WO2003010346A2

WO2003010346A2 - Wet process and reactor for the recovery of platinum group metals from automobile catalytic converters

Info

Publication number: WO2003010346A2
Application number: PCT/IL2002/000602
Authority: WO
Inventors: Vladimir Shipachev
Original assignee: NEGEV METALS PRODUCTS Ltd
Current assignee: NEGEV METALS PRODUCTS Ltd
Priority date: 2001-06-22
Filing date: 2002-07-21
Publication date: 2003-02-06
Anticipated expiration: 2004-01-22
Also published as: RU2209843C2; WO2003010346A3; AU2002355201A1

Abstract

A process is disclosed for recovering platinum group metals from a spent catalytic member, and in particular, from a catalytic converter from an automobile. The process comprises comprising introducing the catalytic member (10) into a reaction chamber (10), wetting the spent catalytic member with an acidic solution of hydrochloric acid, heating the reaction chamber and adding an oxidizing agent, such as HNO3 and H202, continuing heating such that gaseous vapors are produced and caused to circulate through the reaction chamber, and condensing the gaseous vapors so as to obtain a solution containing platinum group metals from the spent catalytic member. Also disclosed is a reactor adapted for performing the recovery process. The reaction chamber (5) comprises a condenser (2) and is advantageously placed in a heating chamber (4) filled with oil (8). Preferably the catalytic member (10) is disposed in a receptacle (11) having a perforated bottom (7).

Description

PROCESS FOR THE RECOVERY OF PLATINUM GROUP METALS FROM

AUTOMOBILE CATALYTIC CONVERTERS AND A REACTOR FOR

PERFORMING SAID PROCESS

FIELD OF THE INVENTION

The present invention relates generally to the field of platinum metallurgy. More specifically, the present invention relates to a process for the recovery of platinum group metals from scrap metal material, particularly from automobile catalytic converters, which contain platinoids in the form of double or triple complexes (Pt/Rh, Rd/Rh, Pt/Pd/Rh), applied on honeycomb-like blocks of cordierite. The present invention also relates to a reactor for carrying out said process.

BACKGROUND OF THE INVENTION

It is well known that certain catalysts may include one or more catalytically active metals, and particularly metals of the platinum series. The rejects from the fabrication of such catalyst, as well as the used catalyst needs to be treated in order to recover therefrom at least the precious metals, in a manner that is as complete and cost-effective as possible.

Various methods are known in the art for recovering platinum group metals from metals.

U.S. 4,077,800 to Peka et al. relates to a method for the recovery of platinum from a spent catalyst involving subjecting the catalyst to fluorination with elementary fluorine or a mixture thereof with hydrogen fluoride at a temperature ranging from 100°C to 600°C. The resultant fluoride is then converted to platinum in elemental form.

U.S. 4069040 to Thomas et al. relates to a method for recovery of platinum and iridium from catalysts. The recovery is accomplished by a solubilization of the catalysts by means of hydrochloric acid and by extraction, for example by ion exchange resins.

These patents and others employ oxidation using gasiform agents (oxidizing roasting with oxygen, chlorination, fluorination) in order to recovery the catalytic components, and subsequent separation of the precious metals from the base. In the chlorination process, for example, the material is treated at a high temperature until volatile platinum carbonychlorides are formed, which are captured by absorption in order to separate the metai by reduction precipitation. These processes are not suitable for use with automobile catalytic converters. This is because highly aggressive gasiform reagents can be extremely dangerous to use and they require expensive equipment, advanced safety measures, and strict regulation over the disposal of toxic compounds.

Other methods for recovering platinum group metals consist of oxidation and lixiviation of the platinoids by liquid solvents such as aqua regia, hydrochloric acid and hydrogen peroxide mixtures, acid chlorine solutions, and hyperchlorite. These methods yield low recovery rates and are only useful for specific source materials. They also require sophisticated machinery and the processes themselves are very time-consuming, and require large amounts of energy. When used with car catalytic converters, the active alumina layer onto which the catalytic compounds are impregnated presents an obstacle to the process. In liquid-phase lixiviation two competing processes always occur due to the large contact surface of aluminum gamma-oxide (up to 200m²/g): the desorption of platinoids from the catalytic surface into the solution, and their resorption. Because of the two reactions that constantly are occurring, it is necessary to perform repeated cycles of lixiviation and washing in order to ensure complete recovery of the metals. Thus, a large volume of acid is required, and the extracted platinum group metal is diluted due to the large amount of solution employed. This translates into a high consumption of energy, and time, as well as high costs.

