Citation: Shafi, M.E.; Alsabi, H.A.; Almasoudi, S.H.; Mufti, F.A.M.; Alowaidi, S.A.; Alaswad, A.A. Catalytic Conversion of Jatropha curcas Oil to Biodiesel Using Mussel Shell-Derived Catalyst: Characterization, Stability, and Comparative Study. Inorganics 2024, 12, 109. https://doi.org/10.3390/ inorganics12040109 Academic Editors: Moris S. Eisen and Axel Klein Received: 1 March 2024 Revised: 31 March 2024 Accepted: 3 April 2024 Published: 8 April 2024 Copyright: © 2024 by the authors. Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (https:// creativecommons.org/licenses/by/ 4.0/). inorganics Article Catalytic Conversion of Jatropha curcas Oil to Biodiesel Using Mussel Shell-Derived Catalyst: Characterization, Stability, and Comparative Study Manal E. Shafi 1, *, Halimah A. Alsabi 2 , Suad H. Almasoudi 3 , Faten A. M. Mufti 3 , Safaa A. Alowaidi 2 and Alaa A. Alaswad 4 1 Sustainable Agriculture Production Research Group, Department of Biological Sciences, Zoology, King Abdulaziz University, Jeddah 21589, Saudi Arabia 2 Department of Biology, Faculty of Sciences, King Abdulaziz University, Jeddah 21589, Saudi Arabia 3 Department of Biology, Faculty of Sciences, Umm Al-Qura University, Makkah 96612, Saudi Arabia 4 Department of Biological Sciences, Faculty of Sciences, University of Jeddah, Jeddah 21589, Saudi Arabia * Correspondence: meshafi@kau.edu.sa Abstract: Biodiesel represents a promising solution for sustainable energy needs, offering an eco- friendly alternative to conventional fossil fuels. In this research, we investigate the use of a catalyst derived from mussel shells to facilitate biodiesel production from Jatropha curcas oil. Our findings from X-ray Fluorescence (XRF) analysis emphasize the importance of carefully selecting calcination temperatures for mussel shell-based catalysts, with 1100 ◦ C identified as optimal for maximizing CaO content. We identify a reaction time of 6 h as potentially optimal, with a reaction temperature of approximately 110 ◦ C yielding the desired methyl ester composition. Notably, a methanol-to-oil ratio of 18:1 is the most favorable condition, and the optimal methyl ester composition is achieved at a calcined catalyst temperature of 900 ◦ C. We also assess the stability of the catalyst, demonstrating its potential for reuse up to five times. Additionally, a thorough analysis of J. curcas Methyl Ester (JCME) biodiesel properties confirmed compliance with industry standards, with variations attributed to the unique characteristics of JCME. Comparing homogeneous (NaOH) and heterogeneous (CaO) catalysts highlights the potential of environmentally sourced heterogeneous catalysts to replace their homogeneous counterparts while maintaining efficiency. Our study presents a novel approach to sustainable biodiesel production, outlining optimal conditions and catalyst stability and highlighting additional benefits compared with NaOH catalysts. Therefore, utilizing mussel shell waste for catalyst synthesis can efficiently eliminate waste and produce cost-effective catalysts. Keywords: Jatropha curcas oil; sustainable biodiesel production; optimization; stability; NaOH catalysts; CaO catalysts 1. Introduction Biodiesel, a promising and environmentally friendly alternative to conventional fos- sil fuels, plays a pivotal role in mitigating the environmental and economic challenges associated with petroleum-based fuels [1]. Renewable feedstocks, including vegetable oils and animal fats, undergo a chemical process known as transesterification to produce biodiesel [2]. It offers benefits such as reduced greenhouse gas emissions, enhanced air quality, and a potential reduction in dependence on finite fossil fuel resources [3,4]. The environmental benefits of biodiesel are primarily attributed to its lower carbon footprint, as it is widely considered a carbon-neutral fuel [5]. This is due to the carbon diox- ide (CO 2 ) released during its combustion being roughly equivalent to the CO 2 absorbed by the plants from which the feedstock was derived [6]. Moreover, biodiesel is biodegradable, less toxic, and produces lower sulphur and particulate matter emissions, enhancing its eco-friendly characteristics [6,7]. Inorganics 2024, 12, 109. https://doi.org/10.3390/inorganics12040109 https://www.mdpi.com/journal/inorganics