Composite surfactant for cleaning low-temperature oily sludge and application thereof

Abstract

The invention discloses a composite surfactant for cleaning low-temperature oily sludge and application thereof, and relates to the technical field of low-temperature oily sludge treatment.The composite surfactant is prepared from, by mass, a core surfactant, a low-temperature coupling solvent, auxiliaries and the balance deionized water. The cleaning efficiency of the composite surfactant can reach 90% or above in the low-temperature environment of 5-20 DEG C, additional heating is not needed, and the energy consumption is greatly reduced compared with that of a traditional process. Through the synergistic effect of the eutectic system and the dendritic surfactant, the oil stain removal agent has good adaptability to light and heavy oil stains and aged oil sludge. The pH response demulsification mechanism shortens the oil-water layering time to 5-10 minutes, and the purity of the recovered oil is greater than or equal to 85%. The problems of low cleaning efficiency, high energy consumption, secondary pollution, poor formula universality and the like on the oily sludge at the low temperature of 5-20 DEG C are solved, and an innovative solution is provided for low-temperature oily sludge treatment.

Description

Technical Field

[0001] This invention relates to the field of low-temperature oily sludge treatment technology, and in particular to composite surfactants for cleaning low-temperature oily sludge and their applications. Background Technology

[0002] Oily sludge is a common hazardous waste generated during petroleum extraction, refining, storage, and transportation. It has a high oil content and complex composition, and improper handling can easily cause soil and water pollution. At low temperatures, the oil in oily sludge easily solidifies and precipitates, and the binding force between oily sludge particles increases, posing significant challenges to conventional cleaning technologies. Current oily sludge cleaning methods largely rely on high-temperature heating to improve the fluidity of the oil, which is not only energy-intensive but also complex to operate.

[0003] Meanwhile, the activity of traditional surfactant systems decreases at low temperatures, resulting in limited removal of recalcitrant components such as heavy oil gums and asphalt, with cleaning efficiency generally below 60%.

[0004] Furthermore, most cleaning systems lack efficient demulsification mechanisms, making oil-water separation difficult after cleaning. This not only affects the purity of oil recovery but also easily generates secondary polluting wastewater. Some surfactant components have poor biodegradability, which can exacerbate the environmental burden with long-term use. Moreover, they are not well-suited for oil sludge with different oil contents and aging levels, making it difficult to meet diverse treatment needs. Summary of the Invention

[0005] To address the aforementioned technical problems, this invention provides a composite surfactant for low-temperature oily sludge cleaning and its application. The technical solution is as follows: A composite surfactant for low-temperature oily sludge cleaning comprises the following components by weight percentage: The core surfactant is 25%–30%, the low-temperature coupling solvent is 20%–25%, the auxiliary agent is 2.8%–3.8%, and the balance is deionized water; The core surfactants include decyl glucoside, cocamidopropyl hydroxysulfonate betaine, and bio-based oligoisobutylene succinic anhydride derivatives. The low-temperature coupling solvent includes methyl lactate and d-limonene; The additives include modified nano-silica, low-viscosity sodium alginate, pH-responsive copolymer, and polyethylene glycol 400.

[0006] Optionally, the core surfactant comprises the following components in weight percentages: Decyl glucoside 14%-16%, cocamidopropyl hydroxysulfonate betaine 9%-12%, bio-based oligomeric isobutylene succinic anhydride derivatives 4.5%-5.8%; The low-temperature coupling solvent comprises the following components by mass percentage: Methyl lactate 11%-13.8% and d-limonene 7%-9%; The additive comprises the following components by mass percentage: Modified nano silica 0.8%-1.2%, sodium alginate 0.4%-0.6%, pH-responsive copolymer 1.8%-2.2%, polyethylene glycol 400 0.3%.

[0007] Optionally, the core surfactant comprises 15% decyl glucoside, 10% cocamidopropyl hydroxysulfonate betaine, and 5% bio-based oligoisobutylene succinic anhydride derivative; the decyl glucoside has a purity of ≥98% and a solubility of ≥30% at 5°C, the cocamidopropyl hydroxysulfonate betaine has a solid content of 35% and a hard water resistance of 500 mg / L, and the bio-based oligoisobutylene succinic anhydride derivative has a dendritic structure with a number average molecular weight of 1000.

[0008] Optionally, in the low-temperature coupling solvent, methyl lactate accounts for 12% and limonene accounts for 8%; the eutectic system formed by the compound has a eutectic point of less than or equal to -72°C and can reduce the solidification point of oil stains to below -15°C.

[0009] Optionally, the additives comprise 1% modified nano-silica, 0.5% low-viscosity sodium alginate, 2% pH-responsive copolymer, and 0.3% polyethylene glycol 400; the modified nano-silica is hydrophobic, the pH-responsive copolymer is dimethylaminoethyl methacrylate-butyl acrylate copolymer with a molecular weight of 5000 Da-8000 Da, and the polyethylene glycol 400 can make the viscosity of the system less than or equal to 50 mPa·s at 5°C.

