JP2022142809A - Recovery method of valuable elements - Google Patents

Abstract

To provide a novel method capable of recovering valuable elements such as molybdenum and so on from a waste catalyst.SOLUTION: A method for recovering valuable elements, where when a waste catalyst containing at least molybdenum is immersed in hydrogen peroxide water to obtain a leachate in which molybdenum is leached from the waste catalyst, a temperature of the hydrogen peroxide water is kept at 85°C or less.SELECTED DRAWING: None

Description

The present invention relates to a method for recovering valuable elements from waste catalysts such as spent desulfurization catalysts used in petroleum refining.

Conventionally, desulfurization using a desulfurization catalyst is performed in petroleum refining. More specifically, hydrodesulfurization is performed in which petroleum and high-pressure hydrogen are reacted on a desulfurization catalyst to remove sulfur contained in petroleum as hydrogen sulfide.
As such desulfurization catalysts are used, they are gradually poisoned by heavy metals and tars contained in petroleum and their catalytic activity decreases, so they are periodically replaced. At this time, a used desulfurization catalyst (waste catalyst) is generated.
Conventionally, from the viewpoint of resource recycling, a method for recovering various elements contained in spent catalysts has been proposed (Patent Document 1).

JP 2013-133233 A

A desulfurization catalyst supports, for example, a metal element such as molybdenum (Mo) on a carrier.
Molybdenum is used in special steels and stainless steels because it increases mechanical strength and rigidity when added to steel, and is also used in greases and the like because it is highly malleable and ductile at high temperatures.
In recent years, it is strongly desired to recover elements (valuable elements) such as molybdenum from waste catalysts such as spent desulfurization catalysts.
Accordingly, an object of the present invention is to provide a novel method for recovering valuable elements such as molybdenum from spent catalysts.

As a result of intensive studies, the inventors of the present invention have found that the above object can be achieved by adopting the following configuration, and completed the present invention.

That is, the present invention provides the following [1] to [4].
[1] A valuable element that keeps the temperature of the hydrogen peroxide water at 85° C. or less when a waste catalyst containing at least molybdenum is immersed in the hydrogen peroxide water to obtain a leachate in which molybdenum is leached from the waste catalyst. collection method.
[2] The method for recovering valuable elements according to [1] above, wherein the waste catalyst is pulverized before being immersed in the hydrogen peroxide solution.
[3] The method for recovering a valuable element according to [1] or [2] above, wherein the mass ratio of the hydrogen peroxide solution to the waste catalyst (hydrogen peroxide solution/waste catalyst) is 2/1 or more. .
[4] The method for recovering valuable elements according to any one of [1] to [3] above, wherein the spent catalyst is a used desulfurization catalyst.

According to the present invention, valuable elements such as molybdenum can be recovered from spent catalysts.

4 is a graph showing the relationship between the temperature of hydrogen peroxide solution and the leaching rate of molybdenum.

In the method for recovering valuable elements of the present invention, a waste catalyst containing at least molybdenum is immersed in hydrogen peroxide water to obtain a leachate in which molybdenum is leached from the waste catalyst. ℃ or less.

For example, in the conventional method described in Patent Document 1, the waste catalyst is first roasted. In this case, equipment such as a roasting machine is required. Practically, heat treatment such as roasting is required to be carried out on a certain scale of equipment to enjoy scale merits.
In contrast, in the present invention, the equipment can be simplified because the waste catalyst need not be roasted.

Preferred embodiments of the present invention are described below.

<Preparation of spent catalyst>
The spent catalyst contains at least molybdenum.
A spent catalyst is, for example, a spent desulfurization catalyst. A desulfurization catalyst carries metal elements, such as molybdenum (Mo), cobalt (Co), and nickel (Ni), _on carriers, such as alumina ( _Al2O3 ), for example. Furthermore, the desulfurization catalyst contains phosphorus (P) when using a phosphate-based binder. In addition, the spent desulfurization catalyst may also contain large amounts of oil, tar, sulfur (S), vanadium (V) from petroleum, iron (Fe), and the like.

