Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
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The present invention relates to a novel process for the extraction
and recovery of vanadium and molybdenum, as well as cobalt and/or nickel,
from a spent desul-furization catalyst.
Desulfurization catalysts are extensively used for the catalytic
hydro-desulfurization of petroleum fractions having a sulfur content sufficie-
ntly high to produce atmospheric pollution when such fractions are burned as
fuels. Treatment of the petroleum fraction with hydrogen at suitable temp-
eratures and pressures in the presence of the catalyst results in the
conversion of the sulfur to hydrogen sulfide, which may be recovered. As a
result of this treatment, the desulfurized fractions can be used as clean
fuels, which produce little or no air pollution.
The conventional desulfurization catalysts, in their freshly
prepared state, comprise an aluminum oxide carrier upon which there are
deposited compounds of molybdeDum and cobalt as the active ingredients, In
the course of the desulfurization some of the hydrogen sulfide formed reacts
with the catalyst components to form sulfur-containing metal compounds, such
as metal sulfides. During desulfurization, moreover, the catalyst gradually
takes up vanadium and nickel from the petroleum until these and other
impurities have so reduced the activity of the catalyst that insufficient
desulfurization takes place and the spent catalyst must be replaced with
fresh catalyst.
The spent catalyst therefore may contain vanadium, molybdenum,
cobalt and nickel, as well as aluminum oxide. These metals may be recovered
for re-use, either in the preparation of fresh catalyst, or for other indust-
rial purposes. Various methods have been proposed in the prior art for the
extraction and recovery of the catalyst components.
In Japanese Patent Specification 47-31892 there is disclosed a
two-stage process in which the spent catalyst is first oxidatively roasted
and the resulting product, which contains the oxides of molybdenum, vanadium,
cobalt and nickel, is mixed with an aqueous solution of sodium hydroxide,
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sodium carbonate, sodium bicarbonate, and the like, after which the mixture
is calcined at a temperature above 600C. These alkaline decomposition agents
are used in an amount which is 1.2 to 1.5 times the theoretical amount needed
to convert vanadium and molybdenum into water-soluble salts, such as sodium
vanadate NaV03, and sodium molybdate NaMoO4. The greatest disadvantages of
this method are the cumbersome two-stage procedure, and the problem of roasting
gas disposal (emission of sulfur dioxide) presented by the first stage. By
using an oxidative roasting stage in treating such a spent desulfurization cata-
lyst, however, the environmental advantages obtained by the desulfurization of
the petroleum fractions are partly undone unless costly provisions are made
for controlling undesirable sulfur dioxide emissions.
In accordance with the present invention, there is provided a process
which obviates the need for the uneconomical two-stage procedure of the prior
art, with its attendant air pollution. It has been found, surprisingly, that
the oxidative roasting stage can be omitted if the treatment with alkaline
decomposition agents in the second stage is carried out with a sufficiently
large amount of a solid alkali metal carbonate in the presence of air. Thus,
in accordance with the invention, there is provided a process for the extrac-
tion of vanadium and molybdenum from a spent desulfurization catalyst containing
the same and having an aluminum oxide carrier, said spent catalyst not having
been subjected to previous oxidative roasting, comprising the steps of: (a)
intimately admixing comminuted spent catalyst with an amount of a solid alkali
metal carbonate sufficient to convert the vanadium, molybdenum, and any sulfur
which may be present, into water-soluble compounds; (b) heating the mixture
produced in step (a) in the solid state in the presence of air at a temperature
between about 650C and about 850C for a period between about 1 and about 2
hours; and (c) leaching the product of step ~b) with water to dissolve the
vanadium and molybdenum compounds and recovering said compounds from the ex- -
tract; the amount of solid alkali metal carbonate also being sufficient so that
the extract of step (c); after filtration, has a pH higher than 7.5 but lower
than 10Ø
-2-
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of about 6J0C ~o d~Ut 850C, in the prFs~5-o-f~~ai~
The amount of alkali metal carbonate required for practically
complete conversion of the sulfur, vanadium and molybdenum present can be
caloulated on the basis of an accurate ~ s of the spent catalyst comp~
osition or, as described hereinafter, can be established experimentally in
a simple and accurate manner. The compositions of spent desulfurization
catalysts may, of course, vary with the starting composition of the fresh
catalyst, and the composition of the hydrocarbon feed treated. The process
conditions under which the hydro-desulfurization is carried out also plays
a part.
