The principle of demulsifiers and their applications

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This post was last edited by sdos34 on 2016-6-2 at 11:59. The principle and uses of demulsifiers: A demulsifier is a substance used to break down emulsions. Since some solids are insoluble in water, when one or more of these solids are present in large quantities in an aqueous solution, they can exist in an emulsified state within the water, forming an emulsion, due to hydraulic or external forces that cause mixing. Theoretically, such a system is unstable, but when certain surfactants (such as soil particles) are present, the emulsification becomes very strong, to the point where it is difficult to separate the two phases. The most typical examples are oil-water mixtures in oil-water separation processes and water-oil mixtures in wastewater treatment; in these cases, relatively stable water-in-oil or oil-in-water structures are formed, and the theoretical basis for this is the \"double-layer structure\". In this case, some chemicals are added to disrupt the stable double-layer structure and stabilize the emulsion system, thereby achieving phase separation. These agents used to break down emulsions are called demulsifiers. Primary use: Demulsifiers are surfactants that can break down the emulsive liquid structure, thereby enabling the separation of the various phases within the emulsion. Crude oil demulsification refers to the use of demulsifiers to separate the oil and water in an emulsified oil-water mixture through chemical action, thereby achieving the purpose of dehydrating the crude oil and ensuring that its water content meets the standards for transportation. For the effective separation of the organic phase from the aqueous phase, one of the simplest and most effective methods is to use demulsifiers, which eliminate the emulsion formation and the resulting strongly structured emulsion interface, thereby enabling the separation of the two phases. However, different demulsifiers have varying capacities to demulsify the organic phase, and the performance of the demulsifier directly affects the efficiency of phase separation. In the penicillin production process, an important step is to extract penicillin from the fermentation broth using organic solvents such as butyl acetate. Since the fermentation broth contains complex substances like proteins, sugars, and mycelium, the interface between the organic phase and the aqueous phase during extraction is not clear, resulting in an emulsion zone of certain intensity, which has a significant impact on the yield of the final product. To this end, a demulsifier must be used to break down the emulsion, eliminate the emulsification phenomenon, and achieve rapid and effective separation of the two phases. Common demulsifiers: The main non-ionic demulsifiers currently used in oil fields are as follows: 1. SP-type demulsifiers. The main component of SP-type demulsifiers is polyoxyethylene polyoxypropylene octadecanol ether, with the theoretical structural formula being R(PO)x(EO)y(PO)zH, where EO represents polyoxyethylene ； PO-Polyoxypropylene ； R-fatty alcohol ； x, y, z – degree of polymerization. The SP-type demulsifier appears as a pale yellow paste, has an HLB value of 10–12, and is soluble in water. The SP-type non-ionic demulsifier exhibits good demulsification efficiency for paraffin-based crude oil. Its hydrophobic portion is composed of carbon chains with 12 to 18 atoms, while its hydrophilic groups enable hydrophilicity by forming hydrogen bonds with water through hydroxyl groups (-OH) and ether groups (-O-) present in the molecule. Due to the weak hydrophilicity of hydroxyl and ether groups, just one or two such groups are not sufficient to draw the hydrophobic carbon chains with 12–18 atoms into water; multiple hydrophilic groups are required to achieve water solubility. The greater the molecular weight of a non-ionic demulsifier, the longer its molecular chain, and the more hydroxyl and ether groups it contains, the greater its tensile strength, and the stronger its ability to demulsify crude oil emulsions. Another reason why the SP-type demulsifier is suitable for paraffin-based crude oil is that it contains little or no gum and asphaltenes, has fewer oil-loving surfactant substances, and a lower relative density. For crude oils with high levels of gum and asphaltenes (or a water content greater than 20%), SP-type demulsifiers have weak demulsifying capacity, due to their simple molecular structure lacking branched structures and aromatic structures. 2. AP-type demulsifier: The AP-type demulsifier is a polyoxyethylene polyoxypropylene polyether that uses polyethylenepolyamine as an initiator; it is a branched non-ionic surfactant. Its molecular structure is represented as: D(PO)x(EO)y(PO)z H, where EO refers to polyoxyethylene ； PO-Polyoxypropylene ； R-fatty alcohol ； D-Polyethylenimine: x, y, z-polymerization degree. Demulsifiers of the AP type are used for demulsifying paraffin-based crude oil emulsions, and they are more effective than SP-type demulsifiers. They are more suitable for demulsifying crude oil with a water content of over 20%, and they can achieve rapid demulsification even at low temperatures. For example, while an SP-type demulsifier requires 55–60°C and 2 hours to achieve demulsification through sedimentation, an AP-type demulsifier only needs 45–50°C and 1.5 hours for the same purpose. This is due to the structural characteristics of the AP-type demulsifier molecules. The initiator, polyethylene polyamine, determines the structural form of the molecule: it results in long molecular chains with numerous branches, giving it a higher hydrophilicity compared to SP-type demulsifiers with simpler molecular structures. The characteristic of multiple branches gives AP-type demulsifiers high wetting and penetration properties. When breaking down crude oil emulsions, the molecules of AP-type demulsifiers can quickly penetrate the oil-water interface film; they occupy a larger surface area compared to the vertical single-molecule layer arrangement of SP-type demulsifier molecules. As a result, less amount is required, and the demulsification effect is significant. Currently, this type of demulsifier is a non-ionic demulsifier that is widely used in the Daqing Oilfield. 3. AE-type demulsifier: The AE-type demulsifier is a polyoxyethylene polyoxypropylene polyether using polyethylenepolyamine as an initiator; it is a branched non-ionic surfactant. Unlike AP-type demulsifiers, the difference is that AE-type demulsifiers are a two-stage polymer with small molecules and short side chains. The molecular structure formula is: D(PO)x(EO)yH, where EO represents polyoxyethylene, PO represents polyoxypropylene, and D represents polyethylene polyamine ； x, y - degree of polymerization. Although there are significant differences in the molecular structure of AE-type demulsifiers and AP-type demulsifiers, their molecular components are the same; the only differences lie in the amount of monomer used and the polymerization sequence. (1) During the design and synthesis of the two non-ionic demulsifiers, different amounts of materials are used at the head and tail ends, resulting in polymers of varying lengths. (2) The molecules of AP-type demulsifiers are bifunctional; using polyethylene polyamine as an initiator, they polymerize with polyoxyethylene and polyoxypropylene to form block copolymers. The molecules of AE-type demulsifiers are also bifunctional, with polyethylene polyamine serving as an initiator for the polymerization of polyoxyethylene and polyoxypropylene to yield bifunctional copolymers; therefore, the molecules of the AP-type demulsifiers designed should be longer than those of the AE-type demulsifiers. Type AE is a crude oil demulsifier with a two-stage, multi-branched structure, and it is also suitable for demulsifying asphaltenic crude oil emulsions. The higher the content of oil-loving surfactants in asphalt-based crude oil, the greater its viscosity; moreover, the density difference between oil and water is small, making demulsification difficult. The AE-type demulsifier achieves a fast demulsification speed, and at the same time, it is also an effective wax inhibition and viscosity reduction agent. Due to the branched structure of its molecules, it is easy to form tiny networks; the paraffin monocrystals already present in crude oil fall into these networks, which prevents the paraffin monocrystals from moving freely and from connecting with each other, thus forming a network-like structure of paraffin. This reduces the viscosity and freezing point of the crude oil and prevents the wax crystals from aggregating, thereby achieving the purpose of preventing wax formation. 4. AR-type demulsifier: The AR-type demulsifier is a new type of oil-soluble non-ionic demulsifier formed by combining alkylphenol resin (AR resin) with polyoxyethylene and polyoxypropylene; it has an HLB value of around 4–8, and the demulsification temperature can be as low as 35–45°C. The molecular structure formula is: AR(PO)x(EO)y H, where EO represents polyoxyethylene ； PO-Polyoxypropylene ； AR-resin ； x, y, z – degree of polymerization. In the synthesis of demulsifiers, AR resin acts as both an initiator and is incorporated into the molecules of the demulsifiers as an oleophilic group. AR-type demulsifiers are characterized by their small molecular size, which enables them to exhibit good dissolution, diffusion, and penetration properties when the freezing point of crude oil is above 5°C. These properties facilitate the flocculation and coagulation of emulsified water droplets. They can remove over 80% of the water from crude oil with a water content of 50%–70% within 45 minutes at temperatures below 45°C, a performance that surpasses that of SP-type and AP-type demulsifiers.