221 Physical and chemical properties of demulsifiers Since demulsifiers are

221 physical and chemical properties of demulsifiers

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2.2.1 Physical and chemical properties of demulsifiers Since demulsifiers are surfactants, understanding the role of demulsifiers as a surface-active agent are very important. Basically, there are two groups in the demulsifier molecule; hydrophobic (water disliking) group and a hydrophilic group (water liking group). The hydrophobic group such as long chain alkyl group is not repelled by water, since the attraction of the hydrocarbon chain for water is approximately the same as itself. In fact, at very low concentration of demulsifier in the water the hydrocarbon chains will lie flat on the surface. The hydrophilic effect is referred to the water-preferring nature of species (atom, molecule, droplet and particle). Hydrophilic usually means that a species prefers the aqueous phase rather than the oil phase. In this sense, hydrophilic has the same meaning of oleophobic. Hydrophilic molecules are believed to decrease the degree of order in water molecules around them. So, ions in solution are hydrophilic such as carboxylate, sulphate, phosphate, sulphonate and quaternary ammonium. Primary amines, amine oxides, phosphine oxide and sulphoxides are polar groups with a highly electronegative character which shown strong electrophilic properties. If the molecules contain electronegative atoms capable of associating with the hydrogen-bonding network in water, these molecules are considered as hydrophilic. The examples of molecules that include in this group are ethers, aldehydes, amides,
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13 esters, oxygen atom in alcohol, nitrogen atom in amides, amines, ketones and nitroalkanes. This effect sometimes can be diminished when the molecules, which contain the hydrophilic effect are attached to the hydrophobic group. But these phenomena will not be happened if a number of such nonpolar groups are attached to the hydrophobic groups, so that limited or entire water solubility can be achieved, depending upon the relative size of the hydrophobic effect and the number of hydrophilic groups. Besides that, there are a lot of water soluble polymeric demulsifiers such as the emulsion tetra polymer of methyl methacrylate, butyl acrylate, acrylic acid and methacrylic acid and dispersions of water-soluble cationic polymers. The hydrophobic effect is referred to the water-avoiding nature of a species (atom, molecule, droplet, and particle). Hydrophobic usually means that a species prefers the oil phase to the aqueous phase. In this sense, hydrophobic has the same meaning as oleophilic. Oil soluble demulsifiers are also known as hydrophobic groups. There are a lot of reasons that causes the insolubility of the hydrogen chain in water. These reasons include the mechanism that involve both entropic and enthalpic contributions and the unique multiple hydrogen bonding capability of water. There is a reorientation and restructuring of water around nonpolar solutes, which disrupts the existing water structure and imposes a new and more ordered structure on the surrounding water molecules. This will result the decreasing in entropy value.
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