The principle and use of demulsifier

Demulsifier

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 be present in water in an emulsified state under stirring by hydraulic or external power, forming an emulsion.
Theoretically this system is unstable, but if there is the presence of some surfactants (soil particles, etc.), it will make the emulsification state very serious, even the two phases are difficult to separate, the most typical is the oil-water mixture in oil-water separation and the water-oil mixture in sewage treatment, the two phases form a more stable oil-in-water or water-in-oil structure, the theoretical basis is the "double electric layer structure".
In this case, some agents are put in to disrupt the stable electric 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.

Main Applications

Demulsifier is a surfactant substance, which can make the emulsion-like liquid structure destruction, in order to achieve the purpose of emulsion in the separation of the various phases. Crude oil deemulsification refers to the use of the chemical effect of emulsion breaking agent to leave the oil and water in the emulsified oil-water mixture to achieve the purpose of crude oil dehydration, in order to ensure the standard of crude oil water content for external transmission.
The effective separation of organic and aqueous phases, one of the simplest and most effective methods is to use demulsifier to eliminate emulsification to form an emulsified interface with a certain strength to achieve the separation of the two phases. However, different demulsifier have different emulsion breaking ability for the organic phase, and the performance of it directly affects the two-phase separation effect. In the process of penicillin production, an important procedure is to extract penicillin from penicillin fermentation broth with organic solvents (such as butyl acetate). Since the fermentation broth contains complexes of proteins, sugars, mycelium, etc., the interface between organic and aqueous phases is unclear during extraction, and the emulsification zone is of certain intensity, which has a great impact on the yield of finished products.

Common Demulsifier - The following are the main non-ionic demulsifier commonly used in the oilfield.

SP-type Demulsifier

The main component of SP-type 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-aliphatic alcohol; x, y, z-polymerization degree. SP-type demulsifier has the appearance of light yellow paste, HLB value of 10~12, soluble in water. SP-type non-ionic demulsifier has better demulsifying effect on paraffin-based crude oil. Its hydrophobic part consists of carbon 12~18 hydrocarbon chains, and its hydrophilic group is hydrophilic through the action of hydroxyl (-OH) and ether (-O-) groups in the molecule and water to form hydrogen bonds. Since the hydroxyl and ether groups are weakly hydrophilic, 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 demulsifier, the longer the molecular chain, the more hydroxyl and ether groups it contains, the greater its pulling power, the stronger the demulsifying ability of crude oil emulsions. Another reason why SP demulsifier 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 demulsifying ability of SP-type demulsifier is weaker because of the single molecular structure, no branched chain structure and aromatic structure.

AP-type Demulsifier

AP-type demulsifier is polyoxyethylene polyoxypropylene polyether with polyethylene polyamine as initiator, a multi-branch type nonionic surfactant with molecular structure formula: D(PO)x(EO)y(PO)zH, where: EO - polyoxyethylene; PO - polyoxypropylene; R - fatty alcohol; D - polyethylene amine: x, y, z - degree of polymerization.
AP-type structure demulsifier for paraffin-based crude oil demulsification, the effect is better than SP-type demulsifier, it is more suitable for crude oil water content higher than 20% of crude oil demulsifier, and can achieve rapid demulsifying effect under low temperature conditions. If the SP-type demulsifier settles and demulsify the emulsion within 55~60℃ and 2h, the AP-type demulsifier only needs to settle and demulsify the emulsion within 45~50℃ and 1.5h. This is due to the structural characteristics of the AP-type demulsifier molecule. 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 demulsifier with a single molecular structure. The characteristics of multi-branched chain determine the AP-type demulsifier has high wettability and permeability, when the crude oil demulsifying, AP-type demulsifier molecules can quickly penetrate the oil-water interface film, than the SP-type demulsifier molecules of the vertical single molecule film arrangement occupies more surface area, thus less dosage, emulsion breaking effect is obvious. At present, this type of demulsifier is the better non-ionic demulsifier used in Daqing oilfield.

AE-type Demulsifier

AE-type demulsifier is a polyoxyethylene polyoxypropylene polyether with polyethylene polyamine as initiator, which is a multi-branch type of nonionic surfactant. Compared with AP-type demulsifier, the difference is that AE-type demulsifier is a two-stage polymer with small molecules and short branched chains. Molecular structure formula is: D(PO)x(EO)yH, where: EO - polyoxyethylene: PO - polyoxypropylene: D - polyethylene polyamine; x, y - degree of polymerization. Although the molecular phases of AE-type demulsifier and AP-type demulsifier are very different, but the molecular composition is the same, only in the monomer dosage and polymerization order differences.
(1) two non-ionic demulsifier in the design of synthesis, the head and tail of the amount of material used is different, resulting in the length of polymerization molecules are also different.
(2) AP-type demulsifier molecule is bipartite, with polyethylene polyamine as initiator, and polyoxyethylene, polyoxypropylene polymerization to form block copolymers: AE-type demulsifier molecule is bipartite, with polyethylene polyamine as initiator, and polyoxyethylene, polyoxypropylene polymerization to form two copolymers, therefore, the design of the AP-type demulsifier molecule should be longer than the AE-type demulsifier molecule.

AE-type is a two-stage multi-branch structure crude oil demulsifier, which is also adapted to the demulsification of asphaltene crude oil emulsions. The more the content of lipophilic surfactant in bituminous crude oil, the stronger the viscous force, the smaller the difference between oil and water density, not easy to demulsify the emulsion. The AE-type demulsifier is used to demulsify emulsion fast, and at the same time, the AE-type demulsifier 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 connect 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.

AR-type demulsifier

AR-type demulsifier is made of alkyl phenolic resin (AR resin) and polyoxyethylene, polyoxypropylene and a new type of oil-soluble non-ionic demulsifier, HLB value of about 4 ~ 8, low demulsifying temperature of 35 ~ 45 ℃. The molecular structure formula is: AR(PO)x(EO)yH, where: EO-polyoxyethylene; PO-polyoxypropylene; AR-resin; x, y, z-degree of polymerization.In the process of synthesizing demulsifier, AR resin acts as both initiator and enters the molecule of demulsifier to become lipophilic group. The characteristics of AR-type demulsifier are: the molecule is not large, in the case of crude oil solidification point higher than 5 ℃ has a good dissolution, diffusion, penetration effect, prompt emulsified water droplets flocculation, agglomeration. It can remove more than 80 % of water from crude oil with water content of 50 %~70 % at below 45℃ and 45 min to remove more than 80 % of water from crude oil with water content of 50 % to 70 %, which is incomparable to SP-type and AP-type demulsifier.