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New insights for the valorisation of glycerol over MgO catalysts in the gas-phase

Smith, Louise R., Smith, Paul J., Mugford, Karl S., Douthwaite, Mark, Dummer, Nicholas F. ORCID: https://orcid.org/0000-0002-0946-6304, Willock, David J. ORCID: https://orcid.org/0000-0002-8893-1090, Howard, Mark, Knight, David W., Taylor, Stuart H. ORCID: https://orcid.org/0000-0002-1933-4874 and Hutchings, Graham J. ORCID: https://orcid.org/0000-0001-8885-1560 2019. New insights for the valorisation of glycerol over MgO catalysts in the gas-phase. Catalysis Science and Technology 9 , pp. 1464-1475. 10.1039/C8CY02214C

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Abstract

Aqueous glycerol solutions of up to 50 wt% were reacted over magnesium oxide catalysts at temperatures greater than 300 °C, the reactivity of which was compared to catalyst-free reactions. Under catalyst-free conditions, modest levels of dehydration to hydroxyacetone were observed at temperatures >400 °C in a steel reactor tube and >320 °C over silicon carbide. For reactions over MgO, the product distribution becomes more diverse, resulting in the formation of methanol, acetaldehyde, ethylene glycol, 1,2-propanediol and acetic acid. The methanol space–time–yield over MgO catalyst samples (0.5 g) was found to be highest at 400 °C (205 g h−1 kgcat−1) with a 50 wt% solution of glycerol, or with a glycerol concentration of 10 wt%; 255 g h−1 kgcat−1 over 0.1 g of catalyst. Despite the high glycerol conversion achieved, the MgO catalyst was found to be stable over 48 h, following a modest decrease in glycerol conversion during the initial 2 h of reaction. Post-reaction characterisation revealed that the level of coking at high glycerol conversions (>90%) was ≥120 mg gcat−1. The carbon mass balance determined by GC analysis for a typical reaction was 75% and so the carbon lost from catalyst coking only represents a modest quantity of the missing carbon; typically <10%. MgO was also found to promote the formation of high molecular weight products via condensation reactions, which were responsible for the remainder of the missing carbon; ca. 15%. Therefore, the total organic content of the post-reaction mixture and coke was calculated to be 94% of the starting solution. We conclude that the catalyst surface directs the formation of methanol, however, the results indicate that the reaction conditions are crucial to obtain optimum yields.

Item Type: Article
Date Type: Publication
Status: Published
Schools: Chemistry
Cardiff Catalysis Institute (CCI)
Publisher: Royal Society of Chemistry
ISSN: 2044-4753
Funders: EPSRC
Date of First Compliant Deposit: 15 March 2019
Date of Acceptance: 7 February 2019
Last Modified: 11 Oct 2023 19:14
URI: https://orca.cardiff.ac.uk/id/eprint/120750

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