- Title
- The selective epoxidation of allyl alcohol to glycidol
- Creator
- Harvey, Luke Martin
- Relation
- University of Newcastle Research Higher Degree Thesis
- Resource Type
- thesis
- Date
- 2020
- Description
- Research Doctorate - Doctor of Philosophy (PhD)
- Description
- With the predicted global increase in biodiesel production, it is anticipated that a market oversupply of glycerol, the major by-product (approximately 10 wt%) of biodiesel manufacture, will occur. It is thus desirable to produce value-added species from waste glycerol. One commercially attractive product is glycidol (2,3-epoxy-1-propanol), a stabiliser used in the manufacture of vinyl polymers, oil additive and a precursor to novel energetic polymeric compounds. In principle, glycerol may be dehydrated to glycidol, however the more commonly used route is through acrolein (acrylaldehyde). This work examines first enhancing the production of allyl alcohol from glycerol using alkali metal-modified iron oxide catalysts supported on alumina. In this case, a feed of 35 wt% glycerol was supplied to a plug flow reactor at 340 degrees celsius under nitrogen carrier gas. It was found that the product distribution varies according to the acid-base characteristics of the catalyst, modified by the alkali metal. The rubidium-modified iron oxide catalyst was found to provide the best allyl alcohol total yield, where the potassium-modified catalyst provided the highest selectivity to allyl alcohol. The effect of the product distribution on the success of the allyl alcohol epoxidation reaction was then examined. It was found that acrolein in particular is detrimental to the epoxidation reaction, decreasing the allyl alcohol conversion from ca. 50% to 21%. It also has the effect of decreasing the reaction kinetics to 0.14 times the control rate. This research then focuses on using operando FTIR to determine the mechanism of catalyst inhibition. Instead, a previously unreported oxidation of the vinyl group in allyl alcohol to carbonyl. This reaction was not found to occur over the Ti-free equivalent material, silicalite-1, hence a titanium species was suggested to be the catalytic site for this transformation. Last, the operando XAFS experiments undertaken in order to determine the structure of the Ti species facilitating the vinyl oxidation reaction is discussed. Using direct interpretation of the post-edge XANES spectra, pre-edge, and theoretical fitting of the EXAFS, it was found that the most likely mechanism is framework titanium with coordinated (-OO-) and H2O groups being dehydrated to a 6-coordinate (HO)2-Ti-(OSi)4 upon re-heating the catalyst wafer. We propose that this is framework titanium with a coordinated -OH ligand which is responsible for the newly-reported vinyl oxidation mechanism.
- Subject
- catalysis; x-ray absorption spectroscopy; in-situ spectroscopy; epoxidation; FTIR; zeolites
- Identifier
- http://hdl.handle.net/1959.13/1421968
- Identifier
- uon:37789
- Rights
- Copyright 2020 Luke Martin Harvey
- Language
- eng
- Full Text
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