Utilisation of Solid Oxide Fuel Cells for Conversion of Biodiesel Waste Streams
Authors: Drewery Matthew , Kennedy Eric , Dlugogorski Bogdan , Stockenhuber Michael 
Published: February 2020

The use of petroleum as a source of energy has recently come under scrutiny due to the adverse environmental effects of its use and issues of sustainability. Petroleum reserves are depleting and as a result more sustainable options for supply of transportation fuels are currently being investigated. One of these is the use of biodiesel as a replacement, which would potentially reduce associated greenhouse emissions, deforestation and pollution. A by-product of this reaction is glycerol (1,2,3-propanetriol), which makes up approximately 10 wt% of the final product (Willke 2008, Zhou 2008). Production of biodiesel has grown exponentially, particularly in the European Union, where production exceeded 5 million metric tonnes in 2006, with an average annual increase of approximately 28% since 2001, making industrial synthesis of glycerol obsolete and causing the market price of glycerol to fall dramatically (Pagliaro 2007, Valliyappan 2008). With this surplus of glycerol, extensive research into the conversion of glycerol into value added products is being conducted.

Glycerol can be used to produce a large variety of chemicals and as such there is significant interest in developing uses for these chemicals. To date, fuel cell research has focussed largely on operation with hydrogen, carbon monoxide and methane due to the ease of use and lower likelihood of coking, however development of composite anodes which inhibit carbon deposition have led to the use of larger hydrocarbons (Park 2000, Lu 2004, McIntosh 2004). The difficulty in suppling hydrogen and carbon monoxide for electricity generation presents a significant hurdle, which promotes the use of hydrocarbons, either through external reforming to produce synthesis gas or through internal reforming or direct oxidation in the solid oxide fuel cell anode chamber (Eguchi 2002, Vasileiadis 2004, Madsen 2005). With this in mind, glycerol can be used as a fuel source in conjunction with solid oxide fuel cells either directly or through reaction derivatives.

When glycerol is used as a fuel in solid oxide fuel cells it is capable of producing high density energy, with mainly water and CO2 as oxidation products. While glycerol can be used as a potential fuel, the ease of production of acrolein and allyl alcohol, through the reforming of glycerol, gives the possibility for additional fuel sources for SOFC’s. With these additional, potentially abundant, fuel sources the variation in functional groups, being hydroxyl and alkene for allyl alcohol and carbonyl and alkene for acrolein, would provide great insight into surface reactions on SOFC anodes.

This work focuses on the operation of a commercially available nickel-based solid oxide fuel cell utilising waste hydrocarbons as potential fuels. The cell is operated on propane, acrolein, allyl alcohol and glycerol to examine the viability of these fuels and further to investigate the effects of varying functional groups on cell operation and surface reactions. Further insight into surface chemical reactions is gained via in situ FTIR investigations, which identify adsorption processes of the different fuels on the anode surface and assist in predicting potential reaction mechanisms.