In-situ SANS study on spatial evolution of coal nanoporosity during pyrolysis at elevated temperatures

Abstract

The nanopore evolution in coal during pyrolysis is vital for optimizing heat and mass transfer in coal conversion processes. Therefore, small-angle neutron scattering (SANS) was utilized to examine the in-situ changes in the nanopore structures of two subbituminous Chinese coal samples during pyrolysis. The nanopore structures were examined in terms of average pore size, pore volume distribution, fractal dimension by SANS at elevated temperatures. Throughout the pyrolysis process, a consistent enlargement of the average size of nanoscale pores was noted as temperatures escalated, with an expansion ranging from 5.3 to 8.2 nm. Particularly during the devolatilization phase (300–500 °C), there was a marked surge in the volume of large pores, exhibiting a growth rate of about 88.1–150.5%. High-temperature (600–800 °C) conditions facilitated the formation of new and smaller pores. While the surface roughness of nanopores experienced a slight reduction throughout the pyrolysis, the directional growth of the pores maintained an isotropic distribution.