Potassium catalysis in air gasification of cellulosic chars

Chars have been prepared by pyrolysis in nitrogen and helium of carboxymethyl cellulose (CMC) that has been ion-exchanged with potassium ions and of cellulose in which potassium acetate has been sorbed from aqueous solution. The chars were gasified in air and the gasification rates determined by rate of weight loss. The gasification rates at constant temperature showed a ‘normal’ dependence on heat treatment temperature (HTT) (i.e. decrease with increasing HTT) for potassium-free samples, but in all potassium-containing samples the gasification rate increased with HTT above 650 °C. This increase was especially dramatic for chars from ion-exchanged CMC. Some preliminary investigations have been made of the chemical nature of the potassium species below and above the inflection temperature (650 °C) and the possible changes in the state of the catalyst with HTT are discussed.