SUMMARY OF THE INVENTION

It is thus the primary object of the present invention to provide a process for the recovery of platinum from a spent catalyst that overcomes all of the aforementioned disadvantages. The process of the present invention allows for a high percentage of recovery of platinoids (platinum group metals) into solution, requiring a relatively small amount of reagent, when compared to analogous methods of the prior art.

The present invention relates to a process for recovering platinum group metals from a waste catalyst such as a honeycomb shaped or pelletized support formed from cordierite or another material containing catalytic metals. The process of the present invention employs a lixiviation process which differs from those of the prior art in that the concentration of oxidized metals in the solution is continuously increased through the use of acid mixtures both in the liquid and in the vaporized state for achieving platinoid oxidation. The transition to the gaseous state eliminates the problem of inadequate contact between the metals and the oxidative substance resulting from diffusion and ensures full transfer of the platinoids to solution, thus obviating the need for so many repeated cycles. To achieve this, the catalyst blocks are placed in the reactor in a container having a perforated bottom. The blocks are sprayed with an acidic (preferably hydrochloric acid) solution, which acts as a complex forming and impregnation agent. The amount of acid is carefully controlled such that the catalyst is kept above the level of the liquid.

The present invention relates to a process for recovering platinum group metals from a spent catalytic member comprising introducing a spent catalytic member into a reaction chamber, wetting the spent catalytic member with an acidic solution, heating the reaction chamber and adding an oxidizing agent. The heating is allowed to continue such that vapors of the oxidizing reagent are produced and recycled through the reaction chamber such that condensate formed from said vapors contain platinum group metals released from the catalytic member. The platinum group metals are subsequently recovered from the collected condensate.

In the recovery process, the reactor is heated and the reagent liquid is added. This process takes a certain amount of time, during which the oxidizing vapor is repeatedly circulated in the channels and pores of the catalyst through which the condensate is subsequently released. The blocks thus act as a condenser until thermal equilibrium is achieved.

Following lixiviation, the resultant solution is transferred and filtered. The catalyst is washed thoroughly and the wash water is combined with the solution. The platinoids and rare-earth cerium, which is also in the solution, can then be recovered from the solution using known methods.

It is appreciated that in the process of the present invention, standard oxidizing agents are used, but in both liquid and gaseous states. This is a non-obvious modification of the lixiviation process, that allows for a much more effective and cost-efficient process. The method also takes into account the chemical properties of the specific metal forming part of the catalyst, which allows for deeper penetration capacity of the gas mixture, and it also allows for washing of platinoids in a solution that is always "fresh". Another distinction between the process of the present invention and processes of the prior art is the possibility for rigorous metering out of the oxidizing agent, and the employment of aqua regia that is depleted in HNO₃, which dissolves the target metals and foreign matter formed during the block operation period. This is achieved through the use of an evaporation-condensation-washoff closed cycle in a specialized reactor that includes a modified column in which the role of reflux plates is played by the catalyst blocks. The reactor is similar to a modified Soxhlet apparatus commonly used in organic chemistry in order to extract valuable components from solid matter through the use of highly volatile solvents.

It is further appreciated that the method of the present invention is universal since it not only allows for treatment of block catalysts having any combination of noble metals, but also enables the recovery of cerium, which is sometimes included in order to reduce the thermal coefficient of expansion. The controlled introduction of measured quantities of highly aggressive oxidizing agent helps to reduce the load on the cleaning devices.

The present invention relates to a process for recovering platinum group metals from a spent catalytic member comprising;

(a) introducing a spent catalytic member into a reaction chamber of a reactor;

(b) wetting the spent catalytic member with an acidic solution;

(c) heating the reaction chamber and adding an oxidizing agent to the chamber;

(d) continuing heating such that gaseous vapors are produced and caused to circulate through the reaction chamber;

(e) condensing said gaseous vapors so as to obtain a solution containing platinum group metals from the spent catalytic member.

According to preferred embodiments of the present invention, the spent catalytic member is an automobile catalytic converter.

Further according to preferred embodiments of the present invention, the acidic solution is a hydrochloric acid solution.

