E. Alazemi, Petrochemical Industries Co., Al Asimah, Kuwait
Plastics are some of the most vastly used materials in modern life. They are the building block of products manufactured by almost every sector, including packaging, building and construction, textiles, consumer products, transportation, electrical and electronics, and industrial machinery.
Over the past several decades, plastics production has significantly increased, driven by a variety of factors, including economic growth linked to increased consumption, a significant expansion in plastic uses and growth in on-demand plastic products. Global consumption of resources comes mostly from fossil fuels, with 87% consumed by energy and transportation, and only 4% of petroleum-based fuels being used for plastics production.1 While plastics contribute tremendously to the standard and quality of living, the main issue arises after their disposal (FIG. 1). Incineration and landfilling are the most common routes for the disposal of plastic waste. Recycling still lags due to high costs and a lack of adequate technologies.
Landfilling has a negative impact on the environment, as it results in land destruction and the loss of soil fertility due to rotting occurring from the waste. Incineration, which involves the burning of plastic waste, is associated with other challenges, such as the possible release of microplastic particles to the environment2 and emissions of harmful gases to the atmosphere.3
The third possible destination for plastic waste is recycling. However, the rate of recycling globally is lagging. For 65 yr (1950–2015), only 1.7% of total plastic waste was reported to have been recycled.2 The reasons for this are complex and include—but are not limited to—the cost of recycling, a lack of robust infrastructure and a lack of available technologies that can handle large-scale plastic waste.
At the same time, the utilization of plastic products is increasing every year, and demand for polymers by the construction, automotive and medical sectors is growing rapidly.4 Therefore, it is paramount that a method that can successfully capitalize on plastic waste is developed and optimized to meet the demands of leading plastic producers.
Plastics are petroleum-based polymers, hence, converting them into useful and economically viable hydrocarbons—such as fuels or feedstock—is possible.1 One such viable method is the pyrolysis of plastic waste, which has been garnering momentum in recent years.
Pyrolysis reaction. Pyrolysis is the process where polymers undergo cracking at a reasonably high temperature in a pyrolysis chamber with an inert environment (i.e., oxygen-free) (FIG. 2). This kind of reaction is irreversible, which leads to a transformation of long-chain hydrocarbons into shorter ones.6 Plastic waste must be treated and grinded into desired shapes before pyrolysis.7 There are two ways to perform pyrolysis: thermal pyrolysis (catalyst-free) and catalytic pyrolysis.
In thermal pyrolysis, plastic waste is charged into a nitrogen-purged pyrolizer to prevent the formation of dioxins.7 In this mode, the temperature can be as high as 800°C.8 Literature has described thermal pyrolysis as not being selective because of its wide product distribution (i.e., C1–C80).
In catalytic pyrolysis, catalysts can lead to less energy consumption and lower capital costs. Selectivity and products distribution are enhanced and altered. In addition, residence times were observed to be shorter when using catalysts.9,10 Deciding which catalyst to use presents advantages and disadvantages. Small-pore catalysts will suffer from lower activities due to the limitation of diffusion to the active sites. In contrast, large-pore catalysts will suffer from blockage of the active sites in the presence of coke.
Process conditions. Another area of discussion is the conditions of the reaction, such as temperature, pressure, residence time, type of reactor and, most importantly, the feedstock. For example, if polystyrene (PS) was pyrolyzed, more aromatics would be expected in the products since styrene is an aromatic. The contrary will occur for polyethylene (PE) due to the lack of aromatic rings in its structure.11
Market analysis. The market direction of initiatives in Europe and the Asia-Pacific region is rapidly improving. Both universities and manufacturers are conducting extensive work on pyrolysis and its viability. The reason for this is that end-user industries are increasingly moving toward sustainable solutions due to growing customer expectations for more end user products with green credentials. Europe is considered a major contributor to recycling plastic waste. For example, within the UK, 45% of plastic packaging waste is recycled,12 whereas Germany recycles 20,000 tpy of low-density PE (LDPE).13
The market share of plastic waste pyrolysis is forecast to increase by 5.3% [compound annual growth rate (CAGR)] from 2023–2032.14 The growth rate of the market depends on the urbanization and industrialization of the region and the regulations in place. Regions with higher environmental motivations and/or with stricter regulations are dominating the market share (FIG. 3).
The pyrolysis of plastics is often seen as a non-profitable technique. However, when examined, the market size is growing every year. Lubongo, et al. conducted a case study regarding the profitability of pyrolysis under two scenarios: where feedstock was bought and used, and where feedstock was provided at no cost and was used.16 The study determined that paying for waste plastic feedstock (Case 1) can heavily challenge profitability opportunities, as all net present values (NPVs) were on the negative side and the payback period was remote. However, when utilizing feedstock at no cost (Case 2), the process can be profitable.
The Gulf Cooperation Council (GCC) region [Bahrain, Kuwait, Oman, Qatar, Saudi Arabia and the United Arab Emirates (UAE)] is home to several projects piloting pyrolysis, particularly in the UAE and Saudi Arabia.17 In Dubai, Quantafuel, BASF and Dubal Holding have teamed up to build a plant that pyrolyzes 80,000 tpy of plastic waste.18 BEEAH Group and Chinook Science have partnered with Japan’s Air Water Inc. to convert plastic waste into fuel, also using pyrolysis.19 In Saudi Arabia, SABIC announced it will target processing 1 MMtpy of plastic waste.20 The GCC region is a major plastic exporter. By adopting stricter regulations and increasing awareness, pyrolysis and plastic waste management techniques can be implemented on a larger scale.
Takeaway. It is important to mention that while plastic waste management is necessary, challenges remain. These challenges can be overcome by developing new techniques such as the one discussed in this article. Often, manufacturers tend to select more convenient paths when dealing with plastic wastes—this is reflected in their tendency to dump plastic waste in landfills and/or incinerate it instead of recycling due to economics and the additional steps to the manufacturer’s process. This can be solved by providing several solutions, such as developing a more convenient process and providing a solution that is financially feasible and profitable.
Pyrolysis is believed to have high potential both technically and economically. This is proven by analyzing the market’s direction, especially initiatives in Europe, as tons of plastic waste are being recycled and pyrolysis has a solid proportion in terms of application. In addition, the author has noticed the intense work that has been completed on recycling techniques from universities and manufacturers. These pathways are helping the oil and gas industry move towards sustainable solutions. HP
LITERATURE CITED
Ebrahim Alazemi is a chemical engineer for Petrochemical Industries Co., a major petrochemicals producer in the GCC region and the Middle East. Alazemi earned an MSc degree in advanced chemical engineering from the Imperial College of London and specialized in polymers. His focus is on environmental solutions in the oil and gas industry.