198 Introduction to Renewable Biomaterials
Technology? 6.5 What Are the Key Considerations for Making a Successful Pretreatment
Pretreatment Technology?
Pretreatment is a key procedure to produce cellulosic ethanol and plays an important
role in decreasing the cost and increasing the total yield during cellulosic ethanol pro-
duction. Pretreatment is the most expensive step of this process, after cost of original
materials (20% of the total cost); therefore, so many researches has been done on biomass
pretreatment (Merino and Cherry, 2007; Mosieret al., 2005, Yang and Wyman, 2008).
Pretreatmentaffectstheamountofthenecessaryenzymetohydrolyzethesubstrates,
and it is also effective in influencing the factors on substrate and its digestibility by
enzyme (Chandraet al., 2007).
The profile of pretreatment can decrease the cost of cellulosic ethanol production.
Hydrolysis of biomass without pretreatment has a total yield of sugar, lower than 20%,
but after pretreatment, the theoretical yield of sugar production increased to 90%
(Alizadehet al., 2005).
Hence, optimal pretreatment should decrease the amount of lignin and crystalline
structure of cellulose and increase the accessible surface for enzymatic hydrolysis. The
methods for increasing pretreatment efficiency are too complicated. Therefore, the
method of pretreatment should be selected based on the following factors:
- Reduction of chemical consumption
Since most of the chemicals are toxic for the environment and microorganisms,
pretreatments should consume lower chemicals.
The temperature of pretreatment should be reduced. Hemicellulose and lignin are
degraded at higher temperatures (about 200∘C) and produce undesirable products such
as furfural, HMF, and phenolic compounds that reduce bioethanol production yield and
efficiency.
The pretreatment should not generate surplus materials that are dangerous for the
environment.
By-products such as lignin and hemicellulose should be recovered by economical
processes.
- Proportional cost of the reactor
The cost of the reactor must be reduced, as increased reactor costs increase the total
costs of cellulosic ethanol production.
There are many methods for biomass pretreatment, which have typical benefits and
defects. Due to difference in structure of plant cell wall, some ways of pretreatment are
effectiveonwood,whereassomeothersareeffectiveongrassyplants.Therefore,one
way cannot be effective for the all kinds of lignocellulosic materials.
