Amid controversy, industry goes all in on plastics pyrolysis

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In brief

Leading chemical corporations are investing in pyrolysis facilities that transform plastic waste into hydrocarbon feedstocks which can be converted back into new plastics. They believe this method can help capture more plastics than traditional mechanical recycling methods. However, scaling pyrolysis effectively poses several challenges. Developers must calibrate their facilities to accommodate various polymers and create products that petrochemical manufacturers can utilize. Additionally, certain plastics like polyvinyl chloride can complicate pyrolysis operations. The practical application of this technology will have a significant influence on public perception of the plastics sector.

Recently, Dow announced a major milestone in its quest to address the plastic waste issue. The chemical giant collaborated with Mura Technology to unveil a facility in Böhlen, Germany, designed to deploy Mura's supercritical steam processing technology. This facility will convert mixed plastic waste into hydrocarbon liquids that can be processed into new plastics in Dow's ethylene cracker located at the same site.

This plant, the largest of its kind in Europe, aims to divert 120,000 metric tons of waste from incineration every year. It is projected to be six times larger than Mura's initial facility currently under construction in Teesside, England. The partners have plans for additional plants across Dow sites in both Europe and the United States, targeting a total capacity of 600,000 tons annually.

According to Mura’s chief commercial officer Oliver Borek, "Böhlen serves as a baseline, and from this point, we can only grow." An executive from KBR, the engineering firm licensing this technology beyond Dow and Mura, mentioned that they are also designing multiple plants in South Korea and one in Japan.

Major petrochemical companies are rallying behind a variety of pyrolysis processes being developed worldwide. Prominent firms including Dow, BASF, Shell, ExxonMobil, LyondellBasell Industries, Sabic, Ineos, Braskem, and TotalEnergies are either partnering with smaller firms to develop innovative processes or are creating their own technologies.

These companies assert that pyrolysis can address the limitations of mechanical recycling, the traditional process where plastics are cleaned and pelletized after being collected in blue bins. Unfortunately, only two polymers—polyethylene terephthalate (PET), used in soft drink and water bottles, and high-density polyethylene found in milk containers—are recycled at any significant scale. Achieving contamination specifications for food-grade applications, even for these polymers, remains a struggle. In total, mechanical recycling captures merely about 9% of plastics in the United States, as per data from the Environmental Protection Agency.

For a broader range of resins, recyclers can utilize depolymerization techniques, which reduce polymers back into their initial chemical components. For instance, methanolysis can recycle PET products, while hydrolysis has been effectively used for nylon for several years.

We kind of joke sometimes that every day we need to make a birthday cake, but the ingredients keep changing all the time, and the birthday cake better be good and taste the same.

Eric Hartz, cofounder, Nexus Circular

However, many commonplace plastics—candy wrappers, stand-up pouches, potato chip bags, protective packaging, single-use cups, frozen food bags, razors, toothpaste tubes, and cotton swabs—pose a serious challenge to recycling through either mechanical methods or depolymerization.

These consumer items are composed of multiple plastics, making them challenging to separate, and predominantly consist of polyolefins like polyethylene and polypropylene, which exhibit robust carbon-carbon bonds and resist depolymerization. For these mixed plastics, pyrolysis represents the only practical method available for reclaiming raw materials and manufacturing new polymers.

Nevertheless, a pyrolysis reactor is not a magical solution to eliminate the waste issues faced by the plastics industry. The process is superficially straightforward: applying high temperatures without oxygen to break down plastics into a blend of smaller molecules known as pyrolysis oil. However, transforming diverse forms of plastics into uncontaminated feedstock, such as the C5-C12 paraffins ideal for naphtha feedstock in an ethylene cracker, poses substantial challenges. Addressing these hurdles is crucial for the plastics industry if it seeks to counter environmentalist criticisms and achieve its waste reduction and carbon emission targets.

The pyrolysis cauldron

As Eric Hartz, cofounder and president of Nexus Circular, pointed out, "We sometimes joke that every day we need to make a birthday cake, but the ingredients keep changing, and the cake must be good and taste the same. There's an art to managing heterogeneous inputs compared to more uniform ones. There’s not a perfect science yet that explains why some compounds behave the way they do in this context."

