Insights into the oxygen-containing groups transformation during coal char gasification in H2O/CO2 atmosphere by using ReaxFF reactive force field

Abstract

In an industrial gasifier, char is exposed to complex H2O/CO2 gasifying agents. Independent, competitive, and synergistic mechanisms have been proposed regarding to the reactivity of char gasification in a CO2/H2O mixture so far. Considering that the carbon-oxygen complex on char surface is of vital importance to the gasification behavior, the ReaxFF MD method was used to simulate the transformation mechanism of oxygen-containing groups on the surface of coal char from the perspective of atomic level. Compared with in the CO2 atmosphere, the degree of dehydroxylation of carboxyl groups and hydroxyl groups is intensified in the H2O atmosphere, and the combination of carbonyl groups in coal char with H radicals hinders the formation of CO or CO2. Ether groups are less stable than other oxygen-containing functional groups and break on the lower side of the bond energy during gasification, attracting H radicals to combine in the H2O atmosphere to promote OH radical generation. The results will provide a further understanding to the essence of interaction between CO2 and H2O during coal char gasification.