Valorisation of Non-Citrus Lignocellulosic Leaf Waste for Limonene Production Using Calcium Hydroxide-Catalysed Thermal Ethanolysis

• Haruina IBRAHIM

  Author

• Abubakar M. ALI

  Author

• Mohammed D. JIBRIN

  Author

The increasing demand for sustainable and renewable sources of industrial chemicals has intensified interest in the valorisation of lignocellulosic biomass into value-added products such as monoterpenes. This study investigates the production of limonene from Gmelina arborea leaf waste via a calcium hydroxide–catalysed thermal Ethanolytic process operated under mild conditions. A three-factor Box–Behnken design within the framework of Response Surface Methodology (RSM) was employed to evaluate the effects of reaction temperature (40-60 ^oC), reaction time (40–60 min), and catalyst loading (1-2 wt.%) on limonene yield, and to develop a predictive quadratic model for process optimisation. Experimental results revealed significant variation in limonene yield (18.75-351.07 mg/g), with a maximum yield of 6.78% (351.07 mg/g) achieved at 40 ^oC, 50 min, and 2% catalyst loading. Analysis of variance (ANOVA) indicated that the model was highly significant (p < 0.0001) with a high coefficient of determination (R² = 0.974), confirming strong agreement between experimental and predicted values. All process variables exhibited significant linear and quadratic effects, while interaction effects between temperature–time and temperature–catalyst loading were also notable. Reproducibility assessment using replicated centre-points yielded a low coefficient of variation (CV = 2.25%), demonstrating excellent experimental precision and reliability. GC-MS analysis confirmed the successful formation of limonene, while the results showed that lower temperatures favour product stability by minimising thermal degradation and volatilisation losses. Although the yield is lower than that obtained from citrus-derived sources, this study demonstrates the technical feasibility of producing limonene from non-citrus lignocellulosic biomass using a low-energy catalytic process. The findings highlight the potential of Gmelina arborea leaves as an alternative renewable feedstock and contribute to advancing sustainable biomass conversion strategies within a circular bioeconomy framework.

• 61_Ibrahim et al. (2026)

Copyright (c) 2026 Haruina IBRAHIM, Abubakar M. ALI, Mohammed D. JIBRIN (Author)

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