CHEMISTRY OF BIOFUELS AND BIOFUEL ADDITIVES FROM BIOMASS - Biomass as a Sustainable Energy Source for the Future - page 556

However, information on the yields of both reactions is also required. For the
fermentation reactions, the yield is close to 100%, while for the conversion of
xylose to furfural, yields close to 90% have been reported. All together,
one could say that based on the atom yield, dehydration of furfural is the
better way to make fuels (21% atom yield for ethanol vs. 58% atom yield for
furfural).
The additional information we need is the heating value and fuel performance of
both fuels. As a first indication, the HHV values for ethanol (29.7 MJ kg −1 ) and

kg −1 ) can be com-
pared. Putting this information together, the atom yield for furfural production
is 2.8 times higher, while the heating value for furfural is 1.4 times lower than
for ethanol, pointing toward furfural as a more sustainable fuel source.

furfural (calculated according to Dulong ' s formula as 21 MJ

Both biotechnological and chemical processes are available to eliminate CO 2 and/or
H 2 Ofrombiomass constituents. Yeasts and other organisms have specific enzymes that
catalyze CO 2 elimination reactions. In chemical transformations however, the elimina-
tion of water from carbohydrates is easier than the elimination of CO 2 . The elimination
of water is commonly carried out using acidic catalysts at elevated temperatures.
Full elimination of all oxygen from sugar is only possible through the introduction
of extra hydrogen. This involves considerably more process steps and thus significant
additional costs. This will be discussed in more detail for selected examples (see
Section 18.4).
In general, three strategies can be distinguished for the conversion of sugar streams
into biofuels:

1. Direct elimination of CO 2 from sugars or cellulosic streams through fermenta-
tion: examples are the production of ethanol and butanol.
2. Release of a combination of CO 2 and H 2 O molecules from sugars or cellulosic
streams leading to platform chemicals, which can then be converted into
biofuels or biobased additives for fuels.
3. Aqueous reforming of glucose streams in the presence of catalysts and at high
temperatures; in this process, a combination of products is formed.

In the following, an overview of strategies 2 and 3 will be presented. For more informa-
tion on the direct fermentation of sugars to biofuels (strategy 1), we refer to Chapter 13.
In 2004, the department of energy in the United States published a top 12 list of
platform chemicals that can be derived from biomass. In 2010, Bozell and Petersen
published a renewed list of chemical opportunities from the biorefinery (see
Figure 18.4) (Bozell and Petersen, 2010).
Here, we highlight those platform chemicals that are most relevant for the
production of biofuels, namely, furanics and levulinic acid (LA).
Extremely relevant is the source of the sugar or cellulosic stream. Transport and
work-up of these biomass sources are surrounded with challenges, which require