Chemical Recycling: How Analytical Solutions Enable an Effective Circular Economy
Fri 20 Oct, 2023
Plastic Waste: A Global Challenge
There is no denying that plastics have become an indispensable part of our daily lives. They offer many benefits. For example, as packaging they prevent food from spoiling, they make cars lighter, and insulate houses. In fact, plastics have many advantages over other materials:
They are lightweight yet robust.
They are resistant to water, and many are even resistant to acids and bases.
Thanks to their smooth surface, they can be easily cleaned.
They do not oxidize.
They are very flexible and can be easily molded.
They are extremely durable and do not rust.
Plastics are shatterproof and hygienic.
However, despite their inherent durability, plastic products end up in the trash too quickly. Globally, around 250 million tons of plastic waste are generated each year. By 2060, this amount is expected to triple. Currently, only 9% of all plastic waste is recycled. The rest is disposed of in landfills, leaks into the environment, or is incinerated thereby releasing CO2.[1]
Chemical Recycling Enables a Sustainable Circular Economy
To solve the plastic waste problem and achieve greater sustainability, we need to shift from "take, make, and waste" to "reduce, reuse, recycle." More and more countries are pursuing this transition from a linear economy to a circular economy. In such a circular economy, plastic waste is no longer a burden but represents valuable raw materials. At the same time, this reduces our dependence on fossil resources.
Recycling of plastic waste has mainly taken place via mechanical recycling until now. However, further increases in the recycling rate are challenging to achieve through this method alone. This is where chemical recycling comes into play. It represents a new and promising technology that enables the recycling of plastic waste that cannot be processed through mechanical recycling.
Advantages of Chemical Recycling
Chemical recycling offers two significant advantages over mechanical recycling:
- It can be applied to mixed plastic waste streams. Naturally, waste is highly heterogeneous, typically containing various types of plastics (e.g., PP, PE, PS), which are furthermore soiled with food residues. Mechanical recycling requires meticulous sorting and cleaning of waste until only a single type of plastic without food contaminants remains. Chemical recycling, on the other hand, can be used for plastic waste for which further sorting is not economically viable, as well as for contaminated plastics and scrap tires that cannot be recycled through other means.
- There are no limitations for new products created via chemical recycling. During chemical recycling, plastic waste is broken down into its chemical building blocks, making the recycled feedstock a perfect substitute for crude oil. The recycled feedstock can be used to produce plastics of any type and color. In contrast, type and color of plastic products created via mechanical recycling are predefined by the corresponding properties of the processed plastic waste. For example, a red yogurt container made from polystyrene cannot be transformed into a white polypropylene bucket via mechanical recycling. Additionally, new products created via chemical recycling are of virgin-grade quality and can be used in demanding applications, such as food packaging or in medical appliances. In contrast, mechanical recycling is not able to generate products that are of sufficient purity.
These two recycling methods complement each other, as chemical recycling picks up where mechanical recycling reaches its limits. Together, they can significantly increase recycling rates, bringing a circular economy for plastics within reach.
Chemical Recycling has Long Advanced Beyond the Theoretical Stage
There are indeed numerous examples of high-quality products being created from plastic waste via chemical recycling.
The first-ever food packaging made from chemically recycled plastic was a Magnum ice cream container. This crucial advancement resulted from a partnership between Unilever, the chemical company Sabic, and the chemical recycling startup Plastic Energy.[2] In 2021, over 30 million Magnum tubs were made from chemically recycled plastic, with plans to transition the entire production to circular plastics by 2025.
Another example is the KitKat packaging. Thanks to a collaboration between Nestle and chemical company LyondellBasell, the packaging for KitKat chocolate bars is now made from chemically recycled polypropylene.[3]
By utilizing chemical recycling, Vaude and Mercedes Benz - together with BASF - are turning scrap tires into high-quality outdoor wear, as well as door handles and crash absorbers for the Mercedes EQE and S-class vehicles.[5,6]
Many chemical companies have committed to chemical recycling as part of their sustainability strategies. BASF, in particular, is taking a leading role and actively advocating for a legislative framework which allows for the accounting of products made via chemical recycling using a mass balance approach.[6]
How Does Chemical Recycling Work?
