Ultrafast and complete drying of ecamsule solution using supercritical carbon dioxide with fluctuating pressure technique

Supercritical carbon dioxide (scCO₂) drying, a green and energy-efficient technology, was investigated for the extraction of ethanol from an ecamsule-ethanol solution and complete drying of the ecamsule powder. Two experimental designs, a constant pressure and a fluctuating pressure scCO₂ drying technique, were tested. In the constant pressure scCO₂ drying technique, the effects of varying the drying parameters, namely, the temperature (40 °C–60 °C), pressure (8 MPa–16 MPa), CO₂ flow rate (20 mL min^–1–40 mL min^–1), and time (15 min–180 min), on the efficiency of ethanol removal were investigated. The scCO₂ drying parameters were further analyzed using response surface methodology (RSM); based on the results of the RSM analysis, the optimum conditions for the constant pressure scCO₂ drying technique were 60 °C, 14.2 MPa, and 71.7 min, at which the minimal amount (0.23 wt%) of residual ethanol remained in the dried ecamsule powder. In contrast, near-complete removal of ethanol was achieved using the fluctuating pressure scCO₂ drying technique within only 37 min at 60 °C and 10 MPa–14 MPa with 60 pressure fluctuation cycles and a CO₂ flow rate of 40 mL min^–1. The physicochemical properties of the ecamsule powder dried using the fluctuating pressure CO₂-technique were similar to those of powder obtained using conventional oven drying. An energy analysis of the ecamsule drying process suggested that the energy required for scCO₂ drying was approximately half that of oven drying.