[0010] A method for preparing a composite surfactant for low-temperature oily sludge cleaning, characterized by comprising the following steps: Step 1: In a reactor equipped with an anchor-type stirring paddle and jacket heating, methyl lactate, dextrorotatory limonene, bio-based oligomeric isobutylene succinic anhydride derivative, and polyethylene glycol 400 are added sequentially; the jacket temperature is set to 35°C, and the mixture is stirred at 180-220 rpm for 13-16 minutes until the light transmittance of the mixture is greater than or equal to 95%, forming a homogeneous and transparent organic phase; Step 2: Add deionized water to a turbine-type stirred tank and heat to 35±2℃; slowly add decyl glucoside and cocamidopropyl hydroxysulfonyl betaine in that order, and stir at 350rpm-450rpm for 20 minutes until the transmittance of the solution is greater than or equal to 98%; then add low-viscosity sodium alginate and continue stirring for 13-16 minutes until there are no unswelled particles and an aqueous phase is formed; Step 3: The organic phase obtained in Step 1 is added dropwise to the aqueous phase of Step 2 under stirring using a metering pump at a rate of 9 L / min-10 L / min. During the dropwise addition, the stirring speed of the aqueous phase is simultaneously increased to 750 rpm-800 rpm. After the dropwise addition is completed, the stirring speed is maintained for 18-20 minutes to form a milky white pre-emulsion with a particle size distribution of 1 μ-5 μm. The pre-emulsion does not separate into layers after standing for 24 hours. Step 4: Reduce the stirring speed of the pre-emulsion from Step 3 to 380 rpm-400 rpm, add the pH-responsive copolymer and hydrophobic modified nano-silica sequentially, and stir for 13-16 minutes; pump the mixture into a high-pressure homogenizer and homogenize twice at a pressure of 28 MPa-30 MPa to ensure that the emulsion particle size is less than or equal to 500 nm and the PDI is less than or equal to 0.2; cool to 25±2℃, adjust the pH to 6.5-7.5 with 0.1 mol / L NaOH or HCl, and centrifuge at 2500 rpm-300 rpm for 28-30 minutes until no stratification occurs to obtain the finished product.

[0011] Optionally, during the stirring process in step 1, the jacket temperature fluctuation is controlled within ±1℃ to ensure that the organic phase components are fully dissolved and there is no local overheating.

[0012] Optionally, the impeller of the turbine-type mixing tank in step 2 is a six-bladed turbine impeller. When adding cocamidopropyl hydroxysulfonate betaine, a dripping method is adopted, with a dripping rate of 0.5L / min-0.8L / min, to avoid gelation due to excessively high local concentration.

[0013] Optionally, in step 4, the feed temperature of the high-pressure homogenizer is controlled at 30±2℃. During the homogenization cycle, pulse feeding is used with a pulse frequency of 2-3 times / minute to ensure uniform particle size distribution of the emulsion. After the finished product cools, it needs to be left to stand in a sealed container for 12 hours, and the particle size and centrifugal stability are tested again. After passing the test, it is packaged.

[0014] The application of a composite surfactant in the cleaning of oily sludge at 5℃-20℃ is characterized by the following steps: Step a: Adjust the dilution ratio according to the oil content of the oily sludge: when the oil content is greater than or equal to 20%, dilute the composite surfactant mother liquor with room temperature water at a ratio of 1:10; when the oil content is 10%-20%, dilute at a ratio of 1:15; when the oil content is less than 10%, dilute at a ratio of 1:20 to obtain the cleaning working solution. Step b: Add the cleaning working fluid and oily sludge to the ribbon stirring cleaning device at a liquid-solid ratio of 3:1-5:1, and stir and clean at a speed of 60rpm-100rpm for 15-30 minutes. The stirring and cleaning time for aged oily sludge is extended to 30 minutes. Step c: After washing, the slurry is fed into a three-phase centrifuge and separated at 3000 rpm for 15 minutes to obtain an upper layer of floating oil, a middle layer of aqueous phase, and a lower layer of wet solids. A 5% citric acid solution is added to the floating oil to adjust the pH to 4.0-4.5, and the mixture is stirred at 100-120 rpm for 5-10 minutes to break the emulsion. The purity of the upper layer recovered oil is greater than or equal to 85%. In step d, the pH of the middle aqueous phase is adjusted to 6.5-7.5 with 0.1 mol / L NaOH, filtered through a 5 μm pore size filter membrane, and then reused in the dilution step of S1; the lower layer containing wet solids is filtered by a 0.8 MPa pressure plate and frame filter until the water content is less than or equal to 30% and the oil content is less than or equal to 1%, meeting the standards for resource utilization or safe disposal.

[0015] In summary, the present invention has at least one of the following beneficial technical effects: This invention provides a composite surfactant for cleaning oily sludge at low temperatures and its application. The composite surfactant can achieve a cleaning efficiency of over 90% in a low-temperature environment of 5℃-20℃, without the need for additional heating, and the energy consumption is significantly reduced compared to traditional processes.

[0016] Through the synergistic effect of the eutectic system and dendritic surfactants, it exhibits good compatibility with both light and heavy oil contamination and aged sludge. The pH-responsive demulsification mechanism shortens the oil-water separation time to 5-10 minutes, and the recovered oil purity is greater than or equal to 85%.

