Browsing by Author "Kahimbi, Henry"

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Insights into antioxidant dosage determination for improving biodiesel oxidation stability: a comprehensive review
(Tylor & Francis Online, 2024-10-10) Kahimbi, Henry; Kichonge, Baraka; Kivevele, Thomas
Concerns about energy security and environmental sustainability have increased the preference for renewable energy sources. Biodiesel, a renewable alternative to conventional diesel, has gained interest as a potential solution. However, biodiesel’s stability during storage and susceptibility to oxidation are significant challenges. Antioxidants are essential to enhance biodiesel’s oxidation stability, ensuring fuel quality and sustainability. While various studies have examined the effects of different antioxidant concentrations on biodiesel oxidation stability on trial and error bases, a consensus on the most effective dosage range has yet to be established. This review emphasizes the importance of predictive models for estimating antioxidant amounts in biodiesel. Using mathematical formulations, statistical analyses, and computational simulations, predictive models offer efficient and accurate approaches to understanding the complex relationships between antioxidants, biodiesel properties, and oxidation stability. The review examines the link between antioxidants and biodiesel stability, discusses predictive models’ role in determining optimal antioxidant dosages, and identifies factors influencing these decisions. It also highlights the limitations of predictive models and suggests future research directions. The conclusion is that systematically integrating data-driven strategies through predictive models facilitates the cost-effective optimization of antioxidant dosages, advancing high-quality and sustainable biodiesel.
Kinetics and energetics of biodiesel oxidation stability: The impact of Uapaca kirkiana-derived natural antioxidants
(John Wiley & Sons, Ltd., 2025-03) Kahimbi, Henry; Kichonge, Baraka; Kivevele, Thomas
Despite considerable progress in understanding biodiesel autoxidation inhibition, the kinetics and energetics of the inhibition reactions involving natural antioxidants remain underexplored. Most existing research on natural antioxidants has focused on enhancing oxidation stability and other fuel properties. This study aimed to investigate the oxidative stability of croton biodiesel (CBD) and assess the kinetics and energetics of natural antioxidants derived from the roots, pulp, and fruit peels of the Uapaca kirkiana plant. The oxidation stability of biodiesel samples was assessed using the OXITEST method at temperatures of 90, 100, 110, and 120 °C. These tests enabled the calculation of kinetic parameters such as reaction rates and activation energies, crucial for understanding the inhibition role of antioxidants during oxidative degradation. Activation energy for antioxidant consumption, determined using the Arrhenius equation, was found to be 81.39 kJ mol−1 for fruit peel extracts, 77.73 kJ mol−1 for pulp extracts, and 63.85 kJ mol−1 for root bark extracts. The higher activation energy for fruit peel extracts suggests that they are more effective at preventing oxidation, especially under high-temperature conditions. Enthalpy, entropy, and Gibbs free energy parameters were calculated using the Eyring equation, indicating a nonspontaneous endothermic process for the antioxidant samples. The study found an inverse relationship between antioxidant concentration and rate constants, demonstrating the antioxidants' effectiveness in slowing down the oxidation process. These kinetics and energetics analyses provide detailed insights into how antioxidants function, facilitating the optimization, selection, and validation of their efficiency in stabilizing biodiesel.
Kinetics and energetics of biodiesel oxidation stability: The impact of Uapaca kirkiana-derived natural antioxidants
(John Wiley & Sons, Ltd., 2025-03) Kahimbi, Henry; Kichonge, Baraka; Kivevele, Thomas
Despite considerable progress in understanding biodiesel autoxidation inhibition, the kinetics and energetics of the inhibition reactions involving natural antioxidants remain underexplored. Most existing research on natural antioxidants has focused on enhancing oxidation stability and other fuel properties. This study aimed to investigate the oxidative stability of croton biodiesel (CBD) and assess the kinetics and energetics of natural antioxidants derived from the roots, pulp, and fruit peels of the Uapaca kirkiana plant. The oxidation stability of biodiesel samples was assessed using the OXITEST method at temperatures of 90, 100, 110, and 120 °C. These tests enabled the calculation of kinetic parameters such as reaction rates and activation energies, crucial for understanding the inhibition role of antioxidants during oxidative degradation. Activation energy for antioxidant consumption, determined using the Arrhenius equation, was found to be 81.39 kJ mol−1 for fruit peel extracts, 77.73 kJ mol−1 for pulp extracts, and 63.85 kJ mol−1 for root bark extracts. The higher activation energy for fruit peel extracts suggests that they are more effective at preventing oxidation, especially under high-temperature conditions. Enthalpy, entropy, and Gibbs free energy parameters were calculated using the Eyring equation, indicating a nonspontaneous endothermic process for the antioxidant samples. The study found an inverse relationship between antioxidant concentration and rate constants, demonstrating the antioxidants' effectiveness in slowing down the oxidation process. These kinetics and energetics analyses provide detailed insights into how antioxidants function, facilitating the optimization, selection, and validation of their efficiency in stabilizing biodiesel.
