Demulsifier for oil-containing wastewater and preparation method thereof

Abstract

The present application relates to a kind of demulsifier for oily wastewater and its preparation method, belong to oily wastewater treatment technical field.The raw material component of the demulsifier includes 15-25wt% iron salt, 10-20wt% aluminum salt, 5-10wt% auxiliary salt and the balance deionized water;Auxiliary salt is the complex system of magnesium salt and zirconium salt;The demulsifier is complexed into intermediate by its raw material component, then polymerized at the temperature of ≤30 ℃.The synergistic effect of iron ion, aluminum ion, magnesium ion and zirconium ion, the prepared demulsifier keeps the oil removal rate at 95% or more in the range of temperature 5-40 ℃, salinity 0.5%-5%, pH 4.0-10.0, COD removal rate is more than 85%, and the performance stability is significantly better than traditional demulsifier, with high demulsification efficiency, low sludge yield, strong adaptability, green environmental protection, low cost and wide application scenarios, with high market value.

Description

Technical Field

[0001] This invention belongs to the field of oily wastewater treatment technology, specifically relating to a demulsifier for oily wastewater and its preparation method. Background Technology

[0002] Oily wastewater is widely generated in industrial sectors such as petrochemicals, machinery manufacturing, metallurgy, and food processing, as well as in daily production activities. The emulsified oil droplets within it are small in size (typically less than 10 μm), negatively charged, and coated with surfactants, forming a kinetically stable oil-water emulsion system that is difficult to separate effectively using conventional physical methods such as gravity sedimentation and flotation. Direct discharge without proper treatment can cause serious harm to aquatic ecosystems and increase the burden on subsequent biological treatment processes.

[0003] Currently, demulsification-flocculation is the core chemical method for treating oily wastewater. The demulsifiers used are mainly divided into three categories: single ferric salts (such as ferric chloride and ferric sulfate), single aluminum salts (such as aluminum sulfate and polyaluminum chloride), and organic polymers (such as polyacrylamide and its derivatives). Each of these products has different performance defects. For example, single ferric salt demulsifiers have a fast demulsification speed and strong charge neutralization ability, but the resulting flocs are small and have poor settling performance, leading to high sludge moisture content, large sludge production, and colored effluent. Single aluminum salt demulsifiers produce dense flocs with good settling properties, but their demulsification efficiency is significantly affected by the pH of the water (the optimal pH range is narrow, usually 6-8), and the demulsification effect drops sharply under low temperature and high salinity conditions. Furthermore, while organic polymer demulsifiers can enhance flocculation through adsorption bridging, they suffer from high dosage costs, poor biodegradability, and a tendency to cause secondary pollution (such as acrylamide monomer residue), and have limited adaptability to highly emulsified and viscous oily wastewater.

[0004] A small number of iron-aluminum composite demulsifiers (such as polyaluminum ferric chloride) have emerged in the current technology, attempting to combine the advantages of both iron and aluminum salts. However, these products are mostly prepared by simple mechanical mixing or conventional copolymerization processes of single iron and aluminum salts. The iron and aluminum ions fail to form an effective complex structure at the molecular level, resulting in insufficient synergistic effect and unstable demulsification efficiency and large fluctuations in floc properties. Especially for complex oily wastewater with low temperature (≤10℃), high salt (3%), and high emulsification (oil droplet size <1μm), the treatment effect of existing iron-aluminum composite demulsifiers is far from meeting the requirements for advanced industrial wastewater treatment and compliant discharge.

[0005] Therefore, developing a novel demulsifier and its preparation method that combines high demulsification efficiency, low sludge production, and strong environmental adaptability has significant industrial application value. Summary of the Invention

[0006] To address the aforementioned deficiencies in the existing technology, this application provides a demulsifier for oily wastewater and its preparation method. By precisely controlling the ratio of iron salts, aluminum salts, and auxiliary salts in the raw materials, and employing a stepwise complexation + low-temperature polymerization process, the synergistic demulsification effect of each ion is fully stimulated, resulting in a highly efficient, low-sludge, and adaptable demulsifier.

