Potassium catalyst recovery process and performance evaluation of the recovered catalyst in the K2CO3-catalyzed steam gasification system

In this study, after conducting K2CO3-catalyzed steam gasification in a bench-scale bubbling fluidized bed reactor, the bench-scale recovery process of potassium catalyst was investigated by changing washing methods and operating parameters. The optimal potassium catalyst recovery efficiency (ηK) from MSJ gasified residue was 87.62%, achieved by utilizing a combined washing method in which the first wash was performed with N2 limewater (0.25 mol ratio of Ca/K) and the last two washes were with CO2 water. The recovered potassium catalyst was re-loaded with MSJ coal and then was utilized for conducting the catalytic steam gasification in a lab-scale fixed bed reactor, in order to evaluate the performance of the recovered potassium catalyst from both experimental and kinetic aspects. Compared with the results obtained from fresh K2CO3, not only the trends of carbon conversion (XC) were similar at each gasifying temperature, but also there was no obvious difference in volume percentage of gases produced. When the random pore model (RPM) was adopted, both reaction rate constant (kRPM) and activation energy (Ea) remained similar. In addition, the lifecycle of the recovered potassium catalyst was studied. Finally, it can be concluded that the potassium catalyst was effectively and efficiently recovered from gasified residue and the recovered potassium catalyst had the same catalytic activity as fresh K2CO3, promoting the commercialization and development of the catalytic gasification process.