Comparative study on devolatilization behavior, microstructural evolution and resultant properties during calcination of petroleum coke with distinct mesophase texture

Abstract

Petroleum coke as an affordable and abundant material represents significant opportunities for using in both traditional and emerging fields, whereas a lack of understanding transformation chemistry during essential calcination hampers its development. Herein, relevance among devolatilization behavior, microstructural evolution and resultant properties during calcination of green coke were investigated. Calcination is found to be roughly distinguished into three regimes according to average stacking height (Lc) and average interlayer spacing (d002) obtained by analysis of WAXS as well as appearance of D2 peak in Raman spectra. The first regime below 800ºC shows starting transformation from semi-coke to coke, mainly induced by volatilization of low-molecular-weight components, dealkylation and intramolecular dehydro-condensation. Simultaneously, progressive healing of in-plane defects, gradual increase of mesogen-layer size and decrease of interlayer spacing was accompanied, causing significant growth of real density. Thereafter, intermolecular dehydro-polymerization and heteroatoms elimination become dominant in 800–1400 °C, leading to removal of interstitial defects. Consequently, larger stacking height and more homogeneous stacking of well-developed hexagonal carbon layers are formed, further promoting microstrength and electric-conductivity of resultant coke. Next, graphite-like microcrystallites would be rearranged into polyhedral configuration in 1400–1600ºC, indicating a transition from coke to semi-graphite. Notably, the mode of arrangement of mesophase units in the green coke would largely predetermine the coke microstructure. This work could give a guidance for regulating structural evolution via selection of green coke and calcination condition according to application.