The major technical and commercial limitations of existing biofuels has catalyzed the development of advanced biofuels such as cellulosic ethanol, biobutanol and mixed alcohols. Biobutanol is generating good deal of interest as a potential green alternative to petroleum fuels. It is increasingly being considered as a superior automobile fuel in comparison to bioethanol as its energy content is higher.
The problem of demixing that is encountered with ethanol-petrol blends is considerably less serious with biobutanol-petrol blends. Besides, it reduces the harmful emissions substantially. It is less corrosive and can be blended in any concentration with petrol (gasoline). Several research studies suggest that butanol can be blended into either petrol or diesel to as much as 45 percent without engine modifications or severe performance degradation.
Production of Biobutanol
Biobutanol is produced by microbial fermentation, similar to bioethanol, and can be made from the same range of sugar, starch or cellulosic feedstocks. The most commonly used microorganisms are strains of Clostridium acetobutylicum and Clostridium beijerinckii. In addition to butanol, these organisms also produce acetone and ethanol, so the process is often referred to as the “ABE fermentation”.
The main concern with Clostridium acetobutylicum is that it easily gets poisoned at concentrations above 2% of biobutanol in the fermenting mixture. This hinders the production of bio-butanol in economically viable quantities. In recent years, there has been renewed interest in biobutanol due to increasing petroleum prices and search for clean energy resources.
Researchers have made significant advances in designing new microorganisms capable of surviving in high butanol concentrations. The new genetically modified micro-organisms have the capacity to degrade even the cellulosic feedstocks.
Biobutanol production is currently more expensive than bioethanol which has hampered its commercialization. However, biobutanol has several advantages over ethanol and is currently the focus of extensive research and development.
There is now increasing interest in use of biobutanol as a transport fuel (drop-in biofuel). As a fuel, it can be transported in existing infrastructure and does not require flex-fuel vehicle pipes and hoses. Fleet testing of biobutanol has begun in the United States and the European Union.
A number of companies worldwide are now investigating novel alternatives to traditional ABE fermentation, which would enable biobutanol to be produced on an industrial scale. In May 2012, Colorado-based synthetic biology firm Gevo announced the startup of the first commercial biobutanol plant having 18 MGPY capacity, to be developed by conversion of the former Agri-Energy corn ethanol plant in Luverne. The company aims to produce 1m gallons of isobutanol per month by the end of this year.
A different four-carbon alcohol, n-butanol, is the target for the UK’s Green Biologics which uses an engineered strain of the Clostridia microbe that can chew up cellulosic and other waste feedstocks that do not compete with food-supply needs. It is also looking to buy up and retrofit old ethanol plants in the United States, but right now has licensed its technology to biobutanol producers in China, such as Laihe Songyuan Chemical. China is also making deep inroads in this sector and its largest biobutanol plant is now producing around 10 million gallons every year.
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