Method for the depolymerisation of polystyrene in the presence of foreign polymers

A process for the production of styrene monomers by depolymerization of a polystyrene-containing polymer composition, comprising the steps of:

• a) introducing a polymer composition (A) containing:
• 10% to 99.5% by weight of a polystyrene (I), based on the total weight of the polymer composition (A);
• and
• II) 0.1% to 89.9% by weight of a polyolefin (II), based on the total weight of the polymer composition (A);
• and/or
• III) 0.1% to 4.9% by weight of an acrylonitrile-based polymer (III), based on the total weight of the polymer composition (A);
• and/or
• IV) 0.1% to 4.9% by weight of a polyester (IV), based on the total weight of the polymer composition (A),
• into a reaction zone (R) of a pyrolysis reactor (P);
• b) thermally cleaving the polystyrene (I) present in the polymer composition (A) in the reaction zone (R) of the pyrolysis reactor (P) at a temperature of from 400° C. to 1000° C. to obtain a product mixture (G) containing styrene monomers and further components;
• c) withdrawing the product mixture (G) obtained in step b) from the reaction zone (R) of the pyrolysis reactor (P);
• d) cooling the product mixture (G) withdrawn in step c) to obtain a condensed product mixture (K) containing styrene monomers and further components;
• and
• e) separating the styrene monomers from the further components of the condensed product mixture (K) obtained in step d),
• wherein an average residence time (Z) of the polymer composition (A) in the reaction zone (R) of the pyrolysis reactor (P) is from 0.01 s to 10 s.