The pretreatment of hydrous pyrolysis on the synthetic graphitization of coal: Insights into temperature, pressure, and water

Unlike natural graphitization, synthetic graphitization, which is a fast heating process, lacks pressure and fluids. To understand the importance of water and pressure, a hydrous pyrolysis pretreatment was designed. The temperature, pressure, and water can all be controlled as variables. Natural coal with a degree of metamorphism similar to that of the pretreated coal was also prepared. The yield, degree of graphitization, stacking height, lateral size, and defect degree of the aromatic rings for the corresponding products after synthetic graphitization were evaluated using 13C NMR, FT-IR spectroscopy, XRD, and Raman spectroscopy.Higher temperatures and pressures in the hydrous pyrolysis pretreatment are beneficial for the yield and structure of the graphitized products. The role of hydrous pyrolysis is similar to that of natural thermal evolution; however, the yield and structure of the graphitized products from the pretreated coal are slightly worse. The presence of water during pretreatment is important. As a hydrogen donor, water increases the fluidity of the thermoplastic stage. Water pressure can break the microporous structure and render the aromatic layer more orderly. Therefore, hydrous pyrolysis pretreatment proves that the combined effect of water and pressure can improve the synthetic graphitization ability of coal, even under low-temperature conditions. A combination of hydrous pyrolysis and synthetic graphitization was found to be suitable.