Defoamer
A defoamer, antifoam agent, or anti-foaming agent is a chemical additive that reduces and hinders the formation of foam in industrial process liquids. The terms anti-foam agent and defoamer are often used interchangeably.
In oilfield, defoamers are most often used to control oil foam in separators to minimize oil-carry-over into the gas stream or gas-carry-under into the oil system. The defoamer chemistry[2][3] is mostly silicone based or fluorosilicone based (which is more effective but much more expensive as well). Over-dosing defoamers can cause fouling problem in refineries.
Depending on the nature of the crude oil and the type of separation scheme used, foaming problems can curtail crude oil production and even cause unwanted and unexpected process shutdowns. The first vessel typically encountered during the production of crude oil and gas is the high pressure separator, often followed by one or more separators operating at successively lower pressures. Foaming can occur in any separator, but the greatest severity is generally encountered in the first stage[4].
Properties
Generally a defoamer is insoluble in the foaming medium and has surface active properties. An essential feature of a defoamer product is a low viscosity and a facility to spread rapidly on foamy surfaces. It has affinity to the air-liquid surface where it destabilizes the foam lamellas. This causes rupture of the air bubbles and breakdown of surface foam. Entrained air bubbles are agglomerated, and the larger bubbles rise to the surface of the bulk liquid more quickly. [5]
Chemistry
Oil based defoamers
Oil based defoamers have an oil carrier. The oil might be mineral oil, vegetable oil, white oil or any other oil that is insoluble in the foaming medium, except silicone oil. An oil based defoamer also contains a wax and/or hydrophobic silica to boost the performance. Typical waxes are ethylene bis stearamide (EBS), paraffinic waxes, ester waxes and fatty alcohol waxes. These products might also have surfactants to improve emulsification and spreading in the foaming medium.
These are heavy duty defoamers and are normally best at knocking down surface foam.
Powder defoamers
Powder defoamers are in principle oil based defoamers on a particulate carrier like silica. These are added to powdered products like cement, plaster and detergents.
Water based defoamers
Water based defoamers are different types of oils and waxes dispersed in a water base. The oils are often white oils or vegetable oils and the waxes are long chain fatty alcohol, fatty acid soaps or esters. These are normally best as deaerators, which means they are best at releasing entrained air.
Silicone based defoamers
Silicone based defoamers have a silicone compound as the active component. These might be delivered as an oil or a water based emulsion. The silicone compound consists of an hydrophobic silica dispersed in a silicone oil. Emulsifiers are added to ensure that the silicone spreads fast and well in the foaming medium. The silicone compound might also contain silicone glycols and other modified silicone fluids.
These are also heavy duty defoamers and are good at both knocking down surface foam and releasing entrained air.
Silicone based defoamers are also suitable in non-aquaous foaming systems like crude oil and oil refining. For very difficult systems fluorosilicones may be suitable.
EO/PO based defoamers
EO/PO based defoamers contain polyethylene glycol and polypropylene glycol copolymers. They are delivered as oils, water solutions, or water based emulsions. EO/PO copolymers normally have good dispersing properties and are often well suited when deposit problems are an issue.
Alkyl polyacrylates
Alkyl polyacrylates are suitable for use as defoamers in non-aqueous systems where air release is more important than the breakdown of surface foam. These defoamers are often delivered in a solvent carrier like petroleum distillates.
Industrial problems
The most noticeable form of foam is foam floating on the stock surface. It is easy to monitor and relatively easy to handle. Surface foam may cause problems with liquid levels and give overflow. This might reduce the process speed and availability of process equipment.
Oilfield
Crude oil foam in two- and three-phase separators creates operational problems:
- Poor level control that can lead to platform shutdowns
- Liquid carryover in the gas outlet that can lead to flooding of downstream scrubbers and compressors
- Gas carryunder in the liquid outlet that can lead to increased compression requirements.
Mechanical problem factors
Mechanical factors that may generate foam and entrapped air:
- Leaky seals on pumps
- High pressure pumps
- Poor system design (tank, pump inlet, outlet and manifold design)
- Pressure release
The main classes of air that are of concern to the mechanical systems are
- Dissolved air behaves as part of the fluid phase, except that it can come out of solution as small bubbles (entrained air)
- Entrained air consists of bubbles that are small enough to collect on top of a fluid
- Bubbles that have sufficient buoyancy to rise to the surface and are described as foam
Test methods
Gas sparging test is typically used to evaluate foaming tendency and screen defoamer chemicals in the oil/gas industry.
The easiest is looking at the surface foam. All that is needed is a system for generating foam. This might be done with a round pumping system with a nozzle and a cylinder or an air injection system into a cylinder. The cylinder is fitted with a scale to measure the foam height. This equipment may have a heater to control the temperature.
Entrained air can be tested with a similar equipment that have a density meter that can record changes of the liquor density over time.
Drainage can be tested with a filter system for measuring the time to drain a liquid through the filter. The filter might be pressurized or have a vacuum.
The gas sparging test is really a laboratory tool for initial screening only. The pressure, temperature and agitation conditions in a first-stage separator bear no relationship to the conditions of the test. Furthermore silicones are extremely substantive to glass surfaces and poor test repeatability is expected unless equipment is rigorously cleaned. Dose optimization is typically done in the field.
Applications
Oilfield
In order to mitigate the foam problems, chemical defoamers or anti-foamers, for example silicone or fluro-silicone based, are typically injected upstream of separators, typically at a dosage level of 5–10 ppmv for fluro-silicone based and 30-50ppm for silicone based defoamers.
Detergents
Anti-foams are added in certain types of detergents to reduce foaming that might decrease the action of the detergent. For example dishwasher detergents have to be low foaming for the dishwasher to work properly.
Food
When used as an ingredient in food, antifoaming agents are intended to curb effusion or effervescence in preparation or serving. The agents are included in a variety of foods such as chicken nuggets in the form of polydimethylsiloxane (a type of silicone).[6]
Silicone oil is also added to cooking oil to prevent foaming in deep-frying.
Industrial use
Defoamers are used in many industrial processes and products: wood pulp, paper, paint, industrial wastewater treatment, food processing, machine tool industry, oils cutting tools, hydraulics, etc
Pharmaceuticals
Antifoaming agents are also sold commercially to relieve bloating. A familiar example is the drug Simethicone, which is the active ingredient in drugs such as Maalox, Mylanta, and Gas-X.
References
- ↑ Anne Kari Vikingstad, Arne Skauge, Harald Høiland, Morten Aarra, "Colloids and Surfaces A: Physicochemical and Engineering Aspects", Volume 260, Issues 1–3, 15 June 2005, Pages 189–198
- ↑ Callaghan, I. C. Antifoams for Nonaqueous Systems in the Oil Industry. Surfactant Sci. Ser. 1993, 45, 119.
- ↑ Callaghan, I. C.; Hickman, S. A.; Lawrence, F. T.; Melton, P. M. Antifoams in Gas-Oil Separation. Spec. Pub.-R. Soc. Chem. 1987,59 (Ind. Appl. Surf.), 48.
- ↑ Callaghan, I. C.; Gould, C. M.; Reid, A. J.; Seaton, D. H. Crude-Oil Foaming Problems at the Sullom Voe Terminal. J. Pet. Technol.1985, 2211.
- ↑ http://www4.ncsu.edu/~hubbe/DFOM.htm
- ↑ McDonald's (2007-01). McDonald's USA Ingredients Listing for Popular Menu Items. Retrieved from http://www.mcdonalds.com/app_controller.nutrition.categories.ingredients.index.html.
