Analysis of Products Generated from the Thermal and Catalytic Degradation of Pure and Waste Polyolefins using Py-GC/MS |
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Authors: | J Aguado D P Serrano G San Miguel |
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Institution: | (1) Universidad Rey Juan Carlos, Escuela Superior de Ciencias Experimentales y Tecnología (ESCET), c/ Tulipán, 28933 Mostoles, Spain;(2) Universidad Politécnica de Madrid, Escuela Técnica Superior de Ingenieros Industriales (ETSII), c/ José Gutiérrez Abascal, 2, 28006 Madrid, Spain |
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Abstract: | The possibility of transforming waste plastics into valuable hydrocarbons via catalytic cracking and reforming is attracting
increasing interest. Pyrolysis coupled with Gas Chromatographic separation and Mass Spectrometry detection (Py-GC/MS) has
been used in this work to study the product selectivity of various catalysts in the conversion of pure and residual polyethylene
samples into hydrocarbon products. Five acid solids of comparable aluminium contents but different textural and acid properties
were tested as catalysts, including three zeolites (standard ZSM-5, nanocrystalline n-ZSM-5 and Beta) and two mesostructured
solids (Al-MCM-41 and Al-SBA-15). Thermal cracking of the pure and residual polymers generated a similar range of products
to each other, with a high proportion of linear paraffins and olefins of varying lengths. The presence of zeolitic materials
resulted in complete elimination of heavy linear products, an increase in the light hydrocarbon fraction and a marked selectivity
towards the formation of single-ring aromatic species, particularly benzene, toluene and xylene. Aromatic formation was particularly
notable with the small crystal size n-ZSM-5 (aromatic selectivity up to 53.9%) and less marked in the case of standard ZSM-5
(up to 36.4%) and Beta zeolite (up to 35.0%). Mesostructured catalysts like Al-MCM-41 and Al-SBA-15 favoured the production
of light C2–C5 hydrocarbons (up to 57.9%) while the formation of aromatic products was significantly lower than with zeolitic materials.
The paper examines the extent and the causes for this product selectivity and discusses its connection with the acid and textural
properties of each catalyst. It was also observed that, under the experimental conditions employed, the products generated
were not significantly affected by the nature and origin of the polymers employed. |
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Keywords: | Waste plastics Plastic recycling Catalytic cracking Zeolites Al-MCM-41 Al-SBA-15 |
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