New insights for the valorisation of glycerol over MgO catalysts in the gas-phase. Issue 6 (4th March 2019)

• Record Type: Journal Article
• Authors: Smith, Louise R.; Smith, Paul J.; Mugford, Karl S.; Douthwaite, Mark; Dummer, Nicholas F.; Willock, David J.; Howard, Mark; Knight, David W.; Taylor, Stuart H.; Hutchings, Graham J.
• Is Part Of: Catalysis science & technology. Volume 9:Issue 6(2019)
• Page Start: 1464
• Page End: 1475
• Publication Date: 2019-03-04
• Subjects: Catalysis -- Periodicals; 541.395
• DOI: 10.1039/c8cy02214c
• Languages: English
• ISSNs: 2044-4753

Abstract

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. 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.