Impact of particle size and catalyst dispersion on gasification rates measured in a thermogravimetric analysis unit: Case study of carbon black catalyzed by potassium or calcium

摘要

Gasification is often studied in the laboratory using a thermogravimetric analysis (TGA) unit with less than 1 g of sample in order to obtain intrinsic rates. Many studies, however, neglect to consider the impact of particle size, of both the gasification feed and the catalyst, and catalyst dispersion on the measured rates. The impact of these factors was demonstrated using catalytic gasification of carbon black, an ash-free feed, as a case study, with K2CO3 or CaCO3 as catalysts at 850 degrees C in a CO2 atmosphere. Hand-mixing and ball-milling were used to alter the initial parameters. Ball-milling reduced both the particle size of both species and increased the catalyst dispersion, resulting in higher interfacial areas and gasification rates than hand-mixing. The changes in gasification kinetics were estimated by modeling the rates using the random pore and extended random pore models (RPM and eRPM, respectively). The impact of the interfacial contact area between carbon and catalysts (varied by particle size and mixing method) was dependent on the activity of the catalyst with the more active (potassium) catalyst being less affected. CaCO3 was found to sinter at 850 degrees C, reducing available catalytic surface area and blocking CO2 access to the carbon feed. It is recommended to consider these factors in future studies and to always report the particle sizes used.