Pyrolysis is the most important chemical recycling technology. It breaks down plastic waste in an oxygen-free environment at approximately 600 °C. During this process, the plastic’s long polymer chains are broken apart, resulting in a viscous pyrolysis oil which contains hydrocarbon chains of varying lengths. Since chemical building blocks – monomers such as ethene, propene and butene – are required to manufacture plastics, the polymer chains of the pyrolysis oil must be broken down even further. Depending on how heavy or light the pyrolysis oil is, this occurs in a refinery or a steam cracker.
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Quality Gates During the Chemical Recycling of Plastics
To avoid corrosion, catalyst poisoning and other problems, the oil fed into petrochemical plants must not exceed a certain threshold of heteroatoms and metals. The most problematic elements in recycled oil typically include oxygen, silicon, halogens like chlorine, and metals such as sodium, iron, lead, calcium, and mercury. Depending on which elements exceed the specified limits, pyrolysis oil may need to undergo specific purification processes. In some cases, it may be advantageous to blend the recycled feedstock with fossil feedstock to reach non-critical element levels.
The quality of the products derived from pyrolysis also depends on the quality of the plastic waste being processed. In consequence, quality control of the incoming plastic waste is crucial.
Indeed, it is the variability of plastic waste composition that poses one of the biggest hurdles towards large scale implementation of chemical recycling. As no single batch of processed waste equals the next, the composition of the resulting pyrolysis oil is also ever-changing. Analytically characterizing the plastic waste as well as the pyrolysis oil is the first step towards dealing with its inherent variability.
During the pyrolysis process, wastewater is generated. Determining whether this wastewater has been purified sufficiently to allow discharging of it into rivers is a critical concern. This concern can be addressed by measuring total organic carbon (TOC), total bound nitrogen (TNb), and adsorbable organic halogens (AOX) in the wastewater.
Analytical Solutions to Support Efficient Chemical Recycling
Analytik Jena's laboratory measurement devices support at key quality control points during the chemical recycling of plastics by quickly providing reliable data for decision-making.
1. Quality Control of Incoming Plastic Waste
Screening for Cl, S, Si, and metals (e.g., Na, Fe, Pb, Hg)
Analyzers: multi EA 4000, PlasmaQuant 9100 Elite
The quality of pyrolysis products is directly dependent on the quality of the processed plastic waste. An assessment of incoming plastic waste is, therefore, essential.
multi EA 4000: When PVC is mixed in with other plastic waste, it can quickly lead to undesirable chlorine levels. To determine chlorine content in inhomogeneous polymer waste, combustion-based elemental analysis offers crucial advantages over traditional analytical techniques like XRF. As a macro elemental analyzer, the multi EA 4000 can analyze large sample quantities without the time-consuming preparation of a homogeneous sample pellet as required for XRF. Depending on the exact PVC content, chlorine levels in polymer waste can vary significantly. With its flexibility in terms of sample sizes and an integrated gas splitting feature, the multi EA 4000 delivers good and reproducible results across a wide measurement range (0–10%). The gas splitting feature is an ideal solution to easily determine high chlorine contents without prior sample dilution.
PlasmaQuant 9100 Elite: Optical emission spectrometry with inductively coupled plasma (ICP-OES) enables quantitative analysis of metals and silicon over a wide measurement range. However, before this technique can be used for analyzing plastic waste, the sample must be converted into a liquid - for example using microwave digestion. Once this is done, a highly organic sample is obtained, which is one of the most challenging sample matrices ICP techniques can encounter.
The high load and carbon content of the organic matrix require robust sample introduction and a plasma system that efficiently excites the sample in the ICP without leading to carbon deposits in the torch system. The vertical geometry of the V-Shuttle torch and the unique high-frequency generator of the PlasmaQuant 9100 Elite have proven effective for this challenge.
Spectral interferences arising from the non-specific carbon background of the sample matrix pose a significant challenge to reliably measure concentrations of elements such as arsenic, lead, mercury, and sodium. To overcome these interferences, traditional ICP-OES analyzers need to employ elaborate calibration strategies like standard addition or need to shift to alternative emission lines with lower sensitivity, affecting achievable detection limits. The high-resolution optical system of the PlasmaQuant 9100 Elite (2 pm @ 200 nm), combined with the CSI software algorithm (spectral interference correction), eliminates the need for such compromises, as the most sensitive emission lines remain free from interferences and available for measurement.
