WO1995001461A1

WO1995001461A1 - Method for extracting metals from catalysts on the basis of al2o¿3?

Info

Publication number: WO1995001461A1
Application number: PCT/NL1994/000148
Authority: WO
Inventors: Cornelis Leonard Van Deelen
Original assignee: Nederlandse Organisatie Voor Toegepast- Natuurwetenschappelijk Onderzoek Tno
Priority date: 1993-06-29
Filing date: 1994-06-24
Publication date: 1995-01-12
Also published as: NL9301133A; AU6985494A

Abstract

The invention relates to a method for extracting metals from spent catalysts on the basis of Al2O3, which method involves calcining the catalyst - if contaminated with carbon and hydrocarbons and the like - in an oxidizing environment, heating the catalysts obtained in the process for 0.5-3 hours to 1000-1200 °C in ordet to bring about a conversion of η-Al2O3 into α-Al2O3 without sintering of α-Al2O3 and concomitant inclusion of the metals to be extracted occurring, then solubilizing the metals cobalt, molybdenum, nickel, vanadium and/or tungsten from the heated catalysts with the aid of an acid, advantageously at a final pH of 1-2, and then extracting the solubilized metals from the leachate. With the aid of this method it is possible to recover optimally the metals from spent catalysts arising in a wide variety of processes, such as, for example, the catalysts used in the hydrodesulphurization of heavy petroleum fractions.

Description

Method for extracting metals from catalysts on the basis of A1₂0₃

The invention relates to a method for extracting metals from metal-containing catalysts on the basis of A1₂0₃. A1₂0₃ is a widely used support material for a wide variety of types of catalysts. More in particular, such catalysts can be used in the hydrogenation, hydrocracking and desulphurization of oil fractions as well as for hydrofinishing and hydroconversion reactions in a wider sense such as H₂S production, Claus T.G. treatment, incineration, etc. All these catalysts as a rule contain metals such as cobalt, molybdenum, nickel, vanadium and/or tungsten. After use, these catalysts contain valuable metals which can potentially be reused and must therefore be recovered.

An example of a catalyst used on a large scale is the HDS catalyst (HDS = hydrodesulphurization) which is employed in the desulphurization of heavy petroleum fractions. A catalyst of this type consists of a γ-Al₂0₃ support bearing the metals cobalt and nickel. During the desulphurization process, deposition of carbon

(coke) , sulphur and other components present in the petroleum, such as metals, inter alia vanadium, takes place on the catalyst.

As a result, the activity of the catalyst gradually decreases and the catalyst is - having been restored a number of times - discarded on economical grounds and regarded as waste. Owing to, inter alia, increasing concern regarding the environment, the option of dumping, even under controlled conditions, is perceived as problematic.

Attempts have therefore been made to recover for reuse those metals which are regarded as valuable, such as molybdenum, nickel and cobalt. To this end, a number of processes have been developed such as a) pyrometallurgical processes, i.e. melting processes which involve - after removal of carbon and sulphur - e.g. reacting the spent catalysts under reducing conditions (in the presence of carbon monoxide or hydrogen) at a temperature of from l600 to 1700 C, resulting in a melt of cobalt, molyb¬ denum, nickel and/or vanadium with an A1₂0₃ slag floating thereon; and b) hydrometallurgical processes, i.e. the wet-chemical route, in which - after removal of carbon and sulphur - the molybdenum and vanadium are dissolved in an alkaline medium at high temperature and under high pressure (autoclave). These metals are then obtained as the oxide or salt. A residue of A1₂0₃ remains behind in which cobalt oxide, nickel oxide or sulphide are present. This method therefore has the drawback that a residue containing valuable metals remains. Another technical drawback of this process is that A1₂0₃ (support material) dissolves in the process and, as colloidally fine particles, may cause separation problems.

A method, which can be carried out industrially and economic¬ ally, for extracting metals from the above-described types of spent catalysts on the basis of A1₂0₃ has now been found which is characterized in that

(a) the catalysts - if required - are calcined in an oxidizing environment;

(b) the catalysts obtained under stage (a) are heated for 0.5-3 hours to 1000-1200°C;

(c) the metals molybdenum, nickel, cobalt, vanadium and/or tungsten present in the catalysts obtained under stage (b) are solubilized with the aid of an acidic medium; and

(d) the solubilized metals obtained are extracted from the leachate.