[0007] The technical solution of the present invention is as follows: A demulsifier for oily wastewater, wherein the raw material components of the demulsifier include 15-25 wt% iron salt, 10-20 wt% aluminum salt, 5-10 wt% auxiliary salt and the balance deionized water; the demulsifier is formed by complexing the raw material components into an intermediate and then polymerizing it at a temperature ≤30°C.

[0008] Furthermore, the iron salt includes ferric sulfate; the aluminum salt includes polyaluminum chloride.

[0009] Furthermore, the auxiliary salt is a complex system of magnesium salt and zirconium salt.

[0010] Furthermore, the mass ratio of the magnesium salt to the zirconium salt is 3:2-4.

[0011] Furthermore, the magnesium salt includes magnesium sulfate; the zirconium salt includes zirconium oxychloride.

[0012] Furthermore, the pH of the demulsifier is 3.5-4.5.

[0013] Furthermore, for oily wastewater conditions of 5-40℃, salinity of 0.5%-5%, and pH of 4.0-10.0, the demulsifier has an oil removal rate of over 95% and a COD removal rate of over 85%.

[0014] A method for preparing a demulsifier for oily wastewater includes the following steps: S1. Mix the iron salt and deionized water and dissolve them completely to obtain the base solution; S2. Add aluminum salt to the base solution, heat to 40-60℃ and stir for 0.5-4 hours, then add auxiliary salt and continue stirring for 1-4 hours to form a complex intermediate. S3. Cool down to below 30°C, add initiator, and stir at a constant temperature to carry out polymerization reaction; S4. Adjust the pH to 3.5-4.5, filter to remove insoluble impurities, and you're done.

[0015] Furthermore, the dissolution temperature in S1 is 30-38℃.

[0016] Furthermore, the insulation temperature in S2 is 45-55℃.

[0017] Furthermore, the stirring reaction time after adding aluminum salt is 0.5-1.5 h; the stirring reaction time after adding auxiliary salt is 1.0-1.5 h.

[0018] Furthermore, the temperature in S3 is lowered to 20-30℃, and the polymerization reaction time is 1.0-5.0h.

[0019] Preferably, the temperature in S3 is lowered to 23-27°C, and the polymerization reaction time is 1.5-3 hours.

[0020] Furthermore, the amount of initiator accounts for 0.3-0.8% of the total mass of the demulsifier components.

[0021] Furthermore, the initiator is ammonium persulfate and sodium sulfite, and the mass ratio of ammonium persulfate to sodium sulfite in the initiator is 1-2:1.

[0022] Compared with the prior art, the present invention has the following beneficial effects: (1) High demulsification efficiency: This invention uses a "stepwise complexation-low temperature polymerization" process to form a stable copolymer with a multi-metal-oxygen bridge structure at the molecular level, consisting of iron salt (ferric sulfate), aluminum salt (polyaluminum chloride), and auxiliary salt (a mixture of magnesium and zirconium salts). This copolymer combines the properties of Fe... 3+ High charge neutralization ability, Al 13 Strong adsorption bridging effect of polynuclear hydroxyl complexes, Mg 2+ The salting-out effect and structural regulation function of Zr, and Zr 4+ Its high charge density and enhanced temperature and salt resistance make it effective in removing oil from various types of oily wastewater (petrochemical, machining, etc.) with an oil content removal rate of over 95% and a COD removal rate of over 85%. The demulsification rate is also more than 30% faster than traditional single iron salt demulsifiers.