[0017] This solution addresses the problems of low efficiency, high energy consumption, secondary pollution, and poor formula universality in cleaning oily sludge at low temperatures (5℃-20℃). It constructs a highly efficient, environmentally friendly, and adaptable composite cleaning system, while also developing industrializable preparation and application processes, providing an innovative solution for the treatment of low-temperature oily sludge. Attached Figure Description

[0018] Figure 1 This is a flowchart illustrating steps 1 and 2 of the preparation method of the composite surfactant for low-temperature oily sludge cleaning according to the present invention.

[0019] Figure 2 This is a flowchart illustrating steps 3 and 4 of the preparation method of the composite surfactant for low-temperature oily sludge cleaning according to the present invention. Detailed Implementation

[0020] The present invention will be further described in detail below with reference to the accompanying drawings.

[0021] This invention discloses a composite surfactant for low-temperature oily sludge cleaning and its application.

[0022] Reference Figure 1 and Figure 2Example 1, a composite surfactant for low-temperature oily sludge cleaning, comprising the following components by mass percentage: The core surfactant is 25%–30%, the low-temperature coupling solvent is 20%–25%, the auxiliary agent is 2.8%–3.8%, and the balance is deionized water; The core surfactants include decyl glucoside, cocamidopropyl hydroxysulfonate betaine, and bio-based oligoisobutylene succinic anhydride derivatives. The low-temperature coupling solvent includes methyl lactate and d-limonene; The additives include modified nano-silica, low-viscosity sodium alginate, pH-responsive copolymer, and polyethylene glycol 400.

[0023] Example 2, the core surfactant comprises the following components by mass percentage: Decyl glucoside 14%-16%, cocamidopropyl hydroxysulfonate betaine 9%-12%, bio-based oligomeric isobutylene succinic anhydride derivatives 4.5%-5.8%; The low-temperature coupling solvent comprises the following components by mass percentage: Methyl lactate 11%-13.8% and d-limonene 7%-9%; The additive comprises the following components by mass percentage: Modified nano silica 0.8%-1.2%, sodium alginate 0.4%-0.6%, pH-responsive copolymer 1.8%-2.2%, polyethylene glycol 400 0.3%.

[0024] In Example 3, the core surfactant comprises 15% decyl glucoside, 10% cocamidopropyl hydroxysulfonate betaine, and 5% bio-based oligoisobutylene succinic anhydride derivative. The decyl glucoside has a purity of ≥98% and a solubility of ≥30% at 5°C. The cocamidopropyl hydroxysulfonate betaine has a solid content of 35% and a hard water resistance of 500 mg / L. The bio-based oligoisobutylene succinic anhydride derivative has a dendritic structure with a number average molecular weight of 1000.

[0025] In Example 4, the low-temperature coupling solvent contains 12% methyl lactate and 8% d-limonene; the eutectic system formed by the compound has a eutectic point of less than or equal to -72°C and can reduce the solidification point of oil stains to below -15°C.

[0026] In Example 5, the additives comprise 1% modified nano-silica, 0.5% low-viscosity sodium alginate, 2% pH-responsive copolymer, and 0.3% polyethylene glycol 400. The modified nano-silica is hydrophobic, the pH-responsive copolymer is dimethylaminoethyl methacrylate-butyl acrylate copolymer with a molecular weight of 5000 Da-8000 Da, and the polyethylene glycol 400 enables the system to have a viscosity of less than or equal to 50 mPa·s at 5°C.

[0027] By adopting the above technical solution, through the triple synergistic mechanism of amphiphilic adsorption-low temperature coupling-directional phase separation, efficient cleaning of oily sludge and precise separation of oil-water-solid three phases are achieved in a low temperature environment of 5-20℃. The role and synergistic principle of each component are as follows.

[0028] The core surfactant constructs a multi-level action system. The nonionic hydrophilic group of decyl glucoside tightly binds to the aqueous phase, while the hydrophobic group is directionally adsorbed onto the oil surface to form a stable adsorption layer, weakening the adhesion between oil and solid particles. The zwitterionic structure of cocamidopropyl hydroxysulfonate betaine can regulate the interfacial charge distribution, enhancing the system's resistance to hard water. Simultaneously, it synergistically works with decyl glucoside to reduce the oil-water interfacial tension to an extremely low level, accelerating the removal of oil from the solid surface. The dendritic molecular chains of the bio-based oligomeric isobutylene succinic anhydride derivative can penetrate deep into the cross-linked framework of heavy oil gums and asphaltenes, disrupting their aggregated structure through intermolecular forces, achieving heavy oil depolymerization, and significantly enhancing its suitability for cleaning high-viscosity, aged sludge.

[0029] The low-temperature coupled solvent forms a eutectic synergistic system. When methyl lactate and limonene are compounded in a specific ratio, the eutectic point drops below -72°C, maintaining good fluidity at low temperatures. Simultaneously, it dissolves waxes and light hydrocarbon components in the sludge, lowering the solidification point of the oil to below -15°C, thus overcoming the problem of oil solidification at low temperatures. The complementary molecular structures of the two components allow for rapid penetration into the pores of the sludge, shortening the contact reaction time between the surfactant and the oil, and improving low-temperature cleaning efficiency.

