Environmental Engineering Reference
In-Depth Information
7.6.3
Butanol
Biobutanol has many similarities to bio-ethanol and also some comparative
advantages. It can be blended with gasoline in relatively large quantities without
damaging unmodified engines, has a roughly 30% higher energy content, is better
able to tolerate water contamination, and can be used together with ethanol and
blended with gasoline. Its low vapour pressure reduces the vapour pressure of the
ethanol/gasoline blend and makes it easier to blend ethanol with gasoline. It can
also be used in existing vehicles without any modification to their engines, does
not require a new distribution system, and can be delivered using the existing fuel
supply infrastructure. It can be produced by the fermentation of biomass from
the same feedstocks as bio-ethanol (e.g. sugarcane, sugar beet, corn, wheat) and
is currently attracting significant commercial interest. A number of companies
across the word are developing processes to turn biomass into biobutanol at a
pilot scale.
7.7 Conclusions
Biomass is a renewable carbon-neutral energy source that reduces CO
2
concentra-
tion in the atmosphere as well as the use of fossil fuels. The collected biomasses
are often bulky and wet and impractical in terms of transportation and storage
requirements. Physical upgrading (pretreatment) such as drying and also densifi-
cation to bales, briquettes, and pellets are therefore essential in many situations.
There has recently been more focus on fractionation of different parts of certain
types of biomass, since they contain varying levels of water and have different
chemical content. For example, heartwood and sapwood have different amounts
of fatty/resin acids; fractionation of heartwood and sapwood before biodiesel pro-
duction may therefore improve the yield and thereby the cost-effectiveness of the
process.
Microorganisms are vital in converting biomass to bioenergy. During biogas
production there is a variety of bacteria involved ranging from aerobic to anaero-
bic. For ethanol production there are several kinds of biomass (e.g. sugarcane,
cereal grain, and lignocellulose) with various accessibility to sugars; different
processes must be applied for separation/isolation of the sugars. Most sugars can
be fermented to either ethanol or butanol, while hydrogen can be produced by
both dark fermentation and photoautotrophy.
To conclude, there are no simple concepts for replacing fossil fuels as energy
sources with biomass due to several factors such as resources, demands, storage,
transportation, and other economic aspects. Fortunately, different processes are
already available for conversion of various biomasses to gaseous, liquid, and solid
energy carrier. There are also a variety of ways to utilize the renewable biomass,
not only as an energy source but also for bulk and fine chemicals production.