One of the important aspects of the invention is that in stage (c) the metals are solubilized in an acidic medium, so that all the metals considered important can be leached in one step and are not, as in the abovementioned wet-chemical route, lost to some extent or do not have to be extracted in for example an additional step. Another important aspect of the invention is that after the application of stage (b) the A1₂0₃ does not dissolve or virtually no longer dissolves in the acidic medium used in stage (c) , so that the separation problems, for example with the filtration of the reaction composition, which are associated with the colloidally fine A1₂0₃ particles which have gone into solution on, for example, the wet-chemical route, are prevented by means of the method according to the invention.

With regard to the stages (a)-(d) of the method according to the invention, the following particulars are given.

Stage (a) is applied if the spent catalysts originate from processes in which they are contaminated with carbon (coke) and hydrocarbons. An example of such a process is the abovementioned hydrodesulphurization process (desulphurization process) of heavy petroleum fractions. Advantageously, the calcining stage (a) is carried out in a fluidized-bed furnace. In this stage, in principle, using oxygen (air) as the oxidant, the following reactions take place: carbon is converted to carbon dioxide, hydrocarbons are converted into carbon dioxide and water, and the metal sulphides into metal oxides. At the same time, under the conditions prevailing in stage (a) , the γ-Al₂0₃ used as the support may partially turn into α-Al₂0₃. In order to control a possible undesirable course of this last reaction, stage (a) is preferably carried out at a temperature in the range of 750-950°C, a time span of 10-30 minutes often.being considered sufficient to achieve complete calcination, i.e. removal of all the carbon and hydrocarbons as well as complete conversion of the metal sulphides into the corresponding metal oxides. It is also possible, however, to employ a longer treatment time of, for example, more than 1 hour.

Regarding the process conditions such as the abovementioned temperature range having an upper limit of 950°C, it should be noted that, when higher temperatures such as 1000°C were employed, it was found that, owing to the relatively large scatter in residence time of the catalyst particles in the fluidized-bed furnace used at this higher temperature, part of the metals considered valuable is trapped in the support material and therefore is no longer liberated in the solubilization, carried out in stage (c) with an acidic medium corresponding to a "standard solubilization test" defined below.

As regards the catalysts used in the fluidized-bed furnace these are often cylindrical and have a diameter, as used in practice, of 1.5~3 mm and a length of 0.5-2 cm. Depending on the conditions in the fluidized-bed furnace, heavy wear of the particles occurs. The smallest particles are discharged via a cyclone connected to the fluidized-bed furnace, while the remainder is extracted as the product stream from the furnace bed.

On process-engineering grounds, the fluidized-bed furnace is operated under slight reduced pressure, e.g. approximately 1 cm of water. This prevents, for example, S0₂ as well as other noxious gases from being able to escape from the installation. Such a reduced pressure can be obtained by mutually matching the blower which controls the air supply and the exhauster which controls the discharge of the combustion air.

In order to carry out stage (a) in a fluidized-bed furnace, air is injected at the bottom of a pipe which is arranged vertically and is advantageously made of ceramic concrete. This air serves both as the combustion air and the fluidization medium. The catalyst can be supplied with the aid of a conveyor belt and then be introduced into the bed via a feed pipe.

For the purpose of starting up the fluidized-bed furnace, the bed is often preheated by means of a gas burner to a temperature of approximately 450°C. If spent catalyst is then added in doses, the temperature rapidly rises to above 750°C.

The calcined catalyst is then heated in stage (b) for 0.5^_3 hours to a temperature of 1000-1200°C. The purpose of this stage is to effect as complete a conversion as possible of γ-Al₂0₃ into α-Al₂0₃, because γ-Al₂0₃ dissolves under the conditions applied in stage (c) and, inter alia, gives rise to serious problems in the separation of liquid and solid, e.g. by filtration, while α-Al₂0₃ does not or virtually does not dissolve under these conditions. Care should be taken, however, in said stage (b) to limit sintering of α-Al₂0₃ as far as possible since, owing to the sintering together of α-Al₂0₃ particles, the metals to be extracted are trapped and are no longer solubilized under the conditions applied under stage (c), which gives rise to loss of the metals to be extracted. Stage (b) is therefore advantageously carried out on a belt furnace or in a rotary calciner, since in such a type of furnace the conditions can be controlled reasonably accurately. Preferably, the calcined catalyst particles from stage (a) are treated for a period of 0-70 minutes at a temperature of 1050- 1100°C on a belt furnace or in a rotary calciner. Thus virtually complete conversion of γ-Al₂0₃ into α-Al₂0₃ is obtained, while the degree of sintering of the α-Al₂0₃ produced remains within accep¬ table limits. Thus treated catalyst particles are obtained from which the metals considered valuable, such as cobalt and molybdenum, can be extracted at a percentage which is more than 90% and even almost 100%. For the purpose of the acidic solubilization of the metals, carried out in stage (c) , any strong inorganic acid such as nitric acid and advantageously hydrochloric acid and sulphuric acid can be used. Particularly good results can be obtained with sulphuric acid, e.g. 0.1-8 M H₂S0^ and, in particular, with 0.3-0.8 M H₂S0_ή. The final pH used of the metal solubilization stage (c) is advantageously 1-2. A final pH of less than 0.5 causes problems, because in that case relatively large amounts of A1₂0₃ go into solution which results in very finely divided, hydrated A1₂0₃ particles, which results in a highly adverse effect on the filtration properties of the suspension. At the same time, an undesirable loss of acid occurs in this process of leaching A1₂0₃. Further, in stage (c) a suspension having a solids content of 2-^0 % by weight is advantageously employed since, if solids contents are higher, some in a practical sense somewhat problematic treatment of the reaction composition takes place, such as agitating the suspension by means of an agitator.

