Utilizing plastic pyrolysis oil to produce new plastics is more than an environmental vision; it is a mature chemical engineering practice. Currently, the industry’s technical focus has shifted from basic pyrolysis to advanced refining integration. After quality upgrading through refining processes, plastic pyrolysis oil becomes qualified feedstock that meets strict feedstock standards for petrochemical steam crackers. The resultant circular polymers and recycled plastics are chemically identical to fossil-based equivalents, fully suitable for high-standard applications including food-grade packaging and medical supplies. Below are the core technical procedures of this process.
Pyrolysis oil production from plastic pyrolysis machine is only the first step; the real challenge lies in upgrading it into qulified feedstock to petrochemical plants. For circular plastics production, refining and pretreatment aim to remove impurities, bringing the quality of pyrolysis oil close to conventional naphtha derived from crude oil. Key technologies include distillation, adsorption dechlorination, and hydroprocessing.
Atmospheric and vacuum distillation units serve as the foundational pretreatment stage. By fractionating crude pyrolysis oil based on boiling point ranges, the complex mixture is separated into distinct cuts optimized for specific downstream processing:
To prevent downstream catalyst poisoning and equipment corrosion, an adsorptive dechlorination stage is integrated prior to hydrotreating. Special adsorbents such as modified alumina and metal oxide composites effectively capture organic chlorides. This step chlorine content from hundreds of ppm down to single-digit ppm levels, meeting the standard refinery feed limit.
This stage is critical for upgrading pyrolysis oil quality. Under hydrogen atmosphere with dedicated catalysts, highly reactive olefins in pyrolysis oil are saturated into stable alkanes. Meanwhile, organic heteroatoms are removed via chemical conversion: sulfur turns into hydrogen sulfide (H2S) and nitrogen into ammonia (NH3). After hydrotreating, the refined pyrolysis oil features similar chemical properties to conventional petrochemical naphtha, enabling co-processing with fossil feedstocks in steam crackers to for new plastic production.
Refined pyrolysis oil is primarily supplied to steam cracking units — the heart of the modern petrochemical industry. At high temperatures of 800°C to 850°C and mixed with steam, steam cracking breaks down feedstocks including naphtha, ethane and LPG into basic chemical monomers such as ethylene, propylene, butadiene and benzene. Ethylene and propylene — the products of steam cracking — are the direct monomers for manufacturing polyethylene (PE) and polypropylene (PP), ready for repolymerization into brand-new plastic pellets. There are two mainstream ways for pyrolysis oil to be processed in steam crackers:
Refined pyrolysis oil is blended with conventional naphtha at a typical ratio of 5% to 20% before being fed into cracking furnaces. This is currently the most mature and rapidly deployable route, requiring no large-scale modifications to existing petrochemical facilities. Major chemical giants including LyondellBasell, SABIC and TotalEnergies have already industrialized this model at European steam cracking sites.
Pyrolysis oil is processed as an independent feed stream, with cracking operating parameters optimized for its unique composition. This approach boosts the yield of ethylene and propylene, yet demands higher pyrolysis oil purity and partial process retrofits at petrochemical plants.
After steam cracking, the resulting cracked gas is a complex mixture, which cannot be directly utilized for polymerization without deep purification. It contains target olefin monomers (mainly ethylene and propylene), unwanted light hydrocarbons (such as ethane, propane, butane), trace contaminants (such as hydrogen chloride, hydrogen sulfide, water vapor and minor heavy substances), alongside inert gases.
Monomer separation and purification aims to separate and purify ethylene, propylene, and other key monomers from the complex cracked gas. The goal is to satisfy rigorous purity standards for downstream catalytic polymerization, which generally demands an ultra-high purity of over 99.9% (Polymer-Grade).
The entire separation and purification process is mainly carried out through a combination of cryogenic distillation, adsorption purification and fractional distillation, following the principle of separating components according to their differences in boiling points and physical-chemical properties. This follows the fundamental engineering principle of separating various components based on their precise differences in boiling points and physicochemical properties.
Inside polymerization reactors, monomers like ethylene and propylene produced from steam cracking are polymerized into long-chain macromolecules. This reaction relies on Ziegler-Natta or metallocene catalysts. Recycled plastics through this chemical process feature identical molecular structures as virgin plastics. Therefore, they are fully qualified for strict high-end applications, including food packaging and medical supplies. This technology effectively fixes the flaws of traditional mechanical recycling: leftover impurities and deteriorated material properties.
In the current industrial transition phase, full-feed production relying solely on pyrolysis oil is not yet economically feasible. Most petrochemical plants adopt co-feeding by mixing pyrolysis oil with conventional naphtha. Since molecules cannot be physically traced after entering the production system, the industry widely adopts the mass balance principle.
This logic is comparable to the grid integration of green electricity . Just as end users cannot trace the origin of every single unit of power, it is impossible to track individual molecules of pyrolysis oil once blended in production. Supported by third-party certifications like ISCC PLUS, manufacturers can certify a corresponding share of finished plastics as recycled materials in accordance with pyrolysis oil input volume. This mechanism has significantly accelerated the large-scale industrial deployment of chemical plastic recycling.
From plastic pyrolysis oil to refined feedstock, then to monomers and final new plastics, the complete chemical recycling process achieves the closed-loop regeneration of waste plastics. It not only addresses waste plastic pollution but also reduces reliance on fossil resources, becoming a key driver for the green development of the petrochemical industry under the global carbon neutrality goal.