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Heterogeneous catalysts for biodiesel production

Figure 2. The manufacture of solid catalysts for the transesterification process using various biomass waste
sources

cost, and high basicity. The non-renewable mineral shells showed the maximum activity, followed by those
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limestone is typically used to make CaO, which may be made from M. meretrix shells and golden apple snails.
costly to generate. Utilizing discarded shells, which are These fluctuations in catalytic activity may be caused
high in calcium, might lessen the reliance on limestone by variations in surface area and calcium content.
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for manufacturing CaO. Waste shells are produced in Therefore, it can be said that the surface area and calcium
significant quantities worldwide due to the extensive content of shell-derived CaO catalysts have a significant
consumption of mollusks and chicken eggs. A high- impact on their catalytic activity. The efficacies of
temperature calcination process may transform over several shell-derived catalysts in transesterification are
95% of calcium carbonate (CaCO ) in these shells into compared in Table 4.
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CaO. During calcination, CaCO decomposes from the Natural CaO surfaces have been shown to deactivate
3
outer surface inward, increasing the material’s porosity when subjected to moisture and ambient carbon dioxide,
and activating the resulting CaO catalyst. 128 forming CaCO and calcium hydroxide, which lowers
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Calcium oxide catalysts made from shells are the substance’s catalytic activity. 132,133 To mitigate this
becoming more popular for their ability to catalyze issue, ammonium carbonate is used in high-temperature
transesterification processes due to their affordability calcination to eliminate these harmful species and
and environmental advantages. Calcined egg shells were improve the basicity of the catalyst. Furthermore,
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investigated as catalysts for the transesterification of a number of strategies have been investigated to
fresh soybean oil versus waste cooking oil at ambient further enhance CaO’s catalytic activity, including
temperature, yielding 97 wt% and 98% FAME yields, chemical treatments, doping with alkali metals,
respectively. In addition, the catalyst only showed a hydration-dehydration cycles, and nanoscale particle
10% reduction in activity after a year, and continued to reduction. 135,136 For instance, Jairam et al. treated
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exhibit catalytic activity for up to 3 months without any discarded quail shells with a 0.005 M hydrochloric acid
notable losses. Similarly, Hu et al., discovered that solution and then calcined them for 2 h at temperatures
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CaO made from mud crab shells had catalytic activity higher than 800°C to create a CaO catalyst. By removing
comparable to that of commercially sold CaO. the thick outer layer of the cuticle, this technique resulted
However, there has been some variance in the in a porous palisade layer that was rich in strong basic
catalytic activity of CaO produced from various shell sites. During five transesterification cycles, the resultant
species. A comparison of CaO made from egg shells, catalyst consistently produced a 98% yield of FAME,
golden apple snails, and Meretrix meretrix shells in similar to potassium methoxide (a potent homogeneous
the process of transesterifying palmolein oil found base) in terms of catalytic activity.
that all of the catalysts functioned well, attaining over By increasing the surface area and the quantity of
90% FAME in 2 h. The driving force made from egg basic or acidic sites, impregnation is another efficient

Volume 22 Issue 5 (2025) 9 doi: 10.36922/AJWEP025130095