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Heterogeneous catalysts for biodiesel production

find novel approaches to lower processing and material the reaction rate during the transesterification process,
expenses. In this context, heterogeneous catalysts present catalysts increase the yield of the end product. Most
a promising alternative to conventional homogeneous commonly, these catalysts fall into one of four
catalysts. Since 2006, a pilot facility in France has categories: (i) homogeneous, (ii) heterogeneous,
been producing 160,000 tons of biodiesel annually (iii) enzymatic, and (iv) non-catalytic procedures that
despite the limited large-scale commercialization in the operate at supercritical conditions.
energy sector. Because heterogeneous catalysts are not
consumed throughout the reaction, they reduce reaction 2.1. Homogeneous acid catalysts
durations and simplify product separation, making them Homogeneous acid catalysts are frequently employed
essential in transesterification processes. 26 in biodiesel synthesis due to their affordability,
Nowadays, several types of catalysts are available accessibility, and fast reaction rates. Base-based and
in the market, such as metal oxides, mixed oxides, acid-based catalysts, with common examples, including
and hydrotalcites. Zeolites, carbon-based catalysts, H SO , NaOH, and KOH, can be used. According to
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2
4
ion exchange resins, and transition metal oxides are research, the main mechanism by which these catalysts
employed in acidic procedures. However, their three- function involves a nucleophilic attack on the carbonyl
phase reaction system, which results in diffusion group. However, homogeneous catalysts have several
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constraints that obstruct the reaction process, is a limitations, such as higher costs, inefficient use,
major disadvantage of these heterogeneous catalysts. 28 significant wastewater production, difficulties in end-
In addition, this system decreases mass transfer product separation, and thermal instability, as they
effectiveness, which is crucial for optimizing reaction tend to break down at temperatures >150°C. Table 1
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rates. Other drawbacks include low active site counts, summarizes the biodiesel manufacturing process using
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microporosity, leaching, toxicity, high expenses, non- various solid acid catalysts, including the sources of
renewability, and adverse environmental effects. 30 raw materials, methods of preparation, parameters of
the response, and relevant references.
2. Classification of catalysts Alkalized homogeneous catalysts further accelerate
transesterification, which may achieve reaction rates
A catalyst speeds up a chemical process without changing up to 4,000 times faster than acid-based catalysts.
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its thermodynamic characteristics. By speeding up Common alkaline catalysts used in biodiesel production

Table 1. Solid acid catalysts for biodiesel production
Catalyst Feedstocks Continuous Reaction operating References
process conditions
manufacturing Molar ratio Yield (%)
Carbon-derived catalyst Calophyllum Pyrolysis 30:1 90 35
inophyllum oil
Cesium phosphotungstate Oleic acid-soybean Precipitation 20:1 90 36
mixture
Mn 3.5× Zr 0.5y Al O 3 Waste cooking oil Co‐precipitation 14:1 75 37
x
Phosphotungstic acid-poly (glycidyl Greases Direct mixing 33:1 96 38
methacrylate)-magnetic nanoparticles
Anion/cation-exchanged resin Pure triolein Neutralization 10:1 96 39
SiO ‐SO H/cobalt ferrite Rambutan oil Co‐precipitation 20:1 95 40
2
3
M-phenylenediamine-SO₃H-ionic liquid Jatropha oil Co‐polymerization 50:1 90 41
Aluminum chloride hexahydrate Brown grease Hydrothermal 10:1 86 42
(AlCl ·6H O)
2
3
Organically modified resin-[C HMTA] Brown grease Co‐polymerization 40:1 95 43
4
[SO H]
3
Cesium hydrogen phosphotungstate Sesame oil Precipitation 40:1 90 44
(Cs H PW O )
12
0.5
2.5
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Volume 22 Issue 5 (2025) 3 doi: 10.36922/AJWEP025130095