Date

2016

Author

Kelebek, Neriman

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Pyrolysis of polymers, which is a process for recovery of the waste polymer, has attracted great attention in recent years due to the high amount of plastic waste present in nature.However, degradation rocess requires high amount of external energy to break long chain of chemical bonds in the polymer. For this reason, suitable catalysts with strong acid sites are necessary. High surface area silica structured mesoporous materials with narrow pore size distributions are excellent catalysts for these reactions. However, these catalysts are synthesized with the incorporation of appropriate materials because they lack acid sites necessary for the pyrolysis reactions. Heteropoly acids having strong acid sites are good choice to load into these catalysts in order to increase their activity in the pyrolysis reactions.Silicotungstic acid (STA) loaded MCM-41 catalysts were synthesized hydrothermally at a calcination temperature of 400 °C with the W to Si molar ratio of 0.25 and synthesis solution pH values of 1.2 and 1.4. X-ray diffraction analysis of the sample with pH value of 1.2 showed that this catalyst had an MCM-like structure. According to the nitrogen adsorption desorption analysis, the synthesized MCM-41 catalysts were in the mesoporous diameter range and the adsorption-desorption branches reflected the typical Type IV isotherms. The surface area of the sample having pH value of 1.2 was 234.08 m2/g. EDS results of this catalyst revealed that there was a good incorporation of STA into MCM-41 structure.DRIFTS analysis of this catalyst showed the existence of Bronsted acid sites in addition to Lewis acid sites with STA loading. STA loaded SBA-15 catalyst was synthesized hydrothermally at a calcination temperature of 250 °C with the W to Si molar ratio of 0.1 in highly acidic synthesis solution. X-ray diffraction analysis of this catalyst showed that an ordered silica structure of SBA was obtained. According to the nitrogen adsorption-desorption analysis, the synthesized SBA-15 catalyst was in the mesoporous diameter range and reflected the typical Type IV isotherms. The surface area of this catalyst was 448.49 m2/g which was higher than that of the synthesized STA loaded MCM-41 catalysts. EDS results of this catalyst showed that there was a low incorporation of STA into SBA-15 structure. To test the activity of the synthesized catalysts, thermogravimetric analysis was performed under nitrogen atmosphere. Among the synthesized catalysts, STA loaded MCM-41 with pH value of 1.2 and STA incorporated SBA-15 catalysts showed good performance in the polyethylene degradation reaction. These catalysts reduced activation energy and degradation temperature significantly (From 130 kJ/mole to 53.4 kJ/mole and 59.3 kJ/mole, respectively). So the two catalysts were active catalysts for the polyethylene degradation reaction

Subject Keywords

Pyrolysis., Catalysts., Polyethylene., Chemical reactions., Mesoporous materials.

URI

http://etd.lib.metu.edu.tr/upload/12619956/index.pdf
https://hdl.handle.net/11511/25624

Collections

Graduate School of Natural and Applied Sciences, Thesis