Raman Spectroscopy of Lignite Gasification Char Morphotypes

The purpose of this study is to characterize and compare the microstructural features of the main morphotypes occurring in the char obtained at 850–950 °C by fluidized bed gasification of lignite from the “Szczerców” deposit (Central Poland), and to bring new insights into the knowledge on the origin of these morphotypes. Optical microscopy and Raman spectroscopy were used. The char is composed mostly of crassinetwork and inertoid, accompanied by tenuinetwork and small amounts of fusinoid. Tenuinetwork originates mainly from textinite, crassinetwork is formed from attrinite, while inertoid results from transformation of strongly gelified macerals such as densinite and ulminite. Similarities in the microstructure of tenuinetwork and crassinetwork as well as inertoid and fusinoid are observed. Inertoid and fusinoid are composed of larger aromatic systems, with lower amount of alkyl-aryl structures, and their microstructure is better organized compared to tenuinetwork and crassinetwork. Inertoid and fusinoid differ in microscopic appearance and were formed from different starting materials, but their microstructural properties converged during gasification. Different morphological features of the network morphotypes (tenuinetwork, crassinetwork) are not reflected in the differences in their microstructural characteristics.