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Rajak, et al.

are often sluggish. Numerous variables, such as site processes, such as pressure swing reactive distillation
strength, surface hydrophobicity, pore size, channel and reactive distillation, both of which have been widely
system dimensionality, and aluminum concentration, all applied in earlier studies. Compared to conventional
affect their catalytic activity. 397 esterification techniques, which frequently have
Some of the benefits of zeolites include high acidity, problems with kinetics and mass transfer, this method
high surface area, superior ion exchange capacity, and enhances reaction speeds and conversion efficiency.
409
both thermal and hydrothermal stability. 398,399 In addition, Microbubble catalysis has been created to overcome
they make shape-selective reactions possible, in which these restrictions and improve the overall effectiveness
the catalyst can only interact with specific reactants, of esterification.
products, and transition states. With customized crystal By reducing buoyancy, the microbubble catalysis
structures, different silicon/aluminum ratios, pore approach lengthens the residence period in the liquid
diameters, and proton exchange levels, zeolites may phase. Its use as a heterogeneous catalyst in reactive
410
be produced for certain acid-base catalyzed processes. distillation processes has been the subject of several
These selective processes are facilitated by zeolites’ investigations. 411-413 The review does not delve deeply
homogeneous crystalline channels. The benefits have into this approach due to it being relatively new.
400
been investigated and validated in several studies. 401 However, when more research becomes available, it is
Making active areas more accessible in microporous anticipated that subsequent reviews will provide a more
zeolite structures has been the subject of recent thorough analysis.
studies. The “top-down” and “bottom-up” techniques
have become the two primary methods for creating 7. A comparative analysis of biodiesel
hierarchical structures in zeolites. Dealumination is production costs versus petroleum diesel
402
a crucial technique in the top-down approach, which
entails synthetically altering microporous zeolites Table 9 provides a comprehensive overview of biodiesel,
to produce a hierarchical structure. The method which offers a renewable alternative to petroleum diesel.
403
creates a more stable type of zeolite that is perfect for However, its economic viability varies significantly
catalytic cracking and optimizes the silicon/aluminum depending on feedstock and production methods
ratio. 404,405 In contrast, by employing template elements (Table 8). According to recent data (2023 – 2024), waste
to manufacture both microporous and mesoporous cooking oil biodiesel (2.50 – 3.50 US Dollar [USD]/gal)
domains, the bottom-up approach produces hierarchical and animal fat biodiesel (2.70 – 3.60 USD/gal) are the
zeolites. Since they are readily available and versatile, most cost-competitive, nearing parity with petroleum
substances containing carbon, including carbon diesel (3.00 – 4.20 USD/gal). In contrast, soybean
aerogels, carbon nanotubes, and carbon black, are (3.20 – 4.80 USD/gal) and rapeseed biodiesel
frequently utilized as templates. 406,407 (3.50 – 5.00 USD/gal) remain more expensive
During synthesis, different mesoporous molecules due to high feedstock costs, while algal biodiesel
that are well-ordered and linked may be created utilizing (8.00 – 15.00 USD/gal) is still prohibitively expensive
the bottom-up method with carbon templates. However, due to high cultivation and extraction expenses. Palm
the use of materials, such as graphene and graphene biodiesel (2.80 – 3.80 USD/gal) is economically
oxide as templates presents difficulties. 408 viable but faces sustainability concerns. Key cost
A summary of biodiesel production using drivers include feedstock availability (70 – 80% of
heterogeneous catalysts made from zeolite is presented production costs), processing efficiency, and policy
here, with details on the catalyst weight and FAME incentives, such as the USs Renewable Fuel Standard
production in regard to the reaction temperature, and the EU’s RED III subsidies, which can reduce
reaction conditions, feedstock sources, and normalized biodiesel costs by 0.50 – 1.50 USD/gal. Despite
time yields. Zeolite-based catalysts have been reported higher production costs for some biodiesel types,
to provide FAME outputs ranging from 79.30% to 98%, their potential for lower greenhouse gas emissions
as Table 1 illustrates. and energy security benefits makes them attractive
alternatives, especially as petroleum prices remain
6.3. Heterogeneous biodiesel production through volatile due to geopolitical factors. Future cost
microbubble-mediated catalysis reductions in algal biodiesel and expanded use of
A new approach in catalyst technology called waste feedstocks could further improve biodiesel’s
microbubble-mediated catalysis expands on well-known competitiveness against conventional diesel.

Volume 22 Issue 5 (2025) 28 doi: 10.36922/AJWEP025130095