[0023] (2) Low sludge production: By precisely controlling the ratio of iron salts to aluminum salts and the synergistic effect of magnesium-zirconium compound auxiliary salts, and by appropriately adjusting the molecular weight through low-temperature polymerization, the generated flocs are denser and have a faster settling speed (up to 2.8 cm / min). Compared with single iron salt demulsifiers, sludge production is reduced by 30%-40%; compared with commercially available iron-aluminum composite demulsifiers, sludge production is also significantly reduced, greatly reducing sludge dewatering and disposal costs.

[0024] (3) Strong adaptability: The demulsifier of the present invention can maintain stable demulsification performance in a wide temperature range (5-40℃), a wide pH range (4.0-10.0) and high salinity conditions (salinity ≤5%). The oil removal rate is above 95% and the COD removal rate is above 85%, which solves the technical problem of poor adaptability of existing demulsifiers to complex oily wastewater.

[0025] (4) Green and environmentally friendly, low cost: The raw materials of this invention are readily available, and no organic polymer additives (such as polyacrylamide) are added. The preparation process does not require high temperature and high pressure, the energy consumption is low, and there is no risk of secondary pollution. The cost per ton of water treatment is more than 50% lower than that of organic polymer demulsifiers.

[0026] (5) Wide range of applications: The demulsifier of this invention can be used directly for the pretreatment of oily wastewater, or it can be used in conjunction with biochemical treatment processes. It is suitable for industrial wastewater treatment stations, sewage treatment plants and other scenarios, and has broad prospects for promotion. Detailed Implementation

[0027] The technical solutions of the present invention will be clearly and completely described below with reference to the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0028] First, this application provides a demulsifier for oily wastewater, wherein the raw material components of the demulsifier include 15-25 wt% iron salt, 10-20 wt% aluminum salt, 5-10 wt% auxiliary salt and the balance deionized water; the demulsifier is formed by complexing the raw material components into an intermediate and then polymerizing it at a temperature of ≤30°C.

[0029] Further, the iron salt includes, but is limited to, one or more combinations of ferric sulfate, ferric chloride, polyferric sulfate, or ferric nitrate; preferably, the iron salt includes ferric sulfate; in one embodiment, the iron salt is ferric sulfate. Ferric sulfate contains Fe. 3+ It has a high content, high dosing efficiency, good water solubility, moderate dissolution rate, and is easy to control in the process. Furthermore, sulfate ions have an auxiliary effect on demulsification. Although polyferric sulfate has a high degree of polymerization and good flocculation properties, its compatibility with aluminum salts is poor. Ferric nitrate has good solubility, and Fe... 3+ High content, but NO3 - It introduces an additional nitrogen source, increasing the risk of total nitrogen in the effluent, and is costly.

[0030] Further, the iron salt content in the demulsifier raw material is any one of 15wt%, 16wt%, 17wt%, 18wt%, 19wt%, 20wt%, 21wt%, 22wt%, 23wt%, 24wt%, 25wt%, etc.; preferably 16-20wt%. In the demulsification process of oily wastewater, Fe... 3+ And its hydrolytic cations, such as [Fe(H₂O)₆] 3+ [Fe2(OH)2] 4+ and [Fe3(OH)4] 5+Electrostatic attraction occurs between the iron salt and the negative charge on the surface of the emulsified oil droplets, compressing the electric double layer, reducing the zeta potential, and causing the oil droplets to lose stability, thus achieving rapid oil-water separation. Furthermore, the highly polymerized Fe(III) hydrolysis products, through hydroxyl bridging, cause different oil droplets to aggregate into larger flocs, enhancing sedimentation performance. When the amount of iron salt is too low, Fe... 3+ Insufficient concentration leads to a significant decrease in demulsification efficiency and results in small, difficult-to-settle flocs. When the iron salt dosage is too high, excess iron ions will form excessive Fe(OH)3 flocs, causing a sharp increase in sludge production.

