Pyrolysis is one of the main methods for chemical recycling of plastics. While plastic recycling is gaining momentum, many companies are still struggling in scaling pyrolysis technology. Pyrolysis plants of sizes 100,000-200,000 tpa are being discussed by industry players and are needed to attain the future goal of seeing a great momen- tum in plastic recycling across all different industries around the globe so that significant progress toward a circular plastics model can be achieved. At present, plastic chemical recycling via pyrolysis is available only at a small scale (3,000-16,000 tpa). Many plants with a capacity from 16,000–100,000 tpa are still under planning and construction, and these firms are increasingly exploring the huge potential under chemical recycling via pyrolysis so that a large volume of plastic waste can be handled. The economics for a large- scale pyrolysis plant are challenging and largely dependent on the availability of upstream waste feedstock, its quality and price, reactor configuration, the type of end-product considered, and the support from different stakeholders. This article discusses the way ahead in the commercialization of pyrolysis technology for a large-scale plastic chemical recycling.

Pyrolysis plant upstream significance

The plastic-to-liquid (PTL) market is challenged by the need for a relatively desirable feedstock whose market price f luctuates with the value of crude oil. Feedstock suppliers are reluctant to commit to long-term binding agreements, as they often hedge on market fluctuations and future price expectations to yield higher profit margins. The feedstock for the mixed plastic pyrolysis plant is generally in bales form and is transported from a typical material recycling facility (MRF) situated in the location. These bales have a price tag reflecting their quality and adding the transportation cost makes the feedstock cost for the plastic pyrolysis plant very high. Each plastic resin has its own unique high heating value (HHV). PVC and PET waste plastics have the lowest heating values, but they carry other problems, such as coproducing hydrochloric acid and benzo- ic acid, etc., that will lead to corrosion and the choking of equipment downstream. However, LDPE and PP carry the highest heating value and are more suitable to be transformed into oil. Thus, the profitability is connected to the composition of feedstock.

For most of the pyrolysis technologies, PET and PVC need to be removed upstream of the pyrolyzer reactor. A strategy focused on lowering the feedstock price needs to be included at the project planning phase. Plant location based on population density, material recycling facility capacity and its location, refinery location etc., all play an important role. For example, companies with a larger and centralized plant tend to be operators of the plant and offer recycling as a service. In such a scenario, the plant will act as a receiver of the waste and will retain ownership of the output product for sale to the chemical sector. Companies with distributed and smaller plants tend to offer their recycling technology solution for purchase to the waste handling operators. In this case, the plant will be built remotely and distributed for installation on existing waste and material handling sites. The technology provider will generate revenue from equipment sales and maintenance agreements, while the waste handler will retain ownership of the output product for sale to the chemical sector. The use of waste feedstocks requires the operations and practices to be in line with local area waste-related legislative framework and the legal obligations concerning waste handling and utilization to be taken care of. The real aim is to ensure a 24/7 waste feedstock availability to run a large-scale pyrolysis plant.

The importance of reactor design and size in economic viability of large-scale plants

The reactor design and its size are the key parameters determining the economic viability of the pyrolysis plant. For a large scale say a 1,000 tpd plant, a few larger reactors (for associated end-products become more significant in the selection of reactor design type and plant scale, with versatile engineering expertise required for a robust design instance, of size 250 tpd) that can handle large plastic where the process yields are not compromised in the long waste volumes are preferred. A modular approach for a large-scale commercialization (e.g., implementing 20 pyrolyzer reactors, each having a size of 50 tpd for this 1,000 run.

The total fixed capital for the plant can be drastically tpd large scale plant) has a significant impact on the total reduced if larger reactor sizes are used. The potential fixed capital. The design of the reactor also changes with the scale. Circular fluidized bed type reactors are more scalable in approach as compared with the auger type traditional pyrolyzer reactors. The type of pyrolysis and its savings could be in the range of 20–35%, depending upon the number of trains further under the large-scale plant. The chart below provides some indication on the potential saving in this context.

If the end-product of a large-scale pyrolysis is liquid fuel (e.g., ultra-low sulfur diesel), the economics of the plant will still be challenging. Our study shows that Case 2 will be economical at a subsidy rate of USD50–55/ton, while Case 3 is economi- cal as it is (without subsidy). Furthermore, the selection of by-product (For example: wax) price along with the subsidy plays an important role. Case 3 might not be attractive anymore if the waste plastic feedstock prices exceed USD110/ton, which in that case, it will be the subsidy (tipping fee) that will save the economics. Regarding the feedstock quality, in instances where wax is not suitable to be produced as a by- product, the basic plant capacity needs to be raised further up, target- ing a higher liquid fuel yield.

Pyrolysis oil hydrotreating economic challenges

Depending on the waste plastic feedstock properties, normally the plastic pyrolysis oil is not stable at temperature above 60 deg C. If the oil is not produced near a cracking plant, it needs to be transported and stored. However, unsaturated compounds in the oil often take this as an opportunity to asso- ciate with each other and create unwanted polymers. These make the oil more viscous, leading to waxy deposits, clogging of pumps, and other issues.

