NAPHTHALENE HYDROGENATION
67
nium thiotungstate (NH4)2WS4 and nickel nitrate X-ray photoelectron spectroscopy (XPS) studies of
the samples were conducted on a Physical Electronics
PHI-5500 ESCA XPS instrument as described in [12].
Ni(NO3)2 · 6 H2O in DMSO were prepared in three
stages. At the first stage, an emulsion based on an
ammonium thiotungstate solution in DMSO was pre-
Reaction products were analyzed by gas–liquid
pared. To this end, an ammonium thiotungstate solu- chromatography. Naphthalene hydrogenation prod-
tion in DMSO was added to a surfactant solution in a ucts were analyzed on a Kristallyuks 4000 M chro-
hydrocarbon feedstock; the resulting mixture was dis- matograph equipped with a flame ionization detector
persed using a LUZD-1.5 laboratory ultrasonic dis- and a SPB-1 capillary column coated with the
perser at room temperature and atmospheric pressure polydimethylsiloxane stationary liquid phase (dimen-
for 2 min. At the second stage, an emulsion based on a sions, 30 m × 0.25 mm; carrier gas, helium; split ratio,
nickel nitrate solution in DMSO was prepared. To this 1 : 90). Chromatograms were processed using the
end, a nickel nitrate solution in DMSO was added to a NetChromWin software program according to
surfactant solution in a hydrocarbon feedstock; the changes in the relative peak areas (in %) of the sub-
resulting mixture was dispersed using the same strate and products.
LUZD-1.5 laboratory ultrasonic disperser at room
temperature and atmospheric pressure for 2 min. At
the final stage, the resulting emulsions were mixed via
slowly dripping the emulsion based on a nickel nitrate
solution in DMSO to the reverse emulsion based on an
ammonium thiotungstate solution in DMSO under
vigorous stirring at room temperature. The W : Ni
molar ratio was 1 : 1.
Naphthalene conversion was calculated as the
degree of conversion of the feed aromatic compound
to tetralin and decalins. Product selectivity was calcu-
lated as the ratio of the weight of the ith product to the
total weight of the products.
RESULTS AND DISCUSSION
Catalytic Properties
Emulsions based on 1-butyl-1-methylpiperidinium
nickel thiotungstate. Emulsions based on a 1-butyl-1-
The choice of SPAN-80 as a stabilizer for emul-
sions and its content (5.0 wt %) was based on previous
data [10]. In addition, it was shown [10, 16] that the
use of DMSO for the in situ synthesis of Ni–W cata-
lysts requires the introduction of an additional sulfid-
ing agent into the hydrocarbon feedstock. Therefore,
in all catalytic tests, DMDS (2.5 wt %) was addition-
ally introduced into the feedstock. Ammonium thio-
tungstate (NH4)2WS4 and 1-butyl-1-methylpiperidin-
ium nickel thiotungstate [BMPip]2Ni[WS4]2 were
used as precursors.
An increase in the DMSO concentration in the
feedstock can lead to the undesirable replacement of
sulfur atoms by oxygen atoms on the surface of the
in situ synthesized catalyst. Using the example of a
catalyst prepared by the decomposition of
[BMPip]2Ni[WS4]2, it was shown (Table 1) that an
increase in the DMSO content from 0.07 to 0.3 wt %
led to a decrease in the naphthalene conversion from
78 to 62%; a further increase in the DMSO concentra-
tion led to an abrupt decrease in the conversion.
methylpiperidinium
nickel
thiotungstate
[BMPip]2Ni[WS4]2 solution in DMSO were prepared
in a single stage. To this end, a 1-butyl-1-methylpiper-
idinium nickel thiotungstate solution in DMSO was
added into a surfactant solution in a hydrocarbon
feedstock; the resulting mixture was dispersed using a
LUZD-1.5 laboratory ultrasonic disperser at room
temperature and atmospheric pressure for 2 min.
Nonionic oil-soluble sorbitan oleate SPAN-80 was
used as the surfactant; in all the prepared emulsions,
the surfactant content was 5.0 wt %.
A 10% solution of naphthalene in n-hexadecane
was used as the hydrocarbon medium. In all cases,
DMDS was additionally introduced into the hydro-
carbon feedstock as a sulfiding agent in an amount of
2.5 wt % relative to the total weight of the feedstock in
terms of sulfur.
Catalyst Testing Procedure
Two milliliters of the resulting emulsion was placed
Therefore, the minimum DMSO concentration in
into a steel autoclave equipped with a glass cartridge; the hydrocarbon medium (0.3 wt %) was selected for
after that, the autoclave was sealed and filled with further experiments. This concentration was sufficient
hydrogen to a pressure of 5.0 MPa. Reaction was run to dissolve the precursor salts in an amount corre-
at a temperature of 350–400°C under vigorous stirring sponding to a naphthalene to tungsten ratio of 105 : 1.
for 5–10 h. The hydrogen to substrate and naphtha-
lene to tungsten molar ratios were 60 : 1 and 105 : 1,
respectively.
In the case of ammonium thiotungstate and nickel
nitrate used as precursors, the naphthalene conversion
at a temperature of 350°C is significantly lower than
that obtained using 1-butyl-1-methylpiperidinium
nickel thiotungstate (40% vs. 62%). An increase in the
reaction temperature leads to an increase in naphtha-
Catalyst and Product Investigation Procedures
The structure and morphology of the in situ syn- lene conversion in the case of emulsions based on both
thesized solid catalyst samples were examined using ammonium thiotungstate and 1-butyl-1-methylpiper-
a JEOL JEM-2100 analytical electron microscope. idinium nickel thiotungstate (Fig. 1). At higher tem-
PETROLEUM CHEMISTRY Vol. 57 No. 1 2017