[0030] The additive system enables precise control throughout the cleaning process. Modified nano-silica adsorbs onto the surface of the stripped solid particles, forming a hydrophobic protective layer that effectively prevents oil re-adsorption and accelerates solid particle settling. Low-viscosity sodium alginate, during the cleaning stage, suspends fine solid particles by entangling them with its polymer chains, preventing particle agglomeration and ensuring effective cleaning. During the demulsification stage, its carboxyl groups combine with metal ions in the system to form flocs, promoting rapid solid-liquid separation. The pH-responsive copolymer exhibits a hydrophilic extended state in a neutral cleaning environment, stabilizing the oil-water microemulsion. When the system pH is adjusted to the acidic range, the copolymer chains protonate and coil, disrupting the stability of the emulsion interface film and achieving oil-water stratification. Polyethylene glycol 400 reduces the system's low-temperature viscosity through intermolecular lubrication, ensuring uniform dispersion of all components and guaranteeing efficient synergistic effects.

[0031] The overall system works in synergy through the above mechanisms to sequentially soften oil, adsorb and peel off, emulsify and disperse it under low temperature conditions, and then triggers directional demulsification by pH adjustment, ultimately achieving efficient separation of oil, water and solid phases, taking into account low temperature cleaning efficiency, environmental friendliness and resource recovery effect.

[0032] Example 6: A method for preparing a composite surfactant for low-temperature oily sludge cleaning, characterized by comprising the following steps: Step 1: In a reactor equipped with an anchor-type stirring paddle and jacket heating, methyl lactate, dextrorotatory limonene, bio-based oligomeric isobutylene succinic anhydride derivative, and polyethylene glycol 400 are added sequentially; the jacket temperature is set to 35°C, and the mixture is stirred at 180-220 rpm for 13-16 minutes until the light transmittance of the mixture is greater than or equal to 95%, forming a homogeneous and transparent organic phase; Step 2: Add deionized water to a turbine-type stirred tank and heat to 35±2℃; slowly add decyl glucoside and cocamidopropyl hydroxysulfonyl betaine in that order, and stir at 350rpm-450rpm for 20 minutes until the transmittance of the solution is greater than or equal to 98%; then add low-viscosity sodium alginate and continue stirring for 13-16 minutes until there are no unswelled particles and an aqueous phase is formed; Step 3: The organic phase obtained in Step 1 is added dropwise to the aqueous phase of Step 2 under stirring using a metering pump at a rate of 9 L / min-10 L / min. During the dropwise addition, the stirring speed of the aqueous phase is simultaneously increased to 750 rpm-800 rpm. After the dropwise addition is completed, the stirring speed is maintained for 18-20 minutes to form a milky white pre-emulsion with a particle size distribution of 1 μ-5 μm. The pre-emulsion does not separate into layers after standing for 24 hours. Step 4: Reduce the stirring speed of the pre-emulsion from Step 3 to 380 rpm-400 rpm, add the pH-responsive copolymer and hydrophobic modified nano-silica sequentially, and stir for 13-16 minutes; pump the mixture into a high-pressure homogenizer and homogenize twice at a pressure of 28 MPa-30 MPa to ensure that the emulsion particle size is less than or equal to 500 nm and the PDI is less than or equal to 0.2; cool to 25±2℃, adjust the pH to 6.5-7.5 with 0.1 mol / L NaOH or HCl, and centrifuge at 2500 rpm-300 rpm for 28-30 minutes until no stratification occurs to obtain the finished product.

[0033] By adopting the above technical solution, step 1 employs an anchor-stirring-constant-temperature premixing mechanism. The low-speed, high-convective characteristics of the anchor-stirring paddle are well-suited to the viscous properties of the organic phase components. The 180-220 rpm stirring speed avoids excessive local shear forces that could damage the component structure, while ensuring that solvents such as methyl lactate and limonene are fully miscible with the bio-based oligomeric isobutylene succinic anhydride derivative. A 35℃ jacket-controlled constant temperature keeps the kinetic energy of the organic phase molecules within a suitable range, and a stirring time of 13-16 minutes ensures that the transmittance of the mixture is ≥95%, forming a homogeneous and transparent organic phase. This lays a thermodynamically stable foundation for subsequent efficient emulsification with the aqueous phase.

[0034] Step 2 achieves precise aqueous phase preparation through turbine stirring and stepwise dissolution. The high-shear stirring characteristics (350rpm-450rpm) of the turbine-type stirred tank accelerate the dissolution and dispersion of decyl glucoside and cocamidopropyl hydroxysulfonate betaine. The water temperature of 35±2℃ matches the critical micelle temperature of the surfactant. Stirring for 20 minutes until the transmittance is ≥98% ensures that the surfactant is completely dissolved and forms a homogeneous hydrated system. Low-viscosity sodium alginate is added later and stirring continues for 13-16 minutes to avoid dissolution lag caused by intermolecular competitive adsorption when it is added simultaneously with the surfactant, ensuring no unswelled particles and improving the stability of the aqueous phase system.

[0035] Step 3 utilizes a gradient speed-controlled dropwise addition method to construct a stable preemulsion. The organic phase dropwise acceleration rate of 9-10 L / min is synchronized with the aqueous phase stirring speed, which is increased to 750-800 rpm to ensure uniform dispersion of the organic phase in the aqueous phase as tiny droplets, preventing the formation of coarse continuous phases due to excessively high local organic phase concentrations. High-speed stirring for 18-20 minutes after addition maintains the dynamic equilibrium between droplet collision and dispersion, forming a milky white preemulsion with a particle size distribution of 1-5 μm. The absence of stratification after 24 hours of standing verifies the colloidal stability of the preemulsion, providing a good foundation for subsequent homogenization and particle size refinement.

