Abstract
Using Raman spectroscopy, temperature-programmed desorption (TPD) and laser-induced breakdown spectroscopy (LIBS), the relationship between microstructural characteristics and molecular emissions was determined. It can be concluded that the enhancement of C2 and CN emissions was related to the generation of small aromatic rings and C(O) groups. Compared with the Ar preheating treatment, the presence of additional amount of O2 and sodium salt accelerated the dissociation of the large aromatic ring skeleton, leading to the significant enhancement of small aromatic rings, C(O) and CONa groups. Subsequently, the combustion performance of preheated semichar was investigated by the TG-DTG method. The experimental results demonstrated that pretreatment under oxidizing atmospheres (without and with sodium salt addition) enhanced the comprehensive combustion index (S) and the combustion stability (Rw) of semichars. The corresponding combustion activation energy (E) was weakened. Furthermore, the DFT method was used to analyse the combustion behaviours of semichars. This result demonstrated that preheating treatment (with or without sodium participation) altered the distribution of the Hirshfeld atomic charge (ADCH) of preheated samples, and the combustion essence of semichar was the fracture and recombination of aromatic clusters. For the semichar preheated in the O2/Ar atmosphere, the energy gap of the most optimized pathway was 436.26 kJ/mol. When sodium participated in the oxidizing pretreatment, the energy gap of the most optimized pathway was 413.80 kJ/mol. The positive effect of sodium on the combustion performance of semichar was identified, which was in good agreement with the experimental results.
Published Version
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