Effect of Metal Compounds and Experimental Conditions on Distribution of Products from PVC Pyrolysis

Effects of heating rate, gas flow rate, and type of metal compounds on the amount of hydrogen chloride, liquid, gas, and solid pyrolyzate obtained from the pyrolysis of poly(vinyl chloride) (PVC) were investigated. The pyrolysis experiments were carried out in both a thermogravimetric analysis (TGA) instrument and a fixed-bed reactor. Products from the fixed-bed reactor were collected and analyzed by using Fourier transform infrared spectroscopy (FTIR), gas chromatography-mass spectroscopy (GC-MS), titration technique, and gravimetry. It was found that heating rate in the TGA experiments did not affect the amount of released hydrogen chloride. However, the TGA profiles significantly changed with the rate. The onset of dehydrochlorination increased with the rate. In addition, as the heating rate was increased from 10 to 20°C/min, there was no solid residue left. The amount of liquid pyrolyzate obtained from the fixed-bed reactor can be either increased or decreased with the heating rate, depending on the gas flow rate and the actual residence time in the reactor. FTIR and GC-MS analysis indicated that the liquid pyrolyzates were mainly benzene, toluene, and styrene. By comparing the efficiency of various metal compounds in trapping the HCl, it was found that Ca(OH)₂ was more efficient than Mg(OH)₂, and that CaO was more efficient than MgO. These results are discussed in light of the reaction mechanism between HCl and the metal compounds.