Optimization of parameters in using two different approaches for palladium-based spent catalysts (ethylene synthesis process) regeneration: supercritical carbon dioxide based extraction process and thermal process

The application of supercritical fluid (SF)-based technologies for catalyst activation has gained increased attention during the past two decades. Respecting this attention, the current investigation seeks to find the optimum operating conditions for activation of Palladium- based spent catalysts. The results indicate that the optimum operating conditions, based on changing one factor at a time (design of experiment approach), are: 45 degrees C and 220 bar for, respectively, extraction temperature and pressure, 80 min for static time and 0.14 cm(3)/s for CO2 flow rate leading catalyst activation up to 97.62% (active area of regenerated catalyst/ active area of fresh catalyst) based on BET analysis. Additionally, the thermal process including heated nitrogen, steam, and a combination of air and steam were examined to find whether or not it is possible to regenerate the deactivated catalyst. The results reveal the optimum conditions of 2.5 bar and 550 degrees C for pressure and temperature with regeneration efficiency of 97.46% (active area of regenerated catalyst/active area of fresh catalyst) based on BET analysis. Finally, the regenerated catalysts were further analyzed by BET, SEM, XRD, and XRF analyses which revealed the efficiency of both SC-CO2 and optimized thermal methods for catalyst activation through industrial purposes.