Biomedical Engineering Reference
In-Depth Information
Limitations of Cellulosic Ethanol
Although ethanol has many benefits as a fuel, i.e., it is readily blended into gasoline
the predominant worldwide transportation fuel, it can be used in most cars at low
blend levels (
15 % ethanol) without modification, and it has favorable production
costs. Compared to conventional gasoline, it does have some drawbacks that have
limited its growth as a transportation fuel. Ethanol has only 2/3 of the energy
content of gasoline and hence will deliver less mileage on a volumetric basis than
gasoline. Additionally ethanol has only limited compatibility with the existing
infrastructure, thus requiring new investments in pipeline or refining infrastructure
for large-scale deployment.
However, the biggest drawback of ethanol has proven to be limited markets. In
the USA, the world's biggest producer and user of ethanol, almost all ethanol is
utilized as E10 with E85 usage being almost negligible [
47
]. Currently, in the USA
almost 97 % of motor gasoline is E10; hence, the E10 market is essentially
saturated. This situation is commonly referred to as the “blend wall” and is the
primary reason potential developers of cellulosic ethanol cite as limiting the
deployment of cellulosic ethanol. This is interesting because the common percep-
tion is it lacks commercially viable cellulosic ethanol technology, which in reality
is not the case. The US Environmental Protection Agency (EPA) did approve the
use of E15 in model 2000 and newer cars [
48
] to address this issue, but the adoption
of E15 has been slow due to a number of logistical factors. Brazil has not faced the
blend wall issue due to a different fuel strategy that is unique to Brazil [
49
]. Two
fuels are offered in Brazil E25 and E100, and since 2003 most new vehicle sales are
rapidly trending towards “flex” vehicles, which can accommodate any amount of
ethanol. Transportation experts are mixed in their opinion if this strategy to avoid
the blend wall issue could be used outside of Brazil.
Although ethanol is a good blend component for gasoline, it is not a good blend
component for diesel and completely not suitable for jet fuel. Since diesel and jet
fuels are growth fuels and gasoline demand is leveling off or declining especially in
the EU and USA, biofuels that do not face the market issues of ethanol and are
suitable for the diesel and jet fuel markets are highly desirable.
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Advanced Biofuels
The nomenclature of “advanced biofuels” is somewhat used inconsistently in the
literature. As it is used here, it refers to hydrocarbon fuels or “drop-in” fuels that can
be directly utilized in the existing gasoline, diesel, and jet fuel pools. Producing
advanced biofuels from biomass has a number of advantages over ethanol. Since
they are essentially substantially similar to current gasoline, diesel, and jet fuels,
they would be completely compatible with the existing fuel distribution and vehicle
infrastructure. This compatibility could be extended all the way to processing inside
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