Process for preparation of anhydrous metallic chlorides from waste catalysts

A process is disclosed for recovering metallic constituents of spent or waste catalysts containing metallic compounds fixed on an aluminous support. The process is particularly applicable for the recovery of metals such as Al, Mo, V, Ni and Co, contained in spent catalyst. The process comprises transforming the metals to be recovered into volatile chlorides by carbochlorination and then separating the chlorides obtained by dry means and fixing them successively in a selective manner. The separation of AlCl.sub.3 is accomplished by passage through granules of anhydrous NaCl, and the separation of MoCl.sub.5 by passage through granules of crystallized KCl. The process is particularly suitable for the treatment of waste catalyst from the catalytic hydrocracking or hydrodesulfurization of oils.

BACKGROUND OF THE INVENTION 
It is generally known that it is possible to treat waste catalysts such as 
those used in oil refining to recover valuable compounds or elements 
contained therein. 
U.S. Pat. No. 2,367,506 describes a process for recovery of the molybdenum 
present in spent hydroforming catalysts having an activated alumina 
support. The process impregnates the catalyst with a sodium carbonate 
solution, then heats the impregnated catalyst to 1150.degree. C. The 
sodium molybdate which is thus formed is dissolved in water, and the 
solution is treated to recover a molybdenum compound. This process, in 
which the final treatment is effected by wet means, is practical only for 
the recovery of an oxide or a salt of molybdenum. 
Dutch (Netherlands) Application No. 74-16155 concerns a process for 
treatment of waste desulfurization catalysts of molybdenum-cobalt alumina 
type, to recover, on the one hand, vanadium and molybdenum, and to 
recover, on the other hand, cobalt and/or nickel. In this process, the 
catalyst is treated such that, without previous roasting in the presence 
of soda or carbonate of soda, the catalyst is air heated to between 
650.degree. and 850.degree. C. The sodium molybdates and vanadates formed 
are extracted with water, and ammonium vanadate is prepared, and then the 
ammonium tetramolybdate is precipitated by hydrochloric acidification. The 
solid residue can be treated separately for extraction of alumina, nickel 
and cobalt. This method is for extraction of molybdenum and vanadium, and 
not for simultaneous extraction of alumina. As in the preceding method of 
the U.S. patent, this method does not permit collection of these metals in 
an anhydrous chloride state. In addition, the process requires direct 
treatment of the waste catalysts by alkaline compounds, which prevents 
recovering the hydrocarbons for subsequent use. 
French Pat. No. 724,905 describes a process of treatment by hydrochloric 
acid or chlorine of materials containing molybdenum, tungsten and 
vanadium, in which it is possible to obtain these metals in chloride form 
if they are found in oxide state in the starting material. The 
chlorination is accomplished at a temperature on the order of 300.degree. 
to 400.degree. C. The carbon necessary for the reaction can be found in 
the starting material, which is the case with catalysts used for the 
hydrogenation of coal. The carbon necessary can also be added in the form 
of coke, lignite, wood charcoal, etc. The chlorides formed in a gaseous 
state can be recovered by condensation and dissolution in water. The 
process does not permit separation of the vanadium and molybdenum 
chlorides. Also, the process conditions are such that there is practically 
no formation of aluminum chloride. 
The processes just described do not permit direct preparation of anhydrous 
metallic chlorides from waste catalysts. 
Moreover, the prior art processes do not provide means for efficiently 
separating the aluminum chloride from at least one of the molybdenum and 
vanadium chlorides. 
THE INVENTION 
The process of the invention solves the above problems in obtaining 
metallic chlorides of high purity from waste catalysts containing 
compounds of these metals along with volatile materials and various 
impurities. This process, essentially using dry, i.e., anhydrous treatment 
steps, has as a significant aspect the recovery of the activated alumina 
support material for the catalysts by transforming them into a very pure 
anhydrous aluminum chloride fixed on the alumina in the form of chloride 
mixtures of NaCl.AlCl.sub.3. It also permits simple and efficient 
separation of the molybdenum and vanadium chlorides from each other and 
also from the aluminum chloride. It is also possible in this process to 
recover the hydrocarbons and the carbon contained in the waste catalysts. 
