In order to provide a method for the thermal preparation of an auxiliary material, which, to clean a stream of untreated gas laden with an organic impurity, can be introduced into the stream of untreated gas and together with the organic impurity forms a stable system comprising the impurity and the auxiliary material, that can be carried out easily and with sparing use of resources, it is proposed that the method comprises the following steps: feeding the system comprising the impurity and the auxiliary material and a stream of carrier gas heated with respect to standard conditions into a thermal preparation device; chemically converting at least part of the organic impurity to produce a prepared auxiliary material; separating the prepared auxiliary material from the auxiliary material laden with an organic impurity by transporting it by means of a gas flow; and removing the prepared auxiliary material from the thermal preparation device.