Kinetics and energetics of biodiesel oxidation stability: The impact of Uapaca kirkiana-derived natural antioxidants
(John Wiley & Sons, Ltd., 2025-03) Kahimbi, Henry; Kichonge, Baraka; Kivevele, Thomas
Despite considerable progress in understanding biodiesel autoxidation inhibition, the kinetics and energetics of the inhibition reactions involving natural antioxidants remain underexplored. Most existing research on natural antioxidants has focused on enhancing oxidation stability and other fuel properties. This study aimed to investigate the oxidative stability of croton biodiesel (CBD) and assess the kinetics and energetics of natural antioxidants derived from the roots, pulp, and fruit peels of the Uapaca kirkiana plant. The oxidation stability of biodiesel samples was assessed using the OXITEST method at temperatures of 90, 100, 110, and 120 °C. These tests enabled the calculation of kinetic parameters such as reaction rates and activation energies, crucial for understanding the inhibition role of antioxidants during oxidative degradation. Activation energy for antioxidant consumption, determined using the Arrhenius equation, was found to be 81.39 kJ mol−1 for fruit peel extracts, 77.73 kJ mol−1 for pulp extracts, and 63.85 kJ mol−1 for root bark extracts. The higher activation energy for fruit peel extracts suggests that they are more effective at preventing oxidation, especially under high-temperature conditions. Enthalpy, entropy, and Gibbs free energy parameters were calculated using the Eyring equation, indicating a nonspontaneous endothermic process for the antioxidant samples. The study found an inverse relationship between antioxidant concentration and rate constants, demonstrating the antioxidants' effectiveness in slowing down the oxidation process. These kinetics and energetics analyses provide detailed insights into how antioxidants function, facilitating the optimization, selection, and validation of their efficiency in stabilizing biodiesel.
Natural Antioxidants For Biodiesel Stability: Predictive Modeling, Kinetics, And Economic Feasibility Of Uapaca Kirkiana Extracts
(NM-AIST, 2025-07) Kahimbi, Henry
Biodiesel, a renewable alternative fuel, is susceptible to oxidative degradation, impacting its performance, stability and shelf life. Traditional methods for optimizing antioxidant dosage have relied heavily on trial and error, leading to inconsistent results and increased costs. This study addresses these challenges by integrating experimental analysis with predictive modeling to evaluate and optimize the use of natural antioxidants extracted from Uapaca kirkiana fruit peels, pulp, stem barks, leaves and root bark. The research primarily focuses on enhancing oxidative stability during storage, where degradation is most likely to begin. Antioxidant potential was assessed through total phenolic content using the Folin–Ciocalteu method and antioxidant activity via 2,2-Diphenyl-1-picrylhydrazyl radical scavenging assays. A predictive model was developed in R software to estimate the optimal antioxidant dosage, using biodiesel's physical-chemical properties as predictors. Storage conditions such as temperature, light and oxygen exposure were standardized to isolate the effects of antioxidant concentration and biodiesel composition. Reaction kinetics were studied to understand antioxidant behavior and degradation pathways. Techno-economic analysis using Aspen Plus® V10 compared the cost-effectiveness of natural and synthetic antioxidants. Results showed that natural antioxidants particularly from fruit peels significantly improved biodiesel stability. Induction periods achieved were 23.9 hours for palm kernel, 21.6 for waste cooking oil, 14.6 for croton, 14.4 for jatropha, and 13.8 for neem seed, all exceeding the 8-hour minimum required by both EN 14112 and ASTM D6751 standards. Predictive model validation with seven biodiesel samples showed close agreement between theoretical and experimental induction periods, with mean absolute percentage errors between 1.69% and 2.44%. Kinetic analysis confirmed that natural antioxidants reduced oxidation rates, with activation energies of 81.39 kJ/mol (fruit peels), 77.73 kJ/mol (pulp), and 63.85 kJ/mol (root bark). The techno-economic analysis demonstrated that natural antioxidants especially from Uapaca kirkiana were not only more effective but also more economically viable, offering shorter payback periods (3.8–12 years) and higher internal rate of returns. In contrast, synthetic antioxidants like BHT and BHA showed negative net present values and longer payback times (11.7–17.8 years). These findings support the use of natural antioxidants as practical, eco-friendly alternatives to synthetic ones in enhancing fuel stability
