JPH0587574B2 - - Google Patents

Description

[Detailed description of the invention]

(Industrial Application Field) The present invention provides a method for separating noble metals, which can separate noble metals in high yield without substantially dissolving them from a catalyst in which a catalyst layer containing noble metals is attached on a metal carrier. It is related to. (Prior Art) Conventionally, catalysts for purifying exhaust gas from internal combustion engines such as automobiles have been made of ceramic carriers with a honeycomb-like integral structure made of cordierite, mullite, etc.
A catalyst to which a catalyst layer containing a noble metal such as platinum, palladium, or rhodium is attached is used. However, because ceramic carriers have large heat capacity and insufficient strength, metal carriers such as nickel steel, stainless steel, iron, Cr-Cu-Ni-Al steel, and high-strength steel are now used. I'm getting used to it. However, since this catalyst uses expensive precious metals, the precious metals must be separated and recovered.
Methods of dissolving noble metals in a wet solution using an acid such as aqua regia, or methods of melting noble metals using an appropriate flux and separating them based on the difference in specific gravity have been adopted. In addition, a method in which a catalyst layer in which a noble metal is supported on alumina is attached to a metal carrier is immersed in an aqueous solution of an alkali metal to remove the noble metal by dissolving a part of the alumina (Japanese Unexamined Patent Application Publication No. 1999-1-1).
263229) has been proposed. (Problem to be solved by the invention) However, applying these methods to metal-supported catalysts, such as dissolving them in a chemical solution or separating them based on the difference in specific gravity, is difficult because the carrier metals such as iron, nickel, and chromium are dissolved. However, the method described in JP-A-1-263229 tends to cause a concentration gradient of the solution within the honeycomb cells. In addition, after long-term use, the alumina becomes chemically stabilized due to its thermal history, making it difficult to dissolve the alumina and making it difficult to peel off.Also, if the cells are collapsed, the liquid may leak into the cells. There are problems such as not being able to penetrate into the film and peeling off partially. An object of the present invention is to solve the above problems and provide a method for separating a carrier metal and a noble metal catalyst layer without substantially dissolving the carrier metal. (Means for Solving the Problems) As a result of intensive research to solve the above problems and achieve the above objects, the present inventor has found that thin metal plates only deform when subjected to impact at room temperature. However, when cooled below the embrittlement temperature, it becomes brittle and shatters when subjected to impact. Therefore, the catalyst supported on the metal carrier is cooled to below the embrittlement temperature of the carrier metal, and then crushed. The present invention was completed based on the discovery that this is effective for separating noble metal catalysts. That is, the present invention provides a method for separating a catalyst layer containing a precious metal from a catalyst having a catalyst layer containing a precious metal adhered to the surface of a metal carrier and recovering the precious metal, in which the catalyst is cooled to a temperature below the embrittlement temperature of the carrier metal. This is a metal separation method in which the carrier metal is then pulverized to separate the carrier metal and the catalyst layer. The metals used as carriers in the present invention are nickel steel (embrittlement temperature -100℃, below, each embrittlement temperature is shown in parentheses), stainless steel (-180℃),
(°C), iron (-45 to -60°C, depending on carbon content), Cr-Cu-Ni-Al steel (-100°C), and high-strength steel (-60°C). Platinum, palladium, rhodium, etc. are used as the noble metal for the catalyst. The means for cooling below the embrittlement temperature must be a means that does not alter or react with the carrier metal or the catalyst layer, and an appropriate refrigerant that can be used to cool the carrier metal below the embrittlement temperature must be used. You can take the method of using . This refrigerant may be one with a boiling point lower than the embrittlement temperature of the carrier metal, but for example, liquefied nitrogen (boiling point: -
Neon (-246℃), methane (-163℃), ethylene (-104℃), ethane (-88℃), and carbon dioxide gas (-78.5℃). ℃), etc. The immersion time of the catalyst supported on a metal carrier in the refrigerant varies depending on the size of the catalyst, but the time required for the catalyst to be cooled to below the embrittlement temperature, that is, 15 seconds or more is required. The cooled catalyst is coarsely pulverized, for example, using a method using a hammer or a machine such as a press.
If it is necessary to make it even finer, it may be pulverized using a pulverizer such as a hammer mill or a roller mill. The degree of pulverization may be such that the particle size allows subsequent separation of the carrier metal and the catalyst layer, but it is 40 mm or less, preferably 30 mm or less. 40
If the diameter is more than 0.1 mm, the separation between the carrier metal and the catalyst layer will not be sufficient, and if the diameter is 0.1 mm or less, the heat generated by the pulverization will rapidly increase, and the amount of refrigerant consumed will also increase rapidly, which is not economical. Although a considerable part of the catalyst layer is peeled off from the support metal simply by pulverization after cooling to below the embrittlement temperature,
As a means for peeling off the part of the catalyst layer remaining on the carrier, a method of peeling off by chemical treatment can be adopted. In other words, chemical stripping methods include (a) a method of dissolving a part of the surface of the carrier metal, and (b) a method of dissolving a part of the surface of the carrier metal.
Examples include a method of dissolving a whisker-shaped fixed layer that facilitates fixing the catalyst layer to a carrier, and (iii) a method of dissolving a part of the catalyst layer. Examples of chemicals used in the method (b) for dissolving a part of the surface of the carrier metal include ammonium chloride, formic acid, dilute sulfuric acid, dilute hydrochloric acid, and aluminum chloride, and the method (b) for dissolving the fixed layer Examples of chemicals used in the method (c) include malonic acid, malic acid, tartaric acid, and acetic acid, and examples of chemicals used in the method (c) for dissolving a part of the catalyst layer include alkali hydroxide. It will be done. Since these chemicals cannot be completely removed at a concentration of 2% or less, they are used at a concentration of 2% or more, preferably 5% or more. The pulverized catalyst is immersed in this solution at room temperature or higher for 5 minutes or more. The effectiveness of soaking can be increased by heating to boiling, mechanical agitation, or vibration using ultrasound. Furthermore, when the pulverized particles are large in size, it is also effective to forcibly wash the inside of the catalyst cells with water using a shower or the like. The catalyst separated from the carrier metal can be separated from the carrier metal by magnetic sorting, by washing with water based on the difference in particle size, by specific gravity sorting using a solution with an appropriate specific gravity, or by a combination of these methods. This can be done by (Example) Hereinafter, an example of the present invention will be described in which a catalyst is used in which a catalyst layer in which platinum and rhodium are supported on alumina is attached to a metal carrier. Example 1 A catalyst layer in which platinum and rhodium were supported on alumina was attached to a stainless steel honeycomb carrier having a diameter of 38 mm, a length of 45 mm, and a number of cells of 400 (platinum 0.23 mm).
