Study on the formation of olefinic-bond-containing asphaltenes during thermal cracking of vacuum residue. (15th November 2021)

• Record Type: Journal Article
• Authors: Wang, Feng; Liu, He; Yu, Yangyang; Jiao, Shouhui; Biney, Bernard Wiafe; Ibrahim, Ummul-Khairi; Chen, Kun; Guo, Aijun; Xia, Daohong; Wang, Zongxian
• Is Part Of: Fuel. Volume 304(2021)
• Publication Date: 2021-11-15
• Subjects: Vacuum residue -- Thermal cracking -- Olefinic-bond-containing asphaltenes -- Instability -- Coke; Fuel -- Periodicals; Coal -- Periodicals; Coal; Fuel; Periodicals; 662.6
• DOI: 10.1016/j.fuel.2021.121365
• Languages: English
• ISSNs: 0016-2361

Abstract

Graphical abstract: Highlights: The occurrence of olefinic bonds in asphaltenes derived from VR during thermal cracking was revealed. The effect of different cracking conditions on the nature of olefinic-bond-containing asphaltenes was discussed. The hypothetical average molecular structure of olefinic-bond-containing asphaltenes was constructed. Abstract: In this study, the occurrence of olefinic bonds in asphaltenes separated from vacuum residue (VR) during thermal cracking was explored. Also, the effect of various thermal cracking conditions on the nature of olefinic bonds was discussed. The results showed that olefinic bonds were formed in asphaltenes during VR thermal cracking. The olefinic structure of asphaltenes detected by Fourier transform infrared (FTIR) and 1 H nuclear magnetic resonance ( 1 H NMR) spectroscopy was mainly in the type of R–CH = CH–R′. An in-depth investigation revealed that increasing the severity of thermal cracking promoted the formation of more olefinic-bond-containing asphaltenes; the percentage of olefinic hydrogen in asphaltenes peaked at cracking under 420 °C for 40 min, was 2.7%. Meanwhile, the olefinic-bond-containing asphaltenes of high concentration consequently became precursors for the formation of coke by increasing the instability of the liquid system. Consequently, further prolongation of the cracking time led to a drastic decline of olefins content accompanying a sharp leap of coke yield. Finally, the hypothetical average molecular structures of the olefinic-bond-containing asphaltenes during VR thermal cracking were proposed based on the modified Brown-Ladner empirical formulas with improvement. They serve as intuitive insights into the existing olefinic bonds in asphaltenes.