<Grinding>
As will be described later, the spent catalyst is immersed in a hydrogen peroxide solution, but prior to this, it is preferable to pulverize it. As a result, highly efficient leaching can be expected. It is particularly useful when the spent catalyst is a desulfurization catalyst having an alumina carrier (having an alumina skeleton).
The method for pulverizing the waste catalyst is not particularly limited, and it can be easily pulverized by a known method using a jet mill or the like.
The particle size of the waste catalyst after pulverization is preferably 500 μm or less, more preferably 100 μm or less.

<Immersion in hydrogen peroxide water: acquisition of leachate>
The spent catalyst is optionally pulverized and then immersed in hydrogen peroxide water (aqueous solution of hydrogen peroxide). As a result, molybdenum contained in the spent catalyst is leached into the hydrogen peroxide solution. That is, the resulting leachate contains the spent catalyst and molybdenum, which is a component leached from the spent catalyst.

By the way, as will be described later, for example, when the spent catalyst is a used desulfurization catalyst, a reaction (oxidation reaction) occurs in which the sulfide in the spent catalyst becomes a sulfuric substance by hydrogen peroxide, resulting in a hydrogen peroxide solution. temperature rises.
If the temperature of the hydrogen peroxide solution rises excessively, the leaching of molybdenum from the waste catalyst into the hydrogen peroxide solution becomes insufficient. Although the reasons for this are not clear, it is thought that the self-decomposition of hydrogen peroxide is accelerated, the solubility of molybdenum is lowered, and the like.

Therefore, when obtaining the leachate, the temperature of the hydrogen peroxide solution is set to 85° C. or lower. As a result, molybdenum is sufficiently leached from the spent catalyst.
Since this effect is more excellent, the temperature of the hydrogen peroxide solution is preferably 75°C or lower, more preferably 65°C or lower, and even more preferably 60°C or lower.
The lower limit is not particularly limited, and for example, it is preferably 25°C or higher, more preferably 30°C or higher.

In addition, when the equipment to be used is scaled up, the surface area per unit volume of various solutions decreases, which deteriorates the efficiency of heat radiation to the outside air, and as a result, the temperature of the hydrogen peroxide solution tends to rise. In this case, molybdenum can be efficiently leached by appropriately maintaining the temperature of the hydrogen peroxide solution within the above-described range using a heat exchanger or the like.

When obtaining the leaching solution, the mass ratio of the hydrogen peroxide solution and the waste catalyst (hydrogen peroxide solution/waste catalyst) is preferably 2/1 or more, more preferably 3/1 or more, because leaching can be performed efficiently. .
In particular, from the viewpoint of efficiently leaching molybdenum and the like, the mass ratio (hydrogen peroxide solution/waste catalyst) is preferably 10/1 or more, more preferably 15/1 or more, and even more preferably 20/1 or more.
On the other hand, the amount of hydrogen peroxide water used is appropriate, and the mass ratio (hydrogen peroxide water/waste catalyst) is preferably 50/1 or less, and 40/1 or less, because it is possible to suppress an increase in the size of the reaction vessel and an increase in cost. is more preferred.

The concentration of the hydrogen peroxide solution used (content of hydrogen peroxide in the hydrogen peroxide solution) increases or decreases in proportion to the mass ratio (hydrogen peroxide solution/waste catalyst).
When the mass ratio (hydrogen peroxide solution/waste catalyst) is within the above range, the concentration of the hydrogen peroxide solution is preferably 3% by mass or more, more preferably 4% by mass or more, for the reason that leaching can be performed efficiently. % by mass or more is more preferable, and 6% by mass or more is particularly preferable.
On the other hand, when the concentration of the hydrogen peroxide solution is excessively increased, the obtained effect tends to saturate. Therefore, from the viewpoint of cost, the concentration of the hydrogen peroxide solution is, for example, 20% by mass or less, preferably 18% by mass or less, and more preferably 15% by mass or less.

The time (immersion time) for immersing the waste catalyst in the hydrogen peroxide solution is, for example, 15 minutes or longer. Although the upper limit is not particularly limited, if the spent catalyst is pulverized in advance, the valuable element inside the spent catalyst can be sufficiently leached out in one hour.

