Turning coal hydrogenation liquefaction residue into high conductivity carbon black with magnesium citrate-assisted steam activation followed by high temperature treatment

Abstract

The high conductivity carbon black was prepared using coal hydrogenation liquefaction residue as raw material, through a combination methods of solvent extraction purification, magnesium citrate-assisted carbonization, steam activation, and high-temperature treatment. The effects of carbonization and activation process parameters, heat treatment temperatures, and other factors on the microstructure, specific surface area, degree of graphitization, and conductivity of the carbon black were studied. The coal direct liquefaction residue was firstly purified using a xylene and tetrahydrofuran solution with a volume ratio of 1:1 by centrifugal separation method to obtain coal liquefaction asphalt. Then, the coal liquefaction asphalt was mixed with magnesium citrate in a mass ratio of 3:7 and ball-milled for 90 min. After carbonizing at 950 °C for 120 min, magnesium ions were leached out with hydrochloric acid. The obtained sample was activated with steam at 900 °C for 100 min and then underwent high-temperature treatment at 1500 °C under a N2 atmosphere for 120 min. The microstructure of the conductive carbon black exhibited an irregular blocky structure with an average particle size of 2–10 μm. The specific surface area of carbon material was 579.69 m2/g, with the pore distribution predominantly microporous, accounting for 69.81 % of the total pore volume. It featured a higher degree of graphitization (ID/IG=1.06) and fewer surface oxygen-containing functional groups compared with coal direct liquefaction residue. Electrochemical testing showed that the electrical resistance of the carbon material was only 1.55 Ω, and the reversible capacity under a current density of 1 A/g was 96 mAh/g, which are superior to those of the existing commercial conductive carbon black. The microporous structure and higher degree of graphitization facilitate efficient electron transmission, while the lower content of surface oxygen functional groups effectively reduces electron transfer resistance. This work offers new insights into the structural design and performance enhancement of coal liquefaction residue-derived conductive carbon black functional materials. Furthermore, it has significant implications for the future development of conductive carbon black in energy saving and energy storage.