Recycling Vehicle Catalytic Converters

Vehicle catalytic converters are employed in the aftertreatment of exhaust gas in vehicles fitted with internal combustion engines.

Modern catalytic converters are able to reduce pollutant emissions in exhaust gas by a considerable amount. In the majority of cases, the whole exhaust gas aftertreatment system will be referred to as a vehicle catalytic converter.

A vehicle catalytic converter is responsible for the chemical conversion of common combustion pollutants such as hydrocarbons (CmHn), carbon monoxide (CO) and nitrogen oxides (NOx) into the non-toxic substances carbon dioxide (CO₂), water (H₂O) and nitrogen (N₂).

The vehicle catalytic converter achieves this via oxidation and reduction, respectively.

It is possible to achieve an almost 100% conversion rate, depending on the operating conditions of the catalytic converter and the operating point of the engine.

The automotive catalytic converter is generally comprised of several components. The carrier is made up of a temperature-stable ceramic honeycomb body with a large number of thin-walled channels.

This component is generally manufactured from cordierite. The washcoat is situated on the carrier, consisting of porous aluminum oxide (Al₂O₃) designed to increase the surface area. A surface area of up to several hundred square meters per gram can be achieved due to the washcoat’s high level of roughness.

Catalytically active substances are embedded within the washcoat, but these will differ depending on the type of catalyst being used. For example, modern three-way catalysts utilize the precious metals rhodium, platinum, or palladium, or a combination of these materials.¹

In the laboratory experiment outlined here, the ceramic honeycomb body was crushed to powder in order to facilitate characterization of catalytically active precious metals.

Initial Experiment

The honeycomb body was initially pre-comminuted in the PULVERISETTE 19 LARGE Universal Cutting Mill. The instrument was fitted with a disk milling cutting rotor with indexable inserts and fixed knives manufactured from hardmetal tungsten carbide.

It also featured a 4 mm sieve cassette square perforation and stainless steel, high performance Cyclone separator. The sample was ground for approximately 1 minute at 1500 rpm.

Figure 1. Ceramic parts catalyst with fleece sides. Image Credit: FRITSCH GmbH - Milling and Sizing

Figure 2. Grinding chamber PULVERISETTE 19 LARGE after comminution. Image Credit: FRITSCH GmbH - Milling and Sizing

Figure 3. Cyclone separator with sample glass with ground sample. Image Credit: FRITSCH GmbH - Milling and Sizing

Second Test

During the second test, a section of the pre-comminuted sample from the PULVERISETTE 19 LARGE was further processed using the PULVERISETTE 14 premium line. Two hundred milliliters of the sample were comminuted within 38 seconds, achieving a final fineness of less than 500 µm.

The PULVERISETTE 14 premium line was fitted with a cutting rotor. This was also connected to the small volume Cyclone separator, which was operated passively.

It is theoretically possible to use the Variable Speed Rotor Mill PULVERISETTE 14 premium line to achieve a maximum final fineness of less than 80 µm on a ground sample.

Figure 4. PULVERISETTE 14 premium line and the small volume Cyclone separator. Image Credit: FRITSCH GmbH - Milling and Sizing

Figure 5. Ground sample. Image Credit: FRITSCH GmbH - Milling and Sizing

Third Test

During the third test, a section of the pre-comminuted sample from the PULVERISETTE 19 LARGE was further comminuted using the Planetary Mill PULVERISETTE 5 premium line.

Grinding time was 1 minute, and the instrument was used with 20 mm zirconium oxide grinding balls and 125 ml volume zirconium oxide grinding bowls. The sun disk’s speed was set to 450 rpm, achieving a final fineness of less than 100 µm.

Because the PULVERISETTE 5 premium line is a totally closed system, there is no chance of harmful substances being inhaled during the grinding process. This robust, powerful mill can also prepare samples with a final fineness down to the nanometer range.

Figure 6. PULVERISETTE 5 premium line with ZrO₂ accessories. Image Credit: FRITSCH GmbH - Milling and Sizing

Conclusion

The tests outlined here demonstrate FRITSCH’s range of solutions designed to comminute catalysts. With further analysis, users could also determine the level of precious metal content in the milled material, allowing them to evaluate the likelihood of recovering these valuable precious metals.

References

1. Wikipedia Fahrzeugkatalysator

Acknowledgments

Produced from materials originally authored by Dagmar Klein from Fritsch GmbH.

This information has been sourced, reviewed and adapted from materials provided by FRITSCH GmbH - Milling and Sizing.

For more information on this source, please visit FRITSCH GmbH - Milling and Sizing.