Co-pyrolysis characteristics and kinetics of coal and plastic blends

Co-pyrolysis behaviors of different plastics (high density polyethylene, low density polyethylene and polypropylene), low volatile coal (LVC) and their mixtures were investigated by TGA. Experiments were conducted under N-2 atmosphere at heating rate of 20 degrees C/min from room temperature to 750 degrees C. The results showed that the thermal degradation temperature range of plastic was 438-521 degrees C, while that of coal (LVC) was 174-710 degrees C. Plastics showed similar pyrolysis characteristics due to similar chemical bonds in their molecular structures. The overlapping degradation temperature interval between coal and plastic provide an opportunity for free radicals from coal pyrolysis to participate in the reactions of plastic decomposition. The difference of weight loss percent (Delta W) between experimental and theoretical ones, calculated as an algebraic sum of those from each separated component, Delta W is 2.0-2.7% at the pyrolysis temperature higher than 530 degrees C, which indicates that the synergistic effect during pyrolysis occurs mainly in the high temperature region. The kinetic studies were performed according to Coats and Redfern method for first-order reaction. It was found that for plastics (HDPE, LDPE and PP), the pyrolysis process can be described by one first-order reaction. However, for LVC and LVC/plastic blends, this process can be described by three and four consecutive first-order reactions, respectively. The estimated kinetic parameters viz., activation energies and pre-exponential factors for coal, plastic and their blends, were found to be in the range of 35.7-572.8 kJ/mol and 27-1.7 x 10(38) min(-1), respectively. (C) 2008 Elsevier Ltd. All rights reserved.