatment system for a comparative example.

[0053] Among them, the reference numerals:

[0054] 1 Evaporation crystallizer

[0055] 2 Static mixer

[0056] 3, 3a First oil-water separator

[0057] 4 Second oil-water separator

[0058] 5 Thickener

[0059] 6 Solid-liquid centrifuge

[0060] 7 Oil-water mixer SPECIFIC EMBODIMENTS

[0061] The technical solutions of the present invention are described in detail below. The following embodiments are implemented on the premise of the technical solutions of the present invention, and the detailed implementation processes are given. However, the protection scope of the present invention is not limited to the following embodiments. For the structures or experimental methods without specific conditions noted in the following embodiments, they are usually in accordance with conventional conditions.

[0062] Refineries generally use the propylene ammoxidation process to produce acrylonitrile. During the production process, the unreacted ammonia discharged from the reactor enters the quench tower and is neutralized by sulfuric acid, thus generating a large amount of dilute ammonium sulfate solution. The acrylonitrile ammonium sulfate wastewater of the present invention is this dilute ammonium sulfate solution. The present invention provides a treatment method for this acrylonitrile ammonium sulfate wastewater, including the following steps:

[0063] Step 1, evaporating and crystallizing the acrylonitrile ammonium sulfate wastewater to obtain evaporation condensate, crystalline solids, and evaporation concentrate;

[0064] Step 2, mixing the evaporation concentrate with a reverse demulsifier;

[0065] Step 3, performing the first oil-water separation on the mixed solution obtained in Step 2 under the action of gravity sedimentation to obtain an oil phase and a water phase;

[0066] Step 4, the aqueous phase undergoes a second oil-water separation, and the method of the second oil-water separation is evaporation. After evaporation, the remaining mixed liquid is mixed with the acrylonitrile ammonium sulfate wastewater and then cycled for the evaporation crystallization.

[0067] The present invention also provides a treatment system for acrylonitrile ammonium sulfate wastewater, which can be used for the above-mentioned treatment method of acrylonitrile ammonium sulfate wastewater, including:

[0068] An evaporation crystallizer for evaporating and crystallizing acrylonitrile ammonium sulfate wastewater to obtain evaporation condensate, crystalline solids, and evaporation concentrate;

[0069] A static mixer connected to the evaporation crystallizer for mixing the evaporation concentrate with an inverse demulsifier;

[0070] A first oil-water separator connected to the static mixer for performing a first oil-water separation on the mixed liquid of the static mixer under the action of gravity sedimentation to obtain an oil phase and an aqueous phase;

[0071] A second oil-water separator, which is an evaporator, connected to the first oil-water separator and the evaporation crystallizer respectively for evaporating the aqueous phase, and the remaining mixed liquid after evaporation is cycled back to the evaporation crystallizer for evaporation crystallization.

[0072] By introducing an inverse demulsifier into the evaporation concentrate and combining with the secondary oil-water separation technology, the present invention can achieve a deep separation of the oil and water phases of the ammonium sulfate evaporation concentrate, extend the operation cycle of the device, reduce the loss of ammonium sulfate, and improve the quality of ammonium sulfate products.

[0073] Please refer to Figure 1 , the acrylonitrile ammonium sulfate wastewater of the present invention is first subjected to evaporation crystallization to obtain evaporation condensate, crystalline solids, and evaporation concentrate.

[0074] In one embodiment, the acrylonitrile ammonium sulfate wastewater of the present invention is transported to an evaporation crystallizer 1 for evaporation crystallization. As described above, the acrylonitrile ammonium sulfate wastewater of the present invention is produced by sulfuric acid neutralizing the unreacted ammonia in the acrylonitrile ammoxidation section in a quench tower, and the mass concentration of ammonium sulfate is, for example, 15-25%. The present invention does not particularly limit the conditions of evaporation crystallization. In one embodiment, the ratio of the flow rate of the evaporation condensate to the flow rate of the acrylonitrile ammonium sulfate wastewater is 1:(1-5), preferably 1:(1.3-2); the ratio of the flow rate of the evaporation concentrate to the flow rate of the acrylonitrile ammonium sulfate wastewater is 1:(1-3), preferably 1:(1.5-2.5).

[0075] In one embodiment, the thickener 5 is connected to the evaporation crystallizer 1. The evaporation condensate is directly discharged or recycled. The crystalline solid ammonium sulfate carrying a certain amount of solution is pumped into the thickener 5 by a pump, and crystal sedimentation is carried out in the thickener 5. The thickener 5 can also be connected to a solid-liquid centrifuge 6. The material discharged from the bottom of the thickener 5 enters the solid-liquid centrifuge 6, and the water is removed by centrifugation to obtain ammonium sulfate products. The overflow circulating liquid at the top of the thickener 5 returns to the evaporation crystallizer 1 for continuous crystallization. In another embodiment, the flow rate ratio of the ammonium sulfate solution flowing into the thickener 5 to the acrylonitrile ammonium sulfate wastewater is 1:(0.1 - 1), preferably 1:(0.3 - 0.5).

