Date

2014

Author

Bursalı, Tülay

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Thermoplastic materials have a wide variety of usage area due to their low costs and easy processing properties. However, these materials cause a serious environmental pollution because of being non-biodegradable and their long-term self-recycling. Considering energy need and clean environment, it is proper to degrade thermoplastic materials into lower moleculer weight products which are potential raw materials for petrochemical industry. In addition, it is possible to decrease the reaction temperature & time and to increase the product yield by using a proper catalyst. In this study, SAPO-34 material was synthesized via hydrothermal route and then it was used in the catalytic thermal degradation of polypropylene and polystyrene. XRD result showed that the synthesized material was SAPO-34. BET analysis revealed that the material was microporous and exhibited Type I isotherm. The material formed in a cubic-like shape. DRIFTS result showed the existence of Lewis and Brønsted acid sites in the structure. Using 27Al and 29Si magic angle spinning nuclear magnetic resonance techniques, it was observed that 27Al atoms were octahedrally and tetrahedrally; 29Si atoms were tetrahedrally coordinated in the structure of the synthesized material. The reaction orders and the activation energy values of polypropylene and polystyrene degradation reactions in the presence of SAPO-34 were determined using TGA data. Both of the reactions were determined as “first order”. The activation energy of polypropylene degradation reaction decreased from 172 kJ/mol to a value of 131±11 kJ/mol and the activation energy of polystyrene degradation reaction decreased from 357±4 kJ/mol to 262±4 kJ/mol in the presence of SAPO-34 catalyst. In the pyrolysis system, the non-catalytic and catalytic degradation experiments of polypropylene and polystyrene over SAPO-34 material were performed and gaseous and liquid products were analyzed using GC. In the degradation reactions of PP, liquid products formed at 425 ºC and higher temperatures. Solid residue was observed only at 400 ºC and lower temperatures. The presence of SAPO-34 increased the gaseous product yield considerable at 400 °C and lower temperatures. There was a slight change in yield values of liquid products in the presence of the catalyst compared to the absence of SAPO-34. During the reaction, the catalyst was not deactivated and coke was not formed. In the catalytic degradation reaction of PP, the gaseous products were mainly composed of ethylene and propene. In addition to these gases, the formation of methane, acetylene, propane and butane was observed at 400 ºC for 30 min reaction time in the presence of the catalyst. However they were not formed at the same temperature & reaction time in the non-catalytic degradation. The highest amount of hydrocarbon in liquid products was C10 in the non-catalytic and catalytic degradation of PP. In the presence of SAPO-34, heavier hydrocarbons degraded to lighter hydrocarbons with an increase in temperature. The amounts of lighter hydrocarbons produced at a reaction time of 30 min in the presence of SAPO-34 were higher than that of lighter hydrocarbons produced in the absence of catalyst. In the degradation reactions of PS at 415 °C, only liquid and gas products were formed. The presence of SAPO-34 did not effect the yields of liquid & gas products. During the reaction, the catalyst was not deactivated and coke was not formed. The majority of the gas products were methane and ethylene in the non-catalytic degradation of PS. In addition to these gases, butane was formed in the presence of SAPO-34. The liquid products were mainly composed of C8 – C10 hydrocarbons. The formation of C9 hydrocarbons was observed in the presence of SAPO-34 compared to the absence of the catalyst. These results showed that the polymer degraded into its monomer & lighter hydrocarbons in the presence of SAPO-34. The TGA and GC results revealed that SAPO-34 was active in the catalytic thermal degradation reactions of PP and PS.

Subject Keywords

Catalysts., Pyrolysis., Polypropylene., Polystyrene., Plastic scrap., Silica-alumina catalysts.

URI

http://etd.lib.metu.edu.tr/upload/12618202/index.pdf
https://hdl.handle.net/11511/24213

Collections

Graduate School of Natural and Applied Sciences, Thesis