Insights into the catalytic mechanism of calcium species during char-H2O/CO2 gasification based on molecular reaction dynamics

Abstract

Calcium has a definite catalytic effect in char gasification and affects the distribution and composition of gasification products. Therefore, a deep understanding of the reaction properties and mechanism of calcium in gasification is of great significance for the gasification process. Reactive Force Field Molecular Dynamics (ReaxFF MD), an approach for exploring complex chemical reactions, has provided an indispensable aid to the insightful study of the reaction properties of calcium in coal gasification processes. In this work, ReaxFF MD was adopted to construct gasification reactions with different conditions, and the effect of calcium on the products during the gasification was investigated by counting the distribution of the gasification products as well as the changes of calcium species in different conditions. At the same time, the catalytic mechanism of calcium in char during gasification was further investigated by calculating the charge and electrostatic potential of the gasification agent and the gasification agent after calcium binding, as well as the radial distribution function between different atoms. Research has shown that during gasification, the release of calcium from char combined with oxygen atoms in the gasifying agent leads to a decrease in the O–H or C=O bond energy, which promotes the cracking of the gasifying agent. It is worth noting that in comparison to CO₂, Ca can easily form ionic bonds with O in the H₂O molecule during the gasification process, which leads to easier breaking of the O–H bonds.