PYROLYSIS

This industry-supported method aims to achieve plastics circularity by chemically breaking down plastic waste into their fundamental components for manufacturing new plastics.

Credit: Alex Tullo/Will Ludwig/C&EN

1. Pretreatment

The feedstock for pyrolysis plants ideally consists of polyolefins such as polyethylene and polypropylene, with mitigating materials like oxygen-containing polyethylene terephthalate and chlorine-laden polyvinyl chloride eliminated beforehand.

2. Pyrolysis

Heating plastics to about 500 °C in the absence of oxygen breaks them down into liquid fractions like naphtha and diesel, along with solid cuts such as waxes and lower-molecular-weight gases. In many plants, about 10% of the output is char, which is a by-product.

3. Landfill disposal

Char can either be disposed of in landfills or integrated into products like asphalt or concrete. Most operations incinerate the gases generated for thermal energy.

4. Upgrading

The output must undergo adsorbents and hydroprocessing to eliminate chlorine, nitrogen, and other contaminants before it is viable for new plastics production. Occasionally, a hydrocracker or similar unit is necessary to further refine larger molecules.

5. Using waste

The naphtha produced is processed in an ethylene cracker to manufacture ethylene and propylene, the building blocks necessary for creating more polyethylene and polypropylene.

One significant obstacle with pyrolysis is the variability in the feedstock. Different polymers subjected to pyrolysis will decompose in various patterns. Interestingly, molecules that exhibit extensive branching will fragment more readily than linear ones. A review conducted by bioproduct engineer Roger Ruan and other scientists from the University of Minnesota Twin Cities revealed that polypropylene disintegrates at temperatures of 378-456 °C, while low-density polyethylene degrades at 437-486 °C, and high-density polyethylene between 452-489 °C. Consequently, firms handling mixed plastic waste must typically select a temperature—often exceeding 500 °C—at which all receiving polymers will break down reliably.

The temperature used in the process also significantly influences the composition of the output. Although pyrolysis can yield useful liquids like naphtha and diesel, less desirable waxes may need further refinement. Additionally, lighter gases produced during pyrolysis are generally incinerated as fuel within the reactor. High temperatures and prolonged residence times might reduce wax production while enhancing naphtha yield; nonetheless, these elevated conditions also lead to the generation of gases with limited application.

When temperatures rise, reactions such as dehydrogenation, cyclization, aromatization, and Diels-Alder reactions occur, often leading to the production of more aromatics. "For fuels, that might be acceptable," Ruan notes, "but we desire naphtha feedstock for new plastic production, avoiding excessive aromatics."

Another problem arises when incorrect plastics are input into pyrolysis reactors, as this leads to inefficiencies and likely contamination of the output. For example, the presence of PET adds oxygen to the mixture, steering reactions toward carbon dioxide formation, while polyvinyl chloride (PVC) produces chlorinated compounds. Moreover, some plastics are laden with inorganic additives such as carbon black, carbonate, and clay, resulting in elevated char formation and requiring operators to dispose of it as solid waste.

Environmentalists cry foul

Environmental advocates significantly criticize pyrolysis, with a rising number of jurisdictions—California being among them—not categorizing it as recycling. Prominent critic Jan Dell, a chemical engineer and head of the Last Beach Cleanup, has collaborated with larger organizations such as the Natural Resources Defense Council and Greenpeace to develop reports addressing concerns about pyrolysis. In her presentations, Dell compiles a striking 16 pages of objections.

One of Dell's primary concerns is that pyrolysis facilities often cannot genuinely accept the mixed plastic waste they purport to. The residual PVC, PET, and other materials entangle the process.

"There are simply too many types of plastics and too many additives. You can't recycle them all together, and segregating them goes against the second law of thermodynamics," Dell argues. "It's practically impossible to reorganize these materials once they've entered a curbside bin, similar to Humpty Dumpty."

She stresses that Renewlogy, a Utah-based enterprise developing a pyrolysis plant, ceased operations for these specific reasons. Dell's findings even include imagery from a Nexus Circular facility in Atlanta showing bales of comparatively clean plastic film, suggesting that the company is not accepting substantial amounts of post-consumer mixed plastic waste.

