Study of chemical structure transition in the plastic layers sampled from a pilot-scale coke oven using a thermogravimetric analyzer coupled with Fourier transform infrared spectrometer

The aim of this study was to characterize the pyrolysis behavior of the plastic layer formed during the coking process in a 4 kg laboratory-scale coke oven facility. The 4 kg coke oven rig was used to produce semi-coke samples that included the plastic layer. The semi-coke samples were analyzed by using the Synchrotron Micro-CT to characterize their physical structures and identify the plastic layer features. Sectioned plastic layer samples corresponding to softening, maximum fluidity, and resolidification of coal were obtained for five coking coals of varying thermoplastic properties. Pyrolysis behavior and structural changes of the plastic layer samples were analyzed by a thermogravimetric analyzer coupled with a Fourier transform infrared spectroscopy (TG-FTIR) and an attenuated total reflection Fourier transform infrared spectroscopy (ATR-FTIR). The TG-FTIR analysis allowed the characterization of the changes in pyrolysis behavior including volatile matter yields, the changes in aliphatic and aromatic C-H structures in the sectioned plastic layer samples. These structure changes agreed well with the ATR-FTIR analysis which also showed chemical structure changes across the plastic layer. The results suggest that the aliphatic C-H bonds of the five coals underwent the greatest reduction with the progression of the coking process in the coal charge. It was observed that the aliphatic C-H across the thermoplastic layer region varied with the thermoplastic properties of the parent coal. This implies that the aliphatic structures in coal may have played a significant role in the development of thermoplastic properties during the formation of the plastic layer.