Contemporary approaches towards augmentation of distinctive heterogeneous catalyst for sustainable biodiesel production

The excessive utilization of petroleum resources leads to global warming, crude oil price fluctuations, and the fast depletion of petroleum reserves. Biodiesel has gained importance over the last few years as a clean, sustainable, and renewable energy source. This review provides knowledge of biodiesel production via transesterification/esterification using different catalysts, their prospects, and their challenges. The intensive research on homogeneous chemical catalysts points to the challenges in using high free fatty acids containing oils, such as waste cooking oils and animal fats. The problems faced are soap formation and the difficulty in product separation. On the other hand, heterogeneous catalysts are more preferable in biodiesel synthesis due to their ease of separation and reusability. However, in-depth studies show the limited activity and selectivity issues. Using biomass waste-based catalysts can reduce the biodiesel production cost as the materials are readily available and cheap. The use of an enzymatic approach has gained precedence in recent times. Additionally, immobilization of these enzymes has also improved the statistics because of their excellent functional properties like easy separation and reusability. However, free/liquid lipases are also growing faster due to better mass transfer with reactants. Biocatalysts are exceptional in good selectivity and mild operational conditions, but attractive features are veiled with the operational costs. Nanocatalysts play a vital role in heterogeneous catalysis and lipase immobilization due to their excellent selectivity, reactivity, faster reaction rates owing to their higher surface area, and easy recovery from the products and reuse for several cycles.

Biodiesel (methyl esters) has been produced using numerous catalysts to enhance its quality and related productivity. Generally, the raw materials for biodiesel production and its catalysts significantly impact the produced biodiesel’s quality. In addition, the heterogeneous catalysts are promising as catalysts in the transesterification for biodiesel production and can be used continuously during this production. In particular, these catalysts are essential for green biodiesel production because of their high activity, thermal stability, and reusability. Hence, several homogeneous and heterogeneous (acidic and alkaline) catalysts for biodiesel production, particularly the naturally derived heterogeneous catalysts, are reviewed in this article. Further, the different heterogeneous catalysts for biodiesel production have been studied extensively as replacements for the respective homogeneous catalyst. Specifically, this replacement is aimed at the simultaneous esterification and transesterification of the nonedible and low-cost biomasses under moderate conditions producing biodiesel. Moreover, this study analyzes biodiesel’s impact and long-term performance in various applications. Finally, it also reports the advancements in biodiesel production in terms of the catalysts used in it and its processes to aid further developments in biodiesel production.

Biodiesel, which is an alternative renewable fuel, is defined as mono alkyl ester of long-chain fatty acids and has properties comparable to those of fossil-based diesel. Biodiesel can be produced from vegetable oils or animal fats. The most common method used to produce biodiesel is a reversible chemical reaction called transesterification. This reaction takes place either in the presence of catalysts at lower temperature and pressure or in the absence of catalysts at higher temperature and pressure in supercritical state. Catalyzed transesterification reaction is preferred in biodiesel production because of the moderate reaction conditions. Homogeneous base catalysis can be used in transesterification when fresh vegetable oil is used as a feedstock due to its low cost, high catalytic activity, and feasibility to operate at low temperatures. Homogeneous acid catalysis is a better choice when the feedstock contains higher amounts of free fatty acids (FFAs). Heterogeneous base and acid catalysis are preferred due to their easy separation from biodiesel, hence reducing number of product purification steps. However, heterogeneous catalysis is still under development and has a promising future in biodiesel industries. In this chapter, various acid- and base-catalyzed esterification and transesterification reactions are discussed, and recent trend in catalyst development is highlighted. It is recommended that a proper selection of catalyst is made in a transesterification reaction, depending largely on the type of feedstock.

The need for fossil fuels and the emissions generated from these fuels are increasing daily. Researchers are concerned with global warming as well as climate change; and energy sustainability and material usages are important issues today. Waste cooking oil (WCO) can be processed into biodiesel as an alternative fuel to replace diesel. Production of biodiesel using WCO as the feedstock has been of growing interest for the last two decades. A number of research papers related to the improvements in production, raw materials and catalyst selection have been published. This paper reviews the various types of heterogeneous solid catalyst in the production of biodiesel via the transesterification of WCO. The catalysts used can be classified according to their state presence in the transesterification reaction as homogeneous or heterogeneous catalysts. Homogeneous catalysts act in the same liquid phase as the reaction mixture, whereas heterogeneous catalysts act in a solid phase with the reaction mixture. Heterogeneous catalysts are non-corrosive, a green process and environmentally friendly. They can be recycled and used several times, thus offering a more economic pathway for biodiesel production. The advantages and drawbacks of these heterogeneous catalysts are presented. Future work focuses on the application of economically and environmentally friendly solid catalysts in the production of biodiesel using WCO as the raw material.

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.

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

Liquid fuel synthesis via CO2 hydrogenation by coupling homogeneous and heterogeneous catalysis

Current status and challenges in the heterogeneous catalysis for biodiesel production

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

Lignocellulosic Materials as the Potential Source of Catalyst

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.

Heterogeneous base catalysts: Synthesis and application for biodiesel production – A review

Recent advancement and prospective of heterogeneous carbonaceous catalysts in chemical and enzymatic transformation of biodiesel

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.

Advances in photocatalytic biodiesel production: Preparation methods, modifications and mechanisms