[0031] Furthermore, the aluminum salt includes polyaluminum chloride (PAC). The polynuclear hydroxyl complex formed by PAC has a large molecular size and long molecular chain segments. In water, it can simultaneously adsorb multiple destabilized emulsified oil droplets and other suspended particles, forming a three-dimensional network floc structure of "particle-polymer-particle". This adsorption bridging effect effectively aggregates dispersed fine particles into larger flocs, accelerating sedimentation and separation. The longer molecular chain contributed by PAC and the higher charge density contributed by the iron salt produce a synergistic amplification effect in the copolymerization system of this application, significantly promoting the demulsification efficiency of the demulsifier.

[0032] Furthermore, the aluminum salt content in the demulsifier raw material is any one of 10wt%, 11wt%, 12wt%, 13wt%, 14wt%, 15wt%, 16wt%, 17wt%, 18wt%, 19wt%, 20wt%, etc.; preferably 13-17wt%.

[0033] Furthermore, the auxiliary salt is a composite system of magnesium and zirconium salts. Magnesium salt primarily compresses the electric double layer of oil droplets and disrupts the hydration film through the salting-out effect, while also acting as a structure regulator to crosslink iron-aluminum polymer chains and prevent over-polymerization. Zirconium salt, with its high charge density and unique hydrolytic polymerization characteristics, forms rigid Zr-O-Zr and Zr-OM (M=Fe,Al) bonds in the multi-metal system, significantly enhancing the floc skeleton strength, broadening the pH adaptation range to 4.0-10.0, and maintaining stable demulsification activity under low temperature (≤10℃) and high salt (3%) conditions. This application combines the above four components and forms a multi-metal-oxygen bridge copolymer through a stepwise complexation-low-temperature polymerization process, Zr... 4+ High charge and Fe 3+ Their rapid neutralization capabilities complement each other, Mg 2+ The synergistic effect of salting out and structural regulation on Al 13 The adsorption bridging effect of the demulsifier achieves both oil content and COD removal rate, while significantly reducing sludge production compared to single iron salts, and remains stable under harsh conditions of low temperature, high salt, and wide pH range.

[0034] Furthermore, the mass ratio of the magnesium salt to the zirconium salt is 3:2-4. Insufficient zirconium salt weakens the structural reinforcement effect; excessive zirconium salt increases the cost and may cause excessive cross-linking. The demulsifier has the best overall performance within this mass ratio range, and deviations from this range will reduce salt resistance or sedimentation rate.

[0035] Furthermore, the magnesium salt includes magnesium sulfate; the zirconium salt includes zirconium oxychloride.

[0036] Furthermore, the pH of the demulsifier is 3.5-4.5.

[0037] Furthermore, for oily wastewater conditions of 5-40℃, salinity of 0.5%-5%, and pH of 4.0-10.0, the demulsifier has an oil removal rate of over 95% and a COD removal rate of over 85%.

[0038] A method for preparing a demulsifier for oily wastewater includes the following steps: S1. Mix the iron salt and deionized water and dissolve them completely to obtain the base solution; S2. Add aluminum salt to the base solution, heat to 40-60℃ and stir for 0.5-4 hours, then add auxiliary salt and continue stirring for 1-4 hours to form a complex intermediate. S3. Cool down to below 30°C, add initiator, and stir at a constant temperature to carry out polymerization reaction; S4. Adjust the pH to 3.5-4.5, filter to remove insoluble impurities, and you're done.

[0039] This application employs a combined process of stepwise complexation followed by low-temperature polymerization. Its core advantage lies in the controllable preparation of the demulsifier's molecular structure through sequential control and precise temperature control. The stepwise complexation stage (dissolution at 35℃ and complexation at 50℃) ensures that iron and aluminum salts preferentially form a stable Fe-Al heteronuclear hydroxyl complex framework, followed by the orderly embedding of magnesium and zirconium salts. This avoids disordered competitive reactions among multiple metal ions, resulting in a well-defined, uniformly charged multi-metal-oxygen bridge intermediate. The low-temperature polymerization stage (composite initiation at 25℃) effectively controls the polymerization rate and molecular chain length, preventing excessive cross-linking and deactivation caused by high temperatures (e.g., 80℃), resulting in a narrow molecular weight distribution and intact active structure. The synergistic effect of these two processes ensures the demulsifier has a suitable molecular weight and abundant adsorption bridging sites, while also endowing it with efficient charge neutralization capabilities. Ultimately, this achieves a 95% oil removal rate and a 30-40% reduction in sludge production, maintaining stable performance under low temperature, high salt, and wide pH conditions. This solves the technical problems of uncontrollable structure and unstable efficiency in traditional simple mixing or high-temperature copolymerization processes.

