The role of potassium carbonate on cellulose pyrolysis

Cellulose pyrolysis with/without potassium carbonate (K2CO3) under relatively high heating rate was carried out to elucidate the role of alkali metals on wood pyrolysis. Gaseous species produced by wood pyrolysis were determined by TCD and FID gas chromatography. Tar was analyzed to quantify polycyclic aromatic hydrocarbons (PAHs) by GC/MS. Changes to the chemical bonds in the solid residue (char) were analyzed by 13C NMR and FTIR spectroscopies. With the addition of potassium carbonate, an increase in gaseous yield and a decrease in tar yield and a significant decrease in the initiation temperature of pyrolysis were observed. The saccharide structure in cellulose was preserved in the structure of char obtained from pyrolysis at 500 °C when potassium was not present. However, with the presence of potassium carbonate, the structure was dramatically changed. The simultaneous occurrence between the CO2 release and the glycosidic linkage cleavage detected by NMR spectrum leads to a comprehensive understanding of the role of potassium in cellulose pyrolysis. A model which explains the mechanism of how the alkali addition enhances the biomass pyrolysis was developed based on the observed experimental results.