Catalytic Pyrolysis Process to Produce Styrene from Waste Expanded Polystyrene Using a Semi-Batch Rotary Reactor

• Published in: Sustainability Vol. 14; no. 22; p. 14914
• Main Authors: Pérez-Bravo, Gerardo, Contreras-Larios, José Luis, Rodríguez, Jorge Francisco, Zeifert-Soares, Beatriz, Angeles-Beltrán, Deyanira, López-Medina, Ricardo, Vázquez-Rodríguez, Tamara, Salmones-Blasquez, José
• Format: Journal Article
• Language: English
• Published: Basel MDPI AG 01.11.2022
• Subjects: Back mixing; Carcinogens; Catalysts; Experiments; Fixed bed reactors; Free energy; Gases; Gibbs free energy; Heat of reaction; Hydrocarbons; Industrial applications; Kinetic equations; Molecular weight; Plastic pollution; Polymers; Polystyrene; Polystyrene resins; Pyrolysis; Raman spectroscopy; Reactors; Solvents; Styrene; Styrenes; Sustainability; Toluene; Viscosity; Mexico; United States > US
• ISSN: 2071-1050; 2071-1050
• DOI: 10.3390/su142214914

Thermal and catalytic pyrolysis of waste expanded polystyrene (WEPS) was studied to obtain mainly styrene monomer, which can be recycled in the polystyrene industry. Initially, preliminary experiments were carried out in a static semi-batch glass reactor with basic catalysts and without catalysts, using toluene as solvent at 250 °C, determining their styrene yields to select the best catalyst. MgO turned out to be the best catalyst due to its stability and cost. This catalyst was characterized by XRD, BET area, SEM-EDS, Raman spectroscopy, UV–VIS, and TGA. The kinetic equation for WEPS pyrolysis in the glass reactor was determined as a first-order reaction. The heat of reaction, the Gibbs free energy change, and the entropy change were calculated. Finally, WEPS pyrolysis experiments were carried out using a rotating semi-batch steel reactor, at higher temperatures and without using solvents, evaluating the styrene yield and its performance for its possible industrial application. In this reaction, the activity remained almost constant after four catalyst regenerations. The best styrene yield was 94 wt%, which could be one of the highest reported in the literature. This result may be associated with the back-mixing obtained in the rotary reactor, in contrast to the performance observed in the static glass reactor.