[0040] Furthermore, the dissolution temperature of S1 is 30-38℃. Temperatures above 38℃ will cause Fe... 3+Early excessive hydrolysis can occur, generating a large amount of highly polymerized hydroxy-iron complexes or even Fe(OH)3 precipitates, thereby weakening the ability to subsequently undergo controlled copolymerization with aluminum salts.

[0041] Furthermore, the insulation temperature in S2 is 45-55℃. If the temperature is too low, Fe... 3+ With Al 3+ The hydroxyl bridging reaction kinetics between the iron salts are too slow; excessively high temperatures lead to excessive molecular chain growth, disordered polymer spatial configuration, and even induce localized gelation, resulting in decreased activity and poor storage stability of the final product. A dissolution temperature of 30-38℃ and a holding temperature of 45-55℃ together ensure that the iron salt enters the system as a moderately hydrolyzed monomer or oligomer, and undergoes ordered and controllable hydroxyl-bridged copolymerization with the aluminum salt under mild heating conditions. This lays the foundation for the formation of a polymetallic oxygen-bridged copolymer with uniform molecular weight distribution and complete active structure in the subsequent low-temperature polymerization stage.

[0042] Furthermore, the stirring reaction time after adding aluminum salt is 0.5-1.5 h; the stirring reaction time after adding auxiliary salt is 1.0-1.5 h.

[0043] Furthermore, in S3, the temperature is lowered to 20-30℃, and the polymerization reaction time is 1.0-5.0h. This temperature and time range ensures that the initiator can decompose at a moderate rate to generate free radicals, allowing the polymerization reaction to proceed smoothly. This avoids polymer runaway and excessive chain growth at high temperatures, which would hinder the demulsification effect, while also preventing insufficient polymerization and low molecular weight products with inadequate adsorption and bridging capabilities at excessively low temperatures.

[0044] Preferably, the temperature in S3 is lowered to 23-27°C, and the polymerization reaction time is 1.5-3 hours.

[0045] Furthermore, the amount of initiator accounts for 0.3-0.8% of the total mass of the demulsifier components.

[0046] Furthermore, the initiators are ammonium persulfate and sodium sulfite, with a mass ratio of ammonium persulfate to sodium sulfite of 1-2:1. Ammonium persulfate and sodium sulfite can efficiently generate sulfate radicals and hydroxyl radicals at low temperatures through electron transfer reactions, achieving low-temperature initiation. Simultaneously, the appropriate presence of sodium sulfite acts as a chain transfer agent, effectively controlling the polymer molecular chain length and preventing excessive cross-linking or gelation due to unlimited molecular weight growth.

[0047] Example 1 This embodiment provides a demulsifier for oily wastewater. The raw material components of the demulsifier include 18wt% ferric sulfate, 15wt% polyaluminum chloride (Al2O3 content 28%), 7wt% auxiliary salt, and the balance deionized water. The auxiliary salt includes magnesium sulfate and zirconium oxychloride, with a mass ratio of 3:4.

