Environmental Engineering Reference
In-Depth Information
production of fumaric acid by fermentation. Fumaric acid could be used as raw material for the
polymer industry. This compound is produced from glucose, with a yield of 0.85 g per gram of
glucose, by
Rhizopus
species. Also, through fermentation it is possible to produce succinic acid,
which is a raw material involved in the making of surfactants, detergents, pharmaceuticals, and
foods. Succinic acid is produced by
Actinobacillus succinogenes
. When this microorganism is
grown on wheat flour, it produces 0.19 g of succinic acid per gram of substrate (Du et al. 2007).
Polyhydroxyalkanoic acids and polyhydroxyalkanaotes are biopolymers stored intracellularly as
a energy source. These biopolymers present attractive properties in the fields of biodegradation
and thermoplasticity. These biopolymers are produced by microorganisms such as
Pseudomonas
guezenni
(Simon-Colin et al. 2008) and
Pseudomonas aeruginosa
ATCC 9027 (Rojas-Rosas et
al. 2007) using glucose as carbon source. Finally xylitol, a sweetener, is produced from xylose
fermentation by
Candida tropicalis
.
This microorganism yields 0.75 g of xylitol per gram of
xylose (Kim et al. 2002). Xylitol possesses a higher sweetening power than sucrose and promotes
oral health and prevents cavities.
8.5 comParIson oF enerGy eFFIcIencIes and costs
oF BIomass ProcessInG technoloGIes
Technology energy efficiency and GHG emissions for biomass-derived energy products are of great
interest to industry, policy-makers, and government regulators. Energy efficiency here is defined as
the ratio of the energy content of the product electricity or biofuel to the energy content of biomass
feedstock to the conversion process. GHGs include CO
2
released from the combustion of fossil
carbon, nitrous oxide (N
2
O), methane, solvents, and refrigerants.
For biofuels especially, GHG emissions over the product life-cycle are of interest to confirm the
magnitude of reduction compared with conventional and next-generation fossil-derived fuels. For
example, the U.S. Congress set Renewable Fuels Standards (RFS) for each year up to 2022 in the
Energy Independence and Security Act (EISA) of 2007 (Congress 2007). The RFS calls for 36 billion
gallons of renewable fuels to be produced by 2022, or approximately 25% of current gasoline
consumption in the United States (Brodeur-Campbell et al. 2008). Advanced biofuels, according to
EISA, are renewable fuels other than corn ethanol, for which the life-cycle emissions of GHG remain
less than 50% of fossil gasoline baseline GHG emissions. Of the 36.0 billion gallons of renewable
fuels in 2022, it will be required that 21.0 billion gallons be advanced biofuels. Cellulosic ethanol is
the nearest to commercialization of the advanced biofuels technologies and is expected to provide a
significant fraction of the 21 billion gallons of advanced biofuel mandated by the RFS. Alternatives to
cellulosic ethanol exist, including biomass-to-liquid (BTL) diesel and importing ethanol from Brazil.
The most likely fulfillment scenario includes a mixture of all of these options (DOE/EIA 2008).
Table 8.11 shows technology energy efficiency of several biomass-to-energy carrier technologies
taken from a recent report (Shonnard et al. 2006; Shonnard and Koers 2009). For liquid and gaseous
energy products, efficiencies range from 43 to 81% and electricity generation efficiencies are from
27.7 to 38%. Biomass-derived fuels are less efficient than fossil fuels, such as petroleum gasoline
or diesel, the conversion efficiencies of which are approximately 80-90%. However, the life-cycle
fossil energy savings of biomass-derived fuels are still very large because process energy is largely
provided by the renewable biomass feedstock itself rather than from fossil resources (Kalnes et al.
2007; Koers et al. 2009). Thus, the lower technology energy efficiency of biofuels is compensated
by substantial savings of fossil energy over the life-cycle.
8.6 conclusIons
The chemical engineering processing routes for converting bioenergy crop plants into liquid
transportation fuels are quite diverse, as demonstrated by the broad range of processing technologies
