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 °C under N2/CO2/O2 atmospheres (N2: 17–100%, CO2: 0–83%, O2: 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 °C. The CO2 gasification rate constants (Kp) of chars derived at 0.02 kPa increased with the Brunauer–Emmett–Teller (BET) specific surface area up to 417 m2 g− 1 and were 1.5–3.2 times those derived at 1.0 MPa. In particular, Kp for the char derived at 0.02 kPa and N2/CO2/O2 = 18/41/41 vol.% exhibited the maximum values and Kp (0.3 min− 1) at 900 °C for the char was 1.7–2.5 times that of chars under other conditions. Kp at a given gasification temperature for chars derived at 1.0 MPa was almost independent of N2/CO2/O2 contents. Chars derived at 0.02 kPa had more amorphous structures and much higher BET specific surface areas (189–417 m2 g− 1) and pore diameters (0.10–0.24 cm3 g− 1) with an average pore of 2.2–2.4 nm. The char derived under N2/CO2/O2 = 18/41/41 vol.% had a BET specific surface area of 417 m2 g− 1 and a pore volume of 0.24 cm3 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 2.1–4.3 m2 g− 1, 0.01–0.02 cm3 g− 1, and 15.9–22.8 nm, respectively, and these properties were almost independent of N2/CO2/O2 contents.

► We produce active chars for CO2 gasification from woody biomass under N2/CO2/O2 atmospheres. ► The CO2 gasification rate constants of chars derived at 0.02 kPa are very high. ► The CO2 gasification rate constants for char derived under atmospheres containing CO2/O2 are high. ► The char derived at 0.02 kPa under atmospheres containing CO2/O2 has very high surface area.