Catalytic converters and diesel particulate filters

The carrier material of a diesel particulate filter differs significantly from normal automotive catalytic converters for exhaust emissions (ACCs). Conventional automotive catalytic converters which have been instituted since the early 1990s consist of approx. 1kg of cordierite. This ceramic, made from aluminium, magnesium and silicon oxide, is easy to melt in electrical high-temperature furnaces. In this smelting process, the precious metals are separated from the ceramic and bound in what is called "collector metal". The smelting process is carried out under reducing conditions (release of oxygen), enabling a high yield in the recovery of precious metals.

In diesel particulate filters, the carrier material generally consists of approx. 3kg of silicon carbide (SiC). This material reacts very differently to the smelting process than cordierite. In this case, we use an oxidizing smelting process (addition of oxygen) to convert the carbon (carbide) into carbon dioxide and the silicon into silicon oxide. Only then it`s possible to efficiently recover the precious metal. If both material types, i.e. ACC and DPF, are mixed together, this makes the recovery of the precious metals extremely difficult or nearly impossible from a certain concentration onwards.

Capacities for the processing of this high-carbon material are currently limited and pose a problem for many smelting companies. Apart from the limited capacities, it is also much more expensive (energy input, toll refining, longer processing cycles). First market participants have already started to reject mixed material products for recycling.

A separate analysis and recycling is unproblematic as economic processes exist for both material types. Furthermore, the Hensel Recycling Group has been working together with partners for some time to develop a special processing procedure, which will provide for additional capacities in the future.

To ensure sustainable and economic processing of the material, it is important to separate the materials at an early stage in the recycling loop. After dismantling the catalytic converter or filters, separating the materials is practically impossible. In addition to visual inspection and weighing, carbon type analysis ultimately provides a clear picture of the material composition and which smelting process must be used. Hensel Recycling has the technical means and the expertise to determine the total carbon content in accordance with DIN EN ISO 21068-2:2008 and is therefore able to deliver a reliable basis.

Weight:

• A regular monolith or a DPF based on aluminium titanate weighs approx. 1 kg
• A DPF made of SiC ceramic usually weighs 2 – 3 kg

Visual inspection:

• SiC – usually grey surface and black ceramic, bonded cuboids with light edges