[0076] The static mixer 2 of the present invention is connected to the evaporation crystallizer 1. The evaporation concentrate is transported to the static mixer 2, and the reverse demulsifier solution is transported to the static mixer 2 to be mixed with the evaporation concentrate. In one embodiment, the amount of the reverse demulsifier added per unit time is 1 - 50 ppm of the flow rate of the evaporation concentrate, preferably 5 - 20 ppm. In yet another embodiment, the solvent in the reverse demulsifier solution is one of methyl ethyl ketone and methyl isobutyl ketone, and the mass ratio of the reverse demulsifier to the solvent is 1:(10 - 100), preferably 1:(30 - 90). In still another embodiment, the residence time of the evaporation concentrate in the static distributor 2 is 0.2 - 1 h, preferably 0.2 - 0.5 h.

[0077] The first oil-water separator 3 of the present invention is connected to the static mixer 2. After the evaporation concentrate and the reverse demulsifier are mixed, they are transported to the first oil-water separator 3, and the evaporation concentrate is separated into an oil phase and a water phase by gravity sedimentation. In one embodiment, the first oil-water separator 3 is also connected to an oil-water mixer 7. The oil phase is transported to the oil-water mixer 7 through the oil phase outlet at the top of the first oil-water separator 3, and a certain amount of acrylonitrile ammonium sulfate wastewater is transported to the oil-water mixer 7 to be mixed and diluted with the oil phase, and the mixed liquid is transported to the incineration unit for incineration treatment. Among them, the flow rate ratio of the acrylonitrile ammonium sulfate wastewater transported to the oil-water mixer 7 to the oil phase is 1:(3 - 10), preferably 1:(3 - 5). In another embodiment, the residence time of the mixed liquid in the oil-water mixer 7 is 0.1 - 2 h, preferably 0.2 - 1 h.

[0078] In one embodiment, the first oil-water separator 3 of the present invention is a horizontal separator, which has a better oil-water separation effect compared with the traditional vertical separator, and does not require structures such as baffles. Its structure is simple, the manufacturing cost is low, and it is easy to maintain in the later stage.

[0079] Specifically, the horizontal separator extends the flow distance of the wastewater, enabling the oil droplets and water droplets to fully float and sink by gravity, further improving the oil-water separation effect. And with the continuous directional flow of the wastewater, its influence by the shock of the inlet material is reduced, and the oil-water interface tends to be stable, avoiding the phenomenon of mutual entrainment of the two phases.

[0080] In another embodiment, the height-to-length ratio of the first oil-water separator 3 of the present invention is 1:(2 - 10), preferably 1:(3 - 8), and the residence time of the mixed liquid of the evaporation concentrate and the reverse demulsifier in the first oil-water separator 3 is 1 - 6 h, preferably 1 - 3 h.

[0081] In yet another embodiment, the flow rate ratio of the acrylonitrile ammonium sulfate wastewater to the oil phase is (1 - 5):1, preferably (1 - 3):1, and the flow rate ratio of the water phase to the oil phase is (1 - 5):1, preferably (1 - 3):1.

[0082] The second oil-water separator 4 of the present invention is connected to the first oil-water separator 3 and the evaporation crystallizer 2 respectively. The second oil-water separator 4 is an evaporator. The water phase is transported to the second oil-water separator 4 for evaporation treatment to obtain an oil-containing water phase and a remaining mixed liquid after evaporation. In one embodiment, the second oil-water separator 4 also replenishes water. On the one hand, it dilutes the ammonium sulfate concentrate discharged from the bottom of the second oil-water separator 4 to prevent the transfer pump from being blocked. On the other hand, it is to maintain the constant liquid level in the evaporation crystallizer 1. The flow rate ratio of the evaporation amount to the water inflow amount is 1:(3 - 10), preferably 1:(3 - 5), that is, the flow rate ratio of the oil-containing water phase to the total amount of the water phase and the replenished water is 1:(3 - 10). In another embodiment, the amount of replenished water is the same as the evaporation amount.

[0083] The second oil-water separator 4 of the present invention is connected to the evaporation crystallizer 2, and the remaining mixed liquid after evaporation is circulated and transported to the evaporation crystallizer 2, and is mixed with the acrylonitrile ammonium sulfate wastewater and then subjected to evaporation crystallization again. In one embodiment, the oil-containing water phase returns to the static mixer 2.

[0084] Based on the introduction of the chemical demulsification technology, the present invention designs and develops a secondary deep separation process formed by connecting a horizontal oil-water separator and an evaporator in series, fundamentally solving the problem of mutual entrainment of the oil and water phases in the acrylonitrile ammonium sulfate evaporation concentrate.

[0085] Specifically, the present invention evaporates and removes a certain amount of water through the second oil-water separator (evaporator), so that the residual emulsified oil and dissolved oil precipitate and float on the water surface. The upper thin oil layer carries part of the aqueous solution back to the static mixer for secondary demulsification, and the oil content (concentration and total amount) in the ammonium sulfate containing water returning to the evaporation crystallizer in the lower layer decreases. Therefore, the oil content in the evaporation crystallizer decreases accordingly. From the perspective of reducing the content (concentration and total amount) of emulsified oil and dissolved oil, this treatment technology solves the problem of the color of the ammonium sulfate product.

[0086] The reverse demulsifier of the present invention can be a demulsifier disclosed in the prior art. However, in order to enhance the oil-water separation effect, the present invention provides an azo-crosslinked polyether-quaternary ammonium salt demulsifier. Through the electrostatic attraction of the cationic quaternary ammonium salt by the azo group with strong power supply ability, the non-ionic polyether and the cationic polyquaternary ammonium salt are miscible to form a uniform and stable demulsification system. This demulsifier system has the characteristics of good oil-water stratification effect of polyether and fast oil removal rate of polyquaternary ammonium salt. It can quickly break the double-layer electric charge balance at the oil-water interface, promote the coalescence of oil droplets, achieve efficient and deep demulsification, and significantly improve the oil-water separation effect. The azo structure in the structure of the reverse demulsifier of the present invention endows it with good oil solubility. After oil-water stratification, it will enter the incineration unit along with the oil phase, ensuring the quality of the ammonium sulfate product while achieving efficient oil-water separation.

