The effect of additives on migration and transformation of gaseous pollutants in the vacuum pyrolysis process of waste printed circuit boards

摘要

The effect of six additives (CaCO_3, HZSM-5, CaO, Al_2O_3, FeOOH and Ca(OH)_2) on the generation, migration, transformation and escaping behaviours of typical gaseous pollutants in the pyrolysis process were studied by vacuum pyrolysis experiments on epoxy resin powder from waste printed circuit boards with tube furnace. The results show that the additives Al_2O_3, CaO, Ca(OH)_ 2 and FeOOH could reduce the yield of the gas phase. The removal rates of pollutants, such as benzene, toluene, ethyl benzene, phenol, p-xylene, HBr, NO_2 and SO_2 in the gaseous products, has changed variously with the increasing percentage of the above additives. Judging from the control of gas-phase pollutant discharge, the calcium-base additives are superior to the others. Ca(OH)_2 has the best inhibition effect among them. The increase of the pyrolysis temperature and vacuum degree enhanced the volatility of organic pollutants and weakened the Ca(OH)_2 inhibition effect on organic pollutants, while it improved the removal rate of SO_2. Under the condition of 500 ℃ pyrolysis temperature and 0.09 MPa vacuum degree, when the additive proportion of Ca(OH)_2 was one-fifth, the average removal rate of pollutants in gas phase is up to 66.4%.