M.Chem. 2000-2004 at the University of Durham. Fourth year project under the supervision of Professor Judith A.K. Howard. PGCE (secondary) Science 2004-2005 at the Universtiy of Durham. Secondary Science teacher 2005-2008. Currently a postgraduate research student working under the supervision of Dr H. C. Greenwell at the University of Durham on the project "Mineral Catalysed Decarboxylation of Lipids for Biofuels".
Globally there is currently a huge drive towards biofuel production, for both petrol- and diesel-based fuel types. This includes ethanol production from the fermentation of carbohydrates (petrol-type fuel) and the upgrading of lipids from plant sources (diesel-type fuel). Targets have been set both at national and international levels from regulatory authorities from an environmental perspective, regarding the levels of biofuels present in fuels that are used for transport use. Biofuels are said to be carbon-neutral since the carbon dioxide released upon their combustion is only temporarily removed from the atmosphere and stored in the biomass, unlike the more permanently entrapped carbon locked up in fossil crude oil sources. With the price of crude oil increasing to unparalled new highs, the option of biofuels is becoming ever more viable on a commercial scale.
Biodiesel is the major commercially produced fossil-diesel replacement fuel, which is usually synthesised via transesterification of triacylglycerides, naturally present in plant and algal oils. These consist of three fatty acid chains esterified to a glycerol molecule (Fig 1). The transesterification process may be carried out with a wide range of homogeneous and heterogeneous catalysts including sodium hydroxide,1 sulphuric acid,2 or layered double hydroxides.3 After chemical upgrading the resulting biodiesel is an oxygenated diesel-type fuel which can be blended with regular crude-oil derived diesel or used directly in vehicles which have been modified to use high levels of this type of fuel. There are issues associated with the viscosity of these fatty acid methyl ester fuels especially in colder climates where the biodiesel may solidify easily in fuel lines.
A promising area of research is in the production of the so-called "green diesel", being a direct replacement for diesel fuel, derived from biological sources. This process was observed by Bertram in 1936,4 studied during times of fuel supply shortage,5 and more recently has been produced via catalytic deoxygenation of fatty acids at temperatures of 250-380°C and pressures of 0.1-5MPa using stearic acid (octadecanoic acid) as the feedstock (Fig 2).6,7 The catalysts employed during the decarboxylation are usually group VIII metals such as Pd/Pt, supported on carbon and the reaction proceeds via removal of carbon dioxide. Reactions proceed to ~100% conversion to n-heptadecane (a reduction of one carbon in the chain), which is observed within hours on a semi-batch scale.
The choice of lipid source is also an area of key importance, with algae being the most promising option, whereby some species are over 80% oils by dry weight and double in mass multiple times a day.8 Algae can be grown in seawater in either open ponds or in purpose built photobioreactors. The feasibility of this option has been further backed up by the announcement of the collaboration of Royal Dutch Shell and HR Biopetroleum to build an algae biofuel production pilot plant in Hawaii.9
Last updated on the 11thJune 2008 by Chris Greenwell.