Different severities of hydrotreatment were performed on a raw decant oil and one of its subsequent hydrotreated decant oils. Six hydrotreated decant oils with different chemical composition were obtained during this process. The products obtained from the raw decant oil showed difficulty in sulfur removal. Higher desulfurization was obtained after repassing the first drum of product (EI-132) at a reduced feed rate (LHSV 0.5h −1 ), higher temperature (734°F and 750°F), and higher reactor pressure (8.3 MPa). Several analyses were performed to characterize the decant oils: elemental analysis, 1 H and 13 C NMR, asphaltene content, average boiling point, API gravity, GC/MS, and viscosity. Two structural parameters derived from the 1 H NMR spectra and elemental analyses were calculated: aromaticity (fa) and the fraction of aromatic edge carbons carrying substituents (σ). All the information gathered from the different techniques was helpful to understand the chemical transformations taking place during hydrotreatment of decant oils. It was observed that hydrogenation of aromatic rings and hydrodealkylation were the dominant reactions in the severely hydrotreated decant oils (EI-137 and EI-138) while the formation of alkyl side chains was observed in the low and intermediate hydrotreated decant oils, (EI-133 and EI-134) and (EI-135 and EI-136), respectively.
The introduction of sorbents into the gasifier during in-situ desulfurization processes using
calcium-based sorbents leads to the occurrence of some reactions, mainly between the calcium
(Ca) in the sorbents and some minerals contained in the ash, especially iron (Fe). These reactions,
which are between solid phases (solid−solid), affect the absorption ability of the sorbents. The
occurrence of solid−solid reactions, however, depends on a number of factors. In this paper, the
effect of sorbent particle sizes on the occurrence of solid−solid reactions in desulfurization
processes has been investigated using a laboratory-scale fixed bed reactor. Mineral compositions
in the spent sorbent−ash mixture were analyzed by X-ray diffraction, and the elemental
distribution within individual particles was determined by the electron probe micro analysis
(EPMA). Results show that the occurrence of solid−solid reactions increases with decreasing
particle size, which is accompanied with the reduction of the sulfur absorption ability of a sorbent.
Increasing the iron concentration in the coal ash led to the occurrence of more solid−solid
reactions, suggesting that in high-iron-content coals, the effects of solid−solid reactions may be
more serious. Despite the fact that iron is the major player in the occurrence of solid−solid
reactions, other minerals present in the ash seem to play a catalytic role.
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