In the flotation process, sometimes in order to improve the dispersion of the agent (such as trapping agent) and flotation effect, it is necessary to add emulsifier first, the agent to emulsify the treatment; some mineral processing agent itself is easy to emulsify, and the emulsion foam in the pulp will affect the latter process, resulting in the loss of concentrate overflow or tailing wastewater pollution of rivers. Translated with www.DeepL.com/Translator (free version)
For this reason, in the above cases, emulsion breakers need to be added to deal with. When using emulsion breaker, the pH value of emulsion should be adjusted first. For strong alkali and acid emulsions, the pH value should be adjusted to the range of 1~10. In the petroleum, chemical, woolen and mechanical processing industries, such as oil-containing emulsion of wastewater treatment, in addition to physical emulsion breaking methods (such as heating, membrane separation, electric field emulsion breaking method), but also commonly used emulsion breakers for chemical treatment. The commonly used emulsion breaker is a highly dispersible mixture composed of various components. For oil-in-water emulsions, inorganic substances with H+, Al3+, Fe3+ and other cations are usually used as emulsion breakers, such as inorganic acids and iron sulfate; for oil-in-water emulsions, anionic and nonionic surfactants or a mixture of both are generally used as emulsion breakers. Translated with www.DeepL.com/Translator (free version)
As some solids are insoluble in water, when one or several of these solids are present in large quantities in aqueous solutions, under the stirring of hydraulic or external power, these solids can exist in water in an emulsified state, forming emulsions. Theoretically this system is unstable, but if there are some surfactants (soil particles, etc.) in the case, it makes the emulsified state very serious, and even the two phases are difficult to separate, typically the oil-water mixture in oil-water separation and the water-oil mixture in wastewater treatment, in which the two phases form a more stable oil-in-water or water-in-oil structure, the theoretical basis of which is ” double electric layer structure”.
In this case, some agents are put in to disrupt the stable bilayer structure as well as to stabilize the emulsification system so as to achieve the separation of the two phases. These agents used to achieve the disruption of emulsification are called emulsion breakers.
Emulsion Breaking Mechanism
Due to the complexity of oil, oil layer water and the composition of the natural emulsifier, the study of the physicochemical processes occurring at the oil-water interface is extremely difficult, and therefore the chemical emulsion breaking process and emulsion breaking mechanism is still under study, but emulsion breakers and emulsifiers are surface active substances, the role of the two is diametrically opposed. Now a variety of emulsion-breaking mechanism of emulsion-breaking agents are summarized as follows.
Surface active role. Emulsion breakers have high performance surface active substances, emulsion breakers have higher activity than emulsifiers, some literature that emulsion breakers should be 100 to 1000 times greater than the emulsifier activity, so that emulsion breakers can quickly dispersed through the external phase of the emulsion to the oil-water interface, replace or neutralize the emulsifier, reduce the interfacial tension of emulsified water droplets and interfacial film strength, so that the formation of W / O emulsion becomes very unstable. The interfacial film is very easy to break under the action of external force, thus making the water in the inner phase of emulsion particles break through the interfacial film into the outer phase, thus separating oil and water. This can not only destroy the already formed crude oil emulsion, but also prevent further emulsification of the oil-water mixture and play a role in reducing the viscosity of the oil-water mixture and accelerating the oil-water separation. However, practice shows that there is no rule that the higher the activity of emulsion breaker, the stronger the emulsion breaking ability.
Reverse-phase emulsification. Crude oil emulsions are formed under the action of water-repellent emulsifiers in crude oil, commonly known as W/O-type emulsions, such as naphthenic acid, asphaltene, etc. The hydrophilic emulsion breaker can be used to convert the emulsion into O/W emulsion, and the oil and water are separated by the conversion of the emulsification process and the instability of O/W emulsion. When the emulsion-breaking agent to promote the formation of oil-in-water trans-phase water-in-oil emulsion, the water outside the collision is easy to gather into large droplets to sink out.
