Use of Antifoams

One of the defects of the synthetic material is its copious foaming power, which generally must be corrected by the use of antifoam agents. The foaming problem is especially important in soft water. 

Delayed Coking. By far, the most extensive use of antifoams is in the delayed coking unit. Coking is a high-temperature thermal operation... 

The solubilization of biological material with TMAH at least permits the determination of As(lll) in human biopsy and autopsy materials by a pH-dependent reaction (pH 5) with sodium borohydride and also the determination of total inorganic arsenic by reaction at pH values around 1-1.5 for this method, however, the use of antifoaming solution is always mandatory (Stoeppler and Apel, 1984). 

The use of antifoams is of special importance for the preparation of water-based paints [202]. Although foam problems also occur in textile and paper industries, there are some special features for paints. First, foam is formed in machines with high and medium shear rates, such as high-speed mills. The presence of a considerable foam volume inhibits the process and considerably reduces the useful load volume of the machine. Besides, foam inhibits the operation of the filling equipment. Problems also occur when paints are applied to a surface, especially using effective sprays, dipping methods and foam-curtain devices. The main reason of foam formation are surfactants used to stabilize aqueous latex dispersions. Thus, nonionic surfactants, instead of anionics, are preferred as they form less foam of low stability. 

Overall value for the system. Values reported are relatively low due to use of antifoaming agent, independent of nozzle type (single/ multiorifice) or diffuser. k ja found to increase with nozzle diameter for diffuser E. 

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. 

The justifications given for the use of mechanical defoaming devices rather than antifoams mostly concerns cost and/or the undesirability of the chemical contamination represented by the latter. Deshpande and Barigou [6,7] also add that the use of antifoams is empirical and based upon a hit-and-miss approach. However, developments in the understanding of the mode of action of antifoams over the past quarter of a century (reviewed earlier in reference [81] and here in Chapters 3-6) suggest that such a comment is unjustified. It would appear to be better directed at the use of the mechanical defoaming methods, which were the subject of the relevant publications [6,7]. 

The use of antifoams in gas-oil separation arguably represents the largest single application of such additives in the petroleum industry according to Pape [2]. Polyorganosiloxane derivatives are often anployed as antifoams in this context. However, as so often with antifoams, there can be undesirable consequences associated with their use. One such potential problem concerns the deposition of polydimethylsiloxanes (PDMSs) on downstream cracking catalyst surfaces, leading to diminished effectiveness [2, 7]. As a consequence, mechanical methods of... 

In this chapter, we first consider the nature of surface activity in gas-hydrocarbon interfaces in general and in gas-crude oil systems in particular. That represents an issue fundamental to understanding the causes of foam formation in gas-oil separators and has relevance for the mode of action of antifoams in that context. In a separate section, we consider the possible causes of foam formation in gas-crude oil systems. There we review the observations of foam behavior in gas-crude oil systems and make the limited comparison with theory which that permits. Finally we consider foam control in gas-oil separators, which usually involves the use of antifoams. Therefore, we describe the design criteria for suitable antifoams and the evidence available concerning their mode of action in a non-aqneons medium such as crude oil. 

It has been known for more than half a century that antifoams consisting of mixtures of PDMS and hydrophobic silica can be used to dispel excessive gas in the gastrointestinal tract. However, the first use of antifoams in this context was reported by Quin et al. [8] more than 60 years ago and concerned treatment of bloat in ruminants. That the hydrophobed silica is a necessary component of an effective PDMS-based antifoam in vivo was first demonstrated by Birtley et al. [9] using X-ray observation of the stomachs of rats in which foam had been artificially produced. 

A, B), and are also available from amine vendors. Use of antifoam should not be regarded as a permanent solution to plant foaming problems. Once foaming is under control, the source of trouble should be investigated and the basic problem corrected. 

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