It's impossible to reorder these plastics once they have been collected.

Jan Dell, founder, the Last Beach Cleanup

Another contention against pyrolysis is that it resembles incineration, despite pyrolysis operating without oxygen. "Looking solely at the pyrolysis vessel shows no combustion, and I agree with that," Dell acknowledges. "However, consider how you heat that reactor to the required 900 to 1,500 °F. You accomplish this by igniting the gases released as a by-product."

Dell highlights Brightmark, which disclosed to the EPA that approximately 70% of the output from a facility it is establishing in Ashley, Indiana, would consist of gases intended for energy or flare. However, Brightmark later clarified that this figure was a mistake; the amount is now reported to be closer to 18% of the output, and the firm is providing an updated claim to the EPA.

Another criticism pertains to capacity. Dell states approximately 120,000 tons annually of pyrolysis and other chemical recycling provisions are currently operational in the United States—certainly a minimal fraction against the 56 million tons of plastics production reported in North America by the American Chemistry Council. To put it in perspective, one new polyethylene facility boasts around 500,000 tons of capacity each year.

To critics like Dell, pyrolysis appears more like a greenwashing tactic meant to mislead the public regarding the recycling capabilities of plastics. She notes that the industry previously built up recycling capacity, only to close it when projects faltered and public interest waned. Dell contends that the industry is repeating these patterns.

Industry steps up

Industry leaders claim they are more committed than ever to recycling efforts and eager to scale pyrolysis implementation. They are erecting facilities larger than before and pilot testing them in real-world scenarios. Decision-makers acknowledge the complexities associated with a pyrolysis-centric recycling framework and are resolving to overcome these obstacles.

Dow’s global sustainability director for hydrocarbons, Manav Lahoti, asserts that experimentation will ultimately benefit the systems over time.

"Sometimes you encounter successes alongside failures, but one shouldn’t simply dwell on failures and declare the whole endeavor fruitless," he explains. "There's a concerted effort among companies like ours to find effective resolutions for these challenges, which is what fuels progress. Along the way, not all efforts will be triumphant."

Credit: Nexus Circular

Brightmark, also in the field, faces its set of challenges. As the company strives to launch a facility in Indiana at a cost of $260 million, it is designed to convert 100,000 tons of mixed plastic waste annually into valuable products like naphtha, diesel, and industrial waxes.

By the close of 2020, CEO Bob Powell stated that construction was 80% complete and the facility was slated to begin operations in 2021. Fast forward to April of this year, and the company had only produced about 2,000 tons of product. Powell now indicates a full-scale operation will commence next year.

"The biggest hurdle right now has been the impacts of COVID," Powell states. "The pandemic delayed equipment delivery and hampered attempts to find sufficient labor for the plant. We also experienced a fire in May, which we deem a minor setback."

Brightmark also recently terminated plans to develop a $680 million plant in Macon, Georgia, which would have quadrupled the Ashley facility's capacity due to local opposition. The company anticipated around $500 million in bonds from the Macon-Bibb County Industrial Authority, but the deal hinged on Brightmark's ability to gain footing at the Ashley site before the county rescinded its support, citing Brightmark’s struggles in Indiana.

Powell perceives Brightmark as having been treated unfairly, stating that "Most inquiries could have easily been answered through a tour of the facility."

Brightmark, an early adopter in pyrolysis technology, faces evolving market demands. When the company began constructing its facility, the primary goal was to divert plastics from the waste stream. Naphtha and diesel output were initially geared toward the fuel market.

However, consumer demand for completely circular plastics has surged in recent years, motivating Brightmark to pivot its strategy to sell naphtha as raw material for the chemical industry while aiming to place diesel into similar markets.

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Additional reading:
The SMT Process: What Engineers Should Know

In light of the rising demand for recycled feedstock, Nexus Circular has garnered considerable attention from major petrochemical manufacturers. The Atlanta-based company's facility boasts an annual capacity of 13,000 tons, with roughly 80% of its output encompassing a blend of naphtha, gasoline, diesel, and heavier waxes, with the remainder being gas utilized for heat.