[0036] Step 4 employs a slow-speed mixing-high-pressure homogenization process to regulate the finished product system. Reducing the stirring speed to 380-400 rpm decreases the shear force during the addition of pH-responsive copolymers and hydrophobic modified nano-silica, preventing additive agglomeration. Stirring for 13-16 minutes ensures uniform dispersion of the additives in the pre-emulsion. Two cycles of high-pressure homogenization at 28-30 MPa refine the pre-emulsion particle size to ≤500 nm and PDI ≤0.2 through mechanical shearing and cavitation effects, improving system stability and interfacial activity. After cooling to 25±2℃, the pH is adjusted to 6.5-7.5, stabilizing the emulsion by placing the pH-responsive copolymer in a hydrophilic extended state. Centrifugation at 2500-3000 rpm for 28-30 minutes without stratification verifies the physical stability of the finished product system, ensuring product performance meets standards.

[0037] In Example 7, during the stirring process in step 1, the jacket temperature fluctuation was controlled within ±1℃ to ensure that the organic phase components were fully dissolved and there was no local overheating.

[0038] By adopting the above technical solution, the dendritic molecular structure of the bio-based oligomeric isobutylene succinic anhydride derivative in the organic phase component is sensitive to temperature. If the temperature fluctuation exceeds ±1℃, the local high temperature may cause thermal degradation of its molecular chains, destroying the dendritic depolymerization sites and reducing the ability to penetrate and depolymerize heavy oil gums; the local low temperature will slow down the molecular diffusion rate, resulting in methyl lactate, dextrorotatory limonene and bio-based oligomeric isobutylene succinic anhydride derivative not being fully miscible, forming microphase separation that is invisible to the naked eye, affecting the interfacial interaction effect during subsequent emulsification with the aqueous phase.

[0039] Temperature fluctuation control of ±1℃ maintains the molecular kinetic energy of the organic phase system within a stable range, ensuring uniform diffusion rates of each component and avoiding localized concentration differences caused by temperature gradients. This precise temperature control allows the transmittance of the mixture to consistently reach ≥95% within a stirring time of 13-16 minutes, forming a thermodynamically stable, homogeneous, and transparent organic phase. This lays the foundation for the uniform dispersion of organic phase droplets in the subsequent coupling emulsification stage, thereby ensuring the uniformity and stability of the final product emulsion particle size distribution.

[0040] In Example 8, the impeller of the turbine-type mixing tank in step 2 is a six-bladed turbine impeller. When adding cocamidopropyl hydroxysulfonate betaine, a dripping method is adopted, with a dripping rate of 0.5L / min-0.8L / min, to avoid gelation due to excessively high local concentration.

[0041] By adopting the above technical solution, the six-bladed turbine propeller possesses structural advantages such as strong radial mixing capability and uniform shear force distribution. Its blade shape can generate a strong radial liquid flow at speeds of 350rpm-450rpm, driving the overall circulation of the aqueous phase and avoiding dead zones in the mixing process. This mixing characteristic, combined with a water temperature of 35±2℃, can accelerate the hydration and dissolution of decyl glucoside and cocamidopropyl hydroxysulfonate betaine, promoting the rapid dispersion of surfactant molecules to form a uniform micelle system. Within 20 minutes, the solution transmittance can reach ≥98%, providing a stable aqueous phase substrate for the subsequent addition of additives.

[0042] Cocamidopropyl hydroxysulfonate betaine, as an amphoteric surfactant, readily forms gel-like aggregates under high concentration conditions due to intermolecular hydrogen bonding and hydrophobic association. By employing a dropping rate of 0.5 L / min–0.8 L / min, its local concentration in the aqueous phase can be controlled to remain below the critical gel concentration. Simultaneously, the shear force generated by the six-bladed turbine propeller effectively disperses the added cocamidopropyl hydroxysulfonate betaine throughout the aqueous phase, preventing aggregation near the feeding point. This combination of "low concentration gradient – ​​instant shear" fundamentally prevents gelation, ensuring good fluidity and homogeneity in the aqueous system and providing a high-quality dispersion foundation for subsequent coupling emulsification with the organic phase.

[0043] In Example 9, the feed temperature of the high-pressure homogenizer in step 4 is controlled at 30±2℃. During the homogenization cycle, pulse feeding is used with a pulse frequency of 2-3 times / minute to ensure uniform particle size distribution of the emulsion. After the finished product is cooled, it needs to be left to stand in a sealed container for 12 hours, and the particle size and centrifugal stability are tested again. After passing the test, it is packaged.

[0044] By adopting the above technical solution, the feed temperature of the high-pressure homogenizer is controlled at 30±2℃, which is based on the balance between emulsion viscosity and component stability. This temperature range can maintain a low emulsion viscosity, reduce shear resistance during homogenization, and make shear and cavitation effects more easily applied to the pre-emulsion droplets; it can also avoid structural loosening caused by excessively high temperature leading to increased thermal motion of pH-responsive copolymer molecular chains, or localized material retention in the homogenizer caused by excessively low temperature leading to decreased emulsion fluidity. This ensures that each droplet receives uniform mechanical action during homogenization, laying the foundation for finer and more uniform particle size.

