Plastics have played a role at Frankfurt’s Industriepark Höchst for almost 100 years. The Hoechst company began producing polyvinyl acetate here in 1928. Later, polyethylene (PE) was added, a polymer that is still found in many different forms in every household today.
Up until recently, the plastics industry did not pay much attention to the circular economy. Industriepark Höchst is one of the places where you can see how this is changing. Trucks regularly drive up to Arcus Greencycling Technologies, which has been based here since 2021, and unload big bags containing compressed plastic waste. “This is our raw material,” explains Daniel Odenthal, the Managing Director of Arcus Greencycling Technologies. The shreds in the bags include material unsuitable for mechanical recycling that has been disposed of in the standard yellow containers that German households use for recyclable trash. But Arcus is also happy to accept industrial waste such as used films from agriculture or production waste.
Contribution to the circular economy
In Germany, however, most of this waste has thus far ended up in incinerators. Elsewhere it is also sent to landfills. Arcus wants to recycle these materials so that other companies can use them to manufacture new plastics, which would make an important contribution to the circular economy. For this type of processing to succeed, the quality of the intermediate products must be assured—and this is where Evonik is playing an important role.
The recycling rates for plastic are still very low. Of the 431 million tons of plastic produced worldwide in 2024, not even one tenth came from recycled material. Moreover, the quantities of plastic waste are vast. In 2022, for example, almost 270 million tons of plastic waste was produced worldwide, and a good ten percent of that in the EU. Only slightly less than 38 million tons of this waste was recycled globally. By contrast, 90 million tons were thermally recycled—i.e. burned to generate energy—and a little more than 103 million tons ended up in landfills.
Only few kinds of plastic are collected and returned by type. Beverage bottles made of polyethylene terephthalate (PET) are one of the rare exceptions. The recycling system here is quite successful at keeping this material in circulation by cleaning, shredding, and melting old bottles and then using them to make new ones. Experts use the term mechanical recycling when the material in question remains chemically unchanged throughout the recycling process.
Chemical hodgepodge
Chemical recycling is used for the large remaining amount of mixed plastic waste that is unsuitable for mechanical recycling. In this process, the polymers are broken down into constituents from which new plastics can be obtained.
So far, this technology has hardly played a role in terms of volume, but companies like Arcus want to change that. To do this, they have to deal with colorful plastic mixtures that contain not only various classes of polymers, but also additives such as dyes, stabilizers, plasticizers, and flame retardants. Impurities and metals or paper from caps and labels are also part of the mix. It’s a chemical hodgepodge—and completely unsuitable for mechanical recycling.
At Arcus, these mixtures are treated with nitrogen and then transported via a suction hose into the pyrolysis furnace, which is the heart of the system. Here, the shredded used polymer mixture is heated to several hundred degrees Celsius in the absence of air. Due to the lack of oxygen, the long molecular chains are broken down into smaller building blocks without being burned. The result of the pyrolysis is a mixture of hydrocarbons in gaseous, liquid, and solid forms, depending on their chain lengths.
»We get 600 to 650 kilograms of oil from one ton of waste«
Marco Tomasi Morgano CTO at Arcus
The liquid—pyrolysis oil—is the largest of these fractions and is an important intermediate product in chemical recycling. “Depending on the feedstock, we get around 600 to 650 kilograms of oil from one ton of waste,” says Dr. Marco Tomasi Morgano, the Technical Director (CTO) of Arcus. The company earns its money with this black liquid, which is purchased by operators of steam crackers, who use it to replace part of their crude oil-based raw material.
Steam crackers are used to produce feedstocks such as ethylene and propylene that are needed to synthesize new plastics. These substances not only form the building blocks of polyethylene and polypropylene (PP); they are also used in the production of many other polymers, such as polyvinyl chloride (PVC) and polystyrene (PS). The oil from the shreds of old yogurt containers or soap dispensers thus provides the raw material for new yogurt containers and soap dispensers.
