MICROCALORIMETRIC STUDY OF OXYGEN-ADSORPTION ON CATALYTICALLY PROMOTED GASIFICATION CHARS

The interaction between oxygen and the surface of raw and catalytically promoted (potassium or calcium) bituminous coal chars was studied using a novel true differential calorimeter. Results clearly indicated that on potassium-promoted chars, oxygen adsorbs onto a thin layer of partially oxidized potassium. Also the oxygen uptake on potassium-promoted chars was found to be much greater than on calcium or unpromoted chars. This supports the view that potassium "spreads" on char surfaces. In contrast, these calorimetric results and the results of parallel XRD studies suggest that on demineralized bituminous coal calcium sinters and alloys with residual sulfur to produce relatively inactive catalysts. These findings strongly support one earlier model of potassium-promoted coal char reactivity: potassium catalyzes char gasification through a process in which a thin partially oxidized potassium film is alternately oxidized by the gas and reduced by the char. © 1991.