Addition Reactions of Olefins to Asphaltene Model
Compounds
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Abstract
Addition reactions have been proposed
as a significant pathway
for coke formation in the liquid-phase cracking of heavy oils and
bitumens. In order to study the kinetics of olefin addition in the
liquid phase, two alkyl-bridged aromatic compounds, with molecular
weights of 899.70 g/mol and 1127.99 g/mol, were thermally cracked
with 1-hexadecene, 1-octadecene, or <i>trans</i>-stilbene,
in a batch microreactor at 375–430 °C for 15 to 45 min.
Reaction products were analyzed by gas chromatography, high-performance
liquid chromatography, matrix-assisted laser desorption/ionization
mass spectrometry (MALDI-MS), and proton nuclear magnetic resonance
(<sup>1</sup>H NMR) spectroscopy. Kinetic data indicate a first-order
reaction in model compound concentration, with energetics consistent
with a free-radical chain mechanism. Tandem MS/MS and <sup>1</sup>H NMR spectra of the products are consistent with olefin addition
through the alkyl bridge of the bridged aromatics. The results imply
that (i) the addition products are able to abstract hydrogen to give
detectable products faster than they decompose, and (ii) the addition
products can react even more readily than the parent compounds