Fuel for thought

15 Feb 2012

Author: Jonathon Moore

Photography: Anthony Calvert


Agave fuel could deliver a cure for the world’s peak oil hangover.
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With concerns about peak oil and the need for increased energy security, not to mention the pressure to reduce greenhouse gas emissions from fossil fuels, finding a reliable, sustainable alternative fuel for cars continues to give the automotive industry a sore head. However, in the research labs of the University of Sydney and the sandy arid fields of rural North Queensland, an unusual suspect is bringing something exciting to the table.

In a novel approach, Dr Daniel Tan, a senior lecturer in the University of Sydney’s Faculty of Agriculture, Food and Natural Resources, in collaboration with the University of Oxford in the United Kingdom, has analysed the potential to produce bioethanol from the agave plant, a high sugar succulent widely grown in Mexico to make the alcoholic drink tequila.

Bioethanol, or simply ‘ethanol’, is an alcohol made by fermenting the sugar and starch components of plant materials on a commercial production scale. It can be a fuel source in its own right or, more commonly, is used as a petrol blend – a proven method for the reduction of greenhouse gas emissions.

Of course, ethanol itself is not an entirely new concept. While still only a small portion of the market, worldwide ethanol production grows each year and it’s estimated that it will have displaced more than five per cent of the world’s standard petrol by 2013.

Currently, the United States and Brazil lead the way accounting for 88 per cent of the world’s ethanol production. Through a 30 year old industry, Brazil has developed a fully sustainable biofuel industry, where all light passenger vehicles operate with petrol blended with no less than 20-25 per cent ethanol. In the United States, where more ethanol is used than anywhere else in the world, most vehicles use blends of at least 10 per cent ethanol, while a large share use blends of up to 15 per cent.

Australia has a small ethanol industry in comparison; however, it is currently producing the fuel at three facilities on the country’s east coast from sugarcane, wheat waste products and sorghum (a species of grass). It is blended with petrol and sold as ‘Unleaded E10’ at major fuel stations across the country.

While sugarcane and corn are established sources for the production of ethanol across the world, their contribution to the industry is increasingly the subject of criticism. Both these crops are a major source of food, they require a large amount of maintenance and water to grow well and they also tend to occupy higher quality agricultural land.

Dr Tan, whose main research interest is in heat tolerance in crop plants such as cotton, chickpea and wheat, turned his attention to agave after discovering its tolerance for extreme heat of up to 60˚C. “This makes it one of the most adaptable plants, capable of tolerating global warming and climate change,” Dr Tan says. Primarily Mexican, agaves also grow abundantly throughout southern and western United States and central and tropical South America. The heart of a fully matured plant is stripped of its leaves and then heated to remove the sap which is, in turn, fermented and distilled.

Dr Tan and his research collaborators analysed the production of ethanol from the agave plant in a hypothetical farm and production facility. As commercial production of ethanol from agave is not yet an established process, the study was based on knowledge of both facilities cultivating agave for production of tequila in Mexico and the already established Brazilian sugarcane industry.

Dr Tan says the agave plant has not yet been widely cultivated as a fuel source, but it promises some significant advantages over existing sources of ethanol such as sugarcane and corn. “The agave plant is probably one of the most promising crops we can grow to produce ethanol-based fuels,” Dr Tan says. “It can grow in arid areas without irrigation; it doesn’t compete with food crops or put demands on limited water supplies.”

In response to this desktop study, a test plantation of agave has now been sown at the Kalamia Estate in North Queensland. While the plantation is still growing, initial progress of the crop has been positive. The plants survived their first two wet seasons, including Cyclone Yasi, and have been developing at an acceptable rate. The next step will be to harvest the matured plants and undertake an experimental pro¬gram of processing them into ethanol.

In Australia, where water supplies are scarce but arid and sandy land is certainly not at a premium, the potential of agave as an alternative source for the production of ethanol is clear. Dr Tan and his research colleagues believe that, if successful, agave plantations like the trial farm in North Queensland could be set up in similar environments, such as countries in Africa, where issues of food, water and fuel security are even greater. The benefits this preliminary research may be able to bring to countries with large amounts of arid land but little food producing capacity may open the door to a brand new industry.

A key finding from the study was that ethanol produced from agave has a ‘positive energy balance’, meaning that the energy created is greater than the energy expended in producing the product. In fact, Dr Tan and his colleagues found this energy balance is five units to one.

“This compares favourably to the highly efficient sugarcane, and to the less efficient corn as a source of biofuel. It also compares favourably to sugarcane-derived ethanol for its ability to offset green¬house gas emissions, which we calculated at 7.5 tons of CO2e per hectare per year - taking into account the crop’s complete lifecycle, from planting and harvesting to production and processing.” Dr Tan said he believes an agave production facility would be self-fuelling, with the plant’s woody by-products (bagasse and residue) matching the production facility’s energy requirements.

 “One day in the future, perhaps large-scale farms of the agave plant could be established in Australia’s arid inland.” Dr Tan says. “It would certainly provide a novel and greenhouse-friendly solution to Australia’s transport fuel problems.”

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