The Potential of Underutilized Plant Resources and Agricultural Wastes for Enhancing Biodiesel Stability: The Role of Phenolic- Rich Natural Antioxidants
(Hindawi, 2023) Kahimbi, Henry; Kichonge, Baraka; Kivevele, Thomas
Growing concerns about energy security and environmental sustainability have fueled demand for sustainable and renewable energy sources in recent years. Biodiesel, a renewable alternative to conventional fuels, has gained significant attention as a potential source of energy. However, the stability of biodiesel during storage and its susceptibility to oxidation remain major challenges. To address these issues, researchers have turned their focus to the utilization of natural antioxidants. Studies on sources of natural antioxidants, particularly those made from waste, such as food, have been extensively conducted. However, there are still some restrictions, such as inconsistency in quality, the development of microbes, and difficulties with regulations, all of which have an impact on sustainability and the phenolic contents. Phenolic compounds are known for their excellent antioxidant properties and ability to inhibit the oxidation process. The review provides an overview of various underutilized plant resources and agricultural wastes that are rich in phenolic contents and demonstrate higher antioxidant activities, such as Vitex doniana, Uapaca kirkiana, Parinari curatellifolia, Tamarindus indica L, fruit peels, and crop residues. It discusses the extraction methods employed to obtain phenolic antioxidants from these sources and highlights their antioxidant activities. Additionally, the review examines the effects of phenolic antioxidants on key parameters, including induction period, peroxide value, acid value, and viscosity. The review concluded by highlighting the potential of underutilized plant resources and agricultural wastes as sustainable sources of phenolic-rich natural antioxidants for enhancing biodiesel stability. According to the literatures, phenolic antioxidants present in underutilized plant resources and agricultural wastes can chelate metal ions, scavenge free radicals, and break oxidation chain reactions, thereby preventing the degradation of biodiesel. Moreover, the limitation of the use of natural antioxidants in the stabilization of biodiesel like instability at high temperatures has been highlighted
Techno‐Economic Evaluation of Synthetic and Natural Antioxidants Used for Enhancing Oxidation Stability of Biodiesel
(sci, 2025-01-07) Kahimbi, Henry; Monge, Emmanuel; Kichonge, Baraka; Kivevele, Thomas
The oxidation stability of biodiesel is a critical factor affecting its storage and performance, necessitating the use of antioxidants to enhance its shelf life and reliability. Both natural and synthetic antioxidants have proven effective in improving the oxidation stability of biodiesel, with numerous studies demonstrating their ability to extend the induction period and delay oxidative degradation. However, while the technical efficacy of these antioxidants is well‐documented, the techno‐economic analysis that evaluates the cost‐effectiveness of using natural versus synthetic antioxidants remains unexplored. This creates uncertainty in selecting the most sustainable and economically viable antioxidant option. This study aimed to conduct a techno‐economic analysis comparing the cost‐effectiveness of synthetic and natural antioxidants in stabilizing biodiesel. The study evaluated synthetic antioxidants, specifically hydrogenated methoxy eugenol, and natural antioxidants derived from the methanolic extract of wild loquat plants, along with a comparison to commonly used synthetic antioxidants. Comprehensive simulations and modeling were conducted using Aspen Plus® V10 commercial simulation software in a block‐wise manner. The technical performance was assessed by considering the quantities and qualities of biodiesel, glycerol, and antioxidants. The synthetic antioxidant processes resulted in negative net present values and longer payback periods of 11.7 to 17.8 years, while natural antioxidants showed shorter payback periods ranging from 3.8 to 12 years. Natural antioxidants, particularly those extracted from clove wastes and wild loquat plant parts, demonstrated superior techno‐economic performance with the lowest operating and raw materials costs, shortest payback period, highest internal rate of return (IRR), and best profitability. Therefore, natural antioxidants are the most economically viable option for biodiesel stabilization, outperforming synthetic antioxidants in terms of operating costs, payback period, IRR, and profitability.