A typical average composition of spent cobalt-molybdenum-aluminum
oxide catalyst, often occur~ingin actual practice is shown in the following
Table A:
Table A
Average Composition of Spent Co-Mo-Al Catalyst
Constituent Per Cent by l~eight
Aluminum Oxide 35 - 37
Hydrocarbon Oil (extractable
with heptane or benzene) 16 - 18
Sulfur 13 - 14
Carbon 12 - 15
Vanadium 8.4-8.8
Molybdenum 3.5-3.8
Nickel 2.6
Cobalt 2.0
Silicon Dioxide 1.0
Iron 0.1
Titanium 0.1
In the process according to the inventionl there may be employed as
alkali metal carbonate, any of the carbonates of sodium, potassium, lithium,
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rubidium or cacsium. (~I economic grounds i1: is preferred to use the inexpen-
sive sodium c~rbonate, for example in the form of calcined soda having an
~a20 content of about 47~ to ~9% by weight.
In practice the weight ratio of spent catalyst to calcined soda
is preferably in the range of 1:0.5 to l:n.9. Thus, in the case of a spent
catalyst having a composition as shown in Table A there is required per 1 kg
of spent catalyst, about 0~6-0.7 kg of calcined soda having an Na20 content
of about 47-49% by weight to convert 96-98% of the vanadium and 97-~8% of
the molybdenum into water-soluble compounds.
The catalyst-soda mixture must be heated in the presence of air
for a period of 1 to 2 hours at a temperature in the range of about 650 to
about 850C., preferably in the range of about 750 to about 825C. The
process may be carried out statically (with a non-moving reaction mass) or
dynamically (with a moving reaction mass).
The air is supplied in an amount varying from about 1 to about
10 Nm3/kg of spent catalyst. It is preferred to apply the air in an amount
in the range of about 3 to about 5Nm3/kg of spent catalyst. In the static
procedure only about 7% of the sulfur contained in the spent catalyst will
get into the effluent gases and in the (preferably used) dynamic procedure
the proportion will be even as low as 2%, Calculated on the weight of the
spent catalyst, about 1% by weight of sulfur (static procedure) and about
0.3% by weight of sulfur (dynamic procedure), respectively, will consequently
be emitted as S02.
Per kg of spent catalyst having the composition given in Table A
(13-14% by weight of sulfur), about 500 g of calcined soda are required for
the bonding of the sulfur. Although this large amount of soda may seem
uneconomical, a multiple compensation is obtained by the simplified one-stage
procedure of the in~ention and the large saving in capital expenditure which
would otherwise be required for the oxidative roasting stage and the purific-
ation of roasting gas.
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~ he product whicll has been treated with alkali metal carbonate is
extracted with water and the vanadium- and molybdenum- containing extract
is separated from the residue. By adding ammonium chloride to the extract,
the vanadium can be directly isolated in very pure state as ammonium vana-
date Nl-l4V03. In the same way the molybdenum can be precipitated as ammonium
tetramolybdate, by using hydrochloric acid at a pll of about 2.5.
After drying, the extraction residue contains about 40 to 42% by
weight of the spent catalyst ald mainly consists of A12o3, CoO and/or NiO.
Calculated on the spent catalyst, the vanadium content of the residue is only
about 0.4% by weight and the molybdenum content about 0 2% by weight. From
the residue, aluminum, cobalt and/or nickel can be recovered by conventional
methods, for example by the method described in German Offenlegungschrift
No, 2,316,837. This method involves treating the residue with sodium hydr-
oxide solution in an autoclave at elevated temperature for a sufficient per-
iod of time for the aluminum to be brought completely into solution as sodium
aluminate. Thereafter the mixture is filtered, and aluminum hydroxide
precipitated from the solution by acidification to a pH of about 4 to 7.
