The catalytic gasification of carbon
The catalytic interaction of potassium salts in the reaction of carbon with oxygen and carbon dioxide has been studied with the aim of elucidating the mechanism of the reaction. In order to achieve this the approach used has been to utilise a wide variety of physical techniques in order to identify the active species. These range from bulk in-situ techniques like X-ray diffraction and thermogravimetric analysis to surface sensitive techniques like photoelectron spectroscopy and scanning electron microscopy. Experimental apparatus was also developed that enabled thermogravimetric analysis of samples to be carried out with mass spectra analysis of gaseous products formed. These techniques enabled the behaviour of K2CO3 with and without the presence of carbon to be characterised over a wide range of temperatures and under inert and reactive atmospheres. This showed that at room temperature K2CO3 would readily react with the atmosphere to form hydrated carbonate as well as KHCO3 however upon heating to above 100oC these phases would decompose to leave K2CO3. This phase remained upto 600oC where decomposition started. The decomposition products evaporated from the solids as CO2 and K2O or K. The presence of K2CO3 enhanced the reaction of graphite with O2 and CO2. C8K and residually intercalated C8K were used as model compounds to aid the identification of the active potassium species present during gasification. This showed K intercalates and K metal to be unstable under gasification conditions and therefore played no role in the mechanism of catalytic gasification. Photoelectron spectroscopy identified C-O-K and carbon oxides to be the predominant surface species present during gasification, while scanning electron microscopy revealed that in general graphite gasification occurred along the prismatic plane, however gasification on the basal plane took place if a fine disperson of catalyst occurred in the graphite surface.