Environmental Engineering Reference
In-Depth Information
knowledge about how the enzymes of sugarcane or microorganisms attack the wall. It is crucial to
find ways to activate these enzymes in vivo so that energy access is gained more easily.
When sugarcane is harvested, sugars are extracted in water by pressing stem tissues. This extracts
approximately one third of the energy contained in the plant as soluble sugars. Leaves and other plant
parts that are left in the field after stem harvesting correspond to another one third of the sugarcane
biomass energy; eventually part or all this material may be collected and used to produce energy. The
remaining one third of energy is composed of the bagasse that is already available at the mill facilities
and is used to produce vapor, mechanic, and electrical power; in some sugarcane and ethanol plants in
Brazil surplus energy is sold and fed to the electric grid. Although part of the bagasse is currently used
for production of thermoelectricity, the current efficiency of this process is far beyond the potential of
producing energy from the hydrolysis of biomass either with acids or with enzymes (Cortez et al. 2008).
The process of production of free fermentable sugars from hemicelluloses and cellulose is the
basis of cellulosic ethanol production. This can be achieved by physical, chemical or biochemical
procedures. The great challenge is finding the combination of processes that could produce free
fermentable sugars in an economically viable way.
There is great potential for an increase in bioethanol production and process optimization, con-
sidering process improvements and the use of sugarcane bagasse as raw material in the hydrolysis
process. The evaluation of the energy consumption of the integrated production of ethanol from sug-
arcane and sugarcane bagasse remains one of the main obstacles for the technical and economical
feasibility of the hydrolysis process. Figure 21.4 shows a possible pathway for the integrated process,
which can be easily incorporated in existing units as soon as the sugarcane hydrolysis process is
sufficiently developed.
A process that may be used to produce bioethanol from lignocellulosic materials, the Organosolv
process with dilute acid hydrolysis, is being tested under semi-industrial scale in Brazil for the
production of 5000 L/day of ethanol (Rossell et al. 2005). A typical large scale plant, that is, one
that produces 1000 m³/day of anhydrous bioethanol crushing approximately 12,000 t sugarcane/
day, was considered for the conventional bioethanol production from sugarcane juice. Sugarcane
bagasse is one of the main byproducts of conventional bioethanol production from sugarcane juice.
Sugarcane
Cleaning
Sand, impurities
Cleaning
Sand, dirt, metals
Pre
hydrolysis
Pentose liquor
Extraction of
sugars
Sugarcane Bagasse
Delignification
Cellulose
Hydrolysis
Organosolv
solvent
Juice
treatment
Sand, fibers, impurities
Solvent
recovery
Lignin
Concentration
Clarified Juice
Juice
concentration
Juice
Sterilization
Glucose liquor
Gases
Absorption
Fermentation
CO
2
Distillation and
rectification
Second grade ethanol,
vinasse, phlegmasse, fusel oil
Centrifugation
Wine
Ye ast
Hydrous bioethanol
Ye ast
treatment
Dehydration
Anhydrous bioethanol
FIGure 21.4
Integrated bioethanol production from sugarcane and sugarcane bagasse.
