Jul-2024

Pyrolysis: Defossilation of the chemical industry with plastic waste - a case for collaboration (TiA)

Plastics are ubiquitous in modern life. Ingrained in our everyday lives, it is no surprise that we are producing twice as much plastic globally as we did two decades ago.

Markus Hartung
Evonik Catalysts

Article Summary

According to the UN Environment Programme (UNEP), 430 million tons of plastic are produced yearly, and production is expected to double yet again by 2050.
Although the helpfulness of plastics cannot be denied, its downsides have been well-publicised. A third of plastics are single use, while the bulk, a significant 72%, end up in landfill, incinerated or leaking into the environment. Only 9% of plastics are reportedly successfully recycled, and the emissions from their production and disposal are expected to double by 2060.

Reasons for low recycling rates vary, and complexity lies with the make-up of many individual plastic products. Materials such as flexible films, multilayer materials, and coloured plastics cannot be recycled by conventional mechanical recycling, or at all. To see statistics improve, a more circular economy that involves the contribution of all entities in the process is required.

With increasing public pressure for the greater collection, recycling, and reuse of plastics, pyrolysis – one method of chemical recycling – is seeing growing international interest. It offers a route to defossilating raw material streams into refineries.

Next step in plastic recycling
Pyrolysis is a process where plastics are collected at the end of their product life cycle and heated to high temperatures (300-900°C) in an inert atmosphere without oxygen. Thermal degradation causes plastic materials to break down into smaller molecules. From this, what once was plastic waste is transformed into pyrolysis (pyrolytic) oil or gas, which can be repurposed and utilised as reusable crude oils.

Boasting multiple applications, pyrolytic oil can reduce dependence on fossil fuels, presenting a lower carbon solution for hard-to-abate sectors, and diversifying energy materials. In petroleum refineries, the oil can replace fossil-based naphtha as a more sustainable feedstock to produce fuels and chemicals. Industries that still rely heavily on crude oil and natural gas (such as shipping, construction, and  manufacturing) can use it as a fuel (once refined and blended with conventional fuels) to power vehicles and machinery.

Diversifying energy materials is a necessity in today’s age. One only needs to look at the global turmoil experienced by the Russia-Ukraine war, which led to supply chain disruptions, energy security risks, and gas and energy price spikes, all on a global level.

However, technical challenges still limit the wider adoption of pyrolytic oil as a raw feedstock – specifically, purity and compositional diversity. Mixed waste plastics are often a complex combination of polymers, and the final composition of these products can differ due to regional and country-specific factors. Plastics such as polyethylene terephthalate (PET) and polyvinyl chloride (PVC) can yield oxygenated and chlorinated compounds.

These factors can contribute to and result in the contamination of pyrolytic oil. With steam crackers featuring very tight specifications that need to be satisfied if the oil is added as a feedstock, removing these impurities in an economical and sustainable way is necessary.

Starting point for a solution: catalysts
Catalysts play a key role in the quality and quantity of recycled plastic waste products, with differing types used to improve the plastic pyrolysis process.

With PVC as an example, where pyrolysis generates toxic and corrosive organochlorine compounds and hydrogen chloride (HCI), catalysts can be used to dechlorinate and condense these gases. To reduce HCI emissions, adsorbents or additives (used in close contact with the plastic vapour in the reactor) assist with dichlorination through adsorption, a method also known as in situ upgrading.

Evonik’s chloride and fluoride adsorbents and hydroprocessing catalysts allow for the separation of impurities and contamination during production. Moreover, hydroprocessing catalysts can be regenerated and reused, further contributing to sustainability goals. In addition to catching unwanted elements and removing contaminants, the other significant benefit of hydroprocessing is a reduction in olefins and aromatics. This leads to decreased heater fouling in steam crackers and increased yields, helping make pyrolysis oil suitable for steam cracking.

Treating light and heavy pyrolysis oil with Evonik’s specialised adsorbents results in significant chloride reduction even for highly contaminated oils (see Figure 1). Light oil saw chloride concentration decrease by 300 parts per million (ppm), for a final figure of 61 ppm. In the treatment of heavy pyrolysis oil, which has a higher total chloride concentration of 500 ppm, there was also a reduction of 300 ppm. In this instance, chloride removal efficiency is expected, as the chloride-containing molecules are larger and more complex.

Separately, Evonik’s proprietary line of SiYPro and Viscoplex additives assists with stabilising the finished pyrolysis oil and minimising crystallisation. This is significant for its ability to manage polymerisation, prevent fouling, inhibit corrosion, and reduce energy, safeguarding the downstream process and enabling easy transportation, storage, and increased processability.

Role of partnership in circular economy success
Businesses and industries are having to adhere to stricter emission rules, with mandates on plastic usage differing across regions and countries. The EU is looking to ensure all plastic packaging is reused or recycled by the year 2030, whereas in the US, the plastics waste management system is at an early stage of development. The high economic cost of plastic waste and the complexity of collecting, sorting, and cleaning said waste are part of the reasons why management of this problem is so varied internationally.
Increasing rates of collaboration, from catalyst providers to refineries and plastic manufacturers, recycling facilities to government and regulatory bodies, is necessary. When the need for virgin plastic production is lowered, the corresponding emissions of manufacturing and end-of-life treatment are also lowered. Recycling remains more energy efficient than producing a product from original materials.

Pyrolysis presents itself as an innovative, forward-looking solution that holds real promise for the sector. As of 2023, at least 10 large chemical companies have built or announced plans for facilities that will produce pyrolysis oil from plastic waste streams. An increased adoption rate of pyrolysis will benefit from economies of scale. However, the crucial integration of knowledge across the entire value chain is first required.

Conclusion
As plastic consumption increases year on year, so does the urgency of finding a solution for plastic waste. Figures suggest that shifting to a circular economy can reduce the volume of plastics entering oceans by 80% by 2040 and greenhouse gas emissions by 25%. In terms of economic impact, it could save governments $70 billion over the same period and create 700,000 additional jobs.

By bringing together the value chain, the supply of pyrolysis oil feedstock and the demand for recycled materials can expand. This will diversify the pool of raw materials available to refineries, which is increasingly important in achieving circular economy targets and sustainability commitments. Increasing current levels of plastic recycling and collaborating in new ways across industries will be key to driving this change forward.

SiYPro and Viscoplex are trademarks of Evonik Catalysts.

This short case study originally appeared in PTQ's Technology In Action Feature - Q3 2024 Issue

For more information: markus.hartung@evonik.com