Still further according to preferred embodiments of the present invention, the process also comprises placing the catalytic member onto a surface having perforations. Said surface is preferably the bottom of a reaction container. Alternately, said surface may be a platform that is mounted at a predetermined height in the reaction chamber. It is appreciated that the surface serves to hold the catalytic member while also allowing vapors from the solution below to rise through said surface (via the perforations) to contact the catalytic member and, subsequently, for droplets (condensate from the vapors) to return to the solution.

Additionally according to preferred embodiments of the present invention, the acid solution is added in an amount corresponding to approximately 25% by weight of the catalyst.

Moreover according to preferred embodiments of the present invention, the process further comprises recovering platinum groups metals from the solution obtained in step (e). This may be accomplished through any appropriate means known in the art. In some preferred embodiments, the catalytic member is washed with water and the wash water is combined with said solution prior to final recovery of the platinum group metals.

Still further according to preferred embodiments of the present invention, the oxidizing agent is a nitric acid.

Further according to preferred embodiments of the present invention, the process also comprises pre-treating the catalytic member with aqua regia.

Additionally according to preferred embodiments of the present invention, the process further comprises pre-roasting the catalytic member.

The present invention also relates to a reactor for carrying out the process as defined above.

The present invention further relates to a reactor for recovering platinum group metals from a spent catalytic member comprising;

(a) a reaction chamber for receiving a spent catalytic member, said reaction chamber and having an inlet for introducing a solution into the reaction chamber and an outlet for withdrawing the solution from the chamber;

(b) means for heating the reaction chamber such that vapors are produced from said solution;

(c) a condenser, located above the reaction chamber, for causing condensing of vapors circulating through said reaction chamber.

Preferably, the reactor parts are formed form titanium metal. Preferably, the spent catalytic member is positioned in the reaction chamber inside of a reaction container, said container having a perforated bottom portion such that vapors from the solution penetrate through the perforated bottom portion.

BRIEF DESCRIPTION OF THE DRAWING

Figure 1 represents a cross-sectional schematic view of a reactor for recovering platinoids from a spent catalyst, according to preferred embodiments of the present invention.

DETAILED DESCRIPTION OF THE DRAWING

A reactor will now be described that is adapted for carrying out the process of the present invention.

Referring to Figure 1, the reactor of the present invention comprises a reaction chamber (5), having an inlet (9) and an outlet (3) for the entry and exit, respectively, of fluids. A spent catalyst (11) is preferably positioned in the chamber (5) inside a container (10) having a perforated bottom (7). The catalyst (11) may be, for example, an automobile catalytic converter. The perforated bottom (7) preferably has about 30-50 holes per centimeter squared. According to certain preferred embodiments, the reaction chamber (5) is disposed inside of a heating chamber (4) that is filled, for example, with oil (8). The oil (8) is heated via electric heaters (12a) (12b). When the oil is heated, this causes an acid solution (6) in the reaction chamber (5) to heat. Other appropriate heating means could also be employed for heating the reaction chamber (5).

The reactor further comprises a condenser (2), located at the top portion of the reaction chamber (5), through which water (1) is conveyed, such that vapors rising to the top of the chamber (5) and contacting the condenser (2) condense into droplets. Some preferred embodiments further include a propeller (not shown) situated beneath the condenser (2) and above the container (11) that facilitates conveying of the condensate to the bottom of the reaction chamber (5) (back to the solution).

During the recovery process, the catalyst (10) is wetted with a predetermined amount of an acid solution and is placed inside the container (11) in the reaction chamber (5). Preferably, part of the remaining acid solution is introduced into the reaction chamber (5) via inlet (9) so as to occupy the lower most section of the chamber (5) (below the container). The oil (8) in the heating chamber (4) is then heated so as to cause the temperature in the reaction chamber (5) to increase. During heating, an oxidizing agent is introduced also via inlet (9). The heating is continued such that vapors from the solution (6) in the lower part of the chamber (5) rise up through the holes in the perforated bottom (7) of the container (11), and circulate throughout said chamber (5), through the openings in the catalyst (10) (the temperature is held such that the liquid continuously produces vapors; this may correspond to any appropriate temperature range depending on other reaction parameters), "collecting" platinum group metals from the catalyst.

Both the catalyst (10) and the condenser (2) act to cause the vapors to re-condense into liquid droplets into which the platinoids from the catalyst (10) are dissolved. When the droplets fall to the bottom of the chamber (5), they again vaporize due to the heat and are caused to circulate again through the reaction chamber (5). Thus, the solution (6) at the bottom of the chamber (5) has an continuously increasing amount of platinum group metals dissolved therein. When the lixiviation process is done, the solution is preferably withdrawn through outlet (3) and the platinoids are recovered from the solution through conventional methods known in the art.

