Kinetic synergistic effect in co-pyrolysis of Eucalyptus globulus with high and low density polyethylene

Abstract

The pyrolysis of Eucalyptus globulus (EG) with different blends of high density polyethylene (HDPE) and low density polyethylene (LDPE) by thermogravimetry has been studied. ASTM-E1641-16 standard method has been used to evaluate the kinetics during the pyrolysis of the studied blends. For all feedstocks (EG, HDPE and LDPE) and blends studied, the relative content (%) of the volatile organic compound has been determined by GC–MS analysis. Different synergistic effects on the activation energy of EG blends with HDPE and LDPE have been found. EG-HDPE blends showed a minimum activation energy (Ea) (125 kJ mol−1) at the 80% EG–20% HDPE ratio, while the minimum Ea value for EG-LDPE blends was found at the 60% EG–40% LDPE ratio (135 kJ mol−1) has been identified. To test which components exert a greater synergistic effect, mixtures of HDPE and LDPE with the main components of eucalyptus (cellulose, hemicellulose and lignin) have also been studied. However, no synergistic effects on the pyrolysis of cellulose have been detected. Moreover, in hemicellulose and lignin with both types of polyethylene mixtures, a significant decrease in Ea has been appreciated. The lowest Ea values for 60% cellulose–40% HDPE (167 kJ mol−1) and 60% lignin–40% HDPE (140 kJ mol−1) has been calculated. On the other hand, minimum values for 40% cellulose–60% LDPE (166 kJ mol−1) mixture and for 40% lignin–60% LDPE (168 kJ mol−1) mixture have been detected. Thus, the decrease in both Ea and the Arrhenius pre-exponential factor on the eucalyptus-polyethylene blends to the presence of hemicellulose and lignin can be attributed. Moreover, during the co-pyrolysis of HDPE-EG mixtures, n-paraffins, ketones, phenols and sugars are the main VOCs identified. In contrast, in LDPE-EG mixtures, only n-paraffins (55%) and olefins (44%) have been identified.