Environmental Engineering Reference
In-Depth Information
acceptor, can also strip the essential water from the active site of the enzyme, result-
ing in deactivation of the enzyme. Enzymes are also expensive and require treatment
such as immobilization, purification, pre-treatment, and modification [32].
New technologies are being developed to produce biodiesel that do not form
glycerol as a byproduct. The hydrocracking process uses hydrocracking, hydrotreat-
ing, and hydrogenation reactions to convert a wide range of feedstocks to biodiesel
with yields of 75-80% [15]. This process is currently being utilized in petroleum
refineries and uses a conventional commercial refinery hydrotreating catalyst.
However, the hydrocracking process requires hydrogen, which is primarily obtained
from natural gas. To reduce the costs of hydrogen, the process could be easily
integrated with a refinery.
The production of biodiesel has significantly increased over the past few years.
The National Biodiesel Board reports an increase in production from 250 million
gallons in 2006 to 450 million gallons in 2007, an increase of 55.6%. European
countries produced 5.7 million tons of biodiesel in 2007 (
1.5 billion gallons),
which is an increase of 16.8% from 2006 according to the European Biodiesel
Board. Germany is the World leader in biodiesel production and produced 2.9
million tons (
∼
790 million gallons) in 2007, which is over 50% of the European
biodiesel market.
∼
2.4 Summary
Biodiesel is a clean-burning fuel that is renewable and biodegradable. A recent
United Nations report urges governments to beware of the human and environ-
mental impacts of switching to energy derived from plants. There should a healthy
debate about turning food crops or animal feed into fuel and the consequences of
the switch to biofuels needs to be carefully thought out. The focus of biodiesel pro-
duction needs to be on sources like waste oil and grease, animal fats, and non-edible
sources. Current research has focused on these areas as well as on algae-based bio-
fuels. Many technical challenges remain and these include development of better
and cheaper catalysts, improvements in current technology for producing high qual-
ity biodiesel, use of solvents that are non-fossil based, conversion of the byproducts
such as glycerol to useful products such as methanol and ethanol, and development
of low cost photobioreactors.
3Biobutanol
3.1 Background
Over the past few years, butanol made from biomass, popularly known as biobu-
tanol, has gained a lot of attention as a biofuel. Butanol is an alcohol-based fuel that
contains four carbons and has chemical properties similar to that of gasoline, thus
making it an attractive substitute or additive. Biobutanol can be produced from the
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