The present invention will now be described with reference to the following examples. The examples, however, are not intended to be limiting in any manner. They are provided only as preferred embodiments of the process of the present invention.

Example 1 :

A 1.2kg catalytic converter from a Mercedes Benz was found to have a residual mass content of 0.12% and 0.008%, respectively, of platinum-rhodium catalyst. Because the percentage of catalyst was small, and did not exceed 2.2%, no preliminary roasting was performed. The catalyst was placed in a fluoroplastic receptacle (of a reactor) and wetted with 260ml of HCl (1:1) solution (25% of the initial catalyst mass). Then the rest of the HCl in the amount of 70ml was added to the reactor. The reactor was then heated such that the solution was brought to a boil, and 60ml of concentrated HNO₃ and by parts 150ml of 30% hydrogen peroxide solution were successively introduced. The lixiviation process was run for 1.5 hours. Then heating was stopped and the catalyst was washed though with distilled water in a liquid: solid ratio of 2:1. The wash water from washing of the catalyst and the solution were combined and the platinum-rhodium was precipitated by carburizing with aluminum powder. The percentage recovery was 98.6% for platinum and 94.8% for rhodium.

Example 2:

A palladium-rhodium catalytic converter from a Volvo was found to have 0.08% palladium and 0.006% rhodium by mass. There was also a deposit of pyrocarbon in the amount of 8.7% by mass. The catalyst was initially roasted for 45 minutes at 540°C. After cooling, it was placed in a fluoroplastic receptacle and treated with a dilute HCl solution (HCl: water in a 1:5 ratio) mixed with hydrogen peroxide at a ratio of 1:4 by volume (the total amount added was 460ml). The lixiviation process was then continued as in Example 1 and the recovery yield was 97.8% for palladium and 92.4% for rhodium.

Example 3 :

A deactivated catalytic converter from a Honda was found to contain 0.04% platinum, 0.06% palladium, 0.007% rhodium, and 1.4% cerium. It was treated with dilute aqua regia followed by the immersion in HCl as in Example 1. The lixiviation process was carried out as in Example 1. The recovery yield was 98% for platinum (0.3878g), 98.2% for palladium (0.5831g), and 94.1% for rhodium (0.0653g).

Claims

1. A process for recovering platinum group metals from a spent catalytic member comprising;

(a) introducing a spent catalytic member into a reaction chamber;

(b) wetting said spent catalytic member with an acidic solution;

(c) heating said reaction chamber and adding an oxidizing agent to the reaction chamber;

2. A process according to claim 1, wherein the spent catalytic member is an automobile catalytic converter.

3. A process according to claim 1, wherein the acidic solution is a hydrochloric acid solution.

4. A process according to claim 3, wherein the acid solution is added in an amount corresponding to approximately 25% by weight of the catalyst.

5. A process according to claim 1, further comprising recovering platinum groups metals from the solution obtained in step (e).

6. A process according to claim 1, wherein the oxidizing agent is a nitric acid.

7. A process according to claim 1, further comprising pre-treating the catalytic member with aqua regia.

8. A process according to claim 1, further comprising pre-roasting the catalytic member.

9. A process according to claim 1, further comprising placing the catalytic member onto a surface having perforations.

10. A process according to claim 9, wherein the surface is the bottom of a reaction container.

11. A process according to claim 9, wherein the surface is a platform that is mounted at a predetermined height in the reaction chamber.

12. A reactor adapted for carrying out the process as defined in any one of claims 1-11.

13. A reactor for recovering platinum group metals from a spent catalytic member comprising;

(a) a reaction chamber for receiving a spent catalytic member, said reaction chamber having an inlet for introducing an acid solution into said reaction chamber and an outlet for withdrawing said acid solution from said chamber;

(b) means for heating said reaction chamber;

(c) a condenser, located above said reaction chamber, for facilitating condensing of vapors circulating through said reaction chamber.

14. A reactor according to claim 13, formed from titanium metal.

15. A reactor according to claim 14, wherein the spent catalytic member is positioned in said reaction chamber inside a reaction container, said container having a perforated bottom portion such that vapors from the solution penetrate through said perforated bottom portion in order to contact said catalytic member.