Anion effects in alkali-catalysed steam gasification

Abstract

Many alkali metal salts are good catalysts for gasification of carbon. Generally, the activity of alkali metal salts increase with the size of the cation, from litium to caesium, but the associated anion can influence activity more than the cation. It is proposed that some anions can compete with the char for the alkali cations and thus inhibit the formation of an alkali-carbon complex which is believed to be the active gasification site. Techniques are described which alter this balance and activate salts which are normally poor catalysts. The activation, by hydrolysis, of relatively inactive chlorides was used to estimate the tendency of the alkalis and alkaline earths to form carbon complexes. Free energies of formation were determined and used to explain the inhibiting effects of CO 2 in catalysed steam gasification of coal char.