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|a This research was focused on green solid-liquid extraction (SLE), one of the most crucial stages for the upstream phytochemical processing because the extracted product would affect the quality of finished product. The influence of process variables for green SLE of andrographolide from Andrographis paniculata (AP) was investigated through exploratory experimentation using a 2 complete factorial experimental design, and a rotatable central composite design (RCCD). The main and interaction effects of the solid-liquid ratio (1/50 - 5/50 mg/L), average particle size (0.175 - 1.200 mm), time (5 - 25 minutes), and temperature (80 - 120 °C) were examined. The process was studied under isothermal condition at 80°C, and other temperatures; 100 °C and 120 °C in a pressurized liquid extractor using water as the greenest solvent. The multiple objectives for the green SLE of andrographolide from AP were simultaneously optimized using the RCCD technique coupled with desirability and penalty functions based on the concepts of extraction yield, and new developed techniques for extraction selectivity of andrographolide. The extraction kinetics was found to follow the second-order rate law. As the particle size decreases and solid-liquid ratio increases, the observed specific extraction rate constant, kobs, and the initial rate of solid-liquid extraction of andrographolide, rB0 significantly increase. It was found at 80 °C that kobs increased to nearly twofold from 0.000653 to 0.00128 Lmg-1min-1 for the solid-liquid ratio of 1:10 g/mL when particle size was decreased from 1.200 to 0.175 mm. Besides, it increased to more than fivefold, 0.00344 Lmg-1min-1 and virtually fourfold, 0.00496 Lmg-1min-1 for particle sizes of 1.200 and 0.175 mm, respectively when the solid-liquid ratio was increased to 1:50 g/mL. kobs increased for a solid-liquid ratio of 1:10 g/mL to more than 143 times, 1.10 X 10-1 Lmg-1min-1 and nearly 221 times, 7.22 X 10-1 Lmg-1min-1 for a solidliquid ratio of 1:50 g/mL when temperature was raised from 80 °C to 100 °C, and 120 °C. Hence, kobs, and the activation energy, Ea significantly increased with a decrease in particle size and an increase in solid-liquid ratio and temperature.
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