[0087] The present invention provides a preparation method of an oil-soluble reverse demulsifier. An azo-type initiator is used to initiate the copolymerization of epoxides to generate polyether, and then high-molecular-weight crosslinked polyether is obtained under the action of a crosslinking agent epichlorohydrin. The high-molecular-weight crosslinked polyether has good lipophilic-hydrophobic properties and high solubility in general organic solvents. The high-molecular-weight crosslinked polyether is dissolved in an oil-soluble solvent, and a cationic quaternary ammonium salt is added to the solution. The strong power supply effect of azo has an electrostatic attraction on the cationic quaternary ammonium salt. Thus, an azo-crosslinked polyether-quaternary ammonium salt reverse demulsifier is obtained, and this demulsifier forms a stable and uniform composite reverse demulsification system in the solvent, combining the advantages of polyether-type and cationic-type reverse demulsifiers. It can quickly sweep the oil droplets, accelerate the oil-water separation speed, and achieve efficient demulsification. Moreover, this reverse demulsifier has extremely low water solubility and will not return to the evaporation crystallizer with the water phase, affecting the quality of the ammonium sulfate product.

[0088] Specifically, the preparation method of the oil-soluble reverse demulsifier of the present invention includes the following steps:

[0089] Step 1: Carry out a ring-opening polymerization reaction between azodinitrile and propylene oxide to obtain an azo polyether oil head;

[0090] Step 2: Carry out copolymerization of the azo polyether oil head, ethylene oxide and propylene oxide to obtain a block azo polyether;

[0091] Step 3: Carry out a crosslinking reaction on the block azo polyether under the action of a crosslinking agent to obtain a crosslinked polyether;

[0092] Step 4: React the crosslinked polyether and the quaternary ammonium salt under heating to obtain an oil-soluble reverse demulsifier.

[0093] In Step 1, azodinitrile is used as the initiator and propylene oxide is used as the monomer. In one embodiment, the azodinitrile is one of azobisisobutyronitrile, azobisisopentanenitrile, and azobisisoheptanenitrile, and preferably azobisisoheptanenitrile; the reaction of azodinitrile and propylene oxide is carried out under the action of a ring-opening polymerization catalyst and in an oil-soluble solvent. The ring-opening polymerization catalyst is one of sodium hydroxide, potassium hydroxide, calcium hydroxide, and magnesium hydroxide, and preferably one of sodium hydroxide and potassium hydroxide; the oil-soluble solvent is, for example, an oil-soluble ketone, and more specifically one of acetone, methyl ethyl ketone, methyl isobutyl ketone, and tetrahydrofuranone, and preferably one of methyl ethyl ketone and methyl isobutyl ketone.

[0094] In another embodiment, the mass ratio of azodinitrile to propylene oxide is 2:1 - 8:1, preferably 3:1 - 5:1. The dosage of the ring-opening polymerization catalyst is 0.05 - 0.3% of the total mass of azodinitrile and propylene oxide, preferably 0.1 - 0.2%; the reaction temperature of azodinitrile and propylene oxide is 100 - 120 °C, and the reaction time is 1 - 3 h.

[0095] In yet another embodiment, the ring-opening polymerization reaction in Step 1 is carried out in a reaction kettle. The initiator azodinitrile and the oil-soluble solvent are added to the kettle, and stirred at 40 - 60 °C for 10 min to mix evenly. The dosage of the initiator is 20 - 60% of the mass of the solvent, preferably 30 - 50%. Then the ring-opening polymerization catalyst is added, and vacuum dehydration is carried out at 90 - 100 °C. The dehydration time is, for example, 20 - 40 min. Then propylene oxide is added, and the polymerization reaction is carried out at 100 - 120 °C, controlling the pressure at 0 - 0.4 Mpa. The reaction time is 0.5 - 3 h, preferably 1 - 3 h. After the reaction is completed, the filter residue is filtered off to obtain the azo polyether oil head solution.

[0096] Among them, the reaction kettle is a stainless-steel reaction kettle with a working pressure of 2 - 5 Mpa.

[0097] The azo polyether oil head obtained by the present invention has, for example, the following structure of Formula 1:

[0098]

[0099] Among them, R is selected from one of methylene, ethylene, and isobutylene.

[0100] Step 2 is the preparation of block polyether. Specifically, using azo polyether oil head, ethylene oxide, and propylene oxide as raw materials, the three components copolymerize to form a block-structured polyether. The copolymerization reaction is carried out in a reaction kettle. First, add the azo polyether oil head and the ring-opening polymerization catalyst into the kettle, perform vacuum dehydration at 90 - 100 °C for 30 min, then raise the temperature to 110 - 120 °C and introduce the first copolymerization component ethylene oxide, control the pressure at 0 - 0.4 MPa, react for 0.5 - 3 h, then introduce the second copolymerization component propylene oxide, control the pressure at 0 - 0.4 MPa, maintain the temperature and react for 0.5 - 3 h, and obtain block azo polyether through filtration.

