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Rajak, et al.

include sodium methoxide, KOH, NaOH, carbonates, ferrite catalysts synthesized by co-precipitation from
sodium peroxide, potassium methoxide, and sodium rambutan oil achieved a 95% yield, highlighting their
ethoxide. Among these, sodium methoxide and potassium potential in biodiesel production. M-phenylenediamine-
methoxide are particularly efficient due to their ease SO H-ionic liquid catalysts prepared through
3
of dissociation into CH O and Na or K , respectively, co-polymerization from jatropha oil attained a 90%
+
+
˗
3
resulting in larger yields of biodiesel. 34 yield, emphasizing their effectiveness in high-acid-value
Homogeneous catalysts offer superior selectivity oils. Aluminum chloride hexahydrate (AlCl ·6H O)
3
2
and activity due to their uniform dispersion in the catalysts synthesized through hydrothermal methods
reaction medium, ensuring precise control over reaction from brown grease yielded 86% biodiesel, indicating
pathways and higher yields with minimal byproducts. their suitability for waste grease conversion. Organically
They operate efficiently under mild conditions, reducing modified resin-[C HMTA][SO H] catalysts prepared
3
4
energy demands and enhancing safety, particularly by co-polymerization from brown grease achieved
for sensitive compounds. Their solubility enables a 95% yield, demonstrating high catalytic activity.
straightforward characterization using spectroscopic Cesium hydrogen phosphotungstate (Cs H PW O )
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2.5
0.5
12
methods, providing valuable mechanistic insights catalysts synthesized through precipitation from sesame
for optimization. In addition, the consistent reaction oil attained a 90% yield, showcasing their efficiency
environment ensures uniform kinetics, enabling better in biodiesel production. Significant advancements
control in complex syntheses. in solid acid catalyst development offer sustainable
Despite their various advantages, homogeneous and efficient pathways for biodiesel production from
catalysts also possess several disadvantages. diverse feedstocks. The high yields achieved across
Homogeneous catalysts face significant separation various catalysts demonstrate their potential to replace
difficulties due to their shared phase with reactants, conventional homogeneous catalysts, providing an eco-
complicating recycling and risking product friendly alternative with enhanced recyclability and
contamination. While solutions, such as multiphase reduced environmental impact.
systems exist, they often add process complexity.
Thermal stability limitations (typically <200°C) restrict 2.2. Solid base heterogeneous catalysts
high-temperature applications, and many catalysts Increased catalytic activity in heterogeneous solid base
pose toxicity concerns with challenging disposal catalysts is attributed to their large effective surface
requirements. Immobilization attempts frequently suffer area and abundance of basic sites. These catalysts
from leaching issues, causing deactivation and potential usually consist of transition metal oxides, alkaline earth
environmental contamination, which are key obstacles metals, or metallic oxides that may be doped, mixed,
to industrial adoption. or single-component. The basic sites in most solid
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Table 1 presents a comprehensive overview of base metal oxide catalysts are formed by the Lewis acid
solid acid catalysts utilized in biodiesel production and Bronsted base sites of metal ions. Typical single
from various feedstocks, highlighting their preparation metal oxide catalysts include barium oxide (BaO),
methods, molar ratios, and biodiesel yields. For instance, strontium oxide (SrO), calcium oxide (CaO), and
a carbon-derived catalyst synthesized through pyrolysis magnesium oxide (MgO). These solid base catalysts
from Calophyllum inophyllum oil achieved a biodiesel can produce biodiesel with similar yields in shorter
yield of 90%. Similarly, cesium phosphotungstate response times and temperatures below 55°C. 46
catalysts prepared through precipitation from However, when utilized with feedstocks containing
oleic acid-soybean mixtures also attained a 90% high FFA (≥2%) content, solid base catalysts have a
yield. Mn 3.5x Zr 0.5y Al O catalysts synthesized by significant drawback: they tend to generate soaps, which
x
3
co-precipitation from waste cooking oil yielded 75% makes them less appropriate for such feedstocks. CaO
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biodiesel, indicating effective utilization of waste oils. is widely used in biodiesel synthesis due to its low cost
Phosphotungstic acid-poly(glycidyl methacrylate)- and strong reactivity. MgO and other single metal
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magnetic nanoparticle catalysts prepared by direct oxides, on the other hand, are less soluble in alcohol
mixing from greases achieved an impressive 96% yield, and less efficient as catalysts. To increase their catalytic
showcasing high efficiency. Anion/cation-exchanged durability, the temperature of calcination can be raised
resin catalysts derived from pure triolein through to 873 K. Studies have shown that CaO has more basic
49
neutralization also reached a 96% yield, demonstrating sites than MgO, resulting in higher catalytic activity.
versatility in feedstock utilization. SiO -SO H/cobalt However, at milder operating temperatures, alkaline
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Volume 22 Issue 5 (2025) 4 doi: 10.36922/AJWEP025130095