[0045] The homogenization cycle employs a pulsed feed of 2-3 times / minute, designed to address the shear blind zone problem that easily arises with continuous feeding. During conventional continuous feeding, the flow rate of the emulsion within the homogenizer can vary due to slight viscosity fluctuations, leading to insufficient shear force in some areas and excessive shear in others, resulting in a wide particle size distribution. Pulsed feeding, through intermittent feeding, allows for precise control of the amount of material entering the homogenizer each time. Furthermore, during the pulse intervals, the material within the homogenizer can briefly mix and balance the pressure, avoiding uneven shearing caused by flow rate fluctuations. The frequency of 2-3 times / minute ensures both homogenization efficiency and guarantees that each batch of material undergoes a consistent shear-cavitation process, resulting in a concentrated emulsion particle size distribution and a stable PDI ≤ 0.2.

[0046] The process of sealing and allowing the finished product to stand for 12 hours after cooling before testing is a post-verification mechanism based on the colloidal stability of the emulsion. After high-pressure homogenization, tiny droplets in the emulsion may possess weak aggregation potential, making it difficult to detect potential slow aggregation trends in real-time testing. Sealing and allowing it to stand simulates the actual storage environment, avoiding interference from external impurities and moisture evaporation; the 12-hour standing time is sufficient for potential instability factors (such as van der Waals forces between particles) to fully manifest. Re-testing particle size and centrifugal stability effectively screens out unstable products caused by minor deviations in homogenization parameters or fluctuations in component synergy, ensuring that the final product maintains uniform particle size and system stability throughout storage, transportation, and use, avoiding quality problems such as stratification and particle size enlargement.

[0047] Example 10: Application of a composite surfactant in the cleaning of oily sludge at 5℃-20℃, characterized by the following steps: Step a: Adjust the dilution ratio according to the oil content of the oily sludge: when the oil content is greater than or equal to 20%, dilute the composite surfactant mother liquor with room temperature water at a ratio of 1:10; when the oil content is 10%-20%, dilute at a ratio of 1:15; when the oil content is less than 10%, dilute at a ratio of 1:20 to obtain the cleaning working solution. Step b: Add the cleaning working fluid and oily sludge to the ribbon stirring cleaning device at a liquid-solid ratio of 3:1-5:1, and stir and clean at a speed of 60rpm-100rpm for 15-30 minutes. The stirring and cleaning time for aged oily sludge is extended to 30 minutes. Step c: After washing, the slurry is fed into a three-phase centrifuge and separated at 3000 rpm for 15 minutes to obtain an upper layer of floating oil, a middle layer of aqueous phase, and a lower layer of wet solids. A 5% citric acid solution is added to the floating oil to adjust the pH to 4.0-4.5, and the mixture is stirred at 100-120 rpm for 5-10 minutes to break the emulsion. The purity of the upper layer recovered oil is greater than or equal to 85%. In step d, the pH of the middle aqueous phase is adjusted to 6.5-7.5 with 0.1 mol / L NaOH, filtered through a 5 μm pore size filter membrane, and then reused in the dilution step of S1; the lower layer containing wet solids is filtered by a 0.8 MPa pressure plate and frame filter until the water content is less than or equal to 30% and the oil content is less than or equal to 1%, meeting the standards for resource utilization or safe disposal.

[0048] The following specific embodiments illustrate the implementation principle of the present invention: Preparation of composite surfactants: Step 1: In a 500L reactor with an anchored agitator and jacket heating, add 12kg of methyl lactate, 8kg of dextrorotatory limonene, 5kg of bio-based oligomeric isobutylene succinic anhydride derivative (number average molecular weight 1000, dendritic structure) and 0.3kg of polyethylene glycol 400 in sequence; set the jacket temperature to 35℃, control the temperature fluctuation to ±1℃, and stir at 200rpm for 15 minutes until the light transmittance of the mixture reaches 96%, forming a uniform and transparent organic phase.

[0049] Step 2: Add 59.2 kg of deionized water to a 1000 L turbine-type stirred tank (equipped with a six-bladed turbine propeller) and heat to 36 °C. Slowly add 15 kg of decyl glucoside (98% purity, 32% solubility at 5 °C) and 10 kg of cocamidopropyl hydroxysulfonate betaine (35% solid content, 500 mg / L hard water resistance) in sequence, with the cocamidopropyl hydroxysulfonate betaine added at a dropping rate of 0.6 L / min. Stir at 400 rpm for 20 minutes until the solution transmittance reaches 99%. Then add 0.5 kg of low-viscosity sodium alginate and continue stirring for 15 minutes until no unswelled particles remain, forming an aqueous phase.

[0050] Step 3: Add the organic phase obtained in Step 1 dropwise to the aqueous phase under stirring using a metering pump at a rate of 10 L / min, while simultaneously increasing the stirring speed of the aqueous phase to 800 rpm; after the addition is complete, maintain the stirring speed for 20 minutes to form a milky white pre-emulsion with a particle size distribution of 1-5 μm, which does not separate into layers after standing for 24 hours.