A substantial upgrading of pyrolysis oils from plastics is necessary to achieve general acceptance and alternately, to achieve a significant contribution to future energy scenarios. This is normally done via hydrotreating the pyrolysis oil. For small-scale plants, it is not feasible to put a separate hydrotreater unit to purify the pyrolysis crude oil. For the large-scale units, the main challenge is to determine the minimum capacity of a hydrotreater unit, which is considered to be economical. Conventional refinery hydrotreaters make economic sense at a minimum capacity of around 5,000 bpd. The typical turndown of such hydrotreaters is around 50%. If this is replicated in plastic pyrolysis oil hydrotreating, the minimum large-scale plant size required is around 600–700 tpd of mixed waste plastic feedstock. This is a relatively high plant capacity when compared with the current modular size plants of 10–50 tpd.

Traditional hydrotreating of pyrolysis oil can take up to 40–45% of the total fixed capital of the plant depending upon the end-product requirement. The main challenge is the technology advancements that can cut down 4 the treatment cost. There are many players in the market for plastic pyrolysis oil hydrotreatment like Axen, JM, Sulzer, SINOPEC, Dalian Institute, Haldor Topsoe, Clariant, etc. It will be interesting to see how these players deal with the economics of hydrotreating plastic pyrolysis oil for small-to- large scale plastic pyrolysis plants (50–1,000 tpd). This is the most important step before the refiners can use the end-products from plastic pyrolysis for circularity. ISCC PLUS / RSB certification is the other key to the economic viability of chemical recycling because it allows producers to mix feedstocks generated from waste plastics with conventional feedstocks, and to use mass-balance accounting to apportion the circularity-incorporated circularity. The objective of the ISCC mass-balance attribution is to get this process off the ground.

Moving forward

While is it true that the pyrolysis commercialization using larger reactor sizes is not yet realized, but moving forward, we will see the use of a traditional modular approach combined together in a number of trains in tackling the question of scalability. This could be because of strategic reasons such as looking to choose a modular unit to address the capacity of a material recycle facility (MRF), or a client choosing 20–50 tpd to fit the present market needs. Making the technology modular not only makes it scalable, but also makes the system immune to failures. Like in a server cabinet, if one module stops working, other modules will continue the operation. This puts more robustness in the system and increases the availability and reliability of the plant. While this comes with a higher price tag, this premium pricing will alleviate critical timing in solving the issue of the plastic circularity and increasing legislation pressure.

Our team at Chemical Market Analytics expects that the advances that will drive the step- change improvements required to achieve the large-scale implementation of pyrolysis technology will be in the areas of reactor design and catalysis. This will drive scale and energy efficiency, as well as quality improvements need to be made to achieve a pyrolysis oil that can be used in steam crackers with limited upgrading.

The success of the initial modular scale technology will decide the implementation of a large-scale pyrolysis. The momentum has picked up and this sector has received immense attention and many announcements from different players. Brightmark is already setting up 100,000 tpa waste plastic pyrolysis plant is Ashley, Indiana. They have also announced several projects of scale of 100,000 tpa with SK Global Chemical in South Korea. OMV Oil along with Borealis is developing the large-scale pyrolysis trails at Schwechat refinery in Austria. They have announced capacity at 200,000 tpa. New Hope Energy along with Lummus Technology is in race to commercialize its pyrolysis technology at a scale of 150,000 tpa. Encina is planning a 350,000 tpa pyrolysis plant in the United States. Their recent plant, which is under development consists of two BTX/P (propylene) trains. Each train is designed to process 20 tons per hour of waste plastic and cost around USD310 million, thus making the total project cost to be more than USD620 million. Our expert team believes that as these technologies are being developed in the long term, they will benefit from the same type of learning that other petrochemical and refining processes have experienced, resulting in improved economics.

The Experience Curve theory implies that as cumulative production using a specific technology increases, fixed costs are expected to decrease. Estimates for 2050 indicate that fixed costs could decline by as much as 50–65% if the chemical recycle technology development follows a path similar to other established technologies. Logistics issues are a challenge to all large- scale efforts to recycle plastics. For chemical recycling, the fact that a large portion of waste plastics recovered from municipal solid waste streams will be located far from the traditional centers of plastics production is a disadvantage. This will require managing the logistics for solid waste (aggregating to achieve a large-scale supply source), for aggregating the sources of pyrolysis oil, and either transporting it to the traditional manufacturing centers or establishing new production centers regionally.

In conclusion, long-term supply agreements with the vendor for such a large volume of waste plastic need to be ensured. Poor feedstock quality and its high price can lower the overall product yield and disturb the process economics. Modular versus large-scale design choice remains in the discretion of the technology licensor based on its technology development and associated process guarantee figures. Pyrolysis oil certainly needs rigorous treatment before its end use in the refinery. As the technologies get more mature in the near future, a significant reduction in capital costs and operating expenses will be achieved when implementing a large-scale waste plastic pyrolysis process.