[0048] The method for preparing the demulsifier includes the following steps: S1. Add ferric sulfate (Fe2(SO4)3・9H2O) to deionized water (48wt% of the total raw material components), mix and stir for 30 minutes at 35℃ and 200r / min to fully dissolve, and obtain the base solution; S2. Slowly add polyaluminum chloride (PAC) to the base solution, heat to 50°C and stir for 1.0 h, then add a mixture of magnesium sulfate and zirconium oxychloride (using the remaining deionized water in the mixture), and continue stirring for 1.5 h to form a complex intermediate. S3. Lower the system temperature to 25°C, add an initiator (a mixture of ammonium persulfate and sodium sulfite, with a mass ratio of 1:1) accounting for 0.5% of the total mass of the demulsifier raw material components, and stir at a constant temperature for 2.0 h to carry out the polymerization reaction; S4. Adjust the pH to 3.5-4.5, cool to room temperature, and filter to remove insoluble impurities to obtain a reddish-brown transparent demulsifier.

[0049] Example 2 This embodiment provides a demulsifier for oily wastewater. The raw material components of the demulsifier include 15wt% ferric sulfate, 20wt% polyaluminum chloride (Al2O3 content 28%), 10wt% auxiliary salt, and the balance deionized water. The auxiliary salt includes magnesium sulfate and zirconium oxychloride, with a mass ratio of 3:2.

[0050] The method for preparing the demulsifier includes the following steps: S1. Add ferric sulfate (Fe2(SO4)3・9H2O) to deionized water (45wt% of the total raw material components), mix and stir at 30℃ and 200r / min for 1h to fully dissolve, and obtain the base solution; S2. Slowly add polyaluminum chloride (PAC) to the base solution, heat to 60°C and stir for 0.5 hours. Then add a mixture of magnesium sulfate and zirconium oxychloride (using the remaining deionized water in the mixture) and continue stirring for 1 hour to form a complex intermediate. S3. Lower the system temperature to 30℃, add an initiator (a mixture of ammonium persulfate and sodium sulfite, with a mass ratio of 1:1) accounting for 0.3% of the total mass of the demulsifier raw material components, and stir at a constant temperature for 3 hours to carry out the polymerization reaction; S4. Adjust the pH to 3.5-4.5, cool to room temperature, and filter to remove insoluble impurities to obtain a reddish-brown transparent demulsifier.

[0051] Example 3 This embodiment provides a demulsifier for oily wastewater. The raw material components of the demulsifier include 25wt% ferric sulfate, 10wt% polyaluminum chloride (Al2O3 content 28%), 6wt% auxiliary salt, and the balance deionized water. The auxiliary salt includes magnesium sulfate and zirconium oxychloride in a mass ratio of 3:3.

[0052] The method for preparing the demulsifier includes the following steps: S1. Add ferric sulfate (Fe2(SO4)3・9H2O) to deionized water (55wt% of the total raw material components), mix and stir for 30 minutes at 38℃ and 200r / min to fully dissolve, and obtain the base solution; S2. Slowly add polyaluminum chloride to the base solution, heat to 40°C and stir for 1.5 hours. Then add a mixture of magnesium sulfate and zirconium oxychloride (using the remaining deionized water in the mixture) and continue stirring for 1.5 hours to form a complex intermediate. S3. Lower the system temperature to 20°C, add an initiator (a mixture of ammonium persulfate and sodium sulfite, with a mass ratio of 2:1) accounting for 0.8% of the total mass of the demulsifier raw material components, and stir at a constant temperature for 1.5 hours to carry out the polymerization reaction; S4. Adjust the pH to 3.5-4.5, cool to room temperature, and filter to remove insoluble impurities to obtain a reddish-brown transparent demulsifier.

[0053] Comparative Example 1 The difference between this comparative example and Example 1 is that the raw material components of the demulsifier include 30wt% ferric sulfate, 15wt% polyaluminum chloride (Al2O3 content 28%), and the balance deionized water.

[0054] The preparation method is as follows: After combining and mixing the above raw materials, directly mix them mechanically until uniform.

[0055] Comparative Example 2 The difference between this comparative example and Example 1 is that the polymerization reaction temperature in S3 is 80°C.

