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OIL SHALE
TABLE 1
ADSORPTION (MOL%) OF INORGANIC NITROGEN COMPOUNDS
ON US-Y ZEOLITE*
Pgse fmo) N Compound
Naph
Zeolite thalene Py An Oil i-Qu ing; Acr Phen Carb
50 81 35 78 97 20 65 68 23
100 98 66 >99 >99 44 99 94 56
100 98 60 >99 >99 60 >99 99 75
200 97 95 >99 >99 >99 >99 99 87
200 50 >99 >99 >99 >99 63 >99 >99 91
200 100 >99 >99 >99 >99 76 >99 >99 93
200 200 >99 >99 >99 >99 94 >99 >99 68
?Using 10 ml of hexane solution of eight bases (1 mg each)
Py= pyridine; An = aniline; Qu = quinoiine; i-Qu= isoquinoline; lnd = indole; Acr = acridine; Phen = phenan
thridine; Carb = carbazole
In a further experiment, increasing amounts of an
aromatic hydrocarbon (naphthalene) were added
to see how selectively the zeolite would adsorb
small concentrations of N heterocycles in the
presence of larger concentrations of aromatic
hydrocarbons, as would occur in a hydrotreated
shale oil. All except indole and carbazole were
still adsorbed efficiently. Table 1 also shows that
N compounds have a much higher affinity for the
zeolite cavities than do aromatic hydrocarbons.
This reflects the high acidity of these cavities. In
accord with this, the more basic N compounds
were more strongly adsorbed. The tendency for
stronger bases to be adsorbed more strongly is
relevant to the expected performance with
hydrotreated oil. During hydrotreatment, the ring
containing the N atom is reduced more easily
than are other aromatic rings in a pdycyciic
molecule, and the reduction of the heterocyclic
ring precedes hydrogenolysis of the N atom. As
a result, much of the residual N in a hydrotreated
shale oil should be more basic than the N in the
2-14
fully
aromatic precursors and therefore should be
more strongly adsorbed by the zeolite.
Finally, a shale oil from Stuart (Queensland)
which had been subjected to mild hydrotreat
ment (380C, 7 MPa, 0.4 h; residual
N = 2,000 ppmw)
was diluted with hexane (to
reduce viscosity) and treated with zeolite. The
total removal of g.c.-volatile, acid-extractable
compounds was >99 percent.
The N compounds recovered from the zeolite
contained only small amounts of alkanes. Hence
only minor losses of hydrocarbons would occur
in heating the zeolite to burn off the adsorbed N
compounds before recycling. The adsorption ef
ficiency
times was the same as fresh zeolite (Table 1).
Conclusions
of zeolite which had been recycled five
Based on their results, the authors suggest that
zeolite adsorption could provide an efficient alter-
THE SYNTHETIC FUELS REPORT, JANUARY 1995