Low sulfur Graphite Coke is a black, solid substance produced by the cracking of residual oil at certain temperatures. It contains between 85-90% carbon, as well as hydrogen, oxygen, nitrogen and sulfur. The sulfur content is mainly determined organic sulfur, which is bonded with aromatic structures on the surface, and inorganic, which is bonded directly with carbon chains. Petroleum coke has a high carbon content with low sulfur, making it an important industrial raw materials. It is used in the preparation of carbon products, such as graphite electrodes, carburizing agents, and reserve carbon.
The present work aims to increase the utilization of petroleum coke with high sulfur content by using a single-step hydrodesulfurization method. To this end, heat treatment of petroleum coke at different temperatures was used to study sulfur release. XRD, FEI Titan Krios 6000 (Canberra, Australia), transmission electron microscopic (TEM), and SEM cross-section were used to characterize microstructures and electrochemical performances of the resulting synthetic graphite. It was found that the higher the sulfur content, the more detrimental it was for the morphology and electrochemical properties of the resultant graphite. This can be attributed because sulfur atoms reduce the compaction of anode materials that have high energy densities and inhibit the growth long-range ordered crystals.
To achieve this, an innovative pre-carbonization desulfurization process was proposed. This involves an in situ hydrodesulfurization at 1400 degC of petroleum coke before the traditional graphitization. This technique reduced the sulfur content in petroleum coke by 40% without changing the calcination process temperature. It was also shown that the sulfur doped hierarchical carbon (HPC), produced from the hydrodesulfurization a high-sulfur petrochemical coke, exhibited good electrochemical behavior with a specific capacitor of 327 Fg-1 and a current densities of 1 Ag-1.
The experimental results indicate the rate of sulfur absorption from petroleum coke increases when mass fractions of NaOH are increased. This rate reaches a critical level of 10%. This threshold depends on the oxidation state of the sulfides present in petroleum coal and is independent from roasting temperature. Furthermore, the sulfur removal rate was found to be dependent on the holding time of the petroleum coke in a NaOH solution, and the optimum holding time was determined as 2 h. These findings suggest that the hydrodesulfurization of petroleum coke with NaOH is a promising method for improving its use in the metallurgical industry and graphitized carbon electrode production. Further research on the mechanisms underlying this phenomenon is needed. Graphite electrodes made from Low-sulfur Graphite Petroleum Coke exhibit excellent electrical conductivity and stable under high temperature and strong currents. This can meet the requirements of various industrial applications.
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