ionic liquids in separations: applications for pyrolysis oil and emulsion systems
Solvent extraction (also known as liquid-liquid extraction) is one of the main separation techniques and has been developed for a wide range of industrial applications. The selection of the solvent and the type of operational equipment are the most important factors for design of liquid-liquid extraction processes. Ionic liquids (ILs) are often considered as environmentally friendly solvents and have been studied widely in various laboratory applications. Aiming to design effective extraction processes, in this work ILs have been employed for fractionation of pyrolysis oil, for demulsifying oil-in-water emulsions to recover surfactant, and for the design of a novel smart separation process type: fixed liquid extraction.
Pyrolysis oil, the liquid product of fast pyrolysis of lignocellulosic biomass, is a complex mixture containing hundreds of components. Direct use of pyrolysis oil is hindered by its high viscosity, high oxygen content and thermal instability. Upgrading of pyrolysis oil can be done by separating the value-added chemicals. Pyrolysis with fractional condensation results in two fractions. Most sugars and aromatics are collected in the first condenser oil, and most light oxygenates (e.g., acetic acid, acetol and glycolaldehyde) in the second condenser liquid. In the chapters 2 and 3 of this thesis, a study on separation of sugar and aromatics from first condenser oil was described, and in chapter 4 a study on fractionation of oxygenates from second condenser oil.
In chemical enhanced oil recovery (CEOR), surfactant together with alkali and polymer are injected in the reservoir to enhance oil recovery yield. Application of CEOR is usually limited by the cost of the chemicals and thus surfactant recovery is desired. The surfactant is usually blended with water and oil in stable emulsions. Therefore, the first step for surfactant recovery is to destabilize these oil emulsions which is called demulsification. In chapter 5, in total 13 ILs were evaluated as demulsifiers for a model oil-in-water emulsion and the efficiency and mechanism of demulsification were discussed.
Application of ILs at industrial scale is restricted by the their major drawbacks, such as high viscosity and corrosivity. IL-based emulsion systems that make use of stabilizers can potentially overcome these drawbacks. In chapter 6 the formation of several IL-based emulsions stabilized by microgel particles was studied, including the parametric influences on the drop size distributions. The influence of microgel particles on the extraction capacity and kinetics were investigated as well.
ILs sometimes have extremely high affinity for solutes so that very low solvent to feed ratios (S/F) are desired. Traditional liquid-liquid contacting methods are not suitable, so that in chapter 7, a novel separation process concept was explored, referred to as fixed liquid extraction.
The last Chapter 8 presents the conclusions of this thesis and recommendations for future work.
