Thermogravimetric study on the steam activation of charcoals obtained by vacuum and atmospheric pyrolysis of softwood bark residues

Abstract

The steam activation of charcoal obtained by vacuum and atmospheric pyrolysis of softwood bark residue was studied by thermogravimetry (TG). Carbons activated in the thermobalance were characterised by gas adsorption. Furthermore, the differential weight loss (DTG) curves were correlated with the specific surface area and surface spectroscopic results of carbons produced in the thermobalance and in a laboratory reactor, respectively. Comparison of non-isothermal TG experiments in nitrogen and nitrogen/steam atmosphere, respectively, showed that charcoal oxidation started at 600 to 640°C, depending on the sample. Two different oxidation regions were observed. In the first region, micropores already present were widened by the removal of carbonaceous deposits, whereas in the second region mesopores were formed. Since more carbonaceous deposits were present in the pores of charcoal from atmospheric pyrolysis, their removal was slower as compared to vacuum pyrolysis charcoal and the crossover to the second oxidation region occurred at higher temperatures. During the isothermal activation experiments, the oxidation of vacuum pyrolysis charcoal was also faster as compared to charcoal from atmospheric pyrolysis.