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Advancements in Plastic Recycling Technologies

Chemicals | Aug, 2023

Plastics are ubiquitous as they serve multiple applications and are cheap to produce. However, the explosion in manufacturing and consumption of plastics has far outstripped the capacity to manage them at the end of their lifecycle. Plastic wastage is rapidly emerging as one of the urgent environmental issues of our times. Only 10% of used plastic is recycled and the rest is either thrown away on landfills, incinerated, or dumped in the oceans. Currently, plastic waste makes up about 40% of the world's ocean surfaces with 5.25 trillion pieces of plastic debris in the ocean. Every year, the United States contributes around 38 million tons of plastic in the oceans. Moreover, the use of raw materials for production of plastics is inherently unsustainable since it requires the use of petroleum-based products, which further perpetuates our dependence on non-renewable resources. Hence, there is a growing need to resort to plastic recycling to promote a circular economy and ensure sustainability in the environment. Even rising pressure from consumers and governments are pushing brand owners and retailers towards using recycle-friendly packaging so that no material is wasted. CSR initiatives to create ambitious targets for incorporating recycled plastics content are also heightening interest in plastic recycling.

Currently, mechanical recycling is the dominant technology for plastic recycling, which involves physical processes such as sorting, grinding, washing, separating, drying, re-granulating, washing, and then melting plastics so that they can be reused later. More than 99% of infrastructure and businesses use mechanical recycling as the primary means of recycling. Mechanical recycling technology is labor and time intensive and generally results in lower quality plastics than virgin plastics. Besides, with mechanical recycling, plastic can only be recycled a maximum of 5 to 7 times. Hence, the plastic recycling industry is resorting to advanced recycling technologies, namely chemical recycling as an alternative or complement to mechanical recycling. In recent years, chemical recycling has gained momentum due to its potential for an infinite number of recycling cycles. Chemical recycling technologies recycle used plastic into virgin-equivalent plastic using heat or chemical reactions. Advances in sorting technologies, common to both chemical and mechanical recycling technologies, are also increasing the efficiency of plastic recycling. For instance, deployment of artificial intelligence and Internet of Things (IoT) can enable automated sorting identifying molecular vibrations and thus enhance operational efficiency.

Here are some of the advances and emerging opportunities in the plastic recycling industry.

Solvent-based Purification (SBP) of Waste Plastics

Even after sorting the plastic waste by type, the material composition of each plastic might still be contaminated with foreign elements, depending on their end-use application. Solvent-based purification involves the use of a selective solvent dissolution process to eliminate impurities from postindustrial and postconsumer plastics. The technique involves extraction and dissolution with precipitation. The extraction techniques involve collection and sorting of waste plastics on the basis of their type and composition. Then, the sorted plastics are cleaned to remove any large debris or non-plastic components. In the dissolution precipitation process, the cleaned plastics are subjected to a solvent to dissolve dyes, pigments, and other such impurities. For instance, polyethylene terephthalate (PET) bottles can be depolymerized using ethylene glycol, which can then be purified and used to produce new resin. Solvents like limonene can be used to selectively dissolve contaminants from waste polystyrene (PS) and enable recycling of this material. Once the contaminants are dissolved, the solution and clean plastic material are separated through methods like filtration and centrifugation. The solvent is then recovered and utilized for further applications whereas the purified plastic undergoes steps like drying and palletization, which makes it suitable for reuse. However, this solvent-based purification of waste plastics faces some sustainability challenges such as the improper disposable of used solvents, which can harm ecosystems and human health. However, there have been advancements in solvent-based purification techniques.

Now, researchers are exploring eco-friendly and bio-based solvents that have lower toxicity and reduced environmental impact compared to conventional solvents. Green alternatives such as supercritical fluids and natural solvents such as terpene oil can prove to be viable for a greater process efficiency and recoverability for subsequent use. Besides, investments are being made towards more efficient and cost-effective recovery methods to reduce energy consumption and increase the solvent recycling rates. Additionally, advanced separation technologies such as membrane filtration or supercritical fluid extraction are being employed to improve the efficacy of contaminant removal. Furthermore, purified plastics after the process are being used in products designed for upcycling or recycling to promote circular economy. Scholars are also investigating the optimal integration of SBP technologies with other treatment methods for the separation of mixed plastic waste more efficiently.

Pyrolysis Technique: Converting Plastic Waste to Fuel

Polymerization refers to the long association of monomers (chemical entities) whereas depolymerization refers to the process of breaking bonds of polymer chains into monomers. The depolymerization process is highly beneficial for plastics since the products of the chemical reaction can then be reused. Pyrolysis technology, a kind of depolymerization technique, is employed to recover energy from waste plastics as hydrocarbons present in plastics offer a great source of fuel. The pyrolysis process involves heating plastic in an oxygen-free environment, which causes materials to break down and create new liquid or gas fuels. Pyrolyzing plastic waste at a temperature of 500 °C and lower in ideal condition produces liquid oil that has a similar performance to conventional diesel oil, which allows it to be used as a fuel or a feedstock.  