[0056] Comparative Example 3 The difference between this comparative example and Example 1 is that the auxiliary salt is magnesium sulfate.

[0057] Comparative Example 4 The difference between this comparative example and Example 1 is that the mass ratio of magnesium sulfate to zirconium oxychloride is 3:1.

[0058] Comparative Example 5 The difference between this comparative example and Example 1 is that aluminum salt and auxiliary salt are added simultaneously during the S2 complexation process, and the mixture is kept at 50°C and stirred for 2.5 hours.

[0059] Performance testing methods: Selection of oily wastewater samples: Oily wastewater from petrochemical industry (oil content 500 mg / L, COD=8200 mg / L, pH=6.8, temperature 25℃) and oily wastewater from mechanical processing (oil content 350 mg / L, COD=5600 mg / L, pH=7.2, temperature 10℃) were selected.

[0060] 1. Demulsification performance test: Refer to the "Performance Test Method for Crude Oil Demulsifiers (Bottle Test Method)" (SY / T5281-2020). Take 100mL of oily wastewater and add 50mg of demulsifier per 1L of oily wastewater according to the sample of the usage example and comparative example. Stir for 10min and let stand for 30min. Detect the oil content of the supernatant (using the test method for animal and vegetable oils, referring to HJ637-2018), COD (using the rapid closed digestion method, referring to HJ / T399-2007), and sludge production (using the mixed liquor suspended solids (MLSS) test method). Calculate the oil removal rate (based on the concentration of oil content) and the COD removal rate (based on the concentration of COD).

[0061] Test results: The demulsifier in Example 1 achieved an oil removal rate of 98.6% and a COD removal rate of 92.3% for petrochemical oily wastewater, with sludge production only 62% of that of traditional iron salt demulsifiers; for mechanical processing oily wastewater, it achieved an oil removal rate of 97.8% and a COD removal rate of 89.5%, with a floc settling velocity of 2.8 cm / min.

[0062] 2. Adaptability test: Adjust the wastewater temperature (5℃, 10℃, 25℃, 40℃), salinity (0.5%, 1%, 3%, 5%) and pH (4.0, 6.0, 8.0, 10.0) and repeat the above demulsification performance test to evaluate the environmental adaptability of the demulsifier. The test data of each example and comparative example for petrochemical oily wastewater are shown in Table 1.

[0063] Table 1. Results of temperature, salinity, and pH adaptability tests of different demulsifier groups to petrochemical oily wastewater.

[0064] This application achieves the synergistic effect of iron ions, aluminum ions, magnesium ions, and zirconium ions through a stepwise complexation-low temperature polymerization process by strictly defining the raw material composition of the demulsifier. The prepared demulsifier has excellent demulsification efficiency and environmental adaptability (high and low temperature, wide pH and high salt).

[0065] The demulsifier of this invention maintains an oil removal rate of over 95% and a COD removal rate of over 85% within a temperature range of 5-40℃, salinity of 0.5%-5%, and pH of 4.0-10.0, demonstrating significantly better performance stability than traditional demulsifiers. Compared to a single ferric sulfate demulsifier, the demulsifier of this invention improves the oil removal rate by 15.2% and reduces sludge production by 38%; compared to commercially available iron-aluminum composite demulsifiers, it improves the COD removal rate by 8.7% and increases demulsification efficiency by 22.3% under low-temperature (5℃) conditions.

[0066] When the demulsifier of Comparative Example 1 was used to treat oily wastewater from petrochemical plants, the maximum oil removal rate was only 83.5%, the maximum COD removal rate was 76.2%, the floc settling velocity was 0.9 cm / min, the sludge production was large, and the demulsification efficiency dropped to 65.8% under low temperature (10℃) conditions. This was because the iron and aluminum ions did not form an effective complex structure and the synergistic effect was weak.

