Distribution of Vanadium, Nickel, and Other Trace Metals in Soot and Char from Asphaltene Pyrolysis and Gasification

Abstract

Vanadium (V) and nickel (Ni) are the most abundant and troublesome metals present in oil sands. During upgrading of the oil sand bitumen, these metals become concentrated in the heavier fraction asphaltenes. Any thermochemical conversion of asphaltene causes the release of these trace metals, and their distribution in the products poses concerns with toxicity, corrosion, and fouling. The pyrolysis, partial oxidation, and steam gasification experiments of asphaltene were carried out in an electrically heated atmospheric entrained-flow reactor, and the products char and soot are analyzed for the trace metal content. It is observed that the main metals present in the char and soot are V and Ni. During pyrolysis, with an increase in the temperature, the quantity of V and Ni present in char decreases as a result of the increased liberation into the gas phase. However, more liberated V and Ni were not captured by soot formed in the same experiment. During partial oxidation of asphaltenes, an increase in the stoichiometric oxygen content decreases the soot yield. The V and Ni contents in both the char and soot decrease with an increase in the stoichiometric oxygen ratio. The V content increases with the increase in the steam/fuel ratio in both char and soot obtained from steam gasification. With the increase in the steam/fuel ratio, the Ni content slightly decreases in char but increases to more than double in soot. Understanding the interaction of inorganic matter with char and soot will help in solving post-gasification fouling and erosion problems.

Transformation of heavy metals in lignite during supercritical water gasification

“…Distribution and volatility behavior of heavy metals in products obtained by conventional coal gasification were investigated, as was the control of heavy metals [18][19][20][21][22][23]. However, the hazard of heavy metals to the environment is not only related to concentration, but also connected with fractions.…”

Asphaltenes: Separations, structural analysis and applications

“…Compared with other metals in asphaltenes, V and Ni are the richest and extensively researched. Usually, the metal ions are chelated with organic groups, and some are located at the defect centers of an imperfect aromatic sheet as porphyrins [30][31][32] , and these possible structures were always hypothesis [32,33] . Meanwhile, amount of experiments confirmed metal compound to be nonporphyrin structure, existing as free molecule, or captured one in asphaltene nanostructure, or a component of asphaltene [34] .…”

“…XRD coupled with GPC, UV, Raman spectroscopy, elemental (C, H, N and S) analysis and metal (Ni and V) analysis were used to investigate how asphaltene molecules changed under different thermal process [30,[172][173][174] . The harshly thermal cracking increased the aromaticity, but decreased asphaltene M W and L c with alkyl chains broken and aromatic sheets reduced.…”

“…It begins with pyrolysis, and pyrolysis starts with volatile combustion leading to cracking reactions. Besides, metals concentrates in the products of carbon oxidation, devolatilization and depletion of the droplet itself [30,205] . Table 11 lists literatures on pyrolysis and gasification of asphaltenes.…”

“…Soot containing more trace metals than char, reversibly at 1400 °C; V and Ni liberated into gas phase; V content increasing in both char and soot [30] Heavy oil and extra heavy oil, Colombian 127-827 °C; steam Greater than 93% The bimetallic active phase increasing the decomposition of the heavy compounds by an increase in aliphatic chains decomposition and the dissociation of heteroatoms bonds. Also, coke forming after steam gasification process reduced.…”