Diesel antifoams

The first publication about diesel antifoams in 1966 described the use of polyether siloxanes [45]. At least 60% of the polyether, which is attached by Si-C linkages, is composed of EO or PO [46]. It was not until 20 years later that commercial interest was raised. Polyethersiloxanes were claimed in which at least 80% of the attached polyether is EO [47]. These antifoams are water-soluble and therefore partially incompatible with the hydrocarbon chains of the diesel fuel, which leads to their surface activity. 

As in other applications, the diesel antifoam has to be incompatible with the foaming media and to be surface-active (see Section III.A of this chapter for a more detailed explanation). A deep understanding of diesel defoaming is difficult to achieve because the nature of the foaming substances is unclear. It is believed that foams occur in nonaqueous systems when components of the mixture are only partially soluble in the bulk. This would mean for diesel fuel that the alkyl chains at the upper limit (C24-C26) would cause the formation of foam. As slight modifications in the chemical structure of the antifoams result... 

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). 

Defoamers, 3 236-254 9 23 applications, 3 245-249 commercial sources, 3 240, 241t components, 3 237-240 defoaming theory, 3 241-245 economic aspects, 3 249-250 health and safety factors, 3 251-252 in paper manufacture, 13 118 in polymer colloids, 20 386 silica in, 22 376 surface tension, 8 244t test methods, 3 250-251 Defoaming, 3 240-242 Defoaming (antifoaming) agents, 25 in diesel fuel, 12 428 in food, 12 63-64... 

Antifoam additives prevent formation of foam. Diesel fuels tend to be prone to foam formation when they are pumped into the tanks. Most antifoam additives are organosilicone compounds and are typically used at very low concentrations (about 10 ppm). 

The foaming of diesel fuel has drawn a certain attention in the last decade. Antifoams are usually one component of a package of diesel additive, which is used to adjust and improve the properties of the distillate from the refinery [44]. Antifoams prevent foam formation of the treated diesel fuel during pumping at refineries and service stations at treat rates between 5 and 15 ppm. They help to shorten substantially the filling time of fuel tanks and avoid splashing over. 

The first generation of antifoams were found to lose their effectiveness in wet diesel fuel, which may be explained by the interaction of water with the EO units of the attached polyether. Provided that there is a certain water concentration in the fuel, it is likely that a water shell forms in the vicinity of the oxygen atoms (as part of the polyether) by forming hydrogen bonds. Thus, the delicate HLB is influenced and consequently the antifoam is less effective. 

This leads to a major improvement of their performance in wet diesel fuel. It has not been possible to provide a completely satisfactory explanation for the effect of a polar ligand in combination with ordinary polyethers. Because the surface tension of diesel fuel remains unaffected by various antifoams, the particle size of the antifoam may be disturbed. Polar substituents on the siloxane backbone may be able to adjust the particle size of the antifoam such that its performance is regained. 

---