Page 89 - Biofuels Refining and Performance

72 Chapter Three

3.3 Overall Process of Bioethanol
Production
The process of ethanol production depends on the raw materials used.
Ageneral simplified representation of these processes is shown in Fig. 3.3,
and a brief description of different units of the process is presented in
the rest of this chapter. It should be noted that if sugar substances,
such as molasses and sugarcane juice, are used as raw materials, then
milling, pretreatment, hydrolysis, and detoxification are not necessary.
Milling, liquefaction, and saccharification processes are usually nec-
essary for production of fermentable sugar from starchy materials, while
milling, pretreatment, and hydrolysis are typically used for ethanol pro-
duction from lignocellulosic materials. Furthermore, a detoxification
unit is not always considered, unless a toxic substrate is fed to the biore-
actors.

Raw materials

Milling &
size reduction
Large polymer structures
Pretreatment or
liquefaction
Small polymers
Hydrolysis or Solid residuals
saccharification
Sugar solution
Detoxification

Fermentation Yeast
Fermented solution
Distillation Ethanol (~90–95%)

Soild separation,
evaporation, drying Dehydration

Dried Wastewater Ethanol (>99%)
by-products
Figure 3.3 A general process scheme for ethanol production
from different raw materials.