Summary of common demulsification methods for the

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Summary of commonly used demulsification methods for emulsified oil wastewater

the particle size of emulsified oil is extremely small. Water oil emulsion is formed in water, a boundary film is formed on the surface with ignition, and a double electric layer is formed around the oil beads, which makes the oil beads mutually exclusive and difficult to approach. Therefore, in order to separate oil and water, the boundary membrane of oil beads must be destroyed first, so that the oil beads are close to each other and gather into large oil drops, so as to float on the water surface. This process is called demulsification. Usually, the demulsified sewage needs to be treated by floating oil removal and dispersed oil removal

Common demulsification methods for emulsifying oil by hand or solvent

1. High voltage electric field method

this method uses the attraction or repulsion of electric field force on lotion particles to make the fine oil particles collide with each other in motion, thus damaging their hydration film and double electric layer structure, so that the fine oil particles gather into larger oil particles and float on the water surface, so as to achieve the purpose of oil-water stratification. AC, DC or pulse power supply can be used for high voltage

2. Agent demulsification method

agent demulsification method is to add demulsifier to the wastewater, destroy the hydration film of oil beads, compress the double electric layer, and make the oil beads larger and separate from water. Agent demulsification can be divided into salting out method, coagulation method, salting out coagulation mixing method and acidification method

(1) salting out method: by adding salt electrolyte, the hydration film of oil beads is destroyed, and the thickness of electric double layer at the interface between oil particles and water is compressed, so that the oil particles become unstable. The simple salting out method has the advantages of large dosage, slow polymerizing speed, large equipment area and poor treatment effect for the emulsion with surfactant. However, it is often used as primary treatment due to its simple operation, low cost and more use. Common electrolytes include calcium chloride, magnesium chloride, sodium chloride, calcium sulfate, magnesium sulfate, etc

(2) coagulation method: the coagulation method is to add flocculants to the wastewater, and use the bridging effect of flocculants to combine the fine oil beads into polymers. Common flocculants include alum, polyaluminum chloride, activated silicic acid, polyacrylamide, ferrous sulfate, ferric chloride, magnesium bauxite, etc

(3) acidification method: the acidification method is to add sulfuric acid, hydrochloric acid, acetic acid or naphthenic acid to the wastewater, which requires us to use the whole city's efforts to destroy the boundary membrane of the emulsion oil bead, so that the fatty acid soap can be changed into fatty acid and separated. This method reduces the pH value of waste water, so it is necessary to adjust the pH value with alkali agent after oil-water separation to make it meet the discharge standard

(4) salting out coagulation mixing method: salting out coagulation mixing method refers to adding salt electrolytes to the wastewater to preliminarily demulsify the emulsion, and then adding coagulant to coagulate and separate the oil particles

3. Centrifugal method

this method refers to the separation of oil and water with the help of centrifugal force generated by centrifugal machinery. There are horizontal and vertical centrifuges. Under the action of centrifugal force, the water phase is discharged from the outer layer of the centrifuge, and the oil phase is discharged from the middle of the centrifuge. The structure of centrifuge is complex, so this method is not widely used in China

4. Ultrafiltration method

ultrafiltration method is a kind of physical demulsification method. Its inspection method, technical indicators or parameters have not changed. The original certified item is to make the emulsified oil wastewater pass through the ultrafiltration membrane filter. Taking advantage of the characteristics that the pore diameter of the ultrafiltration membrane is smaller than that of the oil beads, only water is allowed to pass through, and the oil particles larger than the pore diameter of the membrane are blocked, so as to achieve the purpose of emulsified oil-water separation

among the above demulsification methods, the chemical demulsification method is the most common, which is widely used in China. High voltage electric field method is in the experimental stage, and ultrafiltration method has been used in China

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