The catalytic effect of Benfield waste salt on CO2 gasification of a typical South African Highveld coal

Abstract

The possible catalytic effect of a 5% loading by mass of crystallized salt from spent Benfield solution (SBFS) was investigated and compared with the catalytic influence of a 5 mass% loading of K2CO3 on the char-CO2 gasification reactivity of a bituminous medium rank C South African Highveld coal. The effect was investigated using known thermogravimetric investigation techniques. Coal char samples were prepared using the coal and catalyst-loaded samples by heating the samples in nitrogen to 1000 °C. The prepared char samples were further subjected to thermogravimetric analyses by heating them at isothermal temperatures between 900 and 990 °C in a CO2 atmosphere to simulate gasification reactions of the coal char. Results from isothermal char-CO2 gasification experiments showed that the catalyst-loaded coal samples exhibited higher gasification reactivities than the coal sample and the reactivities increased in the order: coal < coal + 5% SBF < coal + 5% K2CO3. It was observed that the relative initial reactivity of the catalyst-loaded samples increased in order of magnitude > 3.5 in comparison with the coal char sample. The addition of catalysts to the coal was found to reduce the estimated activation energies of the catalyst-loaded samples during the gasification process. The estimated activation energies (calculated from the initial reaction rate of the gasification reaction) of the samples were 215 kJ mol−1 for the coal char, 146 kJ mol−1 for the char from the coal + 5% SBF and 118 kJ mol−1 for the char from the coal + 5% K2CO3. The crystallized spent Benfield salt may be utilized as a CO2 gasification catalyst for coal