Fuelling the dilemma
What are the alternatives to sugar and grain-based biofuel crops?
The production and use of biofuels have entered a new era of global growth, experiencing acceleration in both the scale of the industry and the number of countries involved.
Surging investment in biofuel production is being driven by a variety of factors, including the development of more efficient conversion technologies, strong new government policies, and, primarily, the rising price of oil. Underlying the commitment of an increasing number of governments to biofuel development is the desire to find new markets for farmers and their products and to reduce emissions of greenhouse gases.
The two primary biofuels in use today are ethanol and biodiesel, both of which can be used in existing vehicles. Ethanol is currently blended with petrol, and biodiesel is blended with petroleum-based diesel for use in conventional diesel-fuelled vehicles. Ethanol accounts for about 90 per cent of total biofuel production, with biodiesel making up the rest. Global fuel ethanol production more than doubled between 2000 and 2005, while production of biodiesel, starting from a much smaller base, expanded nearly fourfold. By contrast, world oil production increased by only 7 per cent during the same period.
Potential for growth
The recent pace of advancement in technology, policy, and investment suggests that the growth of biofuel could continue for decades and that these fuels have the potential to displace a significant share of the oil now consumed in many countries.
A study found that advanced biofuel technologies could allow biofuels to substitute for 37 per cent of US petrol within the next 25 years, or 75 per cent if vehicle fuel efficiency doubles during the same period. The biofuel potential of EU countries is in the range of 20-25 per cent if strong sustainability criteria for land use and crop choice are assumed, and assuming that bioenergy use in non-transport sectors is growing in parallel.
The potential for biofuels is particularly large in tropical countries, where high crop yields and lower costs for land and labour, which dominate the cost of these fuels, provide an economic advantage that is hard for countries in temperate regions to match.
It has been estimated that worldwide sugar cane production could be expanded to a level that would enable this crop alone to displace about 10 per cent of petrol use worldwide. This would allow scores of low-income countries to become significant producers, and potentially exporters, of a valuable new commodity.
Overall, biofuels have a large potential to substitute for petroleum fuels. Together with a host of other strategies, including the development of far more efficient vehicles, they can help the world achieve a more diversified and sustainable transportation system. However, this promise will only be achieved if policies are enacted that steer biofuels in the right direction - policies that will need to be adjusted and refined as the state of knowledge advances and as the risks and opportunities of biofuel development become clearer.
In the coming years, the international development of biofuels and bio-based co-products has the potential to increase energy security for many nations; to create new economic opportunities for people in rural, agricultural areas; to protect and enhance the environment on local, regional, and global scales; and to provide new and improved products to consumers.
The various biomass feedstock used for producing biofuels can be grouped into two basic categories. The first is the currently available 'first-generation' feedstock, which comprises various grain and vegetable crops. These are harvested for their sugar, starch, or oil content and can be converted into liquid fuels using conventional technology. The yields from the feedstock vary, with sugar cane and palm oil currently producing the most litres of fuel per hectare.
By contrast, the 'next-generation' of biofuel feedstock comprises cellulose-rich organic material, harvested for its total biomass. These fibres can be converted into liquid biofuels by advanced technical processes, many of which are still under development.
Cellulosic biomass such as wood, tall grasses, and crop residues is much more abundant than food crops and can be harvested with less interference to the food economy and less strain on land, air, and water resources. Promising energy crops include fast-growing woody crops such as willow, hybrid poplar, and eucalyptus, as well as tall perennial grasses such as switchgrass and miscanthus. Another potential 'next-generation' feedstock is the organic portion of municipal solid waste.
The use of 'next-generation' cellulosic biomass feedstock has the potential to dramatically expand the resource base for producing biofuels. Over the next 10-15 years, lower-cost sources of cellulosic biomass, such as the organic fraction of municipal waste and residues from biomass processing, crops, and forestry, are expected to provide the initial influx of next-generation feedstock.
Dedicated cellulosic energy crops, such as switchgrass, poplar, and other fast-growing plants, are expected to begin supplying feedstock for biofuel production toward the end of this period, then expanding rapidly in the years beyond.
For biofuels to reach their full potential in meeting future transportation needs, it is critical to develop and deploy economically competitive technologies that can convert abundant cellulosic biomass resources into liquid.
Development efforts have demonstrated that it is possible to produce a variety of liquid fuels from cellulosic biomass for use in existing vehicles.
Two pathways, gasification (a thermochemical pathway) and hydrolysis (a biochemical pathway), can provide a variety of products in addition to producing liquid fuels.
The hydrolysis pathway relies on advanced enzymes that can catalyze cellulose and lignocellulose into sugars and ethanol. The gasification pathway uses high temperatures, controlled levels of oxygen, and chemical catalysts to convert biomass into liquid fuels.
The gasification pathway is also called the biomass-to-liquid (BTL) pathway, and generally requires a larger-sized facility and a larger capital investment. In general, improvements in this area appear to be occurring more slowly than the advances that are propelling the hydrolysis pathway. However, the BTL pathway can also process lignin, which comprises about one-third of plant solid matter, and can thus achieve higher liquid yields, displacing more petroleum. Accordingly, one detailed analysis of different conversion pathways concluded that a combination of the hydrolysis and BTL pathways was the most economical and energetically efficient approach.
It is expected that cellulosic biomass resources and next-generation biofuel conversion technologies will be able to fully compete with conventional petrol and diesel fuel without subsidies.
The lowest-cost biofuels are expected to continue to be ethanol produced from sugar cane and biodiesel produced from recycled cooking oil and waste grease. The costs for producing next-generation biofuels are expected to be generally competitive with first generation technologies. The ability of next-generation technologies to use abundant cellulosic feedstock that do not rely on food crops offers the promise of dramatically expanding the amount of biofuels that could be produced for transportation needs in the future.