Chemical defoaming

Ross, Sydney. Chemical Defoaming Agents. Chemical Industries. Maclean-Hunter Publishing Corporation, USA, May 1949. 

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... 

Foamed emulsions are disperse systems with two disperse phases (gas and liquid) in the disperse medium (surfactant solution). Water foamed emulsions are formed when foams or aqueous surfactant solutions are used to clean up oil deteriorated surfaces, in the process of oil flotation of waste waters, in firefighting when the foam contacts various organic liquids and in the processes of chemical defoaming (foam destruction by antifoams). Individual foamed emulsions can have practical importance e.g. a foamed emulsion of bitumen is used in road coating foamed emulsions from liquid fuels are used as explosives. 

Foam can be controlled by chemical, thermal and mechanical means. Chemical defoaming agents (generally extremely surface active substances of limited solubility, e.g. silicones) are best, if they do not impair the quality of the product. 

Considerable progress has been made in foam and entrained air management in the pulp and paper industry since the inhoduction of petroleum as a defoaming aid. Because of the complex nature of the paper mill system and the fact that the chemically stabilized foams generally encountered are hard to break down mechanically, more mills are finding it not only helpful but necessary to use chemical defoamer formulations. These are generally emulsifiable combinations of hydrocarbons, alcohols, fatty acids, and various surface active agents, that frequently are specifically formulated for particular applications. 

To address machine performance and paper quality issues, alternative chanis-tries are continuously being evaluated and proven within the industry. Present technology inclndes prodncts with chemistries such as synthetic alcohols, hydro-phobic wax particulates, and synthetic esters. Chemical defoamer formulations containing emnlsifiable combinations of hydrocarbons, alcohols, fatty acids, and various surface active agents are effective foam suppressors and deaerators. 

Ah factors that cause foam in the system should be evaluated. But very often the most efficient way to manage the problem is to use an effective chemical defoamer. 

Most evaporators employ steam-heated, tubular heating surfaces, over which the liquid to be vaporized is circulated. The efficiency of an evaporator may be reduced considerably by the formation of scale on the heating surface, which may be removed by chemical or mechanical means. Another problem is the formation of foam which may seriously restrict the capacity of an evaporator, but this may be controlled by the use of special chemical defoaming agents or gas or air jets. 

Chin, R., Mow, H., Keja, T., Hebert, P, Bermett, J., Yin, T., Chemical defoamer reduction with new internals in the MARS TLP separators SPE paper 56705, presented at SPE Annual Technical Conference and Exhibition, Honston, TX, October 1999. 

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