Relationships between the optical properties of coal macerals and the chars resulting from fluidized bed pyrolysis

In this study the values of the RIS axes and parameters were calculated using Kilby's method to the characterization of the textural anisotropy and structure of the basic structural units of coal macerals (collotelinite, fusinite, and macrinite). Their microstructural evolution after having been subjected to fluidized bed pyrolysis at 800 °C was investigated, using the same parameters, on their respective char portions (fused char, fusinoids, and inertoids). Thus, this work represents the first attempt to determine the variations of the optical properties of fluidized bed chars.After the thermal treatment, the fusinoids and the inertoids presented similar Rr% values and RIS parameters values, indicating that after pyrolysis these materials are texturally and structurally similar.Collotelinite produced fused chars with a higher reflectance than those resulting from fusinoids and inertoids. Their reflectance increase in lower and decrease in higher rank coals. The highest RMAX%, Rev, and Ram increase occurred in the fused char portions derived from the collotelinite of coals in the 0.86–1.60 Rr% range, indicating substantial chemical and spatial rearrangement.

► Reflectance characterization of coal macerals and respective fluidized bed pyrolysis chars.
► The optical parameters of the Reflectance Indicating Surface (RIS) axes were calculated.
► Reflectance values are higher for fused chars.
► Fusinite and macrinite chars are textural and structurally similar.