NL9301133A - Process for recovering metals from AlêOë based catalysts. - Google Patents

Description

Process for recovering metals from A12Q3 based catalysts.

The invention relates to a process for recovering metals from metal-containing catalysts based on Al2 O3.

A1203 is a widely used support material for many types of catalysts. More particularly, such catalysts can be used in the hydrogenation, hydrocracking and desulfurization of oil fractions as well as for the hydrofinishing and hydroconversion reactions in a broad sense such as H 2 S production, Claus T.G. treatment, incineration, etc. All these catalysts generally contain metals such as cobalt, molybdenum, nickel, vanadium and / or tungsten.

After use, these catalysts contain valuable metals, which are suitable for reuse and must therefore be recovered.

An example of a widely used catalyst is the HDS (HDS = hydrodesulphurization) catalyst, which is used in the desulfurization of heavy petroleum fractions. Such a catalyst consists of a carrier of γ-Α1203 on which the metals cobalt and nickel are located. During the desulfurization process, precipitation of carbon (coke), sulfur and other components present in the petroleum, such as metals, including vanadium, takes place on the catalyst. As a result, the activity of the catalyst gradually decreases and - after a number of reprocessing - it is discarded for economic reasons and is considered waste. Partly due to the increasing concern for the environment, the possibility of dumping, even under controlled conditions, is recognized as objectionable.

An attempt has therefore been made to recover the metals considered valuable, such as molybdenum, nickel and cobalt, from such waste catalysts for reuse. A number of processes have been developed for this, such as a) pyrometallurgical processes, i.e. melting processes in which - after removal of carbon and sulfur - e.g. the spent catalysts are reacted under reducing conditions (in the presence of carbon monoxide or hydrogen) at a temperature of 1600 to 1700 ° C. A melt of cobalt, molybdenum, nickel and / or vanadium is hereby obtained with an Al2O3 slag floating thereon; and b) hydrometallurgical processes, i.e. the wet chemical route, wherein - after removal of carbon and sulfur - the molybdenum and vanadium are dissolved in a basic medium at high temperature and under high pressure (autoclave). These metals are then recovered as oxide or salt. A residue of Al2 O3 remains, in which cobalt oxide, nickel oxide or sulfide are present. This method therefore has the drawback that a residue with valuable metals remains. A technical drawback of this process is also that it dissolves Al2 O3 (carrier material) and can cause separation problems as colloidal fine particles.

It has now been found a technically and economically feasible process for recovering metals from the above-mentioned types of finished Al 2 O 3 catalysts, which is characterized by (a) calcining the catalysts, if required, in an oxidizing medium; (b) heating the catalysts obtained under step (a) at 1000-1200 ° C for 0.5 ~ 3 hours; (c) from the catalysts obtained under step (b), decomposes the metals molybdenum, nickel, cobalt, vanadium and / or tungsten present therein with the aid of an acid medium; and (d) recovering the resulting digested metals from the leaching solution.

One of the important aspects of the invention is that in step (c) the metals are digested in an acid medium, so that all metals of interest can be leached in one step and not partly lost, as in the aforementioned wet-chemical route. or in eg an extra step must be won. Another important aspect of the invention is that after using step (b), the Al2 O3 hardly dissolves, if at all, in the acidic medium used in step (c), so that the e.g. the colloidal fine Antiparticles dissolved in the wet-chemical way associated with separation problems, for example in the filtration of the reaction mass, in the process according to the invention are prevented.

More specifically, with respect to steps (a) - (d) of the process of the invention, the following is noted.

Step (a) is used when the spent catalysts come from processes in which they are contaminated with carbon (coke) and hydrocarbons. An example of such a process is the above-mentioned hydrodesulphurization process (desulfurization process) of heavy petroleum fractions. The annealing step (a) is advantageously carried out in a fluidized bed furnace. In principle, the following reactions take place in this step using oxygen (air) as oxidant: carbon is converted into carbon dioxide, hydrocarbons are converted into carbon dioxide and water and the metal sulfides into metal oxides. In addition, under the conditions prevailing in step (a), the γ-Α1203 used as a carrier can partly transfer to α-Α1203. In order to counteract a possible undesired course of this last reaction, step (a) is preferably carried out at a temperature in the range of 750-950 ° C, whereby a time period of 10-30 minutes is usually judged as sufficient to allow a complete annealing. , ie removal of all carbon and hydrocarbons as well as complete conversion of the metal sulfides to the corresponding metal oxides. However, a longer treatment time of, for example, more than 1 hour can also be used.

With regard to the process conditions such as the above-mentioned temperature range with an upper limit of 950 ° C, it is noted that when higher temperatures such as 1000 ° C are used, it has been found that due to the relatively large spread in residence time of the catalyst particles in the applied fluidized bed furnace, at this higher temperature, part of the metals considered valuable is enclosed in the support material and is therefore no longer released during the digestion with an acid medium carried out in step (c) in accordance with a "standard digestion test" defined below.

