The critical limitation of biodiesel from the viewpoint of sustainable fuel production is that it does not offer a large scalable solution to replace gasoline. Biodiesel that is produced from traditional oilseed feedstocks such as soy and palm does not offer large enough returns in terms of fuel per land area of feedstock to be able to meet fuel demand without displacing large land areas currently devoted to food production and without continued deforestation, especially in vulnerable eco-regions such as the Amazon. The negative environmental effects of deforestation and loss of biodiversity, along with considering the polluting effects of expanding agricultural use of fertilizers, pesticides, and herbicides for biodiesel feedstock production, would easily out-weigh the environmental benefits of biodiesel in comparison to petrodiesel if countries sought to replace gasoline and diesel consumption with biodiesel consumption on a large scale (Fargione et al. 2008, Gibbs et al. 2008). Additionally, the food versus fuel debate draws attention to the fact that increasing land use for biofuel production will most likely decrease the amount of fertile land available for food production, resulting in increases in food prices, for which the social costs may out-weigh the positive social externalities accrued from biodiesel use. Other limitations for biodiesel include relatively high freezing temperature (for which reason, blends with petrodiesel are often necessary in colder climates).
Biodiesel’s promise lies mostly in its potential to replace diesel to some degree for vehicles which already run on diesel and its role in a possible shift toward increasing use of diesel vehicles in the United States for fuel efficiency reasons. Given the current costs of gasoline, biodiesel production is likely to continue to increase in the coming years. The National Renewable Energy Laboratory has predicted that biodiesel “could someday supply 3 percent to 5% of the distillate fuel market” (2010). Continued innovation, especially in the area of decreasing the costs involved in converting recycled vegetable oil into fuel, such as through the development of new chemical catalysts, could offer significant social benefits in the form of decreasing fuel costs on a local basis and reducing carbon emissions and pollution. However, in the long run, research into algal biodiesel appears to be the most promising area in terms of developing more ecologically sustainable biofuel sources.
Fargione, Joseph; Hill, Jason; Tilman, David; Polasky, Stephen; and Peter Hawthorne. (2008) “Land clearing and the biofuel carbon debt.” Science 319,5867: 1235-1238.
Gibbs, Holly K. et al. (2008) “Carbon payback times for crop-based biofuel expansion in the tropics: the effects of changing yield and technology.” Environmental Research Letters 3:3.