[0101] In one embodiment, the ring-opening polymerization catalyst is one of sodium hydroxide, potassium hydroxide, calcium hydroxide, and magnesium hydroxide, preferably one of sodium hydroxide and potassium hydroxide. The dosage of the ring-opening polymerization catalyst is 0.05 - 0.3% of the total mass of the azo polyether oil head, ethylene oxide, and propylene oxide, preferably 0.1 - 0.2%.

[0102] In another embodiment, the reaction temperature of the azo polyether oil head, ethylene oxide, and propylene oxide is 110 - 120 °C, the mass ratio of the azo polyether oil head to ethylene oxide is 1:2 - 1:5, preferably 1:2 - 1:3, and the mass ratio of the azo polyether oil head to propylene oxide is 1:8 - 1:12.

[0103] Step 3 is the preparation of crosslinked polyether. Specifically, using block azo polyether as a monomer and epichlorohydrin as a crosslinking agent, react at 60 - 80 °C for 1 - 3 h, then add the oil-soluble solvent used when synthesizing the azo polyether oil head for dilution to obtain a crosslinked polyether solution.

[0104] In one embodiment, first heat the block azo polyether to 60 - 80 °C, and then add the crosslinking agent for reaction.

[0105] In another embodiment, the mass ratio of the block azo polyether to the crosslinking agent is 500:1 - 600:1. In the obtained crosslinked polyether solution, the solvent mass is 200 - 400% of the total mass of the block azo polyether and epichlorohydrin.

[0106] Step 4 is the preparation of an oil-soluble reverse demulsifier. Specifically, dropwise add an aqueous quaternary ammonium salt solution to the crosslinked polyether solution, the dropping time is 0.5 - 3 h, keep stirring during the dropping process, after the dropping is completed, raise the temperature of the above reaction system to 80 - 95 °C, stir and react for 3 - 5 h, then take out the mixed solution, let it stand for 3 - 5 h, separate the upper oil phase, and remove the solvent by vacuum distillation to obtain the azo crosslinked polyether - quaternary ammonium salt reverse demulsifier.

[0107] The quaternary ammonium salt is a long-chain quaternary ammonium salt, such as one having 10-20 carbons, such as dodecyltrimethylammonium chloride, tetradecyltrimethylammonium bromide, hexadecyltrimethylammonium chloride, preferably dodecyltrimethylammonium chloride and tetradecyltrimethylammonium bromide. The dosage of the quaternary ammonium salt is 20-30% of the mass of the crosslinked polyether. In the aqueous solution of the quaternary ammonium salt, the concentration of the quaternary ammonium salt is 20-40 wt%.

[0108] The reverse demulsifier obtained by the above method of the present invention is, for example, azodiisobutyronitrile-dodecyltrimethylammonium chloride and azodiisobutyronitrile-tetradecyltrimethylammonium bromide.

[0109] The reverse demulsifier of the present invention comprises an azo polyether and a cationic quaternary ammonium salt. The high content of nitrogen element in the azo polyether gives it a strong power supply ability, forming a strong electrostatic attraction to the high-cationicity quaternary ammonium salt, so that the nonionic polyether and the cationic polyquaternary ammonium salt form a stable composite system in the solution, and can fully exhibit the advantages of the nonionic polyether and the cationic reverse demulsifier.

[0110] In addition, the oil-soluble azodinitrile structure, long-chain block polyether structure and long-chain quaternary ammonium salt structure in the reverse demulsifier provided by the present invention increase the non-polarity of the system, endowing the reverse demulsifier with good lipophilic and hydrophobic properties. Especially for acrylonitrile ammonium sulfate wastewater, the oil phase in this wastewater is mainly polyacrylonitrile. And the azodinitrile in the structure of the reverse demulsifier of the present invention contains a certain amount of nitrile groups. According to the principle of similar solubility, the solubility of this demulsifier in the oil phase of acrylonitrile wastewater is excellent.

[0111] The technical solution of the present invention will be further described in detail through specific examples below. Examples 1-4 are for the preparation of the reverse demulsifier, Examples 5-8 are for the investigation of the demulsification performance of the commercially available reverse demulsifier SP169, and Examples 9-20 are for the investigation of the demulsification performance of the reverse demulsifier of the present invention. Unless otherwise specified, "%" below refers to mass percentage. The oil content in the aqueous phase of the examples and comparative examples was measured according to "HJ637-2018 Water Quality - Determination of Petroleum and Animal Oils - Infrared Spectrophotometry", the ammonium sulfate concentration was measured using liquid chromatography, and the color of the ammonium sulfate product was visually measured.

[0112] The raw materials for synthesizing the reverse demulsifier of the present invention and the equipment specifications of the process flow are shown in Table 1.

[0113] Table 1 Raw materials / equipment specifications and sources

[0114]

[0115]

[0116] Example 1

[0117] (1) Add 50 ml of methyl isobutyl ketone and 20 g of azobisisobutyronitrile into the reaction kettle, heat up to 50 °C and stir for 10 min to completely dissolve the initiator. Then add 25 mg of KOH, heat up to 90 °C and carry out vacuum dehydration for 30 min. Then add 5 g of propylene oxide, heat up to 100 - 120 °C for reaction and control the pressure at 0.2 Mpa. After 1 h of reaction, filter to remove the filter residue to obtain the azo polyether oil head solution containing azo polyether.

