Environmental Engineering Reference
In-Depth Information
Fig. 1 The production of biogas from biomass: hydrolysis of biomass results in the formation of
sugars, fatty acids and amino acids which are further converted to methane, carbon dioxide and
water
1.8 Second Generation Bioethanol Production
There have been a wide number of reports on second generation bioethanol produc-
tion as it utilises lignocellulosic rest streams (generated from primary agricultural
production) such as straws from grain production, as a potentially abundant, inex-
pensive source of carbohydrates. A key technology in this approach is the use of
bio-refinery where a particular crop may be separated into various fractions for food
and other applications such as animal feed and raw materials for biofuels and mate-
rials. However there are some other technical challenges and in general this focuses
on:
The process(es) of obtaining the fermentable sugars from the cellulose (and
hemi-cellulose).
The conversion of other fermentable sugars e.g. xylose (together with glucose) to
ethanol.
A schematic view of the general process is given in Fig. 2. Based on this general
route there are a number of well documented processes.
The BC International process uses an acidic hemicellulose hydrolysis which
allows the resultant xylose containing liquid to be separated from the solid cellu-
lose and lignin fraction. The cellulose is then hydrolysed to glucose (under acidic
conditions) and two parallel fermentations of xylose (with a modified E. coli ) and
glucose to bioethanol takes place.
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