PLASTIC TO FUELS

As plastic waste stockpiles grow at unprecedented rates around the world, many proponents are pushing for the adoption of fuels derived from plastic waste to ‘substitute’ for fossil fuels and to offset oil, gas, and coal extraction. The reality is that in all but a few cases the resulting product is fossil fuel or simply a repackaged form of plastic waste rebranded as a ‘product’ instead of a ‘waste’ for financial, regulatory, or subsidy purposes. One exception is the conversion of plastic waste to hydrogen, which is a clean burning fuel. But even with this example, the pathway to create hydrogen can involve energy-intensive processes that negate any net carbon footprint benefits. The following section discusses plastic to fossil fuel by depolymerization, plastic to non-fossil fuels (hydrogen), and the use of refuse-derived fuels (RDF) and associated products.

DEPOLYMERIZATION TO (FOSSIL) FUELS

The variability of mixed plastic waste feedstock, whichcan be used in pyrolysis and gasification, and the fuel-like output in terms of hydrocarbon feedstock, whichcan be generated with minimal post-processing, suggests that plastic to fuel will dominate this market sector. The creation of diesels, kerosene, and light oil —essentially fossil fuels for combustion—is currently the only viable market for pyrolysis output products from plastic waste processing. This creates the very real likelihood of ‘linear lock-in’ for plastic waste which would undermine circularity in the context of plastic waste chemical recycling .

Start-up companies using these techniques are in competition with the powerful petrochemical corporations for a share of the chemical/polymer feedstock market. These corporations have well established large-scale production capacities that allow for the production of very cheap feedstock. For the new start-ups, price-based competition will be considerable, and newcomers to the market are at an almost insurmountable disadvantage as low oil prices equate to low virgin plastic prices. Such pressures are likely to drive pyrolysis and gasification processors of plastic waste toward the more readily available market of plastic to fuel in the form of diesel for use by power plants and ships . In low- and mediumincome countries this may also extend to vehicles.

Figure 20. Plastic to fossil fuel via pyrolysis

The use of plastic to fuel has several serious implications for the circular economy, human health, and climate:

· Linearity – Apart from the calorific energy value recovered from plastic waste, the conversion of plastic to fossil fuels is essentially a direct road to resource destruction and maintains the petrochemical linear economic framework of extract – produce – dispose (combust). Adding an energy intensive pyrolytic step of converting petrochemicalbased plastic back to petrochemical for combustion may well undermine the ultimate energy mass balance of the process. With plastic production set to expand on a massive scale, it has to be questioned whether any real offset of virgin fossil fuel is occurring as a result of plastic to fuel implementation.

· Toxic emissions – There is evidence that pyrolysis generates and releases unintentional POPs such as dioxin and Conesa et al. (2008) note, “The formation of PCDD/DFs is important in both combustion and pyrolysis processes. In pyrolysis, there can be a significant increase of congeners and/or an increase of the total toxicity due to the redistribution of the chlorine atoms to the most toxic congeners.” The syngas from plastic waste pyrolysis has been found to be contaminated with a range of pollutants such as dioxins, PAHs, and tars, which make it difficult to use in combustion engines without further refinement . The same contaminants impact the oils and char from pyrolysis. When these oil-like products are combusted, they release their contaminants. While pyrolysis operators may suggest their process emissions of dioxins are low, this is likely be at the cost of transferring such pollutants to the outputs of gas, oil, tar, and char. Indeed, “researchers found that the toxicity rating of PCDD/ DF products from pyrolysis was three times the input at full operational performance and eleven times the input at pilot scale, and that these toxins were also present in both gas and oil”. The entrained POPs and other contaminants in the outputs are released directly to atmosphere on combustion.

· Global Warming Potential – The global warming potential of fossil fuels developed from pyrolysis of plastic cannot be ignored. For plastic products converted to fuels via pyrolysis, their time as a product can be regarded as a short pause in the linear process from their extraction as petrochemicals to their ultimate combustion as fossil fuels. However, in addition to the CO2 that would normally be liberated by the combustion of the calorific fossil fuel content of the plastic, there is the additional ‘embedded energy’ of the original extraction, transport, and production of the plastic article to be considered. Further, there is the energy used to collect, sort, and separate the plastic to be fed to the pyrolysis unit as well as the energy used by the pyrolysis unit itself to generate the necessary heat for the process. Heating energy requirements for a pyrolysis process are very high. All considered, the global warming potential of fossil fuel derived from plastic is very high.