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Understanding Ionic Liquid Properties for Carbohydrate Dissolution

Green, Stephen Mark (2017) Understanding Ionic Liquid Properties for Carbohydrate Dissolution. PhD thesis, University of Leeds.

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The study of ionic liquids (ILs) is one of the fastest growing research fields today, both in academic and industrial spheres. One important use of ILs is in dissolving and processing biological resources, particularly cellulose. There is huge interest in understanding the properties of cellulose-dissolving ILs and how different IL features affect the dissolution environment. The work presented in this thesis is an experimental study into two classes of cellulose-dissolving ILs. Two distinct investigations are undertaken on pure ILs, first with imidazolium-carboxylate ILs and then with 1,5-diazabicyclo[4.3.0]non-5-enium (DBN) carboxylate ILs. A third investigation is then presented, examining solutions of glucose, cellobiose and cellulose in the imidazolium-based IL, 1-ethyl-3-methylimidazolium octanoate ([C2MIM][Oct]). Several NMR techniques are used, along with rheological, conductivity and density data. A novel modelling approach is formulated and then applied to the pure IL series', where simple systems of ion pairs and charged aggregates are considered, in order to accurately model several key experimental features. Four pure imidazolium-based ILs are studied with varying-length carboxylate anions. Microscopic properties, such as NMR data, are compared to macroscopic properties, such as viscosity. Stokes-Einstein-Debye theories are applied to the different datasets, providing an insight into the microscopic structuring in the different ILs. Nernst-Einstein theory and the Walden rule are also examined for these ILs. Inconsistencies between different datasets and theoretical expectations are addressed and several simple models are applied, in order to account for these inconsistencies. An ion pairing model, a charged aggregate model and a combination of both models are tested, indicating that this approach is reasonably successful in describing the imidazolium-based ILs and suggesting a small amount of ion aggregation is present. In a similar study, eight pure DBN-carboxylate ILs are studied, with systematically varying anion sizes between formate and octanoate. Experimental data are presented, indicating a complex dependence on anion chain length. Comparisons of micro- and macroscopic properties are shown, comparing and contrasting the effects of changing anion chain length and changing the cation. The three models of ion aggregation are successfully applied to the six room-temperature DBN-based ILs, indicating a higher degree of aggregation and ion pairing, as compared to the imidazolium-based ILs. Finally, [C2MIM][Oct] is investigated as a solvent for the carbohydrates glucose, cellobiose and cellulose. NMR and rheological data are presented and compared for carbohydrate solutions. Different NMR datasets are studied in-depth, including diffusion, relaxation and chemical shift. The carbohydrate-concentration dependence of each dataset is examined and compared to literature data for the same solutions in [C2MIM][Ac]. The relative time and length scales of the NMR techniques were found to affect how the solutions respond to increasing carbohydrate concentration and changing between glucose, cellobiose and cellulose. This thesis forms part of a project funded by the EPSRC CASE award with Innovia Films, aiming to better understand the process of cellulose dissolution in ILs. The results and techniques described here can aid in understanding the properties of these ILs, both for cellulose dissolution and other IL applications.

Item Type: Thesis (PhD)
Keywords: Cellulose, Ionic Liquids, NMR, Stokes-Einstein, Nernst-Einstein
Academic Units: The University of Leeds > Faculty of Maths and Physical Sciences (Leeds) > School of Physics and Astronomy (Leeds)
Identification Number/EthosID: uk.bl.ethos.723197
Depositing User: Dr Stephen Mark Green
Date Deposited: 26 Sep 2017 11:50
Last Modified: 18 Feb 2020 12:31
URI: http://etheses.whiterose.ac.uk/id/eprint/18123

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