Role of iron oxide in retarding the graphitization of de-oiled asphaltenes for amorphous carbon

The solvent deasphalting (SDA) process is widely recognized as a significant technology in processing inferior oil. However, de-oiled asphaltene (DOA), which accounts for about 30% of feedstocks, is not well utilized in conventional processing methods to date. Considering its complicated structure and high heteroatom and metal contents, DOA is suitable for preparing amorphous carbon. Herein, we obtained amorphous carbon from inferior de-oiled asphaltene through direct carbonization of a mixture of DOA and Fe2O3 and revealed the mechanism of iron oxide in retarding graphitization to increase the disordered structure content. After the addition of Fe2O3, XRD results showed that the content of amorphous carbon increased from 25.57% to 59.48%, and a higher defect degree could also be observed in Raman spectra, thus resulting in better electrochemical performance in Na-ion half-cells. As a coke core, Fe2O3 could accelerate the polycondensation of asphaltene molecules; meanwhile, oxygen species derived from Fe2O3 could capture excess H free radicals in the initial pyrolysis stage, which inhibited the formation of planar polycyclic aromatic molecules and weakened pi-pi interactions. Moreover, O atoms could embed into the carbon skeleton by reacting with DOA at higher temperatures, which could further twist and break the intact carbon layer. Both of the factors enhanced the proportion of amorphous carbon. This work not only provides a new understanding of controlling the carbonization process, but it also promotes the development of the SDA process. Fe2O3 accelerates the polycondensation of asphalt molecules, consumes the excessive H and breaks the intact carbon layer, which weakened the pi-pi interactions, finally enhances the formation of amorphous carbon.