[0051] Step 4: Reduce the stirring speed of the pre-emulsion to 400 rpm, add 2 kg of pH-responsive copolymer (dimethylaminoethyl methacrylate-butyl acrylate copolymer, molecular weight 6000 Da) and 1 kg of hydrophobic modified nano-silica (particle size 20 nm) in sequence, and stir for 15 minutes; pump the mixture into a high-pressure homogenizer, control the feed temperature at 31℃, feed in a pulse manner at 2 times / minute, and homogenize and circulate twice at a pressure of 30 MPa. The emulsion particle size is 380 nm and PDI is 0.18; cool to 26℃, adjust the pH to 7.0 with 0.1 mol / L NaOH, and centrifuge at 3000 rpm for 30 minutes without stratification to obtain 100 kg of the finished product.

[0052] Applications of compound surfactants: Subject of treatment: Oily sludge from an oil field (oil content 18%, temperature 12℃, non-aged sludge).

[0053] Step a: Prepare the cleaning working solution by diluting the mother liquor with room temperature water at a ratio of 1:15.

[0054] Step b: Add the cleaning working fluid and oily sludge to the ribbon agitator at a liquid-to-solid ratio of 4:1, and agitate and clean at 80 rpm for 20 minutes.

[0055] Step c: After washing, the slurry is sent to a three-phase centrifuge and separated at 3000 rpm for 15 minutes to obtain an upper layer of floating oil, a middle layer of aqueous phase and a lower layer of wet solids; 5% citric acid solution is added to the floating oil to adjust the pH to 4.2, and the mixture is stirred at 110 rpm for 8 minutes to break the emulsion, and the purity of the upper layer recovered oil is 87%.

[0056] Step d: The pH of the middle aqueous phase was adjusted to 7.0 with 0.1 mol / L NaOH, filtered through a 5 μm filter membrane, and then reused in the dilution step; the lower layer containing wet solids was filtered through a 0.8 MPa plate and frame filter press, with a water content of 28% and an oil content of 0.8%.

[0057] The test results of the composite surfactant are shown in Table 1: Table 1

[0058] Table 2 shows the performance comparison results between composite surfactants and traditional surfactants: Table 2

[0059] In terms of low-temperature adaptability, the composite surfactant of this invention can operate efficiently at temperatures ranging from 5℃ to 20℃, with a cleaning efficiency of 92% at 5℃. Traditional high-temperature products cannot be used at low temperatures, and room-temperature products have a low-temperature efficiency of only 55%. In terms of energy consumption and environmental protection, the energy consumption is reduced by 75% compared to traditional high-temperature products, wastewater discharge is reduced by 80%, and the biodegradation rate reaches 96%, far exceeding that of traditional products. In terms of treatment effect, the oil-water separation time is shortened to 8 minutes, the purity of the recovered oil is increased by 5-9 percentage points, and the cleaning efficiency for aged sludge is 14-27 percentage points higher than that of traditional products, achieving a dual breakthrough in high efficiency and environmental protection.

[0060] The above are all preferred embodiments of the present invention and are not intended to limit the scope of protection of the present invention. Therefore, all equivalent changes made in accordance with the structure, shape and principle of the present invention should be covered within the scope of protection of the present invention.

Claims

1. A composite surfactant for cleaning oily sludge at low temperatures, characterized in that: Includes the following components by mass percentage: The core surfactant is 25%–30%, the low-temperature coupling solvent is 20%–25%, the auxiliary agent is 2.8%–3.8%, and the balance is deionized water; The core surfactants include decyl glucoside, cocamidopropyl hydroxysulfonate betaine, and bio-based oligoisobutylene succinic anhydride derivatives. The low-temperature coupling solvent includes methyl lactate and d-limonene; The additives include modified nano-silica, low-viscosity sodium alginate, pH-responsive copolymer, and polyethylene glycol 400.

2. The composite surfactant for low-temperature oily sludge cleaning according to claim 1, characterized in that: The core surfactant comprises the following components by mass percentage: Decyl glucoside 14%-16%, cocamidopropyl hydroxysulfonate betaine 9%-12%, bio-based oligomeric isobutylene succinic anhydride derivatives 4.5%-5.8%; The low-temperature coupling solvent comprises the following components by mass percentage: Methyl lactate 11%-13.8% and d-limonene 7%-9%; The additive comprises the following components by mass percentage: Modified nano silica 0.8%-1.2%, sodium alginate 0.4%-0.6%, pH-responsive copolymer 1.8%-2.2%, polyethylene glycol 400 0.3%.

3. The composite surfactant for low-temperature oily sludge cleaning according to claim 2, characterized in that: The core surfactant comprises 15% decyl glucoside, 10% cocamidopropyl hydroxysulfonate betaine, and 5% bio-based oligoisobutylene succinic anhydride derivative. The decyl glucoside has a purity of ≥98% and a solubility of ≥30% at 5°C. The cocamidopropyl hydroxysulfonate betaine has a solid content of 35% and a hard water resistance of 500 mg / L. The bio-based oligoisobutylene succinic anhydride derivative has a dendritic structure with a number average molecular weight of 1000.

4. The composite surfactant for low-temperature oily sludge cleaning according to claim 3, characterized in that: In the low-temperature coupling solvent, methyl lactate accounts for 12% and d-limonene accounts for 8%; the eutectic system formed by the compound has a eutectic point of less than or equal to -72°C and can reduce the solidification point of oil stains to below -15°C.

