A Biobased Economy - Sustainability for the Food Sciences - page 342

thiophenes (Meng et al., 2010). Therefore, desulphurization and the removal of other impuri-
ties from the syngas are mandatory before the Fischer-Tropsch process.
With the right catalysts, syngas can be converted into ammonia, dimethyl ether, methanol,
oxochemicals (e.g., n-butanol and 2-ethyl hexanol), and acetyls (acetic acid and acetic anhy-
dride), or hydrogen separated from the stream and used in other applications (Spath and
Dayton, 2003).
Even when it is technically feasible to produce chemicals from syngas, the main impedi-
ment is the high capital investment for the syngas production. According to estimations, when
syngas comes from solids, such as biomass, the gasification step requires between 50 to 75
percent of the total capital investment. This is because in addition to a reactor to generate the
syngas, solid materials requires special handling systems and syngas purification steps
(Spath and Dayton, 2003).
BIOFUELS
Biofuels are fuels produced from plant or animal materials. They are renewable in essence
because their energy content ultimately comes from carbohydrates stored in plant materials
via sun driven photosynthesis. Even when animal sources (e.g., fats) are feedstocks to produce
biofuels, energy comes from the sun that was accumulated in the feed grown in the fields.
Unprocessed biomass directly burned in a boiler can be considered a biofuel; however, the
term is generally reserved for fluid fuels—solid charcoal can be technically considered a bio-
fuel as well—that have been produced using biomass as feedstock and transformed into a gas
or a liquid using some type of processing.
Today, special interest exists in the development of cost- and energy-effective ways of pro-
ducing liquid biofuels that could substitute petroleum-derived transportation fuels, which
would allow the use of the current infrastructure, including vehicles and distribution networks
without major changes in the system.
Currently, the most well-known transportation biofuels commercially available are ethanol
and biodiesel , which are burned in gasoline and diesel engines, respectively, without engine
modification. Interest also exists in other alternatives such as bio-butanol, biogas, and biohy-
drogen. The direct use of vegetable oil in vehicle diesel engines is practiced in limited cases
after adapting the engines to use dual fuels. The engine is started with regular diesel and after
it warms up, it is switched to vegetable oil. Vegetable oils and animal fats can be burned as
well in stationary systems, including engines and boilers.
Bioethanol
Currently, bioethanol is produced via fermentation from feedstocks containing readily availa-
ble fermentable sugars or starches that are converted into fermentable sugars by hydrolysis.
Different countries select their feedstocks based on crop availability in their region and price.
When feedstocks come from conventional crops that provide sugars or starches, it is often
referred as first generation biofuels to differentiate from second generation ones produced
from lignocellulosic materials.
Starches used for first-generation bioethanol are contained in grains (i.e., corn, wheat, bar-
ley, and rye) or root crops including potatoes and cassava. Starches cannot be directly used by
microorganisms so they need hydrolysis first. The traditional hydrolysis route is the use of
acids; however, acids need neutralization at the end of the reaction and produce secondary
unwanted compounds. Therefore the preferred saccharification method to convert starches