Study of potassium deactivation rule in supercritical water gasification of coal with K2CO3 as catalyst

Abstract

K₂CO₃ has a good catalytic effect in supercritical water gasification (SCWG) of coal. However, researchers have mainly focused on the effects of coal gasification, while the potassium mass transfer process has rarely been studied. Herein, the distribution pattern of potassium during the SCWG of coal and the factors influencing potassium deactivation were experimentally obtained. Through the detection and analysis of the residues after the SCWG of coal, it is found that potassium only exists in the forms of liquid and solid and the potassium in the residue exists in the form of insoluble potassium silica alumina, which does not have a catalytic effect. At a high reaction temperature, the reaction time is longer, and when the silica–aluminum content in coal is higher, the potassium deactivate rate is also higher. The molar contents of potassium and aluminum in the coal gasification residue are linearly correlated, with a ratio of approximately 1:1. Reducing the aluminum content in coal can effectively reduce potassium deactivation. In the SCWG of the Hebi coal, the deactivation rate of potassium reduced from 80.88 % to 17.75 % after acid washing. In the SCWG of the ash-free coal, the carbon gasification efficiency (CE) and potassium content in the liquid were above 95 % after each experiment, there was no deactivation of potassium, and the residual potassium solution remained catalytically effective after the SCWG of the ash-free coal.