[0118] (2) Add the azo polyether oil head solution prepared in the above step and 0.3 g of KOH into the reaction kettle, carry out vacuum dehydration at 90 °C for 30 min, heat up to 110 °C and introduce 75 g of ethylene oxide, control the pressure to be less than 0.4 Mpa, maintain the temperature for reaction for 0.5 - 3 h. Then add 270 g of propylene oxide and control the pressure at 0.2 Mpa. After maintaining the temperature for reaction for 12 h, filter to obtain the block azo polyether solution.

[0119] (3) Add the block azo polyether solution prepared in the above step into the autoclave reactor, heat up to 80 °C, then add 0.68 g of epichlorohydrin as the crosslinking agent, maintain the temperature for reaction for 1 h. After the reaction is completed, add 30 ml of methyl isobutyl ketone for dilution to obtain the crosslinked polyether solution.

[0120] (4) Dropwise add 30 ml of an aqueous solution of dodecyltrimethylammonium chloride (40 wt%) into the crosslinked polyether solution obtained in the above step, and the dropping time is 2 h. Keep stirring during the dropping process. After the dropping is completed, heat the above reaction system to 95 °C, stir and react for 3 h, then take out the mixed solution, let it stand for 5 h, and separate the upper oil phase. Remove the solvent by vacuum distillation to obtain the non-ionic - cationic composite reverse demulsifier, numbered demulsifier 1.

[0121] Example 2

[0122] The difference between this example and Example 1 is that: change 20 g of azobisisobutyronitrile in step (1) to 24 g of azodiisopentylonitrile, and finally obtain demulsifier 2.

[0123] Example 3

[0124] The difference between this example and Example 1 is that: change 20 g of azobisisobutyronitrile in step (1) to 30 g of azodiisoheptonitrile, and finally obtain demulsifier 3.

[0125] Example 4

[0126] The difference between this example and Example 1 is that: change dodecyltrimethylammonium chloride in step (4) to cetyltrimethylammonium chloride, and finally obtain demulsifier 4.

[0127] Comparative Example 1

[0128] The device process flow is asFigure 2 As shown (the same devices as those of the present invention use the same reference numerals), the evaporation rate / flow rate of each device is shown in Table 2. First, the dilute ammonium sulfate solution in the quench tower is introduced into the evaporation crystallizer 1. After evaporation and concentration, evaporation condensate, crystalline solids, and evaporation concentrate are produced. The evaporation condensate is directly discharged; the crystalline ammonium sulfate solids carry a certain amount of solution and are pumped into the thickener 5 by a pump. The bottom discharge of the thickener 5 is centrifuged by a solid-liquid centrifuge 6 to remove moisture to obtain ammonium sulfate products. The overflow circulating liquid at the top of the thickener 5 returns to the evaporation crystallizer 1; the evaporation concentrate of the evaporation crystallizer 1 enters the vertical first oil-water separator 3a. The concentrate completes oil-water separation by gravity sedimentation inside the separator. Acrylonitrile wastewater is introduced at the oil phase outlet at the top of the separator to dilute the upper oil phase. The acrylonitrile wastewater and the oil phase enter the oil-water mixer 7, are stirred and diluted, and then enter the incineration unit. The aqueous phase returns to the evaporation crystallizer 1 from the bottom outlet of the separator. The oil content of the aqueous phase taken from the bottom of the first oil-water separator is analyzed to be 158 mg / L, the ammonium sulfate content of the oil phase taken from the top of the first oil-water separator is analyzed to be 19 wt%, and the appearance of the ammonium sulfate product is reddish-brown.

[0129] Table 2 Evaporation rate / flow rate of each part

[0130]

[0131]

[0132] Comparative Example 2

[0133] According to Figure 1 the process flow, no reverse demulsifier is added, the second oil-water separator is not used, and the evaporation concentrate of the evaporation crystallizer directly enters the first oil-water separator. The first oil-water separator uses the first oil-water separator -1 (250 ml, length / height = 3:1) in Table 1. The residence time of the evaporation concentrate in the first oil-water separator is 1 h. The evaporation rate / flow rate of each part is shown in Table 3. The oil content of the water inlet of the evaporation crystallizer (i.e., acrylonitrile sulfuric acid wastewater) is 245 mg / L. After the device operates continuously for 8 h, the oil content of the aqueous phase taken from the bottom of the first oil-water separator is analyzed to be 120 mg / L, the ammonium sulfate content of the oil phase taken from the top of the first oil-water separator is analyzed to be 8 wt%, and the appearance of the ammonium sulfate product is dark yellow.

[0134] Table 3 Evaporation rate / flow rate of each part

[0135]

[0136] Comparative Example 3

[0137] The difference between the wastewater treatment method of this comparative example and Comparative Example 2 lies in that the first oil-water separator is replaced with the first oil-water separator-2 in Table 1 (450 ml, length / height ratio is 5:1). The residence time of the concentrated liquid in the first oil-water separator is 2 h. After the device runs continuously for 8 h, the oil content in the aqueous phase at the bottom of the first oil-water separator is analyzed to be 97 mg / L, the ammonium sulfate content in the oil phase at the top of the first oil-water separator is analyzed to be 5 wt%, and the appearance of the ammonium sulfate product is dark yellow.

