Environmental Engineering Reference
In-Depth Information
b.
Bioethanol production thermochemically without microorganisms
Biomass is mainly thermochemically converted into gas and then the syngas is
passed through a unit comprising of catalysts, which allow the gas to be con-
verted into bioethanol. Bioethanol yields up to 50 % have been achieved using
syngas—bioethanol way. The quest for an economical thermochemical process
has been problematic (Dhavala et al.
2006
). Thermochemical is encouraging
than biological selection for the transformation of lignin of cellulosic biomass,
which can have an unfavorable consequence on enzymatic hydrolysis but also
helps in processing energy and formation of possible byproducts with signifi-
cant profits (Jansson et al.
2009
).
iii.
Lignocelluloses to bioethanol:
There are numerous choices for bioethanol production using this feed stock
irrespective of which one is selected. The following points need evaluation in
contrast with various well-known feed stocks for bioethanol making (Luque
et al.
2010
): effective de-polymerization of cellulose and hemicellulose; effec-
tive fermentation of a mixed-sugar hydrolysate; innovative method used in
order to lower procedure energy claim, less lignin content of feedstock which
reduces the price of bioethanol.
The benefits of using lignocelluloses are the chances to create a bio plant, gen-
erating byproducts along with the fuel, bioethanol. For example, sugars when
exposed to bacterial fermentation in the absence or presence of oxygen produce
a variation of products like lactic acid, which may be managed into plastics and
other products (Dhavala et al.
2006
). The treatment of lignocelluloses to bio-
ethanol comprises of four leading units: pretreatment, hydrolysis, fermentation
and separation/distillation of product (Luque et al.
2010
).
a.
Pre-treatment:
Pretreatment and size reduction is the first step in lignocellulose to ethanol bio-
conversion. The purpose of pretreatment is to change and eliminate mechanical
and compositional obstructions to hydrolysis so that rate of enzyme hydrolysis
increases leading to more fermentable sugar from cellulose and hemicellulose.
A popular pretreatment should fulfill the requirements like; increase sugar
formation, allow least degradation of carbohydrate, evade the production of
hydrolysis and fermentation inhibitory byproducts and should be cost effective
(Luque et al.
2010
).
b.
Hydrolysis:
When pre-treatment is complete, the cellulose undergoes hydrolysis. This
includes acid hydrolysis and enzymatic hydrolysis. Acid hydrolysis can be of
two types, dilute and concentrated. The dilute acid hydrolysis is for transform-
ing cellulose biomass to bioethanol. The hemicellulosic part is depolymerized at
lower temperature than cellulose. Usually dilute acid procedures are restricted
to 50 % regaining of sugar. The current task is to raise sugar recovery to as high
as 70 % in a favorable industrial use (Luque et al.
2010
). Enzymes are naturally
occuring in nature used for several chemical reactions and both bacteria and