With regard to the catalysts used in the fluidised bed furnace, it is stated that they are usually cylindrical and have a diameter of 1.5-3 mm and a length of 0.5-2 cm which is customary in practice. Depending on the conditions in the fluidised bed furnace, there is considerable wear of the particles. The smallest particles are removed via a cyclone-switched cyclone oven, while the remainder is recovered from the oven bed as product stream.

For product technical reasons, the fluidised bed oven is subjected to a low reduced pressure, e.g. ca 1 cm water column, skilled. In this way it is prevented that e.g. SO2 as well as other harmful gases can escape from the device. Such an underpressure can be obtained by tuning the blower, which provides the air supply and the exhauster, which controls the discharge of the combustion air.

To carry out stage (a) in a fluidized bed furnace, air is blown in at the bottom of a vertically arranged pipe advantageously made of ceramic concrete. This air serves both as combustion air and as a fluidization medium. The catalyst can be supplied by means of a conveyor belt and then brought into the bed via a filling pipe.

Before starting up the fluidised bed furnace, the bed is usually preheated with a gas burner at a temperature of approx. 450 ° C. With subsequent addition of spent catalyst in a dosed manner, the temperature rapidly rises above 750 ° C.

The calcined catalyst is then heated to 1000-1200 ° C in step (b) for 0.5-3 hours. The aim of this step is to achieve the most complete conversion of γ-Α1203 into α-Α1203, because γ-Α1203 dissolves under the conditions used in step (c) and, among other things, leads to serious problems in the separation of liquid and solid, e.g. by filtration, while α-Α1203 hardly dissolves under these conditions. However, in this stage (b) care must be taken to ensure that a sintering of α-Α1203 is limited as much as possible, because by sintering α-Α1203 particles together the metals to be recovered are included and no longer under the sub-stage (c) conditions applied are exposed, leading to loss of metal to be recovered.

Therefore, step (b) is advantageously carried out on a belt oven or in a drum oven since in such a type of oven conditions can be controlled fairly accurately. Preferably, the annealed catalyst particles from step (a) are treated for a period of 50-70 minutes at a temperature of 1050-1100 ° C on a belt oven or in a drum oven. In this way an almost complete conversion of γ-Α1203 into α-Α1203 is obtained, while the degree of sintering of the resulting α-Α1203 remains within acceptable limits. In this way, treated catalyst particles are obtained, from which valuable metals such as cobalt and molybdenum can be recovered with a percentage of more than 90% and even almost 100%.

Any strong mineral acid such as nitric acid, and advantageously hydrochloric acid and sulfuric acid, can be used for the acidic digestion of the metals carried out in step (c). Particularly good results can be achieved with sulfuric acid, e.g. 0.1-8 M H 2 SO 4 and in particular 0.3-0.8 M H 2 SO 4 are obtained. As a final pH of the metal digestion step (c), a value of 1-2 is advantageously used. A final pH value of less than 0.5 presents problems, since a relatively large amount of Al2 O3 then dissolves, resulting in very finely divided, hydrated Al2 O3 particles, which has a very negative effect on the filtering properties of the suspension. In addition, an unwanted loss of acid occurs with this leaching of Al2O3. Furthermore, a suspension with a solids content of 2-40% by weight is advantageously used in step (c), since at higher solids contents a practically somewhat problematic resp. processing of the reaction mass, such as keeping the suspension in motion with a stirrer.

The recovery or digestion efficiency of the acid digestion of the metals carried out in step (c) is determined by means of the "standard digestion test" below.

5 g of the temperature treatment product is carefully weighed and transferred to a 250 ml abrasive conical flask together with a Teflon coated agitator flea. The Erlenmeyer flask is placed on a hob with a magnetic stirrer and equipped with a cooler. Then 200 ml of 4 M sulfuric acid is added via the top-cooler and the magnetic stirrer is started at 250-300 min-1. The suspension is brought to a boil and stirred under continuous boiling for 60 minutes. The suspension then becomes hot over a 0.45 micrometer membrane filter using vacuum filtration filtered. 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. The residue is weighed after drying. The filtrate is then analyzed for the elements Co, Ni, Mo and Al and occasionally for Fe and V.

Finally, in step (d), the digested metals - after filtration of the suspension - are recovered from the leaching solution. For this purpose, the well-known techniques such as ion exchange, crystallization and advantageously solvent extraction such as with Alamine 336R in Shell Sol Rr can be applied. The metals can be recovered from purified solutions by precipitation, electrolysis, crystallization or evaporation.

Example I

A fluidised bed furnace with an internal diameter of 0.5 m and an installation height of 4.5 m has been used to perform step (a). The maximum bed height was 1.5 m. Above the bed was a so-called "freeboard" of over 2 meters. The fluidized bed installation was equipped with a blower (for air supply) and an exhauster (for exhaust of combustion air). By mutual adjustment of the blower and exhauster, a slight underpressure of 1 cm of water column was created in the fluidized bed furnace. Furthermore, the fluidised bed furnace was provided with a cyclone (for collecting the small catalyst particles) and an air preheater.

