Characterization of the porous structure of cokes produced from the blends of three Polish bituminous coking coals

Three Polish coals of varying rank (82.7, 86.2 and 88.7 wt.% carbon content) and caking ability (weak, moderate, and strong), collected from the Krupiński, Szczygłowice, and Zofiówka mines, respectively, were used for the preparation of binary and ternary blends. Many cokes of various internal structure were produced from these blends using a laboratory-scale Jenkner furnace. The bulk porosity and the specific surface area were determined for the resultant cokes using a helium gas displacement pycnometer and the measurements of nitrogen adsorption at − 196 °C, respectively. Pores in cokes were observed using optical microscopy. Structure of pore solid walls was studied with TEM. The bulk porosity, the specific surface area and the coke reactivity to CO2 (CRI) were discussed in relation to strongly caking coal concentration in a blend, i.e., to the Zofiówka coal content ranged from 0 to 100% with steps generally, equal to 10%. The CRI was found to be exactly linear function (correlation coefficient equal to 0.96), while the specific surface area was approximately linear (correlation coefficient equal to 0.5) dependent on content of the strongly caking coal in a blend. The bulk porosity was almost independent on a blend composition. The CRI was found to be additive, dependent on the CRI of the cokes obtained from the individual coals used in a blend and the blend composition, unlike the parameters of porous structure of cokes. The CRI increased with increasing the specific surface area, but this dependence was not exactly linear. Chemical structure of a solid phase of porous cokes was therefore suggested to play an important role in reactivity to gases, not less than that of internal surface area. Cokes with greater molecular orientated domains in solid walls were found to be less reactive to CO2.