Supercritical carbon dioxide extraction of eugenol from tulsi leaves: Process optimization and packed bed characterization

Extraction of eugenol from dried tulsi leaves powder (Ocimum sanctum Linn.) of 'West Bengal origin' (Eastern India), Ram tulsi variety, was carried out using supercritical carbon dioxide (SC-CO2) extraction. The optimized parameters for highest yield of eugenol [2.96 mg (g dry tulsi leaves)−1] were 20 g of tulsi leaves powder (dp = 0.42 mm) extracted at 50 °C, 200 bar and 90 min extraction time at a constant flow rate of 2.5 L min−1 of gaseous CO2. Statistical analyses revealed that only extraction pressure showed significantly effect on the yield of eugenol. The extraction kinetics of eugenol from tulsi matrix followed first order kinetics (Higuchi model). Characterization of the packed bed of tulsi leaves was also carried out during steady and unsteady states of extraction and empirical correlations were developed among dimensionless Reynolds, Sherwood and Schmidt numbers. The correlation coefficients were found to be low owing to leaf mucilage which impeded extraction of eugenol from tulsi leaves.