Structural features and gasification reactivity of coal chars formed in Ar and CO2 atmospheres at elevated pressures

The structural features and gasification reactivity of chars derived from pyrolysis of a bituminous coal under Ar (Ar char) and CO2 atmosphere (CO2 char) have been investigated, respectively. The pyrolysis was performed in a fixed bed reactor at a final temperature of 700 °C and pressures ranging from 0.1 to 1.5 MPa. It was found that CO2 affect the char yield, pore structure and surface area. The N2 surface area of the CO2 char at ambient pressure increased by nearly 42 times compared to the Ar char. The chemical structure features were characterized by using Raman spectroscopy. The recorded spectra between 800 and 1800 cm−1 were curve-fitted with 10 Gaussian bands representing typical structural features of chars to quantitatively compare the char structure difference. The ratio I(Gr+Vl+Vr)/ID between the band intensities of amorphous char structures with small aromatic ring (3–5 rings) systems and condensed aromatic ring systems (>6 rings) is seen to decrease with increasing pyrolysis pressure. The I(Gr+Vl+Vr)/ID of CO2 char is always lower than that of Ar char in the whole pressure range. The non-isothermal CO2 gasification from 700 to 1000 °C in a TGA (thermogravimetric analyzer) indicates that the char prepared under Ar atmosphere was more reactive.