% by weight, rhodium 0.02% by weight) into a stainless steel multi-converter, using unleaded gasoline as fuel, catalyst bed temperature at 950°C, air-fuel ratio: A/F = 16.2
Heat treatment was carried out by flowing exhaust gas similar to actual exhaust gas under the following conditions for 50 hours. The heat-treated catalyst was immersed in liquid nitrogen for 1 minute, then taken out and opened using a hammer mill.
After pulverizing to completely pass through a 40 mm sieve, the carrier metal and catalyst layer were separated by washing with water. Platinum and rhodium contained in the separated carrier metal and catalyst layer were analyzed. The separation rate of platinum and rhodium is calculated by dividing the total amount of platinum and rhodium contained in the catalyst layer by the total amount of platinum and rhodium contained in the separated carrier metal and catalyst layer,
The average value of the separation rate of platinum and the separation rate of rhodium is indicated by 1 in the drawing. Example 2 Platinum and rhodium were analyzed in the same manner as in Example 1, except that they were crushed so as to pass through a 30 mm sieve, and the separation rate of platinum and rhodium were determined in the same manner as in Example 1. The average value was calculated. The results are shown as 2 in the drawing. Example 3 A heat-treated catalyst similar to that used in Example 1 was cooled by immersing it in liquid nitrogen for 1 minute, then taken out and pulverized using a hammer mill so as to pass through a 40 mm sieve. After being immersed in liquid nitrogen again for 1 minute to cool it, it was taken out and crushed using a crusher so that it could completely pass through a 9 mm sieve. This was placed in water, thoroughly stirred, and a magnet was inserted into the water to perform magnetic separation, and the platinum and rhodium contained in the separated carrier metal and catalyst layer were analyzed. In the same manner as in Example 1, the average value of the platinum separation rate and the rhodium separation rate was determined. The results are indicated by 3 in the drawing. Example 4 After processing in the same manner as in Example 3 except for using a sieve with an opening of 5 mm, platinum and rhodium were analyzed, and the average value of the separation rate of platinum and the separation rate of rhodium was determined in the same manner as in Example 1. I asked for 4. Show the results in the drawing.
Indicated by Example 5 A heat-treated catalyst similar to that used in Example 1 was immersed in liquid nitrogen for 1 minute, cooled, and then taken out. It was pulverized using a hammer mill to the extent that it could pass through a 40 mm sieve. After cooling it by immersing it in liquid nitrogen again for 1 minute, take it out and crush it using a crusher so that it passes through a 9 mm sieve, and then transfer it to a roller mill with liquid nitrogen and crush it for 3 minutes. The powder was crushed so that it could pass through a sieve with an opening of 0.8 mm. This was placed in water, stirred thoroughly, and a magnet was plunged into the water to perform magnetic separation. Platinum and rhodium contained in the separated carrier metal and catalyst layer were analyzed, and the average value of the separation rate of platinum and the separation rate of rhodium was determined in the same manner as in Example 1. The results are indicated by 5 in the drawing. Example 6 The process was carried out in the same manner as in Example 5, except that the pulverization time in the roller mill was 13 minutes, and the pulverization was carried out so as to completely pass through a sieve with an opening of 0.35 mm. Platinum and rhodium contained in the separated carrier metal and catalyst layer were analyzed, and the average value of the separation rate of platinum and the separation rate of rhodium was determined in the same manner as in Example 1. The results are indicated by 6 in the drawing. Comparative Example 1 The process was carried out in the same manner as in Example 1, except that the powder was crushed so as to pass through a 50 mm sieve, and the average value of the platinum separation rate and the rhodium separation rate was determined in the same manner as in Example 1. Ta. The results are shown in the drawings as a ratio of 1. Example 7 A catalyst layer in which platinum and rhodium were supported on alumina was attached to a stainless steel honeycomb carrier with a diameter of 50 mm, a length of 75 mm, and 400 cells (platinum 0.18 mm).
% by weight, rhodium 0.013% by weight) was subjected to the same heat treatment as in Example 1. After cooling the heat-treated catalyst by immersing it in liquid nitrogen for 1 minute, it was taken out, compressed using a press, and pulverized. The maximum particle size of the pulverized product was about 35 mm. After placing this pulverized material in water and washing it with ultrasonic waves, magnetic separation is performed using a magnet to separate the carrier metal and catalyst layer powder, and the platinum and rhodium contained in each are analyzed to determine the content of platinum and rhodium. The separation rate was found to be 78%. Comparative Example 2 The same treatment as in Example 7 was performed, except that the catalyst was not immersed in liquid nitrogen, and the separation rate was determined in the same manner. The result was 48%. Note that the maximum particle size of the powder was approximately 50 mm. Example 8 A catalyst (0.62% by weight of platinum, 0.17% by weight of rhodium) in which a catalyst layer of platinum and rhodium supported on alumina was attached to a stainless steel honeycomb having a diameter of 35 mm, a length of 90 mm, and 400 cells was placed in air. 15 to 700℃
Heat treated for hours. After cooling the heat-treated catalyst by immersing it in liquid nitrogen for 1 minute, it was taken out and pulverized using a hammer and blade mill. The particle size at this time is up to 4 mm.
It was moderately hot. This pulverized material was immersed in a 5% by weight acetic acid solution 1 at 70°C for 40 hours, then washed using ultrasonic waves for 30 minutes, and magnetic separation was performed using a magnet while stirring the suspension. Separated stainless steel. The suspension from which metals have been removed is filtered,
It was washed and separated into powder and solution. Metal powder, platinum, rhodium in powder and solution,
Iron, nickel and chromium were analyzed and the separation rate was determined. The results are shown in Table 1.

