Recovery of methyl methacrylate from waste poly (methyl methacrylate) pellets using a low-temperature plasma and zeolites

Abstract

A dielectric barrier discharge (DBD) plasma method with zeolite catalysts was applied to waste poly (methyl methacrylate) (PMMA) pellets to retrieve methyl methacrylate (MMA), methacrylic acid, and methanol at a relatively low temperature. Waste PMMA pellets were provided in the form of post-industrial recycled (PIR) PMMA. Three types of zeolite catalysts such as HY, H-zeolite socony mobil-5 (HZSM-5), and H-mobil composition of matter-22 (HMCM-22) were tested to assess their catalytic performance for retrieval under plasma irradiation. By conducting comparative examples such as non-catalytic, catalytic, and plasma-assisted non-catalytic thermolysis reactions, the cooperative effects of the DBD plasma discharge and zeolite catalyst were investigated. HMCM-22 was found to be more effective, especially for the retrieval of MMA. In the cases of non-catalytic and catalytic thermolysis at 300 °C, conversions of PMMA were found 50.9 % and 52.6 %, respectively. By contrast, plasma-assisted non-catalytic thermolysis showed that the PMMA conversion improved by up to 90.6 %, whereas the yield of MMA was relatively low (34.6 %). Using zeolite catalysts in the plasma bed also improved PMMA conversion by up to nearly 90 %. The liquid products yields were comparable for HY and HZSM-5. By contrast, HMCM-22 afforded the highest liquid product yield. Notably, the HMCM-22 case showed highest MMA yield at nearly 53.1 %, which seems highly related to a large amount of Brønsted acid sites. More importantly, the byproducts having odor issue such as methyl pyruvate and 2,3-butanedione were not produced in such a plasma-assisted catalytic or non-catalytic conversion method.