Partnerships, Future, and Emerging Technologies - Industrial Crops: Breeding for BioEnergy and Bioproducts - page 413

existing petroleum refineries, which will be explained in more detail in the follow-
ing sections.
Another significant advantage of advanced biofuels is that they do not face any
market or new fuel acceptance issues. The challenge to get a new fuel certified can
be very significant in a large part due to emission and air quality concerns. For
instance, in the USA, the US EPA requires a very rigorous testing program to verify
that a new fuel or even a blend limit change, i.e., E10 to E15, does not adversely
affect emissions. Additionally, vehicle manufacturers and engine manufacturers are
very leery of new fuels or blend limit changes because of possible impacts on
performance or reliability. For advanced biofuels, none of these issues or concerns
would come into play since the fuels would be simply gasoline, diesel, or jet, which
are currently certified and accepted by vehicle and engine manufacturers.
However, in the context of nothing is as simple as it first appears, fuel liability
issues would exist and need to be addressed. Most country's fuel liability provisions
are structured in a manner that the fuel supplier accepts all liability issues associated
with the use of the fuel. Therefore, thorough testing would most likely be required
for advanced biofuels before fuel suppliers would be willing to accept them as part
of the fuel supply and accept the liability associated with their sale.
The categorization of conversion routes into biochemical routes and thermo-
chemical routes roughly holds for advanced biofuels as it does for cellulosic ethanol
with the distinction that the biochemical route is more of a sugar intermediate route
because the upgrading to fuels can be by either a fermentation route or a catalytic
route.
Sugar Intermediate Routes
Figure 19.4 illustrates the overall process for advanced biofuel conversion via a
sugar intermediate. The first part of the process, converting the carbohydrate
portion of the biomass to a sugar intermediate, is essentially the same
pretreatment/enzymatic hydrolysis process that was explained in detail in the
biochemical cellulosic ethanol conversion section. From the sugar intermediate,
the upgrading to an advanced biofuel can take two dramatically different routes,
either a fermentative route to an isoprenoid [ 50 ] that can be upgraded to a diesel fuel
in a fairly straightforward manner or a catalytic route that involves a number of
catalytic and upgrading steps to produce an advanced biofuel [ 51 ].
Feedstock Considerations
The feedstock considerations are similar to biochemical cellulosic ethanol conver-
sion. In general feedstocks with high carbohydrate content and correspondingly
lower lignin concentration tend to have better performance. This tends to favor the