[Table] Comparative Example 3 A heat-treated catalyst similar to that used in Example 1 was immersed in a 10% by weight solution of sodium hydroxide at room temperature for 45 minutes while being ultrasonically cleaned, and then taken out and placed in air. It was baked at 500°C for 1 hour. This was immersed in a 5% by weight hydrochloric acid solution 1 at room temperature for 45 minutes while being ultrasonically cleaned. At this time, part of the carrier metal melted, generating heat and reaching a temperature of 35°C. The carrier metal was taken out while washing with water. The two types of solutions were separated by filtration and washing, respectively. Platinum, rhodium, iron, nickel and chromium in the support metal, stripped catalyst layer and solution were analyzed. The results are shown in Table 2 as separation rates.

[Table] (Effects of the Invention) In the present invention, a catalyst consisting of a catalyst layer supported on a metal carrier is pulverized after being cooled to below the embrittlement temperature of the carrier metal, so that the carrier metal is substantially dissolved. It is possible to separate and recover precious metals at a high yield without having to do anything, and an extremely remarkable effect has been recognized.

[Brief explanation of drawings]

The drawing shows the relationship between the grinding degree and the noble metal separation rate in the method of the present invention, with the sieve opening (mm) on the horizontal axis and the noble metal separation rate (%) on the vertical axis.

Claims (1)

[Scope of Claims] 1. A method of separating a catalyst layer containing a precious metal from a catalyst having a catalyst layer containing a precious metal adhered to the surface of a metal carrier and recovering the precious metal, the catalyst being cooled to a temperature below the embrittlement temperature of the carrier metal. A method for separating precious metals, which comprises the steps of crushing and separating a carrier metal from a catalyst layer. 2. The method according to claim 1, characterized in that the catalyst layer is peeled off by chemically treating at least one layer of the surface layer of the carrier metal, the fixing layer for fixing the catalyst to the carrier metal, or the catalyst layer. A method for separating precious metals. 3. A method for separating noble metals according to claim 1 or 2, characterized in that the carrier metal layer and the catalyst layer are separated using magnetic force in water or a chemical solution. 4. A method for separating noble metals according to claim 1, 2 or 3, characterized in that the carrier layer and the catalyst layer are separated using ultrasonic waves in water or a chemical solution.