Journal of Energy Bioscience 2024, Vol.15, No.4, 243-254 http://bioscipublisher.com/index.php/jeb 246 3.4 By-products of palm oil processing Palm oil processing generates several by-products, including palm kernel (PK), mesocarp fiber (MF), and palm kernel shell (PKS). These by-products have significant energy value and can be utilized to improve the overall efficiency of the production process. For example, the energy value of empty fruit bunch (EFB), MF, and PKS can be harnessed to reduce energy losses associated with different processing routes. The industrial route, while having high throughput and producing high-quality crude palm oil (CPO), is associated with higher fruit losses and energy losses compared to small-scale routes (Anyaoha et al., 2018). Proper management and utilization of these by-products can enhance the sustainability of palm oil production. By integrating advanced harvesting and processing techniques, along with stringent quality control measures and efficient by-product management, the palm oil industry can achieve higher yields, better oil quality, and improved sustainability. 4 Conversion of Palm Oil to Biodiesel 4.1 Chemical composition of palm oil relevant to biodiesel Palm oil is a highly suitable feedstock for biodiesel production due to its high content of free fatty acids (FFAs) and triglycerides. The primary fatty acids present in palm oil include palmitic acid, oleic acid, linoleic acid, and stearic acid. These components are crucial for the transesterification process, which converts these fatty acids into fatty acid methyl esters (FAMEs), the main constituents of biodiesel (Ding et al., 2018; Phromphithak et al., 2020). 4.2 Transesterification process The transesterification process is the most common method for converting palm oil into biodiesel. This chemical reaction involves the conversion of triglycerides in palm oil into FAMEs and glycerol by reacting with an alcohol, typically methanol, in the presence of a catalyst. The process can be enhanced using various techniques such as microwave irradiation, which significantly reduces reaction time and increases yield (Ding et al., 2018; Phromphithak et al., 2020). For instance, using microwave irradiation with acidic imidazolium ionic liquids as catalysts has shown to achieve a maximal yield of 98.93% under optimized conditions (Ding et al., 2018). 4.3 Catalysts used in biodiesel production Several types of catalysts are employed in the transesterification of palm oil, including homogeneous, heterogeneous, and enzymatic catalysts. Homogeneous catalysts like sodium hydroxide (NaOH) are commonly used due to their high efficiency, but they pose challenges in separation and purification of the final product (Chinglenthoiba et al., 2020). Heterogeneous catalysts, such as those derived from natural materials like clinoptilolite doped with Na+ ions, offer advantages in terms of reusability and environmental impact (Abukhadra et al., 2021). Additionally, novel catalysts like Na+/K+ trapped muscovite/phillipsite composites have shown high effectiveness, achieving biodiesel yields up to 97.8% under ultrasonic irradiation (Abukhadra et al., 2019). Enzymatic catalysts, particularly lipases, are also gaining attention due to their specificity and mild reaction conditions, although they are generally more expensive (Moazeni et al., 2019). 4.4 Yield and efficiency of palm oil-based biodiesel The yield and efficiency of biodiesel production from palm oil can vary significantly based on the catalyst and process conditions used. For example, using a Na+/Clino nanocatalyst, a biodiesel yield of 96.4% was achieved under optimized conditions (Abukhadra et al., 2021). Similarly, a calcium-modified Zn-Ce/Al2O3 catalyst achieved a yield of 99.41% under specific conditions optimized by response surface methodology (Qu et al., 2021). These high yields demonstrate the potential of palm oil as an efficient feedstock for biodiesel production. 4.5 Comparison with other biodiesel feedstocks Palm oil is often compared with other biodiesel feedstocks such as waste cooking oil, pequi bio-oil, and hybrid feedstocks. Waste cooking oil, for instance, is a cost-effective and sustainable alternative, but it often requires extensive pre-treatment to reduce impurities and FFAs (Milano et al., 2018; Bhatia et al., 2020). Pequi bio-oil has
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