The production volume of biodiesel looks set to increase with stricter legislation governing the blend ratios of fuels to include renewably sourced alternatives. Biodiesel is produced through the esterification of triglycerides typically sourced from plant-based oils. During the production process glycerol is formed and remains an attractive precursor to many useful chemicals. We have developed technology to convert the waste glycerol to methanol, a key component in the esterification of triglycerides. Thereby, potentially forming 100 % renewable fatty acid methyl esters which are used in biodiesel. We detail our latest efforts to optimize the system and provide characterization of the active metal oxide surfaces responsible for methanol production. Glycerol/water mixtures (50 wt.%) were passed over a catalyst bed containing 1.5 g of CeO2 and the product selectivities recorded. High selectivity to methanol was achieved at a reaction temperature of 380°C and corresponds to a production rate of 57 gMeOH kg-1 h-1. Increasing the reaction temperature increased the production of undesired by-products such as acetone and combustion products. We consider that the reaction proceeds via radical mechanism where C-C cleavage occurs concurrently with water splitting on the surface of the catalyst. For example we consider that products such as 2,3-butandione form through two acetyl radicals. We have shown that this reaction can proceed over MgO, CaO, SrO and CeO2 catalysts. Key to the production of methanol appears to be a surface able to support water splitting and the proposed radical mechanism. We relate our bid to characterize the surface of these materials with temperature programmed desorption and reduction studies, along with in situ IR techniques in an effort to suggest the key surface features responsible for this fascinating and novel reaction. Our initial CO2 TPD investigations into the surface basicity reveal that the CeO2 catalysts used in the study have a low CO2 adsorptive capacity (38.6 µL) compared to MgO (676.5 µL) and hence a low density of surface basic sites. Glycerol can be converted to methanol with high selectivity (ca. 61 mol.%) over a ceria catalyst when glycerol is used in high concentrations of up to 50 wt. %. Elucidation of the active surface component(s) able to direct the formation of methanol is discussed. Initial investigations into surface basicity suggest this is not a key element for the reactive surface.

Developing highly active catalysts for the production of methanol from waste glycerol

251st National Meeting (2016)

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