[0138] Comparative Example 4

[0139] The difference between the wastewater treatment method of this comparative example and Comparative Example 2 lies in that the first oil-water separator is replaced with the first oil-water separator-3 in Table 1 (600 ml, length / height ratio is 7:1). The residence time of the concentrated liquid in the first oil-water separator is 3 h. After the device runs continuously for 8 h, the oil content in the aqueous phase at the bottom of the first oil-water separator is analyzed to be 95 mg / L, the ammonium sulfate content in the oil phase at the top of the first oil-water separator is analyzed to be 5 wt%, and the appearance of the ammonium sulfate product is dark yellow.

[0140] Example 5

[0141] The difference between this example and Comparative Example 2 is that an SP169 reverse demulsifier solution (using diisopentyl ether as a solvent) with a concentration of 0.2 wt% and a flow rate of 0.375 ml / h is introduced into the static mixer. The dosage of the reverse demulsifier per unit time is 5 ppm of the flow rate of the evaporation concentrate. The residence time of the reverse demulsifier and the concentrated liquid in the static mixer is 20 min. After the device runs continuously for 8 h, the oil content in the aqueous phase at the bottom of the first oil-water separator is analyzed to be 95 mg / L, the ammonium sulfate content in the oil phase at the top of the first oil-water separator is analyzed to be 6 wt%, and the appearance of the ammonium sulfate product is dark yellow.

[0142] Example 6

[0143] The difference between this example and Comparative Example 2 is that an SP169 reverse demulsifier solution (using diisopentyl ether as a solvent) with a concentration of 0.8 wt% and a flow rate of 0.375 ml / h is introduced into the static mixer. The dosage of the reverse demulsifier per unit time is 20 ppm of the flow rate of the evaporation concentrate. The residence time of the reverse demulsifier and the concentrated liquid in the static mixer is 20 min. After the device runs continuously for 8 h, the oil content in the aqueous phase at the bottom of the first oil-water separator is analyzed to be 90 mg / L, the ammonium sulfate content in the oil phase at the top of the first oil-water separator is analyzed to be 6 wt%, and the appearance of the ammonium sulfate product is dark yellow.

[0144] Example 7

[0145] The difference between the wastewater treatment method of this example and that of Example 6 lies in starting the oil-water secondary separator to investigate the influence of evaporation oil removal on the oil content in the water phase and the colority of the product. In this example, the evaporation rate of the second oil-water separator is set at 24 ml / h, and the water make-up amount is the same as the evaporation rate. After the device runs continuously for 8 h, the oil content (before water make-up) in the bottom water phase of the second oil-water separator is analyzed to be 75 mg / L, and the appearance of the ammonium sulfate product is light yellow.

[0146] Example 8

[0147] The difference between the wastewater treatment method of this example and that of Example 6 lies in starting the oil-water secondary separator to investigate the influence of evaporation oil removal on the oil content in the water phase and the colority of the product. In this example, the evaporation rate of the second oil-water separator is set at 40 ml / h, and the water make-up amount is the same as the evaporation rate. After the device runs continuously for 8 h, the oil content (before water make-up) in the bottom water phase of the second oil-water separator is analyzed to be 55 mg / L, and the appearance of the ammonium sulfate product is light yellow.

[0148] Example 9

[0149] The difference between this example and Comparative Example 2 lies in that a demulsifier 1 solution with a concentration of 0.2 wt% and a flow rate of 0.375 ml / h is introduced into the static mixer, and the addition amount of the reverse demulsifier per unit time is 5 ppm of the evaporation concentrate flow rate. The residence time of the reverse demulsifier and the concentrate in the static mixer is 20 min. After the device runs continuously for 8 h, the oil content in the bottom water phase of the first oil-water separator is analyzed to be 15 mg / L, the ammonium sulfate content in the top oil phase of the first oil-water separator is analyzed to be 3 wt%, and the appearance of the ammonium sulfate product is light yellow.

[0150] Example 10

[0151] The difference between this example and Example 9 lies in that the concentration of the demulsifier 1 solution is 0.4 wt%, and the addition amount of the reverse demulsifier per unit time is 10 ppm of the evaporation concentrate flow rate. After the device runs continuously for 8 h, the oil content in the bottom water phase of the first oil-water separator is analyzed to be 12 mg / L, the ammonium sulfate content in the top oil phase of the first oil-water separator is analyzed to be 2 wt%, and the appearance of the ammonium sulfate product is light yellow.

[0152] Example 11

[0153] The difference between this example and Example 9 lies in that the concentration of the demulsifier 1 solution is 0.8 wt%, and the addition amount of the reverse demulsifier per unit time is 20 ppm of the evaporation concentrate flow rate. After the device runs continuously for 8 h, the oil content in the bottom water phase of the first oil-water separator is analyzed to be 10 mg / L, the ammonium sulfate content in the top oil phase of the first oil-water separator is analyzed to be 2 wt%, and the appearance of the ammonium sulfate product is light yellow.

[0154] Example 12

[0155] The difference between this example and Example 11 is that the demulsifier is replaced with demulsifier 2. The ammonium sulfate content in the oil phase at the top of the first oil-water separator is analyzed to be 1 wt%, and the appearance of the ammonium sulfate product is light yellow.

[0156] Example 13

[0157] The difference between this example and Example 11 is that the demulsifier is replaced with demulsifier 3. The ammonium sulfate content in the oil phase at the top of the first oil-water separator is analyzed to be 1 wt%, and the appearance of the ammonium sulfate product is light yellow.

[0158] Example 14

[0159] The difference between this example and Example 11 is that the demulsifier is replaced with demulsifier 4. The ammonium sulfate content in the oil phase at the top of the first oil-water separator is analyzed to be 2 wt%, and the appearance of the ammonium sulfate product is light yellow.

