Foam control antifoams

Foam Control. Whereas some siUcones are known to be foam promoters, Dow Corning FS-1265 Fluid is a Hquid fluorosiUcone with effective antifoam properties. Petroleum industry appHcation of fluids and dispersions in gas—oil separators on offshore drilling platforms has been successful. Their use peaked in the early 1980s, coinciding with constrained cmde oil capacity and production. Diesel fuels are an excellent solvent for dimethyl silicones and render them ineffective as an antifoam. A new antifoam which does not require the use of added siUca is formulated from a fluorosiUcone copolymer. It has shown promise to antifoam (8) diesel fuel (see Defoamers). 

Activities associated with bioreactors include gas/hquid contacting, on-hne sensing of concentrations, mixing, heat transfer, foam control, and feed of nutrients or reagents such as those for pH control. The workhorse of the fermentation industry is the conventional batch fermenter shown in Fig. 24-3. Not shown are ladder rungs inside the vessel, antifoam probe, antifoam system, and sensors (pH, dissolved oxygen, temperature, and the like). Note that coils may lie between baffles and the tank wall or connect to the top to minimize openings... 

Although silicone oils by themselves or hydrophobic particles (e.g., specially treated silica) are effective antifoams, combinations of silicone oils with hydrophobic silica particles are most effective and commonly used. The mechanism of film destruction has been studied with the use of surface and interfacial tensions, measurements, contact angles, oil-spreading rates, and globule-entering characteristics for PDMS-based antifoams in a variety of surfactant solutions.490 A very recent study of the effect of surfactant composition and structure on foam-control performance has been reported.380 The science and technology of silicone antifoams have recently been reviewed.491... 

Foam Control. Fermentations tend to froth because metabolites have surfactant properties. Prevention commonly is by addition of antifoam agents such as oils, heavy alcohols, fatty acids, or silicones. High-speed rotating impellers destroy bubbles by direct impact and by throwing them against the wall of the vessel. 

The most widely used in foam control are special materials called antifoams. They could be fats, oils, waxes, fatty alcohols and acids, ethers, organic compounds containing nitrogen and sulphur (alkylamines and amides, sulphides, thioethers, etc.), phosphorus organic compounds (in particular, tributylphosphate), silicon-organic compounds (silicon oils) and some non-ionic surfactants [e.g. 4,5]. 

HERCULES 831 defoamer is a quick-dispersing, hydrocarbon oil-based antifoaming agent designed for use where immediate foam-control action is wanted. It is particularly suitable where addition adjacent to the foam-control point is required. Its efficiency is not adversely affected by temperature or pH, and it is effective in the presence of many surfactants. 

Antifoam BTB. [Ivax Irtdustries] Silicone emulsion foam control agent for bleach and scour baths, becks, jets, package dyeing and finishing, free... 

Fermenter studies were carried out in a New Brunswick continuous culture apparatus with 15-liter stirred fermenter jars for culture vessel and nutrient reservoirs and a 20-liter carboy for a harvest vessel. Temperature of the culture was maintained at 28°-29°C. Impeller speed was kept at 120 r.p.m. with a 3-inch diameter set of four impeller blades low in the culture, and a second impeller just above the liquid level to aid in foam control. A few drops of Dow Coming Antifoam AF at 25 mg./ml. (emulsion) were added manually as required to control foam. The rate of aeration was 1 to 3 liters per minute. Contamination through the impeller shaft port was prevented by a loose fitting sleeve through which live steam was continually passed (10). Samples taken from the fermenter were streaked on potato dextrose agar, and Bacto plate count agar, incubated for 7-10 days and inspected for contamination. 

Dow Coming Anilfoam 1400 Dow Coming Antifoam 1410 Dow Coming Antifoam 1430 Dow Coming Antifoam 1520-US Dow Coming Anilfoam H-10 Drewfax 842 Drewplus T-4202 foam control agent, emulsion coatings Drewplus L-496... 

The performance of silicone-based antifoam compounds is independent of water hardness. They are effective at very low addition levels in all types of surfactant systems normally present in detergent formulations and across a wide range of use conditions. Furthermore, silicones cause no yellowing on fabric. Thus, silicone-based antifoam compounds have a number of benefits over soap-based foam control systems. 

U.S. Patent 5,589,449 to Dow Coming discloses a particulate foam control agent on a zeolite carrier. This composition is designed to make the formulation of antifoam into a powdered detergent easier. 

Two developments have been reported (by Wacker Chemie) supplementing its range of foam-control systems Silicone Antifoam Emulsions SE 84 and SE 85. Based on organically modified silicone fluids, they reduce or prevent flow defects in polymer films. 

Zemeth, Z., Racz, G. and Koezo, K., Foam control by silicone polyethers - mechanism of cloud point antifoamers, J. Colloid Interface ScL, 207, 386-394 (1998). 

Hydrocarbon oils often form the main ingredient of antifoams used for the foam control of aqueous systems. As we will describe in Chapter 4, the entry and spreading behavior of such oils is central to both their mode of action and their effectiveness. It is therefore appropriate to review that behavior here. 

It should be emphasized that this chapter is concerned exclusively with the effect of antifoam concentration on foam generation. We are mainly concerned here with foam generation by air entrainment using, for example, shaken, rotated, or stirred vessels and impinging jets, etc. Perhaps the majority of foam control problems for which antifoams are employed concern foam generation by such methods. They are... 

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