2. Making Sure the Pyrolysis Oil is Ready for the Refinery or the Steam Cracker
Screening for metals (e.g., Na, Fe, Pb, Hg), Si, and Cl/S/N
Analyzers: PlasmaQuant 9100 Elite, multi EA 5100
To avoid issues like corrosion and catalyst poisoning during the further processing of recycled oil in the refinery and the steam cracker, the oil must not exceed certain element concentrations. Oxygen, chlorine, sodium, silicon, iron, lead, calcium, and mercury are particularly critical for pyrolysis oils.
PlasmaQuant 9100 Elite: Optical emission spectrometry with inductively coupled plasma (ICP-OES) allows for quantitative analysis of metals and silicon in pyrolysis oil. With its wide measurement range from parts per trillion (ppt) to percent - the largest on the market - the PlasmaQuant 9100 Elite provides a fast and clear decision-making basis for recycled oil, both before and after potential purification steps. High-resolution optics provide interference-free access to the most sensitive emission lines, resulting in detection limits of < 1 ppb for most elements. Additionally, high element concentrations can also be reliably detected using light attenuation.
In the case of organic samples like pyrolysis oil, an unusually large number of chemical bonds need to be broken to ionize the sample. This can weaken plasma stability and lead to significant intensity fluctuations. To ensure long-term signal stability, the performance of the generator plays a central role. With an unmatched generator power of 1700 W, the PlasmaQuant 9100 Elite can easily analyze undiluted organic samples. An optimized design of the plasma torch ensures that no carbon deposits form on the injector, minimizing maintenance work.
multi EA 5100: To reliably determine chlorine, sulfur, nitrogen, and carbon in pyrolysis oil, the elemental analyzer multi EA 5100 with catalyst-free high-temperature combustion is particularly well-suited. Recycled oil has high viscosity. Traditional analytical instruments would require manual dilution prior to analysis, adding extra effort. However, the heated sample introduction system of the multi EA 5100 eliminates this step. The undiluted oil is injected directly, reducing costs, waste, and labor.
Without precise steering of the combustion process, pyrolysis oil burns abruptly and incompletely, resulting in incorrect analysis results and soot formation that must be manually cleaned after each sample. The multi EA 5100 is the only analysis system that monitors and automatically optimizes the sample's combustion. This is done via a flame sensor. The result is a soot-free, safe, and complete combustion in the shortest time. Other systems lack such a flame sensor, requiring the combustion program to be developed empirically through trial and error and manually programmed – a laborious exercise that the operator needs to repeat for each new sample type or differing sample quantity.
Furthermore, recycled oil has highly variable chlorine levels. The multi EA 5100 can reliably detect even 10 ng of chlorine using a special sensor electrode. Simultaneously, quantification of 1 mg of chlorine without prior sample dilution is easily achievable. Correct measurement results over such a wide concentration range require heating of the measurement gas path to ensure effective drying. Otherwise, water condenses and traps the chlorine target analyte, leading to underestimation, which is especially critical for trace analysis. To quantify small concentrations, signal stability is also crucial. For this reason, the electrochemical cell of the multi EA 5100 is cooled to prevent the evaporation of the electrolyte solution and shielded from light to prevent unwanted photochemical reactions.
3. Evaluation of Produced Wastewater
TOC/TNb and AOX
Analyzers: multi N/C 2300 and multi X 2500
The wastewater generated during pyrolysis and subsequent refining processes is characterized by high levels of organic substances, nitrogen compounds, and particles. These can be rapidly and automatically analyzed with sum parameters total organic carbon (TOC) and total bound nitrogen (TNb). Particularly persistent and toxic hydrocarbon compounds are the halogenated hydrocarbons. These chlorinated, brominated, and iodinated organic compounds can be measured via the sum parameter AOX (adsorbable organic halogens).
The analysis of wastewater is subject to international standards:
- TOC/TNb: ISO 8245, EN 1484, EPA 9060, EN 12260, ISO 20236
- AOX: ISO 9562, EPA 1650
multi N/C 2300: The TOC/TNb analysis of undiluted wastewater samples with up to 30,000 mg/l TOC is optimally enabled by the multi N/C 2300. The secret to its extraordinary performance lies in the rarely implemented direct injection method combined with a powerful wide-range NDIR detector. Direct injection means that the sample is drawn into a syringe and from there directly injected into the analyzer's furnace. This ensures that all particles are transferred into the combustion unit of the analyzer. The injection port itself is septum-free, meaning there is no septum that could wear out, cause regular leaks, or clog the injection needle. Direct injection also means that the sample does not pass through valves, removing the potential for clogging even for heavily particle-laden samples. Additionally, the sample does not come into contact with hoses, preventing memory effects for oily samples that would otherwise adhere to hose walls.
