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

Supercritical carbon dioxide (scCO(2)) 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 scCO(2) drying technique, were tested. In the constant pressure scCO(2) drying technique, the effects of varying the drying parameters, namely, the temperature (40 degrees C-60 degrees 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 scCO(2) 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 scCO(2) drying technique were 60 degrees 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 scCO(2) drying technique within only 37 min at 60 degrees 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 scCO(2) drying was approximately half that of oven drying. (C) 2020 Elsevier B.V. All rights reserved.