Extracting key carbonization-bonding fraction as binder from coal tar pitch to prepare high-value-added formed coke from coke breeze: Devolatilization and carbonization behaviors and mechanisms

A novel approach of using trimethylbenzene to extract the key carbonization-bonding fraction from coal tar pitch (CTP) to prepare formed coke using coke breeze was proposed for the first time in this study. Experiments on the extraction-separation of CTP and the preparation of formed cokes were carried out. The strength of formed coke prepared using the trimethylbenzene-soluble (TS) fraction was significantly higher than that using the raw CTP, while the trimethylbenzene-insoluble (TI) fraction failed to prepare formed coke, indicating that the key carbonization-bonding components of CTP were present in the TS fraction. A formed coke product with 36.79 MPa of compressive strength and 42.57% of CSR, meeting the Chinese secondary metallurgical coke standard, was obtained using the TS fraction. The TS fraction consisted of low-condensation aromatic compounds (containing 5–12 aromatic rings) and small molecular chain structures, whereas the TI fraction was rich in highly condensed aromatic compounds (containing 11–20 aromatic rings) and inorganic impurities. Their devolatilization primarily involved the volatilization and cracking of small‑molecular‑weight organic compounds, while the carbonization was dominated by the dehydrogenation condensation reaction of aromatic compounds. The carbonization products of the TS fraction formed relatively thin carbon flakes with noticeable strength, whereas those of TI exhibited a loose and porous structure with brittleness and low mechanical strength, which was attributed to the low carbonization activity of the highly condensed aromatic compounds and interference from inorganic impurities. These behaviors make the TI fraction impossible to be used as a binder for the preparation of formed coke.