Effects of vacuum-distilled carbon residue on the reactivity of carbon anode

The use of vacuum-distilled carbon residues to replace part of prebaked carbon coke reflects the high-value resource utilization of carbon residues and has the potential to improve the anode reactivity. However, the effect of adding vacuum-distilled carbon residues on the anode reactivity and its mechanism on the anode raw materials remain unclear, which has become a technical bottleneck hindering the application of carbon slag anodization. In this study, carbon residue was vacuum-distilled at 1200 ℃, and the degree of vacuum was 0.5–5 Pa. Vacuum-distilled carbon residue was compounded with petroleum coke and asphalt to form anodes with carbon residues, and the phase composition of vacuum-distilled carbon residues in anode reactivity was tested. A simultaneous thermal analyzer (TG-DSC) was used to analyze the influence of vacuum-distilled carbon residue on the pyrolysis reaction of asphalt. A thermogravimetric analyzer (TG), an X-ray diffractometer (XRD), and a scanning electron microscope-energy-dispersive spectrometer (SEM-EDS) were used to explore the reaction mechanism of vacuum-distilled carbon residues on petroleum and pitch coke. The results show that with the addition of vacuum-distilled carbon residues increasing from 3% to 5%, 7%, and 10% (Mass fraction), carbon residue has an inhibitory effect on the anode air reactivity (600 ℃). In the same addition amount change range of vacuum-distilled carbon residues, the anode CO₂ reactivity (970 ℃) is firstly decreased to 27.97 mg·cm^–2·h^–1 and then increased to 50.16 mg·cm^–2·h^–1. Vacuum-distilled carbon residues can catalyze not only the pyrolysis reaction of asphalt but also the polycondensation reaction of asphalt. A small amount of vacuum-distilled carbon residues mainly affects the coking of asphalt through the polycondensation reaction, but has no obvious effect on the pyrolysis reaction of asphalt, which can increase the asphalt coking rate. In contrast, high amounts of vacuum-distilled carbon residues have a large influence on the pyrolysis reaction of asphalt, and vacuum-distilled carbon residues mainly affected asphalt coking through pyrolysis, which reduced the asphalt coking rate. The effect of vacuum-distilled carbon dust on the anode reactivity was attributed to chemical and structural factors. The addition of vacuum-distilled carbon residues can improve the coking rate of asphalt and the carbonization degree of asphalt coke and petroleum coke, which inhibit the anode air reactivity. The catalytic effect of trace elements in carbon residues on the gasification reaction of pitch coke at high temperatures is the main reason for the catalytic the anode’s CO₂ reactivity with the addition of large amounts of carbon residues.