Surfactant aspects of corrosion inhibition

Hicks, Jake Thomas

Abstract

This thesis is concerned with investigating the surfactant aspects of corrosion inhibition. Corrosion inhibitors are of great industrial importance because they are a relatively inexpensive and easily applicable method of protecting oil pipelines against internal corrosion. The performance of corrosion inhibitors is known to depend upon the prevailing conditions within the pipeline.

We have used a range of experimental techniques to study corrosion of steel surfaces, adsorption of corrosion inhibitors and the behaviour of inhibitors in mixtures of oil and water in order to understand more about the factors which affect the performance of corrosion inhibitors under oil field conditions. Firstly, electrochemical and weight-loss measurements were used to measure the corrosion rate of steel immersed in aqueous environments under atmospheric conditions and in the presence of dissolved carbon dioxide and hydrogen sulphide. The measurements were repeated in the presence of dodecylbenzyldimethylammonium chloride and I-aminoethyl-2-(8- heptadecenyl)-2-imidazoline acetate, which are thought of as model corrosion inhibitors. Both surfactants were found to effectively reduce the corrosion rate of steel when the dissolved gas was hydrogen sulphide, but were found to increase the corrosion rate in some aerated and carbonated environments.

The optical technique ellipsometry has been used to study the adsorption of dodecylbenzyldimethylammonium chloride at the steel-water interface. We have determined the thickness of the surfactant film adsorbed from aqueous solution in the absence of electrolyte. The results are consistent with the formation of a monolayer at inhibitor concentrations close to the critical micelle concentration and possible multilayer formation at higher concentrations. Determination of inhibitor film thickness has not been possible in the presence of electrolyte and corrosive dissolved gases which cause rapid corrosion of the steel surface. The technique has been employed subsequently to study the initial stages of corrosion in the presence and absence of dodecylbenzyldimethylammonium chloride. Scanning electron microscopy and elemental analysis have also been used to examine the changes which occur to the steel surface during corrosion. These results show that the optical properties of the steel surface undergo changes as the steel is attacked by corrosive aqueous solutions and that dodecylbenzyldimethylammonium chloride can increase the rate of these changes or completely suppress them, depending on the nature of the dissolved gas present.

Finally, we have investigated the phase behaviour of alkylbenzyldimethylammonium chloride and 1-aminoethyl-2-(8-heptadecenyl)-2- imidazoline acetate using equilibrium partitioning and emulsion phase inversion methods. The results show that variations in common oil field variables, such as temperature, electrolyte concentration and oil type, can lead to the consumption of the aggregated form of water-soluble corrosion inhibitors by partitioning to the oil phase. The results are discussed in terms of the effect of these variables upon the effective geometry of the inhibitor within the monolayer of the aggregates. We have also performed electrochemical corrosion rate measurements in systems containing oil and water, under conditions which cause virtually all of the inhibitor to exist in the oil phase. The results suggest that partitioning of the aggregated form of corrosion inhibitors from water to oil does not adversely affect corrosion inhibition in the aqueous phase.

Citation

Hicks, J. T. (2007). Surfactant aspects of corrosion inhibition. (Thesis). University of Hull. Retrieved from https://hull-repository.worktribe.com/output/4214284

• Thesis Type: Thesis
• Deposit Date: Jul 31, 2013
• Publicly Available Date: Feb 22, 2023
• Keywords: Chemistry
• Public URL: https://hull-repository.worktribe.com/output/4214284
• Additional Information: Department of Chemistry, The University of Hull
• Award Date: Jul 1, 2007