During operation of the fluidized bed, air was blown into the bottom of the vertically arranged ceramic concrete pipe via the blower. The bed was preheated to 450 ° C using a gas burner. The catalyst sample EXD 151, originating from a hydrodesulphurization process, was fed via a conveyor belt and metered into the bed via a downcomer, 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 1R1

Carbon 23.8%

Sulphate 0.60%

Sulfur 4.10%

Cobalt Oxide 2.03%

Molybdenum Oxide 8.25%

Nickel oxide 0.05%

Aluminum oxide 46.9%

Water 3.5%

Rest 10.8%

Under the fluid bed oven conditions, complete oxidation of carbon (coke) as well as hydrocarbons and sulfides was achieved. Full annealing of the EXD 151 sample (3 mm diameter) was about 20 minutes.

An attempt to combine step (a) and step (b) i.e., the catalyst calcination and the conversion of γ-Α1203 to α-Α1203 was verified in the fluidized bed incinerators described above with the tests shown in Table B below.

TABLE B

In sample I, the "standard digestion test" only digested 10 to 12 wt.% Alumina, while only $ 0% of the cobalt could be leached. The slight digestion of A1203 indicated an effective conversion of γ-Α1203 into α-Α1203, but was accompanied by a significant inclusion of the cobalt. In sample IV from the cyclone tap, however, still 5% of the alumina dissolved and only about 60% cobalt was leached. In this sample, therefore, an insufficient conversion of γ-Α1203 to α-Α1203 took place in combination with an insufficient digestion of the cobalt under the conditions of the "standard digestion test". The other samples yielded results intermediate between those of samples I and IV.

It therefore follows from the above data that the fluidized bed used was not applicable to also carry out the above-mentioned alumina conversion without obtaining too much entrapment of the metals or sufficient digestion thereof in the "standard digestion test". Apparently, the problem was not so much the residence time, but mainly the spread. With the heating regime followed, the spread in residence time was very large with an average residence time of 60 minutes. This varied for 90% of the material between 20 and 120 min.

This meant that for some of the treated material the conversion of γ-Α1203 into α-Α1203 had not yet taken place (time = 20 min.), While in another part the metals could already have been trapped (time = 120 min.).

It is further noted that a possible evaporation of the hydrocarbons from the catalyst particles and a post-combustion in the "freeboard" of the fluidised bed furnace did not occur. This was of particular advantage, since no special material engineering measures had to be taken on the freeboard.

The above sample IV was used to perform step (b). This sample was treated on a belt oven at 1100 * 0 for 60 minutes. This sample treated in step (b) yielded a cobalt digestion efficiency of nearly 100 # in a subsequent standard digestion step (c) (in acid medium, viz. 4 M H2S0j), while that for A1203 was reduced to less than 5 # . Values for recovery or digestion yields as well as treatment conditions are shown in Table C below

TABLE C

The yield of molybdenum is quite low, because molybdenum oxide evaporates at the high temperature used. When corrected for the evaporated molybdenum oxide (which can be collected by cooling), the recovery efficiency for molybdenum also turns out to be more than 90 #.

The accompanying Figures 1-3 illustrate the invention in more detail.

Fig. 1 shows the relationship between the digestion yields of Co, Mo and Al and the post-treatment of sample IV performed in step (b).

Fig. 2 shows the relationship between the digestion yields of Co, Mo and Al and the acidity in M H 2 SO 2 /, of the post-treatment of sample IV carried out in step (b).

Fig. 3 shows the relationship between the digestion yields of Co, Mo and Al and the acidity in M H2S0 /, without the post-treatment of sample IV carried out in step (b).

Claims (11)

Process for recovering metals from metal-containing catalysts based on Al2 O3, characterized in that (a) the catalysts - if required - are calcined in an oxidizing medium; (b) heating the catalysts obtained under step (a) at 1000-1200 ° C for 0.5-3 hours; (c) from the catalysts obtained under step (b), decomposes the metals molybdenum, nickel, cobalt, vanadium and / or tungsten present therein with the aid of an acid medium; and (d) recovering the resulting digested metals from the leaching solution. Process according to claim 1, characterized in that step (a) is carried out in a fluidized bed furnace. Process according to claim 1 or 2, characterized in that step (a) is carried out at a temperature in the range of 750-950 ° C. Process according to one or more of claims 1-3, characterized in that step (a) is carried out for 10-30 minutes. Process according to one or more of claims 1 to 4, characterized in that step (b) is carried out at 1050-1100 ° C for 50-70 minutes. Process according to one or more of claims 1 to 5, characterized in that step (b) is carried out on a belt oven or in a drum oven. Process according to one or more of claims 1 to 6, characterized in that step (c) is carried out using hydrochloric or sulfuric acid. Process according to one or more of claims 1-7, characterized in that step (c) is carried out with an acid at a final pH of 1-2. Process according to one or more of Claims 1 to 8, characterized in that step (c) is carried out with 0.3-0.8 M H2S0i. Process according to one or more of claims 1-9, characterized in that step (c) is carried out with a suspension with a solid content of 2-40% by weight. Process according to one or more of claims 1 to 10, characterized in that step (d) is carried out with solvent extraction.