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Shell and Chevron Phillips Chemical have already begun utilizing output from Nexus's facility in their U.S. petrochemical crackers. Dow has agreed to source product from a forthcoming Dallas facility that will be double the size of the Atlanta complex. Nexus also plans to establish a 30,000 tons-per-year unit in Chicago to supply its investor, Braskem.

Hartz points out that one of Nexus Circular's unique advantages is its ability to process various forms of difficult-to-recycle plastic films with minimal presorting requirements. Additionally, the company does not engage in distillation or hydrotreating of its output, procedures that often impose high operational costs and environmental burdens.

Hartz acknowledges that Nexus is selective about the waste plastics it accepts. To avoid complications of sorting and further treatment, Nexus strategically sources relatively homogeneous polyolefin streams, like pallet wraps from retailers, asserting that even these materials were destined for landfills.

While Nexus pays a premium for cleaner plastics, Hartz emphasizes, "Quality comes at a cost; if you want to work with garbage, you'll incur enormous expenses before you can even operationalize them."

Readying for pyrolysis

Numerous other firms are similarly adapting this approach, aiming to acquire a broader collection of mixed waste. Artem Vityuk, a global market manager at BASF, states, "When discussing genuine circularity on a large scale, you must consider mixed plastic waste—not merely pre-sorted polyolefins." This indicates a drive to broaden the feedstock base, necessitating the ability to handle contaminated inputs.

This shift implies that output from pyrolysis facilities which handle a wide array of plastics will require upgrading processes to remove contaminants. Recently, BASF introduced "PuriCycle," a new portfolio of catalysts and adsorbents designed to eliminate such impurities, targeting pyrolysis operations that aim to comply with customer specifications while assisting petrochemical companies in cleaning feedstock sourced from diverse avenues.

Vityuk elaborates that halogens, oxygen, nitrogen, and metals often accompany the hydrocarbons produced from pyrolysis facilities. "This variation in the plastics is what we need to address," he specifies.

These impurities can garner significant attention. Ethylene crackers, for example, may tolerate as little as 1 ppm of chlorine in their input; thus, even a single piece of PVC entering a daily delivery can spark major complications for chemical clients. BASF develops adsorbents that readily absorb chlorine compounds, and their product lineup is also designed to filter out particulate matter while isolating particularly reactive compounds from the feedstock.

Additionally, BASF provides hydroprocessing catalysts modeled after those found in oil refineries, empowering operators to swap sulfur with hydrogen. "We have specifically optimized our catalysts to ensure effectiveness in processing plastic pyrolysis oils," Vityuk mentions, adding that the focus shifted from sulfur to addressing nitrogen content within plastics like nylon.

Steve Deutsch, a consultant from the Catalyst Group, underscores that variability in pyrolysis oil poses a challenge requiring innovative solutions. "While there are benchmarks for raw materials in ethylene crackers, no such standards exist for pyrolysis oil," he states. "The industry must evolve to establish greater consistency."

Petrochemical corporations are now developing the infrastructure necessary to process products generated by pyrolysis operations. Shell, for instance, is constructing upgraders in its chemical facilities at Moerdijk, Netherlands, and Singapore to decontaminate pyrolysis oils sourced from third-party providers, each capable of processing 50,000 tons annually.

"Given the infant status of the chemical recycling sector, we can expect substantial variations in pyrolysis oil quality, making the upgrading process crucial for enhancing usable quantities," remarks Philip Turley, Shell's global general manager for plastics circularity.

Shell has already secured commitments from various companies that may provide pyrolysis oil for its upgrading facilities. For example, it has formed a partnership with BlueAlp, intending to build 30,000 tons of plastics pyrolysis capacity in the Netherlands. Shell also sealed an offtake agreement with another European pyrolysis front-runner, Pryme.

In parallel, Dow is collaborating with Topsoe on the design of a purification unit for pyrolysis oil at its plant in Terneuzen, Netherlands. Dow states its unit aims to purify and standardize feedstocks coming from various pyrolysis facilities. "Some sources may produce output requiring additional cleaning or processing before integration into a cracker; there are others we cannot accept at all due to high aromatic or naphthalene proportions," Lahoti warns.