[0067] The demulsifier in Comparative Example 2 exhibited stratification and poor stability, with an oil removal rate of only 78.3% for oily wastewater. This was because high temperature led to excessive ionic polymerization, resulting in excessively long polymer molecular chains that were unable to effectively demulsify.

[0068] The demulsifier of Comparative Example 3 had a maximum oil removal rate of 82.1%, which was significantly lower than that of Example 1. This is because a single magnesium salt cannot effectively regulate the charge density of the polymer and is difficult to adapt to the emulsion system in a high-salt environment.

[0069] The demulsifier in Comparative Example 4 had a maximum oil content and COD removal rate of 82.3% and 82.6%, respectively. This was because the proportion of zirconium oxychloride was relatively low, resulting in an unstable molecular structure of the demulsifier and an insignificant bridging effect on organic matter.

[0070] The maximum values ​​of oil content and COD removal rate of the demulsifier in Comparative Example 5 were 79.5% and 74.6% respectively during use. This was because the auxiliary salt was added too early in the demulsifier structure building process and did not play an auxiliary supporting role. Instead, it affected the reaction process of the iron salt and magnesium salt reaction system in the demulsifier, resulting in low demulsification efficiency of the demulsifier.

[0071] It should be noted that, in this document, relational terms such as "first" and "second" are used only to distinguish one entity or operation from another, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Furthermore, the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such process, method, article, or apparatus.

[0072] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.

Claims

1. A demulsifier for oily wastewater, characterized in that, The raw material components of the demulsifier include 15-25 wt% iron salt, 10-20 wt% aluminum salt, 5-10 wt% auxiliary salt and the balance deionized water; the auxiliary salt is a compound system of magnesium salt and zirconium salt, and the mass ratio of magnesium salt to zirconium salt is 3:2-4. The preparation method of the demulsifier includes the following steps: S1. Mix the iron salt and deionized water and dissolve them completely to obtain the base solution; S2. Add aluminum salt to the base solution, heat to 40-60℃ and stir for 0.5-4 hours, then add auxiliary salt and continue stirring for 1-4 hours to form a complex intermediate. S3. Cool down to below 30°C, add initiator, and stir at a constant temperature to carry out polymerization reaction; S4. Adjust the pH to 3.5-4.5, filter to remove insoluble impurities, and you're done.

2. The demulsifier for oily wastewater according to claim 1, characterized in that, The iron salt includes ferric sulfate, the aluminum salt includes polyaluminum chloride, the magnesium salt includes magnesium sulfate, and the zirconium salt includes zirconium oxychloride.

3. The demulsifier for oily wastewater according to claim 1, characterized in that, The pH of the demulsifier is 3.5-4.

5.

4. The demulsifier for oily wastewater according to claim 1, characterized in that, For oily wastewater conditions of 5-40℃, salinity of 0.5%-5%, and pH of 4.0-10.0, the demulsifier has an oil removal rate of over 95% and a COD removal rate of over 85%; the oil removal rate is calculated based on oil concentration, and the COD removal rate is calculated based on COD concentration.

5. The demulsifier for oily wastewater according to claim 1, characterized in that, The dissolution temperature in S1 is 30-38℃; the holding temperature in S2 is 45-55℃; the stirring reaction time after adding aluminum salt is 0.5-1.5h; the stirring reaction time after adding auxiliary salt is 1.0-1.5h.

6. The demulsifier for oily wastewater according to claim 1, characterized in that, In S3, the temperature is lowered to 20-30℃, and the polymerization reaction time is 1.0-5.0h.

7. The demulsifier for oily wastewater according to claim 1, characterized in that, In S3, the temperature is lowered to 23-27℃, and the polymerization reaction time is 1.5-3h.

8. The demulsifier for oily wastewater according to claim 1, characterized in that, The amount of initiator accounts for 0.3-0.8% of the total mass of the demulsifier components; the initiator is ammonium persulfate and sodium sulfite, and the mass ratio of ammonium persulfate to sodium sulfite in the initiator is 1-2:1.

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