Steam crackers are normally operated with naphtha, a specific fraction that comes from crude oil refining. In principle, steam crackers can also process pyrolysis oil. However, the oil requires pre-treatment. This is because mixed plastic waste does not consist of pure hydrocarbons. If the waste contains PVC, for example, the oil will also contain chlorine. Nitrogen, in turn, can be introduced via polyamides, polyurethanes or ABS copolymers. Polycarbonates and polyesters bring oxygen bring oxygen and silicones silicon. Plastic waste also contains impurities such as food waste.
Small amounts, big problems
“The three main problems in pyrolysis oil are chlorine, nitrogen, and oxygen,” says Tomasi Morgano. These can cause corrosion or poison the catalyst in the steam cracker, which is why the operators set strict specifications for the quality of the pyrolysis oil fed in. “The limit for chlorine is generally a maximum of tens of ppm,” says Morgano. The abbreviation ppm stands for parts per million, so five ppm is just 0.0005 percent. Some of the waste delivered to Arcus contains more than one percent chlorine by mass. As some of the impurities are deposited in the solid fraction during pyrolysis, oil from the Arcus facility still has a chlorine content in the double-digit ppm range. Steam cracker operators can handle this at present. That’s because up until now, they have only added small amounts of pyrolysis oil to their regular raw material—naphtha—so that the chlorine and other accompanying substances are sufficiently diluted.
Things are unlikely to stay this way, however. The chemical recycling of plastics is likely to become even more important as the political environment increasingly demands a shift away from fossil raw materials (see box on p. 40). Many companies also want to be able to advertise that their products boast a high amount of recycled content. A company that sells its shampoo in a plastic bottle made with polypropylene containing 20 percent pyrolyzed plastic waste can use this figure to promote the product.
That’s why Hendrik Rasch also expects pyrolysis oil to become increasingly available. Rasch is VP Circular Packaging & Plastic Recycling of the Global Next Markets Program at Evonik, and in this capacity he deals with recycling strategies for the plastics industry. “Many new pyrolysis plants are currently being built around the world,” says Rasch. This will also increase the incentive for steam cracker operators to mix in larger quantities of pyrolysis oil from plastic waste.
However, new technical solutions are needed because the impurities pose a risk for the operators. “It costs millions of euros per day when a steam cracker has to shut down,” Rasch explains. The aim is therefore to remove unwanted impurities from pyrolysis oils. “We have developed products for exactly this purpose,” says Rasch.
»Chlorine contamination is the biggest problem for pyrolysis operators«
Dan Miskin chemical engineer at Evonik in Little Rock
Specialists in Arkansas
By “we,” he primarily means an Evonik team in the city of Little Rock, almost 8,000 kilometers away. Colleagues in the capital of the U.S. state of Arkansas have been working on catalysts and adsorption materials for many years. “Pyrolysis processes are in vogue, so a few years ago we asked ourselves whether we could use our expertise to provide something for the treatment of pyrolysis oils,” recalls Dan Miskin, Evonik chemical engineer in Little Rock. “A survey of pyrolysis operators then showed that chlorine contamination is their biggest problem.”
Products that separate chlorine compounds from liquids or gas streams have been around for a long time. Evonik also has its own product line for this—Chlorocel. However, the chlorine in pyrolysis oils is organically bound, and this is where conventional chlorine scavengers reach their limits.
Two process steps in one
To address this market need, the Evonik team first delved deep into the history of chlorine adsorbents. “We wanted to understand how they were originally designed so that we could then further develop them in a suitable way,” Miskin explains. Several years and many series of tests later, this is exactly what has been achieved. At the beginning of 2025, Evonik launched three types of chlorine adsorbent in its Purocel product line specifically for the purification of pyrolysis oils. Purocel 505 stands out among them. Evonik’s developers designed it in such a way that it combines two separate process steps.
ELEMENTS-Newsletter
Get exciting insights into Evonik's research and its societal relevance – delivered conveniently via email.
“First the material catalyzes the removal of hydrogen chloride from the organic molecules,” says Miskin, “and then this HCl is captured directly.” According to Miskin, it is important to enable the second step to take place there and then, as the reactive HCl could otherwise form organochlorides again. Then nothing would be gained.
