The role of water in the aggregation behaviour of surface active molecules in non-polar solvents

Asphaltenes represent some of the largest and most polar molecules found in crude oils and are known to be surface active. Whilst one of the least valuable fractions of a crude oil, asphaltenes have never-the-Iess received a great deal of scientific attention due to the risks their behaviour poses to oil recovery, transportation and processing. Subtle changes in the chemistry of crude oils or physical conditions can cause changes in the aggregation state of asphaltenes, which may precipitate out of solution blocking pores in reservoir rocks, altering surface wettability or fouling pipelines and refinery equipment. The complex and polydispersed nature of asphaltenes and their propensity to aggregate in solution makes them very difficult to characterise and despite many studies a definitive picture of their chemistry, molecular weight and aggregation behaviour has not been found. The aggregation state, geometry and molecular weight of petroleum asphaltenes are investigated using a Langmuir trough in Chapter 2. A novel mathematical model based upon the van der Waals modified equation of state was used to predict aggregation numbers and limiting areas of asphaltene aggregates at the air water interface. Non-ionic surfactants are widely used in many industries including many stages of oil recovery and production. The solubility and aggregation behaviour of a commercial surfactant in non-polar solvents is investigated in Chapter 3. Anomalous solubility behaviour at low surfactant mole fractions is investigated and the underlying mechanisms are discussed. The importance of water to the aggregation behaviour of non-ionic surfactants is a recurring theme in the scientific literature. The interaction between a commercial non-ionic surfactant in non-polar solution and water is reported in Chapter 4. A mechanism is proposed to explain aggregation states which vary significantly with water content and its limitations are discussed.EThOS - Electronic Theses Online ServiceGBUnited Kingdo