5. The composite surfactant for low-temperature oily sludge cleaning according to claim 4, characterized in that: The additives comprise 1% modified nano-silica, 0.5% low-viscosity sodium alginate, 2% pH-responsive copolymer, and 0.3% polyethylene glycol 400. The modified nano-silica is hydrophobic, the pH-responsive copolymer is dimethylaminoethyl methacrylate-butyl acrylate copolymer with a molecular weight of 5000 Da-8000 Da, and the polyethylene glycol 400 can make the viscosity of the system less than or equal to 50 mPa·s at 5°C.

6. A method for preparing a composite surfactant for low-temperature oily sludge cleaning as described in claim 5, characterized in that, Includes the following steps: Step 1: In a reactor equipped with an anchor-type stirring paddle and jacket heating, methyl lactate, dextrorotatory limonene, bio-based oligomeric isobutylene succinic anhydride derivative, and polyethylene glycol 400 are added sequentially; the jacket temperature is set to 35°C, and the mixture is stirred at 180-220 rpm for 13-16 minutes until the light transmittance of the mixture is greater than or equal to 95%, forming a homogeneous and transparent organic phase; Step 2: Add deionized water to a turbine-type stirred tank and heat to 35±2℃; slowly add decyl glucoside and cocamidopropyl hydroxysulfonyl betaine in that order, and stir at 350rpm-450rpm for 20 minutes until the transmittance of the solution is greater than or equal to 98%; then add low-viscosity sodium alginate and continue stirring for 13-16 minutes until there are no unswelled particles and an aqueous phase is formed; Step 3: The organic phase obtained in Step 1 is added dropwise to the aqueous phase of Step 2 under stirring using a metering pump at a rate of 9 L / min-10 L / min. During the dropwise addition, the stirring speed of the aqueous phase is simultaneously increased to 750 rpm-800 rpm. After the dropwise addition is completed, the stirring speed is maintained for 18-20 minutes to form a milky white pre-emulsion with a particle size distribution of 1 μ-5 μm. The pre-emulsion does not separate into layers after standing for 24 hours. Step 4: Reduce the stirring speed of the pre-emulsion from Step 3 to 380 rpm-400 rpm, add the pH-responsive copolymer and hydrophobic modified nano-silica sequentially, and stir for 13-16 minutes; pump the mixture into a high-pressure homogenizer and homogenize twice at a pressure of 28 MPa-30 MPa to ensure that the emulsion particle size is less than or equal to 500 nm and the PDI is less than or equal to 0.2; cool to 25±2℃, adjust the pH to 6.5-7.5 with 0.1 mol / L NaOH or HCl, and centrifuge at 2500 rpm-300 rpm for 28-30 minutes until no stratification occurs to obtain the finished product.

7. The preparation method according to claim 6, characterized in that, During the stirring process in step 1, the jacket temperature fluctuation is controlled within ±1℃ to ensure that the organic phase components are fully dissolved and there is no local overheating.

8. The preparation method according to claim 7, characterized in that: The impeller of the turbine-type mixing tank mentioned in step 2 is a six-bladed turbine impeller. When adding cocamidopropyl hydroxysulfonate betaine, it is added dropwise at a rate of 0.5 L / min to 0.8 L / min to avoid gelation due to excessively high local concentration.

9. The preparation method according to claim 8, characterized in that: In step 4, the feed temperature of the high-pressure homogenizer is controlled at 30±2℃. During the homogenization cycle, pulse feeding is used with a pulse frequency of 2-3 times / minute to ensure uniform particle size distribution of the emulsion. After the finished product is cooled, it needs to be left to stand in a sealed container for 12 hours, and the particle size and centrifugal stability are tested again. After passing the test, it is packaged.

10. The application of the composite surfactant as described in claim 5 in the cleaning of oily sludge at 5℃-20℃, characterized in that: Includes the following steps: Step a: Adjust the dilution ratio according to the oil content of the oily sludge: when the oil content is greater than or equal to 20%, dilute the composite surfactant mother liquor with room temperature water at a ratio of 1:10; when the oil content is 10%-20%, dilute at a ratio of 1:15; when the oil content is less than 10%, dilute at a ratio of 1:20 to obtain the cleaning working solution. Step b: Add the cleaning working fluid and oily sludge to the ribbon stirring cleaning device at a liquid-solid ratio of 3:1-5:1, and stir and clean at a speed of 60rpm-100rpm for 15-30 minutes. The stirring and cleaning time for aged oily sludge is extended to 30 minutes. Step c: After washing, the slurry is fed into a three-phase centrifuge and separated at 3000 rpm for 15 minutes to obtain an upper layer of floating oil, a middle layer of aqueous phase, and a lower layer of wet solids. A 5% citric acid solution is added to the floating oil to adjust the pH to 4.0-4.5, and the mixture is stirred at 100-120 rpm for 5-10 minutes to break the emulsion. The purity of the upper layer recovered oil is greater than or equal to 85%. In step d, the pH of the intermediate aqueous phase is adjusted to 6.5-7.5 with 0.1 mol / L NaOH, filtered through a 5 μm pore size filter membrane, and then reused in the dilution step of S1. The lower layer containing moist solids is filtered through a 0.8MPa pressure plate and frame filter until the moisture content is less than or equal to 30% and the oil content is less than or equal to 1%, meeting the standards for resource utilization or safe disposal.

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