Climate impact of pyrolysis of plastic packaging waste compared to reuse and mechanical recycling - comments

The given tables do not have comparable results - Table 2 shows the Results in kg CO 2 eq./kg recycled production   and Table 3 shows the Greenhouse Gas Emissions in kg CO 2 eq /kg recycled output, while the author states in the note under the table: "(1) without considering the further utilization of the recycling residues"

In point 5.2. the author states:

"On average, the yield of PO in mechanical recycling is 68.7%. This means that from one ton of PO that goes to mechanical recycling, 687 kilograms of PO are obtained as recyclate. The remaining 31.3% are recycled residues that go to pyrolysis" The author uses data on the formation of CO 2 eq./kg of recycled production in his work. This means that 31.3%, scrap from mechanical recycling (part of the process)= 2.91x0.313=0.91 kg CO 2eq /kg. 

This means that Greenhouse gas emissions in kg CO 2eq /kg recycled production (comparable indicators) = 0.91 + 0.311(0.337)=1.221(1.247).

Nevertheless, in the text under Table 3 Yields and emissions of greenhouse gases during the mechanical recycling of polyolefins, the author comments with an obvious bias on the emissions of greenhouse gases during the mechanical recycling of polyolefins as follows:

"0.311 kg CO 2 eq. per kg output of recycled waste for mechanical recycling is almost an order of magnitude lower than 2.91 kg CO 2 eq. per kg of recyclate output for chemical recycling."

A comparison of two different and at the same time incomplete outputs cannot have any explanatory power. 

The entire study is based on incorrect assumptions. The author compares the incomparable. 

Two processes are included in Table 2:

1. Chemical recycling process = equals the recovery of plastic waste, which usually cannot be recycled mechanically. The output of this process is recyclate - a chemical substance in the sense of EU Directive 2008/98/EC Article 3, point 17 ("recycling" is any recovery activity by which waste materials are reprocessed into products, materials or substances intended for their original purpose or other purposes). At this point, the chemical recycling process is complete.
2. From recyclate - a chemical substance that is a virgin material (that is, almost identical to the original raw material), a new plastic that is not a recyclate is produced in a chemical operation using a normal procedure . This means that it is no longer a matter of recycling, but of classic production (a new process for which recyclate - a chemical substance was used).

In Table 3, only one process is included in mechanical recycling - evaluation (recycling) of inputs that form PE and PP foils for regranulate output. This means that the output of this process is a material, that is, not a final product. In this case, the following applies: regranulate from mechanical recycling = chemical substance from chemical recycling.

I don't know what the author's interest or instructions were, but in chemical recycling he included two processes in the compared component (waste recovery into recyclate-chemical + production of products from this recyclate) and in mechanical recycling he included only one process in the compared component (waste recovery into recyclate - regranulate - material for further use). 

In order for the compared components to be comparable, the author should have either compared the recycling process with recyclates as outputs (with chemical recycling, the output is a chemical substance, with mechanical recycling, the output is regranulate), or he should have added to the mechanical recycling also the greenhouse gas emissions created during the production of the product from regranulate (e.g. park bench), then it would be comparable.

In point 6 Carbon efficiency, the author states that during pyrolysis, a loss of 53% of the material is assumed under ideal conditions.

In the last indent of point 6.1. the author states: 

• The industry claims (e.g. in BASF's LCA)28 that burning the pyrolysis gas produced during the pyrolysis of plastic waste can cover almost the entire energy consumption of the process.

This means that the author knows that the by-products of pyrolysis are used for the development of the necessary process heat, that is, as a substitute for fossil fuels for the benefit of sustainable development. Nevertheless, the author of the study claims that this is a loss of material. This is not a loss, this is a significant economic, environmental and social benefit.

Also in point 7 Discussion, the author states "the problem of disposal of pyrolysis gas remains." It is clear that either the author of the study does not know the current state of science and technology in the field of chemical recycling, or he is trying to provide non-representative data. The current development of top chemical recycling equipment is already at such a level that the content of pollutants arising from the combustion of pyrolysis gas, which is not waste, but a product meeting the requirements for fuel quality, is much lower than when burning biogas from generally supported and recognized biogas stations. 

The whole study seems tendentious and misleading. It is based on incomparable, incorrect and incomplete data. 

In the study, the author did not take into account the fundamental attributes of the differences between mechanical and chemical recycling. The author does not consider that it is possible to recycle plastic waste indefinitely with chemical recycling, while the repeatability of mechanical recycling is limited to a few cycles. 

In order for the developed study to provide a realistic and credible output, the author should also have taken into account greenhouse gas emissions and the carbon efficiency of further non-recyclable regranulates and the effects on the climate from their disposal.

At the end of the study, the author raises his finger and threatens:

"If a pyrolysis industry is created in the next few years, it will affect the possibilities of plastic processing in the future. When a plant is built, it needs raw materials. Unless regulations introduce safeguards, industry will use the cheapest and most easily recyclable material (source material that can actually be recycled by mechanical recycling). Without adequate regulations, efforts to design recycling or other measures to enhance mechanical recycling will be severely hampered. The legal equality of the chemical and mechanical recycling processes of packaging waste must therefore be prevented."

In this case, it is surprising that the author, while processing such an important document in terms of considering its impact, did not even bother to conduct basic marketing research in the given segment. In such a case, the author of the study would find that enough equipment is built for mechanical recycling, there are enough necessary input materials, but there is a problem with the sale of products made from recycled materials (except PET), which is solved by legislation (in the form of prioritizing recycled materials with various tools).

Chemical recycling does not need, nor will it need to deal with the sale of the resulting products through legislation.

The author of the study does not at all understand the position and mission of Chemical Recycling, which is neither a competitor nor a threat to mechanical recycling, but is an important synergistic supplement for it.