Page 123 - Refining Biomass Residues for Sustainable Energy and Bioproducts

Application of heterogeneous acid catalyst derived from biomass for biodiesel process 95

carbonization of biomass because of its deoxygeneration and reforming reaction
that, in turn, increase acid density site during the sulfonation process. Solvents with
lower dielectric constants than water have the capacity to dissolve high molecular
weight components such as cellulose, hemicelluloses, and lignin-derived products
(Fang et al., 2004). Huang et al. (2016) have compiled the results of the carboniza-
tion of biomass that takes place in the presence of alcohols, such as methanol, etha-
nol, isopropanol, and 1-2 propanediol and has further found that shorter chain
alcohols are more favorable for char formation. In addition, it was observed that
there was a considerable difference between the char derived through sub as well as
supercritical methods before and after pyrolysis (Huang et al., 2016). In subcritical
conditions, surface area and pore volume are lower, but after pyrolysis both
increase drastically due to the formation of pores in biochars which, in turn, are
formed by the release of volatile gases during pyrolysis. However, the same pyroly-
sis at sub and supercritical methods showed that the catalyst had an acid value of
5.05 mg KOH/g and an acid density of 5.35 mmol/g. Hence, it proves that pyrolysis
at high temperatures does not result in any gain in sulfonated catalyst activity
caused by the vigorous separation of functional groups of lignin char containing
oxygen and decrease of sulfonic group content.
Alcohol thermal carbonization and direct carbonization methods improve the cat-
alytic activity in both esterification and transesterification with minimum leaching
of SO 3 H group. It is also reasonably recycled many times and regenerated by sul-
furic acid treatment (Devi et al., 2014).

4.3.2.4 Carbonization with distinct activating agents
Biomass has some rigid carbon materials after carbonization which are hard to be
sulfonated by concentrated H 2 SO 4 . These rigid carbon materials can be sulfonated
by some special sulfonating agents, such as 4-benzene diazoniumsulfonate (4-
BDS), fuming H 2 SO 4 ,SO 3 , and ClSO 3 H. In the process of sulfonation, temperature
is very low, so it can maintain the original skeleton structure of the biomass
(Konwar et al., 2015). Hence, operation is simple and the catalyst is easily sepa-
rated when compared to the use of concentrated H 2 SO 4 (Dehkhoda et al., 2010).
Sulfonic acid functionalized catalyst produced by using special sulfonating agent is
widely employed for catalyzing both of these esterification and transesterification
reactions as listed in Table 4.2.
In this preparation method, pretreatment is required before adding special sulfo-
nating agent. The porous carbonaceous material was pretreated with the help of
chemical activation method and then was consequently sulfonated through covalent
functionalization with 4-BDS in the presence of H 3 PO 4 . It has been proven to be
the most efficient method with an improved activity of the catalyst due to SO 3 H
density. Functionalization by 4-BDS radicals leads to rapid increase in SO 3 H den-
sity in aromatic carbon sheets. In addition, it improves the porosity of the catalyst
that is clearly visible from the difference in the arrangement of chemically activated
Jatropha curcas and Mesua ferrea L. biomass that had flake as well as particle like
structures. The presence of discontinuous and uneven particles in sulfonated