Abstract
This article deals with the upgrading of bitumen in supercritical water (SCW) using a ZrO2-Al2O3-FeOx catalyst in a batch autoclave reactor. The feed bitumen is diluted using different amount of benzene as solvent in order to provide intimate contact between the solid catalyst particles. It also facilitates the diffusion of the heavy molecules into the catalyst particles. The batch reactor results show that the extra heavy oil is slightly decreased with increasing the bitumen concentration from 20 wt % to 30 wt%. No significant change in the product is observed when bitumen concentration is increased above 30 wt% level. However, the coke concentration is increased with increasing bitumen in the feed. The catalyst deactivation is also higher at higher bitumen concentrations (above 20 wt %). XRD analysis reveals that at high bitumen concentrations (above 30 wt %), transformation of magnetite into hematite is lower than that of hematite to magnetite due to consumption of lattice oxygen by the additional hydrocarbons, which also causes the catalyst deactivation. On the contrary, lower bitumen concentration (~10 wt %) maintains hematite as main phase, which is the desirable for sustained catalytic activity for the oxidative cracking reaction. It is believed that SCW acts as source of reactive hydrogen and oxygen species that favors the upgrading process. The reactive hydrogen species react with cracked hydrocarbons to produce stable lighter liquid products. On the other hand, the reactive oxygen species react with oxygen depleted catalysts, which transforms magnetite into hematite and keep the catalyst active.
Comparison of upgrading of heavy oil and vacuum distillation residues by supercritical water
