Fuel-soluble biocides

Fuel-soluble biocides can be used to treat the contents of the whole storage tank, both fuel and water. As mentioned previously, these biocides are soluble in both phases at varying concentrations. These biocides can be added to a fuel storage tank as follows (1) through a port at the top of the tank, (2) premixed with fuel outside the tank and pumped back into the tank, (3) injected into a flowing stream of incoming fuel, or (4) added to fuel inside the tank to which more fuel will be added. If biocide solubility in fuel is low, the premix method of addition is not recommended. Methods of addition that insure uniform distribution of the biocide in the fuel and water bottom are obviously preferred. It is not recommended to add the biocide to an empty fuel storage tank. The tank should be at least 10% full prior to biocide addition. 

Additional characteristics desired for a fuel-soluble biocide are (Rogers and Kaplan, 1968 Dorris and Pitcher, 1988 Gaylarde et al., 1999)  

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Both water-soluble and fuel-soluble biocides are available for fuel treatment. The advantages and disadvantages of each method of treatment are briefly outlined in TABLE 6-2. 

TABLE 6-2. Advantages and Disadvantages of Water-Soluble and Fuel-Soluble Biocides... 

Water Soluble Biocide Fuel Soluble Biocide ... 

Andrykovitch, G. and Neihof, R. A., 1987. Fuel-soluble biocides for control of Cladosporium resinae in hydrocarbon fuels. Journal of... 

The continuous application of an oil-soluble fuel biocide can often help to minimize the microbial growth throughout the fuel distribution and storage system. 

O/w-droplet micro emulsions are widespread in cleaners, cosmetics and personal care products (see Chapter 8). They are also used as solvents for pharmaceuticals (see Chapter 9) and agrochemicals [16]. In particular, pharmaceutically active ingredients [17] and pesticides [18] which are poorly soluble or insoluble in water can be readily dissolved in o/w-droplet micro emulsions. O/w-droplet micro emulsions are also used as carriers for biocides in wood preservation [19]. W/o-droplet micro emulsions can be found in fuels (see Chapter 11), but also in more sensitive products like cosmetics (see Chapter 8) and food [20,21]. They can also be used as media for enzymatic reactions. 

The degree of partitioning is dependant upon the solubility of the biocide in each of the phases and is effected by the type of fuel, extent of mixing, contact time and the fuel to water ratio (Williams et al., 1992). The partition coefficient (K) of a substance is a measure of the relative solubility of a substance between two immiscible liquid phases. It can describe the affinity of the biocide for one phase over the other. For a fuel/water system ... 

SABS 1434-1987, the South Africa Standard Specification for Biocides , was reaffirmed in 2000. This method covers efficacy testing of three types of organic biocides (differentiated by their physical state - liquid, paste or solid) that are soluble in fuels and soluble in or miscible with water. These biocides are intended for use in hydrocarbon liquid fuels. 

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