[0160] Example 15

[0161] The difference between the wastewater treatment method of this example and that of Example 11 is that the oil-water secondary separator is started to investigate the influence of oil evaporation on the oil content in the water phase and the colority of the product. The evaporation rate of the second oil-water separator in this example is set to 24 ml / h, and the makeup water volume is the same as the evaporation rate. After the device runs continuously for 8 h, the oil content (before makeup water addition) in the water phase at the bottom of the second oil-water separator is analyzed to be 6 mg / L, and the appearance of the ammonium sulfate product is white.

[0162] Example 16

[0163] The difference between the wastewater treatment method of this example and that of Example 15 is that the evaporation rate in this example is set to 30 ml / h, and the makeup water volume is the same as the evaporation rate. After the device runs continuously for 8 h, the oil content (before makeup water addition) in the water phase at the bottom of the second oil-water separator is analyzed to be 5 mg / L, and the appearance of the ammonium sulfate product is white.

[0164] Example 17

[0165] The difference between the wastewater treatment method of this example and that of Example 15 is that the evaporation rate in this example is set to 40 ml / h, and the makeup water volume is the same as the evaporation rate. After the device runs continuously for 8 h, the oil content in the water phase of the effluent at the bottom of the second oil-water separator (before makeup water addition) is 2 mg / L, and the appearance of the ammonium sulfate product is white.

[0166] Example 18

[0167] The difference between the wastewater treatment method of this example and that of Example 17 is that the demulsifier in this example is replaced with demulsifier 2. After the device runs continuously for 8 h, the oil content in the water phase of the effluent at the bottom of the second oil-water separator (before makeup water addition) is 5 mg / L, and the appearance of the ammonium sulfate product is white.

[0168] Example 19

[0169] The difference between the wastewater treatment method of this embodiment and that of Embodiment 17 is that in this embodiment, the demulsifier is replaced with Demulsifier 3. After the device runs continuously for 8 hours, the oil content in the aqueous phase of the effluent discharged from the bottom of the second oil-water separator (before adding makeup water) is 3 mg / L, and the appearance of the ammonium sulfate product is white.

[0170] Embodiment 20

[0171] The difference between the wastewater treatment method of this embodiment and that of Embodiment 17 is that in this embodiment, the demulsifier is replaced with Demulsifier 4. After the device runs continuously for 8 hours, the oil content in the aqueous phase of the effluent discharged from the bottom of the second oil-water separator (before adding makeup water) is 6 mg / L, and the appearance of the ammonium sulfate product is white.

[0172] It can be seen from Comparative Examples 1-4 that the horizontal oil-water separator in the device provided by the present invention has a better oil-water separation effect than the existing vertical oil-water separator; it can be seen from Examples 5-8 that using the reverse demulsifier of the prior art can improve the oil-water separation problem to a certain extent. It can be seen from Examples 9-20 that adding the reverse demulsifier of the present invention greatly reduces the oil content in the aqueous phase and the ammonium sulfate content in the oil phase. Combining with the second oil-water separator in the device provided by the present invention, it can complete the deep removal of the residual emulsified oil and dissolved oil in the aqueous phase, further improve the oil-water separation effect, and make the chromaticity of the ammonium sulfate product white.

[0173] Certainly, the present invention can also have many other embodiments. Without departing from the spirit and essence of the present invention, those skilled in the art can make various corresponding changes and deformations according to the present invention, but these corresponding changes and deformations should all fall within the protection scope of the claims of the present invention.

Claims

1. A treatment method for acrylonitrile ammonium sulfate wastewater, characterized in that, it includes the following steps: Step 1, subject the acrylonitrile ammonium sulfate wastewater to evaporation crystallization to obtain evaporation condensate, crystalline solid and evaporation concentrate; Step 2, mix the evaporation concentrate with an inverse demulsifier; Step 3, perform the first oil-water separation on the mixture obtained in Step 2 under the action of gravity sedimentation to obtain an oil phase and a water phase; Step 4, perform a second oil-water separation on the water phase. The method of the second oil-water separation is evaporation. After evaporation, the remaining mixture is mixed with the acrylonitrile ammonium sulfate wastewater and then cycled for the evaporation crystallization.

2. The treatment method for acrylonitrile ammonium sulfate wastewater according to claim 1, characterized in that, the ratio of the flow rate of the evaporation condensate to the flow rate of the acrylonitrile ammonium sulfate wastewater is 1:(1 - 5); the ratio of the flow rate of the evaporation concentrate to the flow rate of the acrylonitrile ammonium sulfate wastewater is 1:(1 - 3).

3. The treatment method for acrylonitrile ammonium sulfate wastewater according to claim 1, characterized in that, the first oil-water separation is carried out in a horizontal separation tank, and the ratio of the height to the length of the horizontal separation tank is 1:(2 - 10).

4. The treatment method for acrylonitrile ammonium sulfate wastewater according to claim 1, characterized in that, the ratio of the flow rate of the acrylonitrile ammonium sulfate wastewater to the flow rate of the oil phase in Step 3 is (1 - 5):1; in Step 3, the ratio of the flow rate of the water phase to the flow rate of the oil phase is (1 - 5):

1.