It is generally preferable to use waste catalysts as they are withdrawn 
from the petroleum treatment installations and without subjecting them to 
any treatment for separation of the volatile materials which they contain. 
These catalysts are generally in the form of small rods or pellets. The 
largest dimensions are generally less than one centimeter. They are 
constituted of an activated alumina support, or gamma alumina, which is 
porous and which is impregnated with compounds containing certain metals, 
particularly molybdenum, most often associated with cobalt or nickel. In 
the course of use of these catalysts, they fix vanadium compounds, carbon 
resulting from the partial decomposition of hydrocarbons, and sulfur, at 
least partially in the form of sulfides and also a certain number of other 
metallic or nonmetallic impurities, generally in combined form, such as 
for example nickel. Finally, in their raw state, these waste catalysts are 
of course still impregnated with a certain quantity of hydrocarbons. 
The first step of the present process is the elimination of the 
hydrocarbons by a sufficiently selective process to avoid elimination of 
the carbon which is present in noncombined state in the pores of the waste 
catalyst. This can be obtained for example by the action of a solvent, for 
instance an organic solvent, as is conventional in the art, for 
elimination of the major part of the hydrocarbons contained in the pores 
of the catalyst. This solvent is then eliminated by distillation at a 
suitable temperature. The hydrocarbons can also be burned, in a strictly 
limited quantity of air so as to stop the combustion before the 
noncombined carbon is also oxidized. This is obtained by heating a mass of 
catalyst to a temperature on the order of 400.degree. C. for approximately 
one half hour in a furnace in the presence of air but without forced 
circulation of the air. Then a combustion of the hydrocarbons is carried 
out, which is practically complete, but the major part of the noncombined 
carbon is not oxidized. 
Alternatively a bed of spent hydrocarbon containing catalyst can be heated 
from the outside while contained in a closed treatment vessel with a flow 
of nitrogen through it, which engages the bed at a temperature on the 
order of 400.degree. C., or better yet, passes through the bed. The 
nitrogen effluent becomes charged with volatile materials which distill 
slowly, a little at a time, and it is thus possible to recover them by a 
condensation procedure. A part of the hydrocarbons which are thus 
recovered can be used for heating the treatment furnace, and the other 
part is used otherwise. Tests have shown that the quantity of hydrocarbons 
thus extracted from the catalysts was on the order of from 10 to 20% by 
weight of these catalysts. 
After the hydrocarbon extraction, the waste catalyst can be directly 
subjected to the action of the gaseous chlorine at a temperature of 
between 500.degree. and 600.degree. C. This operation can be effected for 
example in a vertical nickel column heated from the exterior and partially 
filled with spent catalyst, with a gaseous chlorine current injected at 
the base of the column while the volatile compounds which are formed are 
discharged at the top. Because of the presence of carbon in the pores of 
the catalyst, a reduction of the oxides is produced simultaneously, and 
particularly of the alumina, with chlorination of the reduced metal. The 
sulfur which is also present in the catalyst, principally in the form of 
metallic sulfides, like the carbon, probably also acts as an oxide 
reducer. However, when there is a great excess of carbon, i.e., a 
stoichiometric excess, relative to the quantities of oxides to be reduced, 
it is noted that the major part of the sulfur, and probably almost all of 
it, is found combined in the form of sulfur chloride in the gases which 
are discharged. Tests have shown that there is a very high yield or 
recovery, of chlorides of aluminum, molybdenum and vanadium from the spent 
catalysts treated, which recovery is generally above 90%. The chloride 
yields depend upon operating conditions and they are often a bit lower 
because an excess of chlorine must be present to optimize the process, but 
this is not a major problem, because this excess can be easily recycled. 
