Slow pyrolysis studies for utilization of impregnated waste timber materials

The increasing environment protection requirements for waste timber materials attract interest regarding the use of traditional slow pyrolysis equipment, which is employed to produce charcoal, for their utilization, since the raw material is lump wood. After carbonization of creosote-impregnated pinewood sleepers, the amount of toluene solubles decreases from 28.5 to 0.81% in sapwood. Having investigated the toxic polycyclic aromatic hydrocarbons (PAHs) content in charcoals, we have found that it partly depends on the wood species, since there are essential differences in the toxic PAH quantities in non-impregnated birch and pinewood charcoals (22 and 145 mg/kg from the oven-dry mass, respectively). However, the greatest growth is induced by the creosote fraction-the charcoal from creosote-impregnated sapwood, where the creosote content is the highest, and the toxic PAH content reaches 289 mg/kg from the oven-dry mass. Much greater differences are observed for the benzo(a)pyrene concentrations, which are 0.31 and 0.57 mg/kg from the oven-dry mass for birch and pine charcoal, respectively, and reach 4.04 mg/kg from the oven-dry mass in the case of pine sleeper sapwood charcoal. In its turn, the pyrolysis of electric transmission line (ETL) poles impregnated with chromated copper arsenate (CCA) shows that arsenic is inevitably partially evaporated, hence is distributed between the solid residue and the gas-vapor phase. CCA does not demonstrate the catalytic action on the charcoal yield during analytical pyrolysis, and only a minor increase is obtained during slow pyrolysis.