Supercritical antisolvent precipitation of andrographolide from Andrographis paniculata extracts: Effect of pressure, temperature and CO2 flow rate

Andrographis paniculata extracts were precipitated using the so-called supercritical antisolvent (SAS) technique. Ethanol was used as the solvent and compressed CO2 as the antisolvent. The effects of process operating conditions (pressure: 5–24 MPa, temperature: 308–328 K and CO2 flow rate: 0.5–1.5 g/min) on particle size and morphology of precipitated andrographolide were evaluated. X-ray diffraction (XRD) patterns showed significant changes in andrographolide morphology depending on process operating conditions; both column-like and slice-like crystals were observed depending on operating conditions. Crystals with mean diameters of 3.30–228.35 μm were produced, smaller crystals were obtained at high pressure, low temperature and high CO2 flow rate and vice versa for large crystals. In addition, SAS process also produced high precipitation yields, since solubility of andrographolide is small in the supercritical CO2 plus ethanol. When operating under subcritical conditions, amorphous particles were produced.