With the multi N/C 2300, you can analyze heavily contaminated samples without prior dilution and obtain representative results thanks to high injection volumes of up to 500 µl. Calibration remains stable for up to one year due to a unique algorithm that detects and compensates for fluctuations in the internal flow. Calibration is also independent of the injection volume, allowing calibration with the injection of various volumes of a single standard.
APU sim or APU 28 + multi X 2500: AOX analysis, which stands for the analysis of adsorbable organic halogens (X = chlorine, bromine, and iodine, but not fluorine), always begins with sample preparation. The analytes are adsorbed onto activated carbon, preferably using the column method. The loaded columns are then rinsed to remove the interfering salt matrix. Subsequently, the columns are combusted inside an AOX analyzer, converting the AOX compounds into halogen acids (HX), which are then determined through coulometric titration.
For automated AOX/SPE sample preparation, Analytik Jena offers two systems, the APU sim and the APU 28 connect. Both systems allow the use of up to three columns per sample. When employing the 3-column method, the first column is filled with quartz wool, which captures sample particles that would otherwise clog the subsequent activated carbon columns, ensuring a smooth flow of the water sample through the columns. The second and third columns are each filled with activated carbon. This ensures that there is enough adsorption capacity to capture all AOX compounds, and comparing the loading of both columns provides an indication of the completeness of the adsorption step. Depending on the chosen autosampler, only the loaded activated carbon or the entire columns can be introduced into the AOX analyzer multi X 2500. The analyzer offers a wide measurement range; reliable measurements can be achieved from 10 ng up to 1 mg of chlorine. The titration cell is light-protected and cooled, resulting in a long-term stable performance of the analyzer. The 3-in-1 ceramic electrode is robust and virtually maintenance-free.
Summary
Chemical recycling is no longer just a theoretical concept. This new technique is an essential component of a circular strategy for plastics adopted by the European Union and many other nations, who seek to become more sustainable. Like any new technology, there are challenges to overcome in order to implement it on a large scale. One of the biggest challenges facing chemical recycling is the high variability associated with plastic waste composition, which in turn results in a highly variable pyrolysis oil composition. The analytical characterization of plastic waste and recycled oil is a crucial first step towards dealing with this inherent variability. Analytical devices from Analytik Jena play a vital role in making the new recycling process as efficient and cost-effective as possible by providing a fast and reliable decision-making basis for the quality of raw materials, as well as end products and byproducts of chemical recycling.
Web Seminar: Is Your Pyrolysis Oil Ready for the Steam Cracker? – Finding the Right Analytical Tools
Interested in learning about analytical tools that help you characterize pyoil? Watch the recording of our web seminar with expert Jean-Francois Borny (Lummus Technology, ASTM vice-chair of D02.P) and find out how to analyze pyoil for total sulfur, nitrogen, halogens, and metals, enabling you to get on top of its inherent variability.
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Chemical Recycling of Plastics ‒ Analysis of Chlorine, Sulfur, Nitrogen and Carbon in Pyrolysis Oils, Waxes, and Secondary Products (EN)
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TOC/TNb Determination in Refinery Effluents (EN)
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Determination of AOX in Wastewater Samples by Column Method According to DIN EN ISO 9562 (EN)
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References
- [1] OECD (2022), Global Plastics Outlook: Economic Drivers, Environmental Impacts and Policy Options, OECD Publishing, Paris, https://doi.org/10.1787/de747aef-en
- [2] www.magnumicecream.com/uk/stories/sustainability/recycled-tubs.html
- [3] www.kitkat.co.uk/recycle-packaging
- [4] experience.vaude.com/nachhaltige-outdoor-ausrustung-aus-recycelten-altreifen/
- [5]media.mercedes-benz.com/article/3de48ee0-8a4d-4e26-b9b5-eb55cf1f8b5b
- [6] www.basf.com/global/de/who-we-are/sustainability/we-drive-sustainable-solutions/circular-economy/mass-balance-approach.html
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