A multitude of chemical processes on an multi-tonne scale, such as, e.g., reforming for fuel production, the production of monomers for polymer chemistry or the production of ammonia, utilise precious metals and precious metal-containing species as catalysts. As a matter of principle, there are two states, in which the precious metal can be present in the process. The catalytically active species is present either in a homogeneous mixture including the reactants or as a heterogeneous mixture including the reactants, and the catalytically active species is deposited on an inert carrier material in most cases. In many cases, heterogeneous catalysts are preferred since they can be removed easily from the reaction mixture, e.g. by filtration. The precious metals in heterogeneous catalysts are often situated on—usually inert—macroscopic carrier materials, such as, for example, form bodies is made of aluminium oxide, silicon oxide or carbon. The materials used for this type of form body are usually highly porous and thus enable a uniform distribution of the precious metal over a large surface. If carbon is used as carry material, the carbon can consist, e.g., of porous graphite or activated carbon.
The activity of a precious metal-containing catalyst decreases after a certain operating time and the catalyst needs to be replaced. Due to the high price of precious metals, the utilisation of precious metal-containing catalysts is often economical only if the precious metal used in the process can be recovered. Typically, spent heterogeneous precious metal catalysts based on porous carrier materials are subjected to a wet chemical treatment to dissolve and recover the precious metal. Since wet chemical dissolution often takes place in strongly oxidising solutions, inorganically- and/or organically-bound carbon disturbs the process, since it can cause strong foaming, among other effects. Said inorganically- and/or organically-bound carbon can originate, for example, from the carrier material or from process residues (e.g.
starting materials, product residues, side products, solvent).
This is the basis of the need to have processes that can be used to remove inorganically- and/or organically-bound carbon from precious metal-containing compositions to allow the precious metals to be further processed more efficiently.
To this aim, EP1951919 A1 describes a two-step process for removing carbon from precious metal-containing materials, in which a pyrolysis of the volatile components in an inert nitrogen atmosphere takes place first, followed by combusting poorly combustible material in the presence of atmospheric oxygen. It is a disadvantage of the process that nitrogen or other inert gas needs to be heated to the process temperature of approximately 800° C. outside of the oven chamber and needs to then be supplied into the oven chamber for the pyrolysis step. Not only is the use of inert gas comparably expensive, but heating the inert gas to process temperature consumes a significant amount of energy.