Catalytic mechanism of sodium compounds in black liquor during gasification of coal black liquor slurry

Abstract

The coal black liquor slurry (CBLS) was composed of coal and black pulping liquor, which has plenty of sodium compounds, lignin and cellulose. The sodium compounds have a catalytic effect on the gasification process of coal black liquor slurry, while lignin and cellulose enhance the heat value. Alkali-catalyzed gasification experiments of CBLS and CWS (coal water slurry) are investigated on the thermobalance and fixed bed reactor. The residues of the gasification of CBLS and CWS are analyzed by XRD, SEM and FT-IR. It is found that many micro- and mesopores and zigzag faces exist in the surface of the CBLS coke, which play a key role in the catalytic gasification. Sodium can enhance the reaction potential, weaken the bond of C–O and improve the gasification reaction rate. XRD results show that sodium aluminum silicate and nepheline are the main crystal components of the CBLS and CWS. The C–O stretching vibration peak in the 1060 cm −1 band in the CBLS shifts to 995.65 cm −1 in the CBLS coke after partial gasification. This means that the energy of the C–O stretching vibration in the CBLS carbon matrix decreases, so the structure of the carbon matrix is more liable to react with an oxygen ion or hydroxide ion. The amplitude of the C–O stretching vibration peak is augmented step by step due to the ground-excited level jump of the C–O band.