Biofuels from woody plants
From the October 2007 edition of Agriculture Today.
Renewed interest in commercial scale production of alternative fuels for transport chiefly emanates from issues relating to the use, impacts and rising demand for traditional fossil fuels.
In selecting alternatives, due consideration must be given to those fuels which serve to combat climate change and produce cleaner air.
Amongst the options is ethanol made from renewable feedstock.
Large-scale ethanol production is currently based on sugarcane cultivation in Brazil and corn in the USA.
However, ethanol produced from corn does not significantly diminish greenhouse gas emissions nor create much energy from the production after accounting for the growing and processing inputs. The International Energy Agency estimates that production of ethanol from corn reduces greenhouse gas emissions by 15 - 25%, relative to fossil fuels.
And as ethanol use increases, demand for cane and corn feedstocks will intensify and clash with the need to produce food and fibre.
In light of these shortcomings, ethanol production from more sustainable feedstocks such as agricultural and forestry waste and residues - together with dedicated energy crops - is rapidly becoming the preferred option.
Moreover, projected greenhouse gas savings from using these types of novel feedstocks is estimated to produce ethanol which is 90% more effective than petrol in reducing greenhouse gases.
The feedstocks of interest are woody plants which contain lignocellulose - lignin and cellulose.
Although there are many approaches for producing ethanol from lignocellulose, most are fundamental variations of either biomass hydrolysis or gasification.
The latter process converts lignocellulosic feedstock into a synthetic gas which is in turn converted into ethanol, via microbial fermentation or chemical catalytic reactions.
Depending on the raw material feedstock, there are four to five operations in ethanol bioconversion using the biomass hydrolysis process.
The first and most expensive step involves pre-treating the lignocellulosic material. Constituent sugars are then released and subsequently separated from the residual lignin.
The lignin portion is either used to fuel the process or is chemically altered to generate value-added products.
The sugar solution is subsequently fermented by yeast or bacteria, and the resulting ethanol stream is concentrated via distillation and/or molecular filtering. This ethanol can then be used for a variety of purposes including as a mixture with petrol in vehicles.
Although various governments and corporations throughout the US and Europe have heavily invested in emerging lignocellulosic technologies, there has been scant activity on the Australian front.
To date, Ethanol Technologies Limited (Ethtec) is the only known Australian entity to undertake pilot scale feasibility studies into ethanol production from lignocellulosic materials such as sugar cane bagasse, timber, and agricultural waste.
The first phase of the project involves construction of a pilot scale concentrated acid pre-treatment facility at the Harwood sugar mill in northern NSW.
For information on Ethtec’s project, see www.ethtec.com.au.
Contact Tony Vancov, Wollongbar, (02) 6626 1359, tony.vancov@dpi.nsw.gov.au