5. The treatment method for acrylonitrile ammonium sulfate wastewater according to claim 1, characterized in that, the evaporation obtains an oil-containing water phase and a remaining mixture. The oil-containing water phase is mixed with the evaporation concentrate and the inverse demulsifier, and the ratio of the flow rate of the oil-containing water phase to the flow rate of the water phase is 1:(3 - 10).

6. The treatment method for acrylonitrile ammonium sulfate wastewater according to claim 1, characterized in that, the preparation method of the inverse demulsifier includes: Step a, subject azodinitrile and propylene oxide to ring-opening polymerization reaction to obtain an azo polyether oil head; Step b, subject the azo polyether oil head, ethylene oxide and propylene oxide to copolymerization to obtain a block azo polyether; Step c, subject the block azo polyether to cross-linking reaction under the action of a cross-linking agent to obtain a cross-linked polyether; Step d, react the cross-linked polyether and quaternary ammonium salt under heating to obtain an oil-soluble inverse demulsifier.

7. The treatment method for acrylonitrile ammonium sulfate wastewater according to claim 6, characterized in that, the azodinitrile is one of azobisisobutyronitrile, azobisisopentanenitrile, azobisisoheptanenitrile; the reaction of the azodinitrile and propylene oxide is carried out under the action of a ring-opening polymerization catalyst and in an oil-soluble solvent. The ring-opening polymerization catalyst is one of sodium hydroxide, potassium hydroxide, calcium hydroxide, magnesium hydroxide; the oil-soluble solvent is one of acetone, methyl ethyl ketone, methyl isobutyl ketone, tetrahydrofuranone.

8. The treatment method for acrylonitrile ammonium sulfate wastewater according to claim 7, characterized in that, In step a, the mass ratio of the azo dinitrile to propylene oxide is 2:1 - 8:1, and the dosage of the ring-opening polymerization catalyst is 0.05 - 0.3% of the total mass of the azo dinitrile and propylene oxide; the reaction temperature of the azo dinitrile and propylene oxide is 100 - 120 °C, and the reaction time is 1 - 3 h.

9. The method for treating acrylonitrile ammonium sulfate wastewater according to claim 6, characterized in that, in step b, the reaction of the azo polyether oil head, ethylene oxide and propylene oxide is carried out under the action of a ring-opening polymerization catalyst, and the ring-opening polymerization catalyst is one of sodium hydroxide, potassium hydroxide, calcium hydroxide, and magnesium hydroxide, and the dosage of the ring-opening polymerization catalyst is 0.05 - 0.3% of the total mass of the azo polyether oil head, ethylene oxide and propylene oxide.

10. The method for treating acrylonitrile ammonium sulfate wastewater according to claim 6, characterized in that, the reaction temperature of the azo polyether oil head, ethylene oxide and propylene oxide is 110 - 120 °C, the mass ratio of the azo polyether oil head to ethylene oxide is 1:2 - 1:5, and the mass ratio of the azo polyether oil head to propylene oxide is 1:8 - 1:

12.

11. The method for treating acrylonitrile ammonium sulfate wastewater according to claim 6, characterized in that, the cross-linking agent is epichlorohydrin, and the mass ratio of the block azo polyether to the cross-linking agent is 500:1 - 600:

1.

12. The method for treating acrylonitrile ammonium sulfate wastewater according to claim 6, characterized in that, the temperature of the cross-linking reaction is 60 - 80 °C, and the time is 1 - 3 h.

13. The method for treating acrylonitrile ammonium sulfate wastewater according to claim 6, characterized in that, the quaternary ammonium salt is one of dodecyl trimethyl ammonium chloride, tetradecyl trimethyl ammonium bromide, and hexadecyl trimethyl ammonium chloride, and the dosage of the quaternary ammonium salt is 20 - 30% of the mass of the cross-linked polyether.

14. The method for treating acrylonitrile ammonium sulfate wastewater according to claim 6, characterized in that, the temperature for heating in step d is 80 - 95 °C, and the reaction time is 3 - 5 h; the reaction mixture of the cross-linked polyether and the quaternary ammonium salt is subjected to oil-water separation, and the obtained oil phase is distilled to obtain an oil-soluble reverse demulsifier.

15. A treatment system for acrylonitrile ammonium sulfate wastewater, characterized in that, comprising: an evaporation crystallizer for evaporating and crystallizing acrylonitrile ammonium sulfate wastewater to obtain evaporation condensate, crystalline solid and evaporation concentrate; a static mixer connected to the evaporation crystallizer for mixing the evaporation concentrate with the reverse demulsifier; a first oil-water separator connected to the static mixer for performing the first oil-water separation on the mixed liquid of the static mixer under the action of gravity sedimentation to obtain an oil phase and a water phase; a second oil-water separator, which is an evaporator, connected to the first oil-water separator and the evaporation crystallizer respectively for evaporating the water phase, and the remaining mixed liquid after evaporation is circulated back to the evaporation crystallizer for evaporation and crystallization.

16. The treatment system for acrylonitrile ammonium sulfate wastewater according to claim 15, characterized in that, the reverse demulsifier is prepared by the following steps: Step a, subject azodinitrile to ring-opening polymerization with propylene oxide to obtain an azo polyether oil head; Step b, subject the azo polyether oil head, ethylene oxide and propylene oxide to copolymerization to obtain a block azo polyether; Step c, subject the block azo polyether to a crosslinking reaction under the action of a crosslinking agent to obtain a crosslinked polyether; Step d, react the crosslinked polyether with a quaternary ammonium salt under heating to obtain an oil-soluble reverse demulsifier.

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