The current state of plastics recycling is a significant challenge to our environment and society. Even though plastic is one of the most pervasive materials used in modern life, only 9.1% of all plastics in the US are ever recycled. Of this, most plastic waste ends up in landfills or incinerators, which can take centuries to break down. Moreover, due to the wide variety of different types of plastics present in waste streams, recycling facilities typically extract only high-value plastics for reuse. This means that re-processing techniques such as pyrolysis are required for lower-value plastic waste recycling.
The pyrolysis of plastics process diagram.
The Pyrolysis process is particularly effective for waste plastics that may otherwise be difficult or impossible to recycle. This process converts these plastics into valuable chemicals and fuels, providing a viable pyrolysis solution for their reuse or disposal in an economically and environmentally responsible manner. Ultimately, pyrolysis can offer a sustainable way of managing plastic waste to reduce its impact on our environment while also providing a profitable opportunity for businesses. Although this process has a promising future, it's not without challenges, particularly regarding technology.
Varied economical and technological challenges of pyrolysis.
Pyrolysis challenges are diverse and varied, with each one presenting unique difficulties. Difficulties include:
These issues are important for pyrolysis recycling facilities to address to ensure success of their operations. It is also important to know what solutions are available to these challenges.
Energy engineer Dr Andrew Rollinson sets out the case as to why pyrolysis and &#;plastic to fuels&#; is not a sustainable solution to the plastics problem.
Compounded by the breakdown of the global recycling market, it seems that most governments and local authorities throughout the world are grasping at straws to find a quick fix for the plastic waste problem. Plastic is piling up on land and threatening the biosphere through its contamination of the oceans. At the same time most governments exhibit a morbid fear of doing anything which could oppose continuous economic growth.
Wonder technology fixes such as pyrolysis for &#;plastic to fuels&#; (1) and green energy from waste (EfW) are therefore offered up as the future solution. For, if such machines were capable of simply and sustainably converting plastic into fuel or energy, then citizens may feel encouraged to buy more and waste more, liberated from guilt with the knowledge that anything they saw and wanted could be purchased.
But this premise is inherently flawed. Pyrolysis of plastic can never be sustainable. In a recent academic journal, I detail why the concept is thermodynamically unproven, practically implausible, and environmentally unsound (2).
Pyrolysis occurs when solid organic matter is heated, resulting in the release of gases, oils, and char, hence the word&#;s etymological root of &#;loosening or change by fire&#;. It is an old technology, formerly applied by heating up wood to produce substances such as methanol, acetone, and creosote, prior to petrochemical refining routes. When wood is slowly pyrolysed the char is called &#;charcoal&#;; when coal is pyrolysed the char is called &#;coke&#;; and with plastics there is little or no char produced at all.
The modern notion is to pyrolyse plastic (and other municipal refuse) into a gas or oil which is then useable as a commodity, invariably a &#;fuel&#;, in its own right. This conveniently ignores the fact that pyrolysis is an energy consuming process: more energy has to be put in to treat the waste than can actually be recovered. It can never be sustainable.
And what of the fuel from these ill-conceived schemes? All pyrolysis EfW or &#;plastic to fuels&#; products must be combusted to liberate energy, thus releasing the same quantity of carbon dioxide than if the plastic had been incinerated directly. The product&#;s existence has merely been an intermediary stage in the combustion of fossil fuels.
But the idea is even more imprudent. There are substantial flaws with the pyrolysis of plastics concept. It has been tacit knowledge for almost one hundred years that this type of waste is practically incompatible with these technologies (3). Also, heavy metals and dioxins become concentrated in the resulting products making then unsuitable as fuels, because when combusted they are released to the environment.
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Despite this many governments continue to waste millions deceiving the public in pursuit of an &#;innovation&#; that holds the sustainable answer. They ignore the above-mentioned scientific antecedents, and a wake of commercial failures (4).
Academic research has also been drawn in, attracted by the competition for financial rewards. With a prevalence in many countries for grant funding which links industry, innovation, and academic research, ethical hazards have been created and these have yielded poisoned fruit (2).
Many modern academic research articles present pyrolysis with positive connotations, appraising it in terms of &#;energy recovery&#; or &#;conversion&#; efficiencies. This is despite huge overall energy demands. In one study the concept was described as &#;high efficiency&#;, but results showed that the system operated with gross negative efficiencies, using between 5 and 87 times more energy than could be obtainable from the pyrolysis products.
Perhaps worst of all, some research groups have recently claimed that pyrolysis plants can be self-sustaining. By doing so they commit a blunder which exposes them to instant discredit, for they ignore the second law of thermodynamics. Such a folly is akin to the antiquated pursuit of perpetual motion.
Perpetual motion is impossible because it violates the laws of thermodynamics. These laws underpin all engineering, and indeed all universal interactions. The first law states that energy must be conserved &#; what goes in must come out. The second law states that whenever there is energy transfer some quantity must always be lost to a system&#;s surroundings (measured as &#;entropy&#;).
The inviolable nature of the second law was perhaps best explained by Arthur Eddington in his famous Gifford Lectures (5):
&#;There are other laws which we have strong reason to believe in, and we feel that a hypothesis which violates them is highly improbable; but the improbability is vague and does not confront us as a paralysing array of figures, whereas the chance against a breach of the second law can be stated in figures which are overwhelming.&#;
Once one fully understands these laws, the folly of such schemes, and the sophistry of corporate attempts to claim &#;sustainability&#;, becomes instantly clear. It is therefore essential to grasp this concept if ever humanity is to make a transition to a sustainable future.
Pyrolysis can never be a sustainable answer to the inconvenient truth of Big Plastic. This lies in the widespread implementation of strategies for &#;reduction&#; and &#;re-use&#;, along with a preference for creating products with in-built recyclability and/or which are built to last. The elephant in the room is capitalism (6) and the throwaway culture that the present version of this economic system has created &#; ever demanding new markets, more sales, more consumption, and more waste.
The full text of the paper can be accessed for free here in Resources, Conservation and Recycling until 23rd December .
1. Phan, A. How we can turn plastic waste into green energy. The Conversation, 1st October .
2. Rollinson, A., Oladejo, J.M. . &#;Patented blunderings&#;, efficiency awareness, and self-sustainability claims in the pyrolysis energy from waste sector. Resources, Conservation and Recycling, 141, pp. 233-242.
3. Mavropoulos, A. . History of Gasification of Municipal Solid Waste through the eyes of Mr Hakan Rylander (online), 19th April .
4. Tangri, N., Wilson, M. . Waste gasification and pyrolysis: high risk, low yield processes for waste management. A technology risk analysis (online).
5. Eddington, A.S., The Nature of the Physical World, . Cambridge University Press: London. pp.68-71.
6. Pigott, A. Capitalism is killing the world&#;s wildlife populations, not &#;humanity&#;. The Conversation, 1st November .
Doctor Andrew Rollinson specialises in small-scale biomass gasification research and is the author of Gasification: succeeding with small-scale systems published by Lowimpact.org.
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