Potential for chemical recycling in the recycling industry?
While waste disposal has been an issue for quite some time, it was not until recent years that public and private sectors have become increasingly aware of the environmental implications associated with this worldwide problem. Since plastics are imbedded in thousands of products that are part of our everyday life, with consumption over 300 million tons per year and growing (as illustrated in the Figure below), they make up a major component of waste material. Thus, local governments, as well as public and private companies, are focusing on ways to reduce/eliminate plastic waste.
Plastics recycling is considered the best option due to its energy and GHG emissions benefits, although there are limitations to conventional methods. There are four basic levels of recycling, commonly referred to as primary, secondary, tertiary, and quaternary recycling. Overall, primary and secondary recycling have been covered extensively and can be considered traditional or commodity recycling markets. Secondary recycling systems are well-established in many areas, but are limited in what is processed. Polymers that are mechanically recycled have limitations as to how many times the material can be recycled before mechanical properties degrade and reach their end-of-life. The key for the future is what to do with these plastics, those that are considered hard-to recycle or end-of-life.
For difficult to recycle plastics, end of life plastics, or those considered non-recyclable (i.e., not mechanically recycled), the main recycling option to date has been to include them in the MSW streams that are sent to waste to energy (WTE) facilities, as an alternative to landfilling. However, for those polymers and plastics that are more difficult to recycle than bottles (such as film or synthetic fibers) that are now part of typical waste stream, chemical recycling is an alternative way to traditional recycling routes. One of the advantages of chemical recycling is that it produces monomers that can be sent back into the production process.
In addition to handling plastics that are considered hard to recycle by conventional methods, chemical recycling can potentially provide the food-grade recycled content needed for brand owners’ sustainability goals (otherwise not provided by conventional mechanical recycling). PET, PS, and mixed plastics have been the targets of recent chemical recycling technology, since they account for more than 80 percent of global polymers produced.
Chemical recycling of polyester, particularly PET resin used in bottle and other container applications, is continuing to grow in importance as a viable means of recycling and it use in applications that come in contact with food. Chemical recycling also offers the opportunity to add value-added products to post-consumer PET. PET can be chemically recycled using glycolysis, hydrolysis or methanolysis methods, among others.
Conventional mechanical recycling of polystyrene (PS) waste has been considered to be difficult because the material is difficult to reprocess, it can be contaminated with food, and the possible release of carcinogens to the environment. With the introduction of pyrolysis, polystyrene waste can converted into styrene monomer used to produce polystyrene material for higher value added applications such as food packaging.
Mixed plastics (mainly polyolefins, along with PS, PVC, and others) are the targets of plastics to fuel and feedstock (PTF) pyrolysis technologies. These polymers are considered difficult to recycle for many reasons, and depending on the PTF technology, can be processed together. Mixed plastics can be chemically recycled via pyrolysis or gasification methods and used for the production of fuels, feedstocks, or chemicals.
Post-consumer plastics recycling technologies have evolved from traditional plastics processing and/or industrial scrap molding technologies. The challenge has been to modify these technologies to accept heterogeneous mixtures of plastic resins, normally incompatible with one another, and to tolerate contamination by various non-plastic materials. While secondary (i.e., physical/mechanical) recycling has been proven to be economically feasible for lower value end-uses, this level of recycling is not the first choice for the production of recyclate used in products that come in direct contact with food (the properties of the recyclate must be close to those of the virgin material). Therefore, advances in recycling technology are important to plastics in general because of the limitations on reuse in food applications. Because mechanical recycling is unable to completely fulfill the needs of these high-value applications, it is imperative that economical technology be developed that can effectively allow for the reuse of resins by more advanced technologies such as chemical recycling.
Nexant has just completed a Special Report titled “Sorting through Plastic Waste – Is Chemical Recycling a Solution.” This report examines the technical, economic and business aspects of chemical recycling of PET, PS and mixed plastics (plastics to fuel). Selected technology developers of chemical recycling are profiled and ranked under different criteria. The economics for chemically recycling several types of plastic waste are provided for different geographic regions, and compared to the production of virgin material by conventional technology. In addition, the report includes an analysis of the MSW stream and the economics for the incineration of waste with energy recovery.
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