The Impact of Reusing Commercial Hydrated Lime as a Heterogeneous Catalyst on the Fatty Acid Methyl Esters Content and its Characteristics in The Methanolysis Process of Rapeseed Oil

Abstract

This study investigates the impact of reusing commercial hydrated lime as a heterogeneous catalyst on the yield of fatty acid methyl esters (FAME) and its characteristics in the methanolysis process of rapeseed oil. The reuse evaluation was conducted by performing consecutive methanolysis reactions up to three times under optimal reaction conditions. Characterization of both unused (fresh) and used catalyst (after the first use and third reuse) was carried out using XRD and SEM/EDS methods, in order to examine structural and morphological changes associated with the catalytic activity of hydrated lime. After the first, second, and third consecutive reuses of comercial hydrated lime under optimal methanolysis conditions, FAME yields of 95.46%, 93.92%, and 80.01%, respectively, were achieved. These yields fall below the minimum requirement set by the EN 14214 standard but meet the specifications of the American D6751 standard for biodiesel fuel blends. Therefore, repeated use of hydrated lime reduces its catalytic activity, resulting in lower FAME yields compared to the yield obtained with fresh catalyst (96.7%). It was demonstrated that the extent of catalytic activity reduction is not necessarily correlated with the number of reuses, but also depends on the chemical, structural, and textural properties of the catalyst. XRD analysis of the catalyst after the first use and third reuse revealed the formation of a new crystalline phase, calcium diglyceroxide (C₆H₁₄CaO₆), identified as the primary crystalline phase, along with Ca(OH)₂ and CaCO₃ as secondary crystalline phases.