Thermal pyrolysis of poly(vinyl alcohol) and its major products

Poly(vinyl alcohol) (PVA) can be used to manufacture the immobilizing support of microorganisms in wastewater treatment systems. The withdrawn activated sludge contains lots of PVA. Before considering the thermal treatment of activated sludge containing PVA, one should investigate the behavior of PVA alone during the thermal treatment. The pyrolysis of PVA is thus examined with a thermal gravimetric analyzer (TGA). The kinetics of the thermal pyrolysis of PVA is conducted using nitrogen as the carrier gas in 378-1073 K and at various constant heating rates (HRs) of 5, 10, and 25 K/min. Major products are collected in 378-1073 K and at the constant HR of 5 K/min. The results indicate that the entire pyrolysis process of PVA under the experimental conditions of this investigation consists of two distinct pyrolysis stages. The corresponding activation energies E, reaction orders n, and frequency factors A of the reactions of two distinct pyrolysis stages are 148.35 and 129.4 kJ/mol for E, 1.04 and 1.48 for n, and 4.319 x 10(11), and 5.169 x 10(6) 1/s for A. The liquid products (condensates of gas at 298 K) consist of two layers (upper and lower layers). The distillation characteristics of the oil portions of both liquid products of upper and lower layers from the pyrolysis of PVA are between gasoline and diesel oil; meanwhile, the oil quality of the lower layer is better than that of the upper one. However, the upper level liquid product does not contain water, but the lower level one contains about 97.37-98.63 wt % water. The major gaseous products (noncondensable gases at 298 K) excluding N-2 are HCs (hydrocarbons, 40.36 wt %), H2O (20.93 wt %), CO2 (19.77 wt %), and CO (18.94 wt %). The HCs mainly consist of C-6 (14.3 wt %) and C-1 (12.53 wt %). All this information is useful not only to the proper design of a pyrolysis system but also to the better utilization of liquid products and understanding of gaseous emission. The oil portions of liquid products can be obtained by the prefractional condensation or postdistillation.