Page 227 - Refining Biomass Residues for Sustainable Energy and Bioproducts

198 Refining Biomass Residues for Sustainable Energy and Bioproducts

Crude glycerol Partially refined Refined glycerol Commercial
glycerol glycerol
(Byproduct from (Major impurities (Requires (Used in
biodiesel industry are removed and purification and cosmetics,
contains copious can be used for suitable for fewer pharmaceuticals,
impurities) fermentation industrial and food
process) application) industries)

Figure 9.1 Improvement of glycerol concentration and its utilization.

methanol can have deleterious effects on the environment and public health. The

boiling point of methanol is 65 C and hence it can be removed by controlled simple
distillation process in large-scale process (Sarma et al., 2012). Denver et al. (2008)
have suggested that crude glycerol can be autoclaved at 121 C at 15 min to remove

a significant amount of methanol before using as a feedstock for bioconversion.
Thus for the economic assessment, the retrieved methanol can be reused again in
the transesterification process (Chozhavendhan et al., 2017; Bohon et al., 2001).
In the next step, removal of nonglycerol substance (soap) is carried out by pre-
cipitation process on adjusting the pH from alkaline to acidic condition (Shannon
et al., 2011). Due to the use of base catalyst in the transesterification process of bio-
diesel production, pH of the crude glycerol is highly alkaline in condition. The alka-
line pH may have a deleterious effect on microbial growth. pH of the glycerol
sample is altered in order to convert the soluble soap into insoluble fatty acid and
to avoid the foam formation during the fermentation process by using mineral acids,
such as phosphoric, hydrochloric, sulfuric, and nitric (Chozhavendhan et al., 2015).
Phosphoric acid showed a substantial result in separation time and the glycerol lib-
eration amount and the presence of salt in the glycerol-rich phase were also low
when compared with other acids. However, a high acidic condition will corrode the
material and results in low glycerol liberation, on a contradictory way the weak
acids may cause the difficulties in the separation of final products. The glycerol-
rich phase separation from the waste stream glycerol is well in the range of pH
4 6(Chozhavendhan et al., 2016b).

9.3.2 Sophisticated purification process
The final step of purification and refining step can be achieved to the desired
degree of purity with the combination of the following methods, such as vacuum
distillation, ion exchange, membrane separation process. In ion exchange adsorption
process, ion materials are employed in purification of crude glycerol for the
removal of impurities, odor, and other inorganic salts through exchanging of ions
(Ardi et al., 2015; Rathore et al., 2019). This technique does not require vaporiza-
tion of crude glycerol and requires a small quantity of water for the removal of salt.
The final product is exceptionally high in quality with 95% 99%, which confirms
the high-grade distilled glycerol. The chromatograph of HPLC shows a single peak
of glycerol with a smooth baseline matching a standard profile. Vacuum distillation
is one of the most common methods employed for the industrial purification