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The fast catalytic pyrolysis of polystyrene in the hydrocarbon medium (light and heavy cycle oil) over zeolite catalysts at 450–550 °C was investigated. The influence of reaction conditions (medium, temperature, vapor residence time, polystyrene concentration) on polymer conversion and product distribution was studied. It was found that the polymer conversion is close to 100%, while ethylbenzene, benzene, and toluene are the main products of its transformation. The maximum yield of ethylbenzene (80%) was achieved at 550 °C, vapor residence time 1–2 s, polystyrene concentration 10%, and heavy cycle oil as the medium. The influence of zeolite topology on product distribution was explored. The possible mechanism of polystyrene pyrolysis was proposed. [ABSTRACT FROM AUTHOR]

• Thermal depolymerization of polystyrene in the hydrocarbon medium was studied. • Maximum styrene yield was 84.4% in LCO at 500 °C and the vapor residence time 2.61 s. • Formation of a styrene dimer in the hydrocarbon medium is inhibited. • Depolymerization products seem suitable for further styrene monomer production. Data from the thermal depolymerization of polystyrene in a highly aromatic hydrocarbon medium (light and heavy cycle oil) have been obtained. The influences of the reaction conditions on the conversion and selectivity have been studied. The maximum yield of styrene obtained in the present work is 84.4% at a polymer conversion of 93.8% in light cycle oil under the following conditions: temperature: 500 °C, vapor residence time: 2.61 s, polymer concentration: 15%. The styrene yield obtained is higher than has been previously reported in the scientific literature. The high selectivity of styrene in the depolymerization reaction can be explained by the fact that under the reaction conditions studied, the formation of styrene dimers in the hydrocarbon medium is inhibited. [ABSTRACT FROM AUTHOR]