The effect of aluminium on the formation of PAH, Methyl-PAH and chlorinated aromatic compounds during thermal decomposition of PVC

At temperatures above 300 degrees C and long gas residence times aluminium reacts almost quantitatively with HCl split off during pyrolysis of PVC/Al combinations, forming catalytically effective AlCl3. According to thermoanalytical investigations and pyrolysis experiments on a gramme scale, the char fraction increases in accordance with with the aluminium percentage. Also, there is an increase of the yield of gaseous alkanes, but a reduction of aromatics in the pyrolysis condensate. Naphthalene as well as 15 PAH of the EPA priority list and some identified methyl-PAH decrease nearly exponentially with increasing aluminium proportion. The half-concentration corresponds to about 1 wt.% aluminium, tantamount to 1 Al-atom for 43 PVC monomeric units. In addition to the thermodynamically stable perchlorinated products as there are hexachlorobenzene (1-2 ppm) and decachloro-biphenyle (PCB 209; < 0.2 ppm) also pentachlorobenzene and smaller amounts of PCB 206 and 208 were identified by means of GC/MS and GC/FT-IR. No dependence on the amount of aluminium was found. Just as in the pyrolysis oil, PAH concentrations in the char decrease exponentially with increasing aluminium fraction, but are lower by a factor of 300. (C) 1997 Elsevier Science B.V.