“Test series have shown that Purocel 505 extracts three times as much chlorine from pyrolysis oils as conventional products,” says Hendrik Rasch. It is supplemented in the Evonik portfolio by Purocel 510 and 515. Which type a user chooses depends on the respective requirements. Purocel 510 is not as powerful as 505 when it comes to chlorine, but it also removes other impurities such as silicon, nitrogen, phosphorus or any acids from the oil. In addition, the product can be used at room temperature and can be regenerated—and thus reused—by heating it intensively.
Steam cracker operators on several continents are already testing the new products on pyrolysis oils. According to Rasch, there is also a complete package for Purocel 510. “That’s where we offer our Rocket technology. This consists of customized and preconfigured column modules with the adsorbent, which we supply together with pumps and complete process control systems.” Similar solutions from Evonik are already being used in oil refining, for example to eliminate odor and color problems.
For example, users can connect a Rocket unit to the outlet of a pyrolysis reactor or immediately upstream of the inlet of a steam cracker. Thanks to the pre-configuration, customers don’t have to do much. Rasch calls this “convenient plug-and-play technology.” The Rocket columns heat up Purocel 510 at regular intervals in order to regenerate it.
A SECOND LIFE FOR CATALYSTS
The new Purocel types and the Rocket unit are also finding favor at Arcus in Frankfurt. However, the company does not currently want to purify the pyrolysis oils itself. This makes more sense and is more economical when larger quantities are involved, i.e. at the steam cracker operators. Managing Director Odenthal sees Evonik products as nothing less than “a success factor for making non-fossil raw materials available for the existing petrochemical infrastructure”—and thus increasing the quantities of pyrolysis oil used there.
“Today’s steam crackers have been optimized over decades,” says Odenthal, “but they’ve been optimized for the conventional fossil types of naphtha. Pyrolysis oils will only become even more widely accepted if we succeed in matching them as closely as possible to these standardized types.”
In traditional petrochemistry, there is another process that could complement the adsorption process in connection with the purification of pyrolysis oils: Hydrotreating. This process involves adding hydrogen, which then reacts with impurities containing chlorine, nitrogen or oxygen to form volatile compounds. Evonik’s experts in Little Rock have developed metal catalysts for this technology, and these are now marketed in the “Purocel H” series.
Unlike other catalysts on the market, these are recycled products. Evonik uses a specially developed technology to regenerate catalysts that have become weak with age. The resulting catalysts are in no way inferior to new materials in terms of performance. Users who rely on these types of Purocel-H not only save money compared to newly manufactured catalysts; they also improve their CO2 footprint by reusing them.
With the new Purocel and Purocel-H products, Evonik has further expanded its range of additives for the petrochemical industry. That industry has long known and used other additives from Evonik, such as the pour point depressants from the Viscoplex brand. These are products that system operators use to keep oils liquid by preventing crystallization so that the oils remain pumpable even at low temperatures. Arcus in Frankfurt also uses Viscoplex to keep the waxes that are produced during pyrolysis free-flowing. Evonik has brought together other additives, especially for cracker operators, in the product range known as SiYPro. The abbreviation stands for “Simplify Your Process”—and that says it all because the purpose of each of these products is to counteract disruptive effects in the cracking process.
»It costs millions of euros per day when a steam cracker has to shut down«
Hendrik Rasch VP Circular Packaging & Plastic Recycling at Evonik
Everything is therefore in place to use pyrolysis oils made from plastic waste in order to ensure that more plastic remains in the cycle. The potential here would be huge: Theoretically, around 120 million tons of pyrolysis oil could be extracted from the more than 200 million tons of plastic waste that was incinerated or sent to landfills worldwide in 2022. However, the capacity for processing such quantities is not yet available. Arcus, for example, currently processes just 4,000 tons a year, but is planning to build a plant with six times this capacity.
For the time being, most steam cracker operators will only add pyrolysis oil to their naphtha. However, Hendrik Rasch believes there is a good chance that the proportion will continue to rise: “I think that ten percent oil is conceivable in the medium term.” Evonik products will then ensure that traces of chlorine, nitrogen, oxygen or silicon do not spoil the process here.
