Particle size influence on the pore development of nanopores in coal gasification chars: From micron to millimeter particles

The influence of particle size on the growth of nanopores arising from gasification of a South African coal-char was investigated using small angle X-ray scattering. Three different char sizes (75 μm, 2 and 20 mm) were gasified between 800 and 1000 °C to specific conversions up to 50% and the pore development during CO₂ and steam gasification was compared. For the CO₂ gasified chars studied here, particle size influenced the rates of individual pore growth for all pore sizes and an increased development of micro-, and macropores was observed as particle size increased. For the steam gasified chars studied here, particle size only influenced the rates of individual pore growth for larger pores, with prevalence of macropore development. A novel application of monitoring pore development as a function of distance from the surface was applied to the 20 mm gasified char, spanning the surface to the interior of the spherical particle. The portion closest to the surface, showed the greatest pore development over the entire pore range, followed by the interior and centre. The radial changes in growth rate for individual pore sizes demonstrated intra-particle mass transfer limitations for the 20 mm particle studied here under these conditions.