Foam prevention

SK 3556 anti-foam prevented foaming in both HP and LP Ninian separators, although the concentration required to prevent foaming varied with the crude GOR. 

Although many factors, such as film thickness and adsorption behaviour, have to be taken into account, the ability of a surfactant to reduce surface tension and contribute to surface elasticity are among the most important features of foam stabilization (see Section 5.4.2). The relation between Marangoni surface elasticity and foam stability [201,204,305,443] partially explains why some surfactants will act to promote foaming while others reduce foam stability (foam breakers or defoamers), and still others prevent foam formation in the first place (foam preventatives, foam inhibitors). Continued research into the dynamic physical properties of thin-liquid films and bubble surfaces is necessary to more fully understand foaming behaviour. Schramm et al. [306] discuss some of the factors that must be considered in the selection of practical foam-forming surfactants for industrial processes. 

Not all foams are wanted though. Foams, other than flotation froths, are generally not wanted in the process industries where they tend to interfere with process unit operations and may cause upsets. Some agents will act to reduce the foam stability of a system (termed foam-breakers or defoamers) while others can prevent foam formation in the first place (foam preventatives, foam inhibitors). There are many such agents and Kerner [327] describes several hundred different formulations for foam... 

Any agent that acts to prevent foaming. Also termed foam preventative . A more general term is antifoaming agent . See also Antifoaming Agent. 

Dispersion/suspension of the oil and dirt particles in the soap foam, preventing these particles from being redeposited on the surface. 

On the other hand, some substances, even in minute concentrations, promote coalescence. Some of the non-ionic surfactants often used as antifoaming agents are so effective that a concentration of 3 ppm is sufficient to halve the kLaL of pure water (Zlokarnik, 1979). Clearly the use of surfactants for foam prevention should be avoided whenever possible, and an efficient mechanical foam breaker should be used (Zlokarnik, 1986). 

In a 12-1. flask fitted with a reflux condenser and an efficient, liquid-sealed mechanical stirrer (Note i) are placed 2.5 1. of 95 per cent ethyl alcohol, 872 g. (3.5 moles) of piu e -dodecyl bromide (Org. S Ti, 15, 24) and 278 g. (3.85 moles) of powdered 90 per cent potassium cyanide (Note 2). The mixture is refluxed for fifteen hours, with stirring, in a water bath (Note 3). At the end of this time another 278-g. portion of potassium cyanide is added and the mixture refluxed, with stirring, for fifteen hours longer. The flask is allowed to cool, and a solution of 670 g. of 90 per cent potassium hydroxide in i 1. of water is added (Note 4). The solution is refluxed and stirred for thirty hours. The flask is fitted with a head for steam distillation (Note 5), and steam is passed in until foaming prevents further distillation. When the flask has cooled somewhat, the steam inlet is replaced by a separatory funnel with a stem reaching to the bottom of the flask, and 1500 cc. of concentrated hydrochloric acid (sp. gr. 1.18) or the equivalent amount of more dilute acid is added. The flask is shaken occasionally to prevent stratification of the hydrochloric acid. The dropping fimnel is then replaced by the steam... 

Foam preventatives, which are thought to adsorb at the air/water interface in preference to the surfactants which stabilise the thin films... 

Glass-fiber incorporation increases the fire resistance of polyisocyanurate foam laminates. The glass fibers embedded in the foam prevent the development of deep fissures in the protective carbonaceous char that is formed when polyisocyanurate foam is exposed to high temperature flames. ... 

Foam Preventative See Antifoaming Agent, Foam Inhibitor. 

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