– The main hemicellulose in Gramineae (such as cereal straws) is arabinoxylans,
which are similar to harwoods xylan, but the amount of L-arabinose is higher
(Peng et al. 2011).
– Lignin is the organic substance which is responsible of binding the cells (Sticklen
2008). The three basic monomeric units constitute lignin: p-Hydroxyphenyls (H);
Guaicyls (G); Syringyls (S).
Hardwood lignins are predominantly G and S monolignols with trace amounts of
H units. Soft wood lignins are composed of mostly G units. Herbaceous plants
contain all three units in significant amounts (Chundawat et al. 2011; Buranov and
Mazza 2008).
1.3
First-Generation Biodiesel
1.3.1 Transesterification Reaction
The transesterification reaction with alcohol is represented by the general equation
shown in Fig. 1.3a which consists of a number of consecutive, reversible reactions.
These are shown in Fig. 1.3b. The first step is the conversion of triglycerides into
diglycerides, and then diglycerides are converted into monoglycerides and
monoglycerides into FFAs and glycerol. Each step yields one methyl ester molecule
(Freedman et al. 1986; Noureddini and Zhu 1997). The transesterification can be
both catalyzed by acid and alkali.
Fig. 1.3 Transesterification reaction (Eckey 1956)
8
P. Bartocci et al.
which are similar to harwoods xylan, but the amount of L-arabinose is higher
(Peng et al. 2011).
– Lignin is the organic substance which is responsible of binding the cells (Sticklen
2008). The three basic monomeric units constitute lignin: p-Hydroxyphenyls (H);
Guaicyls (G); Syringyls (S).
Hardwood lignins are predominantly G and S monolignols with trace amounts of
H units. Soft wood lignins are composed of mostly G units. Herbaceous plants
contain all three units in significant amounts (Chundawat et al. 2011; Buranov and
Mazza 2008).
1.3
First-Generation Biodiesel
1.3.1 Transesterification Reaction
The transesterification reaction with alcohol is represented by the general equation
shown in Fig. 1.3a which consists of a number of consecutive, reversible reactions.
These are shown in Fig. 1.3b. The first step is the conversion of triglycerides into
diglycerides, and then diglycerides are converted into monoglycerides and
monoglycerides into FFAs and glycerol. Each step yields one methyl ester molecule
(Freedman et al. 1986; Noureddini and Zhu 1997). The transesterification can be
both catalyzed by acid and alkali.
Fig. 1.3 Transesterification reaction (Eckey 1956)
8
P. Bartocci et al.