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Pretreatment of agroindustry waste by ozonolysis for synthesis of biorefinery products 323

technology that requires more study. The followings are biochemical synthesis path-
ways that have not been performed on ozone-treated lignocellulosic biomass. The
value of their synthesis product combined with the potential efficiency of ozone
treatment hints at a productive industrial application.

14.3.4.1 5-Hydroxymethylfurfural
5-HMF has become a platform chemicals derived from biomass and an important
intermediate for the production of biofuel and fine chemical (Mukherjee et al.,
2015). It can be synthesized through the dehydration of C6 sugars, that is, glucose
and fructose via acid catalytic reaction. 5-HMF is a high potential chemical derived
from biomass which reacts via rehydration to produce LA and formic acid in an
aqueous system. In 5-HMF synthesis the glucose from biomass carbohydrate is
required to be isomerized to fructose before being converted to 5-HMF (Morone
et al., 2015). In order for the cellulose to be converted into the hexose sugar, bio-
mass pretreatment to remove lignin, and possibly hemicellulose, is obligatory to
expose the cellulose for the acid hydrolysis reaction. In biomass carbohydrate the
pentoses such as xylose are derived from the hemicellulose of biomass that can pro-
duce furfural via acid hydrolysis (Neves et al., 2013). However, there are limited
studies conducted on pretreated biomass to 5-HMF via acid hydrolysis of C6 sugar
(Table 14.5). Ionic liquid usually plays a major role for the catalytic reaction of bio-
mass to 5-HMF. Ionic liquid has been used as a reaction medium with the presence
of acid catalyst to produce 5-HMF. Pretreated rice straw and wood via acid and
base pretreatment have shown high 5-HMF yield via hydrolysis in [BMIM][Cl] cat-
alyzed by CrCl 3 6H 2 O(Nguyen et al., 2016).
Nevertheless, the biomass conversion to 5-HMF synthesis has usually been con-
ducted without a pretreatment process. This includes the reaction via extraction fol-
lowed by hydrolysis (Lee et al., 2011; Yi et al., 2012), two-step acid hydrolysis
(Karimi et al., 2006), or one-pot reaction in ionic liquid (Ito et al., 2016; Alam
et al., 2018). For example, 5-HMF yield via acid hydrolysis of corn stover in
[EMIM][Cl] using CrCl 2 , HCl is 42.0% (Binder and Raines, 2009). Moreover, the
acid hydrolysis in [OMIM][Cl] of acorn (Lee et al., 2011) and potato tuber (Yi
et al., 2012) with HCl, CrCl 2 , chicory root (Yi et al., 2011), and girasol tuber (Yi
et al., 2012) with HCl, in ethyl acetate as cosolvent, yields 52.8%, 54.4%, 50.9%,
and 58.2% of 5-HMF, respectively. However, the ionic liquid also shows some
drawback as the excess loading ionic liquid may increase the collision of reactive
compounds and caused cross polymerization that lead the formation of products
such as furfural, 2-furancarboxyaldehyde, organic acids, and phenolics (Tiong
et al., 2017). As stated by Ramli and Amin (2014), the degradation of reducing
sugars may also occur before their conversion to 5-HMF or LA, with excessive
active sites. This will lead to form humin in the reaction. Instead of using the homo-
geneous acid catalyst, the synthesis of 5-HMF may be improved for future applica-
tion by conducting the pretreatment and the application of the heterogeneous
catalyst in ionic liquid for hydrolysis.