Chemical Recycling Processes of Waste Polyethylene Terephthalate Using Solid Catalysts

Polyethylene terephthalate (PET) is a non-degradable single-use plastic and a major component of plastic waste in landfills. Chemical recycling is one of the most widely adopted methods to transform post-consumer PET into PET's building block chemicals. Non-catalytic depolymerization of PET is very slow and requires high temperatures and/or pressures. Recent advancements in the field of material science and catalysis have delivered several innovative strategies to promote PET depolymerization under mild reaction conditions. Particularly, heterogeneous catalysts assisted depolymerization of post-consumer PET to monomers and other value-added chemicals is the most industrially compatible method. This review includes current progresses on the heterogeneously catalyzed chemical recycling of PET. It describes four key pathways for PET depolymerization including, glycolysis, pyrolysis, alcoholysis, and reductive depolymerization. The catalyst function, active sites and structure-activity correlations are briefly outlined in each section. An outlook for future development is also presented.

Recent Developments and Perspectives of Recycled Poly(ethylene terephthalate)-Based Membranes: A Review

Post-consumer poly(ethylene terephthalate) (PET) waste disposal is an important task of modern industry, and the development of new PET-based value added products and methods for their production is one of the ways to solve it. Membranes for various purposes, in this regard are such products. The aim of the review, on the one hand, is to systematize the known methods of processing PET and copolyesters, highlighting their advantages and disadvantages and, on the other hand, to show what valuable membrane products could be obtained, and in what areas of the economy they can be used. Among the various approaches to the processing of PET waste, we single out chemical methods as having the greatest promise. They are divided into two large categories: (1) aimed at obtaining polyethylene terephthalate, similar in properties to the primary one, and (2) aimed at obtaining copolyesters. It is shown that among the former, glycolysis has the greatest potential, and among the latter, destruction followed by copolycondensation and interchain exchange with other polyesters, have the greatest prospects. Next, the key technologies for obtaining membranes, based on polyethylene terephthalate and copolyesters are considered: (1) ion track technology, (2) electrospinning, and (3) non-solvent induced phase separation. The methods for the additional modification of membranes to impart hydrophobicity, hydrophilicity, selective transmission of various substances, and other properties are also given. In each case, examples of the use are considered, including gas purification, water filtration, medical and food industry use, analytical and others. Promising directions for further research are highlighted, both in obtaining recycled PET-based materials, and in post-processing and modification methods.

Catalytic methods for chemical recycling or upcycling of commercial polymers

Polymers (plastics) have transformed our lives by providing access to inexpensive and versatile materials with a variety of useful properties. While polymers have improved our lives in many ways, their longevity has created some unintended consequences. The extreme stability and durability of most commercial polymers, combined with the lack of equivalent degradable alternatives and ineffective collection and recycling policies, have led to an accumulation of polymers in landfills and oceans. This problem is reaching a critical threat to the environment, creating a demand for immediate action. Chemical recycling and upcycling involve the conversion of polymer materials into their original monomers, fuels or chemical precursors for value-added products. These approaches are the most promising for value-recovery of post-consumer polymer products; however, they are often cost-prohibitive in comparison to current recycling and disposal methods. Catalysts can be used to accelerate and improve product selectivity for chemical recycling and upcycling of polymers. This review aims to not only highlight and describe the tremendous efforts towards the development of improved catalysts for well-known chemical recycling processes, but also identify new promising methods for catalytic recycling or upcycling of the most abundant commercial polymers.

Valorisation of plastic waste via metal-catalysed depolymerisation

Metal-catalysed depolymerisation of plastics to reusable building blocks, including monomers, oligomers or added-value chemicals, is an attractive tool for the recycling and valorisation of these materials. The present manuscript shortly reviews the most significant contributions that appeared in the field within the period January 2010–January 2020 describing selective depolymerisation methods of plastics. Achievements are broken down according to the plastic material, namely polyolefins, polyesters, polycarbonates and polyamides. The focus is on recent advancements targeting sustainable and environmentally friendly processes. Biocatalytic or unselective processes, acid–base treatments as well as the production of fuels are not discussed, nor are the methods for the further upgrade of the depolymerisation products.