Study on synergistic effect of co-pyrolysis of wood chips and its gasification tar on the biochar and subsequent activated carbon upgrading using response surface method

Wood processing and gasification produce large amounts of waste wood chips and tar separately. The utilization of these wastes is highly significant for the comprehensive utilization of wood. In this study, waste wood chips and tar were used as raw materials and the characteristics of biochar and activated carbon obtained using a two-step process (co-pyrolysis followed by activation), were investigated. On the basis of response surface methodology, the comprehensive effects of the three co-pyrolysis factors (proportion of tar, pyrolysis temperature, and residence time) on the properties of biochar and activated carbon were studied. Results showed that there was synergistic effect between waste wood chips and tar during co-pyrolysis. A lower biochar yield was obtained from pyrolysis of tar (25.5%) and wood chips (24.7%) alone, as compared to that of biochar (27.1%) obtained by co-pyrolysis. Additionally, the activated carbon produced by co-pyrolysis (1280 m2/g) had higher specific surface area (SBET), as compared to that produced by pyrolysis of tar and waste wood chips alone. Regression equations were established for the co-pyrolysis conditions with the properties of biochar and activated carbon. The trends for the three experimental conditions were intuitively shown by the 3D response surface diagrams, which facilitated the utilization of waste wood chips and tar.