This study presents a new approach for the recycling of bilayered PET waste in an efficient, continuous process with a depolymerization degree >97%. The complex PET waste was converted by chemolysis into its monomers ethylene glycol (EG) and the corresponding salt of terephthalic acid (TA) in a twin-screw extruder (TSE). Via this method, the starting materials for PET production were recovered, and highly contaminated PET waste and PET composite materials were transformed into valuable starting materials. The PE layer of the composite PET/PE material remained inert under depolymerization conditions and could be separated by filtration. An increase in the rotational speed by 200 rpm in the TSE reduced the residence time, but the degree of depolymerization was not affected in a proportional manner. Thus, the results indicate that a shorter residence time can be compensated with intensified mechanical agitation due to higher rotational speeds to obtain a similar degree of depolymerization. These results support the potential of this recycling concept to substantially contribute to the implementation of a circular PET economy.

Due to the presence of dyes and additives, textile recycling is challenging, therefore the majority of textile waste is downcycled to low‐value products, incinerated or landfilled. In this study, a continuous depolymerization of post‐consumer polyester textiles was conducted by alkaline hydrolysis. The degree of depolymerization was assessed and found to be 94 %. After recovering and analyzing the terephthalic acid and ethylene glycol the monomers were successfully polymerized to regain a food grade quality recycled polyethylene terephthalate. The presented recycling approach allows a closed‐loop recycling of textiles.

Nowadays there is a need for innovative solutions for composite materials in the packaging and textile sectors. These are formed by multilayer structures that improve technical performance however complicates recycling. Consequently, they are mostly sent to energy recovery or downgrade recycling processes. To avoid this, new recycling technologies are needed.The innovative “back-to-monomer” recycling technology “revolPET®” represents a solution for this challenge. In the process, the polyethylene terephthalate (PET) is selectively depolymerized to recover the monomers ethylene glycol (EG) and terephthalic acid (TA) for a new PET production. By an alkaline hydrolysis, the PET reacts continuously with a strong base in a twin-screw extruder. The average residence time in the extruder is less than one minute with a process yield up to 95%. Due to the mild depolymerization conditions, the other polymers remain chemically unchanged and can be easily separated. The produced monomers are regained in virgin quality and can achieve a 33% reduction on the greenhouse gases emissions if compared with the crude oil production route.In this contribution, the technology on a pilot scale as well as the results of the first scale-up investigations are presented and discussed with respect to technical maturity and environmental benefit.

Plastic waste is one of the major challenges facing modern society. Against the background of climate change and finite fossil resources, the realization of a true circular economy for plastics is imperative. Mechanical recycling processes offer a short‐cut path for the recycling of clean, single material waste while they are not capable to handle mixed material or colored feeds. Complementary technologies are necessary to recover pure monomers, hydrocarbon mixtures or syngas from mixed secondary raw material to continuously close the loop in a circular plastics economy. Using the example of PET, this contribution discusses the benefit of integrating a back‐to‐monomer recycling for closing the loop aiming at a holistically approach integrating technological, ecological and economic aspects.

Back-to-monomer recycling offers a perspective for yet unrecyclable polyethylene terephthalate (PET) waste like textile fibers, multilayer food trays, or brittle bottles. In this context, depolymerization by alkaline hydrolysis is a promising method which demands for consecutive acidic or electrochemical precipitation to recover terephthalic acid (TA). This study investigates the influence of temperatures up to 90 °C and acidification agents on precipitation of TA from aqueous disodium terephthalate solution. The experiments were conducted with a model reactant prepared from purified TA dissolved in sodium hydroxide. The influence on the TA crystal size and morphology affecting further processing, such as filterability and flowability, are discussed. In comparison to commonly used bulk chemical sulfuric acid, experiments with acetic acid were conducted. An enhanced solubility by diluted acetic acid and elevated precipitation temperature lead to significantly larger crystals. Likewise, filtration times for sulfuric acid can be shortened by more than 80% upon increasing the precipitation temperature from 36.5 to 90 °C. The comparison of yield in dependence of pH for different precipitation acids (phosphoric, hydrochloric, oxalic, citric) emphasizes the effect of solid product removal since even weaker acids than TA lead to a reasonable yield of up to 78% for acetic acid. These results offer a perspective and show the necessity for optimizing precipitation with respect to product quality and processability.