Carbonization characteristics of ethylene tar narrow fractions

In this study, the feasibility of using ethylene tar (ET) as raw material for needle coke production was investigated. The basic properties, structural compositions, and thermal stability of ethylene tar and its narrow fractions were studied by elemental analysis, Fourier transform-infrared spectroscopy (FT-IR), ¹H nuclear magnetic resonance (¹H NMR), the coke induction period, and simulation of thermal stability of coking feed. The properties of the products were analyzed by a polarized light microscope, X-ray diffraction (XRD), and scanning electron microscopy (SEM). The results showed that the content of asphaltenes was up to 22.04% in ET, and the thermal stability was poor due to the high content of olefin and other thermally sensitive components. Thus, the coke induction period of ET was only 34 min. After distillation, narrow fractions had no asphaltenes and a low quantity of heat-sensitive components, resulting in improved fraction thermal stability with coke induction period of more than 55 min. Due to its narrow molecular distribution and low content of heat-sensitive components of narrow fractions, the semi-cokes formed from narrow fractions possessed better anisotropic and microcrystalline structures than those formed from the ET. Compared with one-stage carbonization, the two-stage carbonization was more conducive to the coalescence, development, and orientation of mesophase, leading to the formation of a fibrous wide-area streamline structure. The needle coke prepared from the fraction of ET-C had a lower thermal expansion coefficient (CTE), as low as 2.49 ×10⁻⁶ ℃⁻¹, meeting the CTE requirement of needle coke.