Valuable elements can be efficiently leached from the spent catalyst by acidifying the hydrogen peroxide solution.
However, if the spent catalyst is a used desulfurization catalyst, the acid may not be added to the hydrogen peroxide solution. This is because the sulfide in the spent catalyst becomes a sulfate by hydrogen peroxide, becomes a sulfate ion, and dissolves in the hydrogen peroxide water, thereby exhibiting the same effect as addition of sulfuric acid. In fact, when a waste catalyst (used desulfurization catalyst) is put into hydrogen peroxide water, the pH drops rapidly and stays at around 1.

The obtained leachate is filtered, for example. As a result, the waste catalyst, which is a solid content, is separated from the leachate to obtain a filtrate. The obtained filtrate contains molybdenum, which is a component dissolved from the spent catalyst.
The method of filtration is not particularly limited as long as the target solid content can be separated and the desired filtrate can be obtained, and conventionally known methods can be appropriately employed.
Thereafter, the molybdenum precipitate is separated, for example, by precipitating the molybdenum contained in the filtrate and then further filtering. The separated molybdenum precipitate can be recycled as a product such as ferro-molybdenum by subjecting it to any treatment such as electric furnace reduction.

EXAMPLES The present invention will be specifically described below with reference to Examples. However, the present invention is not limited to the examples described below.

A used indirect desulfurization catalyst sampled from an oil refining plant was used as the spent catalyst. This waste catalyst had a cylindrical shape with a diameter of 2 to 3 mm and a length of about 3 to 5 mm, and various elements were supported on an alumina carrier. The composition of the spent catalyst was determined by ICP (inductively coupled plasma) emission spectroscopy. The composition of the spent catalyst is shown in Table 1 below.

The prepared waste catalyst was pulverized to 500 μm or less and immersed in a hydrogen peroxide solution (concentration: 7.5% by mass) to obtain a leachate. The mass ratio of the hydrogen peroxide solution and the waste catalyst (hydrogen peroxide solution/waste catalyst) was 20/1. The immersion time was 1 hour.
The obtained leachate was filtered to remove the solid content (waste catalyst), and then the liquid composition was determined. 5C filter paper (retention particle size: 1 μm) was used for filtration (suction filtration). The liquid composition was determined by ICP emission spectrometry. The molybdenum leaching rate (unit: mass %) was obtained from the liquid composition of the leachate from which the solid content (waste catalyst) was removed and the composition of the waste catalyst (see Table 1).
At this time, the temperature of the hydrogen peroxide solution (unit: °C) was changed using a magnetic stirrer with a temperature control function, a water bath, ice, etc., and the leaching rate of molybdenum was determined for each temperature. The results are shown in the graph of FIG.

FIG. 1 is a graph showing the relationship between the temperature of the hydrogen peroxide solution and the leaching rate of molybdenum.
As shown in the graph of FIG. 1, it was found that the molybdenum leaching rate was clearly affected by the temperature of the hydrogen peroxide solution. More specifically, there was a tendency that the lower the temperature of the hydrogen peroxide solution, the higher the molybdenum leaching rate. For example, the leaching rate of molybdenum was better when the temperature of the hydrogen peroxide solution was 85°C or lower than when the temperature was about 90°C.

Claims (4)

When immersing a waste catalyst containing at least molybdenum in a hydrogen peroxide solution to obtain a leachate in which molybdenum is leached from the waste catalyst,
A method for recovering valuable elements, wherein the temperature of the hydrogen peroxide solution is set to 85° C. or lower. 2. The method for recovering valuable elements according to claim 1, wherein the waste catalyst is pulverized prior to being immersed in the hydrogen peroxide solution. 3. The method for recovering valuable elements according to claim 1, wherein the mass ratio of said hydrogen peroxide solution to said waste catalyst (hydrogen peroxide solution/waste catalyst) is 2/1 or more. The method for recovering valuable elements according to any one of claims 1 to 3, wherein the spent catalyst is a spent desulfurization catalyst.

Images