Kinetic and Thermodynamic Analysis of Algal Lipid Extraction and Physicochemical Characterization for Biodiesel...

Marine macroalgae such as Ulva lactuca are a rich source of lipid, offering a renewable, nonedible biomass for clean energy conversion. These biological macromolecules exhibit structural diversity and functional properties that make them suitable feedstocks for biodiesel production. However, efficient utilization is hindered by a limited understanding of their extraction kinetics and thermodynamic behavior under process conditions. This study investigates the apparent extraction kinetics and thermodynamic behavior of lipids from Ulva lactuca using Soxhlet extraction, while evaluating their potential for biodiesel production. Soxhlet extraction was conducted using a methanol-hexane solvent system at varying temperatures (75-95 °C) and durations (60-360 min) for both ground (50-250 μm) and unground (>250 μm) samples. Results revealed that ground biomass exhibited higher lipid yields (5.04%) compared to unground biomass (4.06%). The extraction process followed a second-order kinetic model, indicating intraparticle diffusion behavior. Thermodynamic analysis indicated that the extraction process is endothermic and nonspontaneous, reflecting its strong dependence on temperature. FTIR analysis confirmed the presence of lipid-based functional groups in the extract. Physicochemical characterization showed an acid value of 19.16 mg KOH/g, an iodine value of 56.01 g I₂/100 g, and a kinematic viscosity of 12.1 mm² /s. These findings highlight the potential of Ulva lactuca lipids as a renewable resource for biodiesel production, although further pretreatment is required to meet fuel quality standards.