INEOS Styrolution has reported the final results of research project ResolVe, showing that waste polystyrene can be chemically recycled to produce new products.
Styrenic supplier Ineos Styrolution is the coordinator for the three-year research project exploring how waste polystyrene can be used as a raw material to produce high-quality plastics at a commercial scale. The project has a number of collaborators and was funded by the German Federal Ministry of Education and Research.
The final results of the study show that breaking polystyrene up into its building blocks is a suitable way to recycle polystyrene and therefore polystyrene can contribute to a circular economy.
The project investigated the composition of the waste and its effect on the styrene yield. A stable process is possible with a broad range of feedstock. The most suitable feedstock is lightweight packaging and expanded polystyrene.
Household waste is sorted to remove impurities like other plastics and moisture, and then shredded to produce polystyrene flakes less than 10 mm in size. These are heated to melting point and a vacuum pump removes moisture and oxygen. The polystyrene is then heated above its melting point to break the polymer chains and create the styrene monomer. The gaseous styrene monomer is condensed into styrene oil, which contains high and low boiling components as well as the styrene monomer. The oil is purified to get enriched styrene using two distillation steps. The high and low boiling components are roughly separated in the first step. The second step involves higher separation efficiency to purify the product further. This styrene monomer is then used to create new polystyrene.
Currently, up to 75% of the polystyrene can be made into new material. While all of the polystyrene can be depolymerised, the process also produces other byproducts which could be used as feedstock for other processes.
Ineos Styrolution has performed a life cycle analysis (LCA) for its depolymerised styrene, finding that it saved 50% in emissions compared to fossil-based styrene. The company believes that this can be improved once a plant is in operation, as current life cycle analyses for commercial-scale production are produced using models based on certain assumptions. The LCA took into account waste collection and sorting, pretreatment, extrusion, depolymerisation, and distillation. It was based on an engineering design for an upscaled polystyrene depolymerisation plant.
Ineos Styrolution is currently developing a facility with chemical recycling company Agilyx in Channahon, Illinois, US, which will be capable of processing around 100 t/d of polystyrene waste. Ineos Styrolution is collaborating with waste management company Indaver in planning a demonstration plant in Antwerp, Belgium, that will be capable of recycling 15,000 t/y and aims to be operational in 2021. A commercial-scale plant is planned with Agilyx and materials company Trinseo at a site in Wingles, France, that will process 50 t/d of polystyrene waste.
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