From waste to fuel: Challenging aspects in sustainable biodiesel production from lignocellulosic biomass feedstocks and role of metal organic framework as innovative heterogeneous catalysts

The present review primarily focuses on the perspectives and state-of-the-art of heterogeneous catalysts, nanocatalysts, biocatalysts, bifunctional catalysts, metal-organic frameworks (MOF), and covalent organic frameworks (COF) for biodiesel production. The environmental concern associated with nonrenewable fossil fuels has led to finding alternative energy sources that can be used to meet global energy demands. Biofuels such as biodiesel are one of the energy sources that could replace fossil fuels. The homogeneous acid and base catalysts are generally used for commercial biodiesel production. However, homogeneous catalysts have downsides such as toxicity, corrosion, soap formation, high wastewater output, and non-reusability. Consequently, heterogeneous acid and base catalysts have been introduced that are less sensitive to moisture and free fatty acids (FFAs), easily separated and recovered, and reusable. Recently, novel catalysts such as waste biomass-derived mesoporous heterogeneous catalysts, chemically synthesized heterogeneous catalysts, metal ion-doped heterogeneous catalysts, bifunctional acid-base catalysts, and carbonaceous char-supported hetero catalysts, nanocatalysts, MOF and COF catalysts have potential to replace homogeneous base catalysts, aid in sustainable and cost-effective biodiesel production. This review provides insights into the recent advancement of various catalysts, catalyst preparation and operations, type of catalysts and suitability, catalyst efficiency, life cycle assessment, catalyst-associated challenges, and prospects for sustainable biodiesel production.

The production of biodiesel through chemical production processes of transesterification reaction depends on suitable catalysts to hasten the chemical reactions. Therefore, the initial selection of catalysts is critical although it is also dependent on the quantity of free fatty acids in a given sample of oil. Earlier forms of biodiesel production processes relied on homogeneous catalysts, which have undesirable effects such as toxicity, high flammability, corrosion, by‐products such as soap and glycerol, and high wastewater. Heterogeneous catalysts overcome most of these problems. Recent developments involve novel approaches using biomass and bio‐waste resource derived heterogeneous catalysts. These catalysts are renewable, non‐toxic, reusable, offer high catalytic activity and stability in both acidic and base conditions, and show high tolerance properties to water. This review work critically reviews biomass‐based heterogeneous catalysts, especially those utilized in sustainable production of biofuel and biodiesel. This review examines the sustainability of these catalysts in literature in terms of small‐scale laboratory and industrial applications in large‐scale biodiesel and biofuel production. Furthermore, this work will critically review natural heterogeneous biomass waste and bio‐waste catalysts in relation to upcoming nanotechnologies. Finally, this work will review the gaps identified in the literature for heterogeneous catalysts derived from biomass and other biocatalysts with a view to identifying future prospects for heterogeneous catalysts.

The synthesis of biodiesel is given wide attention due to its environmental benefits, renewability, and long-term sustainability. Importantly, it can also contribute to the elimination of the current global energy and climate change challenges. However, its production has been studied by the diverse catalytic systems. Metal oxide-based heterogeneous acid catalysts exhibit superior properties such as excellent reactivity, high thermal stability, resistance to free fatty acids and water, and reusability. Hence, the development of highly efficient and stable metal oxide-based heterogeneous acid catalysts is essential for future industrial applications. This review systematically explores recent developments in the production of biodiesel using metal oxide-based heterogeneous acid catalysts. The catalyst design and preparation, structural and physicochemical properties, operating reaction conditions, and catalytic behaviors of metal oxide-based heterogeneous acid catalysts, including sulfated metal oxide catalysts, different metal oxide-based acid catalysts, mixed metal oxide-based acid catalysts, and MOF-derived metal oxide-based catalysts, are discussed. Finally, the review concludes with guidance on the rational design of metal oxide-based heterogeneous acid catalysts for eco-friendly and cost-effective biodiesel production and puts forward the current research challenges and future development perspectives, aiming to promote innovation in large-scale industrial biodiesel production.

Chapter 16 - Sustainable production of biodiesel over heterogeneous acid catalysts

Heteropoly acids as supported solid acid catalysts for sustainable biodiesel production using vegetable oils: A review

Recent trends in sustainable biodiesel production using heterogeneous nanocatalysts: Function of supports, promoters, synthesis techniques, reaction mechanism, and kinetics and thermodynamic studies

Sulfonated carbon: synthesis, properties and production of biodiesel

Current status and challenges in the heterogeneous catalysis for biodiesel production

The relevance of heterogeneous catalysis in biodiesel production cannot be overemphasized, as heterogeneous catalysts have eliminated the demerits associated with a homogeneous catalysts. Some heterogeneous catalysts experience drawbacks such as partial recoverability and reusability, energy and waste conservation issues during biodiesel processing and leaching of active catalyst sites. This paper highlights and summarizes several heterogeneous catalysts used in biodiesel production. The catalyst preparation, reaction conditions, feedstock, and biodiesel yield for the heterogeneous base and acid catalysts were emphasized. The inability of heterogeneous base catalysts to trans-esterify low-grade oil with high free fatty acid (FFA) is a primary concern; the cost of processing low-grade oil with high FFA using heterogeneous acid catalysts is also a big issue. Nano-doped heterogeneous catalysts with unique properties were recommended because they can process oil with high FFA transesterification, improve reaction efficiency, simplify production, reduce the leaching of active sites, enable better biodiesel yield by minimizing energy and waste, and increase catalyst recoverability, activity, selectivity and durability.

Recently, numerous advances were reported in the creation of efficient and low-cost heterogeneous catalysts for the transesterification reactions of triglyceride molecules to decrease the overall cost of biofuel production. The heterocatalytic transesterification process has been recognized to be the most emerging approach in biodiesel synthesis as a result of its ease of use and low price. The unique characteristics of seven different kinds of heterogeneous catalysts, containing heteropolyacid, zeolite-based catalyst, layered-double-hydroxide-based catalyst, graphene, graphene oxide, activated carbon, biomass and non-biomass waste materials, and finally metal- and metal-oxide-based catalysts that are frequently employed in current biodiesel research, have undergone extensive studies. The emphasis is on multipurpose catalysts, which have high catalytic efficiency and low production cost because they create biofuel that is more applicable, effective, and eco-friendly. This review highlighted significant factors affecting the efficiency of heterogeneous catalysts, discussed the reaction parameters that affect biofuel production from various vegetable oil feedstocks, also mentioned the reaction mechanism of biodiesel production using heterogeneous catalysts, and last debated process opportunities and challenges that could stimulate future exploration.

Towards sustainable biodiesel and chemical production: Multifunctional use of heterogeneous catalyst from littered Tectona grandis leaves

Comparative analysis of the application of artificial neural network-genetic algorithm and response surface methods-desirability function for predicting the optimal conditions for biodiesel synthesis from chrysophyllum albidum seed oil

Sustainable biodiesel production from waste cooking oil utilizing waste ostrich (Struthio camelus) bones derived heterogeneous catalyst

Sustainable biodiesel production from waste cooking oil using banana peel biochar-Fe2O3/Fe2K6O5 magnetic catalyst

Advancement in utilization of nanomaterials as efficient and recyclable solid catalyst for biodiesel synthesis