478
SIZOVA et al.
This result can be attributed to steric factors. The product of naphthalene hydrogenation is tetralin. The
methyl groups in 1,8ꢀdimethylnaphthalene and 2,3ꢀ decalin selectivity significantly decreases; the amount
dimethylnaphthalene are located closer than in the of decalins formed in the system is no more than 30%.
other studied dimethylnaphthalenes. This feature The DBT conversion remains at a level of 94%. The
gives rise to more significant steric hindrances in the DBT conversion level slightly decreases, although the
adsorption of these molecules on the catalyst surface main reaction product is still phenylcyclohexane (a
and thereby leads to a low dimethyldecalin content in selectivity of 48%); the concentration of bicyclohexyl
the reaction products.
in the system decreases to 10% and that of biphenyl is
still more than 40%.
The conversion of 2,3,6ꢀtrimethylnaphthalene
achieves 97%. The main reaction products are trimeꢀ
thyltetralins. Three main isomers are formed: 2,6,7ꢀ
trimethyltetralin, 2,3,6ꢀtransꢀtrimethyltetralin, and
2,3,6ꢀcisꢀtrimethyltetralin. The aromatic ring conꢀ
taining one methyl substituent is hydrogenated more
rapidly than the aromatic ring containing two methyl
substituents; therefore, the main reaction product is
2,6,7ꢀtrimethyltetralin at a selectivity of 69%. The
selectivity for 2,3,6ꢀcisꢀtrimethyltetralin and 2,3,6ꢀ
transꢀtrimethyltetralin is 7 and 10%, respectively. It
should be noted that the migration of the methyl subꢀ
stituents takes place: the products contain up to 4% of
other isomeric forms of trimethyltetralin. In addition,
the cleavage of the methyl substituents occurs; a small
amount (less than 1%) of dimethyltetralins is identiꢀ
fied in the products. A low trimethyldecalin selectivꢀ
ity—8%—is observed in the hydrogenation of 2,3,6ꢀ
trimethylnaphthalene; this fact can also be associated
with the occurrence of steric hindrances during the
adsorption of 2,6,7ꢀtrimethylitetralin by the dimethylꢀ
substituted aromatic ring on the catalyst surface.
Effect of Water
The effect of water on the activity of the catalysts
synthesized in situ by the decomposition of the in situ
salt precursor was studied. Figure 5a shows the depenꢀ
dence of the naphthalene conversion on the weight
fraction of added water at a naphthalene to tungsten
ratio of 105.3 : 1 and a reaction time of 10 h. The data
show that the water has a negative effect on the activity
of the synthesized catalysts. At a water content of up to
1 wt % of the weight of the HC feedstock, the naphthaꢀ
lene conversion decreases insignificantly; however,
even at a water content of 2 wt %, the naphthalene
conversion drops to 70%. The main product of the
hydrogenation of naphthalene in the presence of water
is tetralin; however, at a water content of 1 wt %, the
amount of decalins formed in the system is about 40%,
while at a water content of 2 wt % and more, the decaꢀ
lin concentration in the system does not exceed 8%.
Figure 5b shows the dependence of the naphthalene
conversion on the reaction time at a water content in
the HC feedstock of 3.5 wt % and comparison of the
results with the data on the use of the precursor in the
feedstock without the addition of water (a naphthalene
to tungsten ratio of 105.3 : 1). It is evident from this
dependence that, in the presence of 3.5 wt % water,
hydrogenation hardly occurs at the initial reaction
stages and a considerable activity becomes apparent
after 5 h of reaction. By the reaction time of 10 h, the
conversion is as low as 40%.
To explain the results, the surface of the catalyst in
situ synthesized by the decomposition of the
[BMPip]2Ni(WS4)2 salt precursor in a HC feedstock
containing 3.5 wt % water was studied by XPS. Peaks
characteristic of W, S, C, Ni, N, and O were identified
on the catalyst surface. Deconvolution of the W4
Ni2 , and S2 levels was conducted. The weight ratios
of the resulting phases are listed in Table 6. Compariꢀ
son of the results with the data on the catalyst prepared
in situ in a HC feedstock containing no water (Table 2)
shows that the surface of the catalyst prepared in the
waterꢀcontaining feedstock is in a higher oxidation
state. Thus, the content of tungsten in the sulfide enviꢀ
DBT Conversion Reaction
The catalysts prepared by the decomposition of the
[BMPip]2Ni(WS4)2, salt precursor were used for
experiments on the conversion of DBT. The reaction
was conducted using a 3.5% DBT solution in nꢀhexaꢀ
decane (a DBT : W molar ratio of 26 : 1 mol/mol). In
a 2ꢀh reaction, the DBT conversion is 43%. The main
reaction products are biphenyl (54%) and phenylcyꢀ
clohexane (33%); the amount of the formed bicycloꢀ
hexyl and isomers thereof is 13%. With an increase in
the reaction time to 10 h, the DBT conversion
achieves 95%. The biphenyl content in the products
considerably decreases (to 8%); the main reaction
products are phenylcyclohexane (53%) and bicycloꢀ
hexyl (28%); the amount of the resulting bicyclohexyl
isomers is about 11%. The data suggest that the process
occurs via the route of the direct desulfurization of
DBT (hydrogenolysis the C–S bonds) followed by the
hydrogenation of the aromatic rings of biphenyl; this
feature is characteristic of nickel–tungsten sulfide catꢀ
alysts and consistent with the literature data [24].
f,
p
p
In addition, an experiment on the simultaneous ronment on the catalyst surface does not exceed 18%,
hydrogenation of DBT and naphthalene was conꢀ while the amount of tungsten in the sulfide form on the
ducted. The reaction time was 10 h; the naphthalene surface of the catalyst synthesized in the waterꢀfree
to tungsten ratio was 105.3 : 1; the DBT : W ratio was feedstock was more than 60%. The concentration of
26 : 1. The naphthalene conversion in the presence of nickel in the sulfide environment on the surface also
DBT is 98% and does not decrease; however, the main decreases; up to 70% of nickel is in the oxygen enviꢀ
PETROLEUM CHEMISTRY Vol. 55
No. 6
2015