This can be calcined to aluminum oxide for use in preparing fresh catalyst.
The cobalt and/or nickel are recovered from the residue, for example, by
reduction of the oxides thereof with hydrogen, leaching with sulfuric acid,
and separating the cobalt as a cobalt-amine complex, or similarly the nickel,
from which the respective metals may be obtained by hydrogen reduction.
The following examples serve to illustrate the practice of the
invention, but are not to be regarded as limiting:
Example 1
A spent cobalt-molybdenum-aluminum oxide desulfurization catalyst
having the composition: A1203 35%, extractable hydrocarbon oil 16%, sulfur
13%, carbon 12%, vanadium 8.4%, molybdenum 3.5%, nickel 2.6%, cobalt 2.0%,
SiO2 1.0%, iron 0.1%, and titanium 0.1%, was prepared in a series of 1 kg
samples, after preliminary grinding. After mixing with various ratios of
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calcined soda (48% by weight ~a20), the samples were ground again. The
catalyst is ground into a sufficient~y small ;particle size, so that upon
admixture with the soda, the color of the mixture will he a uniform black to
dark greY.
In this manncr for the experimental determination of the amount of
soda required, according to the present invention, catalyst-soda mixtures
were prepared which respectively contained 0.8, 0 7, 0.6, 0.5, 0.4 and 0.3
parts by weight of soda to one part by weight of spent catalyst.
For each experiment, starting from 20 g of spent catalyst, mixtures
with 16, 14, 12, 10, 8 and 6 g of calcined soda were prepared, which were
spread over 2 ceramic plates in a layer thickness of 5 mm, the varîous mixtur-
es being spaced at 2-3 cm intervals. The mixtures were heated in the
presence of air (about 4 liters of air per g of spent catalyst) in a muffle
furnace for 2 hours at 800C, evaluated visually, treated as described above
by extraction with water, separating the vanadium- and molybdenum extract by
and filtration,adding ammonium chloride solution to convert these oxides to
ammonium salts.
The results are summarized in the following Table B. In the table
the (dry) residue of the extraction with water is expressed as a percent by
weight of the spent catalyst. The pH values are indicated for the suspension
(left hand figures) and for the clear filtered extract (right hand figures).
The percentages of vanadium and molybdenum in the residue are based on the
weight of the dry residue. The percentages of undissolved vanadium and
molybdenum are calculated on the amounts of V and Mo contained in the untreat-
ed catalYst.
From the precentages of V and Mo in the residue (columns 6 and 7)
it follows that in the case of this spent catalyst the amount of soda should
not be less than that used for mixture 3. As to mixture 1, however, the
percentage extraction residue (35.0) shows that too much soda was used as a
result of which an appreciable amount of aluminum oxide went into solution.
,........... . . ~ . .
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l~lus, the correct catalyst/soda ratio is in the range of 1:0.6 to 1:0.7
(mixtures 2 and 3). ~s the yield of vanadium and molybdenum for mixture 2
is only slightly higher than that for mixture 3, it will for economic reasons
be preferred to use the ratio 1:0.6 (mixture 3).
Visual observation of the alkali metal carbonate treated products
leads to the conclusion that if their color is a pure blue, vanadium and
molybdenum can be extracted almost completely. The lower limit of the soda
proportion to be used is reached when the product is no longer a pure blue.
Green roasted products contain too little soda.
The correct mixing ratio can be established far more accurately-
particularly in view of the going into solution of aluminum oxide - by
determining the pH value of the clear (filtered) extract (column 5, right-
hand figures). The pH value of the filtered solution must be higher than
7.5 but lower than 10Ø
By using a mixing ratio of 1:0.65 a practically complete extraction
of vanadium and molybdenum is assured, and the extraction solution will still
be so weakly alkaline then that aluminum oxide can go into solution in only
very small quantities (1-2%).
1~)48789
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