 | This articleneeds additional citations forverification. Please helpimprove this article byadding citations to reliable sources. Unsourced material may be challenged and removed. Find sources: "Defoamer" – news ·newspapers ·books ·scholar ·JSTOR(June 2022) (Learn how and when to remove this message) |
Adefoamer or ananti-foaming agent is a chemical additive that reduces and hinders the formation offoam inindustrial process liquids. The terms anti-foam agent and defoamer are often used interchangeably. Strictly speaking, defoamers eliminate existing foam and anti-foamers prevent the formation of further foam. Commonly used agents are insoluble oils,polydimethylsiloxanes and other silicones, certain alcohols,stearates andglycols. The additive is used to prevent formation of foam or is added to break a foam already formed.
In industrial processes, foams pose serious problems. They cause defects on surface coatings and prevent the efficient filling of containers. A variety of chemical formulae are available to prevent formation of foams.[1]
Generally a defoamer is insoluble in the foaming medium and has surface active properties. An essential feature of a defoamer product is a lowviscosity and a facility to spread rapidly on foamy surfaces. It has affinity to the air-liquid surface where it destabilizes the foamlamellas. 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.[2]
The first defoamers were aimed at breaking down visible foam at the surface.Kerosene,fuel oil and other light oil products were used to break down foam.Vegetable oils also found some use.Fatty alcohols (C7 – C22) were effective but expensive antifoams. They were added to oil products to boost the efficiency.Milk andcream were forebears for modern-day emulsion type defoamers.[3]
During the 1950s, experiments withsilicone-based defoamers started. These were based onpolydimethylsiloxane (silicone oil) dispersed in water or light oil. Silicone oils worked well, but caused surface disturbances in many applications likepaints andpapermaking. In 1963 the first antifoams withhydrophobic particles (hydrophobic silica) inlight oil were patented. In the early 1970s, hydrophobic waxes likeethylene bis stearamide dispersed in oils developed. These types of defoamers were very efficient, but theoil crisis of 1973 made these too expensive and resulted in a push for reduction of the oil content. The solution was addingwater. So water-extended (water in oil emulsion) and water-based (oil in water emulsion) defoamers appeared.[4]
The development of silicone-based defoamers has continued, using different emulsifiers and modified silicone oils. In the early 1990s, silicone emulsion defoamers that caused less surface disturbance were used in thewood pulping industry with great success. These caused better washing, reducedbiological oxygen demand (BOD) ineffluent and reduced deposits.
Oil-based defoamers have an oil carrier. The oil might bemineral oil,vegetable oil or any other oil that is insoluble in the foaming medium, exceptsilicone oil. An oil-based defoamer also contains awax and/orhydrophobic silica to boost the performance. Typical waxes areethylene bis stearamide (EBS),paraffin waxes,ester waxes andfatty alcohol waxes. These products might also have surfactants to improveemulsification and spreading in the foaming medium.
These are heavy duty defoamers and are normally best at knocking down surface foam.
Powder defoamers are in principle oil-based defoamers on a particulate carrier likesilica. These are added to powdered products likecement,plaster anddetergents.
Water-based defoamers are different types of oils and waxes dispersed in a water base. The oils are often mineral oil or vegetable oils and the waxes are long chainfatty alcohol,fatty acidsoaps oresters. These are normally best asdeaerators, which means they are best at releasing entrained air.
Silicone-based defoamers are polymers with silicon backbones. These might be delivered as an oil or a water-based emulsion. The silicone compound consists of ahydrophobic silica dispersed in asilicone oil. Emulsifiers are added to ensure that the silicone spreads fast and well in the foaming medium. The silicone compound might also containsilicone glycols and other modified silicone fluids.[5]
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-aqueous foaming systems likecrude oil andoil refining. For very demanding applicationsfluorosilicones may be suitable.
EO/PO-based defoamers contain polyethylene glycol andpolypropylene 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.
Alkylpolyacrylates 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 asolvent carrier likepetroleum distillates.
The most noticeable form of foam is foam floating on the stock surface. It is easy to monitor and relatively easy to handle and is more a cosmetic issue. Surface foam may cause problems with liquid levels and give overflow leading to pools of oils around the equipment which is a safety concern.[6]Additionally, this might reduce the process speed and availability of process equipment. The main mechanical problem tends to be when foam enters the system as air is a poor lubricant, meaning metal to metal contact can occur.[6]
Air or other gas dissolved in the fluid can come out of solution as small bubbles (entrained air). If these smallbubbles have sufficientbuoyancy, they can rise to the surface and together form foam. Mechanical factors that may generate entrapped air:
Foam, entrained and dissolved air that are present in coolants and processing liquids, may cause various kinds of problems, including:
There are several ways to test defoamers.
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 similar equipment that has adensity meter that can record changes of the liquid density over time.
Drainage can be tested with afilter system for measuring the time to drain a liquid through the filter. The filter might be pressurized or have avacuum.
Anti-foams are added in certain types ofdetergents to reducefoaming that might decrease the action of the detergent. For example,dishwasher detergents have to be low foaming for the dishwasher to work properly.Defoamer is added into the recovery tank of carpet extractors to prevent too much-foaming damage to the vac motor.
When used as an ingredient infood, antifoaming agents are intended to curbeffusion oreffervescence in preparation or serving.[citation needed] The agents are included in a variety of foods and in materials for food preparation;McDonald's includespolydimethylsiloxane (a type ofsilicone) in its oil to mitigate hazardous splashes of oil caused by foaming in fryers,[7] so it has been listed as an ingredient in theirchicken nuggets,french fries, and other fried menu items.[8][9]
Defoamers are used in many industrial processes and products:wood pulp,paper,paint,industrial wastewater treatment,food processing,oil drilling,machine tool industry, oils cuttingtools,hydraulics, etc. Besides, for many building materials, such as cement, mortar, self-leveling compound, or tile adhesive, foam can be an unwanted side effect that disrupts the subsequent work steps and may even undermine the stability of the construction. It needs defoamers to eliminate or reduce the formation of bubbles and ensure smooth processing of the compound.[10]
Antifoaming agents are also sold commercially to relievebloating. A familiar example is the drugsimethicone, which is the active ingredient in drugs such asGas-X.[citation needed]