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Pyrolysis-based technology can convert plastics-rich refuse-derived fuel into extractor-ready BTX product, but the substantial energy input and processing challenges compel the petrochemical industry to consider waste gasification alternatives. How do you see this evolving?

Dec-2022

Answers

Francis Tsang, KBR, francis.tsang@kbr.com

Waste plastics to BTX is a challenging route, whether that is via pyrolysis or gasification. Most pyrolysis and hydrothermal liquefaction processes focus on waste plastic to oils as opposed to aromatics. The price premium of the renewable BTX product against renewable oils is often offset by additional costs, complexity, and lack of scale in current recycling technology.

A disadvantage of non-gasification recycling technologies is that feedstock to these processes does require a more complex feed preparation step for refuse-derived fuel (RDF), unless extremely high in plastic content, with a high level of pre-sorting if not an ideal feed. This can be addressed at the collection and sorting stage by the implementation of additional equipment to prepare a more suitable, high plastic content feed, which, of course, comes with a cost.

However, gasification has its own challenges in processing plastic-rich RDF, including:
- Capex intensive — modularisation/small-scale design is rare
- Multistep process — waste-to-syngas, syngas cleaning, syngas-to-methanol (catalytic), methanol to BTX (catalytic)
- Low relative yields
- Substantial GHG/CO2 formed as a side-product
- Dioxins and furans emissions
- High total costs and high complexity.

As a result of these challenges, feedstock plays a very important role, whether that is to a renewable oil or a renewable BTX product. Sorting and reserving aromatic-based waste plastic for BTX applications (aromatic feed will result in aromatic products) is the near-term solution until technology can produce renewable aromatics in an economic manner, whether that is via gasification, hydrothermal liquefaction, or pyrolysis.

Dec-2022
Ghoncheh Rasouli, KBC (A Yokogawa Company), Ghoncheh.Rasouli@kbc.global

Recycling chemical plastics drives sustainability and decarbonisation. Additionally, it decreases waste and pollution, reduces the consumption of limited natural resources, such as oil, and leads to the production of synthetic feedstock.

For plastics to be completely recycled, chemical recycling technologies must be developed to achieve the complete recycling of plastics. While the gasification of plastic waste aims to recycle or reuse plastic waste by converting it into valuable gases, it does not provide the required light/heavy hydrocarbon feed for petrochemical plants and refineries. Pyrolysis-based technology, however, recycles synthetic light- and heavy-hydrocarbon feedstock to the petrochemical plant and refinery. This results in high-end quality products while reducing the need for further upgrade downstream.

In addition, plastic pyrolysis technology decreases waste production during polymer production and reduces oil usage, NOx and SOx emissions, and landfill waste. Plastic pyrolysis is an excellent technology for managing plastic waste and mitigating ecological risks, but it can be complex. To reduce this complexity, process simulation and optimisation software can be used to model the kinetic reaction network, calibrate the model, observe and analyse the effect of different feedstocks and operate conditions on KPIs while increasing yield and thermal efficiency.

Pyrolysis can evolve with the development of the following two new technologies where plastic waste could be converted to potential feedstock:
Catalytic pyrolysis Using a catalyst reduces cracking temperature and energy consumption to convert plastic waste into fuel and other commodities. Advantages include improved efficiency and product selectivity, which results in high-end quality products, reducing the need for further upgrade downstream. This method could save 3.5 billion barrels of oil from polymer production and save nearly USD 40 million annually.

Thermal pyrolysis Uses energy provided by electrical jacket, green hydrogen as a fuel, and hydrocarbon-based fuel consumption with optimised combustion to not only reduce emissions but also increase combustion efficiency and carbon capture. This oil can be blended with diesel to be used in engines. Although the process produces corrosive hydrochloric acid, it can be avoided by adding an absorber.