A wide range of catalysts are adopted for the pyrolysis process of plastic waster such as ZSM-5, zeolite, FCC, and MCM-41. In September 2022, chemical company Dow announced its efforts to mitigate the flow of plastic wastage and hence collaborated with Mura Technology to build a plant based on Mura’s supercritical steam process. The facility will be converting mixed plastic wastage into hydrocarbon liquids, and thus divert 120,000 metric tons of waste per year. Other companies such as BASF, Shell, ExxonMobil, LyondellBasell Industries, Sabic. Ineos, Braskem, and TotalEnergies are joining hands with smaller companies to develop a process or create their own for pyrolysis process. Due to significant versatility, pyrolysis has emerged as the ideal chemical recycling choice for major chemical companies around the world. However, this recycling technology also has certain limitations such as the quality of pyrolysis oil may be inferior and unfit for intended purposes. Another drawback of pyrolysis is that it is an energy-intensive process, which requires a lot of heat. Hence, researchers are investigating cost-effective and eco-friendly approaches for pyrolysis.

Advanced Mechanical Recycling

Mechanical recycling still remains one of the most effective techniques to manage plastic waste since the quality of waste significantly impacts the output. Hence, the plastic recycling industries are deploying AI-assisted tools and systems to accelerate plastic waste classification, sorting, and separation at processing sites and enhance reverse logistics to ensure high-quality waste flow. Besides, these innovative solutions enable plastic recyclers to improve the quality of secondary raw materials and convert the otherwise low-quality streams into high-quality ones. Recycleye, a UK-based startup has developed an automated waste sorting system that combines machine learning, computer vision, and robotics to automate waste analysis and sorting. This helps in increasing transparency in recycling conveyors and allows recyclers to increase sort and pick efficiency at facilities. Integrating AI and robotics will enable human workers to focus on high-level cognitive tasks while eliminating personnel from front-line risks. Also, the combination will help to speed up the sorting process while maintaining accuracy. For instance, AMP Robotics uses computer vision to recognize materials early in the recycling process and sort up to twice as fast as manual processing.  

Emergence of Waste-Eating Bacteria

As the quest for tackling plastic wastage is rapidly gaining momentum, scientists and researchers are using every tool in their arsenal. In recent years, scientists have been successful in discovering pathogens that can digest plastics without the need to apply excessive heat. The known plastic-digesting microbes can breakdown plastics at warm temperatures beyond 85 degrees, which is an energy-intensive procedure, and it would emit even more carbon. Microbes found in the Arctic and Swiss Alps can breakdown biodegradable plastics at colder temperatures (at 50 degrees Fahrenheit), which open doors to a more efficient system of recycling plastics. Besides, these organisms could reduce the environmental burden and the costs associated with conventional recycling techniques. Studies are being conducted to determine the optimal temperature of the enzymes of bacteria to function and identify the microbes’ specific mechanisms. Another environmental bacterium, Comamonas testosterone may proved to be nature’s plastic recycling center as it prefers to eat complex waste from plants and plastics. The bacterium is found in soils and sewage sludge and has the ability to breakdown compounds from plastics and the fibrous, woody plant material lignin as well as laundry detergents. Scientists have also discovered a strain of bacteria that can break down polyurethane, which is considered difficult to recycle or destroy. Although many such microbes have been found by scientists around the world, these initiatives have yet to reach the point of mass commercial application.

According to TechSci Research report on “Plastic Recycling Market - Global Industry Size, Share, Trends, Opportunity, and Forecast, 2018-2028 Segmented By Type (Polyethylene Terephthalate (PET), Polyethylene (PE), Polypropylene (PP), Polyvinyl Chloride (PVC), Polystyrene (PS) and Others), By Source (Bottles, Films, Fibers, Foams, and Others), By End-User (Packaging, Building & Construction, Textile, Automotive, Electrical & Electronics, and Others), By Region, and Competition 2018-2028”, the global plastic recycling market is anticipated to grow at a formidable rate throughout the forecast period. The market growth can be attributed to the enhanced focus on circular economy and emergence of revolutionary technologies advancing plastic recycling. 

According to TechSci research report on “Recycled Propylene Market - Global Industry Size, Share, Trends, Opportunity, and Forecast, 2018-2028, Segmented By Process (Mechanical, Chemical), By Source (Bottles & Containers, Films, Bags, Foams, Industrial & Agricultural Waste, Others), By Application (Packaging, Automobile, Building & Construction, Textiles, Pharmaceuticals, Electronics, Others), By Region, and Competition”, the global market for Recycled Propylene is projected to grow at a significant rate. The market growth can be attributed to expanding use of plastics and increasing concerns pertaining to plastic usage for environment and human health.