The gases discharged from the chlorination column contain, besides the 
excess chlorine, all of the chlorides which are volatile at the treatment 
temperature of the elements contained in the treated catalysts. This has 
to do principally with aluminum chloride and molybdenum and vanadium 
chlorides. Sulfur chloride and generally also silicon chloride are also 
found to be discharged. Finally, the oxygen which was combined principally 
with the alumina is principally in the form of CO.sub.2. The nickel and 
cobalt chlorides which are also formed are generally not volatile at the 
process conditions and they remain in the solid residue within the column. 
Their recovery can be effected, for example, by forming an aqueous 
solution with subsequent precipitation of the hydrates or the carbonates. 
The separation of the aluminum chloride from the other compounds contained 
in the gases from the chlorination is effected very simply by passing 
these gases through a column containing granules of sodium chloride, 
heated to a temperature on the order of 115.degree. to 500.degree. C. and 
preferably 300.degree. to 400.degree. C. Under these conditions, a liquid 
phase is formed, the composition of which is generally NaCl.AlCl.sub.3, 
which liquid phase flows to the base of the apparatus, thus isolating it 
from the gaseous phase. This double chloride can be used as is for a 
number of uses, such as for example the electrolytic preparation of 
aluminum. When using sodium chloride it is necessary to use an anhydrous 
sodium chloride. 
Other means can be foreseen for carrying out this method for separation of 
the aluminum chloride. The anhydrous sodium chloride can be replaced by 
anhydrous potassium chloride, or another anydrous alkaline chloride, or a 
mixture of anhydrous alkaline chlorides. 
The chloride vapors thus obtained are free of aluminum chloride and are 
then treated for the separation of the molybdenum chloride. It has been 
determined, totally unexpectedly, that a selective separation of the 
molybdenum chloride from the other compounds contained in the gaseous 
mixture is possible by passing it through a column containing granules of 
potassium chloride, prepared by crystallization from an aqueous solution, 
brought to a temperature between approximately 100.degree. and 500.degree. 
C. According to prior art literature, the vanadium chloride VCl.sub.4 
becomes fixed to the potassium chloride, producing a double chloride 
VCl.sub.3.3ClK (see Pascal Volume XII pages 132-133). In fact, it has been 
determined that, under the operating parameters herein a fixation of the 
molybdenum chloride by the potassium chloride is produced, while the 
vanadium chloride and the other compounds contained in the gaseous mixture 
are not retained. The molybdenum chloride, which is thus fixed in solid 
state to the surface of the granules of KCl, which is crystallized, can be 
recovered by forming an aqueous alkaline solution with subsequent 
precipitation of the molybdic acid in a known manner, or by any other 
suitable method. 
The vanadium tetrachloride can be recovered very simply from a gaseous 
mixture issuing from the column filled with potassium chloride, by passing 
this gaseous mixture through a condenser at a temperature preferably on 
the order of 60.degree. C., to avoid condensation of the silicon 
tetrachloride. Under these conditions, practically all of the vanadium 
tetrachloride can be condensed at a relatively high degree of purity. The 
other compounds of the gaseous mixture are generally not retained by this 
condenser and remain in a gaseous state. The gaseous mixture, at discharge 
from the condenser, can if necessary be passed through another condenser 
at a lower temperature to retain the volatile silicon and sulfur 
chlorides, or can be simply passed into an absorption tower containing 
soda. 
Instead of using selective condensation, the gaseous mixture containing the 
vanadium tetrachloride can also be bubbled into water and after addition 
of a base (sodium or potassium), can be precipitated by addition of 
ammonium chloride, as the corresponding metavanadate of ammonium. 
