Supercritical Water Treatment of Crude Oil and Hexylbenzene: An Experimental and Mechanistic Study on Alkylbenzene Decomposition

High concentrations of fuel-range
hydrocarbons may be recovered
from heavier alkyl-aromatic compounds in crude oil after supercritical
water (SCW) treatment. Arabian Heavy (AH) crude oil was treated in
SCW and analyzed using two-dimensional gas chromatography (GC ×
GC-FID). Cracking mechanisms were investigated using the model compound
hexylbenzene under similar SCW treatment conditions. The results of
the model compound experiments were compared to predictions of a kinetic
model built by the Reaction Mechanism Generator (RMG). AH crude cracked
significantly during SCW treatment. The GC-observable mass fraction
increased by 90%. We conducted studies on the distilled samples of
crude oil and found that significant changes in the composition of
the SCW-treated heavy fraction occurred. Significant formation of
aliphatic hydrocarbons and small-chain BTX-type compounds were found
in the SCW-processed samples. Hexylbenzene conversions differed between
the crude oil studies and the model compound studies. The mechanistic
model for the cracking of hydrocarbons during SCW treatment of the
model compound hexylbenzene predicted the observed major liquid products
toluene, styrene, and ethylbenzene. The selectivity of ethylbenzene
and styrene changed over time. The apparent conversion of styrene
into ethylbenzene was possibly via a reverse disproportionation reaction.
Ultimately, a mechanism was built that serves as a basis for understanding
the kinetics of hydrocarbon cracking in SCW.