Density functional theory molecular modelling and experimental particle kinetics for CO2-char gasification

Abstract

Experimental measurements and DFT atomistic modelling were conducted to elucidate the mechanisms for gasification chemistry of char with CO2 gas. The molecular models used were based on experimental representations of coal chars derived from the vitrinite- and inertinite-rich South African coals at 1000 °C. The HRTEM and XRD techniques were used to construct parallelogram-shaped PAH stacks of highest frequency in the vitrinite-rich (7 × 7) and intertinite-rich (11 × 11) char structures. Computations were executed to get the nucleophilic Fukui functions, at DFT–DNP level, to elucidate the nature and proportions of carbon active sites and quantify their reactivity. The DFT–DNP-computed reaction pathways and transition states, to obtain the energy of reaction and activation energies for the gasification reactions of CO2 with active carbon sites were examined. These results were compared with TGA experimental results at 900–980 °C. The mean nucleophilic Fukui function of the H-terminated char models and active sites located at similar edge positions decreased with increasing size of char molecules and followed the sequence: zigzag > armchair > tip active sites. The mean DFT–DNP values for the activation energy of 233 kJ mol−1 at the reactive carbon edge was in agreement with the experimental 191 ± 25 kJ mol−1 and 210 ± 8 kJ mol−1 for the respective chars