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90 Refining Biomass Residues for Sustainable Energy and Bioproducts

Figure 4.2 Chemical reaction pathway of an acid catalyzed esterification reaction.

densities. They are synthesized using different techniques such as direct sulfonation,
carbonation followed by sulfonation or carbonization with distinct activating agents.
These catalysts have remarkable performance in biodiesel production by both esteri-
fication and transesterification reactions. In comparison, they exhibit highly admira-
ble catalytic activity for esterification than transesterification under identical
reaction conditions. This is due to the complication in transesterification reaction
mechanism and the requirement of lower activation energy for a faster reaction rate
(Yin et al., 2012). Due to these reasons, it is considered the best choice for the pre-
treatment of low-value acid feedstock. Furthermore, it can be easily regenerated
and reused for multiple times after a more straightforward recovery through reacti-
vation. The other factors that determine the efficiency of biodiesel yield include
high active sites and stability of the catalyst. Summarily, this strategy may act as an
efficient and economic way to produce biodiesel.

4.3.1 Direct sulfonation method

Direct sulfonation proves to be the simplest and the most commonly used method
among the existing acid catalyst preparation techniques in which direct carboniza-
tion and sulfonation of biomass are carried out by sulfuric acid at a predetermined
time and temperature (Kang et al., 2014; Guo et al., 2017). The main advantage of
this process is the economical aspect since it does not require any complicated
pretreatment.
Savaliya and Dholakiya (2015) synthesized acid catalyst from sugarcane bagasse
through in-situ sulfonation and carbonization. They recognized this process to be
convenient giving a yield of 25 35 wt.% catalyst. Further, this catalyst was investi-
gated to catalyze soap stock that resulted in a maximum FFA conversion of 97.2%.
A study on its reusability showed that it can be used up to three consecutive cycles
without any significant loss in its activity.