The extraction or solubilization yield of the acidic solubilization, carried out in stage (c) , of the metals is determined with the aid of the "standard solubilization test" below. 5 g of the product of the temperature treatment are weighed accurately and transferred to a ground-thermal joint 250-ml conical flask, together with a teflon-coated stirrer bar. The conical flask is placed on a hotplate with a magnetic stirrer and is provided with a quick-fit condenser. 200 ml of ^M sulphuric acid are then added via the quick-fit condenser, and the magnetic stirrer is started at 250-300 min^"1. The suspension is brought to the boil and is stirred for 60 min with continuous boiling. The suspension is then filtered hot with suction via a 0.45-micrometre membrane filter. The residue on the filter is rinsed with ± 150 ml of demineralized water and then dried at 105^°C. The filtrate is transferred to a volumetric flask and, after cooling to 25 C, made up to 500 ml with demineralized water. After drying, the residue is weighed. The filtrate is then analyzed for the elements Co, Ni, Mo and Al and, in some cases, for Fe and V.

Finally, in stage (d) , the solubilized metals - after filtration of the suspension - are extracted from the leachate. For this purpose, the generally known techniques such as ion exchange, crystallization and, advantageously, solvent extraction such as using Alamine 336^® in Shell Sol R^® can be used. The recovery of the metals from purified solutions is possible by precipitation, electrolysis, crystallization or evaporation.

Example I

In order to carry out stage (a) , a fluidized-bed furnace having an internal diameter of 0.5 m and an overall height of 4.5 m was used. The maximum bed height was 1.5 m. Above the bed there was a so-called freeboard of amply 2 metres. The fluidized-bed installation was provided with a blower (for the purpose of air supply) and an exhauster (for the purpose of discharging combus¬ tion air) . By means of mutual matching of the blower and the exhauster, a slight reduced pressure of 1 cm of water was created in the fluidized-bed furnace. The fluidized-bed furnace was further provided with a cyclone (for intercepting the small catalyst particles) and an air preheater.

During operation of the fluidized bed, air was injected via the blower at the bottom of the vertically arranged pipe of ceramic concrete. The bed was preheated to 450°C with the aid of a gas burner. The catalyst sample EXD 151, which came from a hydrodesulphurization process, was supplied via a conveyor belt and introduced into the bed in doses via a downpipe, the temperature rapidly rising to above 750°C. The composition of the sample EXD 151 used was a Co/Mo catalyst and had the following composition: TABLE A

EXD 151

Carbon 23.8 %

Sulphate 0.60 %

Sulphur 4.10 %

Cobalt oxide 2.03 %

Molybdenum oxide 8.25 %

Nickel oxide 0.05 %

Aluminium oxide 46.9 %

Water 3.5 %

Remainder 10.8 %

Under the conditions prevailing in the fluidized-bed furnace, complete oxidation of carbon (coke) as well as hydrocarbons and sulphides was achieved. Complete calcination of the sample EXD 151 (diameter 3 ^mm) took approximately 20 minutes.

An attempt to combine stage (a) and stage (b) , i.e. the calcination of the catalyst and the conversion of γ-Al₂0₃ into α- A1₂0₃, was investigated in the above-described fluidized-bed furnace by means of the following experiments shown in Table B.

TABLE B

Temp. Time

Sample I 1000°C 200 min

Sample II 1000°C 150 min

Sample III 1000°C 75 min

Sample IV 950°c 75 min

Sample V 1050°C 4 min

In sample I, only from 10 to 12% by weight of aluminium oxide could now be solubilized by means of the "standard solubilization test", while only 50% of the cobalt could be leached. The low degree of solubilization of A1₂0₃ suggested an effective conversion of γ-Al₂0₃ into α-Al₂0₃, but was associated with considerable trapping of the cobalt. In sample IV from the cyclone outlet, however, 45% of the aluminium oxide still went into solution and only about 60% of cobalt was leached. In this sample, incomplete conversion of γ-Al₂0₃ into α-Al₂0₃ took place, therefore, in combination with nevertheless insufficient solubilization of the cobalt under the conditions of the "standard solubilization test". The other samples gave results which were in between those of samples I and IV.

