The present invention is related to the treatment of plastic material to be destined for chemical recycling processes for the valorisation of substantially plastic material otherwise destined for disposal.

In particular, the invention concerns a process for the pyrolysis of substantially plastic material to obtain at least liquid hydrocarbons at 25 C. comprising the following steps: a) feeding to a pyrolysis reactor a substantially plastic material at least partially in the molten state; b) subjecting said substantially plastic material fed to a pyrolysis reactor to at least an analytical measurement Ax with in-line mode; c) determining the value of at least one Px property of said substantially plastic material by means of said at least one analytical measure Ax; d) installing at least one Ox parameter of the pyrolysis process based on the value of this at least one Px property;
characterised by the fact that at least one analytical measurement Ax provides or consists of the measurement of the spectrum in reflection of the light of the substantially plastic material.