Demulsifiers and dehazers

The terms demulsifier and dehazer are often used interchangeably to describe compounds which break fuel emulsions or remove water-initiated haze from fuel. The terms can be distinguished as follows ... 

Two basic mechanisms have been proposed to explain the performance of demulsifiers and dehazers in finished fuels. These two mechanisms are defined as coalescence and adsorption. Both processes rely on the fact that the demulsifier contains both hydrophobic and hydrophilic sites. The mechanisms can be defined as follows ... 

To break through this oil or surfactant layer and free the retained water, it is necessary to chemically disrupt the stability of this layer. Demulsifiers and dehazers can adsorb onto the protective film and subsequently interfere with the electrochemical forces which hold this outer layer together. 

Quaternary ammonium salts and salts of alkyl naphthalene sulfonic acid were some of the first compounds to be used effectively as fuel demulsifiers and dehazers. Today, a wide range of monomeric and polymeric demulsifiers and dehazers exist. 

Given time, water which exists as discrete droplets in finished fuel may coalesce into larger drops and settle by gravity from the fuel. Demulsifiers or dehazers can accelerate this process by functioning as a site for attraction of dispersed water. 

Upon adsorption, demulsifier/dehazer compounds function to break the oil or surfactant layer thus releasing the contained water. Once free, the water can then coalesce into larger drops and be removed from the fuel. 

Sorbitol and glycerine are commonly used as monomers for oxide addition. Various alkyl phenol-formaldehyde compounds are examples of polymeric acceptor compounds having a large number of unreacted hydroxyl groups. The extent of oxide polymerization can have a significant impact on performance and solubility of the dehazer or demulsifier in fuel and oil systems. 

As a general rule, the addition of ethylene oxide to a resin backbone will tend to increase the water solubility of the compound. The addition of propylene oxide or butylene oxide to the resin will tend to increase the hydrocarbon solubility of the compound. Often, the dehazer or demulsifier can be made to perform selectively in oil-water systems by adding both ethylene oxide and propylene oxide to the same molecule. Performance and solubility of the alkoxylated compound can then be finely tuned by closely controlling the amount and order of epoxide addition. A random EO-PO based fuel demulsifier is shown in FIGURE 6-6. 

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