Insight into the mechanisms for pyrolyzing organic macromolecular structure of subbituminous coal by comparing the extraction and flash pyrolysis

Abstract

Investigating the organic structure of coal is an essential basic research for producing clean fuels and value-added fine chemicals by the clean and efficient utilization of coal. As a consequence, the structural characteristics of organic macromolecular in subbituminous coal (SBC) were analyzed at different levels using multiple destructive and non-destructive technical strategies. Correspondingly, the pyrolysis mechanisms of SBC organic macromolecular structure were investigated to understand through the molecular level correlation group component from extraction portion (EP) and flash pyrolysis (FP). In detail, solid-state 13C nuclear magnetic resonance analysis indicates that carbon skeleton of SBC mainly consists of aliphatic carbons (48.5%) and aromatic carbons (50.3%). The number of substituents on each aromatic ring in SBC is up to 2 on average and aliphatic linkages connect 3–4 aromatic rings. X-ray photoelectron spectrometer analysis exhibits that the >C–O- groups, pyrrolic, and sulfonic sulfurs of organic components are the most abundance O-, N-, and S-containing species, which is consistent with Fourier transform infrared and solid-state 13C nuclear magnetic resonance. The destructive analysis with thermogravimetric implies that organic macromolecular structure in SBC consists different types of covalent bonds (>Cal-X) with different strength. Furthermore, the contents of chain alkanes (CAs, 17.4%), arenes (62.7%), and oxygen-containing organic species (OCOSs, 18.0%) in EP from SBC (EPSBC), while the CAs (53.1%), alkenes (7.4%), arenes (27.3%), and OCOSs (7.5%) in FP of SBC (FPSBC). Comprehensive comparative analysis of detectable small molecule species from EPSBC and FPSBC further indicate that the cleavage > Cal-X bridge bonds of organic macromolecular structure in SBC attack by active hydrogen (H‧) through the pyrolysis reaction to obtain more alkenes, CAs, alkanols, and phenols.