The process just described can have numerous variations. The initial step 
for the elimination of hydrocarbons can be carried out continuously in a 
heated column fed with raw waste catalyst at the top, while the catalyst 
with hydrocarbons removed is extracted at the bottom. A nitrogen current 
passing through the column from bottom to top draws the hydrocarbon vapors 
to the outside. The following step of chlorination of the catalyst without 
hydrocarbons, which previously impregnated the catalyst can be effected in 
a column with a chlorine current running through it upwardly and 
constituted of a silica tube heated from the outside by electrical 
resistance heating means. It is also possible to foresee use of a column 
having a refractory lining resistant to chlorine and heated from the 
inside by a carbon electrical resistance heating means. Such a column 
could have means for continuous introduction of waste catalyst to be 
chlorinated at the top, and means for extraction of residues at the 
bottom. 
The column utilized to retain the aluminum chloride by means of the 
anhydrous sodium chloride can also be used continuously, by introducing 
solid granular sodium chloride at the top, while the liquid phase with 
aluminum chloride and sodium chloride is removed continuously at the 
bottom. Finally, continuous operation of the potassium chloride-containing 
column to retain the molybdenum chloride can also be carried out.

The following is a nonlimiting example of the invention carried out on a 
small quantity of waste catalyst. 
A sample of 1 kg of a waste catalyst with an active alumina support and 
containing V, Mo, Co and Ni compounds was used. This sample was first 
treated for two hours at 400.degree. C. in a nitrogen current, to 
eliminate the hydrocarbons and the water. The treatment was carried out in 
a tubular enclosure rotating on its horizontal axis and of 140 mm diameter 
and 600 mm length, heated from the outside and having a flow of nitrogen 
running through at a rate of 20 l./hr. After two hours of treatment, it 
was cooled. 825 g of catalyst with volatile materials removed was 
recovered, and for the most part the volatiles were recovered by 
condensation. These volatiles had approximately 1/3 water and 2/3 a 
mixture of hydrocarbonated compounds. After this treatment the principal 
constituent contents, by weight, were as follows: 
______________________________________ 
C 21% Ni 2.4% 
S 8.4% Co 1.7% 
V 9.4% Si 0.14% 
Mo 5.6% Al 27% 
______________________________________ 
This catalyst was then chlorinated in a vertical nickel tube of 80 mm 
diameter and 500 mm height, heated from the outside to a temperature 
between 500.degree. and 600.degree. C. A chlorine flow was injected from 
bottom to top at approximately 80 l./hr. for 10 hours. A fixed residue of 
245 g was recovered containing by weight: 
______________________________________ 
C 36% Ni 8.1% 
S 4.8% Al 2.8% 
Co 5.6% Si 0.6% 
______________________________________ 
This residue contained only traces of Mo and V, which shows that these two 
metals had been entirely volatilized in the form of chlorides. 
These metals were then separated from an aqueous solution thereof, for 
example, in the form of hydrates or carbonates by known methods. 
The gaseous phase from the chlorination step was introduced to the bottom 
of a column filled with granules of 1 to 2 cm of sodium chloride heated to 
350.degree. C. At the base of the column was observed the outflow of 
approximately 1 kg of a compound, the composition of which corresponded 
essentially to AlCl.sub.3.NaCl. The other constituents of the gaseous 
mixture not retained by the salt were discharged at the top of the column, 
particularly the molybdenum and vanadium chlorides. 
These gases were then injected at the base of a vertical column of 
approximately 60 mm diameter and 40 cm height, filled with potassium 
chloride in crystallized state obtained by crystallization from an aqueous 
solution and comprising grains of approximately 1 to 2 mm and at a 
temperature of 400.degree. C. In this column, the molybdenum chloride is 
fixed to the surface of the KCl grains. 
After passing through the bed of KCl, the gases were discharged from the 
column at the top and then passed through a condenser at a temperature of 
60.degree. C., in which the vanadium chloride VCl.sub.4 is retained. 
Finally, the residual gases were passed over absorbers of known type 
intended to retain the silicon chloride and sulfur chloride. 
Tests have shown that the quantity of molybdenum retained in the form of 
chloride by the column containing the potassium chloride exceeds 90% of 
the molybdenum present in the waste catalyst. The quantity of vanadium 
recovered on the condenser is also more than 90% of the vanadium present 
in the waste catalyst.