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

Abstract 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 to 60 °C), pressure (8 MPa to 16 MPa), CO2 flow rate (20 mL min–1 to 40 mL min–1), and time (15 min to 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 to 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.