Antifoaming and Defoaming

Any additives that can act to reduce the viscosity of foam films, and thereby increase the liquid drainage rate, will tend to reduce foam stability as a result. This includes any chemicals that can reduce surface viscosity and/or surface elasticity. Some alcohols can be use to produce these effects. 

The tests used to determine antifoaming and defoaming action are essentially the same as used for testing foaming ability (see Section 2.6.2), except that the prospective defoaming agents are added in measured amounts and in a reproducible manner. 

(1980) Introduction to Colloid and Surface Chemistry, 3rd edn, Butterworths, London. 

Adamson, A.W. (1990) Physical Chemistry of Surfaces, 5 th edn, John Wiley Sons, Inc., New York. 

---

Adjuncts include antifoams and defoamers, some problem-specific polymers, and alkalinity boosters. 

Boiler water foaming and frothing is undesirable because it contributes to overheating, carryover, and loss of operational control. As a result, antifoam and defoamer products are commonly employed in BW treatment programs. The same active ingredients are also widely used in all types of industrial processes (industrial grades), as well as in cosmetic, food, potable water, and kosher applications (all agents typically are odorless, colorless, and tasteless). 

NOTE In-use concentrations of antifoam and defoamer materials are very small, often as low as 5 to 20 ppm product, or 0.25 to 2 ppm actives . However, the persistence of the agent will vary and if not replenished will eventually fail. When antifoam is fed periodically, it usually is dosed as a stand-alone product at a higher rate, but when fed continuously, it is present at a lower concentration and forms part of a multicomponent additive. 

When evaluating materials for BW antifoam and defoamer duty, some important considerations are ... 

NOTE In cooling water treatment, although temperatures tend to be lower, antifoams and defoamers must be able to withstand strongly oxidizing conditions. 

Antifoams and defoamer surfactants must possess a good surface spreading action (spreading coefficient). 

Derivatives of the nonionic block copolymers that are used as antifoams include chemistries containing silicones. These silicone-block copolymers are molecules that possess improved antifoam and defoamer durability and excellent stability under high alkalinity, high temperature boiler conditions. 

Fluid loss additives Antigas migration agents Antifoam and defoaming agents... 

In many applications we want to prevent the formation of foam or get rid of already existing foam (see, for example, Table 11.1). Usually chemicals are added to achieve this (see Ref. [564] for an introduction). We distinguish between antifoamers and defoamers. An-tifoamers are added to the liquid prior to foam formation and act to prevent or inhibit foam formation. Defoamers or foam breakers are added to eliminate existing foam. They can only reach the outer surface of a foam. 

Chemical Defoamers The addition of chemical foam breakers is the most elegant way to break a foam. Effective defoamers cause very rapid disintegration of the foam and frequently need be present only in parts per million. The great diversity of compounds used for defoamers and the many different systems in which they are applied make a brief and orderly discussion of their selection difficult. Compounds needed to break aqueous foams may be different from those needed for aqueous-free systems. The majority of defoamers are insoluble or nonmiscible in the foam continuous phase, but some work best because of their ready solubility. Lichtman (Defoamers, 3d ed., Wiley, New York, 1979) has presented a concise summary of the application and use of defoamers. Rubel (Antifoaming and Defoaming... 

Lewis, V.E. Minyard, W.F. Antifoaming and Defoaming in Refineries in Foams, Fundamentals and Applications in the Petroleum Industry, Schramm, L.L. (Ed.), American Chemical Society Washington, DC, 1994, pp. 461—483. 

A silicone emulsion for use in antifoaming and defoaming in a wide range of textile applications. FOAMEX AD-50 is effective in preventing foam buildup in an open beck. 

INTEX DEFOAMER 138 is a formulated low silicone antifoam and defoamer. It is formulated with a selected blend of low foam emuslifiers to assure compatibility with all dyestuffs and auxiliaries normally used in dyeing operations. 

Defoamer. [Piedmont Chem. Industries] Antifoams and defoamers for textiles, dyeing, wastewater systems. 

Influence of Unstable Pseudoemulsion Film Antifoaming and Defoaming Action. When the pseudoemulsion films are unstable in the three-phase foam, the oil generally destabilizes the foam. Destabilizing of foam has important applications as antifoaming or defoaming in several industrial processes (83, 84). Foam inhibitors are also used in the petroleum industry, such as in gas—oil separation, in natural gas processing, and in distillation processes (85). 

---