Antifoaming chemicals

Water level control and the use of organic antifoam chemicals are essential in steam plants in order to break dowm the bubbles at the water surface in steam systems, which cause foaming. 

For distillation, E0 is typically in the range 0.5 to 0.9. The vertical spacing between trays ranges from 200 to 900 mm. In some trayed columns, an undesirable bubbly foam can form above the liquid-vapor mixture. Antifoam chemicals must be added to such columns or diameters or tray spacings must be increased. Packed columns foam less often than trayed columns. 

The most important antifoam chemicals used to deal with non-aqueous foams are polydimethylsiloxanes. These are available in a range of molecular weights from low viscosity fluids of 1000 to several million cSt. Silicone fluids of the correct molecular weight have limited solubility in oil and a surface tension of 21 mN/m, lower than that of hydrocarbon oils. Fluorosilicones exhibit even lower surface tension, but their use is limited as they are considerably more expensive. 

Defoamer Chemical additive to control foam and treat existing entrained air problems Deaerator/antifoam Chemical additive to prevent build-up of entrained air EBS Ethylenebis(stearamide) wax, very hydrophobic defoamer component Silicone The most hydrophobic component used in defoamer formulations, may also be identified as siloxane technology... 

Carry-over due to foaming can be controlled by injecting a small amount of silicone antifoam agent. There are a variety of such chemicals on the market and a specific one, effective for many services, can usually be found. However, for most refinery applications, continuous use of antifoam chemicals would be prohibitively expensive. Also the additive may have negative effects on certain down-stream processes. If the wrong defoaming chemical is used, foam formulation can be enhanced. This happened on a distillate fuel desulfurizer when a silicone defoamer, normally used to control foams in a coking unit, was tried. When the correct defoamer is used, concentrations of as little as 1 ppm are effective. 

One successful application of a silicone antifoam chemical reported was in a visbreaker fractionator. At high conversions the tower bottoms tended to carry over into the normally clear distillate product. This situation was brought under control by injecting 10 ppm of an ARCO silicone defoamer into the vapor space above the fractionator bottoms. 

High agitation and aeration rates can result in foam formation inside the bioreactor, which can block the exhaust gas line and cause loss of cells and media and possible contamination when the foam is washed out from the bioreactor. Mechanical foam breakers and antifoam chemicals are used to control foam formation inside the bioreactor. The working volume of the bioreactor is usually 70-80% of the vessels physical volume. 

Questions and Answers Water-Based Antifoams, Nalco Chemical Co., Oak Brook, lU., 1983. 

Many of the unique properties of siUcone oils are associated with the surface effects of dimethylsiloxanes, eg, imparting water repeUency to fabrics, antifoaming agents, release liners for adhesive labels, and a variety of poHshes and waxes (343). Dimethylsilicone oils can spread onto many soHd and Hquid surfaces to form films of molecular dimensions (344,345). This phenomenon is greatly affected by even small changes in the chemical stmcture of siloxane in the siloxane polymer. Increasing the size of the alkyl substituent from methyl to ethyl dramatically reduces the film-forming abiUty of the polymer (346). The phenyl-substituted siUcones are spread onto water or soHd surfaces more slowly than PDMS (347). 

Quahty control testing of siUcones utilizes a combination of physical and chemical measurements to ensure satisfactory product performance and processibihty. Eor example, in addition to the usual physical properties of cured elastomers, the plasticity of heat-cured mbber and the extmsion rate of TVR elastomers under standard conditions are important to the customer. Where the siUcone appHcation involves surface activity, a use test is frequently the only rehable indicator of performance. Eor example, the performance of an antifoaming agent can be tested by measuring the foam reduction when the sihcone emulsion is added to an agitated standard detergent solution. The product data sheets and technical bulletins from commercial siUcone producers can be consulted for more information. 

Dimethylsilicone fluids are used extensively as antifoams although the concentration used in any one system is normally only a few parts per million. They are useful in many chemical and food production operations and in sewage disposal. 

Evaporators require the continuous low level (1-3 ppm) application of a suitable antisealant chemical treatment. Traditionally, polyphosphate has been used (sometimes in conjunction with an antifoam and/or a dispersant agent), but it generally performs poorly because of a lack of thermal stability. Treatments based on polymaleic acid (PMA) and other modem organic polymers tend to perform much better. 

Polyalkylene polyamides and other nonsilicone synthetic antifoams are particularly useful in controlling foaming problems. These chemicals also provide defoaming and demulsification benefits. 

NOTE Early polyalkylene polyamide antifoam formulations (1940s) developed by Dearborn Chemical Company (now G.E. Betz, formerly Hercules Betz-Dearborn) employed protective colloid technology. These products generally were in powder or briquette form. 

NOTE Drew Industrial Division of Ashland Chemicals, Inc. patented such products for BW antifoam duty 25 years ago. 

Typical BW antifoam emulsion products include SAG 10 and SAG 30 (10 and 30% milky white emulsions, each with a viscosity of 2,000 cS at 25 °C) from Union Carbide Corporation. These same products also are used for food processing (under FDA 21CFR 173.340), for petroleum processing (as amine scrubbers, gas-oil separators, etc.), and as functional chemicals (antifreezes, hydraulic fluids, cutting oils, etc.). 

Dearborn. Polyamide Antifoam Treatments. Technical publication. Dearborn Chemical Company (now a division of G.E. Betz), USA 1950. 

The interest in this type of copolymers is still very strong due to their large volume applications as emulsifiers and stabilizers in many different systems 43,260,261). However, little is known about the structure-property relationships of these systems 262) and the specific interactions of different segments in these copolymers with other components in a particular multicomponent system. Sometimes, minor chemical modifications in the PDMS-PEO copolymer backbone structures can lead to dramatic changes in its properties, e.g. from a foam stabilizer to an antifoam. Therefore, recent studies are usually directed towards the modification of polymer structures and block lengths in order to optimize the overall structure-property-performance characteristics of these systems 262). 

Although glycol-water formulations are not prone to foaming, mechanical and chemical factors may cause foaming in the system. The use of corrosion inhibitors and the presence of contaminants may enhance the tendency to form foams. For these reasons, antifoaming agents, such as silicones, polyglycols, or oils, are sometimes added. 

Typical formulations of commercial composite antifoams have been detailed [536,537]. There are many products on the market but evaluation of their relative efficacy depends on the foaming problems to be overcome. Not only does the chemical type of the active defoamer have to be considered, but its state within the emulsion and the intrinsic properties of the emulsion are also of crucial importance. Methods of evaluating defoamers have been described [539,540]. 

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