In-situ catalytic gasification of sodium-rich direct coal liquefaction residue under CO2 atmosphere and kinetic analysis of gasification reaction process

Abstract

Due to attractive features, such as low mineral matter content and strong reactivity, sodium-rich coals are viewed as suitable raw materials for direct coal liquefaction technology. After direct coal liquefaction process, the inherent sodium species in sodium-rich coals will be enriched in direct coal liquefaction residue. In this work, to provide potential guidance for better utilization of sodium-rich direct coal liquefaction residue, catalytic effects of the inherent sodium species on gasification reactivity of sodium-rich direct coal liquefaction residue and kinetic analysis of gasification reaction process were investigated in detail. The results show that inherent sodium species has obvious catalytic effects on gasification of sodium-rich direct coal liquefaction residue. Compared with that for demineralized direct coal liquefaction residue, the time for sodium-rich direct coal liquefaction residue to be completely gasified at 1000 °C and 1100 °C was shortened by 82% and 70%, respectively. With the increase of gasification temperature, CO2 gasification reactivity of all types of direct coal liquefaction residue was enhanced. For instance, gasification reactivity indexes (R0.5) of sodium-rich direct coal liquefaction residue are 0.06 min−1, 0.15 min−1, and 0.23 min−1 at 900 °C, 1000 °C, and 1100 °C, respectively. Kinetic analyses indicate that linear correlation coefficients obtained by homogeneous model and shrinking core model are on high levels and they are closely related with gasification temperature and residue type. According to calculation of homogeneous model and shrinking core model, activation energies of demineralized direct coal liquefaction residue are 78.60 kJ/mol and 73.73 kJ/mol, respectively. In contrast, the corresponding activation energies of sodium-rich direct coal liquefaction residue are 75.42 kJ/mol and 71.55 kJ/mol, which proves that activation energy required for gasification of direct coal liquefaction residue can be reduced by the inherent sodium species. To conclude, catalytic coal gasification may be potentially efficient to process sodium-rich direct coal liquefaction residue.