Page 126 - Refining Biomass Residues for Sustainable Energy and Bioproducts

Application of heterogeneous acid catalyst derived from biomass for biodiesel process 97

catalysts was confirmed from the images of Scanning Electron Microscopy (SEM)
technique (Konwar et al., 2015).
Report from Liu et al. (2010b) suggested that catalyst derived from the 4-BDS sul-
fonation method showed a relatively less difference in the patterns of X-ray
Diffraction (XRD) between the sulfonated and nonsulfonated carbon. These results
clearly indicated a reduction in arylation, though it did not affect the microstructure
of the carbon materials. However, it was observed that there was a reduction in the
pore volume after sulfonation which proved that a part of these pore spaces had been
filled by sulfonic group. It was also reported that there existed a close relationship
between the increase in sulfur content and total acid density in sulfonation process.
In general, these catalysts played a significant role in esterification, although the
same was comparatively less in the transesterification process that was because phe-
nolic and carboxylic did not display adequate acid strength to catalyze the transes-
terification reaction. These groups are created due to the oxidization of aliphatic
groups by strong sulfonation and incomplete carbonization of the supporting mate-
rial. Therefore, the sulfonic group having ample acid strength alone can take part in
transesterification reaction. The total acid density of the sulfonated catalyst impreg-
nated with concentrated sulfuric acid is found to be 100 times lower than that of
catalyst synthesized using fuming acids. This is majorly because of the strong
nature of the sulfonation reagent and higher solid-to-acid ratio during fuming sulfu-
ric acid catalyst preparation (Dehkhoda et al., 2010).
The preparation of the catalyst with the help of special sulfonating agents other
than sulfuric acid exhibit an extraordinary acid exchange capacity, thermal stability,
and reusability. It has been found that they could act as a favorable waste-derived
substitute to H 2 SO 4 for both pretreatment and transesterification of acidic feedstock.

4.3.3 Special ingredient loaded on carbonized biomass
The solid catalyst recovery is usually carried out by means of filtration or centrifugation
method that consumes more time and energy. The magnetization of the catalyst aims to
render help for the simplification of the catalyst separation and recycle process (Liu
et al., 2013b).
Zhang et al. (2017) magnetized the catalyst prepared from pyrolysis and subse-
quent sulfonation. They incorporated magnetic material in the form of γ-Fe 2 O 3 into
the carbon structure. Acid functional groups loaded onto the sulfonated carbon
formed a difunctional acid catalyst that consists of both Lewis as well as Bronsted
acid sites. Hence, the magnetized catalyst is more efficient in biodiesel production.
These above discussions indicate that the sulfonated carbon material can be treated
with the special loaded ingredients to enhance easier separation. Further research in
difunctional or multifunctional catalyst production would be promising.