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Chemical Depolymerization of High- and Low-density Polyethylene Using Acid Treatments and Ozonation
Summary
Researchers investigated two low-energy chemical alternatives to pyrolysis for depolymerizing polyethylene: acid treatment and catalytic ozonation. Acid processing of HDPE yielded predominantly large dicarboxylic acid products with up to 110% mass yields, while ozonation of LDPE produced water-soluble dicarboxylic acids and insoluble oxidized material, with process optimization and repeated stages improving carbon efficiency.
Economic depolymerization of polyolefins is largely limited to high temperature, energy intensive pyrolysis techniques. Achieving sustainable circularity for low-cost plastics requires inexpensive processes that are not energy intensive; two such promising candidates, acid treatment and ozonation, are investigated. These approaches are being investigated to create value-added products while minimizing the generation of carbon dioxide. The acid process utilizes a mixture of acids combined with a catalyst to oxidize high-density polyethylene (HDPE) to predominantly large molecular weight dicarboxylic acid products with acid numbers and mass yields ranging between 1.0-1.2 mmol/g and 70-110% (g product/g HDPE), respectively. The catalytic ozone technique processes low-density polyethylene (LDPE) to provide water-soluble dicarboxylic acids in yields up to 15% (g product carbon/ g LDPE carbon) and insoluble material at acid numbers averaging 2.4-4.8 mmol/g. Process optimization and the use of repeated stages can improve the carbon efficiency of these processes.