It follows therefore, from the above data, that the fluidized bed employed could not be used for carrying out the abovementioned aluminium oxide conversion at the same time without effecting excessive trapping of the metals or adequate solubilization thereof in the "standard solubilization test". The problem, apparently, was not so much the residence time but primarily its scatter. For an average residence time of 60 min, with the firing regimen followed, the scatter of the residence time was very large. The latter varied between 20 and 120 min for 90 % of the material. This implied that for part of the treated material the conversion of γ-Al₂0₃ into α-Al₂0₃ had not yet taken place (time = 20 min) , while for another part it was possible for trapping of the metals to have already occurred (time = 120 min).

It should further be noted that possible evaporation of the hydrocarbons from the catalyst particles and secondary combustion thereof in the freeboard of the fluidized-bed furnace did not occur. This was particularly advantageous, since no particular process-engineering measures had to be taken regarding the freeboard.

For the purpose of carrying out stage (b) , the abovementioned sample IV was used. This sample was treated at 1100°C for 60 minutes on a belt furnace. This sample treated in stage (b) gave, in a subsequent standard solubilization stage (c) (in an acidic medium, i.e. 4M H₂S0,), a solubilization yield for cobalt of nearly 100°C, while that for A1₂0₃ was reduced to less than 5% - The values for the extraction or solubilization yields, as well as the treatment conditions, are shown in Table C below. TABEL C

Conditions stage (b) Loss on Extraction calcination yields

Sample Temp Duration % Co Mo Al C min. % % %

IV bed 1100 60 29.4 98.9 48.3 l.l

IV bed no secondary treatment 25.O 45.1 55.O 44.4 (no stage (b) )

IV cyclone 1100 60 29.4 94.1 71.O 4.7

IV cyclone no secondary treatment 25.O 56.8 69.845.4 (no stage (b) )

The reason for the molybdenum yield being rather low is that molybdenum oxide evaporates at the high temperature employed. If a correction is made for the evaporated molybdenum oxide (which can be collected by cooling) , the extraction yield for molybdenum is likewise found to be more than 90%.

The invention is explained in more detail in the accompanying Figures 1-3-

Fig. 1 shows the relationship between the solubilization yields of Co, Mo and Al and the secondary treatment, carried out in stage (b) , of sample IV.

Fig. 2 shows the relationship between the solubilization yields of Co, Mo and Al and the acid strength in M H₂S0z, of the secondary treatment, carried out in stage (b) , of sample IV.

Fig. 3 shows the relationship between the solubilization yields of Co, Mo and Al and the acid strength in M H₂S0^ without the secondary treatment, carried out in stage (b) , of sample IV.

Claims

1. Method for extracting metals from metal-containing catalysts on the basis of A1₂0₃, characterized in that

(a) the catalysts - if required - are calcined in an oxidizing environment;

(b) the catalysts obtained under stage (a) are heated for 0.5^_3 hours to 1000-1200°C;

(d) the solubilized metals obtained are extracted from the leachate.

2. Metals according to Claim 1, characterized in that stage (a) is carried out in a fluidized-bed furnace.

3. Method according to Claim 1 or 2, characterized in that stage (a) is carried out at a temperature in the range of 750-

950°c

4. Method according to one or more of Claims 1-3. characterized in that stage (a) is carried out for 10-30 minutes.

5« Method according to one or more of Claims 1-4, characterized in that stage (b) is carried out for 50-70 minutes at 1050-1100°C.

6. Method according to one or more of Claims 1-5. characterized in that stage (b) is carried out on a belt furnace or in a rotary calciner.

7. Method according to one or more of Claims 1-6, characterized in that stage (c) is carried out with the aid of hydrochloric acid or sulphuric acid.

8. Method according to one or more of Claims 1-7, characterized in that stage (c) is carried out with the aid of an acid at a final pH of 1-2.

9. Method according to one or more of Claims 1-8, characterized in that stage (c) is carried out with O.3-O.8 M

10. Method according to one or more of Claims 1-9. characterized in that stage (c) is carried out with a suspension having a solids content of 2-40 % by weight.

11. Method according to one or more of Claims 1-10, characterized in that stage (d) is carried out by means of solvent extraction.