Influence of presence/addition of asphaltenes on semi-coke textures and mesophase development in petroleum feed stocks

• Vacuum residues give mosaic type textures of semi-coke.
• Deasphalted oils give improved texture of mesophase.
• Asphaltenes have a negative impact on mesophase development and semi-coke texture.

In this paper, effect of asphaltenes on optical textures of semi-coke and pitches prepared from vacuum residues (VRs) and their deasphalted oils (DAOs) during heat treatment at a temperature 390 °C was investigated. Optical microscopic image analysis shows that VR-1 which contains 10.44 wt% asphaltenes produces semi-coke VR-390-1 having 29 vol% mesophase content and flow type coalescence. On the other hand, VR-2 which contains 24.57 wt% asphaltenes produces semi-coke VR-390-2 having 27 vol% mesophase content and mosaic type texture. Further, it was observed that deasphalting of these vacuum residues improve the optical textures as well as enhance the mesophase content in DAO-390-1 (48 vol%) and DAO-390-2 (36 vol%) semi-cokes. Furthermore, we have also concluded that asphaltenes molecules affect the growth of mesophase development in an adverse manner. In this study, we have prepared pitches from clarified oil (CLO) and aromatic extract (AE) having very low asphaltenes content at temperatures 380 and 390 °C respectively without and with the addition of 3% asphaltenes. Optical microscopic images of these pitches show that mesophase contents were decreases with the addition of asphaltenes externally. In addition, semi-cokes and pitches were also characterized by using elemental analysis, Fourier transform infrared spectroscopy (FT-IR), X-ray diffraction (XRD) and thermogravimetric analyses (TGA). The study revealed that asphaltenes either present in the feed stock or externally added in the feed stock play a negative role on mesophase development as well as on coke texture.

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