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Continuous sugar upgrading using Lewis acid catalysts

Navar, Ricardo 2021. Continuous sugar upgrading using Lewis acid catalysts. PhD Thesis, Cardiff University.
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Sugar upgrading to commodity chemicals has become prevalent over the last decades, owing in part to the potential of Lewis acid catalysts, in particular Sn-Beta zeolites. Sn-Beta has shown to possess high activity for the conversion of glucose to fructose as well as smaller molecules such as α-hydroxy esters (methyl lactate and methyl vinyl glycolate) and trioses (dihydroxyacetone, glyceraldehyde, pyruvaldehyde). Despite its promising kinetic potential, drawbacks that hinder it from being an industrially-used catalyst include the relatively low amount of Sn capable of being incorporated and the requirement of fluoride media to successfully synthesise Sn-Beta. Thus, top-down methods such as solid-state incorporation (SSI) has been of great interest for hard-to-incorporate heteroatoms such as Sn at higher wt. %. With this in mind, this thesis begins with an in-depth mechanistic study in the SSI of Sn-Beta, observing the acetate-zeolite interaction/evolution from the initial mechanochemical step to the ramp rate, both in inert gas flow and air using in situ spectroscopic techniques (Chapter 3). Furthermore, an optimised protocol for the heat treatment is obtained, having no negative impact in the kinetic performance of the zeolite. Chapter 4 investigates the influence of using different initial precursor (B, Fe, Ga, Al) for the zeolites’ subsequent SSI. Tests were done with glucose isomerisation as well as retro-aldol fragmentation in continuous flow. Following this, Chapter 5 demonstrates the application of a different type of Lewis acid catalyst: metal-organic frameworks (MOFs). The MOFs i.e., UiO-66(Zr) were studied in different polar solvents under continuous flow to understand their stability and were subsequently tested for disaccharide (lactose) isomerisation, a substrate which would typically not be possible to upgrade using conventional zeolites. Lactose isomerisation was done using binary mixtures of alcohol/water to successfully carry out the reaction. Chapter 6 sets out to carry out the SSI protocol, conventionally done in hydroxide-assisted zeolites, in fluoride-assisted zeolites. Tests were conducted firstly in a commercial, hydroxide-assisted zeolite using an alkaline media along with a pore directing agent at various temperatures. Thereafter, SSI protocol was conducted for three fluoride zeolites (Hf-, Sn-, Zr-) using the same conditions. Lastly, Chapter 7 discusses the results acquired as well as any pertaining challenges which might have been left open due to aforementioned results.

Item Type: Thesis (PhD)
Date Type: Completion
Status: Unpublished
Schools: Chemistry
Date of First Compliant Deposit: 29 September 2021
Last Modified: 03 Aug 2022 01:40

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