Ethanol (ethyl alcohol), also known as grain alcohol, is the same 'alcohol' found in all alcoholic drinks. Bioethanol is simply ethanol that has been produced using biological materials (biomass) for feedstocks. Since it relies on sunlight and photosynthesis to contribute to the growth of that biomass (plants, grasses, corn, wheat, etc), bioethanol is a renewable fuel. Bioethanol is made when biomass is converted to sugars, which are then fermented into ethanol. The process of hydrolysis seperates most of the water from ethanol, leaving an end product that is generally about 95% ethanol and 5% water. Bioethanol can be blended with conventional gasoline at any ratio, but the most common blend is E10 (10% ethanol, 90% gasoline, sometimes called Gasohol), which can be used in existing gasoline engines without modifications and without affecting vehicle warranty. Higher blends, such as E85, require a Flexible fuel vehicle (FFV).
The energy economy needs alternatives to fossil fuels, as demand rockets skyward and concern mounts over the effects of fossil fuels on climate. One possibility is bioethanol, a renewable, carbon-neutral fuel that can be used as a direct replacement for liquid petroleum gas (LPG) in internal combustion engines. Samir Bhatt gave a talk at the New Cavendish Laboratory on 26 July to describe the production of bioethanol and its possible future uses. Bhatt’s work in this area began with a project he conducted in 2004 at the University of Bath to design a bioethanol facility
from scratch, taking into account everything from material requirements, through detailed process design, to economic viability and environmental impacts. He now works as a bioinformatician at the Sanger Institute. The production of bioethanol can be broken down into five stages: feedstock growth, milling, hydrolysis, fermentation and purification. The raw material for bioethanol production is carbohydrate from plants. Any carbohydrate source can in principle be used as a feedstock. Sugar beet is the most common crop grown in the UK for this purpose. In Brazil, the world’s biggest bioethanol producer, sugar cane is the crop of choice, while the USA and Canada rely heavily on maize.
These feedstocks are processed and ground into homogeneous feed (milling) toincrease the accessible surface area of carbohydrates for hydrolysis. The hydrolysis stage breaks down the chains of complex carbohydrates such as starch into
simple sugars such as glucose. These sugars are then digested in large steel containers called fermenters by microorganisms such as yeast, which produces ethanol as a by-product of its normal metabolism. Ethanol is toxic to yeast at concentrations above about 15%, so it must be continually siphoned from the fermenter in order to maintain production. The ethanol is normally siphoned off at about 6% and must then be purified to greater than 99% to be fuel-grade for internal combustion engines. Because the profit margin for bioethanol production is small, every aspect must be optimised in order to achieve a financial return. Teams of engineers work to refine every detail of production, from recycling undigested starch to choosing the thickness of fermenter rotor blades.
With such precise optimisation, bioethanol production can and has been a success around the world. Brazil has lead the way since the creation of its 'ProAlcool' program in 1975. By 1988 a third of all Brazil’s cars were fuelled solely by
bioethanol. Ethanol/LPG blends are now widely available in the USA, where the bioethanol market is growing by around 15% per year. The USA is close to overtaking Brazil as the largest bioethanol producer.
In the UK, Tesco now sells LPG containing 5% bioethanol as standard at hundreds of petrol stations across the country, while in March Morrisons opened the nation’s first 'E85' pump, delivering a mixture of 85% bioethanol and 15% petrol. Advances in technology have improved production efficiency dramatically over the past three decades. Modern plants now take advantage of enzyme hydrolysis that improves glucose yield from complex carbohydrates, newly developed strains of yeast and bacteria that can take advantage of otherwise indigestible 5-carbon sugars such as xylose, and new
membrane technologies are making ethanol purification to fuel grade 99% quicker and cheaper. Improved efficiency,combined with expected increases in demand as fossil fuel sources become unreliable leading to higher prices, may make bioethanol an even more lucrative business in the coming years.
Indeed, the market is already growing: world production of bioethanol jumped from the energy equivalent of just over 10 million tonnes of crude oil (tonnes of oil equivalent' or 'toe') in 2002 to over 16 million toe in 2005. This is, however, still
dwarfed by total global crude oil production, which was around 4.3 billion toe for 2005. According to Futura Petroleum Ltd, bioethanol has the potential to provide 1.3 billion toe, equivalent to 30% of world crude oil consumption in 2005. Other biofuels also show great promise. Biobutanol can be produced in much the same way as bioethanol, has an energy density closer to petroleum gas and can be used in standard engines at higher concentrations than bioethanol.
No one energy source will meet the world’s needs, especially given that demand is set to grow still further. Although it is unclear how the energy market will play out over the next half-century, it seems that biofuels could play an increasingly
prominent part. David Mackay's homepage, including 'You Figure it Out', a new book on the sustainable energy crisis.
Contributed by Peter Davenport From Source http://www.bluesci.org