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Exploring Sustainable Biofuel Sources: A Comprehensive Overview

1.1 Introduction

The world’s population is expected to increase to over nine billion people by 2050 [1], which will put enormous pressure on the world's energy reserves and accelerate their depletion [2, 3]. Fossil fuel combustion increases greenhouse gas (GHG) emissions, which has a negative impact on the environment [4]. Due to rapid industrialization and rising living standards, primary global energy consumption has increased over the past few decades [5]. For a decent standard of living, developing nations need a significant amount of energy. Currently, the world is made up of fossil fuels majorly gas, oil and coal, oil, and gas with the percentage of 80 approximately. The carbon emissions from these fuels account for approximately 98% [6, 7]. It is crucial to incorporate more renewable energy into the global energy mix to keep the surface temperature high to approximately 1.5 °C above preindustrial levels [8].

In the face of scarce resources, particularly water, and the ever‐growing energy demand, alternative fuels emerge as the most feasible path forward [9]. Researchers are actively pursuing alternatives to meet this demand [10] aiming to address climate change impacts and fossil fuel dependence. Due to their potential to reduce GHG and the climate impacts related to transportation, biofuels are gaining more and more attention on national and international levels [11]. Utilizing bioenergy and/or biofuels offers a viable strategy for the production of renewable energy and low‐cost synthesis [3]. Among biofuels, biodiesel has drawn significant interest due to its potential advantages over conventional fossil fuels and its adaptability in terms of feedstock.

1.1.1 Comprehensive View of the State of Biodiesel, Feedstocks, and Production

Biodiesel has numerous advantages with attributes like sulfur‐free content, adequate oxygen composition, ease of manufacturing, and reduced GHG emissions [12]. It is biodegradable [13], environmentally sustainable [14], nontoxic [15], efficient, and possesses low sulfur and aromatic content [16]. In addition, its higher flash point ensures safer transportation and storage compared to conventional diesel. By leveraging these valuable traits and the varied feedstock spectrum, ranging from waste frying oils to affordable nonedible sources, biodiesel holds substantial potential as an alternative fuel [17]. Positioned as an economical alternative, biodiesel offers promise in reducing global reliance on imported petroleum products. This chapter further delves into diverse biofuels and biomass resources that could potentially serve as biodiesel feedstocks. Supplementary chapters of this book will explore their properties, production procedures, factors influencing biodiesel synthesis, catalyst utilization, and other interesting area. Presentation of the comprehensive view of the state of biodiesel production and its associated prospects is further exposed.

1.2 Biofuels Generation and Types

Based on the sources and the materials used in their production, biofuels are divided into four generations. The traits of each generation of biofuels are presented below, with each generation representing a distinct method of biofuel production.

1.2.1 The First Generation

First‐generation biofuels, which are regarded as conventional, are mainly made from two categories of edible feedstocks: sources based on starch (such as corn, wheat, barley, and potatoes) and sources based on sugar (such as sugarcane and sugar beetroot) [18]. Despite being easily accessible and convertible, these feedstocks are of great concern because they may result in a decrease in the world's food supply and their use them for agricultural purposes other than food production. Environmental concerns are exacerbated by the use of fertilizers and pesticides [11].

1.2.2 The Second Generation

The discussion surrounding the conflict between food and energy has sparked interest in second‐generation biofuels using inedible sources like lignocellulosic biomass. Carbohydrates from various biomaterials, including trees, grasses, and agricultural waste, fall under this category [19]. These feedstocks have the advantage of requiring less agricultural land and edible plants [20]. Biomass exhibits the potential to stimulate the economy, improve energy security, and reduce GHG emissions [21].

1.2.3 The Third Generation

Waste oil and Algal biomass are the main sources of third‐generation biofuels. These have benefits like faster growth rates, less reliance on farmland, more oil content, and less impact on food supplies. For the production of third‐generation biodiesel, significant feedstocks include fish oil, microalgae, animal fat, and used cooking oil [22]. Utilizing algal biomass results in significantly higher yields of biofuel, but it is more expensive due to the processing requirements. Due to its quick cultivation time and high protein, carbohydrate, and lipid content, seaweed or macroalgae is equally gaining popularity [23].

1.2.4 The Fourth Generation

Fourth‐generation biofuels incorporate genetic engineering, molecular biology, and other approaches to optimize biofuel yield. Genetically modified algae, boasting enhanced lipid and carbohydrate content, represent the core of fourth‐generation biofuel production [24]. This approach targets increased biofuel production efficiency and yields through genetic manipulation. Cyanobacteria, micro‐, and macroalgae form the foundation of fourth‐generation feedstocks, demonstrating the potential for advanced biofuel synthesis [24].

Considering the generation of biofuels, it is important to note that the production of biodiesel is possible as considered in the available feedstock with oil content for the firstgeneration. The edible oils include palm, olive, mustard, soybean, and others. Figure 1.1 shows some vital feedstocks and their oil content. It has become more important to focus on identifying sustainable feedstocks for sustainable production of biodiesel in supplementary chapters.

1.3 Biomass Sources for the Production of Biodiesel

Fatty acid methyl ester (FAME) is a refined diesel fuel derived from a variety of biological sources, such as edible and nonedible oils, animal fats, and used cooking oil. FAME, which also stands for an oxygenated, organic, and environmentally friendly ester‐based oil composed of fats and oils, and also contains long‐chain fatty acid monoalkyl esters [2].

When considering factors like yield, price, composition, and purity, the choice of feedstock has a significant impact on the production of biodiesel. For example, while rapeseed and palm oil predominate in Europe and tropical areas, soybean dominates biodiesel production in the United States [25, 26]. This in‐depth analysis highlights the significance of choosing the right feedstock by exploring the unique characteristics each source adds to biodiesel, particularly when combined with petroleum diesel. Exploring higher blends, even those exceeding 20%, becomes increasingly important as biodiesel's popularity grows [2]. In the United States, soybean and canola oil are the main sources of biodiesel, with soybean accounting for close to 50% of the feedstock input [27].

Figure 1.1 The oil content of feedstocks for biodiesel synthesis.

1.4 Feasibility of Using Biofuels in Place of Traditional Fossil Fuels

Several important factors must be taken into consideration for biofuels to be a viable replacement for traditional fossil fuels. One of the primary considerations is the availability of feedstock, which includes various biomass sources such as crops, agricultural residues, algae, and waste oils. The feasibility also depends on the technological advancements in biofuel production processes, which encompass methods such as transesterification, pyrolysis, and hydrothermal liquefaction [28]. Evaluating the scalability of these processes to meet the energy demands of modern society is crucial for determining the feasibility of biofuel adoption. In addition, factors such as energy efficiency, economic viability, and compatibility with existing infrastructure contribute to the overall feasibility assessment.

1.4.1 Environmental Impact of Biofuels

The environmental impact of biofuels compared to conventional fossil fuels is a central consideration in the transition toward sustainable energy sources. Biofuels have the potential to significantly reduce GHG emissions, contributing to the mitigation of climate change. While the combustion of biofuels releases carbon dioxide, the plants used as feedstock absorb CO2 during their growth, forming a closed carbon cycle [28]. This contrasts with the open carbon cycle of fossil fuels, which release stored carbon into the atmosphere. However, the environmental impact of biofuels also depends on factors such as land use change, water consumption, and potential competition with food production [28]. Assessing the net environmental benefit requires a comprehensive analysis of these factors.

1.4.2 Potential Benefits of Biofuel...