COPPER CATALYSIS IN THE AIR GASIFICATION OF CELLULOSIC CHARS

Cellulosic chars containing copper have been prepared by four different methods. An ion-exchanged substrate was prepared from carboxymethylcellulose in the cupric form (CuCMC), 'sorbed' celluloses were prepared by soaking in aqueous solutions of cupric acetate (CuCF11-1) and cupric chloride (CuCF11-2) respectively, and a dry physical mixture from cellulose fibres and finely ground cupric acetate (CuCF11-3). These doped cellulosic substrates were converted at various heat treatment temperatures (HTTs) to chars that were investigated by X-ray diffraction (XRD) and by gasification in air. The XRD investigation showed that the cupric ion is progressively reduced to cuprous and then to elemental copper during pyrolysis. The size of the copper crystallites, and hence the rate of gasification reaction under given conditions, are sensitive to the original mode of introduction of the cupric ions and to the HTTs. All of the chars exhibited a dramatic 'jump' in reactivity with increasing gasification temperatures, e.g. the initial rate of gasification may increase 350-fold for 5 °C temperature increase. This 'jump' is accompanied by a transition from a high activation energy region to a low activation energy region with increasing temperature. The causes of these effects are discussed. The 'jump' phenomenon is attributed to a sharp increase in mobility of the catalytic species at the 'jump' temperature. © 1990.