"As these companies transition from the start-up phase, they will begin assessing how these technologies integrate within the chemical sector," Lahoti adds. "Companies like Dow play a pivotal role in helping these startups thrive by lending our technological expertise and experience, facilitating feed acceptance into our systems."

The technology evolves

Lahoti explains that the pyrolysis techniques themselves are advancing to align better with the petrochemical realm. "There’s a shift away from traditional pyrolysis toward various technologies, some based on conventional pyrolysis but now evolved," he notes.

For instance, Lahoti believes that Mura's technology transcends pyrolysis itself, emphasizing that the innovative use of supercritical steam facilitates direct heat transfer to polymer particles. In traditional pyrolysis, heat is relayed from the kiln to the poorly conductive plastic components, creating challenges as facility sizes increase.

Firms are beginning to incorporate catalytic processes into pyrolysis reactors themselves. By doing so, they lower the activation energy for various reactions and can shape the output toward more desirable products. As Deutsch points out, pyrolysis often yields large molecules containing 40 or 50 carbon atoms, which are not fit for direct feeding to a cracker. Catalytic pyrolysis can help refine the output distribution to focus more on lighter fractions.

Since 2020, LyondellBasell has operated a pilot facility in Ferrara, Italy, evaluating its catalytic pyrolysis technology dubbed MoReTec. Though specific catalyst details remain undisclosed, several research groups are favoring zeolite catalysts (like ZSM-5), often applied in refining applications.

A clear indicator of growing interest in pyrolysis is the trend of large engineering firms licensing their technologies to third-party investigations. KBR is now licensing Mura's approach, while Lummus Technology has begun marketing its technology derived from New Hope Energy. Furthermore, late last year, Honeywell UOP revealed its own pyrolysis process known as UpCycle.

Kevin Quast, leading the global business for Honeywell UOP's plastics circularity initiative, underscores the recognition of the UOP name within the market. "Customers appreciate the reliability associated with the UOP brand," he asserts. The firm has been refining a process that previously yielded success in Europe before being halted in the late 2000s.

Quast points out critical distinctions between UpCycle and other pyrolysis methodologies. Notably, Honeywell UOP implements a pretreatment stage to filter the appropriate plastics and liquefy them prior to entering the primary reactor. The output comprises lighter fractions, including naphtha and diesel, with a heavier strain that can be processed into propylene via fluidized catalytic cracking.

Honeywell UOP is forming two joint ventures, one in Spain with the infrastructure developer Sacyr and another in Texas with the waste management firm Avangard Innovative. They are also providing licensing opportunities for facilities in both China and Turkey.

ExxonMobil, another giant in the oil and petrochemical sectors, is promoting its aspirations. Next month, the company is set to finalize the establishment of a pyrolysis facility at its petrochemical complex in Baytown, Texas, capable of processing 30,000 tons of plastic annually.

As Natalie Martinez, the feed-to-value business manager at ExxonMobil, stated, "We're directly converting plastic waste at our own facility." While specific details about the equipment and postprocessing steps remain under wraps, the integrated nature of colocating pyrolysis operations within a petrochemical complex allows ExxonMobil to harness gases otherwise burned in standalone systems. "Every outcome of the process is utilized within this systematic framework," Martinez adds.

ExxonMobil is also engaged in a joint venture with Agilyx, known as Cyclyx International, focused on sourcing feedstock for their facility. The company is exploring optical sorting technologies and advanced analytics to manage the substantial quantities of material slated for processing, asserting that manual sorting won't suffice.

If corporations as large as ExxonMobil succeed at operating this technology effectively at scale, it could serve as a pivotal rebuttal to skeptics of pyrolysis. ExxonMobil's objective is to broaden this technology across global facilities to achieve a recycling capacity of 500,000 tons of plastics by year-end 2022.

"We recognize that scalability, alongside successfully managing this technology globally, will be key to achieving our goals," Martinez concludes. "While technical challenges posed by processing plastic waste remain plausible to overcome, it is the question of achieving meaningful scale that will offer tangible solutions to society."

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