“Wetting” and “penetration” effect. Emulsion breaker can dissolve the adsorption of gum, asphaltene, solid powder and other natural emulsifiers at the oil-water interface, to prevent the natural emulsifiers constitute the interface film to prevent water droplet agglomeration. Such as clay, iron sulfide, drilling mud and other solid particles with hydrophilic, emulsion breakers can pull these solid emulsifiers from the oil-water interface into the water droplets; asphaltene and high melting point wax crystals with lipophilic, emulsion breakers can make it leave the oil-water interface into the crude oil. In this way, it is conducive to the merging of water droplets when they collide to achieve the purpose of sinking water droplets.
As the water droplets in the crude oil emulsion in the dispersed phase are always negatively charged and adsorb a part of positive ions on their own surface, so that the dispersed phase is often positively charged, because the charges are the same, the droplets in the dispersed phase repel each other and the droplets are difficult to merge. If ionic emulsion breaker is added to the crude oil, ions of opposite polarity are adsorbed on the surface of water droplets and neutralize the positive charge, so that the electrostatic repulsion of water droplets is weakened and the interfacial film protected by same sex electricity is destroyed, so that water droplets merge and settle down from the oil.
Although the emulsion-breaking mechanism of the emulsion-breaking agent is not perfect, but from long-term practice to summarize two conclusions: ① the molecular weight of the emulsion-breaking agent is greater than the molecular weight of the natural emulsifier to effectively break the emulsion; ② if the emulsion-breaking agent is used as an emulsifier for oil-water mixtures, the generation of reverse-phase emulsion, that is, O/W emulsion.
Emulsion breaker is a kind of surface active substance which can break the structure of emulsified liquid to achieve the purpose of separating the phases in the emulsion. Crude oil emulsion breaking means using the chemical effect of emulsion breaker to separate oil and water in the emulsified oil-water mixture, so as to achieve the purpose of crude oil dehydration, in order to ensure the standard of crude oil water content for external transmission.
Emulsion breaker classification
According to the current use of emulsion breakers, emulsion breakers can be divided into two categories: water-soluble emulsion breakers and oil-soluble emulsion breakers.
Emulsion breaker is a surfactant type, emulsion breaker molecule consists of lipophilic and hydrophilic groups, the lipophilic part is composed of hydrocarbon groups, especially long-chain hydrocarbon groups; while the hydrophilic part is composed of ionic or non-ionic hydrophilic groups. There are many types of emulsion breakers, if the classification of surfactants can be divided into: cationic, anionic, non-ionic, two types of ionic emulsion breakers.
Anionic emulsion breaker dissolved in water generated by the hydrophilic group for the negatively charged ion group, according to its hydrophilic group is divided into: carboxylic acid, sulfonic acid, sulfate and phosphate ester class. Anionic emulsion breakers are carboxylic acid salts, sulfonates and polyoxyethylene aliphatic sulfate salts, etc., with large dosage, poor results, susceptible to electrolytes and reduced effectiveness and other disadvantages.
Cationic emulsion breakers dissolve in water to generate hydrophilic groups for positively charged particle groups, hydrophilic groups are mainly basic nitrogen atoms, but also phosphorus, sulfur, iodine, etc. Cationic emulsion breakers mainly have quaternary ammonium salts, which have obvious effect on general crude oil, but are not suitable for thick oil and aging oil.
Non-ionic emulsion breakers do not dissociate ions after dissolving in water, and therefore do not carry an electric charge. Non-ionic mainly with amines as the starting agent of the block polyether, alcohols as the starting agent of the block polyether, alkyl phenolic resin block polyether, phenolamine aldehyde resin block polyether, containing silicon emulsion breakers, ultra-high relative molecular mass emulsion breakers, polyphosphate, block polyether modification products and imidazoline crude oil emulsion breaker as a representative of the amphoteric emulsion breakers.
Two types of emulsion breakers for dissolved in water can generate positive and negative ions. It is cationic in acidic solution and anionic in alkaline solution.
