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Catalytic degradation of poly(methyl methacrylate) by zeolites and regeneration of used zeolites via ozonation

Abstract

Catalytic degradation of PMMA was successfully performed at temperatures below 300°C. The use of zeolite catalyst could reduce reaction temperature in comparison with an ordinary thermal degradation process. It was found that the product distribution obtained from batch experiment depends on zeolite acid properties whereas the composition of the liquid fraction is directly related to the shape selectivity of the catalyst. A continuous fixed bed process was designed that allowed to obtain MMA monomer as main product. The increase of reaction temperature from 200 to 270°C showed a positive effect on the liquid product yield. However, at higher temperatures, the light product was further cracked into gaseous products. Significant deactivation of ZSM-5 catalyst was observed after 120 hours of operation, resulting in a decrease in liquid product yield. Regeneration of the coked ZSM-5 extrudates was achieved by oxidation with ozone at low temperatures, below 150°C. The effects of temperature, GHSV and inlet concentration of ozone on carbon removal efficiency were studied. Carbon removal with ozone started at 50°C and reached a maximum of 80% at 100°C. Higher temperatures were not beneficial due to the strong limitation of ozone diffusion which confines radical production then the regeneration process to the outer surface. In optimal conditions, ozonation almost fully restored the zeolite activity without damaging the texture and active sites of zeolite, as shown from the results of regenerated catalyst in PMMA crackin

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This paper was published in Open Archive Toulouse Archive Ouverte.

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