The simple integral desorption model was used to represent the physical phenomena of the extraction process.20 The extraction vessel is loaded with leaf particles with an initial andrographolide concentration of S0 (g/g leaf particles) to form a packed bed system. Fresh supercritical solvent is fed in to the bed, the pore and void volumes () are initially free of solute, and the process is isothermal. The total mass balance in the supercritical fluid phase of this system can be described by the following expression: α ∂C/∂t+u ∂C/∂z-α(D_z (∂^2 C)/(∂z^2 )+D_r (∂^2 C)/(∂r^2 ))=-(1-α) ∂S/∂t (1)
In spite of extraction vessel dimension with length to diameter ratio (L/D) = 10 <<100 with relatively high axial convective …show more content…
Therefore, the mass balance andrographolide in the dried leaf particles may be written by22 (4)
The initial condition is:
St,z = S0 (5)
The andrographolide concentration in the supercritical solvent (Ce) at the exit end of the extraction column can be calculated by solving equations (2) to (5), and is written by: (6)
Integrating Ce with respect with time will result the total amount of extracted andrographolide. Then, the yield of extracted andrographolide (F(t)) can be estimated using the equation below: (7)
The optimum values of desorption rate constant, kd (1/hour) for each experiment were found by selecting the optimum kd to minimize the sum of the squares of the difference between the extraction yields obtained from experiment (Fexp) and the calculation using the proposed model as given in equation (7) (Fcalc):
Min(SSE)=∑_1^n▒(F_calc-F_exp )^2 …show more content…
Results and Discussion
The A. paniculata dried leaf particles initially contained 2.03 × 10－3 g andrographolide per gram of dried leaf, which was close to those reported values in the literature.16, 18 In an attempt to investigate the effect of various operating parameters on the extraction rate, a set of experiments was performed using 0.375 mm dried leaf particles using supercritical fluid flow rate of 2 mL/minute.16 The results of the extraction of andrographolide using supercritical CO2–ethanol mixture are reported below.
Effect of ethanol
In spite of extraction vessel dimension with length to diameter ratio (L/D) = 10 <<100 with relatively high axial convective …show more content…
Therefore, the mass balance andrographolide in the dried leaf particles may be written by22 (4)
The initial condition is:
St,z = S0 (5)
The andrographolide concentration in the supercritical solvent (Ce) at the exit end of the extraction column can be calculated by solving equations (2) to (5), and is written by: (6)
Integrating Ce with respect with time will result the total amount of extracted andrographolide. Then, the yield of extracted andrographolide (F(t)) can be estimated using the equation below: (7)
The optimum values of desorption rate constant, kd (1/hour) for each experiment were found by selecting the optimum kd to minimize the sum of the squares of the difference between the extraction yields obtained from experiment (Fexp) and the calculation using the proposed model as given in equation (7) (Fcalc):
Min(SSE)=∑_1^n▒(F_calc-F_exp )^2 …show more content…
Results and Discussion
The A. paniculata dried leaf particles initially contained 2.03 × 10－3 g andrographolide per gram of dried leaf, which was close to those reported values in the literature.16, 18 In an attempt to investigate the effect of various operating parameters on the extraction rate, a set of experiments was performed using 0.375 mm dried leaf particles using supercritical fluid flow rate of 2 mL/minute.16 The results of the extraction of andrographolide using supercritical CO2–ethanol mixture are reported below.
Effect of ethanol