The main non-ionic emulsion breakers commonly used in the oilfield are as follows.
1.SP type emulsion breaker
The main component of SP emulsion breaker is polyoxyethylene polyoxypropylene octadecyl ether, the theoretical structural formula is R(PO)x(EO)y(PO)zH, where: EO-polyoxyethylene; PO-polyoxypropylene; R-fatty alcohol; x, y, z-polymerization degree. SP emulsion breaker has the appearance of light yellow paste material, HLB value of 10~12, soluble in water. It has good emulsion breaking effect on crude oil. Its hydrophobic part is composed of carbon 12~18 hydrocarbon chains, and its hydrophilic group is hydrophilic through the hydroxyl group (-OH) and ether group (-O-) in the molecule and water to form hydrogen bond.
As hydroxyl and ether groups are weak hydrophilic, so only one or two hydroxyl or ether groups cannot pull the hydrophobic group of carbon 12~18 hydrocarbon chain into water, there must be more than one such hydrophilic group to achieve the purpose of water solubility. The larger the molecular weight of the non-ionic emulsion breaker, the longer the molecular chain, the more hydroxyl and ether groups it contains, the greater its pulling power, the stronger the emulsion breaking ability of crude oil emulsions. another reason why SP-type emulsion breaker is suitable for paraffin-based crude oil is that paraffin-based crude oil contains no or very little gum and asphaltene, less lipophilic surfactant substances, and less relative density. For crude oil with high gum and asphaltene content (or water content greater than 20%), the emulsion breaking ability of SP-type emulsion breaker is weaker because of the single molecular structure, no branched chain structure and aromatic structure.
2.AP type emulsion breaker
AP type emulsion breaker is polyoxyethylene polyoxypropylene polyether with polyethylene polyamine as initiator, it is a multi-branch type non-ionic surfactant with the molecular structure formula: D(PO)x(EO)y(PO)z H, where: EO-polyoxyethylene; PO-polyoxypropylene; R-fatty alcohol; D-polyethylene polyamine: x, y, z-polymerization degree.
AP-type structure of emulsion breaker for paraffin-based crude oil emulsion breaking, the effect is better than SP-type emulsion breaker, it is more suitable for crude oil moisture content higher than 20% of crude oil breaking, and can achieve rapid emulsion breaking effect under low temperature conditions. If SP-type emulsion breaker settles and breaks the emulsion within 2h at 55~60℃, AP-type emulsion breaker only needs to settle and break the emulsion within 1.5h at 45~50℃. This is due to the structural characteristics of AP-type emulsion breaker molecules. The initiator polyethylene polyamine determines the structural form of the molecule: the molecular chain is long and branched, and the hydrophilic ability is higher than that of the SP-type emulsion breaker with a single molecular structure. Multi-branched characteristics determine the AP-type emulsion breaker has high wettability and permeability, when the crude oil emulsion breaking, AP-type emulsion breaker molecules can quickly penetrate the oil-water interface film, than the SP-type emulsion breaker molecules of vertical single molecule film arrangement occupies more surface area, and therefore less dosage, emulsion breaking effect is obvious. At present, this type of emulsion breaker is the better non-ionic emulsion breaker used in Daqing oilfield.
3.AE type emulsion breaker
AE type emulsion breaker is a polyoxyethylene polyoxypropylene polyether with polyethylene polyamine as initiator, which is a multi-branch type nonionic surfactant. Compared with AP emulsion breaker, the difference is that AE emulsion breaker is a two-phase polymer with small molecules and short branched chains. The molecular structure formula is: D(PO)x(EO)yH, where: EO – polyoxyethylene: PO – polyoxypropylene: D – polyethylene polyamine; x, y – degree of polymerization. Although there are great differences in the molecular phases of AE-type emulsion breakers and AP-type emulsion breakers, the molecular composition is the same, only in the monomer dosage and polymerization order.
The two non-ionic emulsion breakers are designed to be synthesized with different amounts of material used in the head and tail, and produce different lengths of polymerized molecules.
The molecule of AP-type emulsion breaker is bipartite, with polyethylene polyamine as initiator, and polyoxyethylene, polyoxypropylene polymerization to form a block copolymer: the molecule of AE-type emulsion breaker is bipartite, with polyethylene polyamine as initiator, and polyoxyethylene, polyoxypropylene polymerization to form a two-part copolymer, therefore, the molecule of designed AP-type emulsion breaker should be longer than that of AE-type emulsion breaker.
AE type is a two-stage multi-branch structure crude oil emulsion breaker, which is also adapted to the emulsion breaking of asphaltene crude oil. The more the content of lipophilic surfactant in bituminous crude oil, the stronger the viscosity, the smaller the difference between oil and water density, not easy to break the emulsion. The AE type emulsion breaker is used to break emulsion fast, and at the same time, AE type emulsion breaker is a better anti-wax viscosity reducer. Due to its multi-branched structure of molecules, it is very easy to form tiny networks, so that the single crystals of paraffin already formed in crude oil fall into these networks, impede the free movement of single crystals of paraffin and cannot be connected with each other, forming the net structure of paraffin, reducing the viscosity and freezing point of crude oil and preventing the aggregation of wax crystals, thus achieving the purpose of anti-wax.
4.AR type emulsion breaker
AR type emulsion breaker is a new oil-soluble non-ionic emulsion breaker made of alkyl phenolic resin (AR resin) and polyoxyethylene and polyoxypropylene, with HLB value of about 4~8 and low emulsion breaking temperature of 35~45℃. The molecular structure formula is: AR(PO)x(EO)y H, where: EO-polyoxyethylene; PO-polyoxypropylene; AR-resin; x, y, z-polymerization degree. AR resin in the process of synthesizing emulsion breaker, both to play the role of initiator, and into the emulsion breaker molecules become lipophilic group. AR-type emulsion breaker is characterized by: molecules are not large, in the case of crude oil solidification point higher than 5 ℃ has a better Solubilization, diffusion, penetration effect, promote emulsified water droplets flocculation, agglomeration, can be below 45 ℃, 45 min water content in 50 % ~ 70 % of crude oil in the water out of more than 80 %, which is SP type, AP type emulsion breaker can not be compared.
Basic principles for selecting emulsion breakers
Emulsion breaker can make the original emulsion stable factors eliminated, which leads to the aggregation, agglomeration, delamination and breaking of emulsion. The main reason for emulsion stability is the formation of charged (or uncharged) interfacial film with a certain mechanical strength or spatial hindrance by the emulsifier. Therefore, the main role of the emulsion breaker is to eliminate the effective role of the emulsifier, the choice of emulsion breaker should be selected for the characteristics of the emulsifier.
There is a good surface activity to top off the emulsifier from the interface in the emulsion. Emulsifiers have surface activity, otherwise they cannot form adsorption films at the interface, and this adsorption is a spontaneous process. Therefore, emulsion breakers must also have a strong interfacial adsorption capacity to top off the emulsifier.
Emulsion breakers in the oil and water interface to form the interface film can not have a solid, in the role of external conditions or droplet collision is easy to break, so droplets are prone to agglomeration.
Ionic emulsifiers can make droplets charged and stable, and the choice of ionic emulsion breakers with opposite charges can neutralize the droplet surface charge.
Non-ionic or polymeric emulsion breakers with large relative molecular mass dissolved in the continuous phase can cause droplets to aggregate and then agglomerate, delaminate and break the emulsion due to the bridging effect.
Solid powder emulsifier stabilized emulsion can be selected as a good wetting agent for solid powder as an emulsion breaker, in order to make the powder completely wet into the water or oil phase.
As can be seen from these principles, some emulsifiers and emulsion breakers often have no obvious boundaries, depending on the specific system. Of course, there are also some surfactants are only suitable for doing a certain emulsion of emulsion breakers, for other systems can neither do emulsion breakers nor emulsifiers.
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