Page 340 - Refining Biomass Residues for Sustainable Energy and Bioproducts

Pretreatment of agroindustry waste by ozonolysis for synthesis of biorefinery products 309

optimize the TRS and lignin degradation efficiencies. Improvements had to be
adjusted to keep the ozone gas from escaping from the reactor, thus enhancing the
interaction of ozone with the substrate.

14.2.2 Ozonolysis reaction parameters
14.2.2.1 Ozone consumption: effect of ozone flow rate and
reaction time
Ozone consumption is one of the most crucial parameters, and it needs to be opti-
mized to ensure an economically and environmentally sustainable delignification of
lignocellulosic biomass. The ozone consumption should be minimized to ensure the
complete process to be economical while having the ability to degrade high amount
of lignin and increase the TRS (Travaini et al., 2013; Garcı ´a-Cubero et al., 2009;
Shi et al., 2015a). At higher consumption of ozone the sugar compounds would pro-
mote the production of by-product of inhibitory compounds and side reactions with
low-molecular lignin compounds (Binder et al., 1980; Neely, 1984).
In a study by Wu et al. (2013b) the enzymatic hydrolysates showed that under
ozonolysis pretreatment, the TRS yield are increased due to the increasing lignin
removal by ozone consumption which eventually released more cellulose hence
more sugar produced. In addition, Schultz-Jensen et al. (2011) stated that the ozone
consumption was clearly related to lignin degradation and accessibility of sugar
monomers. All types of biomass show similar trends of ozone consumption with
reaction time (Schultz-Jensen et al., 2011; Binder et al., 1980; Garcı ´a-Cubero et al.,
2009; Neely, 1984). At first, the lignin reacts with the ozone, therefore consuming a
higher amount of ozone. This is when the highest delignification rate and sugar
release rates are obtained. When the reaction is stabilized, the ozone consumption
decreased, while the lignin and sugar release rate increased slowly.
The ozone consumption is directly dependent on other parameters, such as ozone
concentration, inlet gas flow, and time consumption. The ozonolysis of sugarcane
bagasse has been studied in a fixed-bed reactor by Travaini et al. (2013). The reactor
was supplied with 0.32 g of ozone more than 180 min of reaction time, 40% (w/w)
moisture content, and 3.07% (v/v) ozone concentration, and the results are 55%
delignification and TRS of 23%. Another experiment showed that 0.12 g of ozone
supplied over 45 min of reaction time with 80% (w/w) moisture and 3.44% (v/v)
yielded around 45% of enzymatic hydrolysis glucose release and 33% of delignifica-
tion. According to Li et al. (2015b), the highest ozone consumption was found at
moisture of 55% and a particle size of 300 mesh, and the relation between ozone con-
sumption and moisture and water activity with particle size can be seen in Fig. 14.3A
and B,respectively (Li et al., 2015b).
Travaini et al. (2016b,c) stated that the ozone concentration range that was stud-
ied and the complex interaction with other parameters make the effect of ozone
concentration not clear in the literature. An increase of ozone flow could lead to a
reduction of reaction time but increases the ozone consumption (Peretz et al.,
2017). Garcı ´a-Cubero et al. (2009) stated that the increase of ozone flow decreased