The effect of N2/CO2/O2 content and pressure on characteristics and CO2 gasification behavior of biomass-derived char

The CO2 gasification behavior of biomass chars derived at 800 degrees C under N-2/CO2/O-2 atmospheres (N-2: 17-100%. CO2: 0-83%, O-2: 0-42%) and at 0.02 kPa and 1.0 MPa was investigated using the random pore model (RPM) at gasification temperatures of 800-1000 degrees C. The CO2 gasification rate constants (K-p) of chars derived at 0.02 kPa increased with the Brunauer-Emmett-Teller (BET) specific surface area up to 417 m(2) g(-1) and were 1.5-3.2 times those derived at 1.0 MPa. In particular, K-p for the char derived at 0.02 kPa and N-2/CO2/O-2=18/41/41 vol.% exhibited the maximum values and K-p (0.3 min(-1)) at 900 degrees C for the char was 1.7-2.5 times that of chars under other conditions. K-p at a given gasification temperature for chars derived at 1.0 MPa was almost independent of N-2/CO2/O-2 contents. Chars derived at 0.02 kPa had more amorphous structures and much higher BET specific surface areas (189-417 m(2)g(-1)) and pore diameters (0.10-0.24 cm(3) g(-1)) with an average pore of 2.2-2.4 nm. The char derived under N-2/CO2/O-2=18/41/41 vol.% had a BET specific surface area of 417 m(2) g(-1) and a pore volume of 0.24 cm(3)g(-1), and an average pore diameter of 2.3 nm. Those derived at 1.0 MPa had BET specific surface areas, pore volumes and average pore diameters of 2.1-43 m(2) g(-1), 0.01-0.02 cm(3) g(-1), and 15.9-22.8 nm, respectively, and these properties were almost independent of N-2/CO2/O-2 contents. (C) 2012 Elsevier B.V. All rights reserved.