Demulsifier
In oil/gas industry, demulsifiers, or emulsion breakers, are chemical products that are applied to facilitate oil/water separation by breaking water in oil emulsion. They are critical to help meet export crude oil specifications (<1% BSW) and produced water discharge environment requirement. Breaking emulsion also reduces the overall fluid viscosity and improve flow performance. Demulsifiers are also applied in refineries to help break emulsion in desalters.
Applications
Demulsifiers are usually injected at the processing facilities before the separator. However, there are additional benefits in injecting a demulsifier further upstream at the wellhead (injection here is becoming increasingly common), or even downhole if a capillary string is available. Emulsions that are only slowly resolved will need adequate time to separate. Therefore, the time available for emulsion resolution is an important parameter.
The produced fluids are hotter further upstream, which is beneficial and will also result in faster emulsion resolution. In addition, the viscosity of the multiphase fluid will be reduced if the emulsion is resolved, leading to lower drag forces and higher transportation rates, providing benefits to overall throughput capacity.
It is important to note that over dosage of demulsifiers can become emulsifiers and exacerbate the emulsion problem.
Mechanisms
There are three main processes by which demulsifiers “unlock” emulsions:
1. Flocculation: Water droplets are brought together like a cluster of fish eggs.
2. Coalescence: The emulsifying film that once stabilized the water droplets in the emulsion is ruptured, and the water droplets grow large enough to settle out as a separate phase. Larger droplets have less surface tension so anything that can be done to increase droplet
size will help in the separation process.
3. Solids wetting: Solids that stabilize the emulsion are dispersed in the hydrocarbon phase or water wetted and removed with the water.
Performance testing
Bottle testing is the best way to evaluate demulsifier products; There have been a number of ideas to create an easier, more accurate, and faster method to evaluate demulsifiers, providing the customer the correct products that meet their needs
Nearly all demulsifier testing uses the simple bottle test, which is simply a visual assessment of
water drop and interface quality, but (in the hands of an experienced technician) is capable of providing product blends that will work in the processing plant. Bottle testing is best to be conducted in the field since lab testing results can sometimes give inaccurate results. A range of demulsifiers from different structural classes are normally tested. The usual bottle
test method is performed to add a dose of the demulsifier to the emulsion in bottles or measuring cylinders, and observe the speed and amount of separation of oil and water. Good demulsifiers are able to drop water rapidly, provide relatively clean interfaces, and produce dry, saleable oil.
Chemistry
It is difficult to categorize classes of water-in-oil demulsifiers, as over the years, chemical suppliers
have developed an ever-increasing range of products in attempts to destabilize emulsions. However,
many water-in-oil demulsifiers are polymeric nonionic chemicals, many with complex comb or
branched structures, with molecular weights (Mw) of about 2000–50,000. However, anionic and
cationic polymers can be used depending on the emulsion-stabilizing chemicals in the feedstream
or as wetting agents. The most common classes of water-in-oil demulsifiers can be summarized in
the following list:
- Polyalkoxylate block copolymers and ester derivatives
- Alkylphenol–aldehyde resin alkoxylates
- Polyalkoxylates of polyols or glycidyl ethers
- Polyamine polyalkoxylates and related cationic polymers (mainly for oil-in-water
resolution)
- Polyurethanes (carbamates) and polyalkoxylate derivatives
- Hyperbranched polymers
- Vinyl polymers
- Polysilicones (also as demulsifier boosters)
See also
References
- Production Chemicals for the Oil and Gas Industry by Malcolm A. Kelland
