Environmental Engineering Reference
In-Depth Information
Ozone generator
Mass flow controller
Sample holder
Industrial grade
oxygen
Ozone destructor
Figure 3.5
Ozonolysis reactor set-up. Reproduced from [38], with permission from Elsevier.
biomass in the bioreactor is then exposed to ozone gas stream which is gener-
ated by an ozone generator, and allows the reaction to proceed. The retention
time of the treatment varies with different types of biomass. The ozone concen-
tration used in most cases is around 2-6% (w/w) [38]. The unreacted ozone
from the reactor outlet is finally removed by passing through potassium iodide
solution.
The major advantage of using ozonolysis as pretreatment process is the low
energy requirement, since ozonolysis can take place at ambient temperature and
normal pressure [24]. Moreover, inhibitory compounds to the subsequent hydrol-
ysis or fermentation are not produced [39, 40]. However, this process is relatively
expensive as a significant amount of ozone gas is required, limiting its application
on an industrial scale [4].
3.2.4
Microwave-Assisted Hydrothermal Biomass Treatment
The hydrothermal treatment of biomass with the addition of either acid or alkaline
catalyst provides an effective pretreatment pathway for the conversion of ligno-
cellulosic biomass to sugars. However, their presence within the aqueous phase
subsequent to the process mean that further treatments are required to render the
products pH neutral.
When these methods are applied to cellulose, it is often found that the yield of
hexose sugars is minimal with little selectivity towards fermentable sugars, for
instance glucose. This is attributed to the limited accessibility of cellulose chains
resulting from their high degree of crystallinity. However, it has been found that
subjecting cellulose to microwave radiation as a source of heating results in the
opening of the crystalline structure (from crystalline to amorphous structure) at
