Hydroconversion Behavior of Asphaltenes under Liquid-Phase Hydrogenation Conditions

To fully utilize deoiled end-cut (DOE) from selective asphaltene extraction process, Venezuela n -pentane DOE was subjected to hydroconversion in an autoclave reactor using tetralin as hydrogen donor. Venezuela DOE and its hydroconversion products were separated into gas, n -heptane maltenes (HM), n -heptane asphaltenes (HAs), and coke. The effects of reaction conditions including reaction temperature, solvent-to-feedstock (S/F) weight ratio, and reaction time on product distribution were investigated. High temperature, large S/F ratio, and long time benefited the generation of gas, HM, and coke to some extent. Under optimal conditions, over 50 wt % HAs in DOE was converted into HM fraction, with less than 3 wt % coke yield. The elemental compositions and molecular weights of HAs and HM, along with reaction time, were also analyzed. The hydrogen-to-carbon (H/C) ratio of HAs declined from 1.115 to 0.871, indicating that HAs underwent dehydrogenation and dealkylation reactions. However, the H/C ratio of HM initially increased from 1.405 to 1.548, showing that hydrogenation reaction occurred, and then decreased to 1.374 because of the cracking of HAs into HM and/or the secondary cracking of HM. The average molecular-weight decrease both for HAs and HM confirmed disaggregation and cracking reactions. The molecular composition and transformation of nitrogen and sulfur compounds before and after hydroconversion were determined by negative- and positive-ion electrospray ionization Fourier transform ion-cyclotron–resonance mass spectrometry, respectively. N 1, S 1, and O 2 classes were dominant in the feedstock. After hydroconversion, N 1 and S 2 compounds decreased in HAs, indicating that they were reactive species. N 1 compounds mainly cracked into small N 1 compounds and also condensed into N 2 compounds, while S 2 compounds generally decomposed into S 1 compounds.