Dec-2022
Matthew Stephens, Imubit, matthew.stephens@imubit.com

When considering the full slate of products from plastics waste pyrolysis, such as ethylene and propylene, which can be recovered and made into virgin polymers again, it really does not seem like that bad of an option. Gasification is likely a much better starting point for chemicals like methanol or liquid fuels, but it might actually be a poor route to traditional pyrolysis-based petrochemical feedstocks like ethylene and propylene. Additionally, it is less of a drop-in technology like pyrolysis that could be bolted onto an existing olefins unit.

Dec-2022
Ioan-Teodor Trotus, hte GmbH, ioan-teodor.trotus@hte-company.de

Pyrolysis of plastic waste to produce a liquid pyrolysis oil requires relatively mild conditions for the pyrolysis process itself, but further treatment is required to obtain a drop in feedstock for further processing in existing plants. Pyrolysis of plastic waste to produce a gas product requires much more energy for the pyrolysis process. Syngas, olefins, dienes, or acetylene could be components of interest in the pyrolysis gas. Further purification processes for these gases would be less complicated and probably less energy intense than the purification processes required for liquid pyrolysis oils.

Whether one or the other is better depends a lot on regional factors such as the availability of cheap and abundant energy and the types and amounts of plastic waste available. Both liquid pyrolysis oil upgrading and syngas conversion to petrochemicals and intermediates are currently hot areas for research and development where hte offers both equipment for catalyst testing and R&D services such as catalyst testing campaigns.

In the end, just like there is not one single refinery configuration that beats all other options, we will probably see multiple technologies emerging, depending on location, for the chemical recycling of plastic waste.

Dec-2022
Mitrajit Mukherjee, Exelus, mmukherjee@exelusinc.com

Catalytic processing of plastics-rich waste streams in a hydrocracker is a preferred alternative. Compared to pyrolysis or catalytic cracking, it delivers a highly saturated liquid product that can be used directly without subsequent processing as a transportation fuel or fuel oil. There are five main types of recyclable plastics.

Effective recycling of mixed plastics waste is a major challenge for the plastics recycling sector. The advantage of using the hydrocracking approach is the ability to handle all types of plastic waste (including PVC and PS), which allows a wider variety of materials to be recycled. To enable the use of plastics as a raw material, a suitable catalyst and optimum operating conditions are critical. One company, Exelus, is developing a versatile bi-functional hydrocracking catalyst ExPURT, to make this transformation possible.

Dec-2022
Scott Sayles, Becht, ssayles@becht.com

Pyrolysis is a promising technology to convert cellulous or plastic waste into an oil that allows processing into either fuels or petrochemical. Pyrolysis designs are varied depending on the process basis. Some are nearing commercial operations, and others are in the pilot stage. The conversion of plastics into feedstock ready for the aromatic extractor tower to produce BTX is an example of pilot stage-level development showing some promise. The liquefaction of plastic using pyrolysis produces an oil that is the decomposition product of the plastic being introduced.

To produce aromatics directly seems to require selective plastic pyrolysis. Gasification is a direct route, converting the plastic into a syngas which can be converted into BTX by Fischer-Tropsch, followed by cyclisation. The gasification of plastic is relatively new, but the conversion to desirable products is well proven commercial technology. Many factors enter the final plans for plastic conversion into marketable products. The technological risk is a key factor, as are the requirements to recover and collect the plastic from the community. The social-economic factors are difficult. Socially plastic recycling is favourable. However, capital investment and operational factors require a governmental position to ensure a future that will encourage investment.

Dec-2022
Ludo Boot, Albemarle Corporation, ludo.boot@albemarle.com

The answer to this question is very much dependent on the actual case at hand. The most applicable solution, whether pyrolysis or gasification, depends on many factors, one being capital investment. If a petrochemical company has certain assets in place, that may lead to using either pyrolysis or gasification technologies.

In terms of environmental impact analysis, LCA, GHG or GWP, there are studies showing a small advantage to one, some to another. Contaminants in waste-derived oils considered for a project can also differ, favouring either of the two technologies. These combined factors determine whether a pyrolysis or gasification technology application makes more sense for a certain case. Moreover, there may be enough space in the market for pyrolysis-based technologies and gasification to co-exist in the future.

Dec-2022