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Heterogeneous catalysts for biodiesel production

frying oil transesterification. Under ideal circumstances, reaction time, and 80°C temperature. Eggshell-derived
this process produced a 96.74% biodiesel conversion CaO also facilitated the transesterification of soybean
(Johari et al.,). To create a high-performance CaO- oil, yielding 93% biodiesel with a 10:1 methanol-to-oil
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based catalyst that helps produce biodiesel, calcined ratio, 3-h reaction time, and 57.5°C temperature.
shrimp shells in a fluidized bed reactor. Notably, mud crab shell-derived CaO achieved a 98.8%
Despite their advantages over homogeneous catalysts, yield from waste oil with a 0.5:1 weight-to-weight ratio,
heterogeneous catalysts need longer reaction periods. 5% catalyst loading, 150 min, and 65°C reaction time.
Process intensification approaches, including co-solvent Cockle shell-derived CaO achieved a 99.4% yield from
technologies, microwave heating, and ultrasound, palm olein with a 0.54:1 weight-to-weight ratio, 4.9%
have been investigated as ways of overcoming this catalyst loading, 180 min, and 65°C reaction time. These
issue. For example, microwave-assisted alcoholysis of studies underscore the potential of utilizing various
used cooking oil with CaO obtained from used oyster shell-derived CaO catalysts in biodiesel production,
shells produced an 87% biodiesel yield under optimal highlighting the importance of optimizing reaction
conditions. The addition of co-solvents has been parameters to achieve high yields.
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shown to accelerate reaction rates. For instance, CaO
made from calcined snail shells generated 98% FAME 3.2. Animal bones
in 2 h when acetone was added as a co-solvent. 149 Leftover animal bones are potentially a reasonably
Furthermore, ultrasound-assisted transesterification of priced supply of CaO. Calcium phosphate is the main
used frying oil with eggshell-derived CaO significantly component of bones, making up over 40% of the
shortened the reaction time, producing 98.62% biodiesel bone’s weight. Bones calcined at high temperatures
in 39.84 min under ideal conditions. 150 yield beta-tricalcium phosphate and calcium oxide.
Table 4 presents a comparative analysis of biodiesel Bones also include hydroxyapatite, a material that
production using transesterification catalysts derived may be utilized as a catalyst or a booster for catalysts
from various shell-based biomass sources. CaO, a solid because of its high thermal stability, porosity, and wide
base catalyst, has been synthesized from different shells surface area. 161,162 Given that different species have
and utilized in the transesterification of various oils. different elemental compositions, the catalytic qualities
For instance, CaO derived from scallop shells catalyzed of hydroxyapatite can vary greatly depending on the
the transesterification of waste cooking oil, achieving source. Thus, common species, including fish, pig,
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a biodiesel yield of 86% under a 6:1 methanol-to-oil cow, and chicken bones, have been the main focus of
molar ratio, 2-h reaction time, and 65°C temperature. research on bone-derived catalysts. Table 5 compares
Similarly, mussel shell-derived CaO facilitated the the efficiency of catalysts generated from different
transesterification of soybean oil, resulting in a 94.1% species in the transesterification process. Several studies
yield with a 24:1 methanol-to-oil ratio, 8-h reaction have assessed the efficacy of biodiesel production using
time, and 60°C temperature. Eggshell-derived CaO catalysts generated from bone.
has also been extensively studied; for example, it Figure 3 illustrates how both the chemical and
achieved a 94.5% yield from waste frying oil under a physical properties of heterogeneous catalysts
12:1 methanol-to-oil ratio, 1-h reaction time, and 65°C significantly impact the transesterification process
temperature. In addition, lithium-doped CaO from in biodiesel production. Chemically, catalysts with
eggshells catalyzed the transesterification of Mesua high basicity, such as CaO, effectively deprotonate
ferrea Linn oil, yielding 94% biodiesel with a 10:1 methanol, facilitating the nucleophilic attack on
methanol-to-oil ratio and a 4-h reaction time at 65°C. triglycerides to form methyl esters and glycerol. The
M-CaO catalysts, incorporating metals, such as Zn presence of active sites in these catalysts enhances the
and Cu, derived from eggshells, were employed in the conversion efficiency. For instance, nanocrystalline
transesterification of eucalyptus oil, achieving a 93.8% CaO exhibits increased surface area and more active
yield with a 6:1 methanol-to-oil ratio and 2.5-h reaction sites, leading to higher catalytic efficiency. Studies
time at 65°C. Furthermore, Turbonilla striatula shell- have shown that nanocrystalline CaO can achieve up
derived CaO catalyzed the transesterification of mustard to 99% conversion of soybean oil at room temperature
oil, yielding 93.3% biodiesel under a 9:1 methanol-to-oil with a 1:27 oil-to-methanol molar ratio. Physically,
ratio, 3-h reaction time, and 65°C temperature. Tourbo the surface area, particle size, and morphology of the
jourdani shell-derived CaO achieved over 99% yield catalyst influence its performance. Nanostructured
from palm oil with a 3:1 methanol-to-oil ratio, a 7-h catalysts offer increased